Abulia Lack of will,
lack of impulse, inability to make decision. See
frontal lobe abulia.
3-part reflex brought into action by looking at a near object: the eyes turn inward,
the pupils constrict and the ciliary muscles relax resulting in thickening of
Inability to perform rapid alternating movements such as pronation-supination
of the forearm or successive touching of each finger to the thumb. This symptom
suggests damage to the cerebellum or its connections. (Synonym dysdiadochokinesis)
Agnosia. The inability
to recognize an object despite having basic sensory abilities (vision, hearing,
touch and language functions, etc.) intact. There are many types of agnosia, for
example see finger agnosia.
Agraphia. (also called
anorthography) The inability to write language. Pure agraphia without disturbance
of other language functions is rare.
to identify a number or letter written on the hand (or other part of the body).
Graphesthesia requires intact epicritic perception.
Alexia. The inability
to understand written language.
Amaurosis fugax. An
episode of abrupt, temporary monocular blindness (or blurring of vision) caused
by transient retinal ischemia.
Amnesia. Loss of memory.
See anterograde amnesia and retrograde
Amyloid. An adjective meaning "starch-like."
Also used as a noun to refer to a protein-polysaccharide complex that forms deposits in organs and
Cause of vascular degeneration in which a protein-polysaccharide complex deposits
within blood vessels. Such vessels are more prone to hemorrhage. This condition
is more likely to be found among the elderly and is associated with lobar
Amyotrophic lateral sclerosis
(ALS, also known as Lou Gehrig's disease). A "system" disease of slow
onset involving destruction of both upper and lower motor neurons.
absence of forebrain and calvaria due to failure of fusion of the neural plate.
Aneurysm. Local dilation
("ballooning") of an artery due to a weakening of the arterial wall.
In large vessels, the mechanism which weakens the wall is almost always atherosclerosis.
technique for imaging blood vessels. In classic methods, the vessels of
the brain are visualized by injection of radiopaque dye. Digital subtraction angiography
(using computer processing to produce images) carries less risk for the patient
because the amount of dye can be reduced. Magnetic resonance angiography is a
newer, noninvasive technique that is helpful for visualizing extracranial and
large intracranial vessles. However, at present, invasive angiograpy is
more sensitive for smaller vessels.
asymmetry. Most people have pupils equal in size; however, mild asymmetry can
Anosmia. Loss of sense
of smell. Not routinely tested in neurological exam (though it probably should
be) unless patient complains of loss of smell or taste. Usually caused by nasal
inflammation but can be caused by trauma or tumor of the orbital frontal lobe.
is unaware that anything is wrong with them. Often accompanies unilateral
neglect following a right parietal lobe lesion.
The internal carotid artery and its branches.
Loss of memory of events occurring after onset of amnesia, inability to form new
memories. Anterograde amnesia is the key component of Korsakoff's
Aphasia. A loss or
impairment of the production and/or understanding of written or spoken language.
Aphasia is an intellectual impairment, and is quite different from the purely
motor problems of dysarthria.
to perform familiar movements despite absence of paralysis or sensory deficit.
See dressing apraxia.
technique for imaging arteries. See angiography.
Hardening and thickening of arterial walls due to pathologic changes in the intima
Abbreviated AVM; congenitally abnormal arteries and/or veins.
to identify, by touch alone, objects placed in the hand such as differentiating
between a dime and a quarter.
of voluntary movement. It is a sign of damage to pathways connecting the cerebellum
with the spinal cord and brainstem, or damage to parts of the cerebellum itself.
disease of large- and medium-sized arteries in which the intima (the layer of
the arterial wall closest to the lumen) accumulates abnormal patches of lipids
and cells that eventually expand to form elevated 'plaques' which can obstruct
blood flow. Established plaques can undergo a series of additional events
that increase the patient's chances of serious vascular complications. For
example, plaques may ulcerate and promote thrombus formation; they may break open
and shed emboli; they may calcify and further stiffen the vessel wall; they may
cause rupture of the entire arterial wall leading to hemorrhage.
slow, sinuous movements. They may alternate smoothly between extension-pronation
and flexion-suppination of the arm or between eversion and inversion of the foot,
to cite just two possible examples. Seen after damage to the striatum.
Athlete's high. A reduction in perception of pain by
sustained, intense concentration of mind and body on a physically and mentally
The diagnostic technique of listening to sounds within the body, usually to ascertain
the condition of blood vessels and thoracic or abdominal viscera. A stethoscope
is often used.
Babinski sign. An
abnormal (dorsiflexor) plantar reflex.
Bell's palsy. Paralysis
of all muscles of facial expression (corner of mouth droops, palpebral fissure
is widened, forehead is unfurrowed) which has a sudden onset. It is due to lesion
of the VIIth nerve, and may be accompanied by loss of taste sensation, and reduced
salivation and lacrimation depending on exactly which components are involved.
Causation is unclear. About 90% of patients have only demyelination of the nerve,
and recover in a few weeks; a longer recovery period is required if axon degeneration
has occurred. Axon regeneration may take over a year, and is often incomplete.
