We have compiled the definitions of over 500 different terms used in brain and spinal cord injury treatment and rehabilitation.Understanding the terms used in the first step in becoming an effective part of the treatment team.

INDEX: To go directly to a section, click on a letter below.


abducens nerve – Cranial Nerve VI. Supplies lateral rectus, an extrinsic muscle of the eye.

abduction – Movement of a limb away from the midline of the body. Clap your hands together and then move them away from each other; this is abduction. The opposite of abduction is adduction.

abcess – A localized collection of pus in a cavity, formed by the disintegration of tissues.

absence epilepsy – A type of epilepsy that occurs especially in children and is manifested by a sudden momentary loss of cosciousness with minimal motor manifestations.

acetylcholine – Reversible acetic acid ester of choline that serves as a neurotransmitter at the myoneural junction, in parasympathetic ganglia, and at parasympathetic nerve endings.

acoustic nerve – The eighth cranial nerve or nervi vestibulocochlearis, which consists of two sets of fibers, the pars vestibularis nervi octavi and the pars cochlear nervi octavi. It connects to the brain by corresponding roots.

acoustic neuroma – A tumor or new growth which involves the acoustic division of the eighth cranial nere, largely made up of nerve cells and nerve fibers.

active myofascial trigger point – Particular spots on the body where a muscle or its fascia is easily irritated and symptomatic in terms of pain.

active range of motion – Degree of movement of a segment of a joint. In testing, the movement should be voluntary.

acute – Of recent onset (hours, days, or a few weeks).

acute care – Care provided during the very early stages following injury, including surgery and intensive care. Focus is on the patient becoming medically stable.

acute rehabilitation program – Primary emphasis on the early rehabilitation phase which usually begins as soon as a person is medically stable. The program is designed to be comprehensive and based in a medical facility with a typical length of stay of 2-3 months. Treatment is provided by an identifiable team in a designated unit.

ADL – Activities of daily living. Routine activities carried out for personal hygiene and health (including bathing, dressing feeding) and for operating a household.

adduction – Describes the movement of a limb toward or beyond the midline of the body. Adduction is illustrated by moving the hands apart and then clapping them together or crossing them at the arms. Adduction is the opposite of abduction.

adipose tissue – Fatty tissue.

adjustment disorder – A maladaptive reaction to an identifiable psychological stressor. May be severe, but is usually resolved by therapeutic intervention or by the passage of time.

affect – The emotional tone characteristic of each person’s presentation. Affect is depressed in dysthymia, elevated in elation. Affect may be described as “flat”, “blunted”, or “inappropriate” to the situation.

afferent – Sensory pathway proceeding toward the central nervous sysem from the peripheral receptor organs.

agnosia – A defect in the ability to recognize and intepret compex stimuli caused by lesion in the angular gyrus.

agraphia – Inability to write.

akinetic mutism – Also known as a persistent vegetative state. The patient neither moves or speaks with volition and is unaware of internal or external stimuli. Such persons may appear to be awake but are not truly conscious.

akinetic seizure – A momentary loss of muscle tone throughout the body resulting in falls.

alar ligament – Ligaments that limit the rotation of the head. Two strong bands that pass from the posterolateral part of the tip of the dens of the axis upward and laterally to the condyles of the occipital bone.

alexia – Inability to read, usually due to lesions of the visual cortex.

alpha rhythm – A uniform rhythm of brain waves in the normal eletroencephalogram, with an average frequency of about 8 to 13 cps.

Alzheimer’s disease – Pre-senile or senile dementia with progressive mental impairment. Characterized pathologically by the presence of excessive neurofibrillary tangles and senile plaques.

amaurosis fugax – Temporary impairment or loss of vision (blindness) in one eye due to impairment of blood supply through the internal cartoid artery of the ophthalmic artery.

amnesia – A defect in memory, usually for a period of time or certain events. Anterograde amnesia is not remembering from the point of stress forward; retrograde amnesia is being unaware of events happening before the point of stress.

amphiarthrosis – Refers to the joints on both sides. Classified by degree of movement, they are slightly movable, allowing a limited amount of motion. (See synarthrosis an diarthrosis.)

amygdaloid body – A small gray mass of several small nuclei located in the roof of the terminal part of the inferior horn of the lateral ventricle.

anaplasia – A characteristic of tumor tissue in which there is a loss of differentiation of cells (dedifferentiation), of their orientation to one another, and to their axial framework and relationship to blood vessels. The degree of anaplasia is related to the malignancy of the tumor.

anatomical position – The standing body with head facing forward, arms at the sides and palms of the hands facing frontward, feet together with the toes also directed forward. In this position, the words posterior, anterior, lateral, medial, etc. describe the body parts as they relate to each other and to the axis of the body.

aneurysm – A sac (or bulging) artery or vein caused by dilatation of the walls of the vessel.

angiography – A method of following and recording the blood supply of a given organ by x-ray recordng of a radio-opaque dye injected into an artery.

ankylosis – A condition that is one of immobility and solidification of joints because of disease, injury, or a surgical procedure.

annulus – Describes a ring, or a ringlike or circular structure.

annulus fibrosus – The outermost, circumferential, ringlike portion of the intervertebral disc composed of fibrocartilage and fibrous tissue.

anomia – The inability to name objects caused by aberrant brain function.

anosmia – Loss of the sense of smell.

antagonists – Portions of muscles or whole muscles that, due to the way they are attached anatomically, contribute force to oppose each other.

antalgic gait – Counteracting or avoiding pain as a posture or gait assumed so as to lessen pain.

anterior – Before or toward the front.

anterior arch fracture – A fracture caused by hyperextension. The atlanto-axial facet holds firm, and the frontal arch of the atlas touches the odontoid bone.

anterior cerebral artery – An artery originating from the internal carotid artery serving principally the frontal lobe, corpus collosum olfactory and optic tracts. Branches include the anterior communicating, ganglionic, commissural, and hemispheral arteries.

anterior commissure – A band of fibers that passes transversely through the lamina terminalis and connects the basal portions of the two cerebral hemispheres.

anterior communicating artery – An artery that originates from the anterior cerebral artery, supplies the caudate nucleus, and helps form the anterior part of the circle of Willis.

anterior cord syndrome – A condition that brings complete motor paralysis, yet with the ability to feel some sensations and body perception in the legs and feet, without sharp-dull discrimination.

anterior longitudinal ligament – Strong, broad, fibrous ligament that covers and connects the frontal aspects of the vertebral bodies and intervertebral discs. It goes from the sacrum’s pelvic surface to the forward raised eminence on C1 (atlas) and the occipital bone of the skull, frontal to the large opening at the base of the skull, through which the spinal cord enters into the cranial cavity (foramen magnum). It maintains the stability of the joints between the vertebral bodies and helps prevent hyperextension of the vertebral column.

anterolisthesis – A condition of spondylolisthesis in which the vertebral slippage is anterior.

anticholinergic drugs – Drugs which block the passage of nerve impulses through the parasympathetic nerves.

aphasia (or dysphasia) – Loss of the ability to express oneself and/or to understand language. The inability to speak (expressive asphasia or dysphasia) or comprehend (receptive aphasia or dysphasia) written and/or spoken language due to cerebral disorder. Caused by damage to brain cells rather than deficits in speech or hearing organs.

aphonia (dysphonia) – Loss of voice due to disorder of the larynx or its neural connection.

aponeuroses – Ribbonlike tendinous expansions connecting muscles with the parts that are moving.

apophyseal joints – Articular facets. See zygapophyseal joints.

apophysis – Refers to any outgrowth or swelling, especially bony expansions that have never been entirely separated from the bones of which they are parts. These are processes, tubercles, or other such protuberances.

apraxia – The inability to carry out correct voluntary movement commanded for a specific situation, although the movement may be performed under other circumstances. Results from disassociation of parts of the cerebrum and is often associated with parietallobe lesion.

aqueduct of sylvius (cerebral aqueduct) – A narrow canal, about three-quarters of an inch long, that connects the third and fourth ventricles.

arachnoid – The middle layer of the meninges of the brain; so-named (“like a cobweb”) because of its delicate network of tissue.

arachnoid mater – A thin and rather insubstantial membrane covering of the brain and spinal cord lying between the dura mater and the pia mater.

arachnoid villus – A microscopic projection of the arachnoid tissue into the venous sinuses. Arachnoid villus absorb CSF.

arcuate fasciculus – A bundle of fibers which connects the superior and middle frontal convoltions with the temporal lobe and temporal pole.

argonists – Muscles, or portions of muscles, anatomically attached so that upon contraction, the developing forces supplement each other.

arteriosclerosis – A condition marked by loss of elasticity thickening, and hardening of the arteries.

arteriovenous – Both arterial and venous; pertaining to or affecting an artery and a vein.

arteriorvenous malformation – An abnormal formation of arteries and veins. It may be only a small tangle of vessels or a large collection of abnormal vessels occupying a large area.

artery – A blood vessel that carries oxygenated blood.

arthritis – Inflammation of a joint, a general term for many specific forms of arthritis.

arthro- – Combined with other words, indicates a relationship to a joint or joints.

arthrodesis – Describes the surgical fixation of a joint. By encouraging bone cells to multiply, the procedure achieves fusion of the joint surfaces. It is also called artificial ankylosis. A spinal fusion is an arthrodesis of the spine.

arthroscopy – Diagnostic and surgical technique in which a small fiber-optic scope is used to look into a joint.

arthrosis – Has to do with a joint, an articulation or a disease of a joint.

arthrosis deformans – Describes rheumatoid arthritis.

articular – Of or relating to a joint or joints.

articular capsule – Type of capsule that lines the synovial cavity in the parts of the joint that are not cartilage. It permits a substantial amount of movement.

articular cartilage – This smooth cartilage is hyaline cartilage. It caps the bones facing the synovial cavity.

articular disc (fibrocartilage) – Disc that accomplishes three things. It absorbs the shocks in a joint; it evens out the joint surfaces; and it enables two simultaneous movements to take place.

articular processes – Four bony joints projecting out from where the pedicles and laminae join. They jut out both above and below, and each bony projection has a facet joint. These facet joint junctures between the upper surface and lower surface of vertebrae help in preventing forward movement of an upper vertebra on a lower one, especially in the thoracic and lumbar areas. The articular facets permit some flexion and extension as well as non-uniform amounts of lateral flexion and rotation. Also called zygapophyses.

articulation – Another word for joint; refers to the place where bones or cartilages or bones and cartilages meet.

association fibers – Fibers which connect various cortical portions of the same cerebral hemisphere.

astereognosis – The inability to discriminate shape, texture, weight, and size of objects. Often occurs with parietal lobe lesion.

astrocytes – Neurological cell of ectodermal origin characterized by fibrous, protoplasmic, or plasmatofibrous processes. Collectively, such cells are called astroglia.

astrocytoma – An intrinsic tumor of the brain that arises from star-shaped cells (astrocytes) of the neuroglia.

astroglia – he astrocytes, thought of as tissue. Previously called microglia.

ataxia – A problem of muscle coordination not due to apraxia, weakness, rigidity, spasticity or sensory loss. Incoordination of movement. May be due to brain disease in cerebellum or sensory pathways and can be part of a drug-induced movement disorder.

atherosclerosis – A degenerative process of arteries in which there are fatty deposits and degeneration of the inner lining of the vessel which, in turn, may lead to narrowing of the lumen of the vessel.

athetosis – Involuntary, purposeless, disordered movements, caused by a brain lesion, in which there is a constant recurrence of slow writhing movements of the hands and feet.

atlanto-axial – Pertaining to the atlas and the axis.

atlanto-occipital – Pertaining to the occiput and the atlas.

atlas – The first cervical vertebra, which unites by way of a joint above, with the occipital bone of the skull, and below, with the axis (C2), upon which it rotates. It is a ring-shaped bone and supports the skull. It has no spinous process or body but consists of arches above and arches below, each of which has a rounded elevation (tubercle) and lumps on the sides (lateral mass).

atrophy – A wasting away or decrease in size of a cell, tissue, organ, or part of the body due to lack of nourishment.

attenuation – Made thin, weak, or fine, as in strength, value, or virulence.

audiometry – A method of determining and quantifying the ability to hear a variety and range of pure tones. Hearing is described as a function of the number or cycles per second (CPS or hertz) that can be detected at a particular intensity (decibels).

auditory brain stem evoked potentials (ABP) – A method of recording sounds as they are integrated and processed in the brain stem.

auditory verbal dysgnosia – An aphasic deficit characterized by impairment of ability to understand the symbolic significance of verbal communication through the auditory avenue (loss of auditory-verbal comprehension).

aura – A period of seizure when sensation is abnormal.

autoimmune disorders – Impairment of the bodily processes by which immunization is effected.

autonomic – Refers to functions over which we have no control, such as respiration, digestion, and circulation.

autonomic nervous system (ANS) – Component of the central nervous system consisting of two divisions, sympathetic and parasympathetic. The ANS regulates and controls (largely) involuntary functions such as digestion, cardiac functioning, etc. Involves the limbic system of the brain.

avulsion – Shows that part of the structure has been torn away.

axial – Pertains to the axis of a form or part. In the body, it relates to the trunk, which is composed of the head, neck, thorax, abdomen, and pelvis.

axial skeleton – Skeleton part that makes up the longitudinal axis of the body. Within its area is the skull, the vertebral column, the sternum, and the ribs.

axial view – The overhead view, or ‘helicopter view,’ as spoken of in imaging.

axilla – The armpit area, a small pyramid-shaped space between the upper and side part of the chest to the middle side of the arm. Besides the armpit, it includes pertinent vessels, the brachial plexus of nerves, a large number of lymph nodes, and fat and areolar tissue. Also called armpit, fossa axillaries, and axillary space.

axis – Line around which certain parts of the body are arranged; also refers to the second cervical vertebra, C2. This vertebra, known as epistropheus, odontoid vertebra, and vertebra ventata, is the strongest of the cervical vertebrae. It is next to the atlas, C1, which rotates on its two large flat bearing surfaces, the upper articular facets. Projecting above from its body is the odontoid process or dens, which is its most noticeable characteristic. The dens is held in place by the transverse ligament of the atlas, and keeps the atlas from being displaced horizontally. When you feel the back-facing groove of the neck, the nuchal furrow, the first spinous process to be felt is the large bifid spinous process.

axon – The main or core nerve fiber which generally conducts impulses away from the cell body.

axon terminals – Ends of branched-out neurons, where impulses are transmitted to other nerve cells or to organs that react to the signals transmitted.

axonotmesis – The nerve is anatomically intact, but there is a complete interruption of all types of nerve fibers with essentially complete motor and sensory loss. The nerve has to recover by axonal regeneration and this starts at the cell body, near or in the spinal column, and progresses outward at approximately 1 mm per day. A nerve may not always have only one type of injury. It is possible to have combined types of injuries within a given nerve.



babinski response – Extension (instead of flexion) of the toes on stimulation of the sole of the foot, occurring in persons with lesions of the pyramidal tract.

bacterial infection – Infection by minute, one-celled organisms which multiply by dividing in one or more directions.

basal ganglia – The site of the brain where the extrapyramidal system originates. Includes caudate nucleus, globus pallidus, and putamen; thalamus, subthalamus, substantia nigra, and red nucleus sometimes included.

basilar artery – An artery formed by the right and left vertebral arteries which supplies blood to parts of the cerebrum and cerebellum. It supplies blood to many brainstem structures and leads to the right and left posterior cerebral arteries.

basophil – A granular leukocyte with an irregularly shaped, relatively pale-staining nucleus with cytoplasm that contains coarse bluish-black granules of variable size. Basophils contain vasoactive amines, such as histamine and serotonin, which are released on appropriate stimulation.

bell’s palsy – Unilateral facial paralysis of sudden onset, caused by a lesion of the facial nerve.

beta rhythm – Rhythmic waves in the electroencephalogram that have a smaller amplitude than alpha waves and have an average frequency of about 25 cps.

bilateral – Refers to using both sides of the body or extremities on both sides.

bilateral sensory stimulation – Stimulation of both sides of the body simultaneously, using touch, hearing, or vision, in order to determine whether an individual imperceives the stimulus on one side or the other.

bilateral transfer – Facilitation of performance of a task by one hand as a result of having practiced the task with the other hand.

biofeedback – The use of sensory feedback to help provide some self-control over autonomic functions, such as blood pressure.

biotechnology – In the most general terms, biotechnology describes guiding natural occurrences to develop useful products. More specifically, it involves using living organism to make products and solve problems.

bipolar disorder – A genetically determined condition characterized by extremes of moods, often to psychotic (cf) proportions. Mania may alternate with depression.

blepharospasm – Spasmodic and frequent blinking of the eyes (tonic spasm of the orbicularis oculi muscle).

blood-brain barrier – A process whereby certain substances fail to leave the blood circulation and enter the gray and white matter of the brain. The “barrier” is more of a physiological concept than a defined anatomic structure. In addition, the barrier does not exist at certain sites in the brain, including the pituitary gland, the pineal gland, and choroid plexus.

blood dyscrasia – A disorder characterized by an abnormal composition of the blood.

body dysgnosia – A deficit, associated with aphasia, in which the subject is impaired in ability to identify body parts.

bone – The hard form of connective tissue that makes up most of the skeleton. The organic component is comprised of cells and matrix, and the inorganic is mineral. The framework of the matrix is collagenous fibers, into which is integrated the mineral component of 85 percent calcium phosphate and 10 percent calcium carbonate, giving bone its firmness. Bone is also called osseous tissue.

bone scan – Radionuclide test usually performed in the radiology department. It can detect fractures, stress fractures, areas of infection in bone, abnormal bone growth, and bone cancer, and also spread of cancer to the bones.

bone window – Used for viewing bone structure and joints in CT scanning, it measures the spinal canal, detects fractures, and shows whether the fracture is displaced inside or outside the spinal canal.

bony end plate – One of the components of the vertebral discs. They are composed of two layers of cartilage that cover the top and the bottom surfaces of the disc. They are also called vertebral end plates.

bony union – Final stage of the body’s repair of a bone fracture.

bow string sign – Test similar to the Lasegue’s sign done in the following way: The patient is lying in bed. The examiner sits on the edge of the bed, flexes the patient’s thigh, and puts the patient’s legs over the examiner’s shoulder in an angulation in such a way that the patient is free of pain. Then, with a finger, the doctor presses the patient’s sciatic nerve behind the knee (popliteal area). If the patient complains that the pain radiates up to the back or down to the foot, the test is positive.

brachia pontis – A pair of peduncles which attach the pons to the overlying cerebellum.

brachial – Refers to the arm.

brachial plexus – Network or tangle of nerves originating from the ventral branches of the last four cervical spinal nerves and most of the ventral branch of the first thoracic spinal nerves. It situates partly in the neck and partly in the armpit area.

bradykinesis – A motor disorder, frequently seen in Parkinson’s disease,resulting from rigidity of muscles and manifested by slow finger movements and difficulty in fine motor performance, such as writing.

bradykinin – Chain of nine amino acids; it is a powerful vasodilator that causes increased permeability. It constricts smooth muscle and stimulates pain receptors.

brain – That part of the central nervous system contained within the cranium, comprising the prosencephalon, mesencephalon, and rhombencephalon. It is developed from the frontal part of the embryonic neural tube. Also called encephalon from the Greek enkephalos, brain.

brain abscess – A localized collection of pus in a cavity in the brain, formed by the disintegration of tissues.

brain contusion – A bruise of brain tissue in which there is capillary bleeding.

brain death – A state of irreversible coma in which cerebral and brain stem functions are absent.

brain electrical activity mapping (BEAM) – A computerized interpretation of brain currents incorporating (usually) sound and visual evoked potentials to produce a colored map of brain electrical functioning.

brain infection – An invasion of brain tissues by pathogenic organisms in such a way that injury of brain tissue follows with symptoms of illness.

brain lesion – Any pathological or traumatic damage of brain tissue.

brain scan – Any A radionuclide test for measuring blood circulation through the brain, or for detecting tumors, infection, or evidence of stroke.

brain stem – Composed of midbrain, pons and medulla.

