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CNS CLERKSHIP > Motor units, muscle spindles, golgi tendon organs and joint receptors > Flashcards

Motor units, muscle spindles, golgi tendon organs and joint receptors Flashcards

1
Q

What does the somatic motor system consist of?

A
  • Skeletal muscles + elements of the nervous system controlling them.
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2
Q

What is the neural element of the motor system comprised of?

A
  • Upper motor neurones within the brain.

- Lower motor neurones with soma within the brain stem and ventral horn of the spinal cord.

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3
Q

UMNs supply input to LMNs to modulate what?

A

LMN activity.

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4
Q

LMNs receive input from UMNs and what else?

A
  • Proprioceptors.

- Interneurons.

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5
Q

LMNs command what?

A

Muscle contraction.

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6
Q

LMNs form what pathway?

A

The “final common pathway”.

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7
Q

LMNs comprise what?

A
  • Alpha motor neurones.

- Gamma motor neurones.

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8
Q

What is the function of alpha motor neurones of LMNs?

A

Innervate most fibres that generate force within a muscle.

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9
Q

What is the function of gamma motor neurones of LMNs?

A

Innervate the muscle spindle - a sensory organ within the muscle.

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10
Q

Biceps brachii and brachialis may be described as?

A

Synergists.

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11
Q

Triceps brachii and anconeous may be described as?

A

Synergistic muscles.

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12
Q

Biceps brachii and brachialis work as what?

A

Flexors of the elbow.

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13
Q

Triceps brachii and anconeus work as what?

A

Extensors of the elbow.

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14
Q

Axial muscles control movement of the what?

A

Trunk.

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15
Q

What is the function of axial muscles?

A

To maintain posture.

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16
Q

Where are proximal muscles found?

A
  • Shoulder.
  • Elbow.
  • Pelvis.
  • knee.
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17
Q

What is the function of proximal muscles?

A

To mediate locomotion.

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18
Q

Distal muscles move what?

A
  • Hands.
  • Feet.
  • Digits (allow fine manipulation of objects).
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19
Q

Axons of LMNs exit the spinal cord via?

A

Ventral roots or cranial nerves.

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20
Q

Each ventral root joins with a dorsal root to form what?

A

A mixed spinal nerve.

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21
Q

A mixed spinal nerve composed of both a dorsal and ventral root contains what fibres?

A
  • Sensory fibres.

- Motor fibres.

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22
Q

Motor neurones/motoneurones belong to a what?

A

A spinal segment.

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23
Q

How are motor neurones distributed in the spinal cord?

A

Unequally.

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24
Q

Where are the greatest numbers of motor neurones found in the spinal cord?

A
  • Cervical enlargement (C3-T1).

- Lumbar enlargement (L1-S3).

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25
Q

At what spinal levels is the cervical enlargement found?

A

C3-T1.

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26
Q

At what spinal levels is the lumbar enlargement found?

A

L1-S3.

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27
Q

The cervical enlargement mostly supplies what?

A

The arm.

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28
Q

The lumbar enlargement mostly supplies what?

A

The leg.

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29
Q

Motor neurones innervating distal and proximal musculature are mainly found in which segments of the spinal cord?

A
  • Cervical.

- Lumbar-sacral.

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30
Q

Motor neurones innervating the axial musculature mainly occur at which segments of the spinal cord?

A

All levels.

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31
Q

What is a motor unit?

A

An alpha-motor neuron and all the skeletal muscle fibres it innervated.

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32
Q

What is the smallest functional component of the motor system?

A

Motor unit.

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33
Q

Collection of alpha-motor neurones innervating a single muscle is termed what?

A

A motor neurone pool.

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34
Q

Force of muscle contraction is graded by alpha-motor neurones by what two principle mechanisms?

A
  • Frequency of AP discharge of a-motor neurone.

- Recruitment of additional, synergistic motor units.

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35
Q

Describe the “twitch” caused by AP discharge of an alpha-motor neuron.

A

A rapid sequence of contraction follow by relaxation.

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36
Q

Cell bodies of LMNs show a distinct somatotropic distribution where?

A

In the ventral horn.

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37
Q

Where are LMNs innervating axial muscles found in relation to those innervating distal muscles?

A

Medially.

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38
Q

Where are LMNs innervating flexors found in relation to those supplying extensors?

A

Dorsally.

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39
Q

What three sources of input to an alpha-motor neuron regulate its activity?

A
  • Central terminal of dorsal root ganglion cells whose axons innervate muscle spindles.
  • UMNs in the motor cortex and brain stem.
  • Spinal interneurones.
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40
Q

Muscle strength is dependent on what?

A

Neuromuscular activation.

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41
Q

What features of neuromuscular activation impact muscle strength?

A
  • (involved) LMN firing rate.
  • Number of LMNs (motor units) innervating a muscle.
  • Co-ordinated movement i.e. agonist vs antagonist, integration/control of reflex responses.
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42
Q

Force production by innervated muscle fibres is dependent on what?