A rare heteronymous hemianopsia that could occur in the unlikely event that there
are aneurysms of both internal carotid arteries at the level of the optic chiasm
thus compressing the chiasm laterally. See visual
A heternomymous hemianopsia consisting of loss of vision in the temporal visual
fields usually caused by damage to the central portion of the optic chiasm. See
visual field defects.
Broca's aphasia. (Synonyms:
anterior, expressive, or nonfluent aphasia). A primary deficit in language output
(production), in which comprehension is largely unaffected. The defect may involve
loss of all propositional speech, or the patient may use a small number of substantive
words which are laboriously enunciated and not combined into grammatical phrases.
The patient can repeat words, but the repetition has the same abnormalities as
the individuals' own speech. The impairment in writing is usually equally severe.
The patient is almost always aware of the problem. In right-handers, the lesion
is in the left inferior frontal lobe; often there is accompanying paralysis of
the lower face or arm on the right side.
A set of findings that may be produced by incomplete or complete hemisection (damage
to one side) of the spinal cord: 1) Ipsilateral upper
motor neuron paralysis involving muscles innervated by segments below the
lesion. 2) Ipsilateral lower motor neuron
paralysis involving muscles innervated by the damaged segments. 3)
Contralateral loss of pain and temperature sensation beginning several segments
below the level of lesion. 4) Ipsilateral loss of
two-point discrimination and joint position
sense below the level of lesion. 5) Anesthesia to all sensations in
dermatomes supplied by the damaged segments.
Bruit. A sound or
murmur, often abnormal, heard during auscultation. For example, the presence
of severe stenosis of the carotid artery in the neck may produce a bruit by causing
turbulent blood flow.
Nystagmus elicited by instilling warm or cool water into
one ear canal. This is a normal physiological response, and is an important clinical
test for the integrity of the membraneous labyrinth, and vestibular components
of the VIIIth nerve.
Cerebral palsy. A
general term sometimes applied to motor abnormalities that have their onset early
in life. It is a catch-all phrase, and encompasses a variety of diseases that
occur before, at, or in the first months after birth.
rapid, jerky movements. Seen after damage to the striatum.
movements with features of both chorea and athetosis. These two movement patterns
have many similarities, and even the experts often use this combined term. Seen
after damage to the striatum.
A benign epithelial tumor of a subset of cells in the anterior lobe of the pituitary.
See pituitary tumor.
A roundabout, indirect or lengthy way of speaking.
Description of the abnormal way that paralyzed limb muscles respond to passive
stretch after pyramidal tract damage. Characteristically, the greater the velocity
of stretch, the greater the resistance of the muscle.
Clonus. An abnormal
response to the stretching of a muscle. It consists of a series of rhythmic involunary
muscle contractions that occur in response to a single stretch, such as tapping
the tendon to elicit a muscle stretch reflex.
Coma. A state in which
patient is incapable of being aroused by external stimuli or inner needs.Can be
characterized by absence of sleep/wake cycles and loss of response to even vigorous
stimulation. Compare to "locked-in state"
in which there is little or no disturbance of awareness (consciousness) but only
an inability of the patient to respond to stimuli.
A deficit in language in which comprehension of language is preserved, but the
individual's speech is defective in ways resembling Wernicke's
aphasia: fluent, properly articulated, but largely nonsensical. The patient
is aware of the problem, but is unable to correct his or her own erroneous speech.
This syndrome occurs when the anterior and posterior speech areas are both intact
but are disconnected from each other because of a lesion in the arcuate fasciculus
on the left side.
To fill in gaps in memories with fabricated facts which he/she believes to be
true. Confabulation is often seen in Korsakoff's
"psychosis" and lesions involving the hippocampus.
Conjugate gaze. The
symmetrical and synchronous movement of the eyes (from Latin conjugatus, yoked
or joined together.)
Convergent gaze. Simultaneous
movements of the eyes toward the midline. They are required to fuse the visual
images by keeping the images focused on corresponding parts of the retinas. This
is essential for near vision.. When we look at near objects, three things occur:
turning of the eyes inward, constriction of the pupils, and relaxation of the
ciliary muscles to allow the lens to thicken. Collectively, this triad is referred
to as accomodation. See accommodation reflex.
Corneal reflex. Light
touch on the cornea produces closure of that eye (a blink), or closure of both
eyes if the stimulus is more intense. Afferent limb of reflex involves trigeminal
ganglion cells whose distal axon branches run in the ophthalmic division of V
and central branches which enter the descending tract of V and synapse with cells
in the interpolar part of the spinal nucleus. Eventually motoneurons in the VIIth
nucleus are activated, and they in turn produce contraction of the orbicularis
oculi. (Note that the corneal reflex does not involve the upper lid, which is
controlled by the IIIrd nerve.)
Corticobulbar tract disease
(supranuclear facial weakness) Results in paralysis of the facial muscles contralateral
to the lesion with sparing of the forehead. Thus patients with supranuclear facial
weakness can raise their eyebrows because motoneurons to forehead are bilaterally
innervated by the corticobulbar tract whereas motoneurons to the rest of the facial
muscles are innervated by the contralateral cortex. Contrast
with Bell's Palsy.
Benign tumors generally believed to originate from remnants of Rathke's pouch
at the junction of the infundibular stalk and pituitary. Usually lies above the
sella turcica and can affect the optic chiasm, pituitary and hypthalamus.