Broca’s (motor or expressive) aphasia – A disturbance of speech or reading caused by a defect in the motor (afferent or affector) apparatus of the brain. Comprehension of speech is usually not affected.

Brown-Sequard syndrome – An incomplete cord injury that is difficult to diagnose and is characterized by paralysis and lack of sensation below the spinal cord injury. The paralysis of the extremity, with loss of discriminatory and joint sensation, is on the side where the spinal cord has been injured. Loss of sensation of pain and temperature is on the opposite side.

bruit – A sound or murmur, especially of an abnormal nature, that is heard in auscultation.

bruxism – Tooth grinding, often associated with emotional tension or a temporomandibular joint disorder.

bulging disc – Delineation abnormality in the intervertebral disc as seen in X-rays. It is subject to various interpretations, and sometimes causes communication difficulties. In simple terms, it refers to a diffuse protrusion of disc material beyond the back margins of the vertebral endplates without significant irregularity or degree of focus. The outer fibers of the annulus fibrosus are intact.

burst fracture – A fracture of the interior and middle vertebral bodies.



calcification – Process by which organic tissue becomes hardened by a deposit of calcium salts within its substance.

calcium crystal – Mineral components that facilitate the healing and repair process of bones.

calor – The heat aspect of the inflammatory phase.

caloric testing – A method of testing the integrity of the inner ear (balance) apparatus by injecting warm or cold water into the ear and by recording the duration of the nystagmus this produces.

calvaria – The cranium, or more specifically, the skull cap.ᅠ The roof of
the skull.

canal, canaliculus – Narrow, cylindrical passage or channel. A general term to describe a variety of small channels.

cancellous bone – Bone substance made of thin intersecting lamellae, usually found internal to compact bone.

capillary – A minute blood vessel which connects an arteriole and venule, forming a network in nearly all parts of the body and effecting a transition from arterial to venous blood flow.

capsula or capsule – General term for a cartilaginous, fibrous, or membranous structure that envelops another structure, organ, or part. The articular capsule envelops the joint. It consists of two parts: a fibrous capsule and a synovial membrane (capsule). When the term joint capsule is used, it is usually the fibrous part that is meant. The synovial membrane is a vascular connective tissue membrane that lines the entire joint cavity, although it does not cover the articular cartilage. The synovial membrane produces synovial fluid that lubricates the joint. It is the synovial membrane (capsule) in the joint that becomes inflamed with arthritis.

capsular ligaments – Ligaments with saclike envelopes, which enclose the cavity of a synovial joint by attaching to the circumference of the articular end of each involved bone. Also called joint or synovial capsule.

carcinogen – Any substance which produces cancer.

carcinoma – A malignant new growth (cancer) that tends to infiltrate surrounding tissue and give rise to metastases.

carotid arteries – Arteries carrying blood to the head. The common carotid artery originates from the brachiocephalic trunk and the aortic arch, goes through the neck, and distributes through its branches, the internal and external carotid arteries. The internal carotid arteriesメ branches distribute into the middle ear, brain, pituitary gland, orbit, and choroid plexus. The external carotid artery via its branches distributes into the neck, face, and skull and is called the facial artery.

carotid system – A system of blood circulation to certain parts of the brain deriving from the internal carotid arteries.

cartilage – Specialized type of connective tissue that supports and aids in movement at joints.

cartilaginous joint – Classified as to structure, this joint has no joint cavity and is joined by hyaline cartilage or a fibrocartilaginous disk. As to movement, they are usually amphiarthroses (Gr. amphi, both sides + arthroses, joint), allowing little or none. The two types are the synchondroses (Gr. synchrondosis, モa growing into one cartilageヤ) that permits growth and the symphyses (Gr. symphusis, growing together, natural junction), which have shock-absorbing intervertebral discs.

cauda – General term for a structure resembling such a continuation.

caudad – Directed toward the tail.

cauda equina – In the human spine, it is made up of a bundle of neural tissue, connective tissue, pia mater, and neuron cells, and starts below the end of the spinal cord, beyond the L2 vertebra in the adult vertebral canal. It derives from the useless remnant of the spinal cord that was in the tail of the embryo. Where it begins, it is made up of remainders of neural tissue, connective tissue, pia mater, and neuroglial tissue. At its lower end, it becomes a thin, fibrous strand descending among the nerve rootlets of the cauda equina. It leaves the lower end of the dural sac, passes through the sacral hiatus, blends with the upper end of the anococcygeal ligament, and ends by inserting into the back of the coccyx. Known as the filum terminale, this tail or tail-like appendage has no functional use.

caudal – Suggesting a position more toward the cauda or tail rather than some specified point of reference. In human anatomy, it means the same as inferior.

caudate nucleus – An elongated, arched mass of gray matter that is adjacent to the lateral ventricle of the brain throughout its entire extent and consists of a head, body, and tail. The caudate nucleus, lentiform nucleus, and putamen compose the corpus
striatum, which is located in front of the thalamus.

cavitation – A physio-chemical process resulting in the production of microscopic explosions of gas within the brain following rapid acceleration of the brain inside the skull.

cellular pleomorphism – Assumption by cells of various distinct forms. Also, the property of crystalizing in two or more forms.

central cord lesion syndrome – A condition usually caused by forceful hyperextension of the neck, especially in old people who have osteoarthritis or spinal canal stenosis. It is characterized by weakness or paralysis of the upper extremities, and to a lesser degree, the lower extremities. The patient may have urinary retention and inability to control defecation. However, some sensation of the sphincter may be preserved. The younger the person is, the better the prognosis. Usually, the leg, the bowel and the bladder function return first.

central dysarthria – Impairment of ability to enunciate words, characterized by
an omission, addition, or transposition of syllables.

central fissure (Rolandic fissure) – A fissure is a deep fold in the cerebral cortex which involves the entire thickness of the brain wall. The central fissure is the deep fold between the frontal and parietal lobes.

central nervous system – The brain and spinal cord.

centrolateral – See paracentral. Synonyms: paracentral, paramedian.

cephalad – Directed toward the head.

cephalic – Pertaining to the head.

cerebellar fits – Episodes of decerebrate rigidity usually associated with large
midline cerebellar masses.

cerebellum – A structure lying in between the undersurface of the occipital lobe and the brain stem, largely concerned with the regulation and control of the muscular tone, coordination, movement, posture, and gait.

cerebral angiogram – A procedure of visualization of blood vessels of the brain, using x-rays taken after injection of radiopaque material into the arterial blood stream.

cerebral anoxia – A condition in which the cells of the brain do not have (or cannot utilize) sufficient oxygen to perform normal functions.

cerebral atrophy – A wasting away or diminution in the size of cells or tissue structures of the brain.

cerebral blood flow – The rate of blood flow through the brain, which may be measured by various techniques and determined for various regions of the brain.

cerebral cortex – The thin surface layer of gray matter (nerve cell bodies) that forms the outer surface of the cerebrum.

cerebral edema – Any extracerebral condition that increases cerebral blood volume, such as a low blood content (hypoxia) and a high carbon dioxide content (hypercapnia).

cerebral embolism – A sudden blocking or obstruction of an artery or vein by a clot which has been brought to the position of blockage by the current of blood flow.

cerebral hemisphere – The large structure representing either half of the cerebrum.

cerebral hemorrhage – Bleeding of a blood vessel within the cerebrum.

cerebral infarct – An area of coagulation necrosis in a cerebral vessel which obstructs circulation and results in pathological changes in the area deprived of blood supply.

cerebral lateralization – The concept that left and right sides of the brain have different but overlapping and integrated functions determining certain personality traits, creativity, and other qualities.

cerebral palsy – Impaired muscular power and coordination as a result of brain damage, usually occurring at, before, or shortly after birth.

cerebral vascular accident (CVA or stroke) – An embolism, infarct, or hemorrhage
of a cerebral vessel.

cerebral vascular insufficiency – Lack of a sufficient supply of blood (which
can be due to many factors) for the brain to perform its normal functions.

cerebrospinal fluid – The fluid contained within the cerebral ventricles, subarachnoid sinus, and the central canal of the spinal cord. It acts as a water cushion to protect the brain and spinal cord from shock.

cerebrum – The paired cerebral hemispheres.

cervical – Pertaining to the neck.

cervical area – The section of the spine that allows movement of the head and permits the nerves of the spinal cord to pass through it, going from the head to the rest of the body.

cervical disc disease – Continuation of the chemical process of aging starting within the nucleus pulposus that results in annular tearing, acute disc herniation, or diffuse cervical spondylosis. A natural process, often asymptomatic, it proceeds at different rates in different people.

cervical spondylosis – This degenerative joint disease affects the cervical vertebrae, their intervertebral discs, and their surrounding ligaments and connective tissue. It is usually related to osteoarthritis. Sometimes it comes with pain or paresthesia radiating down the arms, as a result of pressure on the nerve roots.

cervical vertebrae – Seven small neck bones between the skull and thoracic vertebrae that support the head and allow it to move.

cervicothoracic junction – Where the spine of the neck and the chest meet.

chance-type fracture – The so-called seat belt injury, a horizontal avulsion injury of the intervertebral body as a result of flexion about an axis, in front of the anterior longitudinal ligament. The entire vertebra is pulled apart by a strong tensile force.

chiasm – A crossing or decussation of parts. The optic chiasm refers to the
crossing of fibers of the optic nerve, forming the optic tract, that lies on the ventra surface of the brain.

chondrification – The formation of cartilage; transformation into cartilage.

chondroblast – A specialized cartilage connective tissue cell.

chondrocyte – In the cartilage matrix, there is a small pit or hollow cavity called a lacuna. A chondrocyte is a mature cartilage cell firmly fixed there.

chondroid – Resembling cartilage.

chondromalacia facetae – Softening of the articular cartilage, mostly in the knee.

chordoma – A malignant tumor which arises from the embryonic remains of the notochord.

chorea – Involuntary, jerking, irregular writhing movements usually of limbs, often indicative of CNS disease.

choreiform movements – Movements that occur in the various forms of chorea which consist of rapid, highly complex, jerky movements that appear to be well coordinated but are performed involuntary and go on continuously in a variety of expressions.

choreoathetotic movements – Movements of both a choreic and athetoid nature. Athetosis is marked by ceaseless occurrence of slow, sinuous, writhing movements that are involuntary and may be particularly severe in the hands.

choroid plexus – A highly vascularized fold of the pia matter in the third, fourth, and lateral ventricles that secretes the cerebrospinal fluid.

chromosome – DNA material that carries the genetic information or basic plan for the development of the fetus. Each sperm cell and each egg contain a single set of twenty-three chromosomes.

chronic – Long-standing (months or years) but not necessarily irreversible. Symptoms may be mild or severe.

cicatrix – The new tissue formed in the healing of a wound.

cingulate gyrus – A convolution (gyrus) which is arch-shaped and closely adjacent to the surface of the corpus collosum, from which is it separated by the callosal

Circle of Willis – A circular system of cerebral arteries formed principally by the internal carotid, the anterior and posterior cerebral arteries, and the posterior communicating arteries.

cisterna magna – Enlarged subarachnoid space between the undersurface of the cerebellum and the posterior surface of the medulla oblongata and continuous with the subarachnoid space. It can be tapped by means of a needle inserted through the atlanto-occipital membrane (cisternal puncture). Also called cerebromedullary cistern.

cisternography – Radiographic visualization of the basal cisterns of the brain after injection of a contrast substance.

clinical stability – The spineメs ability, under physiologic loads, to confine patterns of displacement in order not to damage or irritate the spinal cord, cauda equina, or nerve roots and, in addition, to prevent disabling deformity or pain because of structural changes.

clonus – Alternate muscular contraction and relaxation in rapid succession.

coccygeal ligament – Very strong triangular or inverted Y-shaped band that covers the anterior and superior portions of the hip joint. It arises by its apex from the anterior inferior iliac spine and is inserted by its base into the intertrochanteric line of the femur.

coccygeal plexus – Coccygeal nerve plus communications from nerves S4 and S5.

coccyx – At the end of the vertebral column and below the sacrum, three to five vertebrae are called the coccyx, commonly known as the tailbone.

cognitive – Having to do with functions of knowing, including reasoning ability, memory retrieval, and perception.

cognitive/intellectual development – Refers to the process wherein an individual acquires both the intellectual and executive functions, and manner of reasoning which characterize the species. In humans, this process moves from a state of essentially no capacity to reason (even at the simple level of understanding of cause and effect) to the eventual acquisition of the ability to think and reason abstractly.

cogwheeling – A phenomenon that occurs among patients with Parkinson’s disease in which a muscle, when passively stretched, develops a degree of hypertonicity and resistance, occurring in the form of irregular jerkiness of movement.

collagen – The protein substance of white (collagenous) fibers of connective tissue.

collateral sprouting – Intact axons located near damaged areas may sprout to reestablish connections with, and in place of damaged areas; cannot be assured that the new connections function exactly as their damaged neighbors did.

colloid cyst – A cyst that occurs particularly in the third ventricle and contains jelly-like material.

coma – A state of unconsciousness wherein the person is incapable of responding to internal or external stimuli.

comminuted fracture – A fracture that is often the result of a combination of external force on the axis and of flexion force from the side. Usually, a fracture has torn away at the crosswise ligament (avulsion fracture) plus one-sided frontal and posterior arch fractures have occurred. Comminuted fractures are the least likely to unite, and therefore, function is affected afterward.

common peroneal nerve – Sensory and motor nerve that originates in the sciatic nerve in the lower part of the thigh. Its branches supply the short head of the biceps femoris muscle while it is still incorporated with the sciatic nerve. It gives off the lateral sural cutaneous nerve and peroneal communicating branch as it descends into the popliteal fossa. It supplies the knee and superior ribiofibular joints and tibialis anterior muscle, and divides into superficial and deep peroneal nerves.

communicating hydrocephalus – Hydrocephalus is a condition in which there is an abnormal accumulation of cerebral spinal fluid within the skull. Communicating hydrocephalus is a condition in which there is no obstruction in the ventricular system and cerebrospinal fluid is able to pass out of the brain but is not re-absorbed.

compensation neurosis – An outdated term sometimes (erroneously) confused with traumatic neurosis and referring to a set of ill-defined symptoms that arise in the context of a potential for benefit deriving from an accident.

compression – Literally, squeezing together; used to indicate the physical change the body undergoes when an external force decreases its volume and increases its density. In embryology, it refers to the abbreviation or curtailing of some stage or stages during development.

compressive extension lesion – Occurs when the skull is knocked backward and downward against the backbone. A man on a construction job who nearly gets his block knocked off by a モheadache ballヤ that is dropped on him will have this type of injury.

compressive flexion lesion – A kind of trauma that often results from head-on collisions and falls from roofs.

compromise – Word used by surgeons when what they find during a physical examination indicates pressure on the nerve root. Often it is due to pathologically changed spaces in the vertebral canal, especially a herniated disc or degenerative bony overgrowth.

computerized axial tomography (CAT scan) – An x-ray technique which photographs serial “slices” of tissue, producing detailed scanning.

concave – Having a rounded, somewhat depressed surface like the hollowed, inner surface of a piece of a sphere.

concussion – A reversible paralysis of nervous functions following brain trauma, usually involving a transient loss of consciousness and/or a transient state of confusion.

condyle – Knuckle-shaped projection on a bone, either knoblike or convex.

confabulation – The involuntary production of a false or pseudomemory to cover a fundamental defect of memory; arises from brain tissue impairment.

connnective tissue – Supportive and connective tissue consisting of fibers, ground substance, cells, and some extracellular fluid; the most abundant type of tissue.

confusion – A state wherein thinking lacks clarity, direction, and the ability to attend and concentrate.

congenital lesions – Lesions present at or dating from birth.

constructional dyspraxia – Impaired ability to deal with spatial relationships either in a two- or three-dimensional framework. This symptom is commonly manifested by impaired ability to copy simple shapes, such as a cross.

contact – When disc material and the neural structures have no intervening epidural fat between them or noticeable displacement or disfiguration of the nerve roots or thecal sac, the imaging report will refer to the relationship using this term. Synonym: abut.

contained – This word has slightly different meanings according the author involved. Basically, it directs attention to the outer anatomic boundary confining the disc herniation. However, different posterior boundaries may be decided upon, according to the author (either the outer annular layers or the posterior longitudinal ligament or both). Some use contained to show a herniated disc has ruptured through the outer annular layer but is confined by the posterior longitudinal ligament (subligamentous). Others suggest, and it seems more acceptable, for it to be confined by the outer border of the annulus (subannular).

contained disc – In a discogram, when the dye injected into the disc remains inside the annulus fibrosus of the suspected disc, as shown on X-ray, the disc is then referred to as a モcontained disc.ヤ If the dye goes outside the annulus fibrosus, then the fissure has gone all the way through the outer wall of the disc.

contractility – Capacity for becoming short in response to a suitable stimulus.

contraction – The shrinkage and spontaneous closing that takes place in open skin wounds. Contraction pulls normal tissue into the open area to achieve coverage.

contracture – When a scar shrinks, the loss of tissue mobility is known as contracture. The term is also used when fixed high resistance is noted as a muscle is stretched, passively, caused either by fibrosis of the tissues supporting the muscles or joints or disorders of the fibers of the muscle.

contralateral – Pertaining to opposite sides of the body.

contrecoup – Phenomenon employed to explain the location of brain damage which occurs on the side or pole of the brain opposite the impact.

contusions – Microscopic or visible hemorrhages into tissue; a bruise. Following head injury, contusions occur more often in frontal and temporal poles of the brain.

conus terminalis – The cone-shaped lower-most end of the spinal cord, at the level of the upper lumbar vertebrae where it tapers very abruptly, and from which a slender fibrous strand (the cauda) descends among the nerve rootlets; called also terminal cone of the spinal cord.

