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

This page authored by Allyson Zazulia, M.D., Associate 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 saggittal 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 saggittal 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

anosognosia
lack of awareness of or indifference to one’s own neurological deficit, seen with nondominant parietal lobe lesions

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

asomatognosia
inability to recognize part of one’s own body, seen with nondominant parietal lobe (or less commonly premotor cortex) lesions

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

cyclotorsion
(a.k.a. torsion): rotation of the eye around an anterior-posterior axis; see excyclotorsion, incyclotorsion

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 colliculi 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

denervation
loss of nerve supply

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

dysraphism
defective closure of a raphe, particularly the neural tube

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 (hypersomnolence)
subjective difficulty in staying awake and easily falling asleep when sedentary

excyclotorsion
(a.k.a. extorsion): cyclotorsion of an eye such that the superior pole rotates outward

executive functions
higher intellectual functions such as judgment, insight, reasoning, abstraction

exophthalmos
see proptosis

exotropia
an eye with strabismus that deviates outward

Expanded Disability Status Scale (EDSS)
20-point scale, ranging from 0 (normal examination) to 10 (death) by half-points, that measures impairment (gait is heavily emphasized); used in clinical trials of multiple sclerosis

extensor plantar response
extension of the great toe (“upgoing toe”) with fanning of the other toes in response to application of a stimulus to the skin of the foot or leg; signifies a lesion of the corticospinal tract

extensor posturing

stereotyped posture occurring in coma in response to stimulation in which the arms and legs extend (hips and shoulders extend, adduct, and internally rotate; knees and elbows extend; forearms hyperpronate; wrists and fingers flex; feet plantarflex and invert; and trunk extends); reflects "release" of primitive responses from the suppression of more rostral motor areas that have been damaged and is reminiscent of the decerebrate state demonstrated in animals with transection through the midbrain colliculi

extensor response in the arm
stereotyped posture occurring in coma in response to stimulation in which the upper extremity extends (shoulder extends, adducts, and internally rotates; elbow extends; forearm hyperpronates; wrist and fingers flex); may be accompanied by extension of the lower extremity (hip extends, adducts, and internally rotates; knee extends; foot plantar flexes and inverts) as in decerebrate rigidity; reflects "release" of primitive responses from the suppression of more rostral motor areas that have been damaged

extensor spasm
manifestation of spasticity in which the legs involuntarily straighten into an extended position where they remain for several minutes

extinction
see double simultaneous stimulation

extra-axial
within the skull or vertebral column but outside of the brain or spinal cord

extrapyramidal
movement disorder not involving the corticospinal tracts; typically refers to basal ganglia or cerebellar disorders

extrasylvian
outside of the area surrounding the Sylvian fissure; often used synonymously with "transcortical," as in transcortical motor aphasia and transcortical sensory aphasia

F-wave
long latency muscle action potential seen after supramaximal stimulation to a nerve

facial masking (hypomimia)
decreased facial expression due to rigidity of facial muscles

facial nerve (cranial nerve VII)
predominantly motor nerve supplying muscles of facial expression; also carries sensation (external ear, taste from anterior 2/3 of tongue) via the nervus intermedius and preganglionic parasympathetic fibers to the lacrimal, palatal, and nasal glands

fainting

- see syncope

falx cerebri
fold of dura mater in the sagittal sulcus between the two cerebral hemispheres

fascicle
bundle of axons (nerve fascicle) or muscle fibers (muscle fascicle) surrounded by a layer of contractile cells (perineurium for nerves or perimusium for muscles)

fasciculation
spontaneous firing of an axon resulting in a visible twitch of all the muscle fibers it contacts; indicative of denervation

festination
an involuntary tendency to take short accelerating steps in walking that can occur in Parkinson disease

fibrillation
spontaneous firing of a single muscle fiber not visible to the naked eye, indicative of denervation or irritable myopathy; seen electrographically as a brief action potential with initial positive (down) wave followed by negative (up) wave

filum terminale
delicate fibrous tissue structure surrounded by a few nerve fibers that extends downward from the conus medullaris to the first segment of the coccyx

finger agnosia
type of agnosia characterized by inability to identify the fingers; a component of Gerstmann syndrome

Fisher scale
scale for grading CT appearance in patients with nontraumatic subarachnoid hemorrhage; higher scores predictive of developing symptomatic cerebral vasospasm

Description	Group
No subarachnoid blood detected	1
Diffuse subarachnoid blood or vertical layers of blood < 1 mm thick	2
Localized clots and/or vertical layers of blood < 1 mm thick	3
Intracerebral or intraventricular clots with diffuse or no subarachnoid blood	4

febrile seizure
typically benign seizure associated with high fever in children aged 3 months to 5 years

fibrinoid necrosis
brightly eosinophilic lesions in the small vessels of the brain postulated to occur because of disordered cerebral autoregulation in association with aging and hypertension; contributes to the development of lacunar infarction and hypertensive hemorrhage

flaccidity
severe form of hypotonicity

flexor plantar response
flexion (curling down) of all toes (“downgoing toe”) in response to application of a stimulus to the skin of the foot or leg; normal response

flexor posturing
stereotyped posture occurring in coma in response to stimulation in which the upper extremity flexes and the lower extremity extends; reflects release of primitive responses from the suppression of more rostral motor areas that have been damaged and is reminiscent of the decorticate state demonstrated in animals with transaction of corticospinal fibers above the midbrain

flexor response in the arm
stereotyped posture occurring in coma in response to stimulation in which the upper extremity flexes and the lower extremity extends; reflects release of primitive responses from the suppression of more rostral motor areas that have been damaged and is reminiscent of the decorticate state demonstrated in animals with transaction of corticospinal fibers above the midbrain

flexor spasm
often painful manifestation of spasticity in which the legs involuntarily pull upward into a clenched position for a period of a few seconds

floccillation
purposeless picking at clothing or bedding seen in delirium

fluent aphasia (Wernicke’s or receptive aphasia)
impairment of language comprehension including impaired repetition due to lesion of the posterior left superior temporal gyrus (Brodmann area 22)

fontanel
soft membranous gap between the incompletely formed cranial bones of a fetus or an infant; the anterior fontanel (where the metopic, the two coronal, and the sagittal sutures come together), fuses at 7-19 months; the posterior fontanel (where the lambdoid and sagittal sutures come together) is often fused at birth

foramen magnum
large opening at the base of the skull through which the spinal cord and vertebral arteries pass from the vertebral cavity into the cranial cavity

foramen of Magendie
midline exit of CSF from the fourth ventricle into the subarachnoid space

foramen of Monro
permits communication of the third ventricle with each of the lateral ventricles on anterolateral aspect of the third ventricle

foramina of Luschka
lateral exits of CSF from either side of the fourth ventricles into the subarachnoid space

forebrain
portion of the central nervous system derived from prosencephalon; commonly used to denote cerebral hemispheres and diencephalon

fornix
white matter structure containing axons that connect the hippocampus to the hypothalamus and septal nuclei

fortification spectrum (teichopsia)
complex visual migraine aura consisting of zig-zag lines or an arc of scintillating lights forming into a herringbone pattern and expanding to encompass an increasing portion of a visual hemifield

Foster-Kennedy syndrome
ipsilateral anosmia, ipsilateral optic atrophy, and contralateral papilledema due to frontal lobe or olfactory groove mass lesion

fovea
center most part of the macula responsible for detailed central vision

Foville syndrome
ipsilateral lateral gaze palsy, ipsilateral peripheral facial palsy, and contralateral hemiplegia due to a dorsal pontine tegmentum lesion affecting the paramedian pontine reticular formation, facial nerve nucleus or fascicle, and corticospinal tract

fracture-dislocation
fracture through the articular processes and disc with or without associated fracture through a vertebral body due to flexion/extension with axial loading; unstable and often associated with spinal cord injury

freezing
sudden, brief cessation of movement; common in Parkinson disease

Fresnel prisms
clear, flexible polyvinyl chloride plastic sheets composed of a series of small prisms that are used to assess and correct diplopia

fried egg artifact
perinuclear halo around oligodendrocytes caused by formalin fixation artifact

Friedreich’s ataxia
autosomal recessive neurodegenerative disease caused by GAA triplet repeat mutation in the gene that encodes for frataxin, a protein that regulates mitochondrial functioning; characterized by weakness, ataxia, sensory loss, scoliosis, and cardiomyopathy

frontal eye fields (FEF)
region within the frontal lobes from which voluntary lateral eye movements originate; with stimulation (as in seizure), the eyes move conjugately to the opposite side; with destruction (as in a stroke), the eyes look towards the lesioned side (loss of controversion), implying unopposed stimulation from the undamaged side

frontotemporal dementia
group of dementing illnesses in which disordered behavior (e.g., disinhibition) or language (e.g., aphasia) are disproportionately impaired in relation to memory; includes Pick’s disease and corticobasal degeneration

functional
not due to organic disease

gadolinium-enhancing lesion
abnormality on MRI that becomes bright after injection of the chemical compound gadolinium; implies breakdown in the blood-brain barrier

gamma motor neurons
neurons that contract the ends of the muscle spindle so that spindle sensitivity to passive stretch is kept constant throughout muscle shortening

ganglia
aggregations of nerve cell bodies

gegenhalten
see paratonia

gemistocyte
reactive astrocyte having increased glial filaments and glassy eosinophilic cytoplasm

generalized seizure
seizure that affects both cerebral hemispheres simultaneously and causes unconsciousness at the outset

geniculate ganglion
sensory ganglion of the facial nerve that innervates taste buds on the anterior 2/3 of the tongue

genu
kneelike bend in the anterior part of the corpus callosum or internal capsule

germinal matrix
a highly vascular, metabolically active area of the brain located just beneath the ependymal lining of the ventricular walls, which is the source of neurons and glial cells that will later migrate to cerebral cortex. It involutes in the second trimester. Germinal matrix vessels are fragile and are believed to have impaired autoregulation, making them prone to rupture in premature infants, resulting in intraventricular hemorrhage.

Gerstmann syndrome
a neurological disorder that includes a writing disability (agraphia or dysgraphia), a lack of understanding of the rules for calculation or arithmetic (acalculia or dyscalculia), an inability to distinguish right from left, and an inability to identify fingers (finger agnosia) that is due to a lesion of the angular gyrus of the dominant parietal lobe

Glasgow Coma Scale (GCS)
most widely used scoring system to quantify level of consciousness following traumatic brain injury; scores range from 3 to 15, based on the sum of the best eye opening response, the best verbal response, and the best motor response

Eye Opening (E)	Verbal Response (V)	Motor Response (M)
4=Spontaneous	5=Normal	6=Normal
3=To voice	4=Disoriented	5=Localizes to pain
2=To pain	3=Inappropriate	4=Withdraws to pain
1=None	2=Incomprehensible	3=Flexes to pain
	1=None	2=Extends to pain
		1=None
Total = E+V+M

glia
supporting cells of the nervous system that provide structural and metabolic support for the neurons; includes astrocytes, oligodendrocytes, ependymal cells, and microglia

glioblastoma multiforme
WHO grade IV astrocytoma characterized by hemorrhagic necrosis, endothelial proliferation, ± crossing of the corpus callosum, ring-enhancement on imaging, and poor survival

gliosis
scar or dense fibrous network of glial processes in an area of CNS injury

global aphasia
impairment of language production, comprehension, and repetition due to lesion of entire perisylvian region; usually associated with right hemiparesis

globus pallidus
most medial component of the basal ganglia and generator of most basal ganglionic output

glossopharyngeal nerve (cranial nerve IX)
nerve containing motor, sensory, and parasympathetic fibers; motor fibers originate in the nucleus ambiguus and innervate the stylopharyngeus to elevate the palate; sensory fibers originate in the superior and petrosal ganglion and supply taste to the posterior third of the tongue and tactile sensation to the posterior tongue, pharynx, middle and external ear, and eustacian tube; parasympathetic fibers originate in the inferior salivatory nucleus and carry secretory and vasodilatory fibers to the parotid gland