Reflex seen when several segments of spinal cord are intact bilaterally. When
stimulated with active flexion of one limb the opposite limb extends. This reflex
serves the purpose of stabilizing the organism when one limb is withdrawn as in
the withdrawal reflex.
Crossed motor impairment.
A pattern of motor impairment produced by brainstem lesions (i.e., lesions rostral
to the pyramidal decussation) in which there is upper
motor neuron paralysis of the arm and leg contralateral to the lesion, and
lower motor neuron paralysis involving a cranial
nerve motor function ipsilateral to the lesion. Also called crossed weakness.
Crossed pain and temperature
loss. Loss of pain and temperature sensation on one side of the face, and
the opposite side of the body. This can be produced by lateral lesions in the
caudal pons or medulla which damage EITHER the descending (spinal) tract of V
or the caudal part of the spinal nucleus of V AND the spinothalamic tract. By
contrast, single lesions in the rostral pons or midbrain usually produce contralateral
loss of pain and temperature in both face and body, since the part of the trigeminal
system present at these rostral levels (second-order trigeminothalamic fibers)
is mostly crossed.
Crude light touch.
The ability to indicate that an object is touching the body surface, but without
a precise localization, hence crude. When crude light touch is impaired, the threshold
for touch sensation is usually elevated. Many synonyms are used: simple touch,
elementary touch, crude touch, or light touch.
(pontine extensor rigidity, positive supporting reflex) stimulation of plantar
surface of one or more limbs leads to extension of all four limbs. Most likely
mediated by the lateral vestibulospinal tract at the level of the pons.
Refex postures of limbs of a paralyzed or obtunded patient, mediated at the level
of the red nucleus and more complex than decerebrate rigidity. The commonest form
is extension of the leg(s) accompanied by flexion of the arm(s). See Magnus
Dekleijn reflex and red nucleus walking.
Deep tendon reflexes.
See stretch reflexes.
Dementia. A condition
in which intellectual or cognitive functions deteriorate, with little disturbance
of consciousness. Usually the intellectual failure is accompanied by changes in
behavior or personality. Dementia can be caused by cerebral atrophy (mainly Alzheimer's
disease), multiple infarcts, tumors, Huntington's
disease, chronic drug intoxication, AIDS, trauma, to name but a few of the
many possible neurologic or other diseases which may be responsible.
Total atrophy of skeletal muscle fibers which occurs after disconnection from
vision. It can be the result of damage to the brainstem gaze mechanisms, the motor
nuclei or nerves of the extraocular muscles, or disease of the muscles themselves.
Disinhibition of behavior.
Patients say and do the first things that come into their heads without considering
the social correctness or the future consequences of what they say or do. Can
occur with bilateral damage to prefrontal lobes of the cortex or median dorsal
nuclei of the thalamus.
sensory experiences described by the patient as a feeling of rotation or whirling,
but also as light-headness, faintness, or swaying. Many different conditions can
lead to this complaint. One subset of complaints in which the patient descibes
definite feelings of rotation (whether of himself or the environment) is called
vertigo , and occurs almost exclusively with disorders of the peripheral or central
vestibular system. See vertigo.
Inability to put clothes on correctly in the absence of any motor defect which
would interfere with the task. The patient has lost the spatial concept of how
items of clothing fit around the limbs and body. Neglect of the left side is one
conspicuous component of dressing apraxia, though it is not the whole story. Seen
in large lesions of the right parietal lobe (assuming a right-handed patient).
of articulating words (speaking), with normal comprehension and memory of words.
This is a motor disorder which involves the various muscles of the face, lips,
tongue, and vocal cords that are used in speech. Dysarthria can be the result
of lower motor neuron paralysis or upper
motor neuron paralysis. It can also reflect incoordination of muscles due
to cerebellar damage, rigidity of muscles due to damage to the extrapyramidal
system, or even repetitive muscle spasms as occur in stuttering.
Dyslexia. A developmental
language disorder characterized by difficulty with reading, writing and spelling.
There is no loss of the ability to recognize the meaning of objects, pictures,
sensation produced by normal stimuli. See thalamic
"measuring" of distances in voluntary movements. The limb arrests too
soon or overshoots the mark when the subject attempts to make a specific movement.
Dysmetria is a sign of damage to pathways connecting the cerebellum with the spinal
cord and brainstem, or damage to parts of the cerebellum itself.
Dystonia. A persistent
posture or position, which seems to occur when an athetoid movement becomes "frozen"
at one of its extremes. For example, the hand may remain painfully over-flexed
for minutes at a time. The localization of the damage is not clear, but the extrapyramidal
system is involved.
Embolus. Part of a
thrombus that has broken free and traveled through the
circulation until becoming lodged in a small vessel (and impeding flow). Other
types of tissue, such as tumor or fat, and gas (e.g., an air bubble) can also
removal of the lining of an artery that has become occluded or otherwise diseased.
These complex sensory perceptions are highly integrated, precisely localized determinations
about sensory events initially detected by mechanoreceptors.The derivation of
this word is from the Greek "epikrisis" meaning determination. Examples
of epicritic perceptions include two-point
discrimination, joint position sense,
stereognosis, and graphesthesia.
