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Neuro > The motor control hierarchy > Flashcards

The motor control hierarchy Flashcards

1
Q

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

A

Lower motor neurons

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2
Q

What is Fritsch and Hitzig experiment?

A

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

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3
Q

How is the sensory map presented?

A

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

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4
Q

What do axial muscles control?

A

Trunk movement

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5
Q

What do proximal muscles control?

A

Shoulder
Elbow
Pelvis
Knee movement

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6
Q

What do distal muscles control?

A

Hands
Feet
Digits

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7
Q

How does the ventral horn innervate striated muscle?

A

Via the neuromuscular junction

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8
Q

Define a motor unit

A

Motor neuron and the muscle fibres it innervates

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9
Q

Define a motor neuron pool

A

All the motor neurons that innervate a single muscle

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10
Q

What does each muscle fibre receive input from?

A

A single lower (alpha) motor neuron

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11
Q

How are motor pools organised?

A

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

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12
Q

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

A

Retrograde labelling

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13
Q

Where do lower motor neurons receive inputs from?

A

Upper motor neurons
Local spinal cord inputs

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14
Q

How do upper motor neurons project onto lower motor neurons?

A

Via descending tracts

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15
Q

Which lateral pathway is in control of voluntary movement?

A

Corticospinal tract

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16
Q

Where do axons of the CST originate?

A

Layer 5 of the motor cortex

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17
Q

What are the axons of the corticospinal tract derived from?

A

Large pyramidal cells

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18
Q

Where are the main outputs for the motor cortex located?

A

Layers 3, 5 and 6

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19
Q

Where are the main inputs to the cortex located?

A

Stellate cells in layer 4

20
Q

Describe how the axons of the corticospinal tract control distal muscles

A

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

21
Q

Where do CST outputs to the upper body originate from?

A

Lateral motor cortex

22
Q

Where do CST outputs to the lower body originate from?

A

Medial motor cortex

23
Q

What are motor cortex upper motor neurons concerned with?

A

Fine voluntary control of more distal structures

24
Q

What are brainstem upper motor neurons concerned with?

A

Postural movement

25
Q

What do brainstem motor neurons project onto?

A

Medial motor pools

26
Q

What are the ventromedial pathways?

A

Vestibulospinal
Reticulospinal

27
Q

How do the ventromedial pathways project onto the spinal cord?

A

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

28
Q

What does the vestibulospinal tract control?

A

Head balance and turning

29
Q

Where are the vestibulospinal tract inputs from?

A

The vestibular system

30
Q

What does the tectospinal tract control?

A

Orientating response

31
Q

Where are tectospinal inputs from?

A

The visual system via superior colliculus

32
Q

What does the reticulospinal tract control?

A

Antigravity reflexes

33
Q

How do the ventromedial pathways project?

A

Mainly ipsilaterally and medially

34
Q

How does the body compensate for forces applied?

A

An anticipatory feedforward mechanism
- Pre-adjusts body posture

35
Q

What are the 2 areas which indirectly control lower MNs?

A

Area 6 from movement anticipation
Area 4 for movement initiation

36
Q

How does movement anticipation project onto axial muscles?

A

Via reticular formation

37
Q

How does movement initiation project directly onto the spinal cord?

A

Via the corticospinal tract

38
Q

What does activity in the PMA precede?

A

Movement planning and anticipation

39
Q

Where is the circuit for anticipation?

A

Motor cortex to brainstem nuclei

40
Q

What disease is characterised by muscle atrophy and sclerosis?

A

Motor neuron disease

41
Q

What is the typical time course of MND?

A

3 years

42
Q

Describe lower motor neuron disease

A

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

43
Q

Describe upper motor neuron disease

A

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

44
Q

What drug alleviates MND symptoms? What is its mechanism?

A

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

45
Q

A mutation in which gene causes MND?

A

Superoxide dismutase
- SOD1

Neuro (25 decks)

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