When lower motor neurons or there axons are damaged, what signs do the patients show?
Flaccid paralysis followed by atrophy; fibrillations or fasciculations (involuntary contractions of one motor unit or a group of motor units); hypotonia (decreased muscle tone); and weakening or absence of muscle stretch reflexes (hyporeflexia, areflexia)
Ischemic lesions of the internal capsule can potentially involve what fibers?
corticostriatal, corticothalamic, and corticoreticular fibers in addition to corticospinal axons because of the close proximity of these tracts to one another within the internal capsule
Damage to upper motor neurons leads to what signs?
muscles that are initially weak and flaccid but eventually become spastic; exhibit increased muscle tone (hypertonia), seen as an increase in resistance to passive movement of an extremity; and show an increase in muscle stretch reflexes (hyperreflexia), as may be seen in clonus (involuntary and rhythmic muscle contractions caused by a permanent lesion in descending motor neurons)
Upper motor lesions usually affect ______________________
groups of muscles
What is one of the signs that indicates an upper motor neurons lesion?
Babinski sign (inverted plantar reflex)
What is spasticity and in which muscles are the effects most pronounced ?
when a muscle offers increased resistance to passive movement or manipulation; the antigravity muscles which include the proximal flexors in the upper extremity and the extensors in the lower extremity
For spasticity, the increased resistance to passive movement is what?
velocity dependent: the more rapidly the examiner moves the affected extremity, the greater the resistance
For spasticity, after a relatively brief period of applied force, what happens?
the increased resistance totally collapses; this is known as the clasp-knife effect (clasp-knife rigidity)
What is the purpose of the circuitry that involves Renshaw cells?
it serves to prevent reflex stimulation of the extensors when flexors are active
What is clonus and what is it often present with?
Clonus occurs when the an upper motor neuron lesion is present, the inhibition of the antagonistic muscle groups are not present. This results in repetitive, sequential contraction of both ankle flexors and extensors. Clonus is often present with a combination of spasticity and hyperreflexia
Lesions of corticospinal fibers rostral to the motor decussation result in ______________________, whereas lesions of the corticospinal tract caudal to the motor decussation (in the spinal cord) result in _______________________.
contralateral motor deficits; ipsilateral deficits
Lesions that involve only areas of motor cortex outside the M1 usually do not result in ______________________ , and the effects may dissipate over time.
paralysis
Vascular infarcts of the premotor or supplementary cortex may produce what?
apraxia
What is apraxia?
a disorder that involves difficulty in using the affected part of the body to perform voluntary actions, even though there is no obvious spasticity, paralysis, or altered tone in muscles.
A premotor lesion may result in what?
the inability to perform voluntary actions with the contralateral hand, although the strength and tone of the hand muscles are normal
Unilateral lesions in the supplementary motor cortex result in what?
affect the ability to coordinate actions on the two sides of the body
Lesions that affect the primary motor cortex and another motor cortical region result in what?
spastic paralysis and hyperreflexia, signs characteristic with upper motor neuron lesions
A common cause of lesions in the posterior limb of the internal capsule is what?
a hemorrhage from lenticulostriate branches of the M1 segment of the middle cerebral artery
What are the motor symptoms of capsular infarcts?
The contralateral upper and lower extremities show weakness and transient flaccid paralysis of variable duration, which is followed by spastic paralysis that typically never resolves
Lesions of the posterior limb of the internal capsule include what other fibers besides corticospinal fibers?
Fibers projecting to the neostriatum, thalamus, brainstem, and thalamocortical axons involved in somatic sensation and vision
Damage to the thalamocortical axons in the posterior limb of the internal capsule explains what?
it explains why hemisensory loss or homonymous hemianopia may accompany the motor deficits.
In relation to posterior limb of internal capsule lesions, deficits such as ___________________, _______________________, and ____________________, although commonly associated with pyramidal tract lesions, are in fact due to damage of other descending systems in combination with damage to corticospinal fibers.
spasticity, hypertonia, and hyperreflexia
Fibers in the medial two thirds of the crus cerebri (frontopontine, corticonuclear, and corticospinal) and the exiting roots of the oculomotor nerve fibers are served by what arteries?
paramedian branches of P1 and branches from the adjacent posterior communicating artery
Hemorrhage of the paramedian branches of P1 and branches from the adjacent posterior communicating artery will result in what signs and symptoms?
contralateral hemiparesis of the arm and leg with spasticity and deviation of the ipsilateral eye down and laterally because of the damage to the oculomotor nerve resulting in unopposed action of the superior oblique and lateral rectus muscles. Direct and consensual light reflexes and accommodation may also be lost in the eye on the side of the oculomotor nerve lesion.
