BRAIN AND BEHAVIOR I
GLOSSARY
Neuroanatomy, Neurophysiology, Neurology
and Behavioral terms
abducens [L. ab, from + ducens, leading] Abducens
(or abducent) nerve supplies the lateral rectus
muscle that moves the direction of gaze away
from the midline.
abulia [Gr. a + C. boule, without will] Lack of
willpower. Refers to a condition associated with
frontal lobe lesions in which the affected
individual is apathetic and slowed in speech and
other motor actions. The profoundly affected
may lie motionless for weeks.
accommodation In ophthalmology, refers to the
ability of the lens to change its shape to allow a
nearby object to be brought into focus on the
retina.
accommodation center Neurons in the tectum of
the rostral midbrain that receive input directly
from the occipital cortex and integrate the
actions of the ciliary, iris, and medial rectus
muscles in order to maintain a focused image on
the retina during near or far vision.
acoustic neuroma Benign tumor arising from
Schwann cells of CN VIII. As the tumor grows
within the internal acoustic meatus it
progressively affects the cochlear, vestibular,
and facial nerves; with further enlargement it
invades the cerebellopontine angle possibly
affecting the cerebellum and other CNs in the
vicinity; synonym neurilemoma or
Schwannoma; cerebellopontine angle tumor.
action potential The rapid reversal of the neuron's
membrane potential and its subsequent recovery.
The action potential is a signal that conveys
information within the nervous system.
acute sympathetic shock syndrome Characterized
by bradycardia, hypotension, bilateral Horner
syndrome; occurs in acute bilateral cervical
spinal cord injuries due to the interruption of the
descending impulses to the intermediolateral cell
column.
adequate stimulus The notion that a stimulus of a
unique energy form is required to activate a
specific receptor modified especially to receive
that form of energy. In fact, receptors can be
activated by a number of different energy forms
but usually have the lowest threshold for only
one type of energy.
affect External (facial) reflection of internal
feelings.
afferent [L. af-ferens, to bring to] In reference to
the CNS, afferent signals are those that approach
the CNS. They bring information to the CNS.
See efferent.
agnosia [a, neg. + Gr. gnosis, knowledge] Lack of
ability to recognize the significance of sensory
stimuli (e.g. auditory, visual, tactile, etc.
agnosia).
agraphia [a, neg. + Gr. grapho, to write] Inability to
express thoughts in writing owing to a central
lesion.
akathisia Subjective feeling of motor restlessness.
akinesia [a, neg. + Gr. kinesis, movement] Lack of
spontaneous movement, as seen in Parkinson's
disease.
alar plate Region of the embryonic nervous system,
dorsal to the sulcus limitans, from which sensory
neurons intrinsic to the CNS develop.
alexia [a, neg. + Gr. lexis, word] Loss of the power
to grasp the meaning of written or printed words
and sentences.
allocortex [Gr. allos, other + L. cortex, bark]
Phylogenetically older cerebral cortex, usually
consisting of three layers. Includes paleocortex
and archicortex.
-motoneuron Neuron located in anterior horn of
spinal cord and in certain brainstem nuclei
whose axon passes directly to extrafusal fibers
of voluntary muscle; synonym lower motor
neuron.
alpha rhythm A brain potential that occurs during
relaxed wakefulness, especially at the back of
the head; its frequency is 8 to 12 Hertz
alternating hemiplegia Combined upper- and lower
motor neuron brainstem lesion affecting
pyramidal tract, which results in contralateral
spastic hemiplegia, and affecting oculomotor,
abducent, or hypoglossal nerve rootlets, which
results in ipsilateral palsies in the respective
nerves.
alveus [L. trough] Thin layer of white matter
covering the ventricular surface of the
hippocampus. The name seems quite
inappropriate but has become an accepted part of
anatomical terminology.
Alzheimer disease Presenile dementia in which
large numbers of neurofibrillary tangles and
neuritic (senile) plaques occur in the cortex. This
disease is associated with neuronal degeneration
in the hippocampus and parahippocampal gyrus
and decreased cortical levels of choline acetyl
transferase due to degeneration of neurons in
such basal forebrain structures as the basal
nucleus of Meynert and the diagonal band
nuclei.
amacrine cell Local circuit neuron in the internal
nuclear layer of the retina that influences
synaptic transmission between the bipolar and
the ganglion cells.
ambiguus [L. changeable or doubtful] Nucleus
ambiguus occupies an atypically ventral position
for a cranial nerve nucleus, and its limits are
somewhat indistinct.
Ammon's horn Hippocampus, which has an outline
in cross section suggestive of a ram's horn. Also
known as the cornu Ammonis. Ammon was an
Egyptian deity with a ram's head.
amnesia Severe impairment of memory.
amotivational syndrome Lack of drive to advance
in life, often attributable to use of drugs of
abuse.
ampullary crest [L. crista = crest + ampulla = a jug]
Sensory organ of kinetic equilibrium occurring
as an elevation on the inner aspect of the
membranous ampulla of each semicircular duct.
amygdala [Gr. almond] collection of nuclei within
and deep to the uncus of the temporal lobe,
forming an important behavior and emotions
center of the limbic system; synonym
amygdaloid nucleus.
anaclitic depression Apathy, poor growth, and
social withdrawal in a child due to failure of
normal parent-child bonding.
analgesia [Gr. insensibility] Relief of pain without
loss of consciousness.
anandamide An endogenous substance that binds
to the cannabinoid receptor.
anesthesia Loss of sensation as a result of
pharmacologic depression of nerve function or
of neurologic disease.
aneurysm [Gr. aneurysma wide] A weakness in the
arterial wall that causes the artery to widen. A
dissecting aneurysm is one in which the layers
of the artery separate. A berry aneurysm is a
small, balloon-like dilatation in the artery that
communicates with the main branch by means of
a narrow passage, making the aneurysm look
like a berry during angiography.
anhydrosis [Gr. an = without + hidros = sweat]
Absence of sweating.
annulospiral stretch receptor Afferent nerve
ending, located at central portion of a muscle
spindle, which responds to muscle stretch.
anomia The inability to readily name persons or
objects.
anopsia [an, neg. + Gr. opsis, vision] Defect of
vision.
anosmia [Gr. an + osmesis.= sense of smell]
Absence of sense of smell.
anterior commissure Complex fiber system
crossing midline in lamina terminalis;
interconnects middle and inferior temporal gyri,
olfactory bulbs, amygdalae, and other nuclei.
anterior limb of internal capsule That part of the
internal capsule between the head of the caudate
nucleus medially and the lentiform nucleus
laterally.
anterior lobe syndrome Cerebellar disorder
characterized by loss of coordination initially in
the lower limbs (gait ataxia) frequently as a
result of Purkinje cell degeneration due to
chronic alcoholism.
anterior perforated substance Region behind
orbital surface of frontal lobe and medial and
lateral olfactory striae, through which numerous
small arteries reach internal structures.
anterograde axonal transport Passage from the
neuronal cell body; two rates occur-. (1) fast
transport, 400 mm/day; requires neurotubules;
membranous organelles, synaptic vesicles, and
their precursors are carried this way; (2) slow
transport, several millimeters per day; carries
entire cytoskeleton and non- packaged
macromolecules.
anterolateral cordotomy Surgical sectioning of
anterolateral quadrant of spinal cord for relief of
chronic pain
anterolateral quadrant Area of spinal white matter
between attachment of dentate ligaments and
emergence of anterior roots; the spinothalamic
tract is located here.
antidiuretic hormone (ADH) Hormone produced
by neurosecretory cells in the supraoptic and
paraventricular nuclei of the hypothalamus that
stimulates water reabsorption from kidney.
anxiety states A class of psychiatric disorders that
include recurrent panic states, generalized
persistent anxiety disorders, and posttraumatic
stress disorders.
anxiolytics A class of substances that are used to
combat anxiety; examples include opiates,
barbiturates, and benzodiazepines.
aphasia [a, neg. + Gr. phasis, speech] Defect of the
power of expression by speech or of
comprehending spoken or written language.
apraxia [Gr. a + pratto = to do] Inability to carry out
a voluntary movement in the absence of
paralysis, sensory loss, and ataxia.
archicortex [Gr. arche, beginning + L. cortex, bark]
Three-layered cortex included in the limbic
system; located mainly in the hippocampus and
dentate gyrus of the temporal lobe. Also spelled
archeocortex.
arachnoid [Gr. spider] Middle of three membranes
covering the central nervous system (CNS).
arachnoid granulations Groups of arachnoid villi,
found predominantly in lacunae of the superior
sagittal sinus, through which cerebrospinal fluid
(CSF) is absorbed into the venous system;
synonym arachnoid villi.
archicerebellum [Gr. archi = beginning] Oldest part
of cerebellum; the flocculonodular lobe or
vestibulocerebellum located inferiorly, anterior
to the posterolateral fissure.
arcuate fasciculus Large association bundle
connecting the inferior and middle frontal gyri
with the superior temporal gyrus; sometimes
also considered to include the superior
longitudinal fasciculus.
arcuate fibers Short association fibers that lie
immediately beneath the cortex adjacent to a
cerebral sulcus and connect adjacent gyri;
synonym U-fibers.
area postrema. Area in the caudal part of the floor
of the fourth ventricle.
arteriovenous malformation (AVM) An
inappropriate anastomosis between an artery and
vein without an intervening capillary bed.
ascending reticular activating system (ARAS)
Components of the brainstem reticular formation
that project to parts of the thalamus and
subthalamus and pace the activity of the cerebral
cortex; if interrupted at the midbrain, coma
results; associated with the sleep-wake cycle;
sleep centers in the pons, medulla, and
hypothalamus project to the ARAS to turn it off
to induce sleep; synonym reticular activating
system.
associative learning A type of learning in which an
association is formed between two stimuli or
between a stimulus and a response; includes
both classical and instrumental conditioning.
astereognosis [Gr. a + stereos = solid + gnosis,
knowledge] Inability to identify an object by
touch; synonym tactile amnesia.
astrocyte [Gr. astron = star] Star-shaped neuroglial
cell with cytoplasmic processes whose terminal
expansions or "end-feet" ensheath blood vessels
and the surfaces of the brain and spinal cord.
asynergy [a, neg. + Gr. syn, with + ergon, work]
Disturbance of the proper association in the
contraction of muscles that ensures that the
different components of an act follow in proper
sequence, at the proper moment, and of the
proper degree, so that the act is executed
accurately.
atamia [Gr. a + taxis = order] Loss of muscular
coordination.
ataxia [a, neg. + Gr. taxis, order] Loss of power of
muscle coordination, with irregularity of muscle
action.
atheroma [Gr. athere, porridge] Thickening of the
lining of an artery caused by deposition of lipid
material.
atherothrombotic infarction An infarct caused by
an arterial thrombosis. See infarct; thrombosis.
athetosis [Gr. athetos = without position or place]
Disorder of movement involving slow writhing
movements of the limbs, particularly the fingers
and hands; associated with basal ganglia
disorders.
atresia [a, neg. + Gr. tresis, perforation] Absence of
a passage caused by an error in development.
atrophy [Gr. a, without + Gr. trophe, nourishment]
In neurology, a wasting away of muscle mass.
Atrophy of disuse follows immobilization and is
relatively minor. Denervation atrophy is
profound and is an important clinical sign of
lower motor neuron disease.
auditory ossicles The small bones of the middle earmalleus, incus, and stapes-articulated to form a
chain for the transmission of sound-induced
vibrations from the tympanic membrane to the
oval window.
auditory radiation Fibers carrying auditory
impulses from the medial geniculate nucleus via
the sublenticular part of the internal capsule to
the transverse temporal gyri of Heschl.
autism A disorder arising during childhood,
characterized by social withdrawal and
stereotypy.
automatic reflex bladder Incontinence and
retention; occurs after spinal cord lesions above
sacral levels.
autonomic [Gr. autos, self + nomos, law]
Autonomic system; the efferent or motor
innervation of viscera.
autonomic plexus ganglion Sympathetic neurons
located in plexuses along abdominal aorta and
its branches; synonym prevertebral or collateral
ganglion.
AVM See arteriovenous malformation.
axolemma [Gr. axon, axis + lemma, husk] Plasma
membrane of an axon.
axon Nerve cell process conducting impulses away
from neuronal cell body.
axon hillock Region of the nerve cell body from
which the axon arises; it contains no Nissl
material.
axon reaction Changes in the cell body of a neuron
after damage to its axon.
axonotmesis:
- is more severe injury, with disruption of
axons & surrounding endoneurial sheaths;
- perineurium and epineurimum remain
intact;
- Wallerian degeneration occurs;
- after axonotmesis, conduction velocity
may be preserved distally for up to 7 days;
- recovery is good but may require many
months;
axoplasm [Gr. axon, axis + plasm, anything formed
or molded] Cytoplasm of the axon.