conversion disorder (conversion hysteria) – A psychiatric condition in which aberrant bodily functioning arises from psychologic conflict or need. Coded 300.11.

coronal view – Indicates a plane as seen from the front, if you cut across the head from one ear to the other (dividing the front from the back). Cuts made parallel to that would be called coronal cuts. Coronal means, also, pertaining to the crown of the head. Coronal view is of a section passing through the body at right angles to the median plane (midsagittal). You can remember this by visualizing a king from the front, with the downward cuts from ear to ear not disturbing, from your viewpoint, the outline of his crown.

coronalis – Coronal; denotes a structure situated in the direction of the coronal suture.

corpectomy – Surgical removal of a vertebral body of the spine.

cortex – The outer layer of an organ or part.

cortical – Pertaining to the outer layer of an organ or the body structure, as distinguished from the internal substance.

costa – Rib.

costo-central ligaments – Ligaments (both capsular and interarticular) that join the ribsメ heads to the vertebral bodies.

costo-transverse ligaments – Ligaments (anterior, middle, posterior, and capsular) that link the necks and tubercles (small elevations) of the ribs to the transverse processes.

costotransversectomy – The surgical removal of the portion of the rib (costa) that is attached to the transverse process, which is also removed.

costovertebrae – The vertebrae in the spine that correspond to the ribs.

cranial nerves – Twelve very important nerves which originate in the midbrain and which innervate structures in the head, neck and some body

cremasteric cutaneous reflexes – Stimulation of the skin on the front and inner side of the thigh retracts the testis on the same side. The presence of this reflex reflects integrity of the first lumbar nerve segment of the spinal canal or its root; absence indicates damage of the first lumbar nerve segment or its root or lesion of the corticospinal tract.

cruciform ligament of atlantis – Ligament in the form of a cross, of which the transverse ligament of the atlas forms the horizontal bar, and the longitudinal fascicles, the vertical bar of the cross.



decussation – Branching or splitting into two divergent pathways, as at the optic chiasma.

degenerated disc disease (DDD) – Mechanical breakdown of the integrity of a disc, which produces symptoms initially because of mechanical instability and later productive of root or cord compression owing to the development of osteophyte outgrowths.

delirium – A state of confusion often associated with hallucinations and hyperactivity, in which the patient is inaccessible to normal contact.

dementia – A general loss of intellectual abilities of sufficient severity to interfere with social or occupational functioning. Emotions, personality, and behavior are invariably affected. Caused by an organic brain lesion.

dendrite – A fine branching process of the nerve cell which conducts a nerve impulse from the cell body to the structure(s) supplied by the nerve, or toward the cell

denervation – Resection or removal of the nerves to an organ or part.

dens axis – Tooth of the axis (C2); the tooth-like process that projects from the upper surface of the body of the axis, as a pivot, a peglike protrusion, to articulate with the atlas (C1), also called the odontoid bone, etcetera.

depression (dysthymia) – An abnormal lowering of mood of psychologic or physiologic origin which is more prolonged than mourning and is time-limited and related to a specific loss.

dermatomes – The characteristic distribution of sensory innervation on the skin of the body and the limbs.

development – (In general) Refers to the process wherein an organism changes over maturation, according to specifically designed programs encoded in its individual genetic code. In normal development, this code is presumed to reflect the typical development code of the species, with some room for idiosyncratic variation within an anticipated range. In general, development in each of the various areas identified proceeds at a rate consistent with, and supportive of, the development of other areas, and appears as an integrated, interactive process.

diagnostic overshadowing (Concept) – Once a diagnosis is made of a major condition (such as TBI) there is a tendancy to attribute all other problems to that diagnosis, thereby leaving other co-existing conditions undiagnosed.

dermatome – The area of skin supplied by afferent nerve fibers by a single posterior spinal root; used in locating injuries to dorsal roots of the spinal cord. Called also dermatomic area. Also refers to an instrument for cutting thin skin slices for skin grafts.

diarthrodial joints – Joints between individual segments of the spine such as apophyseal, zygapophyseal, or facet joints, which provide for both mobility and stability and, by their arrangement, help to equitably distribute load from the top of the spine to the bottom. These articulations limit the mobility between two vertebrae to a predetermined degree and direction.

diarthrosis – A joint, classified as to the degree of motion, as a freely movable joint.

diencephalon – So called “midbrain” or interbrain connected to the cerebral hemisphere; contains pituitary gland.

differentiation – The process by which cells develop into specialized tissues and organs.

diffuse axonal injury (DAI) – Widespread distribution of and damage to white matter of the brain due to rotational shearing forces coincident with head trauma.

dilatation – The condition of being dilated or stretched beyond the normal dimensions.

digital subtraction angiography (DSA) – Non-invasive exploratory technique that uses a digital computer to produce three-dimensional pictures of blood vessels.

diplopia – Double vision. A muscle imbalance between the eyes causes stimulus to be received in different parts of the retina.

disability – Any restriction or lack (resulting from an impairment) of ability to perform an activity in a manner or within the range considered normal for a human being.

disc degeneration – A wearing down of the disc that generally causes mechanical instability and osteophytes.

disc herniation – General term that describes either disc prolapse, protrusion, or extrusion. (See herniated intervertebral disc.)

disc(k)ogram – Roentgenogram of an intervertebral disc.

dislocation – Displacement of bone in a joint so that two articulating surfaces become separated; also called luxation.

displaced – When either a herniated disc or a degenerative bony overgrowth such as an osteophyte affects the nearby nerves; indicates a change in the usual position of a nerve root or thecal sac.

displacement – Removal from the normal position or place.

distal – Relative directional term indicating remote, farther from any point of reference, away from or farther from the trunk of the body or the attached end of a limb. The wrist is distal to the forearm. Opposed to proximal.

distraction – Distraction occurs when, without rupture of their supporting ligaments or without displacement, the joint surfaces are separated, or when there is too much space between fracture fragments because of interfering tissue, etc. Also refers to the surgical separation, after a bone is transversely divided, of the two parts of a bone.

distraction test – Test to determine if the patient has a disc herniation. The doctor pulls upward on the patientメs head, holding the chin and the back of the skull for thirty to sixty seconds. This should relieve pain if the patient has a disc herniation. The location of the relief will help in the diagnosis.

distractive extension lesion – An injury that is seen in an uppercut to the jaw or in a person who falls and hits their chin on the edge of a bathtub.

dizziness – A subjective and imprecise term which could refer to vertigo or a variety of disturbing conditions with a psychological basis.

dolor – The pain aspect of the inflammatory phase.

dorsal – Relative directional term that directs to the back or to any dorsum. It means more toward the back surface than another point of reference. In the hand or foot it refers to the upper surface and is the same as posterior. It is the opposite of ventral.

dorsiflexion – Upward flexion of the foot at the ankle joint.

dorsum – The back; an anatomical structureメs posterior or back vantage point.

double herniation – Rarely, there will be bilaterial disc herniations at the same intervertebral disc level. Usually, in this condition, the central disc appears normal. However, on both sides, paracentral or foraminal/extraforaminal herniations are found. Since this condition is not often encountered, the lesion is usually simply described in detail.

DMS III-R – The Diagnostic and Statistical Manual of the American Psychiatric Association, Third Edition, Revised; the standard guide to the classification of mental disorders. The manual is generally accepted as providing definitive definitions and descriptive (phenomenologic, not based on a particular theory) criteria for a variety of mental disorders.

DSM-IV – The Diagnostic and Statistical Manual of the American Psychiatric Association Fourth Edition; the standard guide to the classification of mental disorders. Specifically addresses the use of the term mental although acknowledging that there is much physical in mental disorders and much mental in physical disorders (Introduction, xxi). The manual is generally accepted as providing definitive definitions and descriptive (phenomenologic, not based on a particular theory) criteria for a variety of mental disorders.

dura mater – The fibrous tough outer sheath surrounding the brain and spinal cord.

dural sac – As the dura mater extends beyond the lower end of the spinal cord, it is called the dural sac. It is also made up of the arachnoid mater.

dynamic – Pertaining to or manifesting force.

dynamics – That phase of mechanics that deals with the motion of material bodies taking place under different, specific conditions.

dynamic spatial reconstructor (DSR) – Scanning device used to see the blood flow through the brain. Computer generated, it produces three-dimensional pictures of the active brain.

dysarthria – Defective articulation due to disorders of the vocal apparatus.

dysesthesia – Impairment of any sense, especially that of touch.

dysphagia – Difficulty in swallowing.

dysphonia – Any impairment of voice or a difficulty in speaking.



eburnation – Condition in which the articular cartilage thins out because of disorganization and fragmentation of the superficial tissue in osteoarthritis as it extends degenerative changes into the deeper part of the cartilage. The subchondral bone becomes exposed, denser, and its surface worn and polished.

echo gradient – Method used for imaging in myelograms, especially in axial views. Because the spinal fluid and the epidural veins give high signal brightness, these images show the foramina and help detect extradural lesions. Echo gradient imaging has ferro (iron) magnetic sensibility and is therefore recommended for injuries that may have old hemorrhages, because old bleeding contains iron.

ecto- – Prefix denoting situated on, without, or on the outside.

ectomy – Word termination that, when combined within a word concerning an organ of the body, means the organ has been taken out or removed, such as appendectomy (the appendix is out), tonsillectomy (the tonsils are out), laminectomy (the lamina of the vertebra is out).

edema – Swelling of the tissues due to oozing of the serum of blood from the vessels into the extravascular spaces.

effector neuron – The output nerve component of the reflex arc which transmits a reaction to the end of the organ to which the effector neuron connects.

efferent – Motor pathway proceeding from the central nervous system toward the peripheral end organs.

elation – Marked elevation of mood; joyous exaltation, sometimes seen in the manic phase of bipolar disorder.

electrical muscle stimulation (EMS) – Device used to transmit a low-voltage current through the skin, generally to trigger points in a muscle near the junction of nerves and muscle tissue thereby causing the muscle to contract. Used in therapy for muscular pain.

electroencephalogram (EEG) – A device used to measure and record electrophysiologic changes in the surface of, or within the substance of, the brain.

electromyography (EMG) – Procedure in which a monopolar needle electrode is introduced into the muscle to be tested, with a surface electrode acting as the reference. The purpose is to record electrical activities of the muscle fibers.

electronystagmography – A method by which eye movements are recorded and by which the origin of nystagmus may be elucidated.

encroachment – Used when either the normal anatomic volume of the spinal canal or the nerve root opening in the vertebrae is reduced or encroached upon, giving less space for the spinal canal or the nerve roots. Ordinarily, it indicates pressure on the dural sac or the nerve root, due to a degenerative disc and the resulting bony growths such as osteophytes, or by fragmented discs. The word usually describes spinal stenosis.

endochondral ossification – Process by which bone tissue develops by replacing hyaline cartilage.

endosteal – Pertaining to the endosteum or tissue lining the inner core of the bone.

endosteum – Tissue lining the medullary cavity of the bone.

endothelium – The layer of epithelial cells that lines the cavities of the heart, and the blood and lymph vessels, the serous cavities of the body. It originates from the mesoderm.

end plate – The central part of the cartilaginous epiphysis that is formed into a dense, bony end plate on the vertebral surface, and to which is subjected the compressive loads transmitted by the nucleus pulposus.

entheses – Sites of attachment of a muscle or ligament to bone.

environment – The context in which development takes place, including physical properties of stimuli.

environmental feedback loop – Refers to a phenomenon wherein specific environmental influences may influence or alter the process of one or more streams of development. In neurodevelopment this refers to the fact that specific kinds of sensory experience result in specific patterns of synaptic organization in the brain.

ependyma – Lining membrane of the ventricles of the brain and of the central canal of the spinal cord.

ependymal cells – Cells of the neuroglia and the extracellular fluid that are responsible for scar formation in the brain.

epi-, ep- – Prefix denoting on, upon, or over.

epidural – Outside meningeal layers. In head injuries, a hematoma may form between the dura and the skull.

epidural block – In an epidural block, an anesthetic agent is injected into the extradural (epidural) space. It diffuses through the dura and arachnoid, entering the subarachnoid space containing CSF. It acts on the nerve roots and the spinal cord causing loss of sensation below the level of the block. While it is very unlikely to affect the fetus during childbirth, it is effective in preventing pain. Chronic lower backache is also treated with an epidural block.

epidural space – Cavity between the bony and ligamentous walls of the vertebral canal and the dura. Within it there is fat, loose connective tissue, and the front and back vertebral venous plexuses. Also called extradural space. See subdural space.

epilepsy – A neurologic condition originating in disordered and excessive discharge of cerebral neurons. Synonymous with convulsive disorder and seizure disorder. Consciousness is invariably altered in some manner during the seizure.

epimysium – The fibrous sheath about an entire muscle.

epiphysis – Normal outgrowth that is either entirely cartilaginous or separated from the shaft by a disc made of cartilage. They are parts of a bone formed from a secondary center of ossification usually found on the margin of flat bones at projecting bony parts (processes) during the period of growth. Epiphyses are separated from the main portion of the bones by cartilage.

epithelium – Membranous tissue composed of one or more layers of cells separated by very little intercellular substance and forming the covering of most internal and external surfaces of the body and its organs.

equipotentiality – Refers to a hypothetical construct in neuro development which argues that, at very early points in development, all the specific regions of the cortex are sufficiently undifferentiated to permit them equal potential to support the various functions which become localized over time.

esophagus – Musculomembranous passage extending from the pharynx to the stomach.

eu- – Combining form meaning well, easily, or good; the opposite of dys.

euphoria – An abnormal sensation of well-being present even in the presence of distressing circumstances.

evulse – To extract by force.

ex-, ect-, ecto- – Prefix for combining form meaning away from, without, or outside. (Remember the EXIT on theater doors, meaning “out”. Any word ending in -ectomy means that the organ is cut out: tonsillectomy, appendectomy, hysterectomy, cholecystectomy, laminectomy, etc.) It is sometimes used to mean completely, as in exacerbation.

exostotis – Benign bony growth projecting outward from the surface of a bone, characteristically capped by cartilage.

extension – Outward movements of body parts away from the center of the body (straightening).

extracellular fluid – The medium through which energy flows when the body uses and exchanges energy with a chemical action of the metabolites in the circulatory system.

extraforaminal – Anatomic space at the side of the side margin of the neural foramen (openings in the vertebrae allowing the passage of nerves through it) in other words, to the side of the plane joining the side margins of two successive pedicles. Extra-spinal and paravertebral are synonymous with extraforaminal. Extraforaminal, being more specific, is recommended rather than the term lateral/far-lateral.

extremities – Appendages of the body such as the upper extremities (shoulders, upper arms, forearms, wrists, hands) and the lower extremities (thighs, legs, ankles, feet).

extrusion – Disc tissue displacement, by which disc material has herniated through a tear in the outer annulus. It has then come into the frontal epidural space, continuing to be connected to the disc it came from by a stemlike part of disc tissue. When there are both spokelike and peripheral tears in the annulus, the displaced tissue may include parts of the annulus fibrosus itself. The posterior longitudinal ligament may have been perforated through by the herniated disc. The herniated material must remain continuous with the disc in order for this term to be correctly used in description. Sometimes sequestered is used to mean extrusion and is found in reports indicating the anatomic boundary overstepped. Examples: Disc herniation extruded through the PLL. Disc material extruded through the annulus/PLL complex.



F-response – The foot response, one of two parts of late responses, which indicate how fast the messages go to the spinal cord and back.

facet – Small, smooth flat surfaces on a hard body, as on a bone, especially where it articulates with another bone. Articular facets of a vertebra are covered with hyaline cartilage.

facet block – Regional anesthesia to the facet. It is done under radiographic control, with the injection being placed in the facet area. It relieves pain in the lower back caused by osteoarthritis of the spine.

facetectomy – Cutting away of the facet of a vertebra.

facet joint or articular facet – Small flat surfaces (two on each side of a vertebra) on the bones where one vertebra meets with the one above and the one below. They are also zygapophyseal joints and diarthrodial joints.

facial nerve – Cranial Nerve VII, which has motor and sensory components; motor component governs muscles of facial expression; some taste fibers and salivary gland nerve fibers course within the facial nerve.

factitious disorder – A condition wherein physical or psychological symptoms are produced voluntarily, often resulting in multiple hospitalizations, but which, unlike malingering, has no rationally comprehended goal.

fascia – Sheet or band of fibrous tissue such as lies deep to the skin sometimes being the place where muscles and various organs of the body attach.

fascicle – A bundle of nerve or muscle fibers.

fasciculi – Bundles of fibers divided into tracts within each funiculus in the white matter of the spinal cord.

femoral nerve – This general sensory and motor nerve originates in the lumbar plexus, L2-L4, and descends behind the inguinal ligament to the femoral triangle. Its branches are the saphenous nerve and the muscular and anterior cutaneous rami. It distributes to the skin of the thigh and leg, the muscles of the front of the thigh, and the hip and knee joints.

fibrin – Insoluble protein formed from fibrinogen by the proteolytic action of thrombin during normal clotting of blood. Fibrin forms the essential portion of the blood clot.

fibrinogen – Substance in the blood essential for the clotting process and, thus, to the maintenance of normal homeostatis. A high-molecular-weight plasma protein, Factor I, is converted to fibrin through the action of thrombin.

fibrinolysis – Dissolution of fibrin by enzymatic action.

fibroblasts – The most common connective tissue cells, forming the fibrous tissues in the body, the tendons, and aponeuroses, supporting and binding tissues of all sorts. They modify into chrondroblasts, collagenblasts, and osteoblasts. They are the only cells found in tendons. They synthesize matrix materials and are considered to be secretory; assist in wound-healing. Also called fibrocytes and desmocytes.

fibrocartilage – In nonsynovial joints, one of three types of connective tissue that joins the involved bones. Fibrocartilage (symphyses secondary cartilaginous joints) is found in the intervertebral discs with a fluid-filled central cavity, and in the pubis, the front arch of the pelvis, with a hollow central cavity.

fibrocytes – Fibroblasts.

fibromyalgia – A syndrome that affects the connective tissues and muscles throughout the body. A common form of chronic, generalized muscular pain and fatigue.

fibrosis – The formation of fibrous tissue; fibroid or fibrous degeneration.

fribrositis – Inflammatory hyperplasia of the white fibrous tissue of the body, especially of the muscle sheaths and the facial layers of the locomotor systems. It is marked by pain and stiffness.

fibrous capsule – A structure enclosing fibers in a synovial joint. The capsule inserts into the moving bones at some distance from the hyaline cartilage, and on the inner side of the capsule is the synovium, a specialized connective tissue layer.

fibrous connective tissue – Tissue that is frequently used by the body as supportive tissue. Besides that function it is involved in the storage of body materials, transporting them when needed, for instance, in the repair of a wound. Fibrous connective tissue contains fibers, ground substance, and extracellular fluid.

fibrous joints – Joints as classified by structure, with no joint cavity and with fibrous connective tissue uniting the bones. They are joined together tightly and are generally immovable (synarthrosis). Three types are recognized: stures, syndesmoses, and gomphoses. See cartilaginous and synovial joints.

filum terminale – Nonneural fibrous filament extending at or near the tail from the lowermost end of the spinal cord (conus terminalis). It is attached to the coccyx.

fissure – A cleft or groove, normal or otherwise. When one occurs in the pars interarticularis, the yoke of bone connecting the right and left facets, the condition is known as spondylolysis. When discs become old, less firm and less elastic, they begin to tear and create fissures in parts of the disc, through which the nucleus can seep out and cause problems.

flexion – Inward movements of body parts toward the center of the body (bending).

flexion-distraction injury – Injury where the flexion axis is posterior to the anterior longitudinal ligament and there is compressive failure of the anterior column, while the middle and posterior columns fail in tension. The posterior longitudinal ligament is torn, and if the facet joint capsules are disrupted, there may be subluxation or dislocation or fracture of the facets.

flexion-rotation injury – An injury that involves some measure of rotation. For example, a hard right hook to the jaw is the mechanism to the neck in the flexion-rotation injury.

fluent asphasia – A language disorder characterized by clear articulation and normal rhythm but long phrases of nonsense, incorrect words or sounds, and circumlocution.