Golgi tendon organs
sense active stretch and via inhibitory inter-neurons inhibit the motor neurons to provide protection against hurtful contractile forces

Gower’s sign
maneuver used by patients with proximal muscle weakness (as in myopathy) in order to arise from the floor or from a kneeling or squatting position; the hands are used to “walk up” the thighs

Gradenigo Syndrome
ipsilateral lateral rectus palsy, peripheral facial palsy, decreased hearing, and upper facial pain due to a lesion in the apex of the temporal bone

grand mal seizure
see tonic-clonic seizure

graphesthesia
ability to recognize letters or numbers drawn on the finger or palm

gray matter
part of the CNS consisting of neuronal cell bodies and dendrites

Guillain-Barre syndrome (acute inflammatory demyelinating polyneuropathy)
acute, ascending, and progressive neuropathy believed to result from an autoimmune response triggered by an antecedent illness or various medical conditions and characterized by weakness, paresthesias, hyporeflexia, and labile autonomic dysfunction; most patients exhibit absent or profoundly delayed conduction in nerve fibers resulting from demyelination, but in a subset of patients, there is a direct cellular immune attack on the axon itself

gustatory
relating to the sense of taste

gyrus
convoluted ridge on the outer surface of the brain caused by infolding of the cerebral cortex and bound by sulci

habenula
diencephalic structure located on the dorsomedial surface of the caudal thalamus that receives afferents from the septal nuclei and hypothalamus via the stria medullaris and projects to midbrain nuclei; involved in autonomic processing

hangman’s fracture
fracture through bilateral pedicles of C2 via various mechanisms; typically unstable

hemianesthesia
loss of somatosensation on one half of the body

hemianopia
loss of vision in one half of the visual field, indicating a pathological process posterior to the optic chiasm

hemiballismus
involuntary violent flinging or jerking of a limb (or limbs) in an uncoordinated manner caused by a lesion of the contralateral subthalamus

hemicrania continua
indomethacin-responsive headache disorder characterized by steady, moderately intense unilateral head pain on which are superimposed episodes of more intense pain with autonomic symptoms (eye tearing, eye redness, eyelid edema, nasal congestion, runny nose) occurring several times a day

hemifacial spasm
segmental myoclonus of muscles innervated by the facial nerve; may be due to vascular compression of the facial nerve or facial nerve injury or tumor, or it may have no apparent cause

hemifield
one-half of the binocular visual field

hemiparesis
weakness on one side of the body

hemiplegia
paralysis on one side of the body

hemiplegic migraine
familial form of migraine characterized by temporary (usually < 1 hour but occasionally lasting up to a week) hemiparesis ± hemisensory symptoms often associated with visual aura and headache; in about 50% of affected families, a defect may be found on chromosome 19 or on chromosome 1 and involves abnormal calcium channels

heterotopia
tissue occurring in an abnormal anatomical position

hindbrain
medulla, pons and cerebellum

hippocampal formation
cortical structure in the medial temporal lobe comprising the dentate gyrus, hippocampus, and subiculum; involved in short-term declarative memory

hippocampus
convoluted structure at the medial margin of the cortical mantle of the cerebral hemisphere, bordering the choroid fissure of the lateral ventricle, and forming part of the limbic system, which is concerned with memory and emotion

Hoffman’s sign
contraction of fingers and thumb when a stimulus is applied to a distal phalanx in that hand; indication of hyperreflexia in the upper extremity

holoprosencephaly
failure of cleavage at the rostral end of the notochord resulting in midline fusion of the frontal lobes, midline facial abnormalities, and often hydrocephalus and heterotopias

Homer-Wright rosette
halo of cells surrounding a central lumen containing neuropil; found in medulloblastomas and PNETs

Horner's syndrome
ptosis, miosis, and anhidrosis ipsilateral to damaged sympathetic nerve fibers

H-reflex
electrical equivalent of the monosynaptic stretch reflex elicited by selectively stimulating the Ia fibers of the posterior tibial or median nerve

Hunt and Hess scale
scale for grading clinical status in patients with nontraumatic subarachnoid hemorrhage that correlates well with clinical outcome

Description	Grade
Asymptomatic, mild headache, slight nuchal rigidity	1
Moderate to severe headache, nuchal rigidity , no neurologic deficit other than cranial nerve palsy	2
Drowsiness / confusion, mild focal neurologic deficit	3
Stupor, moderate-severe hemiparesis	4
coma, decerebrate posturing	5

Huntington disease
fatal autosomal dominant neurodegenerative disorder characterized by chorea and progressive dementia; due to a trinucleotide CAG-repeat mutation on chromosome 4

hydranencephaly
birth defect in which the majority of the cerebral hemispheres and striatum are absent and replaced by sacs filled with cerebrospinal fluid; considered to be an extreme form of porencephaly

hydrocephalus
literally "water on the brain;" increase in size of ventricles and amount of cerebrospinal fluid in the brain

hyperacusis
abnormally increased sensitivity to sound

hyperpathia
exaggerated response to painful stimuli

hypersomnolence
see excessive daytime sleepiness

hypertensive hemorrhage
intraparenchymal hemorrhage with a predilection to occur deep in the cerebral hemispheres, especially in the putamen, thalamus, and deep white matter, as well as the pons and cerebellum. These sites are all supplied by small penetrating arteries that are subject to high sheer stress and have no collaterals, making them vulnerable to the effects of increased blood pressure

hypertonicity
increase in passive muscle resistance, such as spasticity or rigidity

hypertropia
an eye with strabismus that deviates up

hypnagogic hallucination
vivid dreamlike hallucination that occurs as one is falling asleep; one of the symptoms of narcolepsy, but also experienced by some non-narcoleptic individuals

hypnic headache
indomethacin-responsive headache disorder characterized by diffuse, throbbing headache arising exclusively during sleep, typically between 1:00 and 3:00 AM

hypnic
jerk sensation of falling, and then "jerking" awake just as one drifts to sleep

hypnopompic hallucination
vivid dreamlike hallucination that occurs as one is waking up; one of the symptoms of narcolepsy, but also experienced by some non-narcoleptic individuals

hypoglossal nerve (cranial nerve XII)
motor nerve that innervates all tongue muscles except the palatoglossus; lesions result in deviation of the protruded tongue towards the paralyzed side and deviation of the tongue at rest away from the paralyzed side; nucleus is located in the medulla

hypomimia
see facial masking

hypophysis
see pituitary gland

hypothalamus
basal part of the diencephalon that controls hunger, thirst, body temperature, and various metabolic processes, including the maintaining of water balance

hypotonicity
reduction in passive muscle resistance

hypotropia
an eye with strabismus that deviates down

hypoxia
reduction in the supply of oxygen to the brain or other vital organ

hypsarhythmia
abnormal EEG pattern of excessive slow activity and multiple areas of epileptiform activity; associated with infantile spasms

ice cream headache
nickname given to headaches that are cold induced; common in migraine

ice-pick headache
indomethacin-responsive headache disorder characterized by momentary, sharp, and/or jabbing pain that occurs either once or several times a day at irregular intervals

ictus
sudden attack, stroke, or seizure

idiopathic
occurring without known cause; in the context of epilepsy, indicates cases in which no lesion is found and a genetic cause is presumed

impairment
problem in body function or structure such as a significant deviation or loss (e.g., weakness = impairment in the muscles' capability to produce force)

incisura
fissure that separates the uncus from the apex of the temporal lobe

incyclotorsion
(a.k.a. intorsion): cyclotorsion of an eye such that the superior pole rotates inward

indomethacin-responsive headache
class of primary headache disorders characterized by a prompt and often complete response to indomethacin to the exclusion of other nonsteroidal anti-inflammatory drugs and medications usually effective in treating other primary headache disorders; includes ice-pick headache, chronic paroxysmal hemicrania, hemicrania continua, cough headache, and hypnic headache, among others

infantile spasms
form of cryptogenic generalized epilepsy characterized by sudden, forceful forward flexion of the trunk and extension of the arms

infarction
permanent tissue damage and death of all cellular elements (neurons, glia, vessels) due to prolonged or severe ischemia

inferior cerebellar peduncle (restiform body)
paired bundle of fibers traveling to and from the cerebellum; afferent fibers from the dorsal spinocerebellar tract carry proprioceptive information from the upper body; efferent fibers travel to the vestibular nuclei in the dorsal brainstem

inferior colliculus
paired structures on the dorsal surface of the caudal midbrain overlying the cerebral aqueduct that process and relay auditory signals from brainstem centers to the medial geniculate nucleus of the thalamus; with the superior collicui, make up the tectum and the quadrigeminal bodies

inferior olivary nucleus
prominent nucleus in the ventral medulla located just lateral and dorsal to the medullary pyramids; source of climbing fibers that provide a critical input to the cerebellum involved in Purkinje cell plasticity and motor learning

infratentorial
below the tentorium cerebelli, i.e., brainstem and cerebellum

infundibulum
connection between the hypothalamus and the pituitary gland (also called the "pituitary stalk"); contains the hypophyseal portal veins and the axons of hypothalamic neurons that project to the posterior pituitary

insomnia
difficulty with falling asleep or staying asleep

insula
cerebral cortex lying in the depths of the Sylvian fissure and involved in gustatory, visceral sensory, and emotional processing

intention tremor
tremor whose amplitude increases as the affected body part (typically a finger) nears an intended target and that may the targeted object to be missed; typically results from damage to the cerebellum or its connections

internal capsule
broad compact band of efferent and afferent fibers that travel to or from the cerebral cortex; flanked medially by the thalamus and caudate and laterally by the lentiform nucleus

internal carotid artery
artery that arises from the common carotid artery at the upper border of the thyroid cartilage and terminates in the middle cranial fossa by dividing into the anterior cerebral artery and the middle cerebral artery; constitutes the anterior circulation of the brain

inter-neuron
neurons that receives input from one neurons and projects to another neurons within spinal cord, allowing a greater degree of complexity of movement control

internuclear ophthalmoplegia
failure of adduction of one eye and abducting nystagmus of the other eye due to a lesion of the medial longitudinal fasciculus

intracranial pressure
pressure exerted by the brain, cerebrospinal fluid, and the cerebral blood supply on the intracranial space; measured in centimeters of water (cmH2O) or millimeters of mercury (mmHg); normally < 20 mm/Hg

intrathecal space (subarachnoid space)
space surrounding the brain and spinal cord that contains cerebrospinal fluid

intraventricular hemorrhage (IVH)
bleeding in the ventricles especially from fragile blood vessels in premature infants; in adults may accompany intracerebral or subarachnoid hemorrhage

ipsilateral
located on the same side of the body (brain)

ischemia
impairment of tissue function due to a reduction in blood supply relative to metabolic demand

ischemic penumbra
see penumbra

Jacksonian march
contiguous spread of electrical discharges through superficial cortex occurring with some seizures manifested by spread of muscular jerks to contiguous anatomical areas, such as when the jerking begins in the thumb and then spreads stepwise to the fingers, wrist, forearm, proximal arm, shoulder, and face

JC virus
member of the papovavirus family that produces progressive multifocal leukoencephalopathy; “JC” stands for the initials of the first patient described with the virus

Jefferson fracture
burst fracture of the anterior and posterior arches of C1 due to axial loading; typically stable

jitter
measure of the variability of potentials of two muscle fibers innervated by an individual axon as measured by single fiber electromyography; increased in myasthenia gravis

juvenile myoclonic epilepsy (JME)
primary generalized epilepsy syndrome usually beginning between ages 5 to 17 years, characterized by myoclonic (muscle-jerk), absence, and tonic-clonic seizures

Kernig’s sign
pain in the posterior aspect of the thigh in response to passive flexion of the thigh and extension of the knee; indicative of meningeal irritation

