Motor Control - 2

Question 1

What are the structures involved in the high level of motor control?

Answer 1

Association neocortex and basal ganglion

Question 2

What the structures involved in the middle level of motor control?

Answer 2

Motor cortex and cerebellum

Question 3

What are the structures involved in low level of motor control?

Answer 3

Brain stem and spinal cord

Question 4

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

Answer 4

Strategy - goal and movement strategy to best achieve this goal

Question 5

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

Answer 5

Tactics - sequence of spatiotemporal muscle contractions to achieve a goal smoothly

Question 6

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

Answer 6

Execution - activation of motor neuron and interneuron pools to generate goal directed movement

Question 7

What do lateral pathways control?

Answer 7

Voluntary movements of distal muscles - direct cortical control
Includes the corticospinal and rubrospinal tracts

Question 8

What do the ventromedial pathways control?

Answer 8

Posture and locomotion - brain stem control
Includes tectospinal, vestibulospinal, pontine and medullary reticulospinal

Question 8

Where does the CST cross over?

Answer 8

Decussates at medulla/ spinal cord junction so right motor cortex controls left side and left motor cortex controls right side

Question 9

Where does the corticospinal tract originate?

Answer 9

Longest tract
2/3 originates in areas 4 and 6 in frontal motor cortex and 1/3 is somatosensory

Question 10

Where do CST axons synapse?

Answer 10

On ventral horn motor neurons and interneurons to control muscles voluntarily

Question 11

Where does the RST start?

Answer 11

Is smaller and starts in red nucleus of midbrain and receives input from same cortical areas as CST

Question 12

What happens if there is a lesion to CST and RST?

Answer 12

Fine movements of arms and hands are lost. Cant move shoulders, elbows, wrist and fingers
If CST alone - same deficits but reappear few months later

Question 13

Describe CST axons controlling pools of spinal motor neurons

Answer 13

Large pyramidal neurons in motor cortex project via CST
Mono-synaptically excite pools of agonist motoneurons
Same pyramidal neurons branch and excite inhibitory interneurons - inhibit pool of antagonist motoneurons

Question 14

What is the function of the vestibulospinal and tectospinal tracts?

Answer 14

VST - stabilise head and neck
TST - ensures eyes remain stable with the body

Question 15

Where do pontine and medullary reticulospinal tracts originate?

Answer 15

In brain stem

Question 16

Describe pontine and medullary reticulospinal tracts

Answer 16

Use sensory info about balance, body position and vision
Reflexly maintain balance and body position
Innervate trunk and antigravity in limbs

Question 17

What can the motor cortex activate?

Answer 17

Spinal motoneurons directly
Also free spinal neurons from spinal reflexes by interactions with nuclei of ventromedial pathways

Question 18

Describe upper motor neurons

Answer 18

In cortex and brainstem - innervate lower motor neurons in the spinal cord
LMN distribution is somatotopic

Question 19

What do medial and lateral motor neurons control?

Answer 19

Medial -Axial and proximal limb muscles
Lateral - distal limb muscles

Question 20

What are the origin and function of medial and lateral descending tracts?

Answer 20

Medial - from brainstem control pressure, balance, and orienting mechanisms
Lateral - from cortex control precise skilled voluntary movements

Question 21

Where is the primary motor cortex and supplementary motor areas?

Answer 21

Area 4 is in the precentral gyrus
Area 6 - PMA and SMA lies rostrally

Question 22

What is needed to plan movement by cerebral cortex?

Answer 22

Where body is in space
Where it wants to go
Devise a plan to get there

Question 23

Describe the somatotopic map of motor cortex

Answer 23

Area 4 has somatotopic organisation of precentral gyrus
Area 6 neurons drive complex movements on either side of body
Area 6 has 2 maps - premotor areas and supplementary motor area

Question 24

What does SMA innervate?

Answer 24

Supplementary motor area innervates distal motor units directly

Question 25

What does PMA connect?

Answer 25

Premotor area connects reticulospinal neurons innervating proximal motor units

Question 26

Why is the somatotopic map not precise?

Answer 26

Does not represent upper motor neurons causing individual muscle movements
Functional maps in cortex appear to map movements

Question 27

What generates the mental image of body in space?

Answer 27

By somatosensory, proprioceptive and visual inputs to posterior parietal cortex - area 5 and 7

Question 28

What is the function of the prefrontal and parietal cortex?

Answer 28

Where decisions are taken
Which actions/ movements to take and likely outcome

Question 29

Where do axons o prefrontal and parietal cortex converge?

Answer 29

On area 6
Signals encoding actions are converted into how to carry this out

Question 30

Describe decision making neurons in cortical PMA (area 6)

Answer 30

Big increase in PMA APs when there is instruction stimulus and these keep firing through action
PMA neurons fire APs one second before a movement occurs

Question 31

When do specific neurons in area 6 fire?

Answer 31

When movement is made or imagined - rehearsed mentally
Or when others make the same movement