The following list is intended to be helpful to patients and students in understanding neurological terminology.

This page authored by Allyson Zazulia, M.D., Assistant Professor of Neurology and Radiology at Washington University School of Medicine.

Note: Theicon after an entry indicates a link for further information.

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abducens nerve (cranial nerve VI)
motor nerve innervating the lateral rectus muscle, which abducts the eye; lesions of the nucleus, which is located in the dorsal pons, produce a horizontal gaze palsy; nerve fibers exit the ventromedial pons and because of their long course are vulnerable to damage by mass lesions/increased intracranial pressure

abduct
move away from the saggital plane of the body

absence seizure (petit mal seizure)
generalized seizure characterized by abrupt cessation of ongoing activity with a blank stare and lost or impaired consciousness lasting on average 10-20 seconds

abulia
loss of will, impulse, and decision-making ability

acalculia
"inability to calculate" or difficulty with arithmetic; may be the result of damage to the angular gyrus in the hemisphere dominant for speech and language

acephalic migraine
migraine variant consisting of the migraine aura without the headache; also known as migraine equivalent

accommodation
adjustment of the focal length of the lens of the eye in order to keep objects at varying distances in focus on the retina

acrocephaly action potential
see brachycephaly

action potential
rapid, transient, all-or-none nerve impulse initiated at the axon hillock; electrical signal by which the brain receives, analyzes, and conveys information

action tremor
tremor that appears during movement of the affected body part

activities of daily living (ADLs)
activities a person performs for self-care (feeding, grooming, bathing, dressing), work, homemaking, and leisure; ability to perform ADLs is often used as a measure of ability/disability

activity limitations
difficulties an individual may have in executing specific tasks or actions (e.g., walking independently).

acute
developing over minutes to hours; implies acute metabolic dysfunction (e.g., ischemia, seizure )

Acute Disseminated Encephalomyelitis (ADEM)
acute, classically monophasic demyelinative disease of the CNS that may follow a viral syndrome or vaccination or no identifiable predisposing cause

adduct
move towards the saggital plane of the body

Adie’s syndrome
association of Adie’s tonic pupil with absence of muscle stretch reflexes

Adie’s tonic pupil
irregularly dilated pupil exhibiting minimal or no reaction to light, slow reaction to accommodation, and hypersensitivity to pilocarpine; typically idiopathic and most often seen in young women

adrenoleukodystrophy
typically X-linked recessive demyelinative disease ± adrenal dysfunction due to accumulation of very long chain fatty acids

afferent
sensory pathway proceeding toward the CNS from the peripheral receptor organs

afferent pupillary defect (Marcus-Gunn pupil)
pupillary dilation in the eye with a pre-chiasmic optic pathway lesion (e.g., optic neuritis) in response to shining a light in the damaged eye after first shining it in the normal eye

ageusia
impaired sense of taste

agnosia
inability to recognize and interpret objects, people, sounds, or smells despite intact primary sense organs (e.g., inability to identify a sound despite intact hearing); typically results from damage to the occipital or parietal lobe

agraphia
inability to communicate ideas in written language not due to mechanical dysfunction; typically results from damage to the parietal lobe.

akathisia
motor restlessness; inability to sit still

akinesia
paucity of movement

akinetic mutism disorder of consciousness characterized by periods of sleep and periods of wakefulness during which the patient lies with eyes open but is unresponsive, mute, and immobile; often due to frontal lobe damage

alexia
inability to read, usually due to a lesion of dominant occipitotemporal cortex

alien hand syndrome
syndrome characterized by the involuntary movement of a single upper limb in conjunction with the experience of estrangement from or personification of the movements of the limb; often seen in corticobasal degeneration

allodynia
condition in which an ordinarily painless stimulus is experienced as being painful

alpha motor neurons
large motor neurons that innervate extrafusal skeletal muscle fibers

alpha-synuclein protein expressed predominantly in the CNS that when aggregated, can result in neurodegenerative diseases such as Parkinson disease, dementia with Lewy bodies, and multisystems atrophy

Alzheimer’s disease
most common cause of dementia in older adults; a neurodegenerative disease characterized by the gradual loss of cognitive ability in association with the neuropathological findings of abnormal protein aggregates (neuritic plaques and neurofibrillary tangles) and neuron loss in the cerebral cortex

amaurosis fugax
temporary loss of vision in one eye due to impairment of blood supply through the internal carotid artery or the ophthalmic artery

amblyopia
developmental abnormality in which a child fails to develop sharp visual acuity

amygdala
telencephalic gray matter structure located in the anterior portion of the medial temporal lobe involved in emotion, cognition and the regulation of autonomic processes; part of the limbic system

amyotrophic lateral sclerosis
(Lou Gehrig’s disease) inexorably progressive and fatal disease of unknown cause characterized by slowly progressive degeneration of upper and lower motor neurons

analgesia
loss of pain sensation

anencephaly (aprosencephaly)
CNS malformation involving failure of closure of the cephalic end of the neural tube, resulting in absence of the forebrain and cerebrum; rudimentary brainstem may be present so that reflex actions such as breathing and responses to sound or touch may occur

aneurysm (brain aneurysm, cerebral aneurysm)
a bulging formation on an artery, usually caused by hypertension or an excessive amount of fatty deposits

