The Motor Cortex and Skilled Movements

Question 1

What does each side of the motor contex control?

Answer 1

The left motor cortex controls the right hand

The right side controls the left hand

Question 2

What happens when there is motor cortex damage?

Answer 2

Damaged part of the motor cortex that controlled the hand in monkeys - lesions
without rehab: hand area of motor cortex becomes smaller, whereas elbow and shoulder area become larger. monkeys lose ability to use hand, so don’t recover
with rehab: prevented monkeys using the good hand, have to use bad, so the hand area of the motor cortex retained its size, occupy same space, monkeys got back ability to use hand

may explain recovery after stroke in humans

Question 3

Where does the information from the motor cortex flow through?

Answer 3

Corticospinal tract

Question 4

What is the corticospinal tract?

Answer 4

Bundle of nerve fibres directly connecting cerebral cortex to spinal cord - originates from pyramidal neurons
Branches at the brain stem, into opposite side lateral tract that controls movement of limbs and digits and a same side ventral tract that informs movement of the trunk - also called pyramidal tract

Question 5

What does the corticospinal tract control?

Answer 5

Opposite side lateral tract that controls movement of limbs and digits and a same side ventral tract that informs movement of the trunk - also called pyramidal tract

Question 6

What are the two key tracts from the motor cortex and spinal cord?

Answer 6

Lateral corticospinal tract

Ventral cortisospinal tract

Question 7

What is the lateral corticospinal tract?

Answer 7

Branches at the brainstem level, crossing over to the opposite side of the brain and spinal cord
Moves the digits and limbs on the opposite side of the body
for example, LCT will control the left hand, writing

Question 8

What is the ventral corticospinal tract?

Answer 8

Remains on the same side of the brain and spinal cord
Moves the muscles of the midline body (trunk) on the same side of the body
for example, VCT - sitting up straight

Question 9

What neurons are located in the spinal column’s ventral horns?

Answer 9

Interneurons

Motor neurons

Question 10

What are interneurons?

Answer 10

These project to motor neurons

Question 11

What are motor neurons?

Answer 11

Project to muscles of the body - laterally located motor neurons project to the muscles that control that fingers and hands, intermediately located motor neurons project to muscles that control the arms and shoulder
the most medially located motor neurons project to muscles that control the trunk

Question 12

What muscles do the motor neurons project too?

Answer 12

Laterally located motor neurons project to the muscles that control the fingers and hands
Intermediately located motor neurons project to muscles that control the arms and shoulders
The most medially located motor neurons project to muscles that control the trunk

Question 13

What do acetylcholine do?

Answer 13

Induces contraction of muscle fibres - motor neurons release acetylcholine

Question 14

How are limb muscles arranged?

Answer 14

In pairs
either extensor or flexor
Connections between interneurons and motor neurons ensure that the muscles work together so that, when one muscle constructs, the other relaxes

Question 15

What are extensor or flexor muscles?

Answer 15

Extensor - moves (extends) the limb away from the trunk

Flexor - moves the limb toward the trunk

Question 16

What do connections between interneurons and motor neurons do?

Answer 16

Connections between interneurons and motor neurons ensure that the muscles work together so that, when one muscle constructs, the other relaxes

Question 17

What are the consequences of spinal cord damage?

Answer 17

Quadriplegia - paralysis of the legs and arms due to spinal cord injury, can’t move anything
Paraplegia - paralysis of the legs due to spinal cord injury, still controls arms - recovery of spinal cord is very hard

Question 18

What are the characteristics of motor cortex neurons?

Answer 18

Trained a monkey to flex its wrist in order to move a bar to which weights could be attached

1. Planning and initiating movements - discharge before and during movements, AP started firing
2. Code force of movements - neurons increase their rate and duration of firing in response to heavier weights, when put weight on, fire more
3. Simple coding of movement direction - flexor versus extensor muscles (neurons fire when wrist flexes, but not extends). When flex, changed the way it fired

Question 19

What has live imaging of the motor cortex shown?

Answer 19

Calcium imaging: detect Ca influx with Ca sensitive fluorescent dyes
A subset of neurons or a neuronal ensemble is activated during behaviour (e.g. running) - only some activated at a given time to produce movement