Term
| What are the neural functions corresponding to the descending motor input? |
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Definition
i. mediation of somatic motor activity
ii. control of muscle tone
iii. maintenance of posture and equilibrium
iv. suprasegmental control of reflex activity
v. innervation of visceral and autonomic structures
vi. modification of sensory input |
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Term
| What are the two organization systems of the descending pathway? |
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Definition
i. pyramidal motor system
1. corticospinal (pyramidal) tracts and corticobulbar tracts
ii. extrapyramidal (extracorticospinal tracts)
1. these tracts include the rubrospinal, reticulospinal, vestibulospinal and tectospinal tracts |
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Term
| What is the course of the pyramidal (corticospinal) tract? |
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Definition
| cortex (precentral gyrus, premotor cortex, postcentral gyrus)-->internal capsule (posterior limb)-->brainstem (midbrain, pons, medulla)-->spinal cord-->point of termination |
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Term
| What do the corticospinal axons form in the midbrain? |
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Definition
| part of cerebral peduncle (crus cerebri) |
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Term
| What is the corticospinal tract called in the pons? |
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Definition
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Term
| What does the corticospinal form in the medulla? |
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Definition
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Term
| What percent of the corticospinal axons decussate in the medulla? |
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Definition
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Term
| Where do the decussatating axons of corticospinal descend? |
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Definition
| lateral corticospinal (lateral CST) |
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Term
| Lateral CST axons synapse to do what? |
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Definition
| initiate voluntary muscle activity, particularly distal muscles |
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Term
| Where to the CST axons that remain ipsi descend? |
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Definition
| ventral (anterior) corticospinal tract; synapse primarily with neurons controlling axial musculature to help maintain balance and posture |
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Term
| Which cranial nerves are classified as LMNs? |
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Definition
| (III, IV, V3, VI, VII, IX, X, XI, XII) |
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Term
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Definition
a. the broad definition includes all of the descending fiber systems that can influence and modify the activity of the LMN
b. clinically, UMN usually refer to the axons of the corticospinal and corticobulbar tracts
c. injury to the corticospinal tract is classified clinically as an UMN injury |
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Term
| What is damaged in a LMN lesion? |
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Definition
| ventral horn motor neurons, ventral roots and the spinal nerve itself – i.e., peripheral nerve injury |
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Term
| What are the symptoms of a LMN lesion? |
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Definition
1. flaccid paralysis (or paresis)
2. hypotonia
a. the combination of decreased muscle tone and a paralysis is called a flaccid paralysis
b. muscle tone is defined clinically as the degree of resistance imparted by a limb or body part that is being passively manipulated by the examiner
3. hyporeflexia or areflexia
4. muscle atrophy |
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Term
| Where do all UMN lesions manifest? |
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Definition
| spinal cord injury – all occur ipsilateral from the site of the lesion and below |
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Term
| What are the signs of UMN lesion? |
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Definition
1. spastic paralysis (or paresis)
2. hypertonicity (spasticity)
a. the combination of increased muscle tone and paralysis is known as spastic paralysis
3. hyper-reflexia
a. hyperactive myotactic reflexes (exaggerated knee-jerk and other deep tendon reflexes)
4. Babinski sign (reflex)
a. pathological reflex resulting from an UMN lesion
b. when the sole of the foot is firmly stroked there is a dorsiflexion of the big toe and a fanning of small toes; normal response is a plantar flexion of the toes
c. infants show a Babinski until the nervous system has matured
5. clonus |
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Term
| What are the ipsilateral signs of Brown-Sequard syndrome? |
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Definition
1. UMN lesion (lateral corticospinal tract)
a. may be LMN deficits only in the myotomes supplied by the site of the lesion
2. dorsal column signs: sharp-dull, vibration, proprioception |
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Term
| What are the contralateral signs of Brown-Sequard? |
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Definition
| 1. loss of pain and temperature (spinothalamic tract) usually beginning one or two segments below the site of injury |
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Term
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Definition
| 1. a viral disease of ventral horn cells that results in lower motor neuron symptoms |
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Term
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Definition
1. demyelinating disease (most likely an autoimmune disease affecting the fxn. of oligodendroglia and their myelin)
2. MS affects primarily “long” fiber tracts; therefore the dorsal column and corticospinal tracts are frequently involved |
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Term
| What is ALS or Lou Gehrigs? |
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Definition
1. degenerative disease of the ventral horn and lateral corticospinal tract bilaterally
2. manifested by combination of lower and upper motor neuron signs
a. paralysis, muscular atrophy, fasciculation and fibrillation, exaggerated myotactic reflexes, Babinski sign |
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Term
| What are the four extrapyramidal motor systems? |
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Definition
| rubrospinal tract, vestibulo tracts (medial and lateral), reticulospinal tract, tectospinal tract |
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Term
| What is the pertinent information about the rubrospinal tract? |
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Definition
1. origin from red nucleus of the midbrain
2. fibers decussate in the midbrain and descend in the lateral white column of the cord near the lateral corticospinal tract
3. while the lateral corticospinal tract appears to initiate movements, the rubrospinal tract appear to correct errors in movement |
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Term
| What is the pertinent information about the vestibulospinal tracts? |
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Definition
1. origin from the medial and lateral vestibular nuclei giving the medial and lateral vestibulospinal tracts
2. the lateral tract seems to facilitate motoneurons to extensor muscles that maintain posture
3. the medial vestibulospinal tract descents as part of the medial longitudinal fasciculus and then enters the ventral white column; this pathway appears to control head position |
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Term
| What about reticulospinal? |
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Definition
1. origin from medial and lateral reticular areas giving the medial and lateral reticulospinal tracts
2. function not understood |
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Term
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Definition
1. origin from the superior and inferior colliculi
2. probably function in turning the head in response to light stimulus |
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Term
| What are the functional considerations of the extrapyramidal system? |
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Definition
i. functions in control of muscle tone for maintaining balance and posture
ii. primarily connected to spinal cord to control head, neck, axial and proximal limb muscles |
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