What is a superior alternating hemiplegia?
cranial nerve signs are seen on one side of the body and corticospinal signs on the "alternate" side; it is also known as a crossed deficit
What tracts are affected in Weber's Syndrome and what are the symptoms and signs that result?
Corticospinal fibers in crus: contralateral hemiplegiaOculomotor nerve fibers: ipsilateral oculomotor palsy, dilated pupil, diplopiaCorticonuclear fibers in crus: contralateral weakness of facial muscles on lower half of face; deviation of the tongue to contralateral side on protrusion; ipsilateral weakness of trapezius and sternocleidomastoid musclesSubstantia nigra: contralateral Parkinson-like tremor, akinesia
Corticospinal fibers in the basilar pons and the exiting fibers of the abducens nerve in the caudal pons are within the domain of what artery?
paramedian branches of the basilar artery
Occlusion or rupture of the paramedian branches of the basilar artery results in what?
hemiplegia and upper motor neuron signs in the contralateral extremities. It may also involve intraaxial abducens fibers, resulting in lower motor neuron paralysis of the ipsilateral lateral rectus muscle
The combination of ipsilateral abducens paralysis and contralateral hemiplegia is what?
a characteristic of brainstem lesions, that is, a crossed deficit, called a middle alternating hemiplegia, and one of the variations of the Foville syndrome.
The paramedian branches of the basilar artery may penetrate deep into the pons and also serve the ___________________________.
medial lemniscus
If the paramedian branches of the basilar artery serve the medial lemniscus, what can also happen if those vessels are damaged?
it will produce not only motor deficits but also contralateral loss of vibratory sense and two-point tactile discrimination
The pyramid, the laterally adjacent exiting fibers of the hypoglossal nerve, and the medial lemniscus receive their blood supply through penetrating branches of what artery?
anterior spinal artery
Occlusion of the penetrating branches of the anterior spinal artery results in what?
contralateral hemiparesis of the extremities (with spasticity, corticospinal) and an ipsilateral flaccid paralysis of the tongue (hypoglossal nerve). When it is protruded, the tongue deviates toward the side of the lesion (weak or flaccid side).
The combination of the hemiparesis of the extremities and the ipsilateral flaccid paralysis of the tongue is called a what?
inferior alternating hemiplegia
Because branches of the anterior spinal artery also serve the medial lemniscus, an inferior alternating hemiplegia is typically accompanied by what?
A contralateral loss of the two-point discrimination and vibration sense
Lesions of the medial medulla characterized by crossed (or alternating) deficits, as described earlier for brainstem levels, are known as what?
Dejerine Syndrome
The somatotopically arranged corticospinal fibers within the motor decussation at the medullospinal junction explains what?
Why small vascular lesions in the motor decussation (which is also served by branches of the anterior spinal artery) ay result in selective bilateral weakness or paralysis of only the upper extremities or only the lower extremities. It also explains why the unusual picture of weakness of the upper extremity on one side and of the lower extremity on the opposite side.
For lesions on one side of the rostral half of the somatotopically arranged corticospinal fibers within the motor decussation, what deficits would be expected?
damage to upper extremity fibers that have already crossed (ipsilateral upper extremity weakness) and damage to lower extremity fibers that have not crossed (contralateral lower extremity weakness)
For lesions on one side of the rostral half of the somatotopically arranged corticospinal fibers within the motor decussation, if this lesion were to extend laterally what might it damage?