Extinction (of a sensory
stimulus). Recognition only on one side of bilaterally and simultaneously
contractions of all the muscle fibers in a motor unit (a fascicle of muscle fibers),
which occur in early stages of muscle denervation. They presumably reflect abnormal
activity of the motoneuron. Fasciculations can be seen during physical examination
if the affected muscle is close to the body surface. They appear as subtle ripples
or waves of contraction that pass across the skin surface.
contractions of individual muscle fibers (cells) which occur in early stages of
muscle denervation. They can be detected only by needle electrodes in the muscle,
unlike fasciculations which are visible on physical
Finger agnosia. The
inability to name the different fingers of the two hands. Finger agnosia may be
seen after left parietal lobe lesions (in right-handers). It is often accompanied
by left-right confusion and an inability to
do even the simplest mathematical calculations.
The patient is asked to alternately touch the examiner's finger and his own nose.
This compound movement involves a change in posture at several joints, and if
the duration and timing of muscle contractions and relaxation are abnormal, this
test will demonstrate the problem. An abnormal finger to nose test indicates damage
to the cerebellum and/or its connections with the brainstem and spinal cord.
(lower motor neuron paralysis) . Paralysis with the following characteristics:
1) muscles are soft and lax. 2) muscles provide no resistance at
all to passive stretching. 3) reflexes cannot be elicited (but if the
paralysis is incomplete, any reflexes present will be normal e.g. Babinski
response will be plantar flexion.). 4) muscles show abnormal electrical
activity. Later they undergo denervation atrophy.
Foot drop. Inability
to dorsiflex the foot resulting in gait difficulties, seen with paralysis of anterior
muscles of the leg.
Frontal lobe abulia.
Reduced motor activity of all kinds produced by bilateral damage to the prefrontal
cortex , i.e. frontal lobe cortex which is located anterior to the usual primary
and supplementary or association motor cortices.
Gag reflex. Reflex
elicited by touching the posterior wall of the pharynx. Pharyngeal muscles contract
symmetrically elevating the soft palate. Actual gagging may or may not occur.
Afferent loop involves the glossopharyngeal nerve, the efferent loop involves
the vagus nerve.
Glaucoma. A group
of heterogeneous eye diseases resulting from an increase in intraocular pressure.
Can lead to visual field defects and ultimately blindness.
to identify a number or letter written on the hand (or other part of the body).
Graphesthesia requires intact epicritic perception.
An inherited disease producing rigidity, dystonia, and
choreoathetosis. The globus pallidus, substantia
nigra, and red nucleus degenerate and become filled with intense brown pigmentation
which apparently represents abnormal iron deposits. No current treatment reverses
the disease, and certain individuals may ultimately become completely mute and
rigidly immobile, i.e. "locked-in."
The patient is asked to place one heel on the opposite knee, and then run the
heel down the front of the shin to the ankle. This compound movement involves
a change in posture at several joints, and if the duration and timing of muscle
contractions and relaxation are abnormal, this test will demonstrate the problem.
An abnormal heel to shin test indicates damage to the cerebellum and/or its connections
with the brainstem and spinal cord.
of sensation over one half of the body.
Hemianopsia (or hemianopia).
Loss of one half of the visual field of one or both eyes, referred to as unilateral
or bilateral hemianopsia. See visual field defects.
wide-ranging, flinging movements of entire limb(s). Seen after damage to the subthalamic
nucleus. The abnormal movements occur on the side opposite the damaged subthalamic
of the arm and leg (sometimes lower face as well) on one side of the body.
Caused by rupture of a blood vessel or aneurysm. Hypertension greatly increases
the risk of hemorrhagic stroke especially in the thinner-walled vessels. An embolic
stroke can also have a hemorrhagic component if the embolus blocks the vessel
long enough to kill brain tissue and then breaks up, permitting re-perfusion of
the now dead tissue.
to non-corresponding visual fields. See visual
A loss of one half of the visual field comprised of non-corresponding field losses
from each eye. See visual field defects.
to corresponding visual fields. See visual field
A loss of vision in the corresponding halves of the visual fields in the two eyes.
It is produced by lesions of the visual pathway behind the optic chiasm,
but not by damage to the retina or optic nerve. See
visual field defects.
Loss of corresponding quarters of the visual fields in both eyes. Usually caused
by damage to the temporal or parietal lobe optic radiations. Damage to temporal
results in superior quadrant defect whereas damage to parietal lobe optic radiations
results in an inferior quadrant defect. See visual
One or more of the following findings, indicating sympathetic dysfunction: 1)
uneven pupils, with more constricted pupil on side of lesion. 2) mild
drooping of the eyelid (weak tarsal muscles in upper lid produce little "ptosis")
on side of lesion. 3) hot, flushed, dry skin on same side of face as lesion.
The lesion is always on the same side as the findings. However the lesion can
interrupt the sympathetic system at different levels: reticulospinal tracts of
brainstem/spinal cord; intermediolateral column at T1-2; superior cervical ganglion;
postganglionic sympathetic fibers, etc.