Babinski response Abnormal upward extension
(dorsiflexion) of great toe in response to stroking
outer border of the sole; usually indicates
pyramidal tract damage; synonym-extensor
plantar reflex or response.
BAER See brainstem, auditory evoked response.
ballismus [Gr. ballismos = a jumping about] Violent
jerking or flinging movements of proximal parts
of limbs and shoulders and pelvic girdle
musculature; associated with lesions of the
subthalamic nucleus.
baroreceptor [Gr. baros, weight + receptor,
receiver] Sensory nerve terminal that is
stimulated by changes in pressure, as in the
carotid sinus and aortic arch.
basal nucleus (of Meynert) Extensive group of
neurons located in the substantia innominata of
the anterior perforated substance; major source
of cholinergic projections to neocortex and
implicated in Alzheimer disease.
basal plate Portion of the embryonic nervous
system, ventral to the sulcus limitans, from
which efferent neurons develop. See alar plate.
basilar membrane Membrane supporting the organ
of Corti; stretches between the osseous spiral
lamina and spiral ligament; synonym
membranous spiral lamina.
basis pedunculi Ventral part of the cerebral
peduncle of the midbrain on each side, separated
from the dorsal part by the substantia nigra. Also
called the crus cerebri.
basket cell Inhibitory neuron found deep in
molecular layer of cerebellar cortex, whose axon
forms a basket-like ramification around the base
of a Purkinje cell body.
Bell's palsy Weakness of upper and lower facial
muscles and inability to close the eye
completely; usually caused by inflammation of
facial nerve in the facial canal.
bilaminar disc In embryology, refers to the
embryoblast during early phase of gastrulation
when it consists of two layers, the epiblast and
the hypoblast.
bitemporal hemianopsia Loss of temporal field
vision in both eyes; results from median lesion
of optic chiasm.
blind spot Area in the retina at the origin of the
optic nerve in which there are no photoreceptor
cells.
blood-brain barrier Permeability control system
governing the passage of substances between
capillaries and the CNS parenchyma; partially
related to such morphologic features as tight
junctions between endothelial cells and
perivascular astrocytic end-feet.
bone conduction Sound vibrations conducted to the
internal ear by the temporal bone.
bony labyrinth Series of cavities within the petrous
portion of the temporal bone forming the
vestibule, cochlea,, and semicircular canals of
the inner car; synonym osseous labyrinth.
brachium [L. from Gr. brachion, arm] As used in
the central nervous system, denotes a large
bundle of fibers that connects one part with
another (eg, brachia associated with the colliculi
of the midbrain).
brachium conjunctivum Synonym for the superior
cerebellar peduncle.
brachium pontis Synonym for the middle cerebellar
peduncle.
bradycardia Slowness of the heart beat, usually
defined as a rate under 60 beats per minute.
bradykinesia [Gr. brady, slow + kinesis, movement]
Abnormal slowness of movements.
brainstem auditory evoked response (BAER) A
sensory evoked potential elicited by auditory
stimuli. The response provides information
about the integrity of the auditory brainstem
nuclei.
Broca's area Opercular and triangular parts of
inferior frontal gyrus in dominant hemisphere;
associated with motor programs for production
of words; nonfluent (motor or expressive)
aphasia is attributed to its injury,
Brodmann numerical areas Numerical
subdivisions of the cerebral cortex, originally
based on cytoarchitectural characteristics but
now related to functions.
Brown-Séquard syndrome Hemisection of the
spinal cord; causes ipsilateral spastic paralysis
and loss of touch, pressure, and position sense
and contralateral loss of pain and temperature
sensations below the level of the lesion.
bulb Referred at one time to the medulla oblongata,
but in the context of "corticobulbar tract," refers
to the brain stem, in which motor nuclei of
cranial nerves are located.
bulimia A syndrome in which individuals believe
themselves fatter than they are and periodically
gorge themselves, usually with "junk food," and
then either vomit or take laxatives to avoid
weight gain. Also called bulimia nervosa.
capsular cell Supporting cells surrounding the cell
bodies of dorsal root and autonomic ganglion
cells. synonym satellite cells.
carotid plexuses Postganglionic sympathetic fibers
traveling along carotid arteries to smooth muscle
and glands of head.
carotid siphon Hairpin bend formed by internal
carotid artery within the petrous canal and
cavernous sinus.
carpal tunnel syndrome Paresthesias in the hand,
particularly within the distribution of the median
nerve, caused by compression of that nerve by
the flexor retinaculum.
cauda equina [L. cauda = tail + equus = horse]
Roots of lumbosacral nerves as they travel in the
vertebral canal below the spinal cord to their
respective lumbar intervertebral or sacral
foramina.
caudate nucleus Part of the corpus striatum, so
named because it has a long extension or tail.
cerebellar angle Area on ventrolateral surface of
brainstem where cerebellum, pons, and medulla
meet; VII, VIII, and IX CN attach at this point.
cerebellar peduncle Fiber bundles connecting the
cerebellum to the brainstem.
cerebellum [L. diminutive of cerebrum, brain]
Large part of the brain with motor functions
situated in the posterior cranial fossa.
cerebral aqueduct Midbrain channel connecting
third and fourth ventricles; synonym aqueduct of
Sylvius.
cerebral arterial circle Arterial ring found on base
of brain and formed by branches of the internal
carotid and basilar arteries; connects the anterior
and posterior circulations; synonym circle of
Willis.
cerebral crus Ventral part of cerebral peduncle of
midbrain; contains corticospinal and
corticobulbar fibers in its middle part and
corticopontine in its medial and lateral parts.
cerebral edema Brain swelling due to increased
uptake of water in the neuropil and white matter.
cerebral embolism The passage of a blood clot
from a remote structure such as the heart into the
vasculature of the brain, causing infarction.
cerebral hemorrhage Arterial bleeding into
cerebral tissue or the subarachnoid space. Not to
be confused with a contusion or bleeding into
the epidural space.
cerebral ischemia Decreased blood supply in the
brain.
cerebral peduncle Ventral part of midbrain that
connects the forebrain to the hindbrain and
consists of the cerebral crus, substantia nigra,
and tegmentum.
cerebrocerebellum Posterior lobe of the cerebellum
having strong connections with the cerebrum;
synonym neocerebellum.
cerebrospinal fluid (CSF) Clear, colorless liquid
secreted by the choroid plexuses and found in
the ventricular system and subarachnoid space;
total volume is approximately 150 mL; rate of
formation is approximately 500 mL/day.
cerebrum [L. brain] Principal portion of the brain,
including the diencephalon and cerebral
hemispheres, but not the brainstem and
cerebellum.
chlorpromazine An antipsychotic drug, one of the
class of phenothiazines.
chordotomy [Gr. chorde, cord + tome, a cutting]
Division of the spinothalamic and spinoreticular
tracts for intractable pain (tractotomy). Also
spelled cordotomy.
chorea [Gr. dance] Jerky, spasmodic involuntary
movements of limbs or facial muscles;
associated with lesions of the caudate nucleus
and putamen.
choroid [Gr. chorion, a delicate membrane + eidos,
form] Choroid or vascular coat of the eye;
choroid plexuses in the ventricles of the brain.
choroid plexus Epithelium and blood vessels of the
lateral, third, and fourth ventricles; secretes CSF.
chromatolysis [Gr. chroma, color + lysis, dissolution] Dispersal of the Nissl material of
neurons after axon section or in viral infections
of the nervous system.
ciliospinal center Neurons in the upper one or two
thoracic segments giving rise to sympathetic
preganglionic fibers that convey impulses to the
superior cervical ganglion from whence
postganglionic sympathetic fibers elicit pupillary
dilation.
ciliospinal reflex Dilation of pupils in response to
pain usually elicited by stroking the side of the
head or neck; dependent on intact path that
includes descending central autonomic path,
ciliospinal center neurons, and their
preganglionic sympathetic fibers, which ascend
in the cervical sympathetic trunk, and includes
superior cervical ganglion cells whose postganglionic fibers reach the dilator muscle of the
iris.
cinereum L. [cinereum, ashen-hued, from cinis, ash]
Refers to gray matter, but limited in usage.
Tuber cinereum (ventral portion of the
hypothalamus, from which the neurohypophysis
arises); tuberculum cinereum (slight elevation on
medulla formed by spinal tract and nucleus of
trigeminal nerve); ala cinerea (vagal triangle in
floor of fourth ventricle).
cingulum [L. girdle] a large association bundle
passing longitudinally in the white matter of the
cingulate gyrus; connects frontal, parietal, and
occipital lobes with parahippocampal gyrus and
adjacent temporal cortex.
circadian rhythm Biologic activity (such as sleep)
that occurs in approximately 24-hour periods or
cycles; the "clock" resides in the
suprachiasmatic nucleus of the hypothalamus.
circle of Willis Arterial ring found on base of brain
and formed by branches of the internal carotid
and basilar arteries; synonym cerebral arterial
circle.
circumventricular organs Highly vascularized
areas with fenestrated capillaries; found chiefly
in the diencephalon and lacking the blood-brain
barrier.
Clarke's column Synonym for nucleus dorsalis of
the spinal cord.
clasp-knife response Sudden relaxation or decrease
in resistance to passive stretch of a limb after
initial increased resistance; involves Golgi
tendon organ (lb) activity and is seen in
pyramidal tract damage.
classical conditioning A type of associative
learning in which an originally neutral stimulus
(the conditioned stimulus, or CS)-through
pairing with another stimulus that elicits a
particular response (the unconditioned stimulus,
or US)-acquires the power to elicit that response
when presented alone. Also called Pavlovian
conditioning.
claustrum. [L. a barrier] Thin sheet of gray matter
of unknown function situated between the
lentiform nucleus and the insula.
climbing fibers Axons arising from the contralateral
inferior olivary nucleus and carrying excitatory
impulses to the Purkinje neurons of the
cerebellar cortex; collaterals also excite
cerebellar nuclei.
clonus Series of alternating contractions and
relaxations of flexors and extensors produced by
passive stretch of a limb; seen in pyramidal tract
damage.
clozapine An antipsychotic drug.
cocaine A drug of abuse, derived from the coca
plant, that acts by potentiating catecholamine
stimulation.
cochlea [L. snail shell] Spiral part of internal ear
concerned with audition; located in anterior part
of labyrinth in petrous part of temporal bone.
cognitive map A mental representation of a spatial
relationship.
cogwheel rigidity Type of rigidity in which passive
movements exhibit intermittent resistance as if
cogwheels were moving on one another; a
manifestation of tremor superimposed on
rigidity, frequently seen in Parkinsonism.
colliculus [L. Small elevation or mound] Superior
and inferior colliculi composing the tectum of
the midbrain; facial colliculus in the floor of the
fourth ventricle.
command neuron A higher-level nerve cell that can
selectively activate specific behaviors such as
walking.
commissural syndrome Loss of pain and
temperature bilaterally, due to lesion of ventral
white commissure of spinal cord.
commissure [L. a joining together] Bundle of nerve
fibers that passes from one side to the other in
the brain or spinal cord. Strictly, this term
should be applied to tracts that connect
symmetrical structures (cf. decussation).
communicating hydrocephalus Disruption of CSF
flow outside the ventricular system, usually in
the cisterns, subarachnoid space, or arachnoid
villi.
conduction aphasia Associative aphasia; a form of
aphasia in which the patient can speak and write
in a way, but slops or repeats words or
substitutes; associated with lesions in arcuate
fasciculus.
conduction deafness Incomplete deafness due to
interference with passage of sound waves
through the external ear or sound-induced
vibrations through the middle ear.
confabulate To fill a gap in memory with
falsification, often seen in Korsakoff's syndrome
confusion In medicine, the state of decreased
cerebral cortical function in which the patient is
not entirely oriented to time and place, even
though he is conscious and aware.
conjugate eye movements Coordinated movements
of both eyes.
consensual light reflex Pupillary constriction of one
eye in response to light reaching the retina of the
other eye; dependent on intact optic nerve
ipsilaterally and oculomotor nerve
contralaterally.
contracture Persistent shortening, as in a muscle
paralyzed for a long time. Dupuytren's
contracture.
contralateral [L. contra, opposite + lateris of a side]
Of the other (left or right) side of the body.
