Motor System

Question 1

Overview of Motor Control

Answer 1

Motor cortex projects to brainstem (posture) and spinal cord (voluntary motion), which projects out to skeletal muscle

Question 2

Two types of fibers in skeletal muscles

Answer 2

Extrafusal (which generate force) – fast fatiguable and fatigue resistant

Intrafusal - Sensory apparatus which adjusts sensitivity of muscle spindle.

Question 3

What type of neurons command extra and intrafusal fibers?

Answer 3

Alpha motor neurons (found in ventral horn) for extrafusal.

Gamma motor neurons, shorten intrafusal fibers so they don’t go slack.

Question 4

Where are the cell bodies of lower motor neurons

Answer 4

Ventral horn in columns that are organized by muscle group.

Question 5

Motor unit

Answer 5

One alpha motor neuron and all of the fibers it innervates

Question 6

Are small or large motor neurons first to fire?

Answer 6

Small

Question 7

Myotatic reflex

Answer 7

Spindle stretched, which sends info about contraction via group Ia and II sensory neurons. These synapse with alpha motor neurons in the ventral horn that control agonist and synergist muscles. they also synapse on gabaeric interneurons that inhibit the antagonistic muscle.

Question 8

Golgi tendon organs

Answer 8

Monitor tension in tendons with group 1B neurons.

Question 9

Inverse myotatic reflex

Answer 9

Group 1B sensory neuron senses GTO stretch and fires to anterior horn, synapses with excitatory and inhibitory interneurons that contract the antagonist and inhibit the agonist muscle.

Question 10

What types of motor movement controlled by lateral component of spinal cord? What tracts are there?

Answer 10

Fine motor movement of peripheral muscles. Mostly terminate on interneurons. Lateral corticospinal tract, rubrospinal tract

Question 11

What types of motor movement are controlled by the medial component of the spinal cord? What tracts are there?

Answer 11

Postural control. Tectospinal tract, vestibulospinal tracts (both lateral and medial), reticulospinal tracts.

Question 12

Where does lateral corticospinal tract decussate?

Answer 12

90% decussates in medulla.

Question 13

Function of tectospinal tract?

Answer 13

Head/neck rotation, (superior colliculus)

Question 14

Reticulospinal tracts

Answer 14

Balanced control of axial and antigravity muscles.

Question 15

Reticulospinal nuclei and their functions

Answer 15

Pontine (MRST) and Medullary (LRST) nuclei. Pontine activates extensor MNs, Medullary inhibits extensor MNs. These work via gamma MNs. Medullary system receives cortical input

Question 16

Vesibulospinal tracts

Answer 16

Facilitates axial antigravity muscles via lateral vestibular nucleus. Activates extensors with MRST. Receives inhibitory cerebellar input

Question 17

Decerebrate rigidity

Answer 17

Cut cortex, no inhibitory input from Medullar Reticular nucleus, so Lateral vestibular and pontine reticular constantly activate gammas, leading muscle to believe it’s being stretched. Will contract to counter. Cut 1a’s tho, muscle will stop contracting.

Question 18

Spasticity vs rigidity

Answer 18

S: hyperactive stretch reflexes, hypertonus in extensors, UMN damage

R: Hypoactive stretch reflexes, hypertonus in flexors and extensors, PD and basal ganglia disorders.

Question 19

Where does the concept of a motor plan come from?

Answer 19

Premotor cortex, supplementary motor cortex.

Question 20

Ability to execute motor movement

Answer 20

Comes from motor cortex

Question 21

How to cortical areas fire in relation to movement

Answer 21

PM first, then stops, then MI, then movement

Question 22

How much electrical activity required to initiate motor movement?

Answer 22

Not much, because direct contact with spinal cord neurons

Question 23

Motor cortex layer organization

Answer 23

Output layers 5/6 dominate

Question 24

Large vs small corticospinal neurons

Answer 24

Small are responsive to force (have sensory feedback). Large are all or none.

Question 25

PM function

Answer 25

Preparing motor cues based on sensory related motor cues

Question 26

SMC function

Answer 26

Mental rehearsal

Question 27

Lower face paralysis indicates

Answer 27

Upper motor neuron problem (IE stroke)

Question 28

Whole side of face paralysis indicates

Answer 28

Lower motor neuron sign, bells palsy.