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Yr2 Control - Term 2 and 3 > Motor and sensory innervation of muscle > Flashcards

Motor and sensory innervation of muscle Flashcards

1
Q

What are the main functions of the brain in the motor system? (3)

A
  • Initiation
  • Integration
  • Co-ordination
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2
Q

What are the main functions of the spinal cord in the motor system? (2)

A
  • Simple reflexes

- Pattern generation

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3
Q

What is the function of the basal ganglia in the motor system?

A

Coordination of movement.

-proper initiation and dampens down movement

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4
Q

What is the function of the cerebellum in the motor system?

A

Sensory motor coordination and recognises error.

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5
Q

What are the main collections of UMNs in the brain involved in the motor system? (2)

A
  • Motor cortex

- Brainstem centre

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6
Q

What is the role of the motor cortex?

A

Planning, initiating and directing voluntary movements.

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7
Q

What is the role of the brainstem centres?

A

Basic movements and postural control.

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8
Q

How is information from UMNs passed to LMNs?

A

Most goes via interneurons in the spinal cord.

-5% go directly to LMNs

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9
Q

Where is the 1* motor cortex located?

A

Precentral gyrus.

-frontal lobe

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10
Q

What is the role of the precentral gyrus?

A

Planning and initiating voluntary movement.

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11
Q

What are the main Brodmann’s area associated with the motor cortex?

A

Brodmann’s areas 4 and 6.

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12
Q

Where is Brodmann’s area 4 located?

A

1* motor cortex.

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13
Q

Where is Brodmann’s area 6 located?

A

Premotor cortex.

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14
Q

What are BETZ cells?

A

Pyramidal cells in 5th layer of the 1* motor cortex.

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15
Q

What is the main function of BETZ cells?

A

Provide indirect connection to spinal cord via corticospinal tract.

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16
Q

What is the main function of non-BETZ cells?

A

Provide direct connection from UMNs to LMNS.

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17
Q

What tracts to axons descend in from the motor cortex to the spinal cord?

A
  • Corticobulbar tract
  • to brainstem centres
  • Corticospinal tract
  • to spinal cord
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18
Q

How are the corticospinal and corticobulbar tracts arrange in the primary motor cortex?

A

Corticospinal tract = MEDIAL.

Corticobulbar tract = LATERAL.

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19
Q

What is another name for the corticospinal tract?

A

Pyramidal tract.

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20
Q

How do the axons of the corticospinal tract descend?

A
  • 95% cross the midline in the MEDULLA&raquo_space; descend contralaterally
  • 5% descend ipsilaterally and cross in the SPINAL CORD
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21
Q

Where in the spinal cord are the contralateral and ipsilateral corticospinal tract axons located?

A

CONTRALATERAL - posterior / lateral cord

IPSILATERAL - ventral cord

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22
Q

Where do the axons of the corticospinal tract terminate?

A

Onto lower motor neurons in the ventral horn.

-directly / indirectly (through interneurons)

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23
Q

Where are lower motor neurons localised?

A

Lamina IX of ventral horn.

-dorsal horn = sensory

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24
Q

Where do efferent motor axons exit the spinal cord?

A

Via the ventral root and spinal nerve.

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25
Q

What are the 2 main types of LMNs?

A

Alpha

Gamma

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26
Q

Which LMNs are directly responsible for the generation of force by muscle?

A

Alpha motor neurons.

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27
Q

What are gamma motor neruons mainly responsible for?

A

Proprioception.

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28
Q

How many axons is each fibre within a muscle innervated by?

A

One.

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29
Q

Who introduced ‘the final common pathway concept’?

A

Charles Sherrington.

  • defined motor neurons and units
  • motor neuron = last ste
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30
Q

Why does the size of laminae IX vary down the cord?

A

Size reflects the demands of peripheral muscles and their innervation.

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31
Q

Where is lamina IX largest?

A

Cervical and lumbar regions.

-limb muscles

32
Q

Approximately how many alpha motor neurons are there on each side of the spinal cord?

A

~150,000.

-many more muscles fibres than motor neurons&raquo_space; need collateral nerves

33
Q

What is a motor neuron pool?

A

Alpha motor neuron group that innervate a single muscle.

  • form clusters in ventral horn
  • more powerful muscle&raquo_space; larger pool
34
Q

How are LMNs to flexors and extensors organised within the spinal cord?

A

Motor neurons to flexors (e.g. biceps brachii) = DORSAL.

Motor neurons to extensors (e.g. triceps brachii) = VENTRAL.

35
Q

How are LMNs to axial and distal muscles organised within the spinal cord?

A

Motor neurons to:

  • axial muscles = MEDIAL.
  • distal muscles = LATERAL.
36
Q

What is a motor unit?

A

An alpha motor neuron and all the muscle fibres it innervates.

37
Q

How many muscle fibres can each motor neuron innervate?

A

Each motor neuron can innervate multiple fibres.

-each muscle fibre is innervated by one axon

38
Q

What is the smallest unit of force that can be activated to produce movement?

A

A motor unit.

39
Q

Does damage to a single motor axon reduce the muscle’s ability to contract?

A

Not necessarily.

-muscles fibres innervated by a single nerve are evenly spread out

40
Q

Why do motor unit vary in size?

A

Allows variability in force and level of control.

41
Q

What do small motor units consist of and innervate?