The accessory nucleus and the anterolateral system with corresponding deficits
The decussating corticospinal fibers extend into the lateral funiculus to form what?
the lateral corticospinal tract
The corticospinal axons that do not cross in the decussation continue into the ipsilateral anterior funiculus of the spinal cord as the what?
anterior corticospinal tracts
The crossing of the corticospinal fibers at the _______________________ is the anatomic basis for the contralateral deficits seen in a patient with a lesion in which these fibers are rostral to this decussation.
motor decussation
A patient with a capsular lesion on the right side will have what deficits?
hemiparesis of the upper and lower extremities on the left; deficits related to damage of corticonuclear fibers in the genu of the internal capsule, such as drooping of the face and weakness of the sternocleidomastoid muscle
Interruption of lateral corticospinal axons in the __________________________ results in spastic hemiplegia involving the ipsilateral upper and lower extremities. Common upper motor neuron lesion signs (hypertonia, hyperreflexia, Babinski sign) will be present ipsilateral to the lesion.
upper cervical cord (C1, C2)
If an upper cervical cord lesion is big enough what can become a problem?
if the lesion is big enough, the innervation of the diaphragm (C3 to C5 via the phrenic nucleus) may be disrupted, necessitating the use of a respirator
A lesion of the cervical enlargement results in what deficits?
if the damage involves only the lateral funiculus, the ipsilateral upper and lower extremities will exhibit typical upper motor neuron signs. However, the C6 to C8 anterior horn gray matter and the lateral funiculus white matter are both included in the lesion, lower motor neuron signs will appear in the upper extremity ipsilaterally, whereas upper motor neuron signs will be seen in the ipsilateral lower extremity.
When anterior horn motor neurons or their axons are damaged, the affected muscles exhibit ________________________ signs despite the fact that supraspinal axons providing input to these cells may have been damaged.
lower motor neuron
At ___________________________ levels, injury to the spinal cord frequently affects motor neurons in the anterior horn as well as descending supraspinal fibers. Characteristically, affected patients exhibit lower motor neuron signs in the ipsilateral lower extremity if both the corticospinal fibers and anterior horn motor neurons are damaged.
lumbosacral levels
What causes central cord syndrome?
hyperextension of the neck that results in injury to the cord or in occlusion of the sulcal arteries
What are the deficits of central cord syndrome?
can result in bilateral hemiparesis of the upper extremities secondary to vascular infarcts involving medial regions of both lateral corticospinal tracts. In addition, affected patients may also exhibit both urinary retention and a bilateral patchy loss of pain and temperature sensations below the lesion.
A functional hemisection of the spinal cord, such as may be caused by a tumor or by trauma, results in a characteristic set of deficits known as the ____________________________.
Brown-Sequard Syndrome
What are the deficits of Brown-Sequard syndrome?
the deficits begin about two levels below the lesion and consist of ipsilateral loss of two-point discrimination and vibration (from damage to the dorsal column), contralateral loss of pain and thermal sensation (from damage to the anterolateral system), and ipsilateral paresis or paralysis (from damage to the corticospinal tract). The paralysis depends on the level of the lesion as to if it is UE or LE.
If a Brown-Sequard lesion is large enough that it involves several spinal cord levels, what might result?
Damage to a sufficient number of primary afferent fibers entering the spinal cord which may result in a narrow band of complete anesthesia on the side ipsilateral to the lesion in dermatomes corresponding to the damaged cord segments
A lesion of corticonuclear fibers rostral to the facial motor nucleus results in a drooping of muscles at the corner of the mouth and on the lower portion of the face on the side opposite the lesion. This deficit is called a ____________________________.
central facial paralysis (central seven)
A lesion of the root of the facial nerve will result in flaccid paralysis of facial muscles of upper and lower portions of the face on the ipsilateral side. This deficit is called a what?
Bell (facial) palsy
A lesion of corticonuclear fibers on the right projecting to the left nucleus ambiguus may produce what deficits?
weakness of the palatal arch muscles on the left (the weak side), a slight drooping of the palatal arch and failure to elevate on the weak side, and deviation of the uvula to the right (strong side) on attempted phonation.
Lesions that damage the root of the vagus nerve, result in what deficits?
weakness and slight drooping of the arch on the same side as the lesion, a noticeable deviation of the uvula to the strong side (opposite the lesion side) at rest, and acute deviation on phonation
A lesion of corticonuclear fibers to the hypoglossal nucleus will cause what deficits?
the tongue to deviate toward the weak (contralateral to the lesion) side when it is protruded because of the unopposed pull of the intact muscle.