Foley catheter – A catheter is a tubular, flexible surgical instrument for withdrawing fluids from or introducing fluids into a cavity of the body, especially one for introduction into the bladder through the urethra for the withdrawal of urine. A Foley catheter is an indwelling catheter retained in the bladder by a balloon that may be inflated with air or liquid.

foramen – Natural opening or passage; a general term for such a passage, especially one into or through a bone; a notch bridged by a ligament or bone, opening into a pit or a canal that has an orifice at each end. In the spine foramina open out of the spinal canal through the vertebral bodies allowing the passage of nerves (vertebral foramina).

foramen magnum – Large opening in the front and lower part of the occipital bone that connects the vertebral canal and cranial cavity.

foraminal – The anatomic capacity within the limits of the pedicles above and below, the articular processes toward the back, the vertebral body in the front, and the sagittal planes that connect the middle and side aspects of two adjoining pedicles. Even though foraminal means the same as lateral and far-lateral, the terms foraminal and extra-foraminal are preferred, as they are more specific.

foraminotomy – The operation of removing the roof of intervertebral foramina, done to relieve nerve root compression.

fossa – Long, shallow hollows or depressed areas in bones.

fracture – The breaking of a part, especially the breaking or rupture of a bone.

free fragment – Occurs when the disc material from a herniation is no longer in an uninterrupted flow with the disc from which it came. Free fragment, sequestered disc, sequestrum, and canal mouse are also used in this context. The disc material is found at varying distances from the original level, having broken through its annulus fibrosus. It can be found in the space between the annulus and the posterior longitudinal ligament, between the PLL and the dura, or, rarely, within the dural sac. The herniation is usually large, and usually migrates in an upward course when it is a foraminal herniation or downward when the annular tear is central or paracentral.

frontal lobe – The most anterior area of the cerebrum. Regulates and mediates the モhigherヤ intellectual functions and has intricate connections to other areas of the brain including deeper structures such as the limbic system.

fulcrum – The support on which a level pivots.

funiculi – Three pairs of columns of myelinated fibers that run the length of the white matter of the spinal cord.



Gadolinium-DTP – The most common dye agent used to enhance the image of a defect, if the diagnosis is a scar.

gait – The particular manner of walking (e.g., ataxic, scissor, etc.). Used in diagnosing underlying conditions and in devising interventions.

ganglion – General term for a group of nerve cell bodies located outside the central nervous system, in a knotlike mass.

Ganser syndrome – A form of factitious disorder involving the voluntary production of severe psychological and pseudocognitive symptoms, often of psychotic proportions.

general senses – The senses of touch-pressure, heat, cold, pain, and body position. Also called somatic senses.

genesis – The beginning of anything; the origin or process of originating.

Gerstmann’s syndrome – A brain disorder consisting of right-left confusion, inability to calculate or write, and an inability to name the different fingers of each hand due to parietal lobe lesion.

Glasgow Coma Scale (GCS) – A rating scale devised by Teasdale and Jennett to assess the level of consciousness following brain damage. The scale assesses eye, verbal and motor responses. The GCS is grade 1-15, the lower score indicating the greater neurologic impairment.

gliding – Multiaxial movement of bone (about three axes), on essentially flat articular surfaces; simple movement within narrow limits, as between articular processes of vertebrae.

glio- – Combining form denting relationship to a gluey substance or specifically to the neuroglia.

gliofibrillary – Pertaining to fibrils of the neuroglia.

gliosis – An excess of astroglia in damaged areas of the central nervous system.

global asphasia – Loss of all language function.

glossopharyngeal nerve – Cranial nerve IX, a sensory-motor nerve supplying sensation into pharynx and posterior tongue and supplying motor function to these structures.

glove-and-stocking analgesia – Loss of sensation along symmetrical nonanatomic lines and not having a dermatome distribution; characteristic of hysterical or malingered disorders.

granulation – In wounds, the formation of small, rounded masses of tissue composed largely of capillaries and fibroblasts, often with inflammatory cells present; also a mass so formed.

gray matter – Nerve tissue not covered by myelin which gives the cerebral cortex its characteristic color.



halopelvic traction – Traction applied to the spine by means of two metal hoops, one (the halo) applied to the skull and the other to the pelvis, connected by four extension rods that can be lengthened by turn screws.

halo vest– Apparatus used to immobilize affected area during healing, to support the patient while positioned on the operating table or to immobilize if wiring or instrumentation cannot immediately be relied on the maintain stability.

handicap – A disadvantage that limits or prevents fulfillment of a role that is normal (depending on age, sex, and social and cultural factors).

hard callus – In bone repair, soft callus is transformed by osteoblast cells into hard callus.

hard discs – Discs with osteophyte formations.

head injury criteria (HIC) index – A rating scale which computes the severity and duration of acceleration-deceleration forces exerted on the human head during a crash. HIC is the scale employed by the National Highway Traffic Safety Administration (NHTSA) to judge the adequacy of restraining devices.

hematoma – A blood clot arising from venous bleeding into an enclosed space.

hemianopia – Blindness in one half of the visual field, indicating a pathological process at some point along the visual pathway.

hemiparesis – Weakness or partial loss of muscle power on one side of the body, usually due to brain damage on the opposite (contralateral) side.

hemiplegia – Loss of muscle power on one side of the body, due to brain damage of the opposite (contralateral) side.

hemorrhage – Rapid and poorly controlled arterial bleeding.

hemostastis – The arrest or stopping of bleeding, either by the physiological properties of vasoconstriction and coagulation or by surgical means; the interruption of the flow of blood through any vessel or to any anatomical area.

herniated intervertebral disc – Condition in which the pulpy center (nucleus pulposus) of an intervertebral disc abnormally protrudes through a weakened or torn surrounding outer ring (annulus fibrosus); the pulpy center or the outer ring pushes against a spinal root or even the spinal cord. Also called ruptured or slipped disc.

herniation – In neurology, used to describe the movement of brain tissue through or across small openings due to increased intracranial pressure.

heterotopic ossification – A disorder characterized by the deposition of large quantities of calcium at the site of a bone injury. Often the result of prolonged immobilization (heterotopic bone).

histology – Category of anatomy dealing with the minute structures, composition, and function of the tissues; also called miroscopic anatomy. The microscopic study of the tissues.

homeostatis – The condition of the body wherein chemical and neurologic mechanisms regulate a steady state of normal physiologic functioning.

homonymous hemianopia – Loss of sight in one half of the visual field.

horns – Horn-shaped structures seen in transverse sections of the spinal cord formed by the anterior column of the cord, the lateral column of the cord, and the posterior column of the cord.

hyaline – Glassy and transparent or nearly so.

hyaline cartilage – A type of connective tissue. Hyaline cartilage (synchondroses or primary cartilaginous joints) joins the first rib with the sternum, being the unique synchondrosis in the human adult.

hydrocephalus – Literally, water on the brainヤ; an abnormal collection of fluid within the skull.

hypercapnia – Elevated blood carbon dioxide.

hyperextension – Movement of the spine or the extremities going farther back than the norm. Frequently used to describe whiplash injuries, when the head is thrown back with the chin up.

hyperflexion – Forcible overflexion of a limb or part.

hypoesthesia – Abnormally decreased sensitivity to stimulation.

hypoglossal – Cranial Nerve XII, a motor nerve which innervates the anterior third of the tongue.

hypotension – Pathologically low blood pressure.

hypothalamus – A brain stem structure which regulates several vital life functions; has intricate connections to the pituitary (モmasterヤ) endocrine gland.

hypoxia – Low blood oxygen level.

hysteria – See conversion disorder.



ICP – Intra cranial pressure. Virtually any significant injury to the brain will result in a generalized edema (swelling) with corresponding increase in ICP. Such edema and pressure increases may generate a temporary alteration in the activity of otherwise functional neurons located at sites far distant from a localized injury. Upon the resumption of normal brain size and the restoration of normal pressure, these areas will often resume normal functioning. However, prolonged pressure elevations and/or edema may cause new damage to previously uninvolved tissue, as the parenchyma is flattened against the hard skull axons are stretched to the point of severing, circulatory patterns are disrupted, and cell death causes chemical reactions which are themselves toxic to healthy remaining brain tissue.

iliocostocervicallis – A muscle within the sacrospinalis that allows the vertebral column to extend and laterally flex.

iliolumbar ligament – Strong band that goes from the transverse processes of the fourth and fifth lumbar vertebrae to the internal tip of the adjacent part of the iliac crest.

impairment- Any loss or abnormality of psychological, physiological, or anatomical structure or function.

impingement – Encroaching upon; used to point out compression, deformation, or displacement of the nerve roots or thecal sac. Instead of impingement, in the case of the nerve root or sac not being clearly distorted, but being inseparable from a disc herniation or hypertrophic facet (in MRI reports), モabuttingヤ or モcontactingヤ are better descriptions.

inferior – Shows direction. For example, standing in an upright position, the top of the head is superior to the feet, which are, in turn, interior to the head. Another example, in an upright position, the sole of the foot is inferior while the dorsum (upper part) of the foot is superior. Below. Caudal.

inferior gluteal nerve – General sensory nerve that originates in the posterior femoral cutaneous nerve and distributes into the skin of the lower part of the buttock.

inferior tubercle – Nodule or small eminence such as a rough, rounded elevation, on the lower surface of a bone.

inflammation – Part of the healing process, it has been historically accepted by four cardinal points; pain, heat, redness, and swelling. It involves a lot of metabolic and histological changes.

innervation – Distribution or supply of nerves to a part of the body.

intercostal – Situated between the ribs.

internal vertebral plexuses – Network of veins inside the spinal canal covering the dura and the neural tissue (spinal cord and nerves).

interspinal ligaments – Any of several fine, fibrous membranes that extend from one vertebral spinous process to the next. They consist of fine membranes in the lumbar region and of small cords in the thoracic region, and do not occur in the cervical region.

intertransverse ligaments – Any of several poorly developed fibrous bands that extend from one vertebral transverse process to the next. They consist of fine membranes in the lumbar region and of small cords in the thoracic region, and do not occur in the cervical region.

intervertebral discs – Plates of fibrocartilage placed between two vertebrae, covering their inferior and superior surfaces. They play a primary role in weight bearing and a lesser degree in movement.

intra- – Prefix meaning situated, formed or occurring within the element indicated by the word stem to which it is affixed.

intracerebral hemorrhage – Small, multiple bleeds associated with contusions that occur within brain substance.

intrathecal – Refers to contents in the dura mater. An intrathecal injection refers to inserting a needle into the dura and injecting a substance that will mix with cerebral spinal fluid. The brain, the spinal cord, and the spinal fluid are covered by the dura.

ischemia – Local and temporary deficiency of blood supply due to obstruction of circulation to a part.

isometric – Of or involving no change in the muscle length as the muscle contracts against resistance, such as with the arm forward and the hand flat against a wall.

isotonic – Of equal tone, tension, or activity. An isotonic saline solution refers to concentration of solutes such as the blood. In isotonic muscular contraction, the muscle remains under relatively constant tension while its length changes. For example, with arm bent and muscle bulging.

isthmus – Refers to a narrow connection between two larger bodies or parts; a general term for such a structure or region. Each vertebra, on either side, has facets that constitute the upper and lower joints of the vertebra. They are described as being superior and inferior. The part of the vertebra making up the bony junction between the two is narrower in comparison to the width of the facets. Therefore, that part is called the isthmus. Because they are situated between the superior and inferior articulations of the facets, they are also called the pars interarticularis, meaning the part between the joints. Because of its shape, it is more susceptible to fracture, and a report of spondylolysis means a fracture of the isthmus, the pars interarticularis. These terms are frequently seen in radiological reports where a diagnosis of spondylolysis has been made.

-itis – Suffix meaning inflammation of the part indicated by the word stem to which it is attached.





Kluver-Bucy syndrome – A severe disorder caused by damage to the temporal lobe and/or the limbic system and characterized by cognitive and sexual disturbances.



lacuna – General term for a small pit or hollow cavity within or between the organs or tissues of the body.

lamella – Thin leaf or plate, as of bone; concentric layers of bone that make up cylinders of calcified bone called osteon.

lamina, lamina arcus vertebrae – Lamina of the vertebrae; thin flat plate or layer of the vertebral arch. These broad plates of bone extend to the back from the pedicle of the vertebra and fuse together at the midline to form the spinous process. The ligamenta flava attaches to the superior and inferior border of the laminae; therefore, it is called interlamina ligamentum.

laminectomy – Cutting away of the laminae of the posterior vertebral arch, exposing the spinal cord. This relieves pressure on neural structures from the bony fragments, protruding nuclei pulposi of intervertebral discs, tumors, or hematomas.

laminotomy – The operation of cutting the lamina of a vertebra.

language development – Refers to the process wherein the individual acquires the ability to use the verbal symbols of his/her language for communication of needs, social interaction, and the understanding and expression of complex thought. At birth, all normal individuals possess the capacity to acquire the language in which they are raised; such capacity is “hard wired” and is governed by a process encoded in the DNA. However, the specific set of language symbols acquired by the individual is entirely dependent upon the language of his culture and is not affected by the language spoken by the biological parent(s) unless he is reared in the parent’s language.

laparo- – Combining form showing relationship to the loin or flank. At times, used loosely to refer to the abdomen.

laryng- – Combining form indicating windpipe.

Lasegue’s sign – Pain in the sciatic nerve when, with flexion of the thigh at the hip, the leg is extended at the knee. The maneuver for this sign comes under the category of straight leg raising tests. It is done in patients with low back pain with lumbosacral radiation. Radiating sciatic pain is elicited when the sciatic nerve root that enters into the spine is irritated. One can intensify Lasegue’s sign by dorsiflexion of either foot or the great toe.

late instability – Occurs when there is no healing or fusion after a break, resulting in late pain and often requiring surgery.

later- – Combining form indicating to the side.

lateral – Refers to the side. Example: a person’s profile is the lateral side. Lateral frequently refers to the center in this way: Since the midline is in the center, the lateral (side) is away from the center. Thus, the eyes and ears are lateral, right and left from the center. The center or midline is the nose.

lateral foraminae – Passage formed by the inferior and superior notches on the pedicles of adjacent vertebrae; it transmits a spinal nerve and vessels. See intervertebral foraminae.

lateral masses of the atlas – Thickened unified lump of cells or cohesive tissue of the atlas to which the arches are attached, and that bear the articulating surfaces and the transverse process.

lateral recess – Refers to an indentation or small hollow on the left and right sides within the spinal canal near the pedicles.

lateral rotation – Twisted movement of a limb or head. Example: Lateral rotation of the head is accomplished when we move our heads to the right or left without moving our shoulders.

lateral view – Denoting a position farther from the median plane or midline of the body of a surface; pertaining to a side.

laxity – Unloosed, relaxed; lack of elasticity.

left-sided neglect – Lack of awareness of the left side of the body, or the left side of the body left out of the activities of daily living, due to lesion in the right cerebral hemisphere.

lesion – A wound or an injury; a localized pathological change in a bodily organ or tissue; trauma, infection, tumor, etc.

ligaments – Bands of fibrous tissue connecting bones or cartilages that support and strengthen joints. Most ligaments are deemed to be unyielding, yet they are adaptable enough to permit movement at the joints. When overly stressed, however, rather than stretch, they will tear. Usually, ligaments impede unreasonable motion, being strong enough and having a lot of sensory nerves that discourage people from greatly straining or overstretching them.

ligamentum flavum – Yellow elastic tissue going from the axis and third cervical vertebra to where the fifth lumbar vertebra joins to the sacrum. They are concerned with erect posture.

ligamentum nuchae nuchal ligament – A broad, fibrous, roughly triangular sagittal septum in the back of the neck, separating the right and left sides. It extends from the tips of the spinous processes of all the cervical vertebrae to attach to the entire length of the external occipital crest. Caudally it is continuous with the supraspinous ligament.

limbic system – A complex of cortical and subcortical structures which regulate and integrate bodily functions through the autonomic nervous system and by hormonal control through pituitary gland and which mobilize fundamental survival drives.

limbus – Border, hem, or fringe; a general term for the margins of certain structures, as in limbus vertebral factures.

lipocyte – A kind of adipocyte cell in connective tissue that stores and metabolizes fat.

load – Weight or mass that is supported or carried and sometimes even measured. When we speak of work load, we generally mean the amount of work an individual’s job comprises.

longus capitis muscle – Anterior vertebral muscle that connects with the flexion of the head.

longus colli muscle – Long muscle of the neck that flexes and supports the cervical vertebrae.

lordosis – Alignment of the spine. Normally, the spine has curvatures. In the cervical and lumbar spine, it is called a lordotic curvature, while the thoracic is called kyphotic. The degree of curvature has normal parameters. When they are increased due to injury, the curvature can be lost (straightened) or increased (increased lordosis, increased kyphosis). These abnormal findings are due to several reasons. Lordosis is opposite to kyphosis. The term refers to abnormally increased curvature (hollow back, saddle back, swayback) and to the normal curvature (normal lordosis).

lumbago – Pain in the lumbar region; often used synonymously with low back pain but can suggest low back, buttock, and thigh pain.

lumbar plexus – Plexus is a network of lymphatic vessels, nerves, and veins. The lumbar plexus is the junction of the nerve roots that come out of the spine from L2 to L5, to group together and later form a large trunk of nerves.

lumbar puncture – The tapping of the subarachnoid space in the lumbar region, usually between the third, fourth, or fifth lumbar vertebrae. Since the spinal cord usually ends at the lower border of the L1 vertebra or the upper border of L2, there is no danger of injuring the spinal cord if the needle is inserted between L3 and S1. The nerve roots are seldom damaged because, being suspended in CSF, they tend to move away from the needle. Lumbar punctures are done to acquire cerebrospinal fluid for diagnostic procedures, as, for example, to determine alterations in the concentrations of chemicals or cells, or microbes. Spinal anesthetic agents can also be injected by lumbar puncture. Also known as a spinal tap.

lumbar spine – Part of the spinal column pertaining to the loins, between the thorax and the pelvis.

lumbosacral ligaments – Ligaments that attach the lumbar vertebrae to the sacrum.