A
  • Consist of small motor neurons.

- Innervate small number of fibres

42
Q

What do large motor units consist of and innervate?

A
  • Consist of large motor neurons.

- Innervate large number of fibres

43
Q

Give an example of when small motor units are used.

A

Extraocular muscles in eye.

  • 3 muscle fibres per neuron
  • precise, low strength movements
44
Q

Give an example of when large motor units are used.

A

Gastrocnemius.

  • ~1500 fibres per neuron
  • generates large forces
45
Q

What size motor units are recruited first?

A

Small motor units are recruited first, then large to produce increasing force in the muscle.

46
Q

What are the types of motor unit based on the fibres they innervate?

A
  • Slow motor units
  • Fast fatigable motor units
  • Fast fatigue resistant motor units
47
Q

What are the main features of slow motor units? (4)

A
  • Small motor units
  • Small ‘red’ muscle fibres
  • Low force
  • Resistant to fatigue (^Hb)
48
Q

What are the main features of fast fatigable motor units? (4)

A
  • Large motor units
  • Large paler muscle fibres
  • Large forces
  • Easily fatigued (less Hb)
49
Q

What are the main features of fast fatigue-resistant motor units? (3)

A
  • Intermediate type
  • Moderate force
  • Some fatigue
50
Q

Which type of motor units always work at maximal force?

A

Slow motor units - resistant to fatigue.

fast fatigue start powerful but quickly fatigue

51
Q

What sort of exercise uses fast fatigable and slow motor units?

A

Fast fatigable - weight lifting.

Slow - marathon.

52
Q

What is fatigue mainly caused by?

A

Build up of lactic acid.

-anaerobic repiration

53
Q

What is used to record motor unit activity?

A

Electromyograph (EMG).

54
Q

How is an electromyograph performed?

A

Needle is inserted into selected muscle&raquo_space; picks up electrical activity of motor unit.
-reflects synchronous recruitment

55
Q

What does activation of a motor neuron at low frequency (

A

Muscle twitch.

-contraction followed by relaxation

56
Q

What does increasing the frequency of motor neuron firing (>10Hz) lead to?

A

Summation of the twitch.

57
Q

What does higher frequencies of motor neuron firing (>20Hz) lead to?

A

Smoothing of muscle contraction.

58
Q

What do frequencies of motor neuron higher than 40Hz lead to?

A

Twitch summation&raquo_space; tension generation.

-fused tetanus effect

59
Q

What is the fused tetanus effect?

A

Muscle stimulated at such a high frequency&raquo_space; constant tension.
-doesn’t happen under normal circumstances

60
Q

Summarise what happens with increasing frequencies of action potentials.

A

10 Hz - summation
>20 Hz - smoothing of contraction
>40Hz - tension generation

61
Q

What are the main sources of inputs to alpha motor neurons? (3)

A
  • Sensory from peripheral proprioceptors
  • Local from spinal interneurons (most)
  • Descending from brain UMNs
62
Q

What is the sensory apparatus of muscle?

A

The muscle spindle.

  • parallel to fibres
  • intrafusal fibres
63
Q

What is the main function of the muscle spindle?

A
  • Stretch reflex; detects changes in muscle length
  • Contributes to proprioception
  • Regulates contraction
64
Q

What is muscle tone?

A

The continual partial contraction of muscles.

  • always under some degree of stretch
  • spindle / neuron association
65
Q

What are the 2 main classes of muscle spindles?

A
  • Chain

- Bag

66
Q

What is the function and innervation of chain spindles?

A
  • Encode static response of the fibres (fire as long as muscle is stretched)
  • Innervated by Ia and II afferent fibres
67
Q

What is the function and innervation of bag spindles?

A
  • Encode dynamic response of fibres (change rate)

- Innervated by Ia afferent fibres

68
Q

What are intrafusal fibres?

A

Spindles.

  • have sensory functions
  • do not generate tension
  • receive motor innervation from gamma neurons
69
Q

What are extrafusal fibres?

A
  • Form bulk of muscle
  • Generate tension
  • Receive motor innervation from alpha neurons
70
Q

What does activation of alpha motor neurons lead to?

A

Contraction / shortening of muscle fibres
» collapse of intrafusal spinal.
-Gamma MNs then match intrafusal and extrafusal lengths.

71
Q

What is the golgi tendon?

A

A mechanoreceptor.

  • detects changes in muscle tension (‘strain gauge’)
  • contributes to proprioception
72
Q

What is the golgi tendon innervated by?

A

Ib afferents.

73
Q

What is the relative conduction velocities of afferents?

A

Ia > Ib > II.

-larger diameter&raquo_space; faster conduction

74
Q

What are the main physiological differences between muscle spindles and golgi tendons? (3)

A
  • Spindles detect changes in muscle LENGTH, golgi tendons detect changes in muscle TENSION
  • Isometric contraction; Ib (GT) afferent is active, Ia (spindle) is not
  • Isotonic contraction; Ia in active, Ib is not
75
Q

What does damage to descending motor pathways lead to?

A

Upper motor neuron syndrome.

-Babinski sign, spasticity, hyporeflexia

76
Q

Why do babies have the Babinski sign for the first few days?

A

Corticosinal tract is immature.

-fanning of toes

Yr2 Control - Term 2 and 3 (17 decks)

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