Cortical Control of Movement

Question 1

There are 5 different components of the motor system including: spinal cord, association cortices, basal ganglia, cerebellum, and cortical motor areas. These 5 components have their own hierarchy. What is it?

Answer 1

Spinal cord

Question 2

How do the lowest levels of the motor system differ from the upper levels of the motor system?

Answer 2

Lowest levels: accomplish the most automatic behaviors, like reflexes
Highest levels: complex planning and selection of movement

Question 3

What is the path of a motor neuron from the primary motor cortex to the muscle?

Answer 3

1. Primary motor cortex 2. Internal capsule 3. Crus Cerebri 4. Medullary pyramids 5. Decussation at the caudal medulla 6. Lateral corticospinal tract through the spinal cord 7. Synapse in the ventral white matter 8. Secondary neurons then go to the muscle

Question 4

What is the difference between the lateral corticospinal tract and the ventral corticospinal tract?

Answer 4

Lateral corticospinal tract: in lateral white matter of spinal cord; innervates the distal muscles on the contralateral side and important in skilled movement
Ventral corticospinal tract: in the ventral white matter of the spinal cord; bilaterally innervates the axial muscles and important in posture/balance

Question 5

There are two main categories of descending corticospinal terminations: direct and indirect. How are they different?

Answer 5

Direct: upper motor neurons descend down the corticospinal tract and synapse directly with the lower motor neurons which then go to the muscles
Indirect: upper motor neurons descend down the cortiocospinal tract and then synapse with an interneuron that then synapses with a lower motor neuron; important for proprioception

Question 6

What are other names for local circuit neurons? What is their input? What is their function?

Answer 6

Can also be called interneurons or propriospinal neurons
Can receive input from either UMN (cortex/brainstem) or from local sensory (like in a simple reflex)
Fucntions to get

Question 7

What is the difference between short distance local circuit neurons and long distance local circuit neurons?

Answer 7

Short distance: contain a cell body that can then project 1-2 segments up or down; activates/inhibits a small group of muscles; important for fine movement and located more lateral
Long distance: contain a cell body that can allow for projections to travel a great distance so that a large group of muscles can be activated/inhibited at the same time; important for posture and located more medial

Question 8

There is a relationship between the number of alpha motor neuron terminations in the ventral horn and dexterity between species. What is this relationship?

Answer 8

Species that express more dexterity have more alpha motor neuron terminations

Question 9

Why do babies exhibit a positive Babinski sign, like someone that has a spinal cord injury?

Answer 9

Full development of alpha motor neurons develops postnatally. So at first doesn’t have much dexterity

Question 10

What are the four indirect motor pathways?

Answer 10

Cortio colliculo-spinal, corticorubrospinal, corticoreticulospinal, corticovestibulospinal

Question 11

What are the two direct motor pathways?

Answer 11

Lateral corticospinal and anterior corticospinal

Question 12

What is the vetibulospinal tract used for?

Answer 12

anti-gravity, important for changing position (acceleration/decceleration/ rotation)

Question 13

What is the reticulospinal tract used for?

Answer 13

changing the strength of the muscle and central pattern generation

Question 14

What is the colliculospinal tract used for?

Answer 14

Body orientation and response to auditory and visual cues

Question 15

What is the rubrospinal tract used for?

Answer 15

Arm flexion

Question 16

What are the cells called that are only found in the motor cortex? What happens to these cells as you move away from the primary motor cortex to other motor areas?

Answer 16

Betz cells

The amount of betz cells decreases as you move from the primary motor cortex into other association cortices

Question 17

What are the 5 skeletomotor areas in the brain?

Answer 17

1. Supplementary motor area
2. Cingulate motor area
3. Dorsal premotor area
4. Ventral premotor area
5. Primary motor cortex

Question 18

What are the criteria that are needed to be considered a cortical motor area? (this is important!)

Answer 18

1. Must project to motor neurons in the spinal cord (either directly to the ventral horn that then synapses with an alpha motor neuron or indirectly through an interneuron that then synapses with an alpha motor neuron)
2. Needs to have projections to the primary motor cortex
3. Needs to have betz cells
4. When this area is stimulated a movement is produced
5. A recording on EEG shows that during movement there is a change in activity in this area

Question 19

Based on the criteria needed to be a cortical motor area are association areas such as the prefrontal cortex, pre-supplementary motor area, and the parietal and temporal lobe considered cortical motor areas?

Answer 19

No- but they are still involved in regulating motor function

Question 20

In an experiment, monkey’s were trained to grab a grape and then gave these monkeys a lesion to their lateral corticospinal tract. The monkey was still able to reach out and grab the grape, although it took the monkey much longer to do so, meaning that the monkey was just grabbing the grape on chance. What was still intact allowing the monkey to grab the grape after the lesion?

Answer 20

Local Circuit Neurons that project past the lesions to bridge the area

Question 21

The closer you get to the midline, means that the innervation of cranial nerves will likely be more bilateral or unilateral?

Answer 21

Bilateral

Question 22

True or False: a given muscle is only represented on one portion of the cortex within the precentral gyrus?

Answer 22

False- there are multiple locations in the cortex that are used to represent the same muscle (an area in the primary motor, another in the supplemental etc)
These are arranged in columns

Question 23

A single corticospinal neuron divides so that it can influence multiple motor neuron pools. What does this mean and how is related to function?

Answer 23

One motor neuron influences many different muscles (one UMN synapses with a bunch of LMN) This allows a group of different muscles to contract at the same time

Question 24

By injecting rabies into motor neurons and watching retrograde transport, they were able to determine where corticospinal neurons arise from. Which layers of the cortex do the corticospinal neurons arise from?

Answer 24

Layers 3 and 4

Question 25

What are three components of movement that a cortical motor neuron encodes?

Answer 25

1. The specific muscle used
2. Recruitment (force)
3. Direction- certain motor cortical neurons fire to move your arm in one direction

Question 26

True or False: all cortical muscle neurons change their activity with direction?

Answer 26

False
Some cortical neurons change their activity with direction while others remain unchanged. The changes that do occur do so in a predictable fashion and are important in prosthetics

Question 27

What are the main functions of the primary motor, lateral premotor, medial premotor, pre-supplemental motor area, and prefrontal cortices?

Answer 27

Primary motor: simple movement
Lateral premotor: selection of motor responses based on sensory input
Medial premotor: execution of learned sequences
Pre-supplemental motor area: actual learning of sequences
Prefrontal: decision of action/working memory

Question 28

What is the difference between decorticate and decerebrate postures?

Answer 28

Decorticate: arms flexed, legs extended, lesions above red nucleus
Decerebrate: extension of arms and legs, lesions below the red nucleus