angular gyrus
gyrus located immediately posterior to the supramarginal gyrus at the superior edge of the temporal lobe and involved in recognition of visual symbol; lesions can result in alexia and agraphia

anhidrosis
absence of sweating

anisocoria
pupillary asymmetry

ankle-foot orthosis (AFO)
brace that is worn on the lower leg and foot to support the ankle and correct foot drop

anomia
inability to name objects or to recognize written or spoken names of objects

anosmia
loss of sense of smell

anoxia
lack of oxygen to the brain or other vital organ

anterior cerebral artery
a branch of the internal carotid artery; supplies blood to the medial aspect of the cerebral cortex (leg area predominant), some areas of the frontal lobe, corpus callosum, caudate, and the anterior limb of the internal capsule

anterior commissure
one of the three major groups of commissural fibers that courses through the basal ganglia and cross the midline in the anterior forebrain to interconnect the olfactory bulbs, amygdala, and hippocampal areas, among others

anterior communicating artery
branch of the internal carotid artery that joins together the paired anterior cerebral arteries

anterior cord syndrome
spinal cord injury syndrome associated with damage to the anterior 2/3 of the spinal cord, often due to occlusion of the anterior spinal artery resulting in bilateral paralysis, bladder dysfunction, and loss of pain sensation below the level of the lesion

anterior cranial fossa
portion of the internal base of the skull housing the frontal lobes

anterior horn (ventral horn)
gray matter in the front of the spinal cord that contains motor_neurons

Anton's syndrome
form of cortical blindness in which the patient is unaware of/denies the visual impairment; due to a lesion of the occipital lobe extending from primary visual cortex into visual association cortex

aphasia
syndrome of disordered expression or comprehension of spoken and/or written language caused by brain injury; see also non-fluent, fluent, conduction, global, transcortical motor, and transcortical sensory aphasia

aphemia
inability to speak words despite being able to make other sounds

aphonia
complete loss of voice

apnea test
part of the “brain death exam”; verifies lack of responsiveness to carbon dioxide (paCO2 > 60 mm Hg) in the presence of respiratory acidosis (pH < 7.3)

apraxia
impaired planning/sequencing of movement that is not due to weakness, incoordination, or sensory loss. Although the movements cannot be performed for a specific situation, they may be performed under other circumstances (e.g., inability to lift feet off the floor when attempting to walk but preserved ability to perform bicycling movements of the legs while lying in bed). Results from dissociation of parts of the cerebrum and is often associated with parietal lobe lesions.

aprosencephaly see anencephaly

arachnoid
middle layer of the meninges covering the brain and spinal cord

arachnoid granulations (arachnoid villi) branched tufts of arachnoid that project through the dura mater into the venous sinuses and function to return CSF to the systemic circulation

arachnoid villi
diverticula of the arachnoid mater in the subarachnoid space that extend into the veins and venous sinuses of the dura; a major pathway for the drainage of cerebrospinal fluid and transport across the endothelium into the blood.

arcuate fasciculus
pathway connecting Wernicke’s area in the posterior left superior temporal gyrus to Broca’s area in the left inferior frontal lobe; lesion results in impaired repetition

area postrema
chemoreceptor trigger zone for vomiting that is located on the dorsal surface of the medulla

Argyll-Robertson pupil
pupil exhibiting light-near dissociation due to a lesion in the midbrain periaqueductal gray matter caused by tertiary syphilis

arousal
abrupt change from sleep to wakefulness, or from a "deeper" stage of non-REM sleep to a "lighter" stage

arteriovenous malformation
a tangled collection of abnormal arteries and veins

arteritis
inflammation of an artery

arthrokinetic nystagmus
nystagmus induced by passive rotation of the arm of a stationary subject seated in total darkness inside a rotating drum

ascending tract of Deiters
direct pathway (lying just lateral to the medial longitudinal fasciculus) from the vestibular nuclei to the ipsilateral medial rectus subnucleus; clinical significance of this pathway is unclear

aseptic meningitis
syndrome characterized by headache, neck stiffness, low grade fever, and Cerebro Spinal Fluid lymphocytic pleocytosis in the absence of an acute bacterial pathogen; often used synonymously with viral meningitis, but also incudes meningeal inflammation due to various drugs (e.g., NSAIDs) or diagnostic procedures (e.g., angiography); atypical bacterial, fungal, parasitic, or parameningeal infection; neoplastic processes; and various systemic disorders

associated reactions
movements of body parts other than the ones that are intended to move, often increased with increased effort

association cortex
cortical areas involved in higher order processing of sensory information and integration of multiple sensory and sensorimotor modalities

astasia
inability to stand because of motor incoordination

astasia-abasia
functional stance and gait characterized by bizarre movements, typically swaying wildly and nearly falling, but then recovering at the last minute

asterixis
sudden palmar flapping movement of the hands at the wrists; indicative of metabolic encephalopathy

astrocytes
CNS glia that function to orient neuroblast migration in the cerebral and cerebellar hemispheres, provide mechanical support, react to injury, insulate synaptic surfaces, provide a source and sink for extracellular potassium, and uptake neurotransmitters to terminate their synaptic action

astrocytoma
most common central nervous system tumor derived from astrocytes

astrocytosis
reaction of astrocytes to neuronal injury characterized by an increase in the number and size of astrocytes (primary reaction) and cytoplasmic changes including increased glial filaments and glassy eosinophilic cytoplasm followed by formation of a dense gliotic scar (secondary reaction)