Kernohan’s notch
compression of the opposite cerebral peduncle against the edge of the tentorium contralateral to a herniating uncus; results in ipsilateral hemiparesis

ketogenic diet
high-fat, low-carbohydrate diet sometimes used to control seizures

kindling
process by which repeatedly applying subconvulsive stimulation either electrically or chemically permanently lowers the threshold for having seizures; used as an experimental model for epilepsy

Korsakoff syndrome
chronic phase of thiamine deficiency characterized by impairment in establishing new memories and retrieving previous memories, occurring most commonly in alcoholics

Krabbe disease (globoid cell leukodystrophy)
autosomal recessive disease arising in infancy with progressive motor and mental retardation and peripheral nerve dysfunction due to a deficiency in the enzyme galactocerebrosidase, which is necessary to degrade galactocerebroside, a myelin constituent

kuru
fatal prion disease restricted to the Fore tribe in the highlands of New Guinea as a result of cannibalistic funeral practices; form of spongiform encephalopathy

Lambert-Eaton Myasthenic syndrome
autoimmune disorder of neuromuscular transmission characterized by antibodies directed against the voltage-gated calcium channels on the presynaptic motor nerve terminal leading to impaired release of acetylcholine and causing proximal muscle weakness, hyporeflexia, and autonomic changes (e.g., dry mouth); associated with malignancy (particularly small cell lung cancer) in half to ¾ of affected individuals

laminar necrosis
selective neuronal loss in layers 3 and 5 of the cerebral cortex due to hypoxic-ischemic insult

lateral medullary syndrome (Wallenberg's syndrome)
constellation of symptoms including difficulty swallowing, hoarseness, vertigo, nystagmus, ataxia, loss of pain and temperature sense in the ipsilateral face and contralateral body, and ipsilateral Horner's syndrome in association with an infarct in the lateral medulla; due to occlusion of the vertebral or posterior inferior cerebellar artery

Lennox-Gastaut syndrome
syndrome of mental retardation, generalized epilepsy (with mixed seizures, especially tonic, myoclonic and atypical absence), and a characteristic pattern of slow, generalized spike-and-wave activity on the electroencephalogram

lentiform nucleus (lenticular nucleus)
lens-shaped part of the basal ganglia consisting of the putamen and globus pallidus

leptomeninges
arachnoid mater and pia mater

leukodystrophy
metabolic demyelinative disease

Lewy body
cytoplasmic, bright red sphere often with a surrounding halo on H&E composed of an amorphous granular core with a radiating filamentous periphery; believed to contain alpha-synucein; seen in Parkinson disease and diffuse Lewy body disease

Lewy body dementia
see diffuse Lewy body disease

light-near dissociation
absent pupillary light response but intact near response (i.e., “accommodate but don’t react”) seen with dorsal midbrain lesions, syphilis, and diabetes

limbic
referring to the system comprising the hippocampus, parahippocampal gyrus, cingulate gyrus, fornix, and multiple subcortical structures including portions of hypothalamus and thalamus; important in memory and emotion

lipohyalinosis
eosinophilic deposits in the connective tissue of the walls of perforating arterioles in the deep portions of the brain due to hypertension; contributes to the development of lacunar infarction and hypertensive hemorrhage

Lissauer’s tract
longitudinal bundle of thin, unmyelinated and poorly myelinated fibers capping the apex of the posterior horn of the spinal gray matter, composed of posterior nerve root fibers and short association fibers that interconnect neighboring segments of the posterior horn

lissencephaly (agyria)
smooth brain (absence of secondary sulci)

lobe
one of four major portions of the cerebral cortex named after the overlying cranial bones: frontal, parietal, temporal, and occipital

locked-in state
tetraplegia and aphonia with preserved consciousness due to brainstem (usually pontine) lesion that spares the reticular activating system

locus ceruleus
melatonin-containing nucleus located on the dorsal wall of the upper pons that is one of the main sources of neuroepinepherine in the brain and has widespread projections to other parts of the nervous system; mediates arousal and primes neurons throughout the nervous system to be activated by stimuli

Loftstrand Crutch
type of crutch with an attached holder for the forearm that provides extra support

long-tract signs
signs referable to the corticospinal tract, spinothalamic tract, and dorsal columns/medial lemniscus

lower motor neuron
2nd order neurons whose cell bodies are located in the brainstem or anterior horn of the spinal cord and that leave the CNS to connect to muscle; lesions result in flaccid weakness, reflex loss, atrophy, +/- fasciculations

lumbar puncture
procedure in which a needle is inserted through the skin between the fourth and fifth lumbar vertebrae and into the lumbar subarachnoid space for measurement of cerebrospinal fluid analysis

macrocephaly
head circumference that is more than 2 standard deviations above the mean for age, sex, race, and gestation

macula
part of the retina responsible for detailed central vision

magnetoencephalography (MEG)
noninvasive functional neuroimaging technique used to measure magnetic fields generated by intracellular electrical currents from brain neurons; clinical uses include localization of epileptic discharges and localization of eloquent cortex or surgical planning

mammillary bodies
pair of nuclei in the posterior, ventral and medial hypothalamus that receive hippocampal inputs via the fornix and project to anterior nucleus of the thalamus and the tegmentum of the midbrain and pons; involved in memory processing

Marcus-Gunn pupil
see afferent pupillary defect

mass effect
structural damage due to a lesion’s bulk (e.g., tumor, infarct, or hemorrhage), the blockage of fluid movement (e.g., compression of a ventricle), or excessive accumulation of fluid

medial geniculate nucleus
nucleus of the posterior, dorsal thalamus that receives auditory input from the inferior colliculus and relays this information to the primary auditory cortex (Brodmann's areas 41 & 42) in the superior temporal gyrus.

medial lemniscus
ascending axonal tract in the brainstem that carries tactile and proprioceptive information from the dorsal column nuclei to the ventral posterior lateral nucleus of the thalamus

medial longitudinal fasciculus
pathway connecting the ipsilateral 3rd nerve nucleus in the midbrain to the contralateral 6th nerve nucleus in the pons for ocular motor control

medication overuse headache (analgesic rebound headache)
headache disorder characterized by headache that is present on 15 or more days per month in association with the use of any analgesic (including aspirin, acetaminophen, narcotics, ergotamine, and triptans) at least two or three days each week, with intake of the drug on at least 10 days per month for at least three months; headache resolves or reverts to its previous patterns within two months after discontinuation of the drug

medulla
a part of the brainstem that helps regulate respiration and other behaviors

medulloblastoma
aggressive WHO grade IV primitive neuroepithelial tumor of children and young adults typically involving the posterior fossa sometimes with cerebrospinal fluid seeding (drop metastases); characterized histologically by small blue cells and Homer Wright rosettes

medulla oblongata (myelencephalon)
caudal aspect of the brainstem located between the pons and the spinal cord

megalencephaly
abnormally large, heavy, and usually malfunctioning brain; thought to be related to a disturbance in the regulation of cell reproduction or proliferation

Meissner corpuscles
dermal mechanoreceptors that subserve light touch sensation

MELAS (Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes)
mitochondrial disorder characterized by hearing loss, episodic vomiting, and recurrent cerebral insults resembling strokes and causing hemiparesis, hemianopia, or cortical blindness

meningeal carcinomatosis
diffuse infiltration of the meninges by metastatic tumor cells often with positive cerebrospinal fluid cytology

meninges
three distinct connective tissue membranes (from outer to inner: dura, arachnoid, and pia mater) that enclose and protect the central nervous system

meningioma
slow-growing WHO grade I meningeal neoplasm that has an extra-axial location and often shows a dural tail sign and hyperostosis of adjacent skull; characterized histologically by whorls and psammoma bodies

meningitis
inflammation of meninges and spinal fluid

meningocele
form of spina bifida in which there is herniation of only meninges (no spinal cord parenchyma) through defective posterior arches

meninx
singular form of meninges

menstrual (catamenial) migraine
migraine occurring between one day before and four days after the onset of menses; thought to be due to estrogen withdrawal

Merkel cells
disk-shaped receptor endings in the skin believed to be involved with the sensation of fine touch

mesencephalon
see midbrain

mesial temporal sclerosis
hippocampal scarring and volume loss; most common cause of temporal lobe epilepsy

Mesulam syndrome
eponym for primary progressive aphasia

metachromatic leukodystrophy
autosomal recessive disease associated with large confluent areas of discolored gelatinous white matter caused by deficiency of the enzyme arylsulfatase A, which is necessary for the degradation of sulfatide, a myelin constituent

Meyer’s loop
part of the optic radiations that fans out into the temporal lobe and carries information from the upper visual world

microcephaly
head circumference that is smaller than normal because the brain has not developed properly or has stopped growing; most often caused by genetic abnormalities

microglia
bone marrow derived phagocytic cells that are involved in immune reactions in the CNS

microglial nodules
formation of clusters of activated microglia around foci of necrotic brain tissue

micrographia
small, cramped handwriting

midbrain (mesencephalon)
rostral aspect of the brainstem located between the pons and the diencephalon

middle cerebellar peduncle (brachium pontis)
paired bundle of fibers originating from the pontine nuclei, decussating in the base of the pons, and ending in the contralateral cerebellar cortex

middle cerebral artery
branch of the internal carotid artery; supplies blood to the entire lateral aspect of each hemisphere including the lateral motor strip, lateral sensory strip, language areas, putamen, globus pallidus, and internal capsule

middle cranial fossa
butterfly-shaped portion of the internal base of the skull housing the temporal lobes laterally and the pituitary centrally

migraine headache
attacks lasting 4-72 hours consisting of moderate to severe intensity unilateral, pulsating head pain that is aggravated by routine physical activity, inhibits daily activities, and is associated with nausea/vomiting, photophobia, and phonophobia

migraine aura
focal neurological phenomena (visual, sensory, motor, or language) preceding or accompanying a migraine attack, usually developing over 5-20 minutes and lasting < 1 hour; may occur in isolation or before (most commonly), during, or after the onset of headache

migraine with aura (classic migraine)
migraine attack associated with reversible aura symptoms indicative of focal CNS dysfunction; the aura (scintillating scotoma, vertigo, paresthesias, paresis, etc) typically develops gradually over several minutes, lasts less than 60 minutes, and occurs before, during, or after headache

migraine without aura (common migraine)
migraine attack without associated neurological deficits

mild cognitive impairment (MCI)
cognitive changes intermediate between normal aging and clinically diagnosed Alzheimer disease; identifies individuals believed to be at risk for Alzheimer disease

Millard-Gubler syndrome
ipsilateral lateral rectus palsy, ipsilateral peripheral facial palsy, and contralateral hemiplegia due to a ventral pontine lesion affecting the abducens and facial nerve fascicles and corticospinal tract

miosis
pupillary constriction

mitochondrial myopathies
neuromuscular diseases caused by damage to the mitochondria (small, energy-producing structures found in every cell in the body )

Mollaret meningitis
benign recurrent aseptic meningitis

mononeuropathy multiplex (mononeuritis multiplex)
condition associated with various systemic disorders (e.g., diabetes, polyarteritis nodosa) characterized by isolated damage to two or more nerves; a multifocal peripheral neuropathy

Monroe-Kellie doctrine
doctrine stating that the total cranial volume tends to remain constant. An increase in the volume of any of its three components (brain, blood, or CSF) or the addition of a space-occupying lesion (e.g., tumor) occurs at the expense of the volume of the other components; once the components have redistributed as much as they can, any further increase in volume results in increased intracranial pressure