An autosomal dominant inherited disorder, usually beginning in middle age, featuring
insidious progression of mental abnormalities associated with frontal lobe damage
(emotional, personality, and intellectual) and motor abnormalities associated
with basal ganglion damage (hence the alternate name, Huntington's chorea).
Although there are exceptions, most patients with this disorder deteriorate to
a vegetative state in 10-15 years. Pathological examination of the brain reveals
extensive degeneration of the striatum, and to a lesser extent, frontal cortex.
Molecular biology reveals abnormal expansion of the triplet repeat at the 3' end
for the coding region of a newly characterized gene; its function is not yet understood.
high levels of fat in the blood, increasing the risk of vascular disease.
in resistance that a muscle normally offers to: 1) palpation (muscle feels
soft and lax) 2) passive manipulation like flexion or extension of a limb.
If accompanied by paralysis, hypotonia is a sign of lower motor neuron damage.
Hypotonia also occurs in cases of cerebellar damage where both upper and lower
motor neurons are intact.
Infarct. An area of
dead tissue which is the result of acute ischemia.
In disease of the cerebellum or its connections, the velocity and force of movements
are not properly controlled. If a limb overshoots or undershoots its target, then
the error is corrected with a series of jerky secondary movements in which the
finger (or toe) moves side-to side before it finally reaches the target. These
little movements have been called intention tremor. (In addition, patients with
cerebellar damage or damage to the superior cerebellar peduncle may show a much
wider-range, flapping tremor whenever they try to activate limb muscles.)
Impairment of the ability to adduct one eye, without damage to the IIIrd nerve
or nucleus since that eye can still move toward the midline in convergence. Internuclear
ophthalmoplegia (abbreviated INO by neurologists) is produced by an ipsilateral
lesion in the medial longitudinal fasciculus that damages fibers projecting to
the oculomotor nucleus from the contralateral abducens nucleus.
Ischemia. Loss of
Ischemic stroke. Often
caused by a thrombus or embolus which results in blood supply being blocked.
Compare to hemorrhagic stroke.
Jaw jerk. Monosynaptic
reflex elicited by tapping the chin with the jaw muscles relaxed. If the reflex
is hypereactive (suggesting upper motor neuron problems), contraction of the masseters
can be seen or felt.
Aprocedure to emphasize stretch reflexes. Patient
links fingers of the hands together and makes a slight outward pull. Reflexes
may also be emphasized by having the patient grit the teeth.
Joint position sense.
The ability to distinguish which direction a joint is being moved, without visual
cues. This is an epicritic perception.
A defect in forming new, long-term memories in an alert and responsive individual
whose other cognitive impairments are far less severe. See also Wernicke-Korsakoff
Lacunar Infarct. A
small cavity or lacune, produced by occlusion of a small penetrating arterial
branch and the subsequent death of a small amount of brain tissue. Lacunar
infarcts most commonly occur in the basal ganglia, thalamus, base of the pons,
internal capsule, and deep white matter of the hemisphere.
Lacunar Stroke. A
subtype of ischemic stroke in which the affected
area resembles a lacuna or cavity.
Lateral medullary syndrome.
See Wallenberg's syndrome.
Loss of the concepts of "leftness" and "rightness" due to
left parietal lobe damage. Compare to left-sided neglect.
(unilateral neglect). Patients ignore their left sides and the left external space.
Patient is unaware of this deficit which is caused by damage to the right parietal
lobe. Homonymous hemianopsia and varying degrees of hemiparesis may also be present.
Compare to left-right confusion.
Lesion. Region of
Lobar hemorrhage. A subtype
of hemorrhagic stroke in which the ruptured vessel infarcts a region within
the cerebral hemispheres (rather than, for instance, the cerebellum).
Local reflex. Reflexes
involving neurons in a local region of the CNS; for example, a local reflex in
the spinal cord involves just one segment.
(also called pseudocoma). Can occur from a lesion of both cerebral peduncles or
from an occlusion of the basilar artery resulting in infarction of the basis pontis
but sparing of the tegmentum. Patient is quadriplegic but may be able to communicate
using eye-blinking. Can also occur as the final stages of Parkinson's disease,
Huntington's disease and other disease of the basal ganglia. Compare
Lower motor neuron paralysis.
See flaccid paralysis.
Macular sparing. Visual
field deficit produced by cortical lesions in which central (macular) vision is
relatively unaffected compared to peripheral vision.
A rarely-observed reflex consisting of rhythmic alternating flexion and extension
of the limbs, in a pattern such that flexion of the L arm and R leg and extension
of the R arm and R leg alternates smoothly with extension of the L arm and L leg
and flexion of the R arm and L leg in a pattern reminiscent of four-legged locomotion.
This reflex is "released" in situations where the cerebral cortex is
functioning abnormally. It is thought that decorticate
posturing may represent a "frozen" vestige of this reflex.
rapidly growing embryonic tumor that arises in the posterior part of the midline
cerebellum. Currently it is believed to originate from cerebellar stem cells of
the external granular layer which continue to divide in the perinatal period.
small head. Results from global failure of cortical migration during gestation.
People with microcephaly have extremely low intelligence and no propositional
Reflex involving only an afferent neuron and an efferent neuron, and therefore
only one synapse. See stretch reflexes.
MRC scale (MRC =
Medical Research Council). Standard scale from 0 to 5 used to assess muscle strength
with 0 being no movement and 5 being full strength.
Spinal cord reflexes which involve multiple adjacent segments. The limb withdrawal
reflex is a multisegmental reflex since motoneurons in several segments must be
activated to withdraw an entire limb from a potentially damaging (noxious) stimulus.
speech which utilizes words that are totally made up. See
Neuropathy. A lesion
of peripheral nervous system.
rhythmic movements of the eyes. Most commonly, movements consist of a slow movement
of both eyes in one direction, followed by a fast corrective movement (a jerk)
in the opposite direction. Nystagmus can be either a sign of disease in eye movement
pathways (in brainstem or cerebellum) or a normal physiological response to certain
stimuli. See caloric nystagmus, optokinetic
nystagmus and postrotational nystagmus.
Nystagmus elicited by presenting the subject with a monotonous series of stimuli
steadily moving in the same direction at the same speed. It is a normal physiological
Oscillopsia. A condition
in which stationary objects appear to jerk back and forth or wiggle, because of
involuntary eye movements. Oscillopsia can be the result of labyrinthine, brainstem
or cerebellar disease; occasionally it can also involve just one eye and be the
result of spontaneous contractions of motor units in an eye muscle.
Palsy. Synonym for
paralysis. See also Bell's palsy,
Paralysis. The loss
of voluntary movement. A lesser degree of paralysis is technically paresis. However,
in everyday usage paralysis is used to mean either partial or complete loss of
voluntary movement mild degree of paralysis is often described by both physicians
and patients as weakness.
Spontaneous speech that utilizes words incorrectly. See
or paralysis of both legs.
a mild or incomplete paralysis. However it is commonly used interchangeably with
Paresthesia. A prickling, tingling,
or burning sensation associated with central and peripheral nerve lesions.
Paralysis of conjugate upward gaze from a lesion at the level of the pretectal
A syndrome of expressionless face, poverty and slowness of voluntary movement,
"resting" tremor, stooped posture,
rigidity, soft voice, and an abnormal gait consisting of small, shuffling steps
with difficulty in retaining balance, especially when changing directions. The
disease is produced by the degeneration of dopamine neurons in the substantia
nigra; its cause is unknown.
PET scan (positron emission
tomography). Imaging technique which measures the cerebral concentration of
positron-emitting isotopes which are incorporated into biologically active compounds.
The concentration of the tracers is determined by detectors positioned outside
the head, and tomographic images are constructed by a computer in a way similar
to CT or MRI. PET scanning can be used to measure cerebral blood flow, oxygen
uptake, or glucose utilization. The technology is available at a few large medical
centers where it is used in both research and specialized clinical applications;
however it is not utilized routinely in diagnosis.
One form of tremor seen in Parkinson's disease. Fingers flex and extend and thumb
adducts and abducts as if rolling a small object between them. Typically the tremor
is diminished by voluntary movements..
Pituitary tumor. Due
to the proximity of the pituitary gland to the optic chiasm, pituitary tumors
can result in visual disturbances including heteronymous anopsias.
Plantar reflex. A
primitive reflex elicited by mildly noxious mechanical stimulation of the sole
of the foot. The normal adult responds with curling of the toes (plantar
flexion). An individual whose corticospinal tract is not functioning correctly
responds with extension of the great toe and fanning of the other toes (dorsiflexion).
This abnormal response is also called the Babinski
sign. It is seen in the normal infant under a year of age whose corticospinal
tracts are not yet myelinated and in an adult whose corticospinal tracts have
been injured in some way.
Plegia. Synonym for
Positive supporting reflex.See
Vertebral, basilar, and posterior cerebral arteries and their branches.
Nystagmus elicited by rotating the subject for several minutes, and then abruptly
stopping the rotation. This is a normal physiological response.
Prefrontal leukotomy (also
prefrontal lobotomy). The operation of cutting the central white matter of the
prefrontal cortex (usually bilaterally) historically performed to relieve severe
Reflexes seen during development that are extinguished further along the developmental
process. See tonic neck reflex, Babinski
perceptions which have immediate value to the organism by warning of potential
harm -- they provide information about pain and temperature.
Ptosis. Upper eyelid
drooping. Can be caused by neuromuscular weakness, cranial nerve III disorders
and Horner's syndrome.
Pupillary light reflex.
This is tested by having the patient gaze at a distance point in a darkened room,
and then illuminating one eye. The reflex response is normally prompt constriction
of both that pupil (direct response) and the other pupil (consensual response).
The afferent limb of this reflex is the optic tract, which sends a few axons directly
to the pretectal area. The efferent limb of the reflex involves parasympathetic
components in the IIIrd nerve.
Loss of one-quarter of the visual field. See visual
or paralysis of all four extremities.
(also Wernicke's aphasia). A languge deficit characterized by an impairment in
the comprehension of speech and relatively fluent speech which lacks meaning.
Synonyms: receptive, fluent, posterior aphasia. Contrast with Broca's
Red nucleus walking.