ataxia
incoordination of movement usually due to disease of cerebellar or sensory pathways

athetosis
involuntary, slow, writhing movements

atonia
loss of muscle tone

atonic seizure (drop attack)
generalized seizure characterized by sudden loss of muscle tone and strength; may cause the head to drop suddenly, objects to fall from the hands, or the legs to lose strength, with falling and potential injury

aura

warning symptom (e.g., of vision, smell or perception) occurring prior to a spell such as a migraine or seizure; implies focal brain disturbance

automatism
mechanical, seemingly aimless behavior (e.g., lip smacking or picking at clothes) characteristic of complex partial seizures

autonomic
pertaining to the autonomic nervous system, which controls bodily functions that are not under conscious control (e.g., heartbeat, breathing, sweating)

autonomic nervous system
part of the peripheral nervous system that regulates visceral function and homeostasis independent of voluntary control

autoregulation
physiological process by which blood vessels change caliber to maintain constant cerebral blood flow over a wide range of cerebral perfusion pressures

axial
transverse plane producing a cross-section of the body or head

axon
long, slender projection from the neruonal cell body that is specialized for the conduction of information encoded in the form of action potentials

axonal degeneration
neuropathic process resulting in degeneration of the axon and its myelin sheath; preferentially involves the distal portion of the axon ("dying back neuropathy")

axonal spheroid
stereotypic axonal response to injury consisting of marked swelling due to accumulation of materials undergoing axonal transport

Babinski response
extension of the great toe on stimulation of the sole of the foot, signifying a lesion of the corticospinal tract (a.k.a., upgoing toe); see also plantar response

Balint syndrome
syndrome comprising paralysis of visual fixation, optic ataxia, and impairment of visual fixation due to bilateral lesions of the parietal and occipital lobes

basal ganglia
large subcortical nuclear masses consisting of the caudate, putamen, globus pallidus, subthalamus, and substantia nigra; part of the motor system that permits chosen and inhibits unwanted movement

basal palisading
basal layer of small cells with darkly staining nuclei and little cytoplasm seen in the epithelium of craniopharyngiomas

basilar artery
large brainstem artery located on the ventral surface of the pons formed by the joining of the two vertebral arteries and bifurcating into the posterior cerebral arteries; supplies blood to cerebral circulation and ventral pons

basilar migraine
form of migraine characterized by a visual aura followed by an often occipital headache and one or more of the following symptoms: dysarthria, vertigo, tinnitus, decreased hearing, diplopia, blindness, ataxia, bilateral paresthesia, bilateral paresis, and impaired cognition

behavioral symptom
complex changes in personality and behavior

Bell’s palsy (idiopathic facial paralysis)
cranial neuritis affecting the facial nerve thought to be due to reactivation of the herpes simplex virus; results in lower motor neuron facial weakness, hyperacusis, taste disturbance, and impaired lacrimation

Bell's phenomenon
fluttering of the eyes upward when closed eyelids are opened by the examiner

Benedikt Syndrome
ipsilateral oculomotor palsy and contralateral hemichoreoathetosis due to lesion of the ventral midbrain tegmentum affecting the IIII nerve fascicles and the red nucleus

Berry aneurysm
small saccular aneurysm of an intracranial artery

Binswanger’s disease (subcortical leukoencephalopathy)
degenerative white matter disease producing dementia due to hypertensive microvascular changes lipohyalinosis of the small arteries and fibrinoid necrosis of the larger vessels inside the brain)

blepharospasm
excessive involuntary contraction of the orbicularis oculi sometimes resulting in functional blindness; a focal dystonia

blood-brain barrier
specialized system of capillary endothelial cells that strictly limits transport into the brain through both physical (tight junctions) and metabolic (enzymes) barriers

borderzone infarct
see watershed infarct

brachial
relating to the arm

brachium
anatomical structure comprising a collection of axons that resemble an arm

brachium conjunctivum
see superior cerebellar peduncle

brachium pontis
see middle cerebellar peduncle

brachycephaly (acrocephaly)
premature fusion of bilateral coronal sutures producing a foreshortened skull

bradykinesia
slowed movement due to dysfunction of the basal ganglia and related structures

bradyphrenia
slowing of thought processes that can occur in Parkinson disease or as a side effect of antipsychotic medications

brain death
see death by neurological criteria

brainstem
medulla, pons, and midbrain

brainstem auditory evoked potentials (BAEP)
series of waves that reflect sequential activation of neural structures along the auditory pathways following a brief click or tone transmitted via an earphone or headphone and measured by surface electrodes placed at the vertex of the scalp and ear lobes; provides information regarding auditory function and hearing sensitivity and used to screen for retrocochlear pathology (e.g., acoustic neuroma), universal newborn hearing screening, and intraoperative monitoring

brain death

see death by neurological criteria

Broca’s aphasia
see non-fluent aphasia

Brodmann's areas
distinct regions of the cerebral cortex recognized by variations in cell size, density, and thickness of the cortical layers

Brown Sequard syndrome
spinal cord injury syndrome associated with damage to one lateral half of the spinal cord (spinal hemisection) resulting in ipsilateral weakness and loss of vibration proprioception and contralateral loss of pain sensation

