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MSK SM > Skeletal Muscle Physiology > Flashcards

Skeletal Muscle Physiology Flashcards

1
Q

What types of muscle are smooth muscles

A

Skeletal and cardiac

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2
Q

What are muscle tissues capable of doing

A

developing tension and producing movement through contraction

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3
Q

What types of muscles are striated

A

skeletal and cardiac

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4
Q

What causes striation

A

Thin actin filaments and thick myosin filaments

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5
Q

What are skeletal muscles innervated by and what are they subject to

A

the somatic nervous system - subject to voluntary control

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6
Q

What are cardiac and smooth muscles innervated by and what does this result in

A

Autonomic nervous system - involuntary action

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7
Q

What are the 5 physiological functions of skeletal muscles

A 
maintenance of POSTURE 
purposeful MOVEMENT in relation to external environment
RESPIRATORY movements 
HEAT production
contribution to WHOLE BODY METABOLISM
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8
Q

What are skeletal muscle fibres organised into?

A

motor units

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9
Q

what is a motor unit

A

a single alpha motor neuron and all the skeletal muscle fibres it innervates

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10
Q

Muscles which serve fine movements (external eye muscles, muscles of facial expression and intrinsic hand muscles) have fewer fibres per motor unit. True or false

A

True

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11
Q

When precision is more important than power, how many fibres per motor unit will there be

A

few

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12
Q

In what case will there be hundreds to thousands of fibres per motor unit

A

Power more important than precision

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13
Q

Gap junctions are present in skeletal muscle or cardiac muscle

A

cardiac muscle

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14
Q

What initiates contraction in skeletal muscle

A

neurogenic initiation

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15
Q

What initiates contraction of cardiac muscle

A

myogenic initiation

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16
Q

Where is there a neuromusclular junction present - skeletal or cardiac

A

Skeletal

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17
Q

Where does the Ca++ come from in skeletal muscles

A

sarcoplasmic reticulum

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18
Q

Where does the Ca++ come from in cardiac muscles

A

From ECF and sarcoplasmic reticulum

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19
Q

What is excitation contraction coupling

A

Process whereby the surface action potential results in activation of the contractile mechanism of the muscle fibre

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20
Q

When is Ca2+ released from the lateral sacs of the sarcoplasmic reticulum in Skeletal muscles

A

When the surface action potential spreads down the transverse tubules (T Tubules)

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21
Q

What are T tubules

A

Extensions of the surface membrane that dip into the muscle fibre

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22
Q

What is the transmitter at the neuromuscular junction

A

Acetylcholine

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23
Q

What triggers the release of Ca2+ from lateral sacs of sarcoplasmic reticulum

A

The spread of action potential down the T tubules

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24
Q

Transverse tubules are surrounded by what

A

Lateral sacs

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25
Q

Skeletal muscle consists of parallel muscle fibres bundled by what

A

connective tissue

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26
Q

Skeletal muscle fibres usually extend where

A

The entire length of the muscle

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27
Q

What usually attaches skeletal muscles to the skeleton

A

Tendons

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28
Q

What form lever systems

A

Bones, muscles and joints

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29
Q

What does each muscle fibre contain

A

Many myofibrils

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30
Q

Myofibrils have alternating segments of what

A

Thick and thin protein filaments

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31
Q

Actin and mysocin are arranged into what and what are these

A

Sarcomeres - these are the functional units of muscle

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32
Q

What is the functional unit of any organ

A

The smallest component capable of performing all the functions of that organ

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33
Q

What is the functional unit of skeletal muscle

A

Sarcomere

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34
Q

Where is a sarcomere found

A

Between 2 Z lines - connect the thin filaments of 2 adjoining sarcomeres

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35
Q

What are the 4 zones of the sarcomere

A

A band
H zone
M line
I band

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36
Q

What is the A band made up of

A

THick filaments along the portions of thin filaments that overlap in both ends of thick filaments

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37
Q

What is the H zone

A

the lighter area within the middle of the A band where thin filaments dont reach

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38
Q

Where does the M line extend

A

Vertically down middle of A band within the centre of H zone

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39
Q

What does the I band consist of

A

Remaining portion of thin filaments that do not project in A band

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40
Q

What produces muscle tension

A

Sliding of actin and filaments on myocin filaments

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41
Q

Force generation depends on what

A

ATP dependent interaction between thick and thin filaments

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42
Q

What is ATP required for

A

Both contraction and relaxation

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43
Q

What is Ca2+ required for

A

to switch on cross bridge formation

44
Q

How does Ca 2+ switch on cross bridge formation

A

It binds to troponin. This results in repositioning of troponin - tropomyocin complex to uncover the cross bridge binding sites on actin

45
Q

When a muscle fibre is relaxed, why is there no cross bridge binding

A

Because the cross bridge binding site on actin is physically covered by the troponin tropomyosin complex

46
Q

When a muscle fibre is excited, what happens in terms of Ca2+

A

Released Ca2+ binds with troponin, pulling troponin-tropomyosin complex aside to expose cross-bridge binding site. Cross bridge binding then occurs

47
Q

What do motor units allow

A

simultaneous contraction of a number of muscle fibres

48
Q

How is a stronger contraction achieved?

A

Stimulation of more motor units - motor unit recruitment

49
Q

What helps prevent muscle fatigue

A

Synchronous motor units recruitment during submaximal contraction

50
Q

Tension developed by each contracting muscle fibre depends on what 3 things?

A
  1. Frequency of stimulation and summation of contraction
  2. Length of muscle fibre at the onset of contraction
  3. Thickness of muscle fibre
51
Q

Describe the relationship between action potential and duration of resulting twitch

A

The duration of the AP is much shorter than that of the resulting twitch

52
Q

How is it possible to summate twitches to bring about a stronger contraction of skeletal muscle

A

Through Repetitive fast stimulation of skeletal muscle

53
Q

Both cardiac and skeletal muscles can be tetanised. True or False

A

False - cardiac muscle cannot be tetanised

54
Q

Why can cardiac muscle not be tetanised

A

The long refractory period prevents generation of tetanic contaction

55
Q

How does tension in skeletal muscles increase?

A

With increasing frequency of stimulation

56
Q

What is an important mechanism for modulating the force of contraction in skeletal muscle

A

Increasing the frequency of stimulation

57
Q

When can maximal tetanic contraction be achieved?

A

When the muscle is at its optimal length before the onset of contraction

58
Q

What explain the skeletal muscle length tension relationship

A

The sliding filament mechanism

59
Q

Skeletal muