Functional Hierarchy of the Motor System

Question 1

What four structures govern motor control?

Answer 1

1. Dorsal columns
2. Basal ganglia
3. Cerebellum
4. Local spinal cord (reflexes)

Question 2

What is a lower motor neurone?

Answer 2

A neurone at the spinal level which initiates reflexes and voluntary movements

Question 3

Injury to lower motor neurones causes what?

Answer 3

Paresis/paralysis and flaccidity

Question 4

What are upper motor neurones?

Answer 4

Neurones originating superiorly than lower counterparts which regulate alpha-motorneurone activity by synapsing with many lower circuits

Question 5

Injury to upper motor neurones causes what?

Answer 5

Injury causes spasticity (paralysis may be transient)

Question 6

How are is skeletal muscle mapped onto the spinal cord?

Answer 6

Proximal muscles are mapped medially

Question 7

What is the crucial cord segment being tested during a bicep jerk reflex?

Answer 7

C5/6

Question 8

What is the crucial cord segment being tested during a tricep jerk reflex?

Answer 8

C7

Question 9

What is the crucial cord segment being tested during a achilles jerk reflex?

Answer 9

S1

Question 10

What is the crucial cord segment being tested during a bicep knee reflex?

Answer 10

L3/4

Question 11

How do higher centres have voluntary override control?

Answer 11

Alpha-motorneuron excitation can override GTO inhibition

Question 12

How does GTO prevent damage to muscle spindles even after voluntary override?

Answer 12

Significant GTO (descending inhibition) can hyperpolarise alpha-motorneurones and reflex cannot be overridden

Question 13

What does high activity of gamma motor neurones do?

Answer 13

Spasticity

Question 14

What are the symptoms of spinal shock?

Answer 14

Loss of sensation, loss of bowel control, bladder control and sexual regulation

Question 15

What can be said about reflexes following spinal shock?

Answer 15

Unevokable for 2-6 week and slow to return afterwards (often exaggerated for a time afterwards)

Question 16

Describe the stages of the stretch reflex?

Answer 16

1. Afferent (sensory) impulse from stretch receptor travels to spinal cord
2. Efferent (motor) impulse to a-motoneurones causes contraction of stretched muscle
3. Efferent impulse to antagonist muscles are damped (reciprocal inhibition)

Question 17

What may impaired reflexes indicate?

Answer 17

Areas of nerve damage

Question 18

What is the purpose of the flexor withdrawal reflex?

Answer 18

Protective reflex (of ipsilateral flexion) to withdraw body away from painful stimulus

Question 19

Describe the stages of flexor withdrawal reflex?

Answer 19

1. Increased sensory action potentials from pain receptors
2. Increased activity in flexor muscles + Antagonist extensors are inhibited
3. Contralateral limb extension occurs to maintain body weight: excite contralateral extensors, inhibit contralateral flexors