Spontaneous standing and walking mediated at the level of the red nucleus. Pure
red nucleus walking is seen only in animals surgically deprived of cerebral cortex
and basal ganglia. However, the crawling behavior of infants, the Magnus-Dekleijn
reflex and decorticate posturing, are
all related to red nucleus walking in experimental animals.
Reflex. An involuntary
motor response to a sensory stimulus.
Loss of memory of events prior to onset of anmesia. A component of Korsakoff's
"psychosis" but also seen after transient disturbances of brain
function with little or no permanent damage. Compare
to anterograde amnesia.
A test to discriminate among possible causes of hearing impairment. A vibrating
tuning fork is placed at the external auditory canal and then in contact with
the mastoid process. Disease of the middle ear is suspected if the fork appears
louder via bone conduction (on the mastoid) than air conduction (at the auditory
canal). See also Weber's test.
Patient stands with feet together and eyes closed. This maneuver tests the integrity
of the proprioceptive system necessary for balance.
A pattern of speech in which words are broken up into syllables (the term scanning
is a reference to the way a line of poetry sounds when it is scanned for meter).
In addition to its scanning quality, speech is slow and syllables may be uttered
with either more or less force than in normal speech. This disorder indicates
damage to the cerebellum.
Upon attempting to walk legs are still and adduction of thigh may be stronger
than other movements so legs involuntarily cross.
Scotoma. An area
of deficiency in the visual field surrounded by normal areas. A scotoma is seen
in normal vision at the point of the optic disk.
A dystonia limited to certain head and neck muscles. It involves intermittent
spasms of contraction of face, jaw, and neck muscles, which can be both painful
and embarrassing to the affected individual. The cause is unknown.
Spastic paralysis (upper
motor neuron paralysis) . Paralysis with the following characteristics: 1)
distal muscles more affected than proximal muscles. 2) muscles respond
abnormally to passive stretching. 3) muscle stretch reflexes are exaggerated.
4) abnormal reflexes (like an abnormal Babinski
reflex) are present.
Spina bifida. Congenital
condition produced by failure of fusion of the laminae of the lumbar vertebrae
or of the sacrum. It occurs as a secondary consequence of failure of the posterior
part of the developing neural tube to close correctly. It may be relatively mild
(spinal cord remains in the vertebral canal) or severe (spinal cord or cauda equina
is extruded into a meningeal cyst). In mild cases there may be no neurologic deficit
unless other regions of the developing nervous system have been affected. In the
severe cases where a meningomyelocele is present, there may be perineal sphincter
failure and varying degrees of impaired leg function depending on the level; there
also may be additional neurologic problems reflecting developmental abnormalities
in the brainstem.
of a vessel, duct, or other opening.
ability to describe or identify an unknown 3-dimensional object simply by mechanically
manipulating it. This is an epicritic perception.
Stretch reflexes (deep
tendon reflexes, myotactic reflexes). These muscle reflexes normally help maintain
tone, and set the background tension of postural muscles which is needed for the
performance of voluntary movements. To test these reflexes, the tendon of a muscle
is tapped, causing the muscle to stretch. Sensory endings of large mechanoreceptor
ganglion cell axons in the muscle spindles are stimulated. Central processes of
these ganglion cells synapse directly on the motoneurons of the muscle being stretched.
These excitatory synapses excite the motoneurons, leading to contraction of that
muscle. Stretch reflexes are also referred to as monosynaptic reflexes or deep
Stroke. A sudden,
focal, nonconvulsive neurologic deficit which is produced by a vascular event.
Strokes are characterized by the abrupt onset of the deficit (a few seconds to
a few days depending on the mechanism). They can be produced by either vascular
occlusion (ischemia) or by hemorrhage. The specific neurologic deficits reflect
both the location and the size of the lesion.
syndrome which involves the expansion of the central canal of the spinal cord
and the corresponding damage to surrounding tissue.
Tabes dorsalis. One
manifestation of advanced syphilis of the nervous system. It is due to degeneration
of target cells in the dorsal root ganglia and all their processes including the
posterior columns of the spinal cord.
used to display images for a brief, fixed amount of time.
Tandem gait (heel-to-toe
walking). Similar to field testing for inebriation but is used to assess coordination.
A language problem that is seen with destruction of the pulvinar nucleus of the
Produced by damage to the somatosensory nuclei of the thalamus usually due to
a vascular lesion. As sensation returns, spontaneous pain may appear on the affected
side of the body such that any cutaneous stimulus may have a severely painful
A solid mass made of various
combinations of platelets, fibrin, clotting factors and the cellular elements
of blood that forms within the heart or blood vessels. Thrombus often forms
on the injured wall of a vessel, but loose thrombi can also form in the left atrium
of the heart if it is not contracting normally so that blood stagnates there.
A thrombus may break free and become an embolus.
Tic. (Synonym: habit spasm). Habitual movements which may range from sniffing
to throat clearing to grimacing, etc. which are incessantly repeated in situations
in which they are not called for (or even appropriate). The affected individual
may or may not be aware of them -- and may or may not be able to consciously control
nodding tremor of the head. Often a sign of a medial cerebellar disorder.
Tonic neck reflex.
