Motor control 1

Question 1

Describe the functional hierarchy of motor control.

Answer 1

3 levels:

1) High; for strategy; structures are association neocortex (sight and hearing) and basal ganglia
2) Medium; for tactics; motor cortex; structure is cerebellum
3) Low; execution; structures are brainstem and spinal cord

Question 2

Define strategy, tactics and execution in relation to the hierarchy of the motor system.

Answer 2

1) Strategy: the goal and the movement strategy to best achieve this goal
2) Tactics: the sequence of spatiotemporal muscle contractions to achieve a goal smoothly and accurately
3) Execution: activation of a motor neuron and interneuron pools to generate goal-directed movement

Question 3

What are the lateral pathways?

Answer 3

Corticospinal and rubrospinal tracts. These control voluntary movements of distal muscles and are under direct cortical control.

Question 4

What are the ventromedial pathways and what do they control?

Answer 4

Tesctospinal, vescibulospinal, pontine reticulospinal and medullary reticulospinal tracts.

Posture and locomotion. These are under brainstem control.

Question 5

Which lateral pathway is the largest?

Answer 5

Corticospinal tract - has around 1 million axons. 2/3 motor, 1/3 somatosensory. Decussates at the medullary pyramids.

Question 6

Where does the rubrospinal tract begin?

Answer 6

The red nucleus of the midbrain.

Question 7

What are the consequences of lesions in corticospinal and rubrospinal tracts?

Answer 7

Loss of fine movements in the arms and hands; can’t move shoulders, elbows, wrists and fingers independently.

If the lesion is only in the CST these functions disappear but then reappear after a few months as RST takes over these functions.

Question 8

Which 2 ventromedial pathways control posture and locomotion?

Answer 8

Vestibulospinal (stabilises head and neck) and tectospinal tracts (ensure eyes remain stable as the body moves).

Question 9

Which 2 ventromedial pathways control (innervate) the trunk and antigravity muscles?

Answer 9

Pontine and medullary reticulospinal tracts. Originate in the brainstem and use sensory information about balance, body position and vision. They reflexly maintain balance and body position.

Question 10

What do medial tracts from the brainstem control?

Answer 10

Posture, balance and orientating mechanisms (axial and proximal limb muscles).

Question 11

What do lateral tracts from the cortex control?

Answer 11

Precise, skilled voluntary movements (distal limb muscles).

Question 12

Where are the premotor areas of the cortex?

Answer 12

Rostral (in front of) to the primary motor cortex which is in the precentral gyrus.

Question 13

What is the significance of somatropic maps of the body (homunculus)?

Answer 13

Can map out seizures. These can begin in eg. the fingers and end in the face - can stimulate these areas electrically and know which area of the brain is abnormal.

Question 14

Where is the primary motor cortex?

Answer 14

Area 4 in the precentral gyrus.

Question 15

What are the 2 defined parts of area 6?

Answer 15

Area 6 neurons drive complex movements on either side of the body:

• supplementary motor area (SMA): innervates distal motor units directly
• premotor area (PMA): connects reticulospinal neurons innervating proximal motor units

Question 16

Microstimulation in a specific area of the primary motor cortex elicits:

Answer 16

a) Co-ordinated movements of the hand and mouth

Or

b) Movements that bring the hands into central space to inspect/manipulate objects

Question 17

Describe the originating and coordination of body movements.

Answer 17

• Mental image of the body in space by somatosensory, visual and proprioceptive inputs (areas 5 and 7)
• Prefrontal and parietal cortex decide which actions to take and then their axons converge on area 6
• Area 6: where signals encoding which actions are desired are changed to how these actions are carried out

Question 18

Which areas are activated if you think about movements but don’t actually perform them?

Answer 18

Area 6 is active. Area 4 is not - this is the area that actually ‘does’ the action by activating neurons of the CST and RST.

Question 19

When do neurons from the PMA fire?

Answer 19

1 second before making a movement these start firing AP’s - these are decision making neurons.

Question 20

What is a mirror neuron?

Answer 20

A neuron that fires both when an animal acts, and when an animal observes the same behavior performed by another. Fired from area 6.

These neurons may underpin emotions and empathy, and may be dysfunctional in autism.

Question 21

What is the rediness potential?

Answer 21

A measure of the activity in the motor cortex and supplementary motor area of the brain leading up to voluntary muscle movement.

Question 22

What happens if the medullary reticulospinal pathway is damaged?

Answer 22

Harmless stimuli can elicit a flexor reflex.