Opposite of "ipsilateral."
contusion [L. contusion a bruising] A bruise of the
brain tissue resulting from a severe blow to the
head, but that has not caused cerebral
hemorrhage.
corneal reflex Closure of the eye on stimulation of
the cornea; dependent on afferent impulses in
ophthalmic division of trigeminal nerve and
spinal trigeminal tract and efferent impulses
through facial nucleus and nerve.
cornu [L. horn] See Ammon's horn. Horns of the
lateral ventricle and of the spinal gray matter
also are formally named as cornua.
corona [L. from Gr. korone,, a crown] Corona
radiata fibers radiating from the internal capsule
to various parts of the cerebral cortex.
corona radiata [L. corona = crown] Fibers fanning
out from the internal capsule to the cortex.
corpus callosum [L. body + callosus, hard] Main
neocortical commissure of the cerebral
hemispheres.
corpus luteum [L. body + luteum, yellow]
Progesterone-secreting endocrine tissue that
forms in the ovary after ovulation.
corpus striatum caudate and lentiform nuclei.
cortex [L. bark] Outer layer of gray matter of the
cerebral hemispheres and cerebellum.
cortical columns Neurons in cerebral cortex
oriented perpendicular to six layers of cortex;
make up the vertical functional units of the
cortex.
corticofugal fibers Axons carrying impulses away
from the cortex.
corticopetal fibers Axons carrying impulses toward
the cortex.
cough reflex Coughing response elicited by
irritation of larynx or tracheobronchial tree;
dependent on intact afferent fibers in vagus
nerve,
counter-transference Physician's tendency to
endow patients with characteristics of important
people in the physician's life.
crus [L. leg] Crus cerebri is the ventral part of the
cerebral peduncle of the midbrain on each side,
separated from the dorsal part by the substantia
nigra. Also called the basis pedunculi. Crus of
the fornix.
cuneus [L. wedge] Gyrus on the medial surface of
the cerebral hemisphere. Fasciculus cuneatus in
the spinal cord and medulla; nucleus cuneatus in
the medulla.
cupula of ampullary crest [L. domeshaped cup.;
cupa = a tub] The gelatinous substance lying
over the hair cells of the ampullary crest.
decerebrate posturing Describes one whose brain
has been injured between the vestibular nuclei
and the red nucleus; characterized by extension
of upper and lower limbs.
declarative memory A memory that can be stated
or described.
decorticate posturing Describes one whose brain
has been injured above the red nucleus;
characterized by extension of lower limbs and
flexion of upper limbs.
decussation. [L. decussatio, from decussis, the
numeral X] Point of crossing of paired tracts.
Decussations of the pyramids, medial lemnisci,
and superior cerebellar peduncles are examples.
A decussation connects asymmetrical parts of
the nervous system.
delirium Significant clouding of consciousness.
dementia The loss of cognitive capabilities without
objective loss of sensory or motor functions.
dendrite [Gr. dendron = tree] A branching neuronal
protoplasmic process carrying impulses to the
cell body.
dendritic spine Cytoplasmic bud on surface of a
dendrite for synaptic contact.
dentate [L. dentatus, toothed] Dentate nucleus of the
cerebellum; dentate gyrus in the temporal lobe.
dentate ligament Fibrous sheath attached medially
to the pia at the lateral surface of the spinal cord,
midway between the dorsal and ventral roots;
anchors the spinal cord to the dura mater by its
lateral serrated part consisting of 21 tooth-like
processes. synonym denticulate ligament.
depersonalization Feeling of separateness from the
social situation.
depression Subjective feeling of sadness not
necessarily caused by specific loss.
derailment or loose associations Shift of ideas
from one to the other in an unrelated fashion.
dermatome [Gr. derma = skin + tome = a cutting]
An area of skin supplied by one spinal nerve and
its ganglion.
detrusor muscle Muscle in the wall of the urinary
bladder.
diabetes insipidus Condition caused by
hyposecretion of ADH and characterized by
thirst and the excretion of large amounts of
urine.
diaphragma sellae Dural fold covering the pituitary
gland; extends across sella turcica.
diencephalon [Gr. dia, through + enkephalos, brain]
Part of the cerebrum, consisting of the thalamus,
epithalamus, subthalamus, and hypothalamus.
The posterior of the two brain vesicles formed
from the prosencephalon of the developing
embryo.
diplopia [Gr. diploos, double + ops, eye] Double
vision.
direct light reflex Pupillary constriction in one eye
in response to increased light reaching the retina
,of the same eye; dependent on intact ipsilateral
optic and oculomotor nerves.
disc edema Edema of the optic disk, may be due to
raised intracranial pressure; synonym
papilledema, choked disc.
disorientation Loss of bearing in person, place, or
time.
doll's eye movements Turning of the eyes in the
direction opposite to that of rotation of the head;
signifies intact vestibulo-ocular reflex in
comatose patient; synonym oculocephalic reflex.
dominant hemisphere The hemisphere responsible
for speech, usually the left.
dorsal rhizotomy Section of the dorsal roots of
spinal nerves for the relief of pain or spasticity.
dorsal root entry zone (DREZ) Area in spinal cord
where the dorsal roots attach, just external to
dorsal horn; DREZ lesions are surgical
procedures to abolish chronic deafferentation
pain.
dorsal root ganglion Groups of unipolar afferent
neurons in the dorsal root of each spinal nerve;
synonym spinal ganglion.
dorsolateral fasciculus Spinal cord tract located
between the posterior horn and the posterolateral
sulcus; composed of short ascending and
descending branches of dorsal root fibers
carrying pain and thermal impulses and axons of
substantia gelatinosa neurons; synonym tract of
Lissauer.
Down syndrome Mongolism; trisomy 21 syndrome;
a syndrome of mental retardation associated
with a variable constellation of abnormalities
caused by representation of at least a critical
portion of chromosome 21 three times instead of
twice in some or all cells.
dura mater [L. dura = hard + mater = mother] The
thick outer layer of the meninges.
dural sac Continuation of dura mater from L2-S2
containing CSF and the cauda equina.
dural sinus Valveless, venous channel found in
dural attachments and folds.
dysarthria The inability to articulate speech due to
lack of coordination, spasticity or weakness of
the muscles of speech.
dysdiadochokinesia [Gr. dys + diadochos =
succeeding + kinesis = movement] A cerebellar
disorder manifested by difficulty in rapidly
alternating diametrically opposite movements,
e.g., pronation and supination.
dyskinesia [Gr. dys + kinesis] Disorder of voluntary
movement frequently associated with basal
ganglia disease.
dysmetria [Gr. dys + metron = measure] A
cerebellar disorder manifested by difficulty in
controlling the range and force of movement.
dysphagia [Gr. dys + phagein = to eat] Difficulty in
swallowing.
dysphasia [Gr. dys + phasis = speech] Impairment
of speech, characterized by a lack of
coordination and failure to arrange words in
proper order.
dystonia [Gr. dys, bad + Gr. tonos, tension] A
condition in which a set of antagonistic muscles
are involuntarily kept in prolonged isometric
contraction.
echolalia Repeating another person's words over and
over.
ectoderm. [Gr. ektos, outside + derma, skin] Most
dorsal layer of cells of the early embryo, which
gives rise to the epidermis, neural tube, neural
crest, etc.
edema (oedema) [Gr. oidema, swelling] Abnormal
accumulation of fluid in a tissue.
efferent [L. efferens, to bring out] In reference to the
central nervous system, efferent refers to signals
that evade (i.e., leave) the CNS. Efferent fibers
are axons that convey information away from
the CNS. See afferent.
emboliform [Gr. embolos, plug + L. forma, form]
Emboliform nucleus of the cerebellum.
embolus [Gr. embolos, plug] Fragment of a
thrombus that breaks loose and eventually
obstructs an artery.
emotion Internal psychological state.
endogenous opioids Neuroactive peptides produced
by the body that bind to the same receptors in
the brain that bind morphine.
endolymph Fluid of the membranous labyrinth of
the inner ear.
endoneurium [Gr. endon, within + neuron, nerve]
Delicate connective tissue sheath surrounding an
individual nerve fiber of a peripheral nerve. Also
called the sheath of Henle.
engram [Gr. en, in + gramma, mark] Used in
psychology to mean the lasting trace left in the
brain by previous experience; a latent memory
picture.
entorhinal [Gr. entos, within + rhis (rhin-), nose]
Entorhinal area is the anterior part of the
parahippocampal gyrus of the temporal lobe
adjacent to the uncus. It is included in the lateral
olfactory area.
entorhinal area Part of the parahippocampal gyrus
immediately posterior to the uncus; area 2 8.
ependyma [Gr. epi = upon + endyma = garment]
epithelium lining the central canal of the spinal
cord and the ventricles of the brain.
epidural space Area external to dura; potential
space in cranium, actual space in spinal cord.
epilepsy A chronic disorder of the central nervous
system characterized by seizures that occur
periodically.
epineurium [Gr. epi, upon + neuron, nerve]
Connective tissue sheath surrounding a
peripheral nerve.
epithalamus [Gr. epi, upon + thalamos, inner
chamber] Region of the diencephalon above the
thalamus; includes the pineal gland.
EPSP See excitatory postsynaptic potential.
esotropia [Gr. eso = inward + trope = turn] Inward
deviation of the eye; frequently caused by
abducent nerve lesion; synonym convergent or
internal strabismus.
euphony [Gr. eu, well + phone, sound] Agreeable
sound or easy pronunciation.
euphoria Strong feelings of elation.
euthymia Normal mood.
excitatory postsynaptic potential (EPSP) A
hypopolarizing postsynaptic potential.
expressive aphasia See non fluent aphasia.
extensor plantar response Abnormal upward
extension of great toe in response to stroking
outer border of the sole; indicates pyramidal
tract damage; synonym Babinski reflex.
exteroceptor [L. exterus, external + receptor,
receiver] Sensory receptor that serves to
acquaint the individual with his or her
environment (exteroception).
extrafusal muscle fibers Large skeletal muscle
fibers that produce muscular contraction and are
innervated by -motoneurons; to be
distinguished from intrafusal muscle fibers
within muscle spindles, which are innervated by
-motoneurons.
extrapyramidal system Vague and confusing term
applied to motor parts of the central nervous
system other than the pyramidal motor system.
falx [L. sickle] Two of the dural partitions in the
cranial cavity are the falx cerebri and the small
falx cerebelli.
falx cerebelli Dural fold lying between the
cerebellar hemispheres.
falx cerebri Dural fold lying between the cerebral
hemispheres.
fasciculations [L. fascis, bundle] An involuntary
twitching of a motor unit, frequently but not
always the result of muscle denervation.
fasciculus [L. fascis = bundle] A bundle of nerve
fibers within the CNS.
fasciculus retroflexus See habenulointerpeduncular
tract.
fastigial [L. fastigium, the top of a gabled roof]
Fastigial nucleus of the cerebellum.
fast pain Sharp, pricking pain that is well localized.
fenestra [L. window. A hole] Fenestra rotunda
(round) and fenestra ovale (oval) are between
the middle and inner ear. Capillary blood vessels
are fenestrated when their endothelial cells have
pores, each closed by a diaphragm that does not
prevent the egress of large molecules.
fimbria [L. fringe] Longitudinal band of fibers
coming from the alveus of hippocampus and
continuing as the fornix.
final common pathway Term used for the motoneurons through which are funneled all
impulses from multiple sources to the skeletal
muscles; only connections between CNS and
extrafusal muscle fibers.
fissure of Sylvius Deep groove on lateral surface of
cerebral hemisphere; separates temporal lobe
below from frontal and parietal lobes above;
synonym lateral fissure.
fistula [L. pipe] Abnormal communication between
two cavities or between a cavity and the surface
of the body. In an arteriovenous fistula, blood is
shunted directly from an artery into a vein or
venous sinus.
fixation point Point on which vision is focused.
flaccid paralysis Muscle paralysis with
hypotonicity; the cardinal sign of a lower motor
neuron lesion.
flat affect Complete or almost complete lack of
external emotional responsiveness.
flight of ideas One thought follows another in quick
succession, not necessarily logically.
flocculonodular lobe syndrome Disorder
characterized by instability of the trunk (truncal
ataxia) usually due to tumors near the midline of
the vestibulocerebellum; synonym
vestibulocerebellar midline syndrome.
fluent aphasia Type of language disorder in which
words are formed rapidly but they do not make
sense because of the loss of ability to
comprehend spoken or written words; associated
with lesion of Wernicke's area; synonym sensory
or receptive aphasia.
folium [L. a leaf] One of the folds of the cerebellar
surface.
foramen of Luschka See lateral aperture of the
fourth ventricle.
foramen of Magendie See median aperture of the
fourth ventricle.
foramen of Monro Opening between third ventricle
and lateral ventricle; synonym interventricular
foramen.
fornix [L. arch] Bundle of fibers continuous with
fimbria of hippocampus that is the main output
of the hippocampal formation; runs in the free
margin of the septum pellucidum and divides at
the anterior commissure into a small
precommissural bundle (from the hippocampus
proper) and a larger postcommissural bundle
(from the subiculum), which end in the anterior
hypothalamus and mamillary body, respectively.
fovea centralis Depression in the center of the
macula lutea of the retina caused by
displacement of the inner layers; contains only
cones and is the area of most acute vision.
foveola Minute pit in the center of the fovea
centralis.
frontal eye field Brodmann area 8 of the cerebral
cortex located mainly in the posterior part of the
middle frontal gyrus and concerned with
voluntary eye movements.
fundus [L. bottom] Rounded interior of a hollow
organ. The ocular fundus is lined by the retina,
with its blood vessels, the optic disk, and other
landmarks visible through an ophthalmoscope.
funiculus. [L. diminutive of funis, cord] Area of
white matter that may consist of several
functionally different fasciculi, as in the lateral
funiculus of white matter of the spinal cord.
fusiform L. fusus, spindle + forma, shape. Widest in
the middle and tapering at both ends
GABA -aminobutyric acid, an inhibitory
neurotransmitter.
gag reflex Contraction of pharyngeal muscles on
stimulation of the lateral part of the oral
pharynx; dependent on intact afferent fibers in
glossopharyngeal nerve and efferent fibers in
vagus nerve.
gait ataxia Ataxia affecting the muscles of the lower
limbs.