Luschka joints – See joints of Luschka.

luxation dislocation – Refers to a joint that is out of place. A fracture, dislocation, or dislocated fracture means that the vertebra has been moved out of alignment.

lymph – Liquid of alkaline reaction found in the lymphatic vessels and derived from the tissue fluids. It circulates through the lymphatic system, acting to remove bacteria and certain proteins from the tissues. It also transports fat from the small intestine and supplies mature lymphocytes to the blood. Under the microscope, lymph is shown to consist of a liquid portion and of cells, most of which are lymphocytes.

lymphocytes – Cells made in the lymphoid tissue, constituting from 22 to 28 percent of all the white blood cells found in normal human blood. Their work is in the development of immunity.



macroglia – Part of the connective tissue of the nervous system.

macrophages – Large, mononuclear highly phagocytic cells with small, oval, sometimes indented nuclei and inconspicuous nucleoli, occurring in the walls of blood vessels (adventitial cells) and in loose connective tissue (histiocytes, phagocytic reticular cells). They are usually immobile (fixed macrophages, resting wandering cells), but when stimulated by inflammation become actively mobile (free macrophages, wandering histiocytes).

magnetic resonance imaging (MRI) – Non-invasive exploratory diagnostic technique that uses a strong magnetic field to detect differences in healthy and unhealthy tissues. It uses the hydrogen component of hua tissues. Also called nuclear magnetic resonance (NMR).

malingering – Faking or conscious deception; voluntary production of symptoms for a rationally considered goal, such as financial recompense, avoidance of responsibility, etc.

manic-depressive illness – See bipolar disorder.

medulla – A brain stem structure which controls and regulates essential life support functions such as heart beat.

meninges – Brain coverings, including dura, arachnoid, and pia mater.

meningomyelocele – A condition in which the nerve root or part of the spinal cord goes into a sac that protrudes through the opening of the vertebra and appears on the babyメs back as a big mass. The baby is paralyzed, since the nerves do not go to the legs or hands. The word meningomyelocele is derived from three root words: meningo applies because the membrane of the meninges covers the nerves; myelo means marrow, often used in a specifi reference to the spinal cord; and cele means hernia and relates to a tumor, swelling or cavity.

meniscus – A crescent-shaped disc of fibrocartilage attached to the articular surfaces, usually referred to the tibia.

mental status exam – A part of the psychiatric examination which may be (a) formal, in which very specific questions are asked in order to identify various aberrant functions or (b) informal, in which similar information is garnered from an extended interview.

mesenchyma – Netting of embryonic connective tissue in the mesoderm. The connective tissues of the body are formed from this, as are the blood vessels and the lympathic vessels.

mesoderm – Middle layer of the three primary germ layers of the embryo. It lies between the ectoderm and endoderm. From this, the connective tissue, bone, and cartilage, muscles, blood and blood vessels, lymphatics, lymphoid organs, notochord, pleura, pericardium, peritoneum, kidney, and gonads are derived.

metabolism – Complex physical and chemical processes going on within a living cell, by which living organized substance is produced and maintained (anabolism) for maintaining life. Also, the breaking down of some substances to produce energy for the vital processes (catabolism).

metaplasia – Normal transformation of tissue from one type to another, as in the ossification of cartilage to form bone; transformation of cells from a normal to an abnormal state.

microglia – Small cells of connective tissue of the central nervous system.

midsagittal – Plane dividing the left and right sides of the body lengthwise, symmetrically, along the midline from the nose to the occiput or back of the head, into two sections.

migraine – A type of headache presumed to be related to abrupt changes in caliber of blood vessels, typically characterized by severe, pulsating, one-sided head pains, often with visual disturbances, nausea and unusual or bizarre body sensations.

migration – The change of place, from one location to another, of a tissue, a part of a tissue, or symptoms. When we refer to a herniated disc, migration means that the disc material has moved out of its normal place (migrated).

mild traumatic brain injury (MTBI) – A patient with MTBI is a person who has had a traumatically induced physiological disruption of brain function, as manifested by at least one of the following:
any period of loss of consciousness
any loss of memory for events immediately before or after the accident;
any alteration in mental state at the time of the accident (e.g. feeling dazed, disoriented, or confused); and
focal neurological deficit(s) that may or may not be transient; but where the severity of the injury does not exceed the following:
loss of consciousness of approximately 30 minutes or less;
after 30 minutes, an initial Glascow Coma Scale (GCS) of 13-15; and
postraumatic amnesia (PTA) not greater than 24 hours.

Minnesota Multiphasic Personality Inventory (MMPI) – The most widely used and extensively validated test which describes various aspects of personality and detects various psychological vulnerabilities.

miosis – That stage of disease, during which the intensity of the symptoms diminishes.

mitosis – Process in which the cells multiply in a normal or abnormal way. In the embryo, the cells have a normal mitosis resulting in growth and development. In malignant tumors, the cancer cells have an exuberant increase of mitotic changes.

molecular genetics – The study of how genes function to control cellular activies. (Genetic engineering involves the application of knowledge about molecular genetics in order to change living things by modifying their DNA, so they will produce desired strains).

monocytes – Mononuclear, phagocytic leukocytes. They form in the bone marrow from promonocytes and are transported to tissues such as the lung and liver, where they develop into macrophages.

morphology – Science dealing with the form and structure of organisms, not considering the function; the form and structure of a particular organism, organ, or part.

motor – Muscle, nerve or center that affects or produces movement.

motor development – The gradual acquisition of full control of all voluntary motor movements common to the species.

motor fibers – Fiber in a mixed nerve that transmits impulses to a muscle fiber.

MRA – Magnetic resonance imaging of the arteries.

MRI – See magnetic resonance imaging.

MRN – Magnetic resonance imaging of the nerves.

Munchausen syndrome (pseudologica fantastica) – A form of factitious disorder in which the individual is continually preoccupied with being admitted to hospitals by presenting a wide range of allegedly disabling symptoms, all of psychological origin.

muscles – Organs, which by contraction and relaxation, produce the movements of limbs and certain other organs.

myelin – A fatty white coating or sheath of neurons which facilitates nerve conduction. Myelin gives the “white matter” of the central nervous system its characteristic color.

myelin sheath – Tubular structure surrounding the axon of the myelinated nerve cells, consisting of concentric layers of myelin, formed in the peripheral nervous system by the plasma membrane of Schwann cells, and in the central nervous system by oligodendrocytes. It is interrupted at intervals along the length of the axon by gaps known as nodes of Ranvier. Myelin is an electrical insulator that serves to speed the conduction of nerve impulses.

myelogram, myelography – Radiographic study of the spinal cord after injection of the contrast media into the subarachnoid space.

myelopathy – General term for damage to the spinal cord.

myoclonus – Involuntary, sharp, jerking muscular contractions, often painful.

myofascial sprains – Injuries in a joint wherein the bands of fibruous tissue that form an investment for fibers of a supporting ligament are ruptured, yet the continuity of the ligament remains intact.

myofascial syndrome – Pain that occurs in the soft tissues after an injury and is characterized by its local tenderness, with some irradiation to points removed from the original injury site, where it is called referred pain.

myofibroblast – Specialized muscle connective tissue cells that help keep the body stable as wounds heal.

myotome – Group of muscles innervated from neurons coming out of a single spinal segment.



necrosis – Cell death. The apparent changes indicative of cell death that are caused by the progressive degradative action of enzymes and that may affect groups of cells or part of a structure of an organ. Necrotic tissue refers when a tissue is dead. A common example is when a patient develops gangrene in one of the extremities. That part of the extremity has no circulation, the color is black, and by naked eye looks dead and is called necrotic. Amputation is normally required. Examination of the body after death is necropsy, autopsy, or post mortem examination.

nerve – Bundle of nerve fibers, grouped together like a cord and visible to the naked eye. The nerve fibers are covered by a membrane. The nerves and the membrane are part of the nerve.

nerve conduction velocity (NCV) studies – Motor and sensory nerves are stimulated and recorded by surface electrodes in this procedure. Motor nerves are stimulated at distal and proximal points and the compound muscle action potential (CMAP) is recorded from the muscle, to find out the maximum motor conduction velocity. Mixed/sensory nerves are stimulated at a distal point and the sensory nerve action potential (SNAP) is recorded antidomically by surface electrodes from the nerve at a more distal site or from the skin area supplied by the nerve, to find out the maximum sensory nerve conduction velocity. Late responses (H-response and F-response) are also obtained to find out the conduction in proximal segments of sensory and motor fibers. Also referred to as Nerve Conduction Studies (NCS).

nerve impulse or action potential – The spread of an impulse along the nerve.

neural spinal canal – See vertebral canal.

neurapraxia – The first level of nerve injury. The large motor fibers are predominately affected and anatomic continuity of the nerve is preserved. The prognosis for recovery is excellent and usually complete within a few days to weeks.

neurilemma – Membrane covering the nerve fiber; also called Schwannメs membrane.

neuro- – Combining form denoting relationship to a nerve or nerves, or to the nervous system.

neurocytes – One of the four types of tissue, neurocytes are the nerves and nervous system cells.

neuro-development – The physical process wherein the brain undergoes anatomical changes involving the size, number, and efficiency of interconnections which provide the substrate for virtually all other developmental changes.

neuroendocrine – Pertaining to neural and endocrine influence, and particularly to the interaction between the nervous and endocrine systems.

neurogenic symptoms – Symptoms that indicate spinal nerves are affected in some way.

neurogenic tonus – Tonic contraction of the muscle due to stimuli received through the nervous system.

neuroglia – Supportive or connective structure of the nervous system; also called glia.

neurolemma – A covering or wrapper of a nerve. Also called neurilemma, this thin membrane enwraps the myelin layers of some myelinated nerve fibers, especially peripheral ones, or the extensions of certain unmyelinated nerve fibers.

neuroma – Tumor or new growth largely made up of nerve cells and nerve fibers; a tumor growing from a nerve.

neuron – A nerve tissue cell consisting of the cell body and extensions of the nerve called axons and dendrites.

neuropathy – Related to damage or disturbance in the nervous system.

neuropraxia – Function of a neuron as opposed to structure.

neuropsychiatrist – A medical specialist dealing with the evaluation and treatment of disorders deriving from impaired brain functioning and the concurrent behavioral and emotional changes.

neuropsychologist – A clinical psychologist who conducts testing to quantify and localize impaired brain functioning.

neurosis – A psychogenic disorder of the emotions based upon a fundamental anxiety where origin is usually beyond conscious awareness. Neuroses are characterized by disturbed interpersonal relationships and a sense of chronic psychological discomfort.

neurotmesis – The most severe form of nerve injury. There is complete disruption within the nerve and/or an actual severing of the nerve. This injury needs surgical repair. There is wallerian degeneration of the nerve distal to the site of the injury and the prognosis for recovery is far poorer than in the case of neurapraxia or axonotmesis (the other 2 classes of nerve injuries). A nerve may not always have only one type of injury. It is possible to have combined types of injuries within a given nerve.

neurotransmitter – A chemical synthesized within the nerve cell body, characteristic for this type of nerve, and stored at the nerves in pods as granules. Release of these chemicals into the synaptic cleft between axons facilitates nerve transmissions.

neurovascular – Pertains to both nervous and vascular elements; also pertains to nerves that control the caliber of blood vessels.

newton – The SI unit of force, which, when applied in a vacuum to a body having a mass of 1 kilogram, accelerates it at the rate of 1 meter per second (symbol, N).

nociceptive input – A period of extreme stress and increased pain perception through affective processes.

nociceptor – Receptor responding to stimuli that produce pain.

noncontained – Refers to a herniation of the intervertebral disc that has disrupted the posterior annular fibers.

nonviable – Until the twentieth to twenty-fourth week, the fetus is considered nonviable, or unlikely to survive outside the uterus. An infant is viable at about twenty to twenty-four weeks of gestation.

notch – Indentation at the edge of a bone.

noto- – Combining form meaning related to the back.

notochord – In embryology, a rod-shaped body of cells that is the center of development of the axis of the skeleton; also called chorda dorsalis.

nsaid – Nonsteroidal anti-inflammatory drug. Aspirinlike drug that reduces pain and inflammation arising from injured tissue.

nuclear medicine scanning tests – Imaging processes whereby radioactive chemicals are introduced into the body, and various organs absorb them, giving off gamma rays that are captured by an image-producing device called a gamma camera.

nucleic acid – Complex organic acids found in the nucleus of all living cells that contain the genetic code essential to life.

nucleus – Central portion of the cell that contains chromosomes and positive protons; a general term used to designate a group of nerve cells usually found located within the central nervous system and bearing a direct relationship to the fibers of a particular nerve; the central portion of the cell contains chromosomes and positive protons.

nucleus pulposus – Innermost gelatinous core of the intervertebral disc. It acts like a shock absorber for axial forces and like a semi-fluid ball bearing during flexion, extension, rotation, and lateral flexion of the vertebral column.

nystagmus – A jerking of the eyeballs in extreme directions of gaze. May be a normal variant or indicative of brain tissue or balance apparatus malfunctioning.



obturator nerve – General sensory and motor nerve that originates in the lumbar plexus, L3-L4. Its branches are the anterior, posterior, and muscular rami. It distributes in the adductor muscles and the gracilis muscle, the skin of medial part of the thigh and hip and knee joints.

occipital – Pertaining to the occiput; located near the occipital bone, as the occipital lobe.

occipital bone – Single trapezoidal-shaped bone situated at the back and lower part of the cranium. It is one of the skull bones.

occipital condyle – One of two oval processes on the lateral portions of the occipital bone, on either side of the foramen magnum, for articulation with the atlas.

occipital foramen – Foramen magnum. The large opening in the anterior and inferior part of the occipital bone, interconnecting the vertebral canal and the cranial cavity.

occipital lobe – Posterior area of the cerebrum. The primary visual area. Receives, interprets, and recognizes visual stimuli.

occipito-atlanto-axial complex – The top of the neck, or the upper cervical spine.

occiput – The back part of the head; called also o. cranii and o. of cranium.

oculomotor nerve – Cranial Nerve III. The motor nerve moving in the eyelid, constricting the iris, and moving the eye by its intrinsic muscles.

Odontoid process of axis – See dens axis.

-oid – Word termination signifying resemblance to the thing specified by the stem, to which it is affixed, as ovoid.

olfactory nerve – Cranial Nerve I. Conducts sensation of smell from nerve endings in nasal mucous membrane to olfactory bulbs on the undersurface of the frontal lobe.

oligo- – Combining form meaning few, little, or scanty.

oligodendrocytes – See oligodendroglia.

oligodendroglia – Nonneural cells of ectodermal original forming part of the outermost structure (neuroglia) of the central nervous system. Projections of the surface membrane of each of these cells (oligodendrocytes) fan out and coil around the axon of many neurons to form myelin sheaths in the white matter. With microglia, they form the perineuronal satellites in the gray matter. Oligodendroglia is the tissue composed of such cells.

olisthesis – Slippage that occurs with spondylolisthesis.

oogenesis – Process of forming female gametes (ova).

opisthion – Midpoint of the lower border of the foramen magnum.

optic nerve – Cranial Nerve II. Conducts visual impulses from rods and cones in the retina to visual cortex of occipital lobe.

organelle – Minute organ of protozoa concerned with locomotion, metabolism, or the like.

organogenesis – The origin and development of organs.

ortho- – Combining form meaning straight, normal, correct, etc.

orthosis – Orthopedic apparatus or appliance used to support, align, prevent, or correct deformities or to improve the function of movable parts of the body.

orthotic – Serving to protect or to restore or improve function; pertaining to th use or application of orthoses.

os – General term for a specific type of bony structure.