Moro reflex
normal neonatal reflex consisting of symmetric abduction followed by adduction of both arms, elicited by gently allowing the back of the head to drop; present during the first 4-6 months of life

motor neglect
inability to look or reach toward left-sided objects

Motor neurons
nerve cells that direct movement

motor neuron disease
dysfunction of alpha motor neurons; motor neuronopathy

motor unit
motor neuron axon and the individual muscle fibers it branches to contact

moyamoya syndrome
usually bilateral, progressive occlusive disease of the large cerebral arteries leading to the development of an abnormal collateral vascular network adjacent to the stenotic vessels; manifest most commonly by infarcts in children and hemorrhages in adults

Muller’s muscle
eyelid muscle innervated by the sympathetic nervous system and that functions to elevate the upper eyelid; interruption of these sympathetic fibers results in the ptosis that is part of Horner's syndrome.

multi-infarct dementia
form of vascular dementia involving deterioration of mental function caused by infarcts in multiple brain regions

multiple sclerosis
inflammatory demeyelating disease with relative axonal sparing of the central nervous system usually characterized by recurrent attacks of focal and multifocal neurological disability

multiple sleep latency test (MSLT)
standard test used to quantify the overall daytime sleep tendency by measuring the speed of falling asleep (sleep latency) usually in 5 tests carried out at two-hour intervals

multisystems atrophy (MSA)
collective term for a group of Parkinson plus syndromes involving various degrees of parkinsonism, autonomic failure, cerebellar dysfunction, and, pyramidal signs that are poorly responsive to levodopa or dopamine agonists; pathologic hallmarks are glial cytoplasmic inclusions and a neuronal multisystem degeneration; replaces the older designations Shy-Drager syndrome, striatonigral degeneration, and olivopontocerebellar atrophy

muscle spindle
stretch receptor in vertebrate muscle that is innervated by both sensory and motor neurons axons and sends proprioceptive information about the muscle to the central nervous system

muscle stretch reflex
two-neurons reflex in which a sensory neurons senses muscle extension and provides direct excitatory feedback to a motor neurons innervating the same muscle, causing the muscle to contract

mutism
inability to produce any verbal utterance; may be due to disordered language, speech, or voice

myasthenia gravis
disease of the neuromuscular junction in which an antibody-mediated attack on nicotinic acetylcholine receptors impairs neuromuscular transmission, resulting in fluctuating, fatigable weakness that responds to cholinergic drugs

mycotic aneurysm
infective aneurysm typically developing distal to the Circle of Willis and reflecting local bacterial or fungal intramural growth with rupture of the vascular wall

mydriasis
pupillary dilation

myelencephalon
see medulla

myelin
fatty substance forming an insulating sheath around axons to increase the velocity of action potential conduction; produced by oligodendrocytes in the CNS and by Schwann cells in the PNS

myelitis
inflammatory disease of the spinal cord

myelogram
diagnostic procedure in which contrast material is injected into the spinal subarachnoid space allowing visualization of the spinal cord and nerve roots

myelomeningocele
form of spina bifida in which there is herniation of meninges and spinal cord parenchyma through defective posterior arches

myelopathy
symptoms and signs associated with spinal cord compression

myoclonus
sudden, shock-like, jerking contraction of a group of muscles

myokymia
involuntary repetitive contractions of muscle fibers lasting a few seconds and giving a continuous rippling or undulating appearance to the overlying skin; associated with nerve irritation

myopathy
muscle disease; manifested by lower motor neurons weakness that is usually proximal>distal

myotonia
muscle disorder characterized by abnormally prolonged contraction (delayed relaxation of the muscle after a forceful contraction)

narcolepsy
sleep disorder characterized by excessive daytime sleepiness and dysregulated REM sleep

(cataplexy, sleep paralysis, hypnagogic hallucinations, and an abnormal tendency to pass directly into REM sleep from wakefulness)

near reflex triad
convergence, accommodation, and pupilloconstriction evoked by targets that move close to you

negative symptom
reduction (weakness, numbness) or complete loss (paralysis, analgesia) of function; implies at least partial or complete failure of impulse conduction in a functional system

neglect
failure to acknowledge stimuli toward the side of space opposite to a hemispheric (usually parietal) lesion

Negri body
viral inclusion in hippocampal, neocortical, or Purkinje cell neurons that is the diagnostic hallmark of rabies encephalitis

neologism
made-up word

nerve conduction velocity study
method of diagnosing the type and location of nerve injury using application of electrical stimulation to the nerve

network inhibition hypothesis
proposed pathophysiological mechanism for complex behavioral phenomena and impaired consciousness in complex partial seizures; theory is that the seizures induce excitation in the temporal lobe that propagates to the dorsomedial thalamus and upper brainstem reticular formation, disrupting the normal activating functions of these areas, and resulting in widespread functional depression of bilateral frontal and parietal association cortex

neuralgia
pain that follows the paths of specific nerves, e.g., trigeminal neuralgia; postherpetic neuralgia

neural plate
ectodermal tissue on the dorsal surface of the embryo that forms the neural tube, which develops into the central nervous system

neural tube
embryonic brain and spinal cord

neural tube defect
malformation of the brain and/or spinal cord in embryo; classified based on location, extent, and the presence or absence of exposed neural tissue (open or closed)

neuraxis
often used synonymously with central nervous system (even though some suggest that it represents only the unpaired portions of the CNS)

neurilemma
thin membrane surrounding the axons and myelin of peripheral nerves; outermost layer of nerve fibers

neurite
terminal axon or dendrite

neuritic plaque
mature plaque composed of a) silver-positive swollen neurites engorged with aggregates of paired helical filaments and round dense bodies and b) an amyloid core; seen in Alzheimer's disease

neurofibrillary tangles
flame-shaped intracytoplasmic inclusions in cortical neurons consisting of paired helical filaments; characteristic of, but not unique to, Alzheimer's disease

neurogenic bladder
bladder dysfunction associated with a lesion in the brain, spinal cord, or peripheral nerves and characterized by underactivity (failure to empty) or overactivity (failure to store); symptoms include urinary urgency, frequency, hesitancy, nocturia, and incontinence

neuroglia
see glia

neuroleptic
drug that blocks dopamine receptors; antipsychotic drug

neuroleptic malignant syndrome
rare, but life-threatening, idiosyncratic reaction to antipsychotic drugs that is characterized by high fever, hypertension, severe rigidity, altered mental status, and autonomic dysfunction; may occur with either severe blockade (high doses of neuroleptics) or sudden depletion (withdrawal of neuroleptics) of dopamine receptors

neurologist
a physician who specializes in the diagnosis and treatment of disease of the nervous system

neurology
medical specialty dealing with the nervous system and the diseases affecting it

neuroma
tumor composed of nerve tissue

neuromelanin
dark brown pigment seen in selected neuronal populations (most characteristically in the substantia nigra and locus ceruleus) that represents the residua of catecholamine metabolism

neuromuscular junction
junction (synapse) between the terminal of a motor neurons and a muscle fiber; myoneural junction

neuron
nerve cell body

neuronopathy
dysfunction and reflex loss due to disease of cell bodies (sensory=dorsal root ganglion; motor=alpha motor neurons, more commonly called motor neuron disease)

neuropathy
nerve disease; manifested by varying combinations of lower motor neuron weakness that is usually distal>proximal, sensory loss, and reflex loss

neuronophagia
engulfing of degenerating neurons by hematogenously derived monocytic cells and activated microglia

neuropil
unmyelinated neuronal processes (axons and dendrites) in the gray matter of the central nervous system

neuroprotection
strategies that ameliorate the biochemical and metabolic derangements induced by cerebral ischemia, thus limiting delayed neuronal injury

neurotransmitter
chemical substance that transmits electrical impulses between neurons

neurulation
process by which the neural tube is formed; consists of folding of the neural plate on the dorsal side of the embryo (resulting in the formation of the brain and spinal cord) followed by canalization (resulting in the development of the caudal spinal cord)

nightmare
unpleasant and/or frightening dream that usually awakens a person from REM sleep; affected individual usually remembers the event, unlike in night terror

night terror (sleep terror; pavor nocturnes)
sleep disorder (usually of children) involving abrupt awakening from sleep in a terrified state that represents incomplete arousal from nonREM sleep; affected individual is usually confused and does not remember details of the event, unlike in nightmare

nociceptive
painful

nodulus
posterior part of the cerebellar vermis; medial portion of the vestibulocerebellum

non-communicating hydrocephalus
blockage of CSF flow along one or more of the narrow pathways connecting the ventricles (most commonly the cerebral aqueduct)

non-fluent aphasia (Broca’s or expressive aphasia)
selective impairment of language production including impaired repetition due to a lesion of the left inferior frontal lobe (Brodmann areas 44 and 45)

non-REM sleep (non-rapid eye movement sleep, slow wave sleep)
sleep stages 1 through 4; characterized by a slowing of brain waves and some physiological functions

normal pressure hydrocephalus (NPH)
clinical symptom complex characterized by abnormal gait, urinary incontinence, and dementia in the setting of hydrocephalus with normal cerebrospinal fluid pressure; proposed pathophysiology is that there is diminished cerebrospinal fluid absorption at the arachnoid villi, which leads to transient high-pressure hydrocephalus with subsequent ventricular enlargement and return of cerebrospinal fluid pressure to normal

Nothnagel Syndrome
ipsilateral oculomotor palsy and contralateral ataxia due to a midbrain tegmental lesion affecting the III nerve fascicle and superior cerebellar peduncle

notochord
embryological predecessor of the vertebral column

nuchal rigidity
stiff neck

nucleus
collection of neuronal cell bodies

nucleus ambiguus
motor nucleus in the dorsolateral medulla that innervates striated muscle in the neck and thorax

nucleus cuneatus
nucleus located in the lower medulla containing the second-order sensory neurons that relay mechanosensory information from peripheral receptors in the upper body to the thalamus via the medial lemniscus

nucleus gracilis
nucleus located in the lower medulla containing the second-order sensory neurons that relay mechanosensory information from peripheral receptors in the lower body to the thalamus via the medial lemniscus

nystagmus
involuntary, rhythmic oscillation or trembling of the eyeballs

obstructive sleep apnea
repetitive cessation of breathing during sleep for 10 seconds or more due to complete closure of the throat; characterized by snoring, excessive daytime sleepiness, and morning headache

obtundation
mild to moderate reduction in alertness with slow response to stimulation, decreased interest in environment, and increased number of hours of sleep

ocular migraine
form of migraine characterized by monocular visual loss typically followed by an ipsilateral periorbital (or less commonly diffuse) headache

oculocephalic response (OCR/Doll’s phenomenon)
reflex eye movements assessed in an uncooperative or unresponsive patient to determine whether brainstem extraocular pathways are intact; performed by quickly turning the head, stimulating proprioceptive afferents from the neck and/or the vestibular system; considered positive (brainstem pathways intact) if head turn produces conjugate eye deviation in the opposite direction; absent response implies that either brainstem pathways are impaired or the patient is too awake to assess

oculogyric crisis
acute dystonic reaction to neuroleptic drugs manifested by sudden sustained twisting of the head and upward deviation of the eyes; responsive to anticholinergic or antihistamine medications

oculomotor nerve (cranial nerve III)
motor nerve innervating the superior, inferior, and medial recti, inferior oblique, and levator palpebrae superioris muscles and providing preganglionic parasympathetic fibers to the ciliary ganglion to control pupillary constriction; III palsy causes down and out eye deviation, ptosis, and a dilated unreactive pupil (pupillary fibers on the outside so spared with intrinsic lesion); lesions of the nucleus, located in the medial midbrain, typically cause weakness of all muscles innervated by the ipsilateral III nerve, contralateral superior rectus weakness, and bilateral incomplete ptosis;

oculovestibular response (OVR/cold calorics/vestibulo-ocular response/VOR)
reflex eye movements that keep vision stable upon head rotation and involve connections between the ipsilateral 8th and 3rd and the contralateral 6th nerve nuclei; horizontal movements are tested by instilling ice water into one ear, stimulating the lateral semicircular canal; in a normal awake patient, the eyes will slowly deviate towards the irrigated ear and then beat quickly away from the irrigated ear as the supratentorial frontal eye fields try to re-fix vision

odontoid fracture
fracture through the odontoid process of C2 due to horizontal shearing and axial loading; type I usually stable and type II usually unstable

olfactory nerve (cranial nerve I)
sensory nerve mediating smell

oligemia
reduction in blood flow associated with an increase in oxygen extraction fraction but maintenance of normal metabolism

oligoclonal bands
two to five bands of immunoglobulins on protein electrophoresis of cerebrospinal fluid seen in multiple sclerosis and other central nervous system disorders

oligodendrocytes
form of CNS glia responsible for the synthesis and maintenance of myelin and the formation of perineuronal satellites

oligodendroglioma
WHO grade II primary CNS tumor typically involving the cerebral hemispheres; characterized histologically by uniform round nuclei with a perinuclear halo (fried egg artifact) and perineuronal satellitosis

olivopontocerebellar atrophy (OPCA)
older term for a variant of multisystems atrophy characterized by preferential degeneration of the cerebellum and brainstem producing symmetric parkinsonism and ataxia, dysarthria, dysphagia, pyramidal signs, and often ocular motility disorders