-loop Three-neuron reflex arc, consisting of a ,motoneuron and its fusimotor axon, which
causes intrafusal muscle fibers to contract; an la
afferent fiber and its dorsal root ganglion cell;
and an -motoneuron and its motor end-plates,
which cause extrafusal muscle fibers to contract.
Allows for initiation or influence of movements
and tone by -motoneurons.
-motor neuron Neurons located in same places as
-motoneurons but which innervate intrafusal
muscle fibers; maintain muscle spindle
sensitivity.
ganglion [Gr. knot or subcutaneous tumor] Swelling
composed of nerve cells, as in cerebrospinal and
sympathetic ganglia. Also used inappropriately
for certain regions of gray matter in the brain
(e.g., basal ganglia of the cerebral hemisphere).
gemmule [L. gemmula, diminutive of gemina, bud]
Minute projections on dendrites of certain
neurons, especially pyramidal cells and Purkinje
cells, for synaptic contact with other neurons.
genu [L. genu, knee] Anterior end of corpus
callosum; genu of facial nerve. Also geniculate
ganglion of facial nerve and geniculate bodies of
thalamus.
genu of internal capsule That part of the internal
capsule between the posterior part of the head of
the caudate nucleus and anterior part of the
thalamus medially and the lentiform nucleus
laterally.
Gilles de la Tourette syndrome A neurological
disorder characterized by involuntary tics and
repetitive compulsive behavior, often including
involuntary cursing (coprolalia). Thought to be a
hereditary disorder carried by an autosomal
dominant gene with variable penetrance, it is
associated with abnormally low levels of
dynorphin and defective dopamine uptake
mechanisms.
glabrous skin [L. glaber, smooth] Smooth, hairless
skin.
glia [Gr. glue] Neuroglia, the interstitial or accessory
cells of the central nervous system.
glioblast [Gr. glia, glue + blastos, germ] Embryonic
neuroglial cell.
gliosome [Gr. glia, glue + soma, body] Granules in
neuroglial cells, in particular astrocytes.
globus pallidus [L. a ball + pale] Medial part of
lentiform nucleus of corpus striatum. Also
globose nuclei of cerebellum.
glomerulus [Diminutive of L. glomus, ball of yarn]
Synaptic glomeruli of the olfactory bulb and
cerebellum.
glomus [L. a ball] The choroid plexus in the trigone
of the lateral ventricle; probably the most
prolific producer of CSF.
glutamate Excitatory neurotransmitter.
Golgi neuron (of cerebellum) Nerve cell of
granular layer of cerebellar cortex whose
dendrites in the molecular layer are excited by
the granule cell axons and whose axon inhibits
granule cells.
Golgi tendon organ Proprioceptive ending found in
tendons; its appropriate stimulus is an increase
in tendon tension.
gracilis [L. slender] Fasciculus gracilis of the spinal
cord and medulla; nucleus gracilis and gracile
tubercle of the medulla.
granule [L. granulum, diminutive of granum, grain]
Used to denote small neurons, such as granule
cells of cerebellar cortex and stellate cells of
cerebral cortex. Hence granular cell layers of
both cortices.
granule cell (1) Nerve cell of the inner or granular
layer of the cerebellar cortex; axon enters
molecular layer and forms the parallel plexus;
only excitatory neuron in the cerebellar cortex.
(2) intracortical neurons found predominantly in
layers 11 and IV of the neocortex.
graphesthesia Ability to recognize and identify
figures drawn on the skin.
Guillain-Barré syndrome Also known as LandryGuillain-Barré syndrome, acute inflammatory
polyneuropathy, acute autoimmune neuropathy,
and postinfectious polyneuritis-An autoimmune
disease directed against peripheral myelin. See
multiple sclerosis.
gustatory nucleus Rostral part of the solitary
nucleus receptive for taste fibers.
haarschelbe [Ger. haar, hair + scheibe, disk] Small
elevated area of skin that develops in association
with specialized hair follicles and serves as a
receptor for tactile stimuli.
habenula Mass found at dorsal and posterior edge
of the third ventricle near the pineal body; part
of the epithalamus.
habenulointerpeduncular tract Compact bundle of
fibers arising in the habenula and passing
ventrally to the interpeduncular nucleus of the
midbrain and the adjacent reticular formation;
synonym fasciculus retroflexus.
habituation A form of nonassociative learning
characterized by a reduction in response strength
following repeated presentations.
hallucinogens A clan of drugs that alter sensory
perception and produce peculiar experiences.
hallucination False, sensory perception (e.g.
hearing voices, smelling odors).
heat gain center Neurons in posterior hypothalamus
that initiate cutaneous vasoconstriction,
piloerection, and shivering.
heat loss center Neurons in anterior hypothalamus
that initiate sweating and cutaneous
vasodilation.
helicotrema [Gr. helix = coil + trema = hole] Area
at the apex of the cochlea where the scala
vestibuli and scala tympani communicate with
one another.
hemiballismus [Gr. hemi, half + ballismos,
jumping] Violent form of motor restlessness that
involves one side of the body, caused by a
destructive lesion involving the subthalamic
nucleus.
hemiplegia [Gr. hemi, half + plege, a blow or
stroke] Paralysis of one side of the body.
heteronymous [Gr. having a different name]
Different visual fields of both eyes.
hindbrain Medulla, pons and cerebellum; synonym
rhombencephalon.
hippocampal formation Curved band of
archipallium located in temporal lobe between
choroidal fissure and parahippocampal gyrus;
consists of hippocampus proper, dentate gyrus,
and subiculum; responsible for memory and
processing of new information.
hippocampus. [Gr. hippos, horse + kampos, sea
monster; also the zoological name for a genus of
small fishes known as sea-horses] Rather
inappropriate name given to a gyrus that
constitutes an important part of the limbic
system; produces an elevation on the floor of the
temporal horn of the lateral ventricle.
homonymous [Gr. of the same name] same visual
field of both eyes.
horizontal cell Local circuit neuron in the internal
nuclear layer of the retina that influences
synaptic transmission between the photoreceptor
cells and the bipolar neurons.
horizontal gaze center See lateral gaze center.
Horner's syndrome Disorder characterized by
ptosis, miosis, and anhydrosis; due to central or
peripheral interruption of sympathetic impulses
to face and eye.
Huntington disease Hereditary disorder
characterized by progressive increase in
choreoid movements and dementia; inherited by
a dominant gene that causes degeneration of
striatal and cortical acetylcholine and GABA
neurons.
hydrocephalus [Gr. hydro = water + kephale =
head] Excessive accumulation of CSF due to
obstruction of flow, interference with drainage,
or increased formation.
hyperacusis Abnormal acuteness of hearing.
hypercarbia Increased C02 at the tissue level.
hyperkinetic disorders Increased or excessive
speed in the initiation or performance of a
movement.
hyperphagia A condition involving increasing food
intake, often related to damage to the
ventromedial hypothalamus.
hyperthermia Fever or increased body temperature.
hypertonia, hypertonicity [Gr. hyper + tonos =
tension] Excessive tone in skeletal muscles;
manifested by increased resistance to passive
stretch.
hypocarbia Decreased C02 at the tissue level.
hypnagogic hallucination Hallucination that occurs
when falling asleep.
hypokinetic disorders [Gr. hypo = under + kinesis
= movement] Decrease or slowing in the
initiation or performance of a movement.
hypophysial portal system Vascular connection
between the median eminence and adjacent
infundibular stalk and the anterior lobe of the
pituitary by means of which the hypothalamic
releasing factors are transported.
hypothalamic regulatory hormones Substances
formed in hypothalamic neurons that are
transported to pituitary gland to regulate the
release of its hormones.
hypothalamic syndrome Disorder manifested by
diabetes insipidus, endocrine disorders,
impairment of temperature regulation,
abnormalities in sleep patterns, and behavior
changes; results from a lesion of the
hypothalamus.
hypothalamohypophysial tract Unmyelinated
fibers from the supraoptic and paraventricular
nuclei of the hypothalamus, which reach the
posterior pituitary.
hypothalamus [Gr. hypo, under + thalamos, inner
chamber] Region of the diencephalon that serves
as the main controlling center of the autonomic
nervous system.
hypotonia Decrease in resting muscle tone.
hypoxia Lack of adequate 02 at the tissue level.
hysteresis [Gr. hysteresis, a coming later] A delay in
effect on the application of a force.
Ia nerve fiber Axons of dorsal root ganglion cells
that supply muscle spindles and excite motoneurons; form afferent limb of myotatic
reflex.
Ib nerve fiber Axons of dorsal root ganglion cells
that supply tendon organs and inhibit motorneurons via spinal interneurons; form
afferent limb of inverse myotatic reflex and
clasp-knife response.
ideational apraxia An impairment in the ability to
carry out a sequence of actions even though each
element or step can be done correctly.
ideomotor The inability to carry out a simple motor
activity in response to a verbal command even
though the same activity is readily performed
spontaneously.
idiopathic [Gr. idios, individual. + Gr. pathos,
suffering] Without known cause.
illusion Misrepresentation of real external stimuli.
induction [L. inducere, to bring in] In embryology,
action of one population of cells on the
development of another population nearby.
indusium [L. a garment, from induo, to put on]
Indusium griseum, thin layer of gray matter on
the dorsal surface of the corpus callosum (gray
tunic).
infarction [L. infarcire, to stuff or fill in] Regional
death of tissue caused by loss of blood supply.
inferior cerebellar peduncle Fiber bundle
connecting the cerebellum and medulla;
synonym restiform body.
infranuclear lesion Lower motor neuron lesion
involving axons in peripheral nerve.
infundibulum [L. a funnel] Median eminence and
infundibular stem of neurohypophysis; synonym
neural stalk
inhibitory postsynaptic potential (IPSP) An
alteration in the membrane permeability that
buffers the membrane potential of neurons
against subsequent hypopolarization. Generally,
but not always, a hyperpolarizing postsynaptic
potential.
insight Understanding one's own feelings and
behavior.
insula [L. island] Lobe of the cerebrum located deep
to the lateral fissure; synonym island of Reil.
intention tremor To and fro shaking that occurs
when a voluntary movement is made; associated
with posterior cerebellar lobe dysfunction.
internal arcuate fiber Secondary touch, pressure,
and position sense axons from the dorsal column
nuclei that arch around the central gray in the
caudal half of the medulla.
internal capsule White matter between the caudate
nucleus and diencephalon medially and the
lentiform nucleus laterally; continuous rostrally
with corona radiata, caudally with cerebral crus.
internuclear ophthalmoplegia [Gr. ophthalmos eye
+ plege = stroke] Disorder of eye movements
due to damage to the medial longitudinal
fasciculus between the abducent and oculomotor
nuclei; manifested during horizontal conjugate
movements by lack of adduction in eye on same
side as lesion.
interoceptor [L. inter, between + receptor, receiver]
One of the sensory end organs within viscera.
interpeduncular fossa Deep depression on the
ventral surface of the midbrain between the
cerebral peduncles.
intrafusal muscle fiber Muscle fiber part of a
muscle spindle, innervated by -motoneurons.
inverse myotatic reflex Contraction of a muscle
causes an increase in tension, which fires a
Golgi tendon organ that carries this information
by lb fibers to excite the antagonists and inhibit
the synergists.
interstitial [L. inter, between + statum, placed]
Within spaces.
ipsilateral [L. ipse, itself + lateris of a side] Of the
same side (left or right) of the body. Opposite of
"contralateral."
IPSP See inhibitory postsynaptic potential.
irritable Easily bothered and quickly angered.
ischemia [Gr. ischein, to check + haimos, blood]
Condition of tissue that is not adequately
perfused with oxygenated blood.
isocortex. [Gr. isos, equal + L. cortex, bark]
Cerebral cortex having six layers (neocortex).
isometric In physiology, the contraction of a muscle
held at constant length.
isotonic In physiology, the contraction of a muscle
under constant tension.
juxtarestiform body Medial portion of inferior
cerebellar peduncle carrying primarily vestibular
fibers.
keratoconus [Gr. keras, horn + Gr. konos, cone]
Deformation of the normally spherical cornea
into a cone shape due to thinning of the cornea
at the margin.
kinesthesia [Gr. kinesis = movement + aisthesis
sensation] Awareness of position and movement
of body parts.
kinocilium [Gr. Idneo = to move + cilium] Longest
cilium found on hair cell in crista ampullaris;
bending of stereocilia toward or away from
kinocilium results in excitation or inhibition
(respectively) of vestibular nerve fibers.
Klüver-Bucy syndrome Disorder characterized by
docility, oral tendencies, bulimia, and bizarre
sexual behavior; results from bilateral ablation
of anterior temporal lobes.
koniocortex [Gr. konis, dust + L. cortex, bark]
Areas of cerebral cortex that contain large
numbers of small neurons; typical of sensory
areas.
Korsakoff amnesic state A type of anterograde
amnesia characterized by the inability to
consolidate short-term memory into long-term
memory. Correlated with specific damage to the
CA region of the hippocampal formation.
Korsakoff syndrome Disorder involving memory
loss, confusion, and confabulation; lesions
frequently found in the walls of the third
ventricle involving the mamillary bodies, medial
dorsal thalamic nuclei, or anterior thalamic
nuclei.
labile Readily changeable.
labile memory An early stage of memory formation
during which the formation of a memory can be
easily disrupted by conditions that influence
brain activity.
Lambert-Eaton syndrome An autoimmune disease
affecting the voltage-gated Ca2+ channels,
characterized by motor weakness and an
incrementing electromyelographic response to
repetitive stimulation.
latency The time delay before a subject displays the
behavior of interest.
lateral aperture Lateral opening connecting fourth
ventricle with subarachnoid space; synonym
foramen of Luschka.
lateral fissure Most prominent cleft on lateral
surface of cerebral hemisphere; begins anteriorly
and proceeds posteriorly separating the frontal
and parietal lobes from the temporal lobe;
synonym Sylvian fissure.
lateral gaze center Neurons in the paramedian
pontine reticular nucleus that elicit horizontal
eye movements to the ipsilateral side; formerly
called parabducent nucleus; synonym horizontal
gaze center.
lateral lemniscus Tract in the lateral part of the
pontine and midbrain tegmentum from the
pontomedullary junction to the inferior
colliculus; comprised of the central acoustic
fibers, although sometimes the spinothalamic
tract is included.
lateral medullary syndrome Disorder characterized
by loss of pain and thermal sensations over
ipsilateral half of face and contralateral half of
body; nausea; vertigo; ipsilateral ataxia;
ipsilateral paralysis of soft palate, pharynx, and
vocal cord; and Horner's syndrome. Due to
vascular lesion involving the vertebral or the
posterior inferior cerebellar artery; synonym
Wallenberg syndrome.
lead-pipe rigidity Bidirectional hypertonicity
resulting from increased tone in all of the
muscles acting on a joint; associated with basal
ganglia disorders.
lemniscus [Gr. lemniskos = ribbon or fillet] A
secondary sensory tract ascending through the
brainstem to the thalamus.
lentiform [L. lens (lent-), a lentil (lens) + forma,
shape] Lens-shaped. Lentiform nucleus, a
component of the corpus striatum. Also called
lenticular nucleus.
leptin A protein manufactured and secreted by fat
cells, that may communicate to the brain the
amount of body fat stored.
leptomeninges [Gr. leptos = slender or delicate +
meninx = membrane] Arachnoid and pia mater,
the two thin membranes covering the brain and
spinal cord.
lesion [L. laesum, hurt or wounded] Applied to any
abnormality. In the nervous system, a lesion may
be destructive (such as an infarct, injury,
hemorrhage, or tumor), or it may stimulate
neurons (as in epilepsy).
leukodystrophy A generic term describing any
degeneration of the white matter of the brain.
Lhermitte's sign A sensation of electric shocks
descending the spine upon flexion of the neck. A
sign of meningeal irritation.
ligand-gated ion channels A membrane protein that
adjusts its permeability to one or more ions
when a specific ligand is bound to a specific
receptor on the protein.
light reflex Constriction of pupil on increased light
reaching the retina.
limbic lobe [L. limbus = border] Structures on
medial surface of cerebral hemisphere bordering
the corpus callosum and rostral brainstem;
includes the cingulate and parahippocampal
gyri.
limbic system [L. limbus = border] Cortical and
subcortical structures that influence behavior
and autonomic responses chiefly through the
hypothalamus; includes the limbic lobe,
amygdaloid nucleus, hippocampal formation,
septal region, and hypothalamus. Some also
include the anterior thalamic nucleus, medial
part of the midbrain tegmentum, orbitofrontal
cortex, and anterior cingulate gyrus.
limbus [L. a hem or border] Limbic lobe: C-shaped
configuration of cortex on the medial surface of
the cerebral hemisphere that consists of the
septal area and the cingulate and
parahippocampal gyri. Limbic system: limbic
lobe, hippocampal formation, and portions of the
diencephalon, especially the mamillary body and
anterior thalamic nuclei.
line of Gennari An unusually prominent band of
white matter in layer IV of the primary visual
cortex (Brodmann area 17) that is visible to the
naked eye and gives this area its name, the
striate cortex.
Lissauer's tract Synonym for the dorsolateral tract.
locus ceruleus [L. place + caeruieus, dark blue]
Small dark spot on each side of the floor of the
fourth ventricle; marks the position Of a group
of nerve cells that contain melanin pigment.
long term depression (LTD) A lasting decrease in
the magnitude of responses of neurons after
afferent cells have been stimulated with
electrical stimuli of relatively low frequency.
loop of Meyer Those fibers of the optic radiation,
which, after leaving the lateral part of the lateral
geniculate nucleus and passing into the temporal
lobe, arch over the inferior horn of the lateral
ventricle before turning back toward the
occipital lobe.
loose associations Shift of ideas from one to another
in an unrelated fashion.
lower motor neuron Brainstem or spinal cord motoneuron; axon carries impulses to extrafusal
muscle fibers; synonym final common pathway.
lower motor neuron syndrome Disorder
characterized by flaccid paralysis, decreased or
absent reflexes, and severe atrophy; due to loss
of the final common pathway, i.e., the loss of the
-motoneurons or their axons innervating a
muscle.
lumbar puncture Procedure by which the dural sac
is entered by inserting a needle usually between
L3-L4 or L4-L5 in adults and always below L4
in infants.
macroglia [Gr. makros, large + glia, glue] Larger
types of neuroglial cells: astrocytes,
oligodendrocytes, and ependymal cells.
macrosmatic [Gr. makros, large + osrne, smell]
Having the sense of smell strongly or acutely
developed.
macula lutea [L. macula = spot + luteus = saffronyellow] Yellowish area of retina lateral and
slightly below the optic disc at a point
corresponding to posterior pole of retina.
macula of saccule Sensory neuroepithelium in
anteromedial part of wall of saccule.
macula of utricle Sensory neuroepithelium in
anterolateral part of wall of utricle.
mamillary [L mammillia, diminutive of mamma,
breast (shaped like a nipple)] Mamillary bodies:
swellings on the ventral surface of the
hypothalamus. Also spelled mammillary.
MAO inhibitor An antidepressant drug that inhibits
the enzyme monoamine oxidase, thus
prolonging the action of catecholamine
transmitters.
Marcus Gunn pupil In neurology, this term applies
to a pupil that paradoxically dilates when light is
shone into the eye.
massa intermedia Bridge of gray matter that
connects the thalami of the two sides across the
third ventricle; present in 70% of human brains.
Also called the interthalamic adhesion.
mechanoreceptor Receptor that is excited by its
distortion due to touch, pressure, muscle, or
tendon stretch, etc.
medial forebrain bundle Diffuse system of fibers
located in the lateral hypothalamus;
interconnects with septal region rostrally and
midbrain reticular formation caudally.
medial lemniscus Tract located medially in the
medulla, ventrally in the pontine tegmentum,
and dorsolaterally in the midbrain tegmentum;
carries touch, pressure, and position sense
impulses from the contralateral gracile and
cuneate nuclei to the ventral posterolateral
nucleus of the thalamus.
medial longitudinal fasciculus Bundle of fibers
extending from the midbrain to the spinal cord;
located close to the midline in the dorsal part of
the tegmentum adjacent to the nuclei of the
external ocular muscles; composed largely of
fibers ascending to motor neurons of the external
ocular nuclei, and descending to spinal
motoneurons innervating the paravertebral
musculature.
median aperture Midline opening between
posterior part of fourth ventricle and
subarachnoid space; synonym foramen of
Magendie
median eminence Part of neurohypophysis that is
frequently considered to be the raised portion of
the tuber cinereum; together with the
infundibular stem and process forms the
neurohypophysis (neural lobe).
medulla [L. marrow, from medius, middle] Medulla
spinalis: spinal cord. Medulla oblongata: caudal
portion of the brain stem. In current usage,
"medulla" means the medulla oblongata.
medulloblastoma Glioma consisting of neoplastic
cells that resemble the undifferentiated cells of
the primitive medullary tube.
Meissner corpuscle Encapsulated tactile receptor in
dermal papilla.
melanin Dark brown or black pigment found in
cytoplasm of neurons in some nuclei (substantia
nigra, locus ceruleus, etc.).
melatonin An amine hormone that is released by the
pineal gland.
membranous labyrinth System of endolymphcontaining ducts and chambers of the inner ear;
includes utricle, saccule, semicircular ducts,
cochlear ducts, and their connections.
memory trace A persistent change in the brain that
reflects the storage of memory.
Ménière's disease A neurological disorder
characterized by extreme vertigo due to
inappropriate unilateral stimulation of the
labyrinth.
meningioma [Gr. meninges + oma = tumor] Benign
tumor of arachnoid origin; tends to occur along
superior sagittal sinus, sphenoid ridges, and near
optic chiasm.
mesencephalon [Gr. mesos, middle + enkephalos,
brain] Midbrain; second of the three primary
brain vesicles.
mesoderm [Gr. mesos, middle + derma, skin]
Middle layer of cells of the early embryo, which
gives rise to connective tissues, muscle, etc.
metabolic coma Coma of chemical rather than
structural origin, such as hypoxia, the presence
of hypnotic drugs, or hypoglycemia.
metathalamus [Gr. meta, after + thalamos, inner
chamber] Medial and lateral geniculate bodies
(nuclei).
metencephalon [Gr. meta, after + enkephalos,
brain] Pons and cerebellum; anterior of the two
divisions of the rhombencephalon or posterior
primary brain vesicle.
microsmatic [Gr. mikros + osme = to smell] Having
a feeble sense of smell.
microglia [Gr. mikros, small + glia, glue] Type of
neuroglial cell.
middle cerebellar peduncle Fiber bundle
connecting the cerebellum and the pons;
synonym brachium pontis.
middle cerebral candelabra Shape branches of
middle cerebral artery in lateral fissure as seen
radiographically.
mimetic [Gr. mimetikos, imitative] Muscles of
expression supplied by the facial nerve;
sometimes referred to as mimetic muscles.
miosis [Gr. meiosis = a lessening] Constriction of
the pupil.
mitral. [L. mitra, a turban; later the tall, cleft hat
(miter) of a bishop] Mitral cells of the olfactory
bulb.
mnemonic [Gr. mneme, memory] Pertaining to
memory.
molecular [L. molecula, diminutive of moles, mass]
Used in neurohistology to denote tissue that
contains large numbers of fine nerve fibers and
that, therefore, has a punctate appearance in
silver-stained sections. Molecular layers of
cerebral and cerebellar cortices.
monoplegia [Gr. mono + plege = stroke] Paralysis
or paresis in one limb.
mood Internal emotional feelings.
mossy fibers Afferent axons arising from cerebellar
input nuclei other than the inferior olivary
nucleus; branch repeatedly in white matter and
granule layer and are excitatory to granule cells
and deep cerebellar nuclei.
motor aphasia See nonfluent aphasia.
motor end-plate Acetylcholine synapse of -motor
neuron on extrafusal muscle fiber; synonym
myoneural junction.
motor unit -motoneuron, its axon, and the
extrafusal muscle fibers it innervates.
multiple sclerosis (MS) An autoimmune disease
directed against central myelin. See GuillainBarré syndrome.
muscle spindle Mechanoreceptor in skeletal muscle.
muscle stretch reflex (MSR) A reflex initiated by
the rapid stretching of a muscle that stimulates
the primary receptors of the muscle spindle
apparatus and results in a facilitation of the
motor neuron pools serving the homonymous
muscle.
mutism. [L. mutus, silent or dumb] Inability to
speak.
myasthenia gravis [Gr. mys = muscle + asthenia
weakness] Autoimmune disease characterized
by muscular weakness, beginning usually in the
orofacial region, due to increased turnover of
acetylcholine receptors at the neuromuscular
junction.
mydriasis Extreme dilation of the pupil.
myelogram A radiographic procedure in which the
subarachnoid space of the spinal cord is filled
with a radio-opaque dye. Subsequent spinal xrays reveal the outline of the dural sac.
myelencephalon [Gr. myelos, marrow + enkephalos,
brain] Medulla oblongata; posterior of the two
divisions of the rhombencephalon or posterior
primary brain vesicle.
myelin [Gr. myelos, marrow] Layers of lipid and
protein substances that form a sheath around
axons.
myotatic reflex [Gr. myo = to shut + tasis
stretching] contraction of a muscle induced by
stretching; synonym stretch, deep, or tendon
reflex.
myotome Skeletal muscles supplied by a single
spinal cord segment.
myotrophic [Gr. mys, muscle + trephein, to
nourish] Responsible for maintaining the
structural and functional integrity of muscle.
