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Control lectures > 16 Innervation of muscle > Flashcards

16 Innervation of muscle Flashcards

1
Q

Which cortical layer are the upper motor neurones located in?

A

V.

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2
Q

Which Brodmann areas contain the cortex?

A

4 + 6.

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3
Q

How do axons from the corticospinal tract descend through the spinal cord?

A

95% are contralateral in posterior/lateral CST.

5% are ipsilateral in anterior/ventral CST.

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4
Q

What is the function of the minority of CST neurones that descend ipsilaterally?

A

Innervation of postural muscles.

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5
Q

Where do UMNs meet LMNs?

A

Ventral grey horn of the spinal cord.

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6
Q

Which lamina are LMNs localised to in the ventral grey horn?

A

IX.

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7
Q

Where is lamina IX largest and why?

A

At cervical and lumbar segments.

Control the muscles of the limbs.

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8
Q

What is the motor neurone pool?

A

The group of alpha neurones that innervates one muscle.

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9
Q

How are motor neurone pools distributed the spinal cord?

A

Rostro-caudally.

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10
Q

What is the segmental distribution of lower motor neurones in the spinal cord?

A

Dorsal: flexors.
Ventral: extensors.
Medial: axial muscles.
Lateral: distal muscles.

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11
Q

What is a motor unit?

A

Alpha motor neuron and all the fibres it innervates.

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12
Q

How many axons are received by a muscle fibre?

A

ONE.

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13
Q

Why do motor units vary in size?

A

Degree of force and level of control needed.

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14
Q

How are motor units recruited?

A

Small units (that control small number of fibres) are recruited first.

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15
Q

Describe slow motor units: (3).

A

Small motor units.
‘Red’ fibres that generate low force.
Resistant to fatigue.

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16
Q

Describe fast fatiguable motor units: (3).

A

Large motor units.
Pale muscle fibres that generate large force.
Fatiguable.

17
Q

Describe fast, fatigue resistant motor units: (2).

A

Intermediate force produced.

Some fatigue.

18
Q

What does an EMG measure?

A

Electromyograph.

Measures the electrical activity of one motor unit.

19
Q

What are the three sources of input into alpha motor neurones?

A

Sensory from peripheral proprioceptors.
Local from spinal interneurons.
Descending from upper motor neurones.

20
Q

Describe the location of muscle spindles:

A

Intrafusal and parallel to muscle fibres.

21
Q

What is the function of muscle spindles?

A

Detect changes in muscle length and contribute to proprioception.

22
Q

What are the two classes of muscle spindle fibres?

A

Bag and chain.

23
Q

What are chain spindles innervated by?

What do they encode?

A

Ia and IIa fibres.

Static muscle response (stretch vs no stretch).

24
Q

What are bag spindles innervated by?

What do they encode?

A

Ia fibres.

Dynamic muscle response (rate of stretch change).

25
Q

Differentiate between intrafusal and exrafusal muscle fibres.

A

Intrafusal: innervated by gamma fibres, sensory function.
Extrafusal: innervated by alpha fibres, generate tension.

26
Q

How do gamma motor neurones regulate muscle tension?

A

Alpha neurones cause muscle contraction. Shortening of fibres causes spindle collapse and loss of sensitivity. Gamma MN matches length of spindle to muscle.

27
Q

What is the role of the golgi tendon organ?

A

Mechanoreceptor in series with muscle fibres.

Detects changes in muscle tension. Contributes to proprioception.

28
Q

What are golgi tendon organs innervated by?

A

Ib afferents.

29
Q

What is isometric contraction and which fibre type is active?

A

Tension without change in muscle length.

Ib.

30
Q

What is isotonic contraction and which fibre type is active?

A

Change in length but not tension.

Ia.

31
Q

What are the signs of upper motor neurone syndrome? (4).

A

Babinski’s sign.
Spasticity.
Hyporeflexia.
Loss of fine movements.

32
Q

What is Amyotrophic Lateral Sclerosis?

Which fibre degenerates in this disease?

A

Motor neurone disease.

Alpha neurones.

Control lectures (17 decks)

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