Motor System

Question 1

Describe corticobulbar fibers

Answer 1

Descend from head region of precentral gyrus
Course through genu of internal capsule and cerebral peduncles
Uncrossed CBT are at and above level of trigeminal nerve
Decussate in lower pons between V and VI: crossed CBT
Innervate somatic motor nuclei of brainstem

Question 2

Describe lesions of corticobulbar fibers

Answer 2

Lesions above decussation may result in some contralateral cranial nerve palsies (supranuclear facial palsy)
Unilateral lesions below decussation may result in some ipsilateral cranial nerve palsies
In first year post-stroke, some deficits are ameliorated due to varying degree of bilateral innervation of these nuclei and contributions from corticoreticulobulbar fibers (indirect CBF)

Question 3

Describe supranuclear facial palsy

Answer 3

Results from unilateral lesions of corticobulbar fibers above level of facial nucleus
Contralateral mimetic muscles on the lower quadrant of the face are paralyzed
However, upper quadrant facial muscles are unaffected by unilateral lesions of corticobulbar fibers due to bilateral innervation of facial nucleus

Question 4

What is the extrapyramidal system?

Answer 4

Involved in crude, stereotyped, associative movements of axial and proximal limb musculature, such as swinging the arms while walking
Initiates movement patterns

Question 5

What makes up the striatum?

Answer 5

Caudate and putamen

Question 6

Describe the dorsal and ventral divisions of the ansa lenticularis

Answer 6

These pallido-thalamic fibers join together to form thalamic fasciculus
These projections are shared in common with those fibers from dentato-thalamic and dentato-rubro-thalamic pathways

Question 7

Fibers from globus pallidus and substantia nigra do not terminate in the same areas as VL and VA. Importance?

Answer 7

For sterotaxic surgery for Parkinson’s disease

Question 8

Describe nigrothalamic fibers

Answer 8

Nondopaminergic fibers that orignate from pars reticularis of substantia nigra and terminate in VA and VL thalamic nuclei

Question 9

Describe nigrostriatal fibers

Answer 9

Dopaminergic fibers that originate in pars compacta of substantia nigra and terminate in caudate and putamen
Neurons in this area are destroyed by Parkinson’s

IN contrast, Destruction of inhibitory GABAnergic fibers in strianigral fibers are involved in Huntington’s chorea

Question 10

Describe subthalamus and lesions

Answer 10

Subthalamus receives major inputs from globus pallidus and motor cortex
Neurons contain glutame and exert excitatory influence
Unilateral lesions result in contralateral hemiballism, characterized by violent, involuntary, flinging movements of limbs. These movements usually involve shoulder and pelvic girdles and proximal limb musculature. Always associated with hypotonus

Question 11

Describe Parkinson’s disease

Answer 11

Due to degeneration of substantia nigra, globus pallidus, brainstem RF, and postganglionic sympathetic neurons
bradykinesia, tremor during rest, rigidity, masked face “reptilian gaze”, glabellar reflex, postural embarrassment, autonomic effects, cognitive changes

Question 12

Describe Huntington’s chorea

Answer 12

Autosomal dominant disorder. Degeneration of corpus striatum and cerebral cortex results in excessive dopaminergic influence in degenerated striatum or loss of inhibition from GABAnergic neurons of striatonigral pathway
Onset age 30-40, choreiform movements, severe dementia, choreoathetosis, behavioral disturbances

Question 13

What is Bell’s cruciate paralysis?

Answer 13

Characterized by midline involvement of upper portion of pyramidal decussatoin resulting in paralysis of upper extremity without lower extremity involvement
May also be caused by damage to odontoid process because of its proximity to medial decussating arm fibers