(Principally by chemical agents from motor
neurons, hence the earlier but ambiguous term
"neurotrophic.")
negative signs Functional deficits resulting from a
lesion.
neglect syndrome Perceptual disorder related to
lack of recognition of the opposite side of the
body and its surroundings.
neocerebellum [Gr. neos, new + diminutive of
cerebrum] Phylogenetically newest part of the
cerebellum present in mammals and especially
well developed in humans. Ensures smooth
muscle action in the finer voluntary movements.
neocortex [Gr. neos, new + L. cortex, bark] Sixlayered cortex, characteristic of mammals and
constituting most of the cerebral cortex in
humans.
neospinothalamic system Newer spinothalamic
system, which carries fast pain to the ventral
posterolateral thalamic nucleus; its peripheral
fibers are of the A delta type and it arises chiefly
from marginal neurons in the dorsal horn of the
spinal gray.
neostriatum [Gr. neos, new + L. striatus, striped or
grooved] Phylogenetically newer part of the
corpus striatum that consists of the caudate
nucleus and putamen; the striatum.
nerve deafness Perception deafness due to damage
to sensory cells of inner ear or to cochlear nerve;
degree of hearing loss depends on amount of
damage.
neurinoma Benign tumor arising from Schwann
cells.
neurite [Gr. neurites, of a nerve] Cytoplasmic
processes of neurons. The term embraces both
axons and dendrites.
neurobiotaxis. [Gr. neuron, nerve + bios, life +
taxis, arrangement] Tendency of nerve cells to
move during embryological development toward
the area from which they receive the most
stimuli.
neuroblast. [Gr. neuron, a nerve + blastos, germ]
Embryonic nerve cell.
neuroepithelium Epithelial cells that serve as the
special receptors in the auditory, vestibular,
olfactory, and gustatory systems; synonym
neurepithelium.
neurofibril. [Gr. neuron, nerve + L. fibrilla, diminutive of fibra, fiber] Filaments in the
cytoplasm of neurons.
neurofibrillary bodies Collections of tubules found
within neurons of patients suffering from
Alzheimer's disease. These tubules are similar to
but not identical with the microtubules that are
normally found in neurons and other cells.
neurogenic bladder Abnormal functioning of the
urinary bladder as a result of a CNS or PNS
lesion.
neuroglia [Gr. glia = glue] Non-neuronal support
cells of the CNS; 10 times more numerous than
neurons; four types:. astrocytes,
oligodendrocytes, microglia, and ependymal
cells; synonym glia.
neurokeratin [Gr. neuron, nerve + keras (kerat-),
horn] Fibrillar material consisting of proteins
that remains after lipids have been dissolved
from myelin sheaths.
neurolemma Cytoplasmic sheath of Schwann cells
surrounding a peripheral nerve fiber.
neuroma Nerve cell or nerve fiber tumor.
neuron [Gr. a nerve] Morphological unit of the
nervous system consisting of the nerve cell body
and its processes (dendrites and axon).
neuropil [Gr. neuron, nerve + pilos, felt] Complex
net of nerve cell processes that occupies the
intervals between cell bodies in gray matter.
neuropraxia:
- least severe injury, is characterized
by a conduction block;
- continuity of all structures is
preserved;
- Wallerian degeneration does not (no
axonal loss) occur but there is focal
demyelination;
- complete recovery is evident in 3 to
6 weeks;
- after a simple crush injury function
may return within days;
- w/ neuropraxia there is immediate
conduction block across the site of injury
with normal conduction distally;
- with severe trauma, there is focal
demyelination without disruption of axons,
and slowing of the conduction
velocity can be demonstrated
across the lesion;
- conduction block is restored once
myelin regeneration is restored (taking
weeks to months);
NEUROTMESIS
- most severe nerve injury;
- complete disruption of axons, endoneurium,
perineurium, & epineurium;
- Wallerian degeneration occurs;
- recovery requires operative repair and the
prognosis is variable, ranging from complete
recovery to no recovery;
- factors that influence the degree of recovery;
- the age of the patient
- type of injury
- degree of injury
- level of injury
- if an injury causes division of the
nerve close to the cell body, cell death occurs;
- presence of associated injury
- composition of the severed nerve trunk
- if axonal regeneration into the empty
endoneural sheaths is delayed, these sheaths
undergo shrinkage that becomes
more severe with time;
- nerve injury results in changes within the cell
body, the axon proximal & distal to site of injury,
and the functional unit innervated;
- more proximal the injury, the greater the cell
body damage, as evidenced by changes in the
size and internal organization;
- after injury, the cell body progressively
enlarges for approx 20 days and remains
enlarged until axon regeneration is complete;
- proximal nerve stump swells in response to
the accumulation of gel like, amorphous
substance containing large quantities of acid
mucopolysaccaride;
- schwan cells begin proliferating 48 to 72
hours after injuries and assume a phagocytic
role (Wallerian degeneration);
neurotransmitter [L. neuro + transmitto = to send
across] Any specific chemical agent released by
a presynaptic cell on excitation, which crosses
the synaptic cleft to stimulate or inhibit the
postsynaptic cell.
Nissl body Plates of rough endoplasmic reticulum
and free ribosomes found in cytoplasm of nerve
cell perikaryon and large dendrites.
nociceptive [L noceo, I injure + capio, I take]
Responsive to injurious stimuli.
nociceptor [L. noceo = to injure, hurt + capio to
take] Receptor that is stimulated by actual tissue
injury or anticipated injury; a receptor for pain.
node of Ranvier Discontinuity in the myelin sheath
of a nerve fiber where one Schwann cell in
peripheral nerves or one oligodendrocyte in
central nerves meets the next.
nonassociative learning A type of learning in which
preservation of a particular stimulus alters the
strength or probability for a response according
to the strength and temporal spacing of the
stimulus; includes habituation and sensitization.
nondeclarative memory A memory that is shown
by performance rather than by conscious
recollection; also called procedural memory.
nonfluent aphasia Language disorder characterized
by difficulty in forming words; associated with
lesion of Broca speech area; synonym motor or
expressive aphasia.
nonreflex neurogenic bladder Incontinence and
severe retention; a "lower motor neuron" type
disorder resulting from lesions of sacral spinal
cord or cauda equina.
nuclear lesion Lower motor neuron lesion involving
cell body.
nucleus [L. nut, kernel] (1) Body in a cell that
contains, in the DNA of its chromosomes, the
genetic information that encodes the amino acid
sequences of proteins. (2) Collection of neuronal
cell bodies, which may be large (like the caudate
nucleus) or microscopic (like many nuclei in the
brain stem).
nystagmus [Gr. nystagmus = a nodding] Involuntary
rapid movements of the eyeballs consisting of
fast and slow phases; named according to
direction of fast phase.
obex [L. barrier] Small transverse fold over- hanging
the opening of the fourth ventricle into the
central canal of the closed portion of the
medulla.
obsession Recurrent, persistent thoughts.
obsessive-compulsive disorder (OCD) A syndrome
in which the affected individual engages in
recurring, repetitive acts that are carried out
without rhyme, reason, or the ability to stop.
obstructive hydrocephalus Blockage of CSF flow.
within the ventricular system.
occipital eye field Of the cerebral cortex, which are
concerned with eye movements chiefly of a
reflex nature.
oculocephalic reflex Turning of the eyes in the
direction opposite to that of rotation of the head;
Signifies intact vestibulo-ocular reflex in
comatose patient; synonym doll's eye
movement.
odorant Molecule that elicits a perceived odor.
oligodendrocytes [Gr. oligos = few + dendron tree +
glia = glue] Neuroglial cells with small electrondense oval nuclei and scanty cytoplasm; form
myelin sheath of CNS.
olive [L. oliva] Oval bulging of the lateral area of
the medulla. Inferior, accessory, and superior
olivary nuclei.
operculum [L. cover or lid] Those parts of the
cerebrum that cover the insula and form the
margins of the lateral fissure.
ophthalmoplegia [Gr. ophthalmos = eye + plege
stroke] Paralysis of the eye muscles. .
opiates A class of compounds that exert an effect
like that of opium, including reduced pain
sensitivity.
optic disc or papilla Area where the optic nerve
fibers leave the retina.
optokinetic nystagmus Nystagmus induced by
looking at a moving object; synonym railroad
nystagmus.
orexin A group of proteins expressed in the lateral
hypothalamus that trigger feeding.
organ of Corti Sensory end organ for hearing found
in cochlear duct of internal ear; synonym spiral
organ.
orthograde [Gr. orthos, correct, straight + L.
gressus, to walk] Moving in the normal
direction. In neuroscience, moving along an
axon beginning at the soma, as in orthograde
conduction. See anterograde; retrograde.
osseous labyrinth [L. osseus = bony] Spaces found
in petrous part of the temporal bone comprising
cochlea, vestibule, and semicircular canals;
synonym bony labyrinths
otoconia [Gr. otos = ear + konis = dust] Crystalline
particles of calcium carbonate and a protein
adhering to the gelatinous otolithic membrane of
the maculae of the utricle and saccule; synonym
statoconia or otoliths.
otolith [Gr. otos + lithos = stone] One of the
particles constituting the otoconia; synonym
statoconium, otoconium, statolith.
otolithic membrane Gelatinous substance overlying
the maculae of utricle and saccule into which
their cilia are embedded; contains calcium
carbonate crystals, the otoliths.
ototoxic Toxic to the hair cells of the vestibular
apparatus or cochlea.
oval window Opening between tympanic cavity and
scala vestibuli of cochlea; synonym fenestra
vestibule.
oxytocin Hormone secreted by magnocellular
neurons in the supraoptic and paraventricular
nuclei of the hypothalamus that stimulates
contraction of the smooth muscle fibers (cells) in
the pregnant uterus and contractile cells around
the ducts of mammary glands.
pachymeninx [Gr. pachys, thick + meninx,
membrane] Dura mater.
paleocerebellum [Gr. paialos, old + diminutive of
cerebrum] Phylogenetically old part of the
cerebellum that functions in postural changes
and locomotion.
paleocortex [Gr. palaios, old + L. cortex, bark]
Olfactory cortex consisting of three to five
layers.
paleospinothalamic system Older spinothalamic
system, which carries slow pain to a broader
area including the reticular formation and
intralaminar thalamic nuclei, therefore less
localized than the neospinothalamic system;
peripheral fibers are of the C type; arise from
neurons chiefly in laminae IV, V, and VI of the
dorsal horn.
paleostriatum [Gr. palaios, old + L. striatum,
striped or grooved] Phylogenetically older and
efferent part of the corpus striatum; the globus
pallidus or pallidum.
pallidum [L. pallidus, (-um), pale] Globus pallidus
of the corpus striatum; medial portion of the
lentiform nucleus comprising the paleostriatum.
pallium [L. cloak] Cerebral cortex with subjacent
white matter, but usually used synonymously
with cortex.
palsy weakness Paralysis of muscles.
Papez circuit Neural circuit concerned with shortterm memory and learning and thought to be
reverberating; includes hippocampus, fornix,
mamillary bodies, mamillothalamic tract,
anterior thalamic nucleus, cingulate gyrus,
cingulum, and parahippocampal gyrus.
papilledema [papilla + edema] Choked disc;
papillary stasis; edema of the optic disc; may be
due to raised intracranial pressure; synonym disc
edema.
paralysis [Gr. paralysis, secret undoing; from para,
beside + lyein, to loosen] Loss of the power of
motion.
paralysis agitans See Parkinson disease.
paraplegia [Gr. para = beside + plege = a stroke]
paralysis of the lower limbs.
parenchyma [Gr. parenchein, to pour in beside]
Essential and distinctive tissue of an organ. (The
name is from an early notion that internal organs
contained material poured in by their blood
vessels.)
paresis [Gr. a letting go, slackening, relaxation]
Partial paralysis or weakness.
papilledema Edema of the papilla, the point of
entry of the optic nerve into the eye. This is
caused by an increase in intracranial pressure.
Not to be confused with papillitis.
papillitis Inflammation of the head of the optic
nerve where it enters the eye, usually caused by
an exacerbation of multiple sclerosis. Not to be
confused with papilledema.