Ondine's curse (central alveolar hypoventilation)
condition in which the respiratory center in the brain is unable to stimulate breathing in response to an increased amount of carbon dioxide in the blood; typically worsens during sleep

one-and-a-half syndrome
combination of an abducens nerve nuclear lesion and an ipsilateral medial longitudinal fasciculus lesion resulting in an ipsilateral gaze paralysis and loss of adduction of the ipsilateral eye

on-off phenomenon
sudden, unpredictable changes in motor performance by patients on levodopa therapy

opening pressure
cerebrospinal fluid pressure obtained upon entering the subarachnoid space by spinal puncture

ophthalmoplegia
paralysis or weakness of one or more of the muscles that control eye movement

ophthalmoplegic migraine
form of migraine characterized by periorbital pain and ocular cranial nerve palsy (usually the third nerve and including ptosis and a dilated pupil)

opisthotonos
abnormal posturing of the body with severe arching of the back and the head thrown backwards; may occur with meningeal irritation, especially in infants, or with depressed brain function

optic atrophy
wasting of the optic disc that results from partial or complete degeneration of optic nerve fibers and is associated with a loss of visual acuity

optic chiasm
partial crossing of about half the axons in each optic nerve to enter the contralateral optic tract; lesion results in loss of vision in the temporal hemifield of both eyes

optic disc (optic nerve head)
location where all the ganglion cells exit the retina to form the optic nerve; known as the blind spot since there are no receptors in this part of the retina

optic nerve
extent of the visual system pathway from the retina to the optic chiasm; contains axons of ganglion cells in the retina of the ipsilateral eye; lesion results in loss of vision in one eye

optic neuritis
inflammation or demyelination of the optic nerve with transient or permanent loss of vision +/- pain

optic radiations
extent of the visual system pathway from the lateral geniculate nucleus of the thalamus to primary visual cortex in the occipital lobe; involves temporal (Meyer’s loop) and parietal lobes

optic tract
extent of the visual system pathway from the optic chiasm to the lateral geniculate nucleus of the thalamus; contains axons from ganglion cells in the retinas of both the left and right eyes, but information from only one half (either left or right) of each eye's visual field; lesion results in loss of vision in contralateral hemifield of both eyes

optokinetic nystagmus
reflexive eye movement that consists of the intermittent rotation of the eye when a subject looks at moving objects; designed to keep an entire moving scene stable on the retina so that it doesn’t blur

orthostatic hypotension
sudden drop in blood pressure experienced upon standing up

orthotic
mechanical appliance such as a leg brace or splint that is designed to control, correct, or compensate for impaired limb function

oscillopsia
visual disturbance characterized by continuous, involuntary, and chaotic eye movements, which make objects appear to be jumping or bouncing

osmophobia
enhanced sensitivity to odors

oxycephaly
premature fusion of all cranial sutures producing an elongated head

oxygen extraction fraction
the fraction of available oxygen extracted by the brain from the blood

Pacinian corpuscle
largest of the skin receptors located deep in the dermis and responsible for sensation of vibration and deep pressure

palsy
paralysis of a muscle group

papilledema
swelling of nerve head usually but not always due to increased ICP

parachute reflex
protective reflex of normal infants (present by 7-9 months) in which both arms go out in front in response to the head being held down and pointed toward the floor

paralysis
loss of motor function in a body part

paramedian pontine reticular formation (PPRF)
collection of premotor neurons located in or near the abducens nucleus that drive horizontal gaze when excited by the cerebral cortex

parameningeal
adjacent to the meninges; includes nasal cavity, middle ear, paranasal sinuses, mastoid, infratemporal fossa, and pterygopalatine fossa

paraphasia
speech error characterized by substitutions of letters (e.g., "bree" for "tree") or words (e.g., "house" for "tree")

paraplegia
paralysis of both legs

parasagittal
sagittal section that is lateral to the midline

parasomnia
disorder in which abnormal behavior intrudes into the sleep process; includes somnambulism, night terrors, and bruxism

parasympathetic nervous system
part of the autonomic nervous system concerned with conservation and restoration of energy; its  preganglionic fibers arise from the motor nuclei of  cranial nerves III, VII, IX and X in the brainstem and from the second, third and fourth sacral segments of the spinal cord

paratonia (gegenhalten)
increased muscle tone that increases in proportion to the speed and strength with which the examiner tries to move the joint; indicative of extensive bihemispheric or bifrontal dysfunction

parenchyma
tissue

paresis
reduced ability to activate motor neurons; weakness

paresthesia
skin sensation, such as burning, prickling, itching, or tingling, with no apparent physical cause

Parinaud’s syndrome (dorsal midbrain syndrome)
syndrome characterized by a supranuclear palsy of vertical conjugate movements, convergence-retraction nystagmus, and light-near dissociation of the pupillary reflex; eyes may be forced downward; due to lesion of the dorsal midbrain including pressure on the it from hydrocephalus or increased intracranial pressure

Parkinson disease
neurodegenerative disease characterized by initially asymmetric resting tremor, bradykinesia/akinesia, rigidity, and postural instability due to loss of cells in the substantia nigra with striatal dopamine deficiency and residual Lewy bodies

parkinsonism
complex of symptoms including resting tremor, bradykinesia/akinesia, rigidity, and postural instability that are due to striatal dopamine deficiency or reduced function; may be seen in a variety of neurodegenerative disorders including idiopathic Parkinson disease, Lewy body dementia, corticobasal degeneration, progressive supranuclear palsy, multisystems atrophy

Parkinson plus syndromes
primary neurodegenerative disorders associated with complex clinical presentations including parkinsonism that reflect degeneration in various neuronal systems in addition to the substantia nigra; parkinsonian features are characterized by symmetry of signs, truncal>appendicular signs, and lack of response to levodopa or dopamine agonists

partial (focal) seizure
seizure that starts in a single cortical region

participation restrictions
problems an individual may experience in their own involvement in life situations (e.g., inability to return to work).

penumbra
area surrounding the dense core of irreversibly damaged cells that has preserved ionic homeostasis and reduced neuronal electrical activity but that is capable of recovery

perceptual neglect
inability to distribute spatial attention to objects in the visual field

periaqueductal gray
tegmental gray matter surrounding the cerebral aqueduct within the midbrain that is important in the processing of pain

perimetry
visual field testing designed to determine the sensitivity of specific locations of peripheral and central vision

perineurium
connective tissue sheath surrounding a bundle of nerve fibers

periodic limb movement disorder
sleep disorder characterized by repetitive stereotyped movements during sleep, most commonly an extension of the big toe and dorsiflexion of the ankle; often associated with a partial arousal or awakening of which the patient is typically unaware

peripheral nervous system
nerve cell body, spinal nerve root, plexus, peripheral nerve, neuromuscular junction, and muscle

perisylvian plexus
referring to structures around the Sylvian fissure; includes Wernicke's area in auditory association cortex and Broca's area in front of motor cortex

perimysium
connective tissue sheath surrounding a bundle of muscle fibers

petit mal seizure
see absence seizure

phonophobia
abnormal intolerance to sound that commonly occurs in migraine and other headaches

photophobia
abnormal intolerance to light, usually associated with eye pain; characteristic of meningeal irritation, migraine, optic nerve disease, and ocular or retinal disorders

physiologic tremor
subtle low amplitude, high frequency tremor most easily observed in the hands that is present in healthy persons and most prominent during posture and action

pia
innermost layer of the meninges that is intimately applied to the surface of the brain parenchyma and spinal cord and separated from the arachnoid by the subarachnoid space

Pick’s disease
form of frontotemporal dementia characterized by a slowly progressive deterioration of social skills and changes in personality in addition to impairment of intellect, memory, and language; defined pathologically by Pick bodies (rounded tau-posiotive inclusions similar to neurofibrillary tangles) and Pick cells (swollen or ballooned neurons) in a predominantly frontal location

pincer grasp
finger-thumb opposition

pineal
midline body attached to the posterior part of the third ventricle and lying between the superior colliculi, below the splenium of the corpus callosum; major site of melatonin biosynthesis

pituitary apoplexy
spontaneous hemorrhagic infarction of a typically large and nonfunctioning pituitary adenoma presenting with headache, nausea and vomiting, cranial nerve II, III, IV, or VI palsies, altered mental status, and hypopituitarism

pituitary gland (hypophysis)
endocrine organ lying ventral to the hypothalamus and optic chiasm; includes an anterior glandular lobe made up of hormone-secreting cells and a posterior neural lobe containing the terminals of neuropeptide-secreting, hypothalamic neurons

placing (stepping) response
normal neonatal reflex consisting of elevating the foot and moving it forward when its dorsal surface is touched; the infant will appear to attempt to stand or walk

plagiocephaly
premature fusion of a unilateral coronal and/or lambdoid +/- sagittal suture

plantar response
superficial (cutaneous) reflex elicited by applying a stimulus to the skin of the foot or leg; flexion (curling down) of all toes (“downgoing toe”) is a normal response, while extension of the great toe (“upgoing toe”) with fanning of the other toes is abnormal and signifies a lesion of the corticospinal tract. Many methods of eliciting the plantar reflex have been described, including the following:

