Motor Control I

Question 1

What are the three levels of motor control and what are their functions?

Answer 1

1. High -> strategy: involves association neocortex, basal ganglion
2. Middle -> tactics: motor cortex, cerebellum
3. Low -> execution: brain stem, spinal cord

Question 2

What are the functions for the different levels of the motor control?

Answer 2

• Strategy – the goal and the movement strategy to best achieve this goal
• Tactics – the sequence of spatiotemporal muscle contraction to achieve a goal smoothly and accurately
• Execution – activation of motor neuron and interneuron pools to generate goal-directed movement

Question 3

What are the fibres that run the lateral pathways of the spinal tract responsible for?

Answer 3

Control voluntary movements of distal muscles – under direct cortical control.

Question 4

What are the fibres that run the ventromedial pathways of the spinal tract responsible for?

Answer 4

Control posture and locomotion under brain stem control (involuntary)

Question 5

What are the two tracts in the lateral pathways on the spinal tract?

Answer 5

Corticospinal tracts and Rubrospinal tracts

Question 6

Describe the pathway of the corticospinal tracts

Answer 6

1. Most start in areas 4 and 6 of the front motor cortex, and the rest is somatosensory.
2. Decussation at medulla
3. CST axons synapse on ventral horn neurons and interneurone to control muscles

Question 7

What side of the body does the R motor cortex control?

Answer 7

L side (due to decussation of corticospinal tracts at the medulla)

Question 8

What is the function of the rubrospinal tract?

Answer 8

• It exerts control over the tone of limb flexor muscles, being excitatory to the motor neurones of these muscles.
• It is a non-pyramidal route by which the motor cortex and cerebellum influence spinal motor activity.

Question 9

Where does the rubrospinal tract (RST) begin?

Answer 9

Much smaller tract that starts in the red nucleus of midbrain (appears red in histological staining) and receives inputs from the same cortical areas as the CST

Question 10

What do lesions in CST and RST cause?

Answer 10

Fine movements of arms and hands are lost. Can’t move shoulders, elbows, wrist and finger independently.

Question 11

What do lesions in CST cause?

Answer 11

Fine movements of arms and hands lost as well, but after a few months functions reappear.

This is because the function is taken over by the RST, so if RST has a lesion, then restored function is lost.

Question 12

How to CST axons frontal pools of spinal motor neurons?

Answer 12

• They monosynaptically excite pools of agonist motorneurones (cause extensor muscle contraction)
• The same pyramidal neurones branch and via interneurons inhibit pools of antagonist motorneurones (cause flexor muscle relaxation)

Question 13

What are two tracts in the ventromedial pathways which control posture and location?

Answer 13

Vestibulospinal (VST) and tectospinal tracts (TST)

Question 14

What are the different function of the vestibulospinal tract and the tectospinal tract?

Answer 14

• VST stabilises head and neck

* TST ensure eyes remain stable as body moves

Question 15

Where does the TST begin?

Answer 15

TS fibres arise from the superior colliculus of the midbrain which receives visual input. So the TST mediate reflex movement is response to visual stimuli.

Question 16

Where does the VST begin and how does it aid in its function?

Answer 16

VS fibres arise from the vestibular nuclei of the pons and medulla which receives input from the labyrinth via the vestibular nerve and cerebellum. VST fibres mediate excitatory influences on extensor motor neurones to use tone in the anti-gravity maintenance of posture.

Question 17

What are two tracts in the ventromedial pathways which control trunk and anti-gravity muscles??

Answer 17

Pontine and medullary reticulospinal tracts

Question 18

Describe the pathway and function of pontine and medullar reticulospinal tracts

Answer 18

• Originate in the brain stem
• Uses sensory information about balance, body position and vision
• Reflexly maintain balance and body balance and body position
• Innervate trunk and antigravity muscle in limbs

Question 19

Describe the low motor neurone distribution in the ventral horn

Answer 19

Somatotropic:
• Medial neurones control axial and proximal limb muscle (i.e. shoulder), lateral ones innervate distal limb muscle (i.e. fingers)

Question 20

Describe the different control of medial tract and lateral tract in the white matter (UMN)

Answer 20

• Medial tracts from brainstem control posture, balance and orienting mechanisms (ventromedial pathways)
• Lateral tracts from cortex control precise skilled voluntary movements (CST + RST)

Question 21

Where do the lateral pathway tracts synapse to in the ventral horn?

Answer 21

LMN in the lateral ventral horn (-> distal muscle)

Question 22

Where do the anterior-medial pathway tracts synapse to in the ventral horn?

Answer 22

LMN in the medial ventral horn (-> proximal muscles)

Question 23

Where is the primary motor cortex found?

Answer 23

In the precentral gyrus (area 4)

Question 24

Where are the premotor and supplementary motor areas found?

Answer 24

Area 6 - prefrontal cortex

Question 25

To plan a movement, what information does the cerebral cortex need to know?

Answer 25

1. Where the body is in space
2. Where is wants to go
3. Select a plant to get there

Question 26

What is the function of the premotor area and supplementary motor area?

Answer 26

SMA innervates distal motor units directly, and PMA connects with reticulospinal neurones innervating proximal motor units.

Question 27

Describe the somatopic motor map (homunculus)

Answer 27

• It does not represent upper motor neurones causing individual muscle movements
• Microstimulate arm region of primary motor cortex (area 4) causes movements that brings hands to mouth or other movements into central space: to inspect, to manipulate, to defend

Maps in the cortex don’t have a precision to them, they cause collective movements to carry out a function (i.e. bring hand to mouth) rather than movement of a specific muscle

Question 28

What area of the brain is responsible for decisions on what movement to take and their likely outcome?

Answer 28

Posterior parietal cortex (areas 5 and 7 behind postcentral gyrus) and prefrontal cortex (area 6) –> Strategy stage

Somatosensory generates mental image of body in space

Question 29

What inputs does the posterior parietal cortex have (area 5 and 7)?

Answer 29

Proprioceptive and visual

Question 30

What is the tactic stage of movement?

Answer 30

Axons from both converge on area 6- here signals encoding desired actions are converted into how to carry this out.

Question 31

What is the execution stage of movement?

Answer 31

Signals rom area 6 take to primary motor cortex to activate movement.

Question 32

If you only think about movements, but do not carry them out, what areas are activated?

Answer 32

Area 6 is active but area 4 is not (area 4 is for carry out movement by activating neurones of the CST and RST)

Question 33

Describe firing of action potentials in the premotor area (PMA)

Answer 33

Fire action potentials one second before a movement occurs. They are decision making in command centres.