Brudzinski’s sign
involuntary flexion of the hips in response to passive flexion of the neck; indicative of meningeal irritation

bruxism
grinding one's teeth while asleep

bulbar
pertaining to the lower cranial nerve nuclei

burst fracture
compression fracture of vertebral body with expansion in sagittal and coronal planes due to axial loading; unstable and often associated with spinal cord injury

calcarine cortex
primary visual cortex located in the occipital lobe (striate area 17)

carotid sinus
arterial baroreceptor located at the bifurcation of the external and internal carotid arteries that regulates arterial pressure and heart rate in response to changes in stretch and transmural pressure

carphologia
see floccillation

catamenial
referring to menses; with regard to women with epilepsy or migraine, a tendency for seizures/migraines to occur around the time of menses

cataplexy
sudden loss of postural tone, often triggered by an emotional stimulus and resulting in falls to the floor; seen in narcolepsy

cauda equina
(“horse’s tail”) collection of intradural spinal nerve roots caudal to the spinal cord that supply the lower limbs and pelvis; since this structure is part of the peripheral nervous system, lesions produce lower motor neuron deficits

caudal
toward the tail

caudate
portion of the basal ganglia that lies in the floor of the lateral ventricle

cavernoma (cavernous malformation)
vascular malformations composed primarily of large venous channels without a clear-cut arterial component

cavernous sinus
paired, venous structures located on either side of the sella turcica that receive blood from the superior and inferior orbital veins and drain into the superior and inferior petrosal sinuses; contains the carotid artery and its sympathetic plexus, the oculomotor nerves (III, IV, VI), and the ophthalmic branch of V; lesions typically result in ophthalmoplegia, orbital congestion, and proptosis

central chromatolysis
regenerative response to axonal injury consisting of neuronal swelling, nuclear eccentricity, and loss of Nissl substance

central cord syndrome
spinal cord injury syndrome associated with damage to the central portion of the spinal cord characterized by bilateral weakness of distal>proximal muscles in the arm>leg, bladder dysfunction, and a variable degree of sensory loss below the level of injury

central herniation
downward displacement of the cerebral hemispheres pushing the diencephalon and midbrain through the tentorial notch; symptoms classically follow a rostrocaudal deterioration

central nervous system (CNS)
brain and spinal cord

central pain syndrome
intense pain arising from injury to the central nervous system, most often in patients who have had a stroke, multiple sclerosis, or brain injury.

central sulcus
prominent sulcus on the dorsolateral aspect of the cerebral hemispheres formed by the precentral and postcentral gyri; defines the boundary between the frontal and parietal lobes

centrum semiovale
expansive region of white matter in the dorsal core of the frontal and parietal lobes, named because of its central position in the forebrain and its semi-oval shape

cephalic
relating to the head

cerebellar peduncle
three major white matter structures containing #efferent and afferent axons of the cerebellum; named the inferior, middle, and superior cerebellar peduncles

cerebellar tonsil
lateral portions of the uvula located in the posterior lobe of the cerebellum

cerebellopontine angle
space located at the junction of the cerebellum, pons, and medulla containing cranial nerves V-XI, blood vessels, the flocculus of the cerebellum, and choroid plexus

cerebellum
brain structure in posterior fossa that coordinates the many muscles active in any given movement; receives input from spinal cord and cerebral cortex and projects to postural and voluntary motor control systems and red nucleus

cerebral amyloid angiopathy (congophilic angiopathy)
vascular disorder in which beta amyloid protein is deposited within the media and adventitia of small- to medium-sized meningeal and cortical blood vessels, causing them to become brittle and break; important cause of predominantly lobar intracerebral hemorrhage in the elderly

cerebral aqueduct
portion of the ventricular system that lies in the dorsal midbrain and connects the third and fourth ventricles

cerebral arteriosclerosis
thickening and hardening of the arteries within the brain

cerebral atherosclerosis
build-up of fatty deposits in the inner wall of cerebral arteries; form of cerebral arteriosclerosis

cerebral atrophy
the shrinking of the brain or brain cells.

cerebral autosomal dominant arteriopathy with subcortical infarcts & leukoencephalopathy (CADASIL)
familial arterial disease of the brain caused by mutations in the Notch3 gene and consisting of recurrent subcortical strokes starting in midadult life, dementia, depression, and migraine

cerebral cortex
highly convoluted layer of gray matter that constitutes the outermost layer of the cerebrum and is responsible for integrating sensory impulses and for higher intellectual functions

cerebral hemisphere
symmetrical half of the cerebrum as separated by the sagittal sulcus and containing the cerebral cortex, basal ganglia, hippocampus, and amygdala

cerebral peduncle (crus cerebri)
white matter tracts (corticospinal and corticobulbar) on the ventral surface of the midbrain containing the efferent axons of cerebral cortex that project to brainstem and spinal cord

cerebral perfusion pressure (CPP)
mean arterial pressure (MAP) – intracranial pressure (ICP)

cerebral salt wasting
centrally-mediated hypovolemic hyponatremia associated with negative sodium balance that occurs in approximately 30-50% of patients with subarachnoid hemorrhage despite their being given maintenance volumes of fluids; excessive sodium loss is thought to be due to impaired sodium reabsorption in the proximal tubule and may be caused by disruption of sympathetic input to the kidneys, production of a circulating natriuretic factor, or both

cerebritis
inflammation of the brain

cerebrospinal fluid (CSF)
clear, colorless fluid bathing the entire surface of the CNS, most of which is secreted by the choroid plexus and the remainder by brain capillaries; flows through the ventricles and out into the subarachnoid space via the foramen of Magendie in the midline and the two foramina of Luschka at the lateral margins of the roof of the 4th ventricle, then is absorbed through the arachnoid villi in the walls of dural sinuses and returned to the systemic circulation

cerebrum
anterior portion of the brain consisting of the two cerebral hemispheres that each contain four lobes