Eponym	Technique
Babinski	Stimulation of the plantar surface of the foot with a blunt point from the heel forward, crossing the metatarsal pad from the small to the great toe
Chaddock	Stimulation of the lateral aspect of the foot with a blunt point from the heel forward to the small toe
Oppenheim	Application of heavy pressure with the thumb and index finger to the anterior surface of the tibia with downward stroking from the infrapatellar region to the ankle
Gordon	Squeezing or applying deep pressure to the calf muscles
Strümpell	Forceful pressure on the anterior tibia
Moniz	Forceful passive plantar flexion of the ankle
Gonda-Allen	Downward snapping of the distal phalanx of the second or fourth toe
Stransky	Gentle extension of the small toe laterally
Bing	Application of pinprick to the dorsal surface of the great toe

plegia
inability to activate any motor neurons; paralysis

polymyositis
inflammatory muscle disease associated with primarily proximal limb weakness; considered to be an autoimmune disease of disordered cellular immunity and often associated with a specific collagen-vascular disease

polysomnogram
continuous and simultaneous recording of multiple physiological variables during sleep

pons
middle aspect of the brainstem, lying between the midbrain rostrally and the medulla caudally

porencephaly
cerebral hemispheric cyst that is usually the remnant of a destructive lesion (e.g., stroke or infection) or is due to abnormal brain development

positive sharp wave
spontaneous muscle activity seen on electromyography in association with denervation or irritable myopathy consisting of long action potentials with initial positive (down) wave followed by wide negative (up) wave

positive symptom
exaggeration of a physiological phenomenon; implies abnormal excessive (irritative”) discharges in gray matter or (e.g., seizure or hemifacial spasm) or chronic imbalance in complex integrated motor pathways (e.g., chorea)

postdrome
period following a migraine during which a person has impaired concentration, fatigue, or irritability

posterior cerebral artery
paired arteries that arise from the top of the basilar artery; supply blood to the posterior areas of the brain, including the medial occipital lobes (visual cortex), the inferior temporal lobes, and thalamus

posterior commissure
one of the three major groups of commissural fibers that crosses the midline of the epithalamus just dorsal to the point where the cerebral aqueduct opens into the third ventricle

posterior communicating artery
branch of the internal carotid artery that joins the middle cerebral artery (anterior circulation) to the posterior cerebral artery (posterior circulation); supplies thalamus, hypothalamus, optic chiasm, and mammillary bodies

posterior cord syndrome
spinal cord injury syndrome associated with damage to the posterior portion of the spinal cord resulting in bilateral loss of vibration /proprioception +/- bilateral weakness below the level of the lesion

posterior fossa
brainstem and cerebellum

posterior horn (dorsal horn)
gray matter in the back of the spinal cord that receives sensory information from the body through the dorsal root ganglia

post-herpetic neuralgia
condition following an acute varicella zoster infection (shingles) characterized by persistent pain (3 or more months) in the dermatomal distribution of the previous zoster rash

postural instability
loss of ability to make postural adjustments in response to perturbations, i.e., defect in righting reflex; common in Parkinson disease

postural tremor
tremor that occurs with the maintenance of a posture or position against gravity

posture
ability to stand upright automatically against gravity; controlled by the vestibulospinal, reticulospinal, and tectospinal pathways

Pott’s disease
tuberculous involvement of the vertebral column with vertebral collapse

praxis
ability to plan, time, sequence, and spatially organize skilled movements

prefrontal cortex
cortical region of the frontal lobe lying anterior to primary and premotor cortex; mediates various executive functions, with the dorsolateral division involved in working memory processes, planning, and decision making, and the ventromedial division involved in emotion and the organization of appropriate social behavior

premotor cortex
cortical region (Brodmann's area 6) in the posterior frontal lobe anterior to the primary motor cortex involved in planning or programming of voluntary movements

primary progressive
clinical course of multiple sclerosis characterized from the beginning by progressive disease, with no plateaus or remissions, or an occasional plateau and very short-lived, minor improvements

primary progressive aphasia
progressive form of dementia characterized by global loss of language abilities and initial preservation of other cognitive functions; pathologically, there may be spongiform changes in teh frontal and temporal lobes rather than Alzheimer-like changes

primitive neuroepithelial tumor (PNET)
tumor histologically similar to the medulloblastoma but located outside the posterior fossa

prion
proteinacious infectious agent responsible for various fatal brain diseases classified as spongiform encephalopathy

prodrome
premonitory phenomena occurring hours to days before headache onset in migraine consisting of psychological, neurological, or constitutional symptoms

progressive multifocal leukoencephalopathy (PML)
fatal demyelinating CNS disease of immunocompromised patients caused by reactivation of the JC papovavirus

progressive supranuclear palsy (Steele-Richardson-Olszewski syndrome)
Parkinson plus syndrome characterized by predominantly axial rigidity, akinesia, supranuclear ophthalmoplegia (impairment of voluntary vertical gaze—downward more than upward), and pseudobulbar palsy

proprioception
joint position sense

proptosis (exophthalmos)
abnormal protrusion of the eyeball

prosencephalon
see forebrain

prosody
emotional content of language

pseudoathetosis
involuntary slow, writhing movements of a limb (usually the hand or fingers) occurring when the eyes are closed due to impaired proprioception. Unlike in athetosis, the movements are not present when the eyes are open because visual feedback provides the necessary information to know where the limb is in space.

pseudobulbar affect
condition in which episodes of laughing and/or crying occur with no apparent precipitating event

pseudobulbar palsy
syndrome characterized by dysarthria, dysphagia, dysphonia, impairment of voluntary movements of tongue and facial muscles, and emotional lability; caused by diseases such as multiple sclerosis, motor neuron disease, and stroke that affect the motor fibers traveling from the cerebral cortex to the lower brainstem (i.e., corticobulbar tracts)

pseudorosette
spoke-wheel arrangement of cells with tapered cellular processes surrounding a blood vessel, creating a perivascular nuclear free zone; seen in most ependymomas and less commonly in other CNS tumors

ptosis
eyelid droopiness

pupillary light response
contraction of the pupil on exposure of the retina to light; dependent on proper functioning of the optic and oculomotor nerves

putamen
largest and most lateral component of the basal ganglia

pyramid
prominent column of white matter on the ventromedial margin of the medulla containing axons of the corticospinal tract

pyramidal tract
see corticospinal tract

quad cane
cane that has a broad base on four short “feet,” which provide extra stability

quadrantanopia
loss of vision in either the upper or lower aspect of one hemifield (involving both eyes)

quadrigeminal bodies
two pairs of elevations on the dorsal surface of the midbrain; includes the superior colliculi and inferior colliculi

quadriplegia (tetraplegia)
paralysis of all four extremities

rachischisis
fissure of the spinal cord resulting in exposure of the incompletely folded cord along the back

radiculopathy
symptoms and signs associated with spinal nerve root compression

Ramsy-Hunt syndrome
facial paralysis, hyperacusis, loss of taste, and vesicles on the eardrum, external auditory meatus, or palate due to herpes zoster infection of the geniculate ganglion

raphe
ridge of tissue

raphe nuclei
nuclei located within the medial portion of the reticular formation in the brainstem that secrete serotonin

Raymond syndrome
ipsilateral lateral rectus palsy and contralateral hemiplegia sparing the face due to a ventral pontinelesion affecting the abducens nerve fascicles and corticospinal tract (but sparing the facial nerve)

recurrent-remittent
episodic attacks of symptoms with rapid recovery to normal health; implies repeating episodes of a single process (e.g., transient ischemic attacks (TIA), seizures, migraine, and multiple sclerosis)

red desaturation
finding of dimmer perception of the color red in an eye affected by optic nerve disease such as optic neuritis; sign of subtle asymmetry in optic nerve function since color desaturation may occur despite normal visual acuity

red nucleus
oval nucleus centrally placed in the upper midbrain reticular formation that receives fibers from the deep cerebellar nuclei and cerebral cortex and projects to the cerebellum, brainstem, spinal cord, and probably thalamus

relapsing-remitting
clinical course of multiple sclerosis characterized by episodic attacks of symptoms with recovery to normal health

REM behavior disorder
disorder occurring during REM sleep in which the normal motor atonia is partially or completely absent such that dreams can be acted out with punching, kicking, and jumping out of bed

REM sleep (rapid eye movement sleep)
sleep stage in which vivid dreaming occurs; identified by the occurrence of rapid eye movements under closed eyelids, motor atonia, low voltage EEG pattern, bursts of muscular twitching, irregular breathing, irregular heart rate, and increased autonomic activity.

repetitive nerve stimulation
nerve conduction study in which a brief series of shocks is applied to a motor nerve before and after brief exercise of a muscle supplied by that nerve; useful for evaluating disorders of neuromuscular transmission such as myasthenia gravis (decremental response see) and Lambert Eaton myasthenic syndrome (incremental response seen).

restiform body
see inferior cerebellar peduncle

resting tremor
medium-frequency (3-6 Hz) tremor that occurs maximally with the affected body at rest rather than with holding a sustained posture or making an intentional movement; common in Parkinson disease

restless legs syndrome
sleep disorder characterized by tingling, creepy-crawly, or aching sensation in the legs and sometimes arms as well as motor restlessness that tends to occur at rest (especially around the patient’s usual bedtime) and to be relieved temporarily by movement

reticular activating system (RAS)
the activating mechanisms that lie in or near the central gray matter of the diencephalon, midbrain, and rostral pons and are responsible for mediating consciousness

reticular formation
heterogeneous collection of neurons scattered throughout the brainstem tegmentum that either modulate forebrain and spinal cord activity or coordinate the firing patterns of lower motor neurons engaged in reflexive or stereotypical somatic motor and visceral motor activities

reticulospinal tract
descending pathway from the reticular formation of the brainstem to spinal inter- and motor neurons that control anti-gravity posture and locomotion

retina
light-sensitive neuronal layer lining the back of the eye that sends impulses through the optic nerve that are translated into a visual image; part of the central nervous system

retropulsion
a tendency to walk backward involuntarily that can occur in Parkinson disease

rhombencephalon
hindbrain; includes the pons, cerebellum, and medulla

righting reflex
ability to make postural adjustments in response to perturbations

rigidity
increased resistance throughout the range of motion when passively moving a body part due to co-contraction of agonist and antagonist muscles ("lead pipe")

ring-enhancement
CT or MRI contrast enhancement surrounding a lesion that has blood-brain barrier breakdown, such as metastatic tumor or abscess

Romberg test
inability to maintain upright posture when feet together and eyes closed; indicates impaired proprioception

rooting reflex
normal neonatal reflex consisting of turning the head towards a stimulus presented to the side of the mouth, latching on, and sucking

Rosenthal fibers
eosinophilic corkscrew or rod-shaped inclusions seen in pilocytic astrocytoma

rostral
toward the head or nose

rostrocaudal
literally “from the nose to the tail”; used to describe the sequence of symptoms referable to progressively lower parts of the brainstem characteristic of transtentorial herniation

rubral tremor
low-frequency (<4.5 Hz) tremor often of irregular, coarse rhythm that is present during both rest and intentional movements and typically follows cerebellar outflow pathway lesions

Ruffini corpuscles
thermoreceptors in the skin

saccade
discrete, rapid conjugate eye movements from one object to another

saccular aneurysm
spherical outpouching from one side of an artery that occurs at an arterial bifurcation point and reflects weakness of all layers of the vessel wall

sagittal
vertical plane passing through the standing body from front to back

sagittal sulcus (longitudinal fissure)
long, deep, sagittally oriented cleft that separates the two cerebral hemispheres on the dorsal midline

salivatory nuclei
small nuclei in the pontine tegmentum that provide parasympathetic preganglionic innervation to ganglia associated with the lacrimal and salivary glands to control salivation and tearing

scanning speech (ataxic dysarthria)
abnormal staccato-like speech due to a lesion of the cerebellum or cerebellar pathways

scaphocephaly (dolichocephaly)
premature closure of the sagittal suture

schizencephaly
developmental birth defect characterized by abnormal slits or clefts in the cerebral hemispheres extending from the cortical surface to the underlying ventricle

Schwann cell
glial cell of the PNS that forms the insulating myelin sheath of peripheral axons

schwannoma
WHO grade I benign peripheral nerve sheath tumor occurring commonly in the cerebellopontine angle (cranial nerve VII) or in the bony foramina around the spinal cord (spinal nerve root); characterized histologically by Antoni A and Antoni B tissue and Verocay bodies (zones of nuclear palisading)

scintillating scotoma
visual migraine aura consisting of shimmering lights followed by a dark spot or partial loss of vision that may move across the visual field

scotoma
island-like gap or blind spot in the visual field; pleural=scotomata

secondary progressive
clinical course of multiple sclerosis that initially is relapsing-remitting and then becomes progressive at a variable rate, possibly with an occasional relapse and minor remission

secondary symptoms
symptoms referable to secondary effects of a lesion e.g., edema, blockage of cerebrospinal fluid pathways, stretching of vessels

sectoranopia
loss of vision in a wedge of the visual field

seizure
discrete event due to sudden, transient, excessive neuronal discharges in the brain

sella turcica
saddlelike prominence on the upper surface of the sphenoid bone of the skull, situated in the middle cranial fossa and containing the pituitary gland

senile plaque
see neuritic plaque

sensory trick
specific trigger a patient uses to relieve dystonia, e.g., touching the outer canthus of the eye to temporarily relieve blepharospasm

septal nuclei
neuronal structures in the rostral forebrain adjacent to the septum pellucidum that communicate with the hippocampus, amygdala, hypothalamus,midbrain, habenula, cingulate gyrus, and thalamus

septum pellucidum
membrane extending ventrally from the body of the corpus callosum that separates the two lateral ventricles from each other

setting sun sign
forced depression of the eyes due to pressure on the dorsal midbrain in the setting of hydrocephalus; see also Parinaud’s syndrome

shadow plaque
foci of myelin preservation at the periphery of active multiple sclerosis plaques thought to represent partial remyelination

sharp wave
EEG pattern consisting of a transient electrical discharge with a pointed peak and a duration of 70-200 milliseconds that stands out from ongoing background activity; has a strong association with epilepsy

