The motor control hierarchy

Question 1

What are all movements produced by the skeletal musculature initiated by?

Answer 1

Lower motor neurons

Question 2

What is Fritsch and Hitzig experiment?

Answer 2

Electrical stimulation of anterior cortex elicits contraction of contralateral body muscles
- Became motor cortex

Question 3

How is the sensory map presented?

Answer 3

Lower body is represented medially
Upper body is represented laterally
Proportions reflect density of innervation and behavioural significance

Question 4

What do axial muscles control?

Answer 4

Trunk movement

Question 5

What do proximal muscles control?

Answer 5

Shoulder
Elbow
Pelvis
Knee movement

Question 6

What do distal muscles control?

Answer 6

Hands
Feet
Digits

Question 7

How does the ventral horn innervate striated muscle?

Answer 7

Via the neuromuscular junction

Question 8

Define a motor unit

Answer 8

Motor neuron and the muscle fibres it innervates

Question 9

Define a motor neuron pool

Answer 9

All the motor neurons that innervate a single muscle

Question 10

What does each muscle fibre receive input from?

Answer 10

A single lower (alpha) motor neuron

Question 11

How are motor pools organised?

Answer 11

Grouped in rod shaped clusters within the spinal cord
- Extending over several vertebral segments
- Somatotopically (both mediolaterally and rostrocaudally)

Question 12

What technique would you use to trace where motor neurons go back to in the spinal cord?

Answer 12

Retrograde labelling

Question 13

Where do lower motor neurons receive inputs from?

Answer 13

Upper motor neurons
Local spinal cord inputs

Question 14

How do upper motor neurons project onto lower motor neurons?

Answer 14

Via descending tracts

Question 15

Which lateral pathway is in control of voluntary movement?

Answer 15

Corticospinal tract

Question 16

Where do axons of the CST originate?

Answer 16

Layer 5 of the motor cortex

Question 17

What are the axons of the corticospinal tract derived from?

Answer 17

Large pyramidal cells

Question 18

Where are the main outputs for the motor cortex located?

Answer 18

Layers 3, 5 and 6

Question 19

Where are the main inputs to the cortex located?

Answer 19

Stellate cells in layer 4

Question 20

Describe how the axons of the corticospinal tract control distal muscles

Answer 20

Cross the midline in the pyramidal decussation
- Project laterally in spinal cord
- Synapse onto laterally located lower motor neuron circuits that control distal muscles

Question 21

Where do CST outputs to the upper body originate from?

Answer 21

Lateral motor cortex

Question 22

Where do CST outputs to the lower body originate from?

Answer 22

Medial motor cortex

Question 23

What are motor cortex upper motor neurons concerned with?

Answer 23

Fine voluntary control of more distal structures

Question 24

What are brainstem upper motor neurons concerned with?

Answer 24

Postural movement

Question 25

What do brainstem motor neurons project onto?

Answer 25

Medial motor pools

Question 26

What are the ventromedial pathways?

Answer 26

Vestibulospinal Reticulospinal

Question 27

How do the ventromedial pathways project onto the spinal cord?

Answer 27

Medially onto the spinal cord - Synapse on medially located lower motor neuron circuits that control axial muscles

Question 28

What does the vestibulospinal tract control?

Answer 28

Head balance and turning

Question 29

Where are the vestibulospinal tract inputs from?

Answer 29

The vestibular system

Question 30

What does the tectospinal tract control?

Answer 30

Orientating response

Question 31

Where are tectospinal inputs from?

Answer 31

The visual system via superior colliculus

Question 32

What does the reticulospinal tract control?

Answer 32

Antigravity reflexes

Question 33

How do the ventromedial pathways project?

Answer 33

Mainly ipsilaterally and medially

Question 34

How does the body compensate for forces applied?

Answer 34

An anticipatory feedforward mechanism - Pre-adjusts body posture

Question 35

What are the 2 areas which indirectly control lower MNs?

Answer 35

Area 6 from movement anticipation Area 4 for movement initiation

Question 36

How does movement anticipation project onto axial muscles?

Answer 36

Via reticular formation

Question 37

How does movement initiation project directly onto the spinal cord?

Answer 37

Via the corticospinal tract

Question 38

What does activity in the PMA precede?

Answer 38

Movement planning and anticipation

Question 39

Where is the circuit for anticipation?

Answer 39

Motor cortex to brainstem nuclei

Question 40

What disease is characterised by muscle atrophy and sclerosis?

Answer 40

Motor neuron disease

Question 41

What is the typical time course of MND?

Answer 41

3 years

Question 42

Describe lower motor neuron disease

Answer 42

Muscle paresis or paralysis Loss of stretch reflexes Leads to severe muscle atrophy - Patients usually die from lung dysfunction

Question 43

Describe upper motor neuron disease

Answer 43

Muscle weakness Spasticity Hyperactive reflexes Loss of fine voluntary movement - Patients usually die from loss of bulbar muscles via corticobulbar tract

Question 44

What drug alleviates MND symptoms? What is its mechanism?

Answer 44

Riluzole - Blocks glutamate release leading to neuronal cell death - Only works for a few months

Question 45

A mutation in which gene causes MND?

Answer 45

Superoxide dismutase - SOD1