Charcot-Bouchard aneurysm
aneurysmal dilation of small intraparenchymal vessels commonly seen in the brains of patients with hypertensive hemorrhage

Charcot joint
progressive destruction and deformity of bone and soft tissue at weight bearing joints due to severe sensory or autonomic neuropathy

cheiro
relating to the hand

Chiari malformation
CNS disorder characterized by cerebellar elongation and protrusion through the foramen magnum into the cervical spinal cord. Type I consists of caudal displacement of the medulla and inferior pole of the cerebellar hemispheres through the foramen magnum. Type II=type I + hydrocephalus and lumbosacral spina bifida. Type III involves herniation of the entire cerebellum through the foramen magnum with a cervical spina bifida cystica. Type IV involves cerebellar hypoplasia

chorea
involuntary, irregular, rapid, jerking movements

choroid plexus
intraventricular structure that secretes cerebrospinal fluid

choroid plexus papilloma
histologically benign intracranial tumor of neuroectodermal origin that is most commonly located in a ventricle (lateral>fourth>third), where it often presents with non-communicating hydrocephalus due to overproduction of CSF; may also be seen in the cerebellopontine angle

chronic daily headache
headache disorder consisting of frequent headache occurring 15 or more days per month and including headache associated with medication overuse

chronic paroxysmal hemicrania
indomethacin-responsive headache disorder characterized by the occurrence of multiple daily attacks lasting 5 to 30 minutes of severe unilateral head pain often associated with autonomic phenomenon (eye tearing, eye redness, eyelid edema, nasal congestion, runny nose); also known as atypical cluster headache

chronic-progressive
developing over months to years; implies gradual deterioration as occurs with degenerative diseases like Alzheimer disease, Huntington disease, etc.

cingulate gyrus
cortical component of the limbic system located on the medial aspect of the hemisphere superior to the corpus callosum; involved in emotional and cognitive processing

cingulate herniation
horizontal displacement of a cerebral hemisphere due to an expanding lesion that forces the cingulate gyrus under the falx cerebri, compressing the internal cerebral vein and the contralateral hemisphere

circadian rhythm
innate daily fluctuation of physiological or behavioral functions, including sleep-wake states generally tied to the 24-hour daily dark-light cycle

Circle of Willis
the main arterial anastomatic trunk located at the base of the brain; place where the two internal carotid arteries and the basilar artery come together, allowing blood to be redistributed to the anterior, middle, and posterior cerebral arteries

“clasp knife”
spring-like resistance to passive extension at the elbow or flexion at the knee that increases up to a certain length and force before suddenly relaxing as the Golgi tendon organ is activated; sign of spasticity

classic migraine
see migraine with aura

Claude Syndrome
ipsilateral oculomotor palsy and contralateral ataxia and hemichoreoathetosis due to a dorsal midbrain tegmental lesion affecting the III nerve fascicles, superior cerebellar peduncle, and red nucleus

claustrum
thin plate of gray matter lying in the white matter between the insula and the basal ganglia that modulates cortical activity

clay shoveler’s fracture
typically stable fracture through a spinous process due to hyperextension injury

clonic seizure
generalized seizure characterized by jerking movements on both sides of the body

clonus
rhythmic contraction relaxation tremor due to cyclic alternations of the spindle stretch reflex and the Golgi tendon organ reflex; indicative of exaggerated stretch reflexes

cluster headache
primary headache syndrome characterized by intense, unilateral orbital, supraorbital, and/or temporal pain lasting 15-180 minutes and occurring in "clusters" up to several times per day for a period of one or more months before going into "remission" for months or years; diagnosis requires one or more of the following autonomic abnormalities ipsilateral to the headache: conjunctival injection, lacrimation, ptosis, miosis, eyelid edema, nasal congestion, rhinorrhea, or facial sweating

CNS
central nervous system

CNS metastasis
metastatic tumors typically spread by a hematogenous route and found at the junction between gray matter and white matter where they are trapped by the acute angle branching of the microvasculature

cogwheeling
ratchety movement due to superimposition of tremor on rigidity

coital headache
indomethacin-responsive headache disorder characterized by sudden, severe, throbbing, occipital headache that occurs just before or during orgasm

cold calorics
see oculovestibular response

coma
state of unarousable unresponsiveness with closed eyes, no speech, and no purposeful movements

common carotid artery
artery that arises from the brachiocephalic artery on the right and from the aortic arch on the left, ascending in the neck and dividing at the upper border of the thyroid cartilage into the external and internal carotid arteries to supply the head and neck