Shy-Drager syndrome
older term for a variant of multisystems atrophy characterized by preferential degeneration of the intermediolateral cell column of the spinal cord and substantia nigra producing symmetric parkinsonism and autonomic failure

sialorrhea
drooling; increased salivation

simple tic
tic involving a limited number of muscles; simple vocal tics are meaningless noises such as grunting or throat clearing; simple motor tics are focal movements such as eye blinking or facial grimacing

single fiber electromyography
electrodiagnostic test in which potentials of muscle fibers innervated by a single axon are recorded; normal response is for fibers to be activated with consistent latencies whereas in neuromuscular junction disorders, latencies among muscle fibers in a single motor unit are variable (increased jitter); most sensitive test for myasthenia gravis

Sjogren's syndrome
an autoimmune disorder that prohibits production of tears and saliva

skew deviation
hypertropia in which the eyes move vertically in opposite directions due to acquired supranuclear or vestibulo-ocular disruption

sleep latency
speed of falling asleep

sleep paralysis
temporary (seconds to minutes) inability to move or talk that occurs during sleep-to-wake or wake-to-sleep transitions; one of the symptoms of narcolepsy, but also experienced by some non-narcoleptic individuals

slow wave sleep
see non-REM sleep

smooth pursuit
smooth following eye movements that maintain fixation

solitary nucleus and tract
sensory nucleus of the medulla that receives afferent taste information from nerves VII, IX, and X and mediates the gag, cough, carotid sinus, and other visceral reflexes

soma
cell body, which contains the nucleus and endoplasmic reticulum

somatosensory evoked potentials (SSEP)
series of waves that reflect sequential activation of neural structures along the somatosensory pathways following electrical stimulation of peripheral nerves (typically elicited by stimulation of the median nerve at the wrist, the common peroneal nerve at the knee, and/or the posterior tibial nerve at the ankle and recorded from electrodes placed over the scalp, spine, and peripheral nerves)

somesthesia
sensation

somnambulism (sleep walking)
arising from bed during a period when there is a simultaneous occurrence of incomplete wakefulness and nonREM sleep; typically occurs in the first third of the night during deep sleep

soporific
causing or tending to induce sleep, such as a hypnotic drug

spasticity
abnormal increase in muscle tone and reflexes, manifested as a velocity dependent spring-like resistance to moving or being moved; indicates an upper motor neuron lesion

spike
EEG pattern consisting of a transient electrical discharge with a pointed peak and a duration of less than 70 milliseconds that stands out from ongoing background activity; has a strong association with epilepsy

spike-and-wave complex
generalized synchronous pattern seen on electroencephalogram, consisting of a sharply contoured fast wave followed by a slow wave; seen in generalized epilepsy

spina bifida
failure of bone fusion in the posterior midline of the vertebral column resulting in a bony cleft through which the meninges and varying quantities of spinal cord tissue protrude

 spina bifida occulta
closed spinal dysraphism characterized by posterior vertebral defect and various overlying cutaneous anomalies (e.g., lipoma, patch of hair); often associated with other spinal cord abnormalities

spinal dysraphism
failure of bone fusion in the posterior vertebral column; classified as open (not covered by skin) or closed (covered by skin); see also meningocele and myelomeningocele

spinocerebellar ataxia
group of hereditary neurodegenerative disorders caused by expansion of a CAG triplet repeat and characterized by progressive ataxia and variable other features such as neuropathy and hearing or visual loss

spinal accessory nerve (cranial nerve XI)
motor nerve originating partly from the medulla (nucleus ambiguus—innervating laryngeal muscles) and partly from the spinal cord (accessory nucleus in the ventral horn of the cervical cord—innervating the sternocleidomastoid and trapezius muslces); lesion results in weakness in turning the head to the opposite side and elevating the shoulder

spinocerebellar tract
fiber tract originating in the spinal cord and carrying proprioceptive input to the ipsilateral cerebellum

spinothalamic tract
axonal tract carrying information on pain and temperature that arises from the posterior nerve roots, which ascend a few segments in Lissauer’s tract before synapsing in the substantia gelatinosa, crossing to the opposite side of the cord in the anterior commisure, and traveling in the anterolateral aspect of the cord up to the thalamus and cortex

splenium
thickened posterior border of the corpus callosum

spondylosis
degenerative disease of the vertebral column that can result in spinal cord compression

spongiform encephalopathy
progressive neurodegenerative disorder associated with various prion agents that produce spongy changes in the brain (e.g., Creutzfeldt-Jakob disease, kuru)

spreading cortical depression
brief wave of intense cortical activation followed by a marked decrease in neuronal activity and reduced blood flow that starts in the occipital cortex and spreads anteriorally at a rate of 2-6 mm/min; thought to underline migraine aura

status epilepticus
medical emergency defined as more than 30 minutes of either continuous seizure activity or two or more sequential seizures without full recovery of consciousness in between

status migrainosus
migraine attack that persists for > 72 hours and often leads to hospitalization

stereognosis
ability to recognize objects by touch

stereotypy
repetitive stereotyped movements commonly seen in tardive dyskinesia, Tourette syndrome, or autism

stocking-glove
typical distribution on the body where symptoms/signs of peripheral neuropathy are evident (toes to knee and fingers to wrist)

strabismus
misalignment of the eyes that is either developmental (due to a miscalibration of the binocular vergence system in the cerebral cortex at some point in infancy or childhood) or acquired (due to a palsy of a cranial nerve or extraocular muscle)

stria medullaris
white matter tract connecting the anterior hypothalamus and septal nuclei in the medial basal forebrain with the habenula

stria terminalis
white matter tract containing amygdaloid efferents to the septal nuclei in the medial basal forebrain and nuclei of the anterior hypothalamus

striate cortex
see calcarine cortex

striatonigral degeneration (SND)
older term for a variant of multisystems atrophy characterized by degeneration of the striatum and the substantia nigra producing symmetric parkinsonism that does not respond to levodopa or dopamine agonists

striatum
part of the basal ganglia consisting of the caudate and putamen separated by fibers of the anterior limb of the internal capsule

stroke
sudden loss of neurological function caused by a blockage or rupture of a blood vessel to the brain or spinal cord; includes infarction and hemorrhage subtypes

stupor
condition of unresponsiveness from which the patient can only be aroused by vigorous and repeated stimuli; once stimulus ceases, patient lapses back into unresponsiveness

subacute
developing over days to weeks; suggests an expanding lesion (e.g, tumor or abscess)

subarachnoid hemorrhage
bleeding in the subarachnoid space most commonly due to trauma or rupture of an aneurysm or arteriovenous malformation

subarachnoid space
actual space separating the pia and arachnoid that surround the brain and spinal cord; contains cerebrospinal fluid, arteries and veins, and filaments of arachnoid matter, giving it the appearance of a spider web

subclinical seizure
electrographic seizure without clinical manifestations

subcortical
portion of the brain immediately below the cerebral cortex; includes corona radiata, internal capsule, basal ganglia, and thalamus, among others

subcortical leukoencephalopathy
see Binswanger’s disease

subdural hemorrhage
collection of blood in the subdural space following trauma to small bridging veins or in elderly patients with cerebral atrophy or those with clotting abnormalities

subdural space
potential space between the dura and arachnoid that can be filled with blood, cerebrospinal fluid, or pus

subhyaloid hemorrhage
accumulation of blood near the optic disc seen on fundoscopic exam in subarachnoid hemorrhage

subiculum
division of the parahippocampal gyrus adjacent to the hippocampal fissure that is the major source of efferent fibers from the hippocampal formation to rostral structures in the basal forebrain

substantia gelatinosa
narrow, dense, vertical band of gray matter forming the dorsal part of the posterior column of the spinal cord and serving to integrate the sensory stimuli that give rise to the sensations of pain and temperature

substantia nigra
nucleus in the midbrain tegmentum that is divided into the pars compacta, a region of compactly organized dopaminergic cells that innervate the striatum and cerebral cortex, and the pars reticulata, a region containing loosely organized cells that is a pallidal division of the basal ganglia and sends its output to the thalamus and superior colliculus

subthalamic nucleus (subthalamus)
nucleus in the ventral diencephalon that modulates the output of the basal ganglia from the internal segment of the globus pallidus to the thalamus

sulcus
groove in the cerebral cortex separating two gyri

superior cerebellar peduncle (brachium conjunctivum)
principle efferent fiber bundle from the cerebellum; fibers decussate in the midbrain and end primarily in the red nucleus and dorsal thalamus; lesions of the caudal SCP before the decussation result in ipsilateral deficits in motor coordination whereas lesions rostral to the decussation result in contralateral deficits; afferent fibers from the ventral spinocerebellar tract travel in the SCP to bring proprioceptive information from the lower body to the cerebellum

superior colliculus
paired structures on the dorsal surface of the rostral midbrain that receive unconscious visual input directly from the retina and help orient the head and eyes to all types of sensory stimuli

superior sagittal sinus
venous structure occupying the convex margin of the falx cerebri and draining the upper part of the cerebral hemispheres

supranuclear
central connections rostral to the cranial nerve nuclei

suprasellar
above the sella turcica

supratentorial
above the tentorium cerebelli, i.e., cerebral cortex, thalamus, and basal ganglia

suture
junction between two bones of the skull: coronal separates the 2 frontal bones from the parietal bones; metopic separates the frontal bones; sagittal separates the 2 parietal bones; lambdoid separates the occipital bone from the 2 parietal bones

Sylvian fissure (lateral fissure or lateral sulcus)
prominent long, deep fissure on the lateral surface of the cerebral hemisphere that divides the posterior frontal and anterior parietal lobes from the superior temporal lobe

sympathetic nervous system
part of the autonomic nervous system concerned with preparing the body for fear, fight, or flight; preganglionic fibers arise from the lateral horns of the spinal segments T1-L2

symptomatic epilepsy
epilepsy that is due to a known cause (e.g., tumor)

syncope
temporary loss of consciousness due to a lack of blood flow to the brain

syndrome of inappropriate ADH secretion (SIADH)
disorder of osmoregulation involving excessive release of arginine vasopressin (antidiuretic hormone), which causes excessive water retention by the kidney, leading to a dilutional hyponatremia; occurs in a wide range of neurological disorders and other medical conditions

synesthesia
condition associated with involuntary perceptual experiences that are elicited by stimuli that would not be expected to elicit such a response—a crossing of sensory modalities, e.g., experiencing colors in response to numbers, letters, and words

syringobulbia
central cavitation (cystic lesion) within the spinal cord (syringomyelia) that extends up to the medulla and pons

syringomyelia
central cavitation (cystic lesion) of the spinal cord, usually in the cervical region, producing a distinctive cape-like distribution of spinothalamic tract sensory loss while leaving the dorsal columns relatively intact

tardive
symptoms that develop slowly or appear long after inception, e.g., tardive dyskinesia occurring after chronic exposure to dopamine antagonists

tau
microtubule-associated protein that is functionally modulated by phosphorylation and is hyperphosphorylated in several neurodegenerative diseases.