-osis – Word termination denoting a process, production, indicating abnormal increase. Example: Spondylosis means formation of bone (osteophyte).

osseous tissue – Bone; a tissue composed of cells embedded in a matrix of ground substance, inorganic salts, and collagenous fibers.

ossification – The conversion of fibrous tissue or cartilage into bone or a bony substance.

ossification center – Where the initial development of bone tissue begins. It starts with a ring of cells forming around a blood vessel.

osteo- – Combining form denoting relationship to bone or the bones.

osteoblasts – Bone cell capable of synthesizing and secreting new bone matrix as needed; usually found on growing portions of bones.

osteochondrosis – Disease of the growth or ossification centers of children, which begins as a degeneration or necrosis followed by regeneration or recalcification.

osteoclasts – Large multinuclear cell associated with the absorption and removal of bone.

osteocytes – An osteoblast that has become embedded in the bone matrix, occupying a flat oval cavity (bone lacuna) and sending, through the canaliculi, slender cytoplasmic processes that make contact with processes of other osteocytes.

osteoid – Bone matrix not yet calcified.

osteomyelitis – Inflammation of bone caused by a pyogenic organism. It may remain localized or may spread through the bone to involve the marrow, cortex, cancellous tissue, and periosteum.

osteophytes – Bony excrescence or osseous outgrowth that curves around the disc. It comes with age and degeneration of the disc; also called a モhard disc.ヤ

osteoporosis – When both the organic and inorganic components of bone decrease, and there is a reduction in the quantity of bone or atrophy of skeletal tissue, causing them to lose their elasticity and fracture easily. Fractures of the neck of the femur (hip fractures) and vertebral bodies of the spine are common in the elderly.



pannus – Inflammatory exudates overlying the lining layer of synovial cells on the inside of a joint, usually occurring in patients with rheumatoid arthritis or related articular rheumatism, and sometimes resulting in fibrous consolidation of the joint.

para- – Prefix meaning beside, beyond, accessory to, apart from, against, etc.

paracentral – Anatomic position in the back part of the spinal canal where the focal point of the lesion is to the side of the midline plane and to the center of the central margin of the pedicle. Synonyms: centrolateral and paramedian.

paramedian – See paracentral.

paraplegia – Loss of motor or sensory function in both lower extremities due to damage to the spinal cord.

parasagittal – Term describing cuts that go parallel and to the sides of sagittal.

paratnon – Fatty aerolar tissue that fills the interstices of the fascial compartment, in which a tendon is situated.

parasthesia – Abnormal sensation such as burning, prickling, or a feeling that small insects are crawling on the skin.

parenchyma – Organ tissue substance, exclusive of blood vessels, connective tissue and bone.

paresis – Weakness in voluntary muscle or slight paralysis.

parietal – Walls of a body cavity or the membrane lining the walls of a body cavity.

parietal bone – One of the two quadrilateral bones forming part of the superior and lateral surfaces of the skull, and joining each other in the midline at the sagittal suture.

parietal lobe – Lies behind the frontal lobe and above the temporal lobe. Identifies touch and three dimensions, governs reading, calculation ability, etc.

pars – General term for a particular portion of a larger area, organ, or structure.

pars interarticularis – Isthmic portion of an area situated between articular (joint) surfaces.

patella – Triangular sesamoid bone, about 5 cm in diameter, situated at the front of the knee in the tendon of insertion of the quadriceps extensor femoris muscle; also called knee cap.

patellar clonus (knee jerk) – Diagnostic reflex in which tapping the patellar tendon produces the contraction of the quadriceps femoris muscle, causing the lower leg to jerk upward.

patho- – Combining form meaning disease, injuries, disturbances, not within the range of normal.

pathology – Study of changes in diseased cells and tissues.

pectoral muscles – There are major pectoral muscles and minor pectoral muscles. The major ones are across the upper part of the chest, adducting, flexing, and rotating the arms medially. They originate in the clavicle, the sternum, the six upper ribs, and the aponeurosis of the obliquus externus abdominis. These origins are reflected in the subdivision of the muscle into clavicular, sternocostal, and abdominal parts. Their insertion is into the crest of the intertubercular groove of the humerus. Innervation is through the anterior thoracic. The minor pectoral muscles lie under the major pectoral muscles, drawing the shoulder downward. They originate in the third, fourth, and fifth ribs and insert into the coracoid process of the scapula, receiving innervation from the anterior thoracic.

pedicles of the vertebral arch – Short, sturdy, strong, projecting bones of the vertebral arch that are secured to the upper part of the vertebral body on each side. Paired, they project backwards, connecting the vertebral body, found in front of the posterior parts, the broad, flat laminae, the facets, and the spinous process. Part of the lateral side of the spinal canal is formed by the pedicles.

pelvis – Lower portion of the trunk of the body, bounded on the front and sides by the hip bones and in the back by the sacrum and the coccyx. It is basin-shaped; the front part is the pubis; and it rests on the lower limbs as it supports the spinal column.

penetrating or blunt trauma – Trauma inflected by a knife, machete, or bullet produces penetrating trauma; a blow to the neck with a pipe or baseball bat produces blunt trauma.

per- – Prefix meaning throughout, in space or time, or completely or extremely.

perceptual development – The process wherein the individual becomes capable of organizing various sensory stimuli into meaningful units of information.

perched facets – Displacement of facets to the extent that the tips of the facets on one level are touching but not making an even contact with the tips of the facets of the other level.

percutaneous rhizolysis – Pain-relieving procedure that destroys the nerve root. It does so by coagulation with radio frequency waves.

peri- – Prefix for all-around, about, round; near; enclosing or surrounding, such as tissue surrounding a specific part.

perikaryon – The cell body as distinguished from the nucleus and the processes; applied particularly to neurons.

perimetry – A method of mapping the visual field to determine defects in this field.

periosteum – All the bones in the body are covered by this specialized connective tissue. It has the potential of forming bones. The periosteum has two layers: The outside one is a network of dense connective tissue with blood vessels, and the deep one is loosely arranged collaginous bundles with spindle-shaped connective tissue cells and a network of thin, elastic fibers. The periosteum is very sensitive to pain. Example: A kick in the shin.

peripheral – Relative directional term that describes structures other than internal organs such as are located or directed away from the central axis of the body.

peripheral nervous system (PNS) – That part of the nervous system consisting of the nerves and ganglia outside the brain and spinal cord.

peripheral neuropathy – Functional disturbances and/or pathological changes in the peripheral nervous system.

periscapular – Around or near the shoulder blade.

peroneal nerve – The branches of the sciatic nerve that go to the leg and the foot.

perseveration – After an action or response is started, repetition of it continues.

persistent vegetative state – See akinetic mutism.

personality disorder – An inflexible and maladaptive trait which can cause significant impairment in social or occupational functioning. Such disorders are recognizable by
adolescence and tend to persist throughout adult life.

phago- – Combining form suggesting relationship to eating or consumption by ingestion or engulfing.

pharynx – The throat is the musculomembraneous passage between the mouth and the back part of the nostrils to the larynx and esophagus.

phobia – A persistent and irrational fear of a specific object, activity, or situation that results in a compelling desire to avoid the phobic stimulus.

phon-, phono- – Combining form denoting relationship to sound, often specifically to the sound of the voice.

phospholipase a2 – An enzyme that produces an increase in chemical reaction in the splitting of a phospholipid.

physaliphorous cell – Cell that contains a globular cavity.

physical development – Refers to the process wherein the individual members of a species mature and the individual attains the characteristics and capacity typical of the species.

physiology – The study of how the body functions.

-phyte – Suffix meaning related to plant.

pia mater – Membranous covering of the brain and spinal cord largely adherent to the surface.

pigment cells – Any cells that contain pigment granules.

pivot joints – Joints that allow rotation where a rounded process of bone rotates within a sleeve or ring. In the atlantoaxial joint, the fingerlike dens (odontoid process) of the axis (C2) rotates in a collar formed by the upper front arch of atlas (C1) and the transverse ligament.

plantar reflex response – The toes contract in response to irritation of the sole of the foot.

plasma – Fluid portion of the blood, in which the particular components are suspended. It should be distinguished from モserum,ヤ which is the cell-free portion of the blood, from which the fibrinogen has been separated in the process of clotting.

plasticity – The capacity of the developing nervous system to functionally compensate for acquired structural deficits by “relocating” specific functions which ordinarily would have localized to a particular region of the cortex/brain.

platelets – Disc-shaped structures, found in the blood of all mammals and chiefly known for their role in blood coagulation.

platyspondylia – Platyspondylisis; congenital flattening of the vertebral bodies.

-plegia – Word ending meaning paralysis or stroke.

plexus – Complex network of interlaced nerves.

polarization-depolarization – The method of electrical charge and discharge which propagates an impulse along a nerve fiber.

Polymorphonuclear neutrophils (PMNs) – Granular leukocyte that moves to a cell, adheres to immune complexes, and engulfs microorganisms, etc., with phagocytes. These, in turn, eat the microorganisms, along with other foreign particles.

positron emission tomography (PET) – A method by which certain radioactive substances (isotopes) may depict metabolic functioning within brain tissue.

postconcussion syndrome – The constellation of somatic, cognitive, and emotional symptoms that emerge after a mild traumatic brain injury (MTBI).

posterior – Refers to the back or dorsal surface of the body; opposite of anterior; in back of or in the back part of a structure.

posterior arch fracture – A hyperextension injury, usually related to odontoid fractures or injury causing axial spondylolisthesis.

posterior cord syndrome – A syndrome that involves some ability to move the arm or leg, but o ability to feel sensations (pain, touch, pressure, body position sense, and perception of weight).

posterior longitudinal ligament – Single midline fibrous band attached to the back surfaces of the bodies of the vertebrae, extending from the occipital bone to the coccyx.

post-traumatic amnesia (PTA) – A period of loss of memory following head trauma. The duration of PTA may correlate with the persistence of symptoms of brain tissue impairment.

post-traumatic stress disorder (PTSD) – A condition characterized by the development of severe anxiety-related symptoms in response to a psychologically traumatic event that is generally outside the range of usual human experience.

poultice – Soft, moist mass about the consistency of cooked cereal, spread between layers of material of some sort and applied hot to a given area to create moist, local heat or counter-irritation.

Power’s ratio – Used by radiologists to diagnose anterior-occipital-atlantal dislocatioin. It has to do with the relation between the atlas, the tip of the odontoid process, and the margin of the occipital bone. A line is measured from the basion or median point on the anterior rim of the foramen magnum (B) to the posterior arch of C1 (C). This line is divided by another line that goes from the opisthion or midpoint of the lower border of the foramen magnum (O) to the anterior arch of the atlas (A). Normally, the line between B and C is shorter than the line between O and A. The ratio of BC:OA should be less than 1 or approximately 0.77 as it is in the normal population. Greater than 1:15 indicates an anterior dislocation.

prefrontal area – The location of processes of foresight, abstract thinking, and judgment.

primary brain damage – The cellular lesions created as a direct result of trauma.

primary cartilaginous joint – One of three types of connective tissue that joins the bones. Primary cartilaginous joints are hyaline cartilage that join the first rib with the sternum, being the unique synchondrosis in the human adult.

primary center of ossification – Site where bone cell development occurs by the second or third prenatal month.

primary gain – The overt and direct benefit to be obtained by a symptom or disorder, physiologic or psychologic; the nature of the conflict which causes the symptoms is excluded from awareness.

primary germ layers – Three layers of embryonic tissue called endoderm, mesoderm, and ectoderm, which form the organs and tissues of the body.

process – Prominence or projection, as of bone, such as the spinous process, designed to produce desired changes in the original material or to achieve other results.

prognosis – A forecast as to the probable outcome of a disease or the prospect of recovery from a disease as indicated by the nature and symptoms of the case.

prolapse – Rupture of the nucleus pulposus through the annulus fibrosus, but not through the posterior or anterior longitudinal ligament. It can also refer to a herniation of the nucleus pulposus through an inner annular tear, yet confined by the outer annular fibers, or to herniation of disc material through the posterior longitudinal ligament into the epidural space, as a continuum of the originating disc (extruded disc). The meaning is so idistinctive, covering such a wide range of definitions, that radiological reports using the term must be clarified.

proprioception – The perception of the position of a body part in space and in relation to other parts of the body.

prostaglandins – Group of naturally occurring, chemically related, long-chain hydroxyl fatty acids that stimulate contractility of the uterine and other smooth muscle and have the ability to lower blood pressure, to regulate acid secretion of the stomach, and body temperature and platelet aggregation, and to control inflammation and vascular permeability, etc.

proteoglycans – Any of a group of glycoproteins in connective tissue, made of carbohydrates and protein. They serve as binding or cementing materials. Also called protein-polysaccharide.

proton – Elementary particle of positive charge, which forms the nucleus of the ordinary hydrogen atom of mass.

proton density – Proton density represents a stage between T1 and T2 in which the cerebral spinal fluid is not as bright, helping to differentiate between the CSF and the lesion.

protoplasm – The viscid, translucid, polyphasic colloid with water as the continuous phase that makes up the essential material of all plat and animal cells. It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts. The protoplasm surrounding the nucleus is known as the cytoplasm and that composing the nucleus is the nucleoplasm.

protruded disc – When the nucleus pulposus bulges through a weakened annulus fibrosus, generally in a poster or posterolateral direction.

protrusion – Type of disc tissue displacement; a generic term that indicates deformity in the intervertebral disc. The distortion may be either focal (disc herniation), or diffuse (disc bulge). It is generally in a posterior of posterolaterial direction.

provisional callus – A firm, flexible bridge created when bone fractures, converted from a blood clot that develops and is later replaced by highly vascular connective tissue.

proximal – Relative directional term. Nearer the trunk of the body. Used with extremities; nearest; closer to any point of reference such as an origin, a point of attachment, or the midline of the body. Opposite is distal. For instance, the shoulder is proximal while the hand is distal.

pseudo-, pseud- – Combining form meaning something false.

psychic – Pertaining to or of the human mind.

psychoanalysis – A method of psychotherapy developed by Sigmund Freud. By the methods of free association and dream analysis, the origins of neurotic (cf) disturbances may be elucidated and brought into consciousness.

psychogenic – Arising from psychological or motivational causes, as opposed to organic causes such as brain tissue impairment.

psychometry – Measurement of the duration and force of mental processes. The measurement of intelligence.

psychomotor activity – The observable and overt reaction of a person to his environment. Usually described in quantifying terms, such as reduced or accelerated, or as mannerisms, grimacing, etc.

psychosis – A severe disturbance of the ability to interpret reality or to appreciate the actual qualities of the external world. May be due to organic or psychogenic causes.

ptosis – Prolapse of an organ or part. Usually, it refers to the drooping of the eyelid, closing the eye. Clinically, it refers to paralysis of the 3rd cranial nerve.

pyramidal systems – These two systems originate in the cerebellum. They are responsible for the regulation and coordination of complex voluntary coordinated muscular movement, as well as maintenance of balance and posture. One, called the pyramidal system or tract, has fibers that allow the motor action, generating the movement. The other, the extra-pyramidal system, regulates and refines movements involved in control and coordination, especially of postural, static, supporting, and locomotor mechanisms. It is a functional rather than an anatomical unit. All these fibers from the brain come through the spinal cord.



quadri – Prefix signifying four.

quadriplegia – Paralysis of all four limbs (from the neck down). British authors often use the prefix “tetra” to mean four, so they may describe a patient as having tetraplegia.



rad – Prefix indicating roots.

radial pulses – Those pulses felt over the radial artery, on the forearm, wrist, and hand.

radicular pain – Pain the root of the nerve.

radiculopathy – Refers to injury or damage in the nerve roots that is manifested by muscle weakness, numbness, tingling, pain, etc.

radioisotope – Naturally or artificially produced radioactive isotope of an element.

radionuclide – Nuclide that exhibits radioactivity.

ramus – Endings or final distribution of the nerve. A branch of a spinal nerve.

receptor (afferent) neuron – The input nerve component of the reflex arc which
conducts stimuli from the environment toward the CNS.

rectic capitus anterior muscle – Anterior vertebral muscle that gives the head flexion at the atlanto-occipital joints.

rectis capitus lateral muscle – Anterior vertebral muscles that make the headメs lateral flexion possible.

reduction – Amount by which something is lessened or diminished. In a medical context, it usually refers to what happens when parts of the broken bone are brought together in a normal position.

referred pain – Pain felt in one part of the body away from the site of the injury. For instance, injuries to C3 can produce pain in the pectoral (chest) area.

reflex – The whole of any special involuntary action.

reflex arc – In its simplest form, three components. Receptor, association, and effector (efferent) neurons facilitate one-way transmission of nerve impulses in a repetitive manner.

regeneration – FN/69

reliability – Fundamentally, consistency. That is, if a test is given repeatedly, under the same circumstances, predictable results will be obtained.

remodeling – In term of scar tissue, it implies synthesis of collagen as well as collagen lysis or breakdown. For example, it happens in the process of healing when in the fracture of a bone, the broken bone tries to regain its previous shape.

reticular tissue – Connective tissue made up of reticular cells and fibers.

reticulin – Makes up collagen, which is a component of the fibers of connective tissue.

reticuloendothelial system – Functional (rather than anatomical) system that serves as an important bodily defense mechanism. It is composed of highly phagocytic cells with both endothelial and reticular attributes and the ability to take up particles of colloidal dyes. These cells include macrophages lining the lymph sinuses and the blood sinuses of the liver (Kupfferメs cells) spleen, and bone marrow, and the microglia, reticulum cells of lymphatic tissue, tissue macrophages, and circulating monocytes. Also called macrophages.

reticulum – Network of cells and fibers.

retro- – Prefix meaning backward or behind.

retrolisthesis – A condition of spondylolisthesis in which the vertebral slippage is posterior.

rheumatism – Variety of disorders marked by inflammation and metabolic an degenerative changes of the connective tissue of the body, especially the joints.

rheumatoid arthritis – Chronic, systemic, inflammatory disease primarily of the joints, but usually of more than one. There are inflammatory changes in the synovial membranes and articular structure. In late stages deformity and ankylosis develop. The cause is unknown, but autoimmune mechanisms and virus infection have been suggested. Also called atrophic arthritis, arthritis deformans, arthritis nodosa, arthritis pauperum, chronic inflammatory arthritis, proliferative arthritis, arthronosos deformans, arthrosis deformans, and rheumatic gout.

rheumatoid arthritis, juvenile – Rheumatoid arthritis of children that leads to impaired growth and development, limitation of movement, and ankylosis and flexion contractures of the joints. Characterized by swelling, tenderness, and pain in one or more joints. Systemic manifestations include spiking fever, rash on the trunk and extremities, hepatosplenomegaly, generalized lymphadenopathy, and anemia.

rheumatoid arthritis of the spine – See rheumatoid spondylitis.

rheumatoid spondylitis – Form of rheumatoid arthritis that affects the spine. Mainly striking young males, it is a systemic illness of unknown origin. Inflammation produces pain and stiffness of the sacroiliac, intervertebral, and costovertebral joints. Complete rigidity of the spine and thorax can be produced by paraspinal calcification, with ossification and ankylosis of the spinal joints. Also called Bekhterevメs disease and Marie-Strumpell disease.

rhizotomy – Surgery where spinal nerve roots are cut to relieve pain.

ridge – Long, narrow or crested elevation on a bone, such as the nose. Prominent ridges are called crests.

ring epiphysis- Secondary ossific nuclei. When they are completely developed, they are made up of hard cortical bone, forming a ring about the margins of the vertebral bodies.

rongeur – Surgical instrument designed to cut through tissue and bone.

rostral – Situated toward a breaklike part that means superior (in relation to areas of the spinal cord) or anterior or ventral (in relation to brain areas). Example: The face is in the rostral part of the head.

rotation – Pivoting movement that twists a body part, head art, or leg on its long axis.

rotational acceleration – Velocity changes around the center of gravity of a sphere.



sacral spine – Part of the spinal column that contains the sacrum.

sacrococcygeal ligament – The joining of the narrow anterior longitudinal ligament, which broadens as it goes down to the end of the spine, securely uniting with the sacral periosteum and extending on to the pelvic surface of the coccyx.

sacroiliac ligaments – Bands of fibrous tissue that include the anterior, dorsal, interosseous, long posterior and short posterior, and ventral ligaments. The dorsal sacroiliac ligaments are numerous small bands that pass from the tuberosity of the ilium and the posterior inferior and posterior superior iliac spines to the intermediate sacral crest and adjacent areas of the sacrum. The interosseous sacroiliac ligaments are numerous short, strong bundles that connect the tuberosities and adjacent surfaces of the sacrum and the ilium. The ventral sacroiliac ligaments are also numerous thin fibrous bands passing from the ventral margin of the auricular surface of the sacrum to the adjacent portions of the ilium.

sacrospinalis – A large muscular and tendinous mass, found in grooves to the sides of the vertebral column, that changes size at different levels.

sacrum – Wedge-shape bone, positioned like an arrowhead at the end of the arrowメs shaft (the spine).

sagittal – Longitudinal plane that divides the body into symmetrical left and right sections. It goes from the center of the nose over the top of the head, following the sagittal suture down over the center of the back. Parasagittal cuts are parallel to that plane. It is perpendicular to the coronal.

sagittalis – Sagittal; general term for a structure situated in the direction of the sagittal suture.

sarcolemma – Delicate plasma membrane that surrounds every striated muscle fiber.

scab – Crust discharged from and covering a healing wound.

scalene muscles – Any of three muscles originating in the cervical spine. On each side of the neck, they bend and rotate the neck and assist breathing by raising of fixing the first two ribs. Also called scalenus.

scapula – Flat, triangular bone in the back of the shoulder; the shoulder blade.

scar – Tough superficial covering made up of dried tissue and/or fibrin; also known as eschar.

scar formation – The appearance of new tissue following coagulation, inflammation, and granulation of a wound.

schizophrenia – A psychotic disorder which, in its active phase, is characterized by characteristic symptoms involving a number of psychological processes. Can be very disabling, even incapacitating.