common migraine
see migraine without aura

communicating hydrocephalus
blockage of CSF flow outside the ventricular system, either at the level of the arachnoid granulations or because of overproduction of CSF (e.g., from a choroid plexus papilloma) that exceeds the rate of absorption

complex partial seizure
partial seizure in which consciousness or awareness is impaired; epileptic discharge either originates in limbic structures (hippocampus) or spreads to them from neocortex, especially from the frontal lobe

complex tic
distinct, coordinated patterns of successive movements involving several muscle groups; complex vocal tics include meaningful syllables, words, or phrases; complex motor tics are coordinated or sequential patterns of movement such as twirling a pencil or touching other people

concussion
traumatic closed head injury that results in temporary impairment of neurological function, e.g., transient loss of consciousness

conduction aphasia
selective impairment of the ability to repeat due to a lesion of the arcuate fasciculus, which connects Wernicke’s area to Broca’s area

conduction block
failure of impulse conduction along an anatomically intact axon; characteristic of demyelinating neuropathy

contracoup
opposite to the site of impact

contracture
permanent shortening of the muscles and tendons adjacent to a joint, which can result from severe spasticity and interferes with normal movement around the affected joint

contralateral
located on the opposite side of the body (brain)

contusion
edematous brain lesion containing punctuate parenchymal hemorrhages on the surface of the brain that may extend bidirectionally into the white matter and the subdural and subarachnoid spaces; occur at the site of impact (coup contusion) with direct trauma and at a site opposite to the site of impact (contracoup contusion) with acceleration/deceleration injury

conus medullaris
caudal-most part of the spinal cord located between the first and second lumbar vertebrae. Since this structure is part of the spinal cord but is in close proximity to spinal nerve roots, lesions often produce both upper motor neuron and lower motor neuron deficits

convergence
coordinated inward movement of the eyes in order to fixate on a near object

convergence-retraction nystagmus
form of nystagmus consisting of jerking eye movements inward and backward; associated with dorsal midbrain lesion

coprolalia
uncontrolled, often obsessive use of obscene language occasionally seen in Tourette syndrome

coronal
vertical plane from head to foot and parallel to the shoulders

corona radiata
fan-like arrangement of fibers projecting from all aspects of the cerebral cortex and converging toward the thalamus where they will form the internal capsule

corpus callosum
large fiber structure that makes connections between homotopic regions of the cerebral hemispheres; bend at its anterior limit is called the genu; bend at its caudal end is called the splenium; portion between the two is called the body.

corpus striatum
see striatum

cortical
referring to the cerebral cortex, the outermost layer of the cerebrum

cortical blindness
apparent lack of visual functioning in spite of anatomically and structurally intact eyes due to bilateral lesions of the primary visual cortex

corticobasal degeneration
progressive neurological disorder characterized by nerve cell loss in the cerebral cortex and basal ganglia and producing parkinsonism, dementia, visual-spatial impairment, alien hand syndrome, apraxia, and myoclonus

corticobulbar tract
axons originating in the posterior frontal lobe and projecting to lower motor neurons in the brainstem

corticospinal tract (pyramidal tract)
motor pathway responsible for voluntary movement that arises from primary motor cortex, area 6, and somatosensory cortex and descends through the corona radiata, internal capsule, cerebral peduncle, medullary pyramid (where it decussates), and spinal cord to alpha motor neurons in spinal cord gray matter

cough headache
indomethacin-responsive headache disorder characterized by transient, severe, explosive head pain upon coughing, sneezing, weight lifting, bending, or stooping

coup
lesion at the site of impact

Cowdry A inclusion bodies
eosinophilic nuclear inclusions surrounded by a clear halo in neurons or glial cells occurring in herpes simplex encephalitis

Cowdry B inclusion bodies
large glassy eosinophilic nuclear inclusions occurring in herpes simplex encephalitis

craft palsy
dystonia occurring in the setting of a highly learned skilled task, e.g., writer’s cramp, yips in golfers

craniectomy
surgical removal of a section of bone (bone flap) from the skull for the purpose of operating on the underlying tissues or relieving intracranial pressure, in which the bone flap is not replaced at the end of the procedure

craniopharyngioma
suprasellar WHO grade I tumor of children/young adults that causes significant morbidity and mortality; characterized histologically by basal palisading, wet keratin, and infiltrative fingers of tumor that make it difficult to cure

cranioplasty
surgical repair of a defect or deformity of the skull; replacement of a bone flap

craniorachischisis totalis
fatal neural tube defect consisting of total failure of neurulation; a neural plate-like structure is entirely exposed without overlying bony or dermal covering

craniosynostosis
premature closure at birth of one or more cranial sutures, which limits head growth perpendicular to the suture(s); see also brachycephaly, oxycephaly, plagiocephaly, scaphocephaly, trigonocephaly

craniotomy
surgical removal of a section of bone (bone flap) from the skull for the purpose of operating on the underlying tissues, in which the bone flap is replaced at the end of the procedure

creatine kinase
enzyme that catalyzes the conversion of creatine to phosphocreatine and is released into the blood by tissues—particularly muscle—that consume adenosine triphosphate (ATP) rapidly; elevated levels are seen in myopathy

cremasteric reflex
superficial (cutaneous) reflex elicited by stroking the superior and medial part of the thigh in a downward direction; normal response is contraction of the cremasteric muscle that pulls up the scrotum and testis on the side stroked; dependent on nerve roots L1 and L2

