descending pathways

Question 1

lower motor neurons (LMN)

Answer 1

alpha and gamma motor neurons that innervate the extrafusal and intrafusal muscle fibers
-final path outward
-from central out to the periphery

Question 2

LMN lesions may result from damage to the …..

Answer 2

peripheral nerves, spinal roots, alpha motor neurons, and muscles
-show muscles involved in dermatome patterns
-usually ipsilateral symptoms

Question 3

upper motor neurons (UMN)

Answer 3

descending motor pathways from the cortex and brainstem to the spinal cord
-pathway coming from the brain down before the final pathway
-neurons are completely in the CNS and do not exit to the periphery

Question 4

UMN lesions may result from …

Answer 4

muscle being affected in groups, an entire extremity of even half of the body
-usually contralateral symptoms

Question 5

corticospinal pathway (pyramidal tract)

Answer 5

begins in M1 and leaves through the spinal nerves (ventral roots) to innervate muscles
-function : control of voluntary, discrete, skilled movements, and fine motor skills

Question 6

pathway description of the corticospinal pathway

Answer 6

-begins in the cortex and goes to corona radiate to internal capsule through cerebral peduncles of midbrain through basal pons and medulla
-crossed fibers descent to all levels of the spinal cord as the lateral corticospinal tract and to anterior gray horn with few synapses directly onto motor neurons cell bodies and to lamina 9 of the spinal cord
-the few uncrossed fibers descend as the anterior or ventral corticospinal tract, the spinal nerves leave as the ventral roots to innervate the muscles

Question 7

contralateral (crossing over) is known as the

Answer 7

lateral corticospinal tract
-stronger

Question 8

ipsilateral (straight down) is known as the

Answer 8

ventral/anterior corticospinal tract

Question 9

corticobulbar tract

Answer 9

fibers from the face region of the motor cortex
-descending through corona radiata and internal capsule
-projections to the bulb (within brainstem)

Question 10

the corticobulbar tract goes to the motor nuclei’s of what cranial nerves

Answer 10

5, 7, 9, 10, 11, and 12

Question 11

rubrospinal tract

Answer 11

path from red nucleus in brainstem and going down to the spinal cord
-function : control of dexterous movement of the upper extremity (fine movement)

Question 12

reticulospinal tract

Answer 12

coming from reticular formation down to the spinal cord
-medial and lateral tracts
-control of movement

Question 13

medial/pontine reticulospinal tract

Answer 13

arises from pontine reticular formation, mostly uncrossed
-function : facilitates lower extremity extensors (increases lower extensor muscle tone)

Question 14

lateral reticulospinal tract

Answer 14

arises from medullary reticular formation, crossed and uncrossed fibers
-function : inhibits lower extremity extensors (reduces extensor tone in lower extremities), facilitates lower extremity flexors

Question 15

vestibulospinal tracts

Answer 15

vestibular nuclei in cortex to brainstem, running in the MLF
-medial and lateral
-axons will send out of spinal cord when ready
-controlling the vestibulo-ocular reflex

Question 16

medial vestibulospinal tract (MVST)

Answer 16

cell bodies descend uncrossed to the cervical and high thoracic level of the spinal cord (runs in the descending portion of the medial longitudinal fasciculus to act via interneurons, to provide excitation and inhibition to alpha and gamma motor neurons of the flexors and extensors for upper extremities
-vestibulocolic reflex (VCR)
-head and neck

Question 17

lateral vestibulospinal tract (LVST)

Answer 17

cell bodies in the lateral vestibular nucleus descend uncrossed to all levels of the spinal cord facilitating extensor alpha and gamma motor neurons of the lower extremities and flexors of the upper extremities
-muscle groups known as the antigravity muscles

Question 18

tectospinal tract

Answer 18

tectum (quadrigeminal plate) down to spinal tract
-function : mediates reflex postural movement of the head and neck in response to novel visual stimuli
-travel with MVST and MLF