Schmorl’s nodes – Named for Dr. Schmorl, who described a bony defect seem by x-ray of the spine in the upper or lower margin of a vertebral body caused by prolapse of a nucleus pulposus into an adjoining vertebra. Also called intervertebral herniation of the disc.

Schwann membranes (neurolemma) – Thin membranes that spirally enwrap the myelin layers of some myelinated nerve fibers, especially peripheral ones.

sciatic nerve – Largest nerve in the body, a general sensory and motor nerve. It originates in the sacral plexus at L4-S3 and leaves the pelvis through the greater sciatic foramen, and branches by dividing into the tibial and common peroneal nerves, usually in the lower third of the thigh. It distributes through its individual branches.

sciatica – Painful condition where pain goes down along the sciatic nerve. It is ordinarily due to a herniated disc in the lumbar region of the spine, radiating to the buttocks and to the back of the thigh, to the leg or foot. Sciatica has been described in medical literature for 3,000 years, but only for sixty years has the herniated disc been attributed as the cause.

sclero- – Combining form meaning hard; denote relationship to the sclera of the eyeball. Also refers to the bone and joints.

sclerotic – Hard or hardening; refers to sclerosis (hardening or overgrowth of fibrous tissue).

sclerotome – Area of the bone or joint or periosteum innervated by a single spinal segment.

scoliosis – Perceptible abnormal lateral deviation in the normally straight vertical line of the spine in the thoracic, lumbar, or thoracolumbar region. Compare with kyphosis and lordosis.

scotoma – A defect in the visual field which is surrounded by a normally functioning field; can be detected by perimetry.

seat-belt injury – See chance-type fracture.

secondary brain damage – Lesions in the brain which arise subsequent to and as a result of primary brain damage and from pathologic processes in other body systems (e.g., cardiac, pulmonary, etc.).

secondary gain – The production or maintaining of bodily or psychological symptoms to satisfy a (largely) unconscious need.

segmental instability – Spinal instability, a condition in which the anatomic elements of the functional spinal unit or its supportive structures are disrupted, so that loads that are normally tolerated result in excessive or abnormal spinal motions, displacements, or strains, causing progressive deformities to develop.

sella – Saddle-shaped depression.

senescence – The process or condition of growing old, especially the state resulting from the changes and accumulations of the harmful effects of the aging process.

sensation – The sensory functions of the nerves sent from the extremities to the brain.

sense fibers – Fibers that carry sensations through the spinal cord to the brain. The cells of the spinal cord receive the sensation, interconnect at that point with the cells that relate with motion, and reaction takes place.

sensory – Impression conveyed by an afferent nerve to the sensorium.

sequestered disc – See free fragment.

sequestration – Type of disc displacement where the extruded segment is fragmented, occasionally with displacement of the free fragment into the spinal canal, often to a site far removed from the point of rupture.

serotonin – Vasoconstrictor that, in humans, is released by the blood platelets and found in high concentrations in many body tissues. It inhibits gastric secretion, stimulates smooth muscle serves as a central neurotransmitter, and is a precursor of melatonin.

sexual development – Refers to the rather abrupt process wherein the reproductive organs mature and the individual attains the sexual characteristics and reproductive capacity typical of the species.

shearing – The tearing or rending of different tissue planes (of the brain) resulting from rotational acceleration and consequent tearing of nerve cell tracts.

sheath – Case or cover such as an enveloping tubular structure like the tissue that encloses a muscle or nerve fiber.

shock – A rapid and substantial drop in blood pressure caused by lowering of effective blood volume.

single proton emission computerized tomography (SPECT) – Specialized form of radionuclide scanning, producing images much like those of a CT scanner, with cross-sectional images (slices).

sinuvertebral nerve – Meningeal branch of spinal nerves: the small branch of each spinal nerve that reenters the intervertebral foramen to supply the dura mater, vertebral column, and associated ligaments. (Ramus meningeus nervorum spinalium.)

-sis – Word termination of Greek origin signifying a state or condition. With a combining vowel it appears as ヨasis, -esis, -iasis, or -osis.

skeletal traction – Traction applied directly upon the long bones by means of pins Kirschner’s wire, etc.

slices – Planes of the body 2 to 5 mm apart that are photographed during CT scans, which use special computer software to concentrate the x-ray on otherwise inaccessible areas of the body.

social/emotional development – Refers to the process wherein the individual members of a species acquire the “rules” which govern social interaction and emotional functioning. From the perspective of ethnology or evolutionary or sociobiology, this social/emotional development proceeds upon a course which more or less parallels sexual and physical development, aimed at creating a state of “conscious” readiness for the evolutionary goal of reproduction and protection of the young for species survival. Because such parallel social/emotional development is REQUIRED in order to render an individual “available” for reproduction, evolutionary and sociobiological theory argues that the normal course of such social emotional development follows a “program” common to the species and is encoded in the individual’s DNA.

soft disc – The annulus fibrosus and the nucleus pulposus portion of an intervertebral disc.

soft-tissue injury – In the neck, a syndrome due to damage to the muscles, ligaments, discs, and blood vessels. They are often referred to as whiplash, hyperextension/hyperflexion, acceleration/deceleration injury, cervical strain, or cervical sprain.

soft-tissue window – Used in CT scanning to view discs, the thecal sac, and ligaments.

soma – The body as contrasted to the mind; the body tissue as distinct from the germ cells; the cell body.

somatic – Pertaining to or characteristic of the soma or body; pertaining to the body wall in contrast to the viscera.

somatic nervous system – Those parts of the nervous system concerned with the transmission of impulses to and from those components of the body not included in the three great cavities. That would include the skeletal muscles, bones, joints, ligaments, skin, eye, and ear, etc.

somatic senses – The general senses, such as the senses of touch pressure, heat, cold, pain, and body position.

somato- – Combining form denoting relationship to the body.

somatoform disorders – A group of disorders in which physical symptoms suggesting physical disorder predominate and in which there is strong evidence for a psychologic causation. These disorders include somatization disorder, conversion disorder, psychogenic pain disorder, and hypochondriasis.

somatosensory evoked potential responses – The adequacy of reception of various sensations on the skin surface, can be measured by determining the speed of transmissions of these sensations through the brain stem.

somatosensory evoked potentials (SSEP) – The stimulation of nerves at different points where surface electrode are placed and recordings made, to find out the proximal sensory conduction in (mainly) proprioceptive fibers, including spinal nerve root, tracts in the spinal cord, and brain stem.

somite – One of the paired blocklike masses of mesoderm, arranged segmentally alongside the neural tube of the embryo, forming the vertebral column and segmental musculature; called also mesoblastic or mesodermal segment.

sonography – Test where images are formed from echoes of the sound waves.

sperma-, spermato- – Combining form denoting relationship to seed, specifically to the male generative element.

spermatogenesis – The process of formation of spermatozoa, including spermatocytogensis and spermiogenesis.

spermatozoid cells – Generated by the testes; a single sperm cell fuses with an ova to create pregnancy.

spheno- – Combining form showing relationship to the sphenoid bone or to a wedge or meaning wedge-shaped.

sphenoid – Wedge-shaped; designating, especially, a very irregular wedge-shaped bone at the base of the skull.

sphenoid bone – Single, irregular, wedge-shaped bone at the base of the skull that forms a part of the floor of the anterior, middle, and posterior cranial fossae.

spina bifida – Describes a wide range of developmental defects of the vertebral column; commonly called cleft spine.

spina bifida cystica – More serious congential malformation, in which the meninges and/or spinal cord herniated through the defect in the vertebral arch.

spina bifida with meningocele – Condition where the meninges alone are herniated.

spina bifida with meningomyelocele – Condition where the meninges and spinal cord and/or nerve roots herniated. Frequently, patients have spinal cord and/or spinal nerve root malfunction such as paralysis of the limbs and incontinence of urine and feces.

spina bifida occulta – Simplest form of spina bifida; in it, the two sides of the neural arch (laminae of the vertebral arch) of one or more vertebrae fail to develop fully and fuse during embryonic development. Diagnosed by x-ray.

spinal accessory nerve – Cranial Nerve XI. Largely motor, this nerve supplies sternomastod and trapezius muscles.

spinal block – Lumbar puncture where a local anesthetic agent is injected directly into the cerebral spinal fluid. Usually, within one minute, the nerve roots are affected, as compared to ten to twenty minutes for an epidural block. A spinal block uses only about 10% as much anesthetic agent as needed for the epidural block, since the anesthetic does not have to diffuse through the meninges to reach the CSF. The nerve roots in the dural sac are blocked by spinal anesthesia, and control of the amount of anesthetic injected and the positioning of the patient relates to the number of spinal cord segmental levels being blocked. So that the anesthetic agent will flow in the right direction and not toward the head, affecting the nerves controlling vital functions (respiration, etc.) the patientメs head should be higher than the feet. (See epidural block)

spinal canal – Vertebral canal. A relatively narrow tubular passage or channel in the spine, encasing the spinal cord and the nerves. It changes in size at different levels, and its diameter can be measured very well with axial views of the CT scan.

spinal compression- Condition where pressure is exerted on the spinal cord, as by a tumor, spinal fracture, etc.

spinal cord – Part of the central nervous system that extends caudally from the foramen magnum down the spine; it has thirty-one pairs of nerves and connects the brain with the rest of the body.

spinal instability – When the anatomic elements of the functional spinal units, composed of the motion segment (two adjacent vertebral bodies, the intervening disc, the facet joints, and connecting ligamentous structures) and its supportive structures are disrupted, the result is spinal instability. This makes loads that are normally tolerated result in excessive or abnormal spinal motions, displacements, or strains, bringing about the development of progressive deformities.

spinal nerves – Sensory and motor nerves which connect the spinal cord to the periphery of the body.

spinal segmental unit – Complex of two vertebrae, between which is a disc. The disc lies in front of the segmental unit. The facets are on the arches in back and toward the sides. These three places are the only areas of movement in the spine.

spinal tap – Lumbar puncture.

spinous processes – Posterior parts of the vertebrae that result from the fusion of the laminae. They are felt like knuckles in the midline of the back.

splenius capitis – Deep back muscles that control the veretebral column, acting in concert with many other muscles. The splenius capitis and splenius cervicis, working together, retract the head. Singly, they turn it to the side, working with the sternocleidomastoid muscle.

splenius cervicis – Deep back muscles that control the vertebral column, acting in concert with many other muscles. The splenius capitis and splenius cervicis, working together, retract the head. Singly, they turn it to the side, working with the sternocleidomastoid muscle.

spondyl-, spondylo- – Combining form meaning vertebra. A general term that designates a specific type of bony structure.

spondylarthritis – Arthritis of the spine.

spondylitis – Inflammation of the veretebrae.

spondylodesis – Vertebral or spinal column fusion.

spondylogenic – Originating in the spine.

spondyloisthesis – Forward displacement or slip of one vertebral body over an adjacent vertebral body, ordinarily of the fifth lumbar over the body of the sacrum, or of the fourth lumbar over the fifth, usually due to a developmental defect in the pars interarticularis. Spondylolytic spondylolisthesis is one of six different categories of this entity; the other ones include dysplastic, degenerative, traumatic, pathologic, and iatrogenic spondylolistheses.

spondylolysis – Dissolution of a vertebra; a condition marked by a defect in the vertebral arch, and refers to a cleft or separation of the pars interarticularis that divides the neural arch into two segments. The diagnosis is made by x-ray.

spondylosis – Degenerative condition that involves two facet joints and an intervertebral disc in the lumbar spine, caused by osteoarthritis. It can be started by the failure of the disc. As the disc volume decreases, the facets become involved, and abnormal motion comes into play. When an osteophyte forms, the condition is then called spondylosis.

spondylosis deformans – Changes in the spine, in which bone production such as osteophytes have resulted from anterior displacement of the intervertebral disc.

sprain – Joint injury in which some of the fibers of a supporting ligament are ruptured, but the continuity of the ligament remains intact.

Spurling;s test – The doctor presses the top of the patientメs head down, gradually, to determine the location of the pain and numbness.

stability – The quality of maintaining a constant character in the presence of forces that threaten to disturb it.

static – At rest; in equilibrium; not in motion. Not dynamic.

statis – Stoppage or diminution of the flow of blood or other body fluid in any part; a state of equilibrium among opposing forces.

stenosis – Narrowing; pathological compression within the spinal canal. This abnormal narrowing impedes the flow of contrast medium during imaging and has been defined as narrowing of the spinal canal, including the lateral recesses, and the intervertebral foramina due to encroachment on the neural and vascular structures by the surrounding bone and soft tissues. It can stem from a congenital defect or be acquired from tumors, osteophytes, discs, hypertrophy of the facets and ligaments, hematomas, fractures, or other causes.

stereognosis – Ability to perceive and understand the form and nature of objects by touching them.

sternocleidomastoid muscle – Large, thick muscle that passes obliquely across the side of the neck, being enclosed between the two layers of the deep cervical fascia. It is thick and narrow at its central part but is broader and thinner at each extremity. It arises by two heads from the sternum and clavicle. These two portions are separated from one another, at their origin, by a triangular cellular interval, but become gradually blended, below the middle of the neck, into a thick, rounded muscle, which is inserted, by a strong tendon, into the outer surface of the mastoid process.

sternohyoid muscle – Thin, narrow, and ribbonlike muscle that arises from the inner extremity of the clavicle, the posterior sterno-claviular ligament, and the upper and posterior part of the first piece of the sternum. It passes upward and inward, and is inserted by short tendinous fibers into the lower border of the body of the os hyoids. This muscle is separated, below, from the same by a considerable interval, but the two muscles come into contact with one another in the middle of their course, and from this upward, they lie side by side.

sternum – Long, flat bone situated along the frontal midline of the chest, joining with the ribs on each side and with the collarbone above.

strabismus – Weakness of eye muscles allowing eyes to cross.

straight leg raising test – Test in which the patient lies flat on the bed. The doctor keeps the leg straight, puts one hand over the patella and the other one under the heel, and elevates the leg away fro the bed. The test is positive if the patient complains of leg pain and not backache when angled to some degree between 20 degrees and about 80 degrees. The test has more value when it is a small angle, such as 20 to 30 degrees, and has even more significance if the other variations, Lasegue and bow string signs, are positive.

strain – Overstretching or overexertion of some part of the musculature.

striated muscle – Muscle responsible for the skeletonメs movement (and the movement of organs such as the orb of the eye and the tongue). Also called voluntary muscle and skeletal muscle.

stroma – Supporting tissue or matrix of an organ, as distinguished from its functional element, or parenchyma.

stupor – A substantially lowered level of consciousness wherein arousal is difficult; mental and physical activity are minimal.

sub- – Prefix signifying under, near, almost, or moderately.

subannular – Anatomic position deep in the outer fibers of the annulus fibrosus.

subarachnoid space – Space between the arachnoid and pia mater that contains cerebrospinal fluid (CSF) and the vessels of the spinal cord. This space in the spinal region is narrow, except here it is below the conus medullaris. It is largest in the lower part of the vertebral canal, where the CSF surrounds the nerve roots comprising the cauda equina. Within the dural sac, fro L2 to S1, it is known as the lumbar cistern and besides the CSF, it contains the cauda equina and filum terminale.

subdural hemorrhage – Results from venous bleeding between the dura and arachnoid; its presence is generally indicative of a severe head injury.

subdural hygroma – An excessive collection of cerebrospinal fluid (CSF) in the subdural space.

subdural space – Potential space between the dura and the arachnoid that contains only a capillary layer of fluid.

subligamentous – Anatomic position beneath the posterior longitudinal ligament.

subluxation – Incomplete or partial dislocation, such as when one vertebra slides beneath another.

submental – Situated beneath the chin.

substance – Peptide composed of eleven amino acids, present in the intestine, where it serves to contract the intestine and dilate blood vessels. It is also present in a number of neuronal pathways in the brain and in primary sensory fibers of peripheral nerves and has been suggested to be a neurotransmitter associated with transmission of pain impulses.

super- – Prefix showing that something is exceptional or above the average.

superior – Relative directional term meaning toward the head, situated above, or facing above. It is the opposite of inferior.

superior gluteal nerve – Motor and general sensory nerve that originates in the sacral plexus, L4-S1. It distributes to the gluteus medium and minimus muscles, tensor fasciae latea, and hip joint.

supraspinous ligament – A single long, vertical, fibrous band, passing over and attached to the tips of the spinous processes of the vertebrae from the seventh cervical to the sacrum. It is continuous above with the ligamentum nuchae.

surgical fixation – The act or operation of holding, suturing, or fastening in a fixed position. The fastening internally of the ends of a fractured bone by means of wires, plates, screws, or nails applied directly to the fractured bone. The open reduction and stabilization of fractured bony parts by direct fixation to one another with surgical wires, screws, pins, and/or plates.

suture – Fibrous joint in which the opposed surfaces are closely united, as found in the skull. They allow flexibility in fetuses for growth and passage through the birth canal and for young children, for growth of the brain. In adults, bone has replaced the fibrous tissue, with a fusion allowing complete protection for the brain from external factors.

swelling (edema) – Enlargement of the working space in the bodyメs place of injury that takes place within the interspaces of the tissue during the process of inflammation.

sympathetic ganglion – Aggregation of cell bodies of primarily adrenergic neurons of the sympathetic nervous system. These ganglis are arranged in chainlike fashion on either side of the spinal cord.

sympathetic nervous system – Thorocolumbar portion of the autonomic nervous system. The system plays a role in the excitation and relaxation of muscle and provides an important additional surface for the exchange of metabolites between muscle and the extracellular space.

sympathetic phenomena – Sweating, discoloration of the skin, shiny skin, or changes in temperature; also called autonomic phenomena.

symphysis – When originally separate bones grow together. For example, the two pubic bones of the two halves of the lower jawbone. It also refers to the line or the place where they are joined. It can be called a symphysis whee bones are joined together by cartilage without a joint cavity lining or a cartilaginous joint two bony surfaces covered with thin layers of hyaline cartilage, cushioned by flattened plates or discs of fibrocartilage. They usually have slight movement called amphiarthroses. A good example is the intervertebral joints between the bodies of vertebrae. Also called secondary synchondrosis.

syn- – Prefix signifying union or association.

synapse – The connection between the end of a nerve and the adjacent structure, such as a muscle cell or another nerve ending. Various transmitter chemicals liberated into the synapse make nerve transmissions possible.

synarthrosis – Joint, classified as to degree of movement, as an immovable joint See amphiarthrosis and diarthrosis.

synchondrosis – Usually temporary, this type of cartilaginous joint ordinarily converts into bone before adult life. It allows growth, not movement.

syncytiotrophoblast – Outermost cyncytium layers of the trophoblast. This mass of protoplasm results from the merging of cells.

syndesmophytes – Bony excrescence or outgrowth from a ligament.

syndesmosis – Fibrous joint in which bones are held closely together, but not touching, by collagenous fibers or interosseous ligaments. They are generally synarthroses (immovable joints), although, if thee is a small amount of movement, it is related to the distance between the bones as well as the flexibility of the fibrous connecting tissue. This limited movement adds strength to the joint.

syndrome – Complex of symptoms occurring together. In morbid states, a syndrome is the sum of signs of any diseased state.

synostosis – When adjacent bones join together, having normally been separate bones. This includes parts of a single bone formed by osseous material (ossified connective cartilage or fibrous tissue). Compare with ankylosis.

synovial – Pertaining to or secreting a transparent alkaline viscid fluid, resembling the white of an egg.

synovial cavity – Space between two articulating bones; also called joint cavity.

synovial fluid – The fluid surrounding synovial joints that makes them slippery and smooth.

synovial joint – Classified as to structure, it has a joint cavity, with the ends of the bones covered by a smooth hyaline articular cartilage; the joint is lubricated and nourished by thick synovial fluid. It is enclosed by a flexible articular capsule. Most permanent joints I the body are synovial, and of all the types of joints, these allow the greatest range of movement (diarthroses), due to their special form of articulation.

synovial membrane – Membrane lining the cavity of joints and similar areas where friction needs to be reduced; composed of loose connective and adipose tissues covered by fibrous and connective tissue.

synovium – The specialized connective tissue layer that lines the inside of the synovial capsule and varies in thickness and density.

synthesis – The artificial building up of a chemical compound, by the union of its elements or from other suitable starting materials.

system – Group of organs that work together to perform a major body function.