Creutzfeldt-Jakob disease
fatal prion disease characterized by spongiform changes in the brain, progressive dementia, psychiatric changes, and myoclonus; form of spongiform encephalopathy

crossed adductor reflex
reflex contraction of the adductor magnus caused by tapping the opposite knee; indication of hyperreflexia on the side of the adductor contraction; commonly thought to be due to stimulation of the adductor muscle on the hyperreflexive side through slight jarring of the pelvis

“crossed signs”
ipsilateral cranial nerve signs and contralateral long-tract signs: implies lesion of the brainstem; sometimes used synonymously with dissociated sensory deficits due to spinal cord or brainstem lesions

crural
relating to the leg

crus cerebri
see cerebral peduncle

cryptogenic
occurring without known cause; in the context of epilepsy, indicates cases in which a lesion and distinct pathogenesis are presumed

Dawson’s fingers
ovoid demyelinating lesions with their long axis perpendicular to the ventricular surface seen in multiple sclerosis

death by neurological criteria
irreversible loss of all brain function

decerebrate rigidity
stereotyped posture consisting of extension of all four limbs occurring with transaction between the superior collicui and inferior collicli in the midbrain; often used synonymously with extensor posturing

decorticate rigidity
stereotyped posture consisting of flexion of the forelimbs and extension of the hindlimbs occurring with transaction between the diencephalon and midbrain; often used synonymously with flexor posturing

decussate
to cross

deja vu
feeling as if one has lived through or experienced this moment before; may occur in people without any medical problems or as a seizure aura_

delayed sleep phase syndrome
circadian rhythm disorder in which in the daily sleep/wake cycle is delayed with respect to clock time such that sleep occurs well after the conventional bedtime; common in young adults

delirium
abnormal mental state characterized by disorientation, inattention, confusion, fear, irritability, perceptual disturbance, and fluctuating level of consciousness; common with toxic and metabolic disorders and acute febrile systemic infections

dementia
acquired and sustained loss of memory and other intellectual functions that is of sufficient severity to interfere with daily functioning

dementia pugilistica
chronic traumatic encephalopathy caused by cumulative and repetitive head trauma and manifesting as dementia and parkinsonism

demyelination
destruction or loss of the myelin sheath surrounding axons; results in impaired nerve impulse conduction

dendrite
receiving portion of the neuron

dermatome
distribution of sensory innervation on the skin of the body and the limbs

diabetes insipidus
inability to concentrate urine resulting from decreased secretion of antidiuretic hormone; reflects a lesion of the hypothalamic osmoreceptors, supraoptic or paraventricular nuclei, or the supraopticohypophyseal tract and may occur in transtentorial herniation due to downward traction on the hypothalamic median eminence

diaphragma sellae
thin dural membrane overlying the sella turcica that is fenestrated to allow passage of the infundibulum

diaschisis
depression of metabolism at sites distant from, but connected with, a site of cerebral injury (e.g., infarction) due to interruption of afferent or efferent fiber pathways

diastematomyelia
longitudinal division of the spinal cord by a septum of bone

diencephalon
thalamus, hypothalamus, subthalamic nucleus, and pineal

diffuse axonal injury
widespread damage to white matter due to rotational shearing forces with head trauma

diffuse Lewy body disease (Lewy body dementia)
form of dementia associated with fluctuating alertness, recurrent visual hallucinations, and parkinsonism and defined pathologically by cortical (as well as nigral) Lewy bodies

diplegia
see paraplegia

diplopia
double vision

dissociated sensory deficit
impairment of pain/temperature sensation with preservation of vibration/proprioception or vice versa; implies lesion of brainstem or spinal cord involving 1 sensory tract but sparing the other

dolichocephaly
see scaphocephaly

doll’s phenomenon
see oculocephalic response

dorsal
posterior

dorsal columns
ascending axonal tract running in the dorsal funiculus of the spinal cord that carries tactile and proprioceptive information to the brain; fibers cross in the ventromedial medulla to become the medial lemniscus

dorsal horn
see posterior horn

dorsal motor nucleus of the vagus
parasympathetic nucleus that stimulates secretion from glands of the pharynx and thoracic and abdominal viscera

dorsal rhizotomy
surgical procedure involving sectioning of the dorsal spinal nerve roots performed to reduce spasticity

dorsal root ganglion
collection of cell bodies located in the intervertebral foramina that transduce sensory information into neural signals and transmit these signals to the CNS

dose failure
phenomenon in which an individual dose of medication has no effect; occurs in Parkinson disease possibly in association with a tablet getting stuck in the throat or delayed gastric emptying

double simultaneous stimulation (DSS)
ability to detect two stimuli applied simultaneously to opposite sides of the body; for tactile DSS, if a patient is able to identify which side is being touched when each side is touched individually, but extinguishes or neglects one of the sides when both sides are touched simultaneously; indicates dysfunction of the contralateral posterior parietal lobe

drop metastases
tumor masses in the lumbosacral spinal cord due to CSF spread of neoplastic cells (e.g., medulloblastoma)

duction
movement of one eye

dura mater
outermost layer of the meninges covering the brain and spinal cord; consists of a thick fibrous tissue that is adherent to the inner table of the skull and forms a protective sheath in the vertebral canal

dural tail sign
tail of dural enhancement seen on CT or MRI in association with meningeal neoplasms such as meningioma

