Lecture 6: Descending Motor Pathways

Question 1

Describe the relative position of the alpha motor neurons traveling in the ventral horn that innervate proximal v. distal muscles or flexors v. extensors.

Answer 1

aMN innovating proximal muscles are medial and aMN innervating distal muscles are lateral ; aMN innervating flexors are more dorsal while aMN innervating extensors are more ventral

Question 2

List the different types of muscle fibers (1, 2a and 2b) regarding their speed and endurance.

Answer 2

1 slow response, slow fatigue; 2b big fast response, rapid fatigue, 2a are intermediate

Question 3

What are the three fundamental inputs to aMN?

Answer 3

peripheral sensory, spinal cord interneurons and higher center UMN

Question 4

What are the signs for LMN lesions?

Answer 4

flaccid paralysis, sever atrophy, absent (all) reflexes and possible muscle fasciculation

Question 5

What are the signs for UMN lesions?

Answer 5

spastic paresis, little atrophy, increase tendon reflex, babinski sign possible and reduced superficial reflexes. muscle fasiculations are absent

Question 6

What is the intermediate zone?

Answer 6

contains cells that project to ventral horn, other side, up and down and is arranged in the same fashion as other neurons so later IZ projects to lateral LMN and medial LMN to medial

Question 7

What areas of the body does the cerebral cortex send direct inputs to?

Answer 7

directly to spinal cord, red nucleus, the reticular system, the superior colliculus and the vestibular system

Question 8

What are the two named pathways of descending input from the motor cortex

Answer 8

lateral pathways (directly to spinal cord and red nucleus) and the ventro medial pathways (reticular system, superior colliculus and vestibular nuclei

Question 9

How is the cortex divided?

Answer 9

into 4 basic functional cortical regions (primary sensory, primary motor, association and limbic) and also in 6 layers of cells described by Brodman)

Question 10

Where do corticospinal fibers arise from (which layer of the cortex)

Answer 10

layer 5 in several regions (primary motor cortex 31%, pre and supplementary motor cortex 29%, primary somatosensory cortex 40%

Question 11

Describe the corticospinal path (lateral pathway)

Answer 11

pyramid cells from the cortex travel through the internal capsular bordering the thalamus the cerebral peduncle, basilar pons (in little islands) the medulla , they cross at the pyramid descussation and travel downward in the lateral funiculus (10% cross a bit later descending in the anterior corticospinal tract) (indicated in fine motor control)

Question 12

Describe the path of the rubospinal tract

Answer 12

fibers cross immediately after the exit the red nucleus and travel in the lateral funiculus, it is primarily associated with fine motor control

Question 13

Corticospinal lesions from the cortex to the medulla SC junction relate in what type of injury vs. lession below the junction

Answer 13

contra problems v. ipsi problems

Question 14

Why could a small stroke in the middle branches of the cebral artery give you major problems?

Answer 14

large tracts of axons descend from the cortex through these areas (20% of strokes), lots of nerves converge on the internal capsule, the higher the lesion the more probability that body parts would not be spared

Question 15

Describe the vestibulospinal pathway.

Answer 15

vestibular nerves synapse in the vestibular nuclei, some descend ipsilaterally in the ventral funiculus to synapse on the ventral/intermediate horn

Question 16

What is the purpose of the vestibulospinal path

Answer 16

works mostly on proximal/axial muscles to stabilize and coordinate need, neck and and body position to control reflex tone and posture

Question 17

Describe the reticulospinal pathway.

Answer 17

the diffuse clusters of cells in the reticular formation, some cell in pons and medulla descend and for the reticulospinal tracts– the medial pathway excites both alpha and gamma motor neurons and the lateral pathway inhibits both alpha and gamma neurons (part of the ventromedial pathway) basically there are many inputs and complex affects on motor neurons as a result

Question 18

Describe the Tectospinal path.

Answer 18

the cells that map the superior colliculus tell cell in deeper motor layers which activate muscles to move the eye and head to a given event, it is a pathway that only goes down to the cervical spinal cord, mostly contralateral (ventromedial pathway

Question 19

What is decorticate v. de cerebrate?

Answer 19

removal of cortical v. removal of cortical and ventral medial pathways

Question 20

What is the head ganglion of the autonomic system? (autonomics are another descending pathways)

Answer 20

the hypothalamus

Question 21

Describe 2 pathways that descend to control body homeostasis from the the hypothalamus

Answer 21

1) pituitary via the neuroendocrine system 2) brainstem and spinal cord via the autonomic system (requires inputs about the state of the body in order to initiate compensatory changes

Question 22

What funiculus do autonomics travel in?

Answer 22

Lateral funiculus