Reflex induced when head is turned passively to one side. Results in extension
of arm and leg on the ipsilateral side to the head turn and flexion of the contralateral
limbs. Seen in most normal infants. In adults it can be a sign of pyramidal or
extrapyramidal tract abnormality. This reflex is mediated at the level of the
"Top of the Mark"
syndromes (also called "top of the basilar" syndrome). Syndromes
produced by occlusion of branches at the bifurcation of the basilar artery. Clinical
findings may include bilateral motor and sensory signs, cranial nerve III findings,
visual problems, cerebellar ataxia and coma.
A rare syndrome of multiple tics, which may include snorting, involuntary grunting
or high-pitched vocalization, swearing, or repetitive motor behavior like jumping
up and down or turning in a circle. Afflicted individuals often report a mysterious
compulsion to carry out these motor activities. So-called Touretters can be highly
intelligent, creative individuals. Oliver Sacks' account of a successful surgeon
who has Tourette's syndrome in An Anthropologist on Mars is fascinating.
A number of drugs currently on the market can reduce the symptoms in these individuals.
However many report that these drugs also blunt their energetic and creative personalities,
and they prefer to live with the "compulsions" of their disease. Tourette's
syndrome apparently involves metabolic alterations centered in the caudate nucleus,
although other parts of the extrapyramidal system may also be involved.
Transient ischemic attack.
(Commonly abbreviated TIA) A brief, self-reversing episode of focal, nonconvulsive
neurologic disturbance produced by temporary ischemia. There are no lasting neurologic
deficits once the attack has ended. However, TIAs provide a warning of an imminent
stroke; more than 25% of individuals who have a TIA will have a stroke (often
producing permanent neurologic deficits) within 5 years.
Attacks of extreme pain in a distribution of one or more divisions of the trigeminal
The ability to distinguish whether the skin is being touched by 2 objects very
close together or by a single object, without visual cues. This is an example
of a complex epicritic perception.
Upper motor neuron paralysis.
See spastic paralysis.
Vertigo. A feeling
that objects in the environment are spinning around or moving, or the sensation
that the head is whirling, or sometimes the feeling that the floor and walls seem
to sink and rise, or that the body is leaning. Often the feelings are accompanied
by nausea, vomiting, and difficulty walking, and can be relieved by sitting or
lying still. Usually vertigo indicates disease of the vestibular end-organ, the
vestibular division of the VIIIth nerve, vestibular brainstem nuclei, or vestibular
parts of the cerebellum. See dizziness.
Reflex which stabilizes the optical axis during motor activity, by producing counteracting
movements of the eyes, head, or body.
The ability to detect vibrating objects through touch. A tuning fork is used to
assess this sense which is carried by large heavily myelinated axons in the dorsolateral
Visual Field Defects.
A heterogenous group of visual problems that can result in blind areas of the
visual field. Visual field defects can result from damage anywhere along the visual
pathway including lesions at the retina, optic nerve, optic chiasm, optic tract,
lateral geniculate nucleus, optic radiations and at the visual cortex. Examples
of visual field defects include: homonymous
hemianopsia, heteronymous hemianopsia
(such as binasal hemianopsia,
bitemporal hemianopsia), homonymous
(Lateral medullary syndrome). A group of signs/symptoms produced by damage to
the dorsolateral regions of the medulla. Deficits may include some or all of the
following: 1) Loss of pain and temperature sensation: ipsilateral on face,
contralateral on body. 2) Hoarseness, impaired swallowing, diminished gag
reflex. 3) Ataxia of ipsilateral arm and leg,
falling or veering to the side to the lesion. 4) Decreased muscle tone
in ipsilateral arm and leg (no paralysis). 5) Nystagmus,
diplopia. 6) Vertigo. 7)
Horner's syndrome. This is the commonest brainstem
Loss of axons and any surrounding myelin distal to the point where an injury has
disconnected axons from their nerve cell bodies of origin.
Weakness. Mild degreee
Weber's Test. A test
to detect whether a hearing loss is sensory (i.e. inner ear and eighth nerve)
or conductive (i.e. middle ear) in origin. A vibrating tuning fork is placed midline
on the forehead. In a normal person the sound is heard equal in each ear. If the
patient has a conductive hearing loss than the sound is heard best in the ear
with the loss. If the patient has a sensory hearing loss then the sound is heard
best in the unaffected ear.
A disease produced by thiamine deficiency (most often in patients with long-standing
chronic alcoholism). Symptoms include ocular abnormalities (nystagmus, conjugate
gaze paralysis), ataxia, and global confusion, all of which
may be corrected by giving thiamine. However there will then be an enduring defect
in learning and memory (this is the Korsakoff component). Compare with
(Synonyms: posterior or fluent aphasia) A primary deficit in the
comprehension of speech, accompanied by relatively fluent speech which is properly
intoned and articulated, but is largely nonsensical. The patient is unaware of
the problem. He or she cannot understand what is said, or read with comprehension.
In right-handers, the lesion usually lies in the planum temporale of the left
temporal lobe or in adjacent regions.
reflex. The involuntary pulling back of a limb from a noxious stimulus.
This is an example of a multisegmental spinal reflex. It is often accompanied
by crossed extension of the opposite limb,
which enables the organism to stay upright.