T1-weighted images – In MRI’s, these are images where a relatively short TE (transverse plane sampling time) of generally 17 msec, but less than 30 msec, and short TR (sampling time in the T1) of generally 500 msec, but less than 800 msec, are utilized. These images typically generate the best anatomic images and are valuable for demonstrating marrow disorders. T1-weighted images are also well suited for evaluating contrast enhancement.

T2-weighted images – In MRI’s, these are images where a relatively long TE (transverse plane sampling time) of generally more than 80 msec, and long TR (sampling time) of generally greater than 2000 msec are used. These images are the most sensitive for detecting the hydration state of the disc and are valuable in detecting extradural lesions. These pulsing sequences are important to establish the presence of intramedullary lesions of the spinal cord. At higher field strengths these images are also useful in identifying marrow disorders.

tactile – Pertaining to the touch.

tempora – The temples; the region on either side of the head, above the zygomatic arch.

temporal lobe – Lobe at lateral-anterior area of the cerebrum; governs and regulates memory, olfactory, recognition, sexual expression, etc.

temporomandibular joint syndrome (TMJ) – A disorder, sometimes caused by trauma to the head and neck, characterized by pain arising from the articulation between the skull and the mandible.

tendon – Fibrous cord, by which a muscle is attached.

teno- – Combining form denoting relationship to a tendon.

tenoblasts – Immature tendon cells.

tenocyte – The cell of a tendon.

tensile – Of, undergoing, or exerting tension. Capable of being stretched.

tension – The act of stretching; the condition of being stretched or strained; the degree to which anything is stretched or strained.

tera- – Combining form referring to abnormal congenital defects.

teratogen – Substance, agent, or factor that interferes with embryonic development and causes gross deformities in the embryo.

teratology – The part of embryology that deals with grossly abnormal development and congenital malformations. In earlier times, they were considered warnings or portents of the future, magical, and divinatory. A few hundred years ago, fetal disease, by way of a transplacental route, was suggested as a cause. Genetics and a hereditary aspect were suspect. Now, factors in the maternal environment as well as genetics are the concerns of teratology, which became a science in the early nineteenth century.

testes – Male gonads that produce hormones and generate sperm cells.

theca – Surrounding case or sheath, usually refers to the dura mater.

thoracic spine (dorsal spine) – Part of the spine that corresponds to the chest, behind the chest.

thoraco- – Pertaining to the chest.

thoracolumbar junction – Pertains to the area where the rigid thoracic spine joins with the flexible lumbar spine. Usually it refers to segments T11, T12, an L1. It is a common site of fracture because the thoracolumbar junction acts as a fulcrum for the spineメs motion.

thoracostomy tube – Tube inserted through an opening in the chest wall, for application of suction to the pleural cavity that is often used to reexpand the lung in spontaneous pneumothorax.

three-column principle – Classification system that divides vertebral bodies in order to identify locations of certain injuries. We use it to visualize how injury can cause instability of the spine. Physiologically, when damaged, the spine follows a pattern as if it had three columns, close to each other. This principle refers to the thoracic and lumbar spines.

three joint complex – Since, in the intervertebral joint, the joint articulates in three places, between the two facet joints with the adjacent two facets joints and between the intervertebral disc and the adjacent intervertebral disc, this motion segment is called the three joint complex. Each independent articulation allows the motions of flexion, extension, and torsion.

thrombo- – Combining form denoting relationship to thrombus or blood clot.

thromboxane – An intermediate in the metabolic pathway of arachidonic acid, formed from prostaglandin endoperoxides and released from suitably stimulated platelets.

tibial nerve – One of the nerves affected when a disc herniation occurs between L5 and S1. Pain is in the posterior part of the thigh behind the knee, the popliteal space (underside of the knee), the calf, the heel, and on the lateral (outside) aspect of the foot and big toe.

tic – A coordinated, repetitive movement, often of the face.

tinnitus – A sound experienced subjectively with no external source. May be due to a disorder of the auditory apparatus or of the brain.

tissue factor – Tissue factor, evoked by damaged tissue, acts to produce blood clots.

-tomo, -tomy – Combining form relating to a cutting or operation, or to a layer achieved by cutting or slicing.

tonicity – Sustained partial contraction of muscles when they are relaxed or resting.

tonus – The steady contraction of the muscles to maintain the posture of the body.

tors- – Combining form meaning twist or rotation.

torsion – The act of twisting and rotating along the axis of the structure.

torticollis – Condition in which the neck twists to one side of the head by contraction of the cervical muscles. Also called wry neck.

trachea – Tube descending from the larynx and branching into the right and left main bronchi.

tract – Bundle of nerve fibers having the same origin, function an distribution.

traction – A form of pulling one structure by another, along its axis. For instance, cervical traction separates the vertebrae of the spine by pulling the head up against the weight of the body.

traction rings – Horizontal projections of bone, growing parallel to the surface of the vertebrae. As seen in lateral plain x-rays, they are 1 mm above or below the discal border. They indicate segmental instability and do not represent degeneration of the disc.

transaction – Section or cut made transversely across a long axis.

transcutaneous electrical nerve stimulation (TENS) – Way to reduce pain through electrodes applied to the skin.

translational acceleration – Velocity changes of an object moving along a straight line or vector through the center of gravity.

transligamentous – In the spine, this refers to disturbing and going across into the posterior longitudinal ligament (PLL) fibers.

transthoracic decompression – Surgery done for the release of pressure on the spinal canal. It is done by way of (trans) a surgical incision in the chest (thoracic) approach.

transverse – Placed crosswise; situated at right angles to the long axis of a part.

transverse arteries – Vertebral arteries that go through the foramina from the sixth to the first cervical vertebrae up to the brain.

transverse foraminae – Natural openings in ether transverse processes of cervical vertebrae that, in the upper six vertebrae, transmit the vertebral vessels. In the seventh vertebra, it is small or possibly absent.

transverse ligament of the atlas (atlantis) – The strong horizontal part of the atlasメs cruciform ligament that attaches at each end to the atlasメs lateral masses and curves at the back around the dens of the axis. In this way it divides the atlantal ring into a smaller anterior division of the dens, and a larger posterior division for the spinal cord and related structures. Also called Lauthメs ligament.

transverse processes – Part of the vertebrae that project posterolaterally from the junction of the pedicles and laminae. They resemble wings of the vertebral body, acting as levers and providing attachments for the deep back muscles.

transversospinalis muscles – General term that includes the semispinalis and multi-fidus muscles and the rotators.

trapezius muscles – Muscles that rotate the scapula to raise the shoulder in abduction of the arm. They draw the scapula backward. Innervation is from the accessory nerve and the cervical plexus. It originates in the occipital bone, the ligamentum nuchae, and the spinous processes of seventh cervical and all thoracic vertebrae. It inserts into the clavicle, acromion, and the spine of the scapula.

treadmill exercises – Walking, as on a treadmill, for physical therapy.

tremor – Rhythmic movement of a joint, usually the hands. Indicative of anxiety states or CNS disease, common as a drug reaction.

trigeminal nerve – Cranial Nerve V. A complex motor and sensory nerve with three sensory components (ophthomologic, maxillary, mandibular) receiving sensation from face and underlying structure and with motor components to tear glands, etc.

trigeminal nerve nuclei – Nuclear complex of the trigeminal nerve that is located chiefly in the pons and medulla oblongata, but also in the mesencephalon and upper cervical cord. They are the nuclei motorus nervi trigemini; the nuclei sensorius principalis nervi trigemini; the nuclei mesencephalicus nervi trigemini, and the tractus spinalis nervi trigemini.

trigger point – See active myofascial trigger point.

trochlear nerve – Cranial Nerve IV. Supplies superior oblique muscle of the eye.

tropho- – Combining form denoting relationship to food or nutrition. Many words contain it, since in the embryonic stage nutrition is involved in the development of the embryo.

trophoblast – Also called trophoderm, this is the outermost layer of extraembryonic tissue of the blastocyst, attaching the fertilized ovum to the uterine wall. It supplies nutrition to the embryo.

trophoectoderm – Surrounding epithelial layer of a blastocyst, composed of cells called trophoblasts. It develops into a fetal membrane system.

tubercle – Rounded elevation on a bone; a small raised eminence.

tuberosity – Large rounded elevation on a bone.

turgor – The condition of being swollen and congested. Turgor vitalis: the normal consistence of living tissue.



ultra- – Combining form indicating beyond, on the other side of, beyond the range, scope or limit of, the normal or proper degree of; excessively.

ultrasound – Physical therapy used in, controlled doses, to selectively break down pathologic tissues, as in treatment of arthritis and lesions of the nervous system; a noninvasive exploratory technique that sends pulses of ultrahigh-frequency sound waves into designated body cavities.

umbilical cord – Encompasses two arteries that carry carbon dioxide and nitrogen wastes from the fetus to the placenta. It has one vein that also carries oxygen and nutrients from the placenta to the embryo, or fetus.

uncinate process, uncus – Bony excrescences placed laterally or posterolaterally on C3 through C7, and which form a defensive rampart of bone, preventing disc herniation in this area. The uncinate processes are of great significance in the cervical spine, because they act as barrirs to the extrusion of disc material posterolaterally, preventing compression of the nerve roots.

unconscious – A term which has two possible interpretations: (a) as synonymous with a totally diminished awareness of the external world, as in stuporor coma, or (b) as a psychological term for those forces and drives which are not normally available to the person’s awareness due to the forces of repression.



vagus nerve – Cranial Nerve X. Supplies motor and sensory nerve fibers to and from heart, lungs, larynx, pharynx, diaphragm, and other gastrointestinal organs.

validity – The usefulness of a procedure. That is, does the test measure what it is assigned to measure?

Valsalva’s maneuver – Maneuver whereby the patient holds his or her breath or gives a voluntary cough or sneeze to produce pain. These activities, holding the breath, coughing, or sneezing, increase the pressure of the cerebrospinal fluid. This enlarges the pressure against the already pressured nerve, causing pain and numbness. The location of this intensified pain also contributes to the diagnosis.

vasoconstriction – Reduction of the inner diameter of vessels, especially constriction of arterioles, leading to decreased blood flow to a part.

vasodilation – Vessels stretched beyond the normal dimensions, especially arterioles. This leads to increased blood flow to a part.

venous plexus – Network of interconnecting veins.

ventral – Relative directional term denoting a position more toward the belly surface than some other object of reference; also called anterior, opposite of dorsal.

vertebra – Pieces of a special type of bone that form the spinal column. Any of the thirty-three bones of the spinal column, comprising the seven cervical, twelve thoracic, five lumbar, five sacral, and four coccygeal vertebrae.

vertebral arch – Shaped like the arch on a padlock where the spinal canal compares to the solid part of the padlock. The vertebral arch is the part of the vertebra that encloses the vertebral foramen, or nerve openings. The vertebral arch (neural arch), which is attached on each side to the body, protects the neural tissues (spinal cord and nerve roots) from injury. Two pedicles (L. little feet) form the arch and project at the back, meeting two laminae (L. thin plates), which meet to form a spinous process down the back. Arising from the vertebral arch are also four articular processes/facets and two transverse processes. The space enclosed by the body and arch is the vertebral foramen.

vertebral arteries – Vertebral arteries distribute into the muscles of the neck, vertebrae, spinal cord, cerebellum, and interior of the cerebrum. They originate in the subclavian artery. Their branches are spinal and meningeal, posterior inferior cerebellar, basilar, and anterior and posterior spinal arteries.

vertebral body – Large, heavy, anterior part of a vertebra with the form of a short cylinder. Its function is to support weight. The bodies of the vertebrae, especially from T4 downward, become larger in order to bear greater weight.

vertebral canal – The spinal canal, which contains the spinal cord.

vertebral column – Assemblage of the vertebrae from the cranium through the coccyx into a column; also called the spinal column, the backbone, and the spine.

vertebral column movement – Movement in a vertebral column that includes flexion, extension, lateral flexion (bending), and rotation. At the joints of the vertebral column, rocking, rotation and gliding occur with gliding movements at the zygapophyseal (facet) joints. Movements are freer in the cervical and lumbar regions. The thoracic region, connected to the sternum by way of the ribs and costal cartilages, moves very little with flexion being almost non-existent there.

vertebral foramen – Large opening in a vertebra formed by its body and arch. Also called medullary foramen and spinal foramen or aperature.

vertebral segment – Segment of the spinal column composed of two vertebral bodies, a disc, and the corresponding facets and ligaments. See spinal segmental unit.

vertebrogenic symptoms – Refers to the neural innervation of the anterior longitudinal ligament and the anterior annulus fibrosus. Vertebrogenic pain localized to the spine is sharp and deep.

vertical compression lesion – A type of injury that occurs when divers hit the bottom of the pool with their head or when a car rolls over and someoneメs head is crushed against the roof of the car.

vertigo – A subjective sense of imbalance usually noted as an illusion of moving or spinning of the external world. May be due to disturbance of the labyrinth, a part of the vestibular apparatus.

vestibular apparatus – The balance apparatus in the inner ear (semicircular canals) which helps orient the individual in space. The eighth cranial nerve supplies this apparatus.

vestibular nerve (eighth cranial nerve) – The auditory or the vestibular cochlear nerve. It conveys information about equilibrium, balance, position, and movement of the head, etc.

vestibulocochlear (auditory-vestibular) – Cranial Nerve VIII. Transmits sensation to the brain from the labyrinth for hearing reception and transmits sensation to the brain from the cochlea, the hearing end organ.

vestibulospinal tract – Bundle of nerve fibers that connect the vestibular nuclei of the medulla with the nuclei of the spinal cord.

viable – Capable of living; especially said of a fetus reaching a stage of development that it can live outside of the uterus.

viscera – Organs inside the chest, abdomen, and pelvis, such as the heart, lungs, stomach, liver, spleen, and uterus.

visceral – Related to the organs.

visceral muscle – Found in large interior organs of the three great cavities of the body, especially in the abdomen.

visual attention and visual motility – Refer to the individual’s ability to attend, localize, and follow stimuli for efficient processing of visual information.

visual brain stem evoked potentials (VBP) – A method of recording visual stimuli as they are processed and integrated in the brain stem.

visual field defect – A problem in relation to what is seen as opposed to location of damage in optic system; occurs because of the crossing of half of the optic fibers at the optic

visual motor coordination – The coordination of visual perception with motion; the ability to see something and react with a movement.

visual perception – The ability of the eyes and brain to use incoming visual stimuli to form a complete picture of the visual world.

volition – Self-initiated, goal-directed activity, manifest as “drive,” persistence, etc.

voluntary muscle – Muscle responsible for the skeleton’s movement (and the movement of organs such as the orb of the eye and the tongue). It is often called voluntary muscle because it can be controlled voluntarily.



weighted – Having an assigned value that expresses the relative importance of a thing as the result of measuring it in some fashion.

Wernicke’s aphasia – Disturbance of speech or reading, caused by a defect in the receptive (afferent) brain connections. Comprehension of speech is affected, while expressive speech may appear superficially normal.

whiplash – Popular term for an acute cervical sprain; an acceleration extension injury of the cervical spine.

whirlpool bath – Therapeutic bath, in which a whirling, churning stream of hot water is forcibly directed against part of the body.

white matter – Myelinated axons in the central nervous system; inner layer of the cortex.

white substance – See white matter.

window – Used in CT scanning to view discs, the thecal sac, ligaments, bone structure, and joints.

wrapped disc – Fragment of herniated disc material surrounded by a rim of contrast-enhancing granulation tissue.



xantho- – Combining form resembling the color yellow.

xanthochromia – Related to the color of a tissue, like the skin, or spinal fluid.

xeno- – Combining form meaning foreign, such as foreign material. Example: xenophthalmia, ophthalmia caused by a foreign body in the eye.

X-ray or Roentgen rays – Electromagnetic vibrations of short wavelengths produced when electrons moving at high velocity impinge on various substances, especially the heavy metals. They can penetrate most substances to some extent, some much more readily than others, and can also affect a photographic plate. These qualities allow us to use them to take roentgenograms (x-rays) of various parts of the body and thus reveal the presence and position of fractures or foreign bodes or of radiopaque substances that have been purposely introduced.



yolk – Stored nutrient of the ovum. Example: the yolk of an egg.

yolk sac – Extraembryonic membrane that is the primitive respiratory and digestive system before the placenta develops. It becomes nonfunctional and incorporated into the umbilical cord by the sixth or seventh week after fertilization.

yolk stalk – The primary or first respiratory and digestive structure of an embryo is the yolk sac, which, by the sixth week, is reduced to the yolk stalk and at some time becomes part of the umbilical cord. During the second and third weeks, before the placenta is fully developed, it brings the nutrients to the embryo.



zona pellucida – Thick, transparent noncellular layer or envelope of uniform thickness surrounding an oocyte (a developing egg cell); the outer wall of an ovum.

zygapophyseal joints – These joints are called facets and are flat surfaces where articulation between upper and lower joint-forming processes takes place.

zygapophyses – Articular processes of a vertebra.

zygote – Cell formed by the union of male and female gametes.