Descending (motor) pathways

Question 1

what do descending motor pathways work directly and indirectly on?

Answer 1

alpha and gamma motor neurons of the ventral horn of the spinal cord and cranial nerve motor nuclei

Question 2

T/F descending pathways are excitatory to all motor neurons

Answer 2

False. excitatory to some and inhibitory to motor neurons

Question 3

the descending pathways and the somas they arise from are considered?

Answer 3

UMN

Question 4

the alpha and gamma motor neurons (whose axons innervate muscle are considered?

Answer 4

LMN

Question 5

Pathway of the corticospinal tract

Answer 5

1. axons arise in somas that lie mostly in the primary motor cortex
2. descend through the corona radiata
3. tightly packed in the internal capsule
4. descend through the cerebral peduncles and through pons
5. decussate in the pyramids of the medulla
6. crossed axons descend to all levels of the spinal cord as the lateral corticospinal tract in the lateral funiculus

Question 6

what happens to the 10-15% of uncrossed corticospinal tract fibers?

Answer 6

descend in the anterior funiculus as the anterior corticospinal tract

Question 7

functional difference between the lateral and anterior corticospinal tracts

Answer 7

lateral = voluntary discrete skilled movements
anterior = bilateral axial musculature

Question 8

pathway of the corticobulbar tracts

Answer 8

1. axons arise from somas in the face region of motor cortex
2. descend through corona radiata, internal capsule, and cerebral peduncles
3. project to and synapse with motor nuclei of cranial nerves in brainstem

Question 9

crainal nerves associated with the corticobulbar tract

Answer 9

CN III, IV, V, VI, VII, IX, X, XI, XII

Question 10

most of the corticobulbar tract fibers are crossed, except?

Answer 10

the ones to the facial nucleus which are bilateral

Question 11

pathway of the rubrospinal tract

Answer 11

1. somas in red nucleus
2. cross to the opposite side in ventral tegmentum as they exit red nucleus
3. run down lateral funiculus of spinal cord

Question 12

what tract does the rubrospinal tract run just anterior to down the lateral funiculus?

Answer 12

the lateral corticospinal tract

Question 13

function of the rubrospinal tract

Answer 13

skilled dexterous movements of upper extremity

Question 14

2 parts of the reticulospinal tracts that begin in the reticular formation regions of pons/medulla?

Answer 14

1. pontine (medial) reticulospinal tract

2. medullary (lateral) reticulospinal tract

Question 15

pathway/function of medullary reticulospinal tract

Answer 15

• descends both crossed and uncrossed in the anterior funiculus of the spinal cord to all spinal levels
• inhibits lower extremity extensors and facilitate flesors, reducing muscle tone in the lower extremities

Question 16

pathway/function of pontine reticulospinal tract

Answer 16

• descends mostly uncrossed in anterior funiculus of the spinal cord to all spinal levels
• facilitates lower extremity extensor motor neurons

Question 17

two vestibulospinal tracts

Answer 17

medial (MVST) and lateral (LVST)

Question 18

LVST arises where?

Answer 18

lateral vestibular nucleus AKA Deiter’s nucleus

Question 19

Function of LVST

Answer 19

facilitate extensor alpha and gamma motor neurons of the lower extremities and flexors of the upper extremities

Question 20

Which pathway is the primary antigravity pathway?

Answer 20

LVST

Question 21

primary function of MVST

Answer 21

inhibit upper extremity extensors and facilitate flexors

Question 22

Function of the tectospinal tract?

Answer 22

mediate reflex postural movements of the head and neck in response to novel visual stimuli

Question 23

Which tracts cross?

Answer 23

1. lateral corticospinal @ pyramids
2. corticobulbar @ medulla (CN11) or pons (CN3,4,5,6,9,10)
3. Rubrospinal as they exit red nucleus
4. medullary reticulospinal 50%
5. MVST
6. Tectospinal

Question 24

which tracts dont cross?

Answer 24

1. Anterior corticospinal
2. Pontine (medial) reticulospinal
3. LVST

Question 25

motor neurons exit at each spinal cord level through?

Answer 25

ventral horn

Question 26

what can occur if only 1 or 2 ventral roots are damaged?

Answer 26

paresis

Question 27

Paralysis occurs when?

Answer 27

all roots innervating a particular muscle are destroyed (UMN can be destoyed in a stroke with same outcome)

Question 28

spinal cord lesions above ______ leave a patient ventilator-dependent.

Answer 28

C3

Question 29

bladder and bowel control are innervated by what spinal cord segments

Answer 29

S2-S4

Question 30

biceps

Answer 30

C5-C6

Question 31

Alpha motor neuron (diameter, conduction, function)

Answer 31

12-20 microns
15-120 m/sec
innervates extrafusal skeletal muscle fibers (motor unit) heavily myelinated

Question 32

Gamma motor neurons (diameter, conduction, function)

Answer 32

2-10 microns
10-45 m/sec
innervates intrafusal muscle fibers of muscle spindle, myelinated

Question 33

autonomic pre ganglionic (B-motor) (diameter, conduction, function)

Answer 33

~3 microns
3-15 m/sec
pre ganglionic fibers (lightly myelinated)

Question 34

autonomic post ganglionic (C motor) (diameter, conduction, function)

Answer 34

~1 microns
2 m/sec
post ganglionic fibers (unmyelinated)