A
  • Fibre size (hypertrophy).

- Fibre phenotype (“fast” or “slow” contracting muscle).

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43
Q

A single AP in an alpha-motor neuron causes what?

A

A muscle fibre to twitch.

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44
Q

Summation of muscle fibre twitches causes what?

A
  • Sustained contraction.
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45
Q

Why does summation of muscle fibre twitches cause sustained contraction?

A

Increasing number of incoming action potentials.

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46
Q

What is the function of small motor units?

A

Fine movements e.g. extra-ocular eye muscles.

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47
Q

Give a function of large motor units.

A

E.g. large postural (antigravity) muscles - leg muscles.

48
Q

Small motor units are innervated by what size of alpha-motor neurones?

A

Small alpha-motor neurons.

49
Q

Large motor units are innervated by what size of alpha-motor neurones?

A

Large alpha-motor neurons.

50
Q

Force of contraction that each motor unit produces is dependent on what?

A

Its size.

51
Q

Alpha-motor neurons innervating fast-type muscle fibres tend to be what and have what?

A
  • Larger.
  • Faster conducting units.
    (Than those of slow units).
52
Q

Each muscle fibre innervation occurs via what?

A

A single motor axon at endplate (NMJ), usually at the centre of the fibre.

53
Q

How do fast and slow muscle fibres differ (generally)?

A

In the speed of myosin ATPase splitting ATP to provide energy for cross bridge cycling.

54
Q

In slow-oxidative Type I muscle fibres, ATP is derived from what?

A

Oxidative phosphorylation.

55
Q

Describe the action of slow-oxidative (type-I) muscle fibres.

A

Fatigue resistant fibres performing slow contraction and relaxation.

56
Q

Why are slow-oxidative fibres red?

A

High myoglobin content.

57
Q

In fast type-IIa muscle fibres, ATP is derived from what?

A

Oxidative phosphorylation.

58
Q

Describe the action of fast type-IIa fibres.

A

Fatigue resistant fibres performing fast contraction and relaxation.

59
Q

How does vascularisation differ between fast type-IIa and IIb/x muscle fibres?

A

Type-IIa: (red) reasonably well vascularised.

Type-llb: (pale) poorly vascularised.

60
Q

Describe the action of fast type-IIb/x fibres.

A

Non-fatigue resistant muscle fibres performing fast contraction.

61
Q

In fast type-IIb/x muscle fibres, ATP is derived from what?

A

Glycolysis.

62
Q

What are the three types of motor unit?

A
  • Fast fatiguing.
  • Fatigue resistant.
  • Slow.
63
Q

Describe fast fatiguing motor units.

A
  • Very high tension.
  • Fast fatiguing.
  • Large alpha-motor neurons of high threshold.
  • Type IIb/x fibres.
64
Q

Describe fatigue resistant motor units.

A
  • High tension.
  • Slow fatiguing.
  • Intermediate alpha-motor neurons and threshold.
  • Type IIa fibres.
65
Q

Describe slow motor units.

A
  • Low tension.
  • Fatigue resistant.
  • Small alpha-motor neurons of low threshold.
  • Type I fibres.
66
Q

Which motor units are more easily activated and “trained” by training that activates the muscle?

A

Slow motor units.

67
Q

Which motor units are associated with muscles of fine gradation of force?

A

Small motor units.

68
Q

Which motor units are associated with muscles of coarse gradation of force?

A

Large motor units.

69
Q

Recruitment of alpha-motor neurons by size allows for what?

A

Fine and graded development of muscle force.

70
Q

Which reflex is being described? When a skeletal muscle is pulled, it pulls back.

A

Myotatic reflex.

71
Q

What sensory organ registers change in length within a muscle?

A

Muscle spindle.

72
Q

What does a muscle spindle consist of?

A
  • Fibrous capsule.
  • Intrafusal muscle fibres.
  • Sensory afferents.
  • Gamma-motor neuron efferents.
73
Q

What is the function of sensory afferents in a muscle spindle?

A

To innervate intrafusal muscle fibres.

74
Q

What is the function of gamma motor neurone efferents in a muscle spindle?

A

To innervate intrafusal fibres.

75
Q

Striking of the paterllar tendon with a tendon hammer elicits what?

A

A knee jerk reaction underpinned by the myotatic reflex.

76
Q

Describe the myotatic reflex (basic).

A

It is a monosynaptic reflex arc. Rapid and most prominent in extensor muscles.

77
Q

Describe the myotatic reflex in detail.

A
  1. Muscle spindle is stretched.
  2. Ia afferent activated.
  3. Excitatory synaptic transmission in spinal cord (monosynaptic).
  4. Alpha-motor neuron activated.
  5. Contraction of homonymous muscle.
78
Q

The only monosynaptic reflex humans.

A

Myotatic reflex.

79
Q

Intrafusal fusal fibres consist of?

A
  • Non-contractile equatorial region.

- Contractile polar ends.

80
Q

The non-contractile equatorial region of intrafusal fibres is innervated by?

A
  • Ia sensory neurones.
81
Q

Contractile polar ends of intrafusal fibres receive efferent input from what?

A
  • Gamma-motor neurons with cell bodies in the ventral horn of the spinal cord.
82
Q

Stimulation of what causes the spindle to contract?

A
  • Gamma motor neurons.
83
Q

Why are alpha- and gamma-motor neurons normally co-activated during voluntary movement?

A

To allow parallel contraction of intrafusal and extrafusal fibres thus maintaining the sensitivity of the spindle.

84
Q

Intrafusal fibres can be divided broadly into which two categories?

A
  • Nuclear bag fibres.

- Chain fibres.

85
Q

Name the 2 types of nuclear bag fibres (intrafusal fibre subtype).

A
  • Bag 1/ dynamic.

- Bag 2/ static.

86
Q

Describe Nuclear bag fibres - Bag 1/ dynamic.

A
  • Very sensitive to rate of change in muscle length.

- Innervated by dynamic, but not static Gamma-motor neurons.

87
Q

Describe Nuclear bag fibres- Bag 2/ static.

A
  • More sensitive to the absolute length of the muscle.

- Innervated by static gamma-motor neurons.

88
Q

Describes chain fibres of intrafusal fibres.

A

Sensitive to the absolute length of the muscle and innervated by static gamma-MNs.

89
Q

What two types of afferent fibre innervate the intrafusal fibres?

A
  • Ia afferents.

- II fibres.

90
Q

Ia afferents form a primary annulospiral nerve ending, winding around the centre of all what?

A

Intrafusal fibres.

91
Q

II fibres, form flowerspray endings on all intrafusal fibres except what?

A

Bag 1/ dynamic type.

92
Q

Ia sensory fibres respond to what?

A
  • Rate of change of muscle length.

- Absolute length of muscle.

93
Q

Stimulation of static gamma fibres causes what?

A
  • Steady state/static response to increase.
94
Q

Stimulation of dynamic gamma fibre enhances what?

A

Dynamic response to stretch.

95
Q

In activities in which muscle length changes slowly and predictably, what type of gamma-MNs are active?

A

Only static gamma-MNs.

96
Q

Which type of gamma-MNs are active during activities in which muscle length changes rapidly and unpredictably?

A

Dynamic gamma-MNs.

97
Q

Where are golgi tendon organs located?

A

At the junction of muscle and tendon.

98
Q

What is the function of golgi tendon organs?

A

Monitor changes in muscle tension to regulate it.

99
Q

Describe the anatomical relationship of golgi tendons and extrafusal fibres.

A

They exist in series, rather than parallel to each other.

100
Q

Golgi tendon organs are innervated by what?

A

Group Ib sensory afferents.

101
Q

Why do golgi tendon organs regulate muscle tension?

A
  • To protect the muscle from overload in extreme circusmtances e.g. weight lifting.
  • Generally to regulate muscle tension to an optimal range.
102
Q

Group Ib afferents enter spinal cord and synapse upon inhibitory interneurones, which then synapse onto what?

A

Alpha-motor neurons of the homonymous muscle.

103
Q

Group Ib afferents enter spinal cord and synapse upon inhibitory interneurones, which then synapse onto Alpha-motor neurons of the homonymous muscle to form what?

A

The basis of the reverse myotatic reflex.

104
Q

An inhibitory interneuron interposed between the Ib afferent and alpha-MN is an example of what kind of pathway?

A

Polysynaptic pathway.

105
Q

How do golgi tendon organs gauge the force generated by a muscle?

A

By measuring the tension in its tendon.

106
Q

Coding of force by the Golgi Tendon Organ and the Reverse Myotatic reflex supplies important proprioceptive feedback for what?

A

Proper execution of fine motor acts.

107
Q

Proprioceptive axons are present in connective tissue of joints and therefore respond to what?

A

Changes in joint:

  • Angle.
  • Direction and velocity of movement.
108
Q

The position of a joint is transmitted to what?

A

The CNS.

109
Q

Free nerve endings are found where within a joint?

A
  • Capsule.

- Connective tissue.

110
Q

Free nerve endings within a joint have which function?

A

Nociceptive.

111
Q

Golgi-type endings are only found where within a joint?

A

Only in ligaments.

112
Q

Function of golgi-type endings in a joint?

A

Protective?

113
Q

Paciniform ending are found where within a joint?

A
  • In periosteum near articular attachments.

- Fibrous part of joint capsule.

114
Q

Ruffini endings are found where within a joint?

A

Mainly in joint capsules.

115
Q

Function of Ruffini endings in joints?

A

Static position and speed of movements.

116
Q

Proprioceptive information arises from?

A
  • Muscle spindles.
  • Golgi tendon organs.
  • Joint receptors.

CNS CLERKSHIP (43 decks)

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