Lecture 9: Descending Pathways

Question 1

How are the descending motor pathways musculotopically organized?

Answer 1

lateral pathways = distal, medial pathways = proximal/axial

flexors medial to extensors

Question 2

Describe the lateral pathways

Answer 2

Lateral corticospinal tract: originates in frontal lobe (layer 5) from PMA, SMA, CMA. 90% decussate at the medulla, goes to interneurons or motor neurons in the lateral ventral horn, innervates distal limbs

Rubrospinal tract: orginates in the midbrain and decussates immediately. ends at either motor neurons or interneurons, spinal gray matter. innervates distal end of limbs

Question 3

Describe the medial pathways

Answer 3

Medial corticospinal

Medullary reticulospinal: originates in the medulla, ipsilateral. ends on interneurons of medial motor neurons. mainly inhibitory.

Pontine reticulospinal: originates in the medial pontine reticular formation, goes to ipsilateral medial interneurons. innervates proximal extensors.

Vestibulospinal: originates from vestibular apparatus, input from otolith organs and semicircular canals. innervates postural extensor muscles, adjustments in response to linear/rotational acceleration

Question 4

Describe the effects of injuries to the lateral or medial pathways

Answer 4

lateral: loss of fine control, distal limbs
medial: loss of posture, balance, manual manipulation normal

Question 5

Describe 3 postural reflexes

Answer 5

vestibular reflexes: rotation of head sends signals via vestibulospinal tract, activates postural muscles to prevent falling
tonic neck reflexes: spindles in neck muscles - fencing reflex
righting reflexes: vestibular apparatus, stretch receptors, corrects posture back to expected

Question 6

What is the primary locomotor region?

Answer 6

midbrain locomotor region