Duret hemorrhages
secondary hemorrhages occurring in the diencephalon, midbrain, and pons as downward movement of the brainstem relative to the immobile blood vessels on the surface of the brainstem results in injury to small penetrating blood vessels; sequelae of cerebral herniation

dysarthria
inability to pronounce or articulate words due to disorders of the vocal apparatus (e.g., lips, tongue, larynx)

dysdiadochokinesia
impaired ability to perform rapid alternating movements (e.g., pronation/supination of hands); indicates cerebellar dysfunction

dysesthesia
pain or discomfort in response to a stimulus (e.g., touch) that would not be expected to cause pain

dysgeusia
distorted taste perception

dysgraphia
a writing disability that results in incorrectly spelled or written words

dyskinesia
blanket term for movement disorders characterized by increased motor activity

dyslexia
disorder that limits the ability to read

dysmetria
difficulty judging and controlling the speed, distance, or power of motor actions; tendency to over- or underestimate the extent of motion needed

dysphagia
difficulty in swallowing

dysphonia
voice disorder, often related to weakness of laryngeal muscles, in which sound production is impaired

dyssomnia
disorder in which the main complaint is about inadequate or unrefreshing sleep

dystonia
involuntary muscle spasms that produce peculiar postures of different body parts

echolalia
imitation of sounds without comprehension of their meaning

echopraxia
imitative repetition of the movements, gestures, or posture of another person occasionally seen in Tourette syndrome

Edinger-Westphal nucleus
accessory nucleus of each oculomotor nerve that supplies preganglionic parasympathetic fibers for pupillary constriction and lens accommodation; located in the midline between the extraocular oculomotor nerve nuclei

efferent
motor pathway proceeding from the CNS toward the peripheral end organs

electromyography
graphical representation of the electrical activity in a muscle

eidetic memory (photographic memory)
ability to vividly recall visual images, sounds, or objects in memory with extraordinary detail

electroencephalogram (EEG)
system for recording the electrical potentials of the brain derived from electrodes attached to the scalp

eloquent cortex
regions of the cerebral cortex responsible for motor, sensory, language or other cognitive processing that if removed, will result in a neurological deficit; identification of eloquent cortex through brain mapping is a vital part of the planning for epilepsy surgery and resection of brain tumors and vascular malformations in order to minimize adverse outcomes from surgery

empty sella
downward displacement and compression of the pituitary gland by cerebrospinal fluid filling the sella turcica; primary empty sella syndrome occurs when a small defect in the diaphragma sellae increases pressure in the sella and compresses the pituitary; secondary empty sella syndrome occurs when the sella is empty because the pituitary has shrunken following injury, surgery, or radiation

encephalitis
inflammation of brain tissue

encephalocele
failure of bone fusion in the posterior midline of the skull resulting in a bony cleft through which meninges and/or brain parenchyma protrude

encephalomalacia
focal softening of the brain in areas of tissue death following cerebral infarction, infection, trauma, etc.

encephalopathy
literally, "brain suffering"; diffuse brain dysfunction that may be caused by toxins, infection, metabolic or mitochondrial disease, tumor or increased intracranial pressure, trauma, or lack of blood flow or oxygen to the brain; the hallmark is impaired level of consciousness

endomysium
innermost layer of connective tissue that forms an interstitial layer around each individual muscle fiber

endoneurium (epilemma)
innermost layer of connective tissue of a peripheral nerve that forms an interstitial layer around each individual axon / Schwann cell unit

enophthalmos
recession of the eyeball within the orbit

eosinophilic neuronal necrosis
neuronal response to ischemia and hypoxia characterized by brightly eosinophilic (red) cytoplasm and nuclear shrinkage

ependyma
epithelial lining of the ventricles of the brain and the canal of the spinal cord

ependymal cells
type of glia consisting of cuboidal cells lining the adult ventricles and spinal canal

ependymal true rosette
halo of cells surrounding an empty lumen; fairly specific for, though infrequently seen in, ependymomas

ependymoma
WHO grade II primary CNS tumor of children (involving the 4th ventricle) and young adults (involving the spinal cord); characterized histologically by perivascular pseudorosettes, ependymal true rosettes, sharp demarcation, and enhancement on CT/MRI

ephaptic
electrical conduction of a nerve impulse across a non-synaptic contact site between nerves and without the mediation of a neurotransmitter

epilepsy
chronic brain disorder of various etiologies characterized by recurrent unprovoked seizures

epilepsy syndrome
disorder defined by seizure type, clinical and EEG findings, age of onset, family history, response to therapy, and prognosis

epineurium
outermost layer of a peripheral nerve containing connective tissue and an anastomotic vascular network

epithalamus
dorsal posterior subdivision of the diencephalon generally considered to include the habenula, the pineal body, and the epithelial roof of the third ventricle

esotropia
an eye with strabismus that deviates inward

essential tremor
medium or high frequency (4-9 Hz) tremor that occurs with action or holding a sustained posture that typically affects the arms, the head/neck, or the voice

evoked potentials
recordings of the nervous system’s electrical response to the stimulation of specific sensory pathways; see also somatosensory evoked potentials, brainstem auditory evoked potentials, and visual evoked potentials

excessive daytime sleepiness