L40 Other Motor Pathways

Question 1

what forms muscles spindles

Answer 1

specialized aggregations of intrafusal fibers

Question 2

what is the role of the muscle spindle in the gamma loop

Answer 2

• muscle shortens = extrafusal fibers contract
• spindles gets “slack”
• spindle unable to measure length/stretch
• gamma motor neuron tightens end of spindle
• now spindle can monitor stretch/length

Question 3

what do the descending fibers of the lateral corticospinal , rubrospinal and reticulospinal tracts coactivate?

Answer 3

LMN during volutnary movement

Question 4

what tract can activate muscle contraction by the gamma loop

Answer 4

pontine reticulospinal tract - because of major excitatory influence on gamma motor neurons

gamma neurons stimulate muscle spindles which stimulate alpha motor neurons

Question 5

describe decorticate posturing

Answer 5

following a noxious stimulus

lesion rostral to red nucleus that impairs corticobulbar and corticospinal fibers

flex upper limb
extend lower limbs

corticospinal tract - impaired
corticobulbar tract - impaired
rubrospinal tract - flexion of arms
medullary reticulospinal tract - flexion of extremities
pontine reticulospinal tract - extension of extremeties
vestibulospinal tracts - extension of extremities

Question 6

describe decerebrate posturing

Answer 6

following a noxious stimulus

lesion at or caudal to the red nucleus that impairs the corticobulbar and corticospinal and rubrospinal

extends upper and lower limbs

corticospinal tract - impaired
corticobulbar tract - impaired
rubrospinal tract - impaired
medullary reticulospinal tract - flexion of extremities - overcome by extension…
pontine reticulospinal tract - extension of extremeties
vestibulospinal tracts - extension of extremities