tauopathies
group of neurodegenerative diseases characterized predominantly by abnormalities of tau protein; includes frontotemporal dementia, progressive supranuclear palsy, corticobasal degeneration

teardrop fracture
triangular fracture of the anteroinferior aspect of a vertebral body due to axial loading with flexion or extension; often unstable associated with ligamentous injury and/or spinal cord injury

tectospinal tract
descending pathway from midbrain tectum to spinal inter- and motor neurons that control anti-gravity posture and locomotion and that probably mediate tonic neck reflexes

tectum
dorsal surface of the midbrain that contains the superior and inferior colliculi

tegmentum
floor of the midbrain that contains the substantia nigra and the red nucleus

teichopsia
see fortification spectrum

telencephalon
anterior portion of the prosencephalon, constituting the cerebral hemispheres

temporal lobe epilepsy
partial epilepsy arising from the temporal lobe of the brain

tendon release (tenotomy)
surgical procedure involving division of a severely contracted tendon in the management of spasticity

tension-type headache
nonspecific headache that is typically dull, aching, and bilateral, and is often described as a tightening band-like sensation around the head or neck; may be related to muscle tightening in the back of the neck and/or scalp

tentorium cerebelli
fold of dura mater that covers the cerebellum and supports the occipital lobes of the cerebrum

tetany
repetitive, spontaneous axonal discharges at high rates of up to 300 Hz producing intense muscle spasm in the setting of electrolyte or acid-base disturbance

tethered cord
attachment of the spinal cord to the vertebral column or subcutaneous tissues by a thickened filum terminale, fibrous band, diastematomyelia, dermal sinus tract, or lipoma resulting in a low-lying conus medullaris (i.e., below the L2-3 interspace)

tetraplegia
see quadriplegia

thalamus
large ovoid mass of gray matter in the dorsal aspect of the diencephalon that is located medial to the internal capsule and caudate and functions as a relay station between the cerebral cortex and the brainstem and spinal cord

thunderclap headache
sudden onset of severe head pain with neck stiffness that may be associated with altered consciousness or focal neurological deficits; suggests subarachnoid hemorrhage

tic
repetitive, stereotyped, simple or complex movements that can be voluntarily suppressed for short periods of time (e.g., eye blinking or throat clearing)

tilmus
see floccillation

time-intensity profile
of the temporal features of a patient’s symptoms that provides clues about etiology of the disease process; acute, subacute, recurrent-remittent, or chronic-progressive

tinnitus
sound experienced subjectively with no external source, most commonly ringing, buzzing, or roaring

titubation
tremor of the head and neck

Todd's paralysis
temporary (minutes to hours or rarely days) post-seizure mono- or hemiplegia; indicates seizure was focal onset; sometimes term used for other temporary focal post-seizure deficits, such as aphasia or sensory abnormalities

tolerance
gradual loss of response to a drug with prolonged use

Tolosa-Hunt syndrome
rare painful ophthalmoplegia due to a granulomatous inflammation of the cavernous sinus (paralysis of the third, fourth, and/or sixth cranial nerves) typically relieved by corticosteroids

tomacula
focal area of myelin thickening creating a sausage-like appearance of nerves; common in the genetic neuropathy, Hereditary Liability to Pressure Palsies

tonic-clonic seizure (grand mal seizure)
generalized seizure characterized by initial contraction of the muscles (tonic phase), which may involve tongue biting and urinary incontinence, followed by rhythmic muscle contractions (clonic phase)

tonic neck reflexes
movements and postures of the arm and leg when the neck is bent forwards, backwards, or to the side that are present in normal infants and are incorporated in many bodily movements of normal children and adults

tonic seizure
generalized seizure that involves stiffening of the entire body

tonsilar herniation
herniation of the cerebellar tonsils through the foramen magnum

torsion
see cyclotorsion

torticollis
form of dystonia in which the neck muscles contract involuntarily, causing the head to turn

Tourette syndrome
childhood onset movement disorder characterized by simple or complex tics and often associated with obsessions, compulsions, and attention deficit disorder

transcortical motor aphasia
impairment of language production (non-fluent aphasia) sparing repetition due to a lesion in the anterior extrasylvian region (prefrontal and medial frontal cortex)

transcortical sensory aphasia
impairment of language comprehension (fluent aphasia) sparing repetition due to a lesion in the posterior extrasylvian region (inferior temporo-occipital cortex)

transcutaneous electric nerve stimulation (TENS)
method of pain control involving application of electrical impulses to nerve endings via electrodes that are attached to a stimulator by flexible wires and placed on the skin; thought to block the transmission of pain signals to the brain

transformed migraine
migraine pattern that has changed from episodic to chronic, often related to the overuse of analgesics (medication overuse headache)

transient ischemic attack
abrupt focal loss of neurologic function caused by reduction in blood flow that persists less than 24 hours and clears without residual disability

transtentorial (central) herniation

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

transverse myelitis
inflammatory disease involving both sides of the spinal cord in which motor and sensory deficits occur below the level of the lesion; occurs commonly in multiple sclerosis and various infectious and connective tissue disorders

tremor
involuntary, rhythmic oscillatory movements about a fixed point due to alternating or synchronous contractions of agonist and antagonist muscles; see also action, essential, intention, physiologic, postural, resting, and rubral tremor

trigeminal nerve (cranial nerve V)
mixed sensory and motor nerve made up of ophthalmic, maxillary, and mandibular divisions responsible for sensation from the face, oral and nasal cavities, and supratentorial dura(but not posterior scalp) and motor innervation of the muscles of mastication; sensory fibers originate in the gasserian ganglion and (1) descend to the upper cervical cord in the spinal tract of V then ascend in the trigeminothalamic tract to the thalamus (pain, temperature, touch), (2) enter the main sensory nucleus of V and ascend to the thalamus (tactile and proprioceptive sensation), or (3) enter the mesencephalic nucleus (jaw proprioception)

trochlear nerve (cranial nerve IV)
motor nerve innervating the superior oblique muscle, which depresses and intorts the eye; only cranial nerve to exit dorsally and cross the midline before emerging from the brainstem—thus a lesion of the nucleus (which is in the caudal midbrain) affects the contralateral eye

trigonocephaly
premature closure of the metopic suture producing bowing of the forehead

triple flexion
spinal reflex consisting of flexion at the hip, knee, and ankle in response to stimulation of the sole of the foot; indicates corticospinal tract lesion

truncal sensory level
level on the trunk below which sensation is impaired; sign of spinal cord lesion

two-point discrimination
ability to detect two stimuli presented simultaneously at decreasing distance as being two separate stimuli; for normal tactile two-point discrimination, the two points of calipers or a paperclip should be recognized at a separation of 2-4 mm on the lips and finger pads, 8-15 mm on the palms, and 3-4 cm on the shins

U fibers
short U-shaped white matter tracts that lie just beneath the cerebral cortex and connect adjacent gyri

uncal herniation
displacement of the uncus of the temporal lobe and the hippocampal gyrus towards the midline and over the lateral edge of the tentorium due to an expanding lesion in the lateral middle cranial fossa or temporal lobe; earliest consistent sign is an ipsilateral dilating pupil due to compression of the ipsilateral third cranial nerve

uncus
most anterior part of the parahippocampal gyrus

upper motor neuron
1st order neurons that remain in the CNS and synapse with lower motor neurons; lesions result in spasticity, hyperreflexia/extensor plantar response (upgoing toe)

vacuolar myelopathy
vacuolation of myelin in the posterior and lateral columns of the primarily thoracic spinal cord occurring in AIDS and resulting in paraparesis, sensory ataxia, and incontinence; resembles the myelopathy associated with vitamin B12 deficiency

vagus nerve (cranial nerve X)
nerve containing motor, sensory, and parasympathetic fibers; motor fibers originate from the dorsal motor nucleus of the vagus (to innervate the pharynx and the thoracic and abdominal viscera) and the nucleus ambiguus (to innervate the palate, pharynx, and larynx); sensory fibers originate in the nodose ganglion and mediate taste and sensation in the pharynx and thoracic and abdominal viscera

vascular dementia
dementia with a stepwise deteriorating course and a patchy distribution of neurological deficits caused by cerebrovascular disease; includes multi-infarct dementia and Binswanger’s disease

vasospasm
blood vessel constriction in response to irritative stimuli

vegetative state
subacute or chronic condition following coma and consisting of return to wakefulness but apparent total lack of cognition

ventral
anterior

ventral horn
see anterior horn

ventricles
four cerebrospinal fluid filled cavities (paired lateral, third, and fourth) deep with the brain that communicate with each other and with the central canal of the spinal cord and the subarachnoid space

vergence
movement of the eyes in opposite directions so that images of an object are placed on both foveas and thus appear single

vergence (dysconjugate eye movements)
movement of both eyes in different directions at the same time; includes 2 types: convergence and divergence

vermis
median region of the cerebellum lying between the cerebellar hemispheres

version (conjugate eye movements)
movement of both eyes in the same direction at the same time; includes 4 types: saccade, smooth pursuit, optokinetic nystagmus movements, and vestibulo-ocular response movements

vertebral artery
paired arteries that arise from the subclavian arteries and fuse to form the basilar artery on the ventral surface of the brainstem; supply blood to the lower brainstem and posterior cerebellum.

vertigo
subjective sense of imbalance usually noted as an illusion of moving or spinning of the external world

vestibulocochlear nerve (cranial nerve VIII)
sensory nerve carrying information from the semicircular canals, utricle, and saccule to mediate equilibrium and hearing

vestibulo-ocular response
see oculovestibular response

vestibulospinal tract
descending pathway from vestibular nuclei in the brainstem to spinal inter- and motor neurons that causes contraction of many muscles in the trunk and limbs as the head moves in space, providing automatic anti-gravity control to maintain upright stance

vicariation
process by which adjacent or remote cortex may assume the function previously carried out by damaged cortex

Virchow-Robin Spaces
perivascular extensions of subarachnoid space

visual evoked potentials (VEP)
series of waves that reflect sequential activation of neural structures along the visual pathways following checkerboard stimulation; most useful in screening for optic nerve pathology (e.g., optic neuritis) and less useful in postchiasmatic disorders

Wallenberg syndrome
see lateral medullary syndrome

Wallerian degeneration
stereotyped degenerative reaction of axons and Schwann cells distal to a site of mechanical damage; occurs simultaneously in many of the axons in a fascicle

watershed infarct
infarct occurring in brain tissue that receives blood supply from the distal portions of two major arteries; generally a result of global hypoperfusion

wearing off phenomenon
waning of the effects of a dose of levodopa prior to the scheduled time for the next dose, resulting in decreased motor performance

Weber Syndrome
ipsilateral oculomotor palsy and contralateral hemiplegia due to ventral midbrain lesion affecting the III nerve fascicles and cerebral peduncle

wet keratin
nodules composed of often calcified stacks of keratin characteristic of craniopharyngioma

Wernicke’s aphasia
see fluent aphasia

Wernicke’s encephalopathy
syndrome of confusion/short-term memory loss, ophthalmoplegia (especially abducens palsy), and ataxia due to thiamine deficiency, occurring in the setting of alcoholism, starvation, or protracted vomiting; may progress to coma if untreated; associated with neuronal damage that is most prominent in the mammillary bodies, inferior colliculus, and thalamus

West’s syndrome
epilepsy syndrome characterized by infantile spasms, mental retardation, and hypsarrhythmia on EEG; begins before 1 year of age

white matter
part of the CNS that contains axons

WHO grade
scheme for grading central_nervous_system neoplasms histologically developed by the World Health Organization

1. benign
2. low grade (atypia only)
3. intermediate grade (mitotic activity)
4. high grade malignant (necrosis or endothelial proliferation, typically with atypia and mitosis)

xanthochromia
yellowish discoloration of cerebrospinal fluid resulting from lysis of red blood cells seen ~ 12 hours to 2 weeks after subarachnoid hemorrhage