Parkinson disease Neurologic syndrome
characterized by tremors at rest and rigidity
ascribed to lesions of the substantia nigra;
synonym paralysis agitans.
parkinsonism A generic term used to describe all
diseases of the basal ganglia that have the
common features of resting tremor,
bradykinesia, and rigidity. This includes
Parkinson's disease as well as a number of other
significantly different illnesses such as
supraoptic ophthalmoplegia.
paroxysmal The sharp or sudden onset and
recurrence of the manifestations of disease.
pathway Route within the central nervous system
consisting of interconnected populations of
neurons that serve a common function. A
pathway often contains one or more tracts.
perforant path The route of axons that "perforate"
the subiculum to provide the main inputs to the
hippocampal formation.
perikaryon [Gr. peri, around + karyon, nut, kernel]
Cytoplasm surrounding the nucleus. Sometimes
refers to the cell body of a neuron.
perineurium. [Gr. peri, around + neuron, nerve]
Cellular and connective tissue sheath
surrounding a bundle of nerve fibers in a
peripheral nerve.
pernicious anemia [L. per, through + necis, of
murder + Gr. an, negative + haimos, blood]
Disease caused by failure to absorb vitamin B12
(cyanocobalamin). The vitamin deficiency
results in defective production of red blood cells
and degeneration in the central nervous system,
including subacute combined degeneration in the
spinal cord.
peritrichal receptor [Gr. peri, around + Gr. thrix,
hair] Sensory receptor located at the base of the
hair shafts and sensitive to their movement.
perseveration In neurology, the repeated and
inappropriate naming of each object in a series
by the name given to the first object, even
though they are all different.
PGO wave An EEG wave of activity from the pons
to the lateral geniculate and on to the occipital
cortex, usually seen during REM sleep.
phobia Irrational fear.
photopic vision Vision when eye is light adapted.
phylogeny [Gr. phylon, race + genesis, origin]
Evolutionary history, typically as deduced from
comparative anatomy.
pia mater Innermost layer of the meninges.
pineal. [L. pineus, relating to the pine] Shaped like a
pine cone (pertaining to the pineal gland).
plasticity Phenomenon whereby neurons alter or
modify their connections; occurs freely in the
developing nervous system and in response to
injury in the mature nervous system;
mechanisms include collateral sprouting,
paraterminal axonal sprouting, and contact
synaptogenesis; thought to be responsible for
some of the behavioral changes following CNS
lesions.
plexus [L. plaited, interwoven] Arrangement of
interwoven and intercommunicating nerve
trunks or fibers or of blood vessels.
pneumoencephalography [Gr. pneuma, air +
enkephalos, brain + graphe, a writing]
Replacement of cerebrospinal fluid by air
followed by x-ray examination
(pneumoencephalogram); permits visualization
of the ventricles and subarachnoid space. This
technique has been replaced by computed
tomography (CT scan).
poikilothermal [Gr. poikilos, varied + Gr. therme,
heat] Varying temperature in accordance with
the environment.
poikilothermy [Gr. poikilos = varied + therme heat]
A condition in which the body temperature
varies with the environment; can result from a
lesion in the posterior hypothalamus.
poliomyelitis [Gr. polios, gray + Gr. myelos,
marrow + Gr. itis, inflammation] Literally, an
inflammation of the gray matter of the spinal
cord. A viral disease that, among other things,
kills  motor neurons, particularly those of the
lumbosacral spinal cord.
pons [L. bridge] Part of the brain stem that lies
between the medulla and the midbrain; appears
to constitute a bridge between the right and left
halves of the cerebellum.
positive signs Spontaneous, uncontrollable activity
resulting from a lesion.
positron [From positive electron] Subatomic particle
with the same mass as an electron and equal but
opposite charge. Positrons emitted by
radioactive elements combine with electrons,
with elimination of matter and emission of xrays. Detection of the latter forms the basis of
positron emission tomography (PET).
posterior lobe syndrome Disorder characterized by
ataxia, hypotonia, intention tremor, dysmetria,
dysdiadochokinesia, and, if bilateral, explosive
speech; results from a lesion in the posterior
lobe of the cerebellum, dentate nucleus, or
dentatothalamic tract; synonym neocerebellar
syndrome.
postsynaptic potential (PSP) An alteration in
membrane potential produced by
electrochemical events originating at synapses
terminating on that neuron.
presynaptic inhibition An electrochemical
alteration in the bouton membrane that reduces
the efficiency of transmitter release from that
bouton, thereby making its effect less
pronounced on the postsynaptic neuron.
presbyacusis [Gr. presby, old + Gr. akouo, to hear]
The decrease in high-frequency sensitivity to
sound that occurs with the advancement of age.
presbyopia [Gr. presbys, old + Gr. ops, eye] The
decreased elasticity of the lens that results in the
inability to bring near objects into focus, a
process that occurs with advancing age.
progesterone Steroid hormone secreted by the
corpus luteum and the placenta.
projection [L. proiectus, thrown forwards] Applied
to the axons of a population of neurons and their
sites of termination. Often used when the axons
do not constitute a circumscribed tract.
projection fibers Axons that connect the cerebral
cortex with subcortical neurons.
proprioceptor [L. proprius, one's own + receptor,
receiver] One of the sensory endings in muscles,
tendons, and joints; provides information
concerning movement and position of parts of
the body (proprioception).
propriospinal neurons Spinal cord cells whose
axons make up the fasciculi proprii adjacent to
the gray matter.
prosencephalon [Gr. pros, before + enkephalos,
brain] Forebrain, consisting of the telencephalon
(cerebral hemispheres) and diencephalon;
anterior primary brain vesicle.
prosopagnosia [Gr. prosopon, person or face +
agnosia (q.v.)] Inability to recognize previously
familiar faces.
psychosis Loss of touch with reality, characterized
by hallucinations and delusions in a person with
a normal level of consciousness.
ptosis [Gr. fan] Drooping of the upper eyelid.
pulvinar [L. a cushioned seat] Posterior projection
of the thalamus above the medial and lateral
geniculate bodies.
putamen [L. shell] Larger and lateral part of the
lentiform nucleus of the corpus striatum.
Purkinje neuron Large efferent neuron of the
cerebellar cortex whose massive dendritic tree
spreads chiefly transverse to the long axis of the
folium in the molecular layer, and whose axon
inhibits neurons chiefly in the cerebellar nuclei,
pyramidal cell Large triangular neuron of cerebral
cortex having apical dendrite extending toward
pial surface as well as horizontally directed basal
dendrites; axon emerges from base of cell and
passes to the white matter as an association,
commissural, or projection fiber.
pyramidal system Corticospinal and corticobulbar
tracts. So-called because the corticospinal tracts
occupy the fancifully pyramid-shaped area on
the ventral surface of the medulla. The term
pyramidal tract refers specifically to the
corticospinal tract.
pyriform [L. pyrum, pear + forma, form] Pyriform
area is a region of olfactory cortex consisting of
the uncus, limen insulae, and entorhinal area;
has a pear-shaped outline in animals with a welldeveloped olfactory system.
quadriplegia [L. quadri, four + Gr. plege, stroke]
Paralysis that affects the four limbs. Also called
tetraplegia.
rapid-eye-movement (REM) sleep A stage of sleep
characterized by small -amplitude, fast EEG
waves, no postural tension, and rapid eye
movements. Also called paradoxical sleep.
raphe [Gr. seam] Anatomical structure in the
midline. In the brain, several raphe nuclei are in
the midline of the medulla, pons, and midbrain.
Their names are partly latinized, as in nucleus
raphes magnus (great nucleus of the raphe), etc.
Raynaud's syndrome Paroxysms of pain and
cyanosis in the distal portions of the extremities,
brought on by emotion or cold. Commonly
associated with sympathectomy of the
extremities, as in peripheral neuropathy or
peripheral nerve compression.
receptive aphasia See fluent aphasia.
receptor [L. receptus, received] Word used in two
ways in neurobiology: (a) Structure of any size
or complexity that collects and usually also edits
information about conditions inside or outside
the body. Examples are the eye, the muscle
spindle, and the free ending of the peripheral
neurite of a sensory neuron. (b) Protein molecule
embedded in the surface of a cell (or sometimes
inside the cell) that specifically binds the
molecules of hormones, neurotransmitters,
drugs, or other substances that can change the
activity of the cell.
referred pain Pain that is perceived as coming from
a site other than its origin.
reflex neurogenic bladder "Upper motor neuron"
type resulting from CNS lesions rostral to sacral
spinal cord.
Reissner's membrane See vestibular membrane.
repression Pushing unacceptable feelings out of
consciousness.
restiform body Synonym for the inferior cerebellar
peduncle.
reticular [L. reticularis, pertaining to or resembling
a net] Reticular formation of the brain stem.
retrograde amnesia Lack of memory for past
events.
retrograde axonal transport Passage toward the
cell body; worn-out material is brought back
toward the soma by a rapid (200 to 300 mm/day)
transport; toxins, e.g., tetanus, and viruses, e.g.,
herpes, polio, and rabies, can 'also be brought
back.
rhinal [Gr. rhis, nose, therefore related to the nose]
Rhinal sulcus in the temporal lobe indicates the
margin of the lateral olfactory area.
rhinencephalon [Gr. rhis (rhin-), nose +
enkephalos, brain] Obsolete term that referred to
components of the olfactory system. In
comparative neurology, structures incorporated
in the limbic system (especially the
hippocampus and dentate gyrus) were included.
rhodopsin Visual pigment of the rods.
rhombencephalon [Gr. rhombos, a lozenge- shaped
figure + enkephalos, brain] Pons and cerebellum
(metencephalon) and medulla (metencephalon);
posterior primary brain vesicle.
rigidity [L. rigidus = rigid, inflexible] Stiffness or
inflexibility manifested by pervasive resistance
to passive movement.
Rinne tuning fork test Vibrating tuning fork heard
longer and louder when in contact with the skull
(usually the mastoid process) than when held
near the pinna-indication of some disorder of the
sound-conducting apparatus.
roentgenogram [After Wilhelm Konrad Roentgen,
who discovered x-rays, + Gr. gamma, a letter or
record] Picture made with x-rays; more often
called an x-ray or a radiograph.
Romberg sign If a patient standing is more unsteady
with the eyes closed, dorsal column ataxia rather
than cerebellar ataxia is indicated.
rostrum [L. beak] Recurved portion of the corpus
callosum, passing backward from the genu to the
lamina terminalis.
round window Opening between tympanic cavity
and scala tympani of cochlea.
rubro- [L. ruber, red] Pertaining to the red nucleus
(nucleus ruber), as in rubrospinal and
corticorubral.
saccade Small, quick eye movements on changing
point of fixation.
sacral sparing Normal motor and sensory functions
in sacral region following spinal cord injury
more rostrally.
satellite [L. setteles, attendant] Satellite cells:
flattened cells of ectodermal origin that
encapsulate nerve cell bodies in ganglia. Also
satellite oligodendrocytes adjacent to nerve cell
bodies in the central nervous system.
Schwann cell Cell of ectodermal origin that forms
the neurolemma of a peripheral nerve fiber and
contains the myelin if the axon is myelinated.
scotopic vision [Gr. skotos = darkness + opsis
vision] Vision when the eye is dark adapted.
semantic memory Generalized memory - for
instance, knowing the meaning of a word
without knowing where or when that word was
learned.
sensorineural hearing loss Hearing loss due to
damage to cochlear structures or the auditory
nerve. See conductive hearing loss.
sensory aphasia See fluent aphasia.
septal area Area ventral to the genu and rostrum of
the corpus callosum on the medial aspect of the
frontal lobe that is the site of the septal nuclei.
septal region Limbic system area anterior and
lateral to lamina terminalis; includes subcallosal
area and septal nuclei deep to it; associated with
reward or pleasurable feelings.
septum pellucidum [L. partition + transparent]
Triangular double membrane between the frontal
horns of the lateral ventricles; it fills in the
interval between the corpus callosum and the
fornix.
sheath of Schwann See neurolemma.
short-term memory (STM) Memory that usually
only lasts for seconds or as long as the rehearsal
continues.
sign In medicine, an abnormality observed by the
physician and independent of the observation of
the patient. See symptom.
sleep paralysis A state in which the ability to move
or talk in temporarily lost.
sleep spindle A characteristic 14-18 Hz wave in the
EEG of a person in stage of sleep.
slow pain Dull, burning pain that is diffuse rather
than localized, resulting from tissue injury.
slow-wave sleep Sleep, divided into stages1-4, that
is defined by the presence of slow-wave EEG
activity.
somatic [Gr. somatikos, bodily] Denoting the body,
exclusive of the viscera (as in somatic efferent
neurons that supply the skeletal musculature).
somatosensory system Pertaining to the general
somatic senses: somatic pain and temperature,
touch, vibration, and limb position and motion
sensibility.
somatotopic [Gr. soma, body + topos, place]
Representation of parts of the body in
corresponding parts of the brain.
somesthetic [Gr. soma, body + aisthesis, perception]
Consciousness of having a body. Somesthetic
senses are those of pain, temperature, touch,
pressure, position, movement, and vibration.