If a corticonuclear lesion were to be on the right side, what deficits would be present?
tongue will deviate to the left on protrusion, maybe symptoms characteristic of a lesion of the genu of the internal capsule (central seven or deviation of the uvula)
An injury to the right hypoglossal nerve will lead to what?
deviation of the tongue toward the left side on protrusion, appearance of lower motor neuron signs in the tongue (muscle atrophy and flaccid paralysis)
For a lesion in the medial medulla that involves the root of the hypoglossal nerve, pyramid, and medial lemniscus, what will the patient experience?
an ipsilateral deviation of the tongue along with a contralateral hemiparesis(corticospinal fiber involvement) and a contralateral loss of posterior column modalities (medial lemniscus involvement); this combination of deficits is an inferior alternating hemiplegia (medial medullary or Dejerine syndrome)
Clinical observations in patients with cortical or internal capsule lesions reveal what deficits?
that the sternocleidomastoid and trapezius muscles (targets of accessory motor neurons) are affected mainly on the side ipsilateral to the lesion. The patient is unable to shrug or to elevate that shoulder (especially against resistance) or to turn the head away from the side of the lesion.
corticonuclear fibers distribute primarily to the __________________________.
ipsilateral accessory nucleus.
______________________ arteries serve portions of the genu and most of the posterior limb of the internal capsule.
Lenticulostriate arteries
Hemorrhage of the lenticulostriate arteries on the right side results in what deficits?
left spastic hemiparesis of the extremities (corticospinal damage), a central facial paralysis on the left, a deviation of the uvula to the right on phonation, and a deviation of the tongue to the left when it is protruded. The last three are due to damage of the corticonuclear fibers. Effects on the trapezius and sternocleidomastoid muscles are variable but if present will usually involve the muscles ipsilateral to the lesion of corticonuclear fibers .
Lesions that impinge on or are located within any level of the brainstem may produce what deficits?
corticospinal and corticonuclear signs in various combinations, depending on the level of the brainstem involved and what cranial nerve root is damaged along with the corticospinal fibers.
For a herniation of the uncus through the tentorial notch, what causes it and what are the deficits?
increased intracranial pressure in a supratentorial compartment forces the uncus over the edge of the tentorium and into the midbrain, damaging the oculomotor nerve and the crus cerebri on that side. The deficits experienced by the patient are an ipsilateral paralysis of most eye movement, diplopia, and a dilated pupil (oculomotor damage) and a contralateral hemiplegia (damage to corticospinal fibers in the crus).
In patients with corticospinal signs accompanied by cranial nerve signs on the opposite side of the body, what are two important facts that come to mind?
First that these alternating or crossed deficits are a hallmark of brainstem lesions. Second, the cranial nerve deficit is the best localizing sign because it provides, in combination with a long tract deficit, the most precise location and level of the lesion.
What are false localizing signs?
cases in which the signs are counter to what one would expect
What is an example of a false localizing sign?
Kernohan syndrome (Kernohan notch phenomenon)
What is Kernohan syndrome?
a variation on uncal herniations against the midbrain; the herniating uncus displaces the midbrain (and crus cerebri) against the edge of the tentorium cerebelli on the side contralateral to the herniation.
What are the deficits of Kernohan Syndrome?
oculomotor nerve palsy and a hemiplegia of the extremities, both on the side of the herniation. The oculomotor nerve palsy indicates damage to the oculomotor nerve root (by avulsion of the root or by compression of its blood vessels with resultant necrosis of the root) on the side of the herniation, and the hemiplegia results from the crus cerebri being forced against the edge of the tentorium on the contralateral side with subsequent damage to the corticospinal fibers on that side.
In the example of ipsilateral oculomotor paralysis plus ipsilateral hemiplegia in Kernohan syndrome, what is the false localizing sign?
the hemiplegia
The Kernohan syndrome illustrates an important general concept concerning posterior fossa lesions that may affect the brainstem. What is the concept?
That lesions at any brainstem level may displace the stem to one side, damage ipsilateral cranial nerve roots at that level, and damage long tracts on the contralateral side by compression of the stem against bony or meningeal structures. The result is a patient with cranial nerve and long tract signs on the same side of the body.
In a patient with decorticate rigidity, the flexion of the upper extremities reflects an intact what?
red nucleus and rubrospinal tract
If a supratentorial lesion producing decortication extends through the tentorial incisure (tentorial notch) and damages the midbrain, the flexed upper extremities convert to _______________________________; this signals destruction of the red nucleus and rubrospinal fibers and the onset of decerebrate posturing
extended upper extremities