Motor Control 1

Question 1

What is the function of the high level of motor control?

What structures does this involve?

Answer 1

• Strategy: what is the goal and how to accomplish it

- Association neocortex, basal ganglion

Question 2

What is the function of the middle level of motor control?

What structures does this involve?

Answer 2

• Determining the sequence of spatiotemporal muscle contractions needed to accomplish a goal smoothly
• Motor cortex and cerebellum

Question 3

What is the function of the low level of motor control?

What structures does this involve?

Answer 3

• Execution: activation of motor neuron and interneuron pools to generate movement
• Brain stem, spinal cord

Question 4

What are the different (motor) pathways that link the brain and spinal cord? What do they control?

Answer 4

• Lateral pathways: control voluntary movements of distal muscles, under direct cortical control
• Ventromedial pathways: control posture and locomotion, under brainstem control

Question 5

What are the lateral pathways? Where do they originate? Receive input from?

Answer 5

• Corticospinal tract (CST) - originates at areas 4 & 6, input from same place
• Rubrospinal tract (RST) - originates at red nucleus of midbrain, receives input from areas 4 & 6

Question 6

What happens if there is a lesion in the CST?

Answer 6

• Fine movements of limbs lost
• Functions reappear after a few months if the RST is still in tact, if there is also a lesion there functions are permanently lost

Question 7

Describe the action of pyramidal neurons in the CST

Answer 7

• They monosynaptically excite agonist motoneuron pools

- The same neurons branch and activate inhibitory interneurons which inhibit antagonist motor neuron pools

Question 8

What are the ventromedial pathways?

Answer 8

• Tectospinal tract (head and eye)
• Pontine reticulospinal tract
• Vestibulospinal tract
• Medullary reticulospinal tract

Question 9

Function of the vestibulospinal tract?

Answer 9

change the position of the limbs and head with the goal of supporting posture and maintaining balance of the body and head

Question 10

Function of the tectospinal tract?

Answer 10

Ensure eyes remain stable as the body moves

Question 11

Where do the pontine and medullary reticulospinal tracts originate?
What do they innervate and what is their function?

Answer 11

Originate in the brainstem (pontine - pons, medullary - medulla)

Innervate the trunk and antigravity muscles in the limbs to reflexly maintain balance and body position

Question 12

When undergoing complex voluntary movements how do the motor cortex and reflex centres interact?

Answer 12

The motor cortex can free spinal neurones from reflex control via interactions with ventromedial nuclei

Question 13

Where do the axons of upper motor neurons from the motor cortex lie in the spinal cord?

Answer 13

Laterally - in the white matter

lateral to grey matter

Question 14

Where do axons of upper motor neurons from brainstem lie in the spinal cord?

Answer 14

Ventromedially - in the white matter

Question 15

Which muscles do LMN’s originating from the medial grey matter control?
LMN’s originating from lateral grey matter?

Answer 15

Medial - control proximal muscles

Lateral - control distal muscles

Question 16

Where is the primary motor cortex in the brain?

Where are the premotor and supplementary motor areas?

Answer 16

• Primary motor: precentral gyrus, area 4

- Premotor/supplementary motor: anterior to precentral gryus, area 6

Question 17

How are the neurons of area 6 organized?

Answer 17

Area 6 divided into premotor area (PMA) and supplementary motor area (SMA)

Each of these has their own somatotopic organization, two motor maps in area 6

Question 18

Is the somatotopic motor map precise?

Answer 18

Not really

Maps seem to represent movements instead of upper motor neurons causing individual muscle movements

• Eg. if you stimulate an area of area 4, can cause the movement of hand to mouth, not just the flexion of a single muscle as somatotopic rep would suggest

Question 19

Where in the brain is our image of body in space generated?

Answer 19

In the posterior parietal cortex (areas 5 & 7)

• generated from somatosensory, proprioceptive and visual inputs

Question 20

Which parts of the brain are responsible for making decisions on which actions/movements to make and their likely outcome?
Where do axons from these areas converge?

Answer 20

• Prefrontal and parietal cortexes

- Axons converge onto area 6, converts desired actions into “how to carry this out”

Question 21

If you only think about actions instead of doing them, is area 4 or area 6 active?

Answer 21

Area 6

Area 4 is for doing actions, activating the CST & RST

Question 22

When do PMA neurons start firing when making a movement?

Answer 22

Start firing a second before movement occurs, continue to fire throughout the movement

Slide says: “they are decision making neurones in command centres” but everywhere else seems to say that it just plans movements

Question 23

Which neurons fire when we watch another person do something? What may this suggest?

Answer 23

Neurons in area 6 fire

May suggest that these neurons not only plan our movements but may give us insight into the intentions of others with their movements (may be dysfunctional in autism)