Also spelled somaesthetic.
somnolence Excessive and inappropriate sleepiness.
sound pressure level (SPL) Sound pressure of
0.0002 dyne/cm2 used to establish a 0 dB
reference for audiological testing.
spasticity An increase in muscle tone resulting from
an increased sensitivity of the muscle stretch
reflex (MSR). This is the cardinal sign of an
upper motor neuron lesion. See cogwheel
rigidity; lead pipe rigidity.
spina bifida [L. bifidus, cleft] The generic term used
to describe any of a set of developmental
disorders in which the structures dorsal to or
derived from the neural tube do not close during
development.
spinal shock Spinal cord areflexia due to sudden
interruption of cortical input.
spiral organ Sensory end organ for hearing found in
cochlear duct of internal ear; synonym organ of
Corti.
splenium [Gr. splenion, bandage] Thickened
posterior extremity of the corpus callosum.
split brain Brain in which the corpus callosum and
sometimes the anterior and hippocampal
commissures have been severed in the median
plane.
squint From Middle English asquint, with the eyes
askew. See also strabismus.
stellate [L. stella, star] Stellate neuron has many
short dendrites that radiate in all directions.
stenosis [Gr. stenos, narrow] Abnormal narrowing
of a tube or passage.
stereocilia Groups of extremely long, slender,
nonmotile microvilli projecting from epithelial
cells.
stereognosis [Gr. stereos = solid + gnosis =
knowledge] Ability to recognize an object by
touch alone.
stereotypy Repeated, often stereotyped speech or
actions.
strabismus Deviation of an eye due to impaired
function of an extraocular muscle or nerve.
stria terminalis [L. a furrow, groove + boundary,
limit] Slender strand of fibers running along the
medial side of the tail of the caudate nucleus.
Originating in the amygdaloid body, most of the
fibers end in the septal area and hypothalamus.
striatum [L. striatus, furrowed] Phylogenetically
more recent part of the corpus striatum
(neostriatum) consisting of the caudate nucleus
and the putamen or lateral portion of the
lentiform nucleus. In comparative anatomy,
striatum refers to a region of the brain in fishes,
amphibians, and reptiles that is comparable to
the corpus striatum of mammals.
stroke The rapid loss of neural function that can be
explained by infarction of a portion of the brain
located within the territory of a single artery, and
that does not resolve within 24 hours.
stupor A state of unconsciousness from which the
patient can be aroused, but not brought to full
awareness.
subarachnoid space Beneath the arachnoid, refers
to space filled with CSF.
subdural space Beneath the dura, between the dura
and the arachnoid; refers to a potential space
containing a serous fluid.
subiculum [L. diminutive of subex (subic-), a layer]
Transitional cortex between that of the
parahippocampal gyrus and the hippocampus.
substantia gelatinosa Column of small neurons at
the apex of the dorsal gray horn throughout the
spinal cord.
substantia innominata Gray matter of the anterior
perforated substance; contains basal nucleus of
Meynert.
substantia nigra Pigmented nuclear mass located in
the midbrain; one of the basal ganglia;
malfunction associated with Parkinson disease.
subthalamic nucleus Nuclear mass located in
subthalamus; one of the basal ganglia;
malfunction associated with ballismus.
subthalamus Part of the diencephalon found
between the thalamus dorsally, the cerebral
peduncle ventrally, and the hypothalamus
medially; composed of subthalamic nucleus,
zona incerta, and prerubral field; synonym
ventral thalamus.
sudomotor [L. sudor, sweat + motor, mover]
Applies to sympathetic neurons that stimulate
secretion from sweat glands.
superior cerebellar peduncle Fiber bundle
connecting the cerebellum and the midbrain;
synonym brachium conjunctivum.
superior longitudinal fasciculus Large association
bundle connecting cortex on the lateral surfaces
of the frontal, parietal, and occipital lobes;
sometimes described as dorsal part of arcuate
fasciculus.
superior medullary velum Thin lamina of white
matter between the superior cerebellar
peduncles; forms the roof of the pontine part of
the fourth ventricle in the midline, beneath the
lingula of the cerebellum; synonym anterior
medullary velum.
supranuclear lesion Upper motor neuron lesion.
sylvian fissure See lateral fissure.
sympathetic [Gr. syn = with + pathos = suffering]
That division of the autonomic system having
the origin of its preganglionic component in the
thoracic and lumbar cord segments and playing a
role in the preparation of the organism for
emergency situations.
synapse [Gr. syn = together + haptein = to touch]
Site of functional contact between neurons
where impulses pass from one neuron to
another.
syndrome [Gr. syndrome, the act of running
together or combining] Collection of concurring
clinical symptoms and signs. A syndrome
usually is due to a single cause. The word is
often used incorrectly as a synonym for
"disease."
syringomyelia [Gr. syrinx, pipe, tube + myelos,
marrow] Condition characterized by central
cavitation of the spinal cord and gliosis around
the cavity.
tabes dorsalis [L. tabes = a wasting away]
Deterioration of dorsal spinal roots and dorsal
columns of the spinal cord resulting from
syphilis and manifested by pain and paresthesia,
impairment of postural and vibratory sensibility,
ataxia, and decreased stretch reflexes; synonym
locomotor ataxia.
tachycardia [heart hurry] Rapid beating of the heart,
usually applied to rates over 100 per minute.
tangential [L. tangens, touching] In the direction of
a line or plane that touches a curved surface.
Used in anatomy for a plane of section
approximately parallel to the surface of an
organ.
tanycyte [Gr. tanyo, to stretch + kytos, hollow
(cell)] Specialized type of ependymal cell
present in the floor of the third ventricle.
tapetum [L. tapete, a carpet] Fibers of the corpus
callosum sweeping over the lateral ventricle and
forming the lateral wall of its temporal horn.
tectum [L. roof] Roof of the midbrain consisting of
the paired superior and inferior colliculi.
tegmentum [L. cover, from tego, to cover] Dorsal
portion of the pons; also the major portion of the
cerebral peduncle of the mid- brain, lying
between the substantia nigra and the tectum.
tela choroidea [L. a web + Gr. chorioeides, like a
membrane] Vascular connective tissue
continuous with that of the pia mater that
continues into the core of the choroid plexuses.
telencephalon [Gr. telos, end + enkephalos, brain]
Cerebral hemispheres; anterior of the two
divisions of the prosencephalon or anterior
primary brain vesicle.
telodendria [Gr. telos, end + dendrion, tree]
Terminal branches of axons.
tentorium [L. tent] Tentorium cerebelli is a dural
partition between the occipital lobes of the
cerebral hemispheres and the cerebellum.
tetraplegia [Gr. tetra-, four + plege, a blow or
stroke] Paralysis that affects the four limbs. Also
called quadriplegia.
thalamus [Gr. thalamos, an inner chamber; also
meant a bridal couch, so that the pulvinar was its
cushion or pillow] Galen made up the word
thalamus, and Willis was probably the first to
use the word in its modern sense.
thrombus [Gr. thrombos, clot] Clotted blood in a
living blood vessel. Thrombosis occurs at sites
of irregularity, typically due to atheroma in
arteries.
TIA See transient ischemic attack.
tic An involuntary rapid and repeated contraction of
a small group of muscles that results in
spasmodic movement.
tic douloureux [Fr. tic, spasmodic movement + Fr.
douloureux, painful] Synonym for trigeminal
neuralgia.
tinnitus [L. tinnio, a jingling] The nonhallucinatory
perception of sound where none exists.
tolerance A condition in which, with repeated
exposure to a drug, the individual becomes less
responsive to a constant dose.
tomography [Gr. tomos, cutting + grapho, to write]
Production of images of sections through a part
of the body. Computed tomography with x-rays
and nuclear magnetic resonance imaging are
valuable diagnostic techniques.
tone, tonus [Eng. from Gr. tonos, pitch, tension]
Normal firmness and elasticity of muscles
caused by partial contraction of some of their
fibers.
tract [L. tractus, a region or district] Region of the
central nervous system largely occupied by a
population of axons that all have the same origin
and destination (which often form the name, as
in "spinothalamic tract").
transcutaneous electric nerve stimulation (TENS)
Selective electrical stimulation of large
cutaneous afferent fibers in order to inhibit slow
pain conduction in spinothalamic neurons; used
for treatment of chronic pain.
transducer [L. tranducere, to lead across] Structure
or mechanism for converting one form of energy
into another; applied to sensory receptors.
transference Patient's tendency to endow the
physician with characteristics of important
people (such as parents) in the patients life.
trapezoid body Transverse fibers of the auditory
pathway situated at the junction of the dorsal
and ventral portions of the pons.
tremor [L. tremere = to shake] Involuntary
trembling or shaking.
trigeminal [L. born three at a time] Trigeminal
nerve has three large branches or divisions.
trigeminal neuralgia Pain of a severe, throbbing, or
stabbing character in the course or distribution
of the trigeminal nerve.
trochlear [L. trochlea, a pulley] Trochlear nerve
supplies the superior oblique muscle, whose
tendon passes through a fibrous ring, the
trochlea. This ring changes the direction in
which the muscle pulls.
truncal ataxia Ataxia affecting the muscles of the
trunk; most often caused by a lesion of the
vestibulocerebellar midline.
uncinate. [L. hook-shaped] Uncinate fasciculus:
association fibers connecting cortex of the
ventral surface of the frontal lobe with that of
the temporal pole. Also a bundle of
fastigiobulbar fibers (uncinate fasciculus of
Russell) that curves over the superior cerebellar
peduncle in its passage to the inferior cerebellar
peduncle.
uncinate fasciculus [L. uncinatus = hook shaped]
Association bundle connecting the frontal and
temporal lobes.
uncus [L. hook] Thickening on the medial side of
the parahippocampal gyrus overlying the
amygdala and resting near the free edge of the
tentorium cerebelli.
uninhibited reflex bladder Incontinence but no
retention; occurs after bilateral frontal lobe
lesions.
upper motor nerve syndrome Disorder
characterized by spastic paralysis, exaggerated
myotatic reflexes, and abnormal superficial and
deep reflexes; due to lesion of corticospinal
system although some include other corticofugal
paths also.
uvula. [L. little grape] A part of the inferior vermis
of the cerebellum.
vagus. [L. wandering] Tenth cranial nerve is so
named on account of the wide distribution of its
branches in the thorax and abdomen.
vasopressin See antidiuretic hormone (ADM.
velate. [L. velum, sail, curtain, veil] Velate or
protoplasmic astrocytes have flattened
processes.
vallecula. [L. diminutive of vallis, valley] Midline
depression on the inferior aspect of the
cerebellum.
velum. [L. sail, curtain, veil] Membranous structure.
Superior and inferior medullary vela forming the
roof of the fourth ventricle.
ventricle. [L. ventriculus, diminutive of venter,
belly] Lateral, third, and fourth ventricles of the
brain.
vermis [L. worm] The midline portion of the
cerebellum; its connections are primarily with
the fastigial nucleus, which affects the vestibular
nuclei for equilibrium and eye movements.
vertical gaze center Neurons at the levels of the
superior colliculus and pretectal area, which
control vertical eye movements; upward
movements represented more dorsally,
downward more ventrally.
vestibular membrane (Reissner membrane)
Membrane within the cochlea that separates the
scala vestibuli and the cochlear duct.
vestibulo-ocular reflex Three-neuron reflex
resulting in turning of eyes in a direction
opposite to that of head rotation: (1) vestibular
ganglion, (2) vestibular nuclei, (3) III, IV, VI
nuclei.
vibration sense Awareness of deep touch and
pressure tested with a vibrating tuning fork.
Virchow-Robin space Spaces that surround blood
vessels where they enter the CNS.
Wallenberg syndrome See lateral medullary
syndrome.
wallerian degeneration Synonym for orthograde
axonal degeneration.
Weber syndrome Disorder characterized by
contralateral spastic hemiplegia with ipsilateral
ophthalmoplegia (with the eye turned down and
out, ptosis, and mydriasis); results from a lesion
of the cerebral crus and oculomotor nerve of one
side in the midbrain; synonym superior
alternating hemiplegia or alternating oculomotor
hemiplegia.
Weber tuning fork test Application of a vibrating
tuning fork to the midline of the forehead to
ascertain in which ear the sound is heard better;
the better heard ear being abnormal in
conduction deafness or normal in sensorineural
deafness.
Wernicke's area Posterior part of the superior
temporal gyrus of the dominant hemisphere,
which functions as a receptive speech center.
zona incerta. Gray matter in the subthalamus
representing a rostral extension of the reticular
formation of the brain stem.
zonula occludens [L. diminutive of zona, belt +
occluding] Also known as a tight junction. Form
of continuous close apposition of the membranes
of neighboring cells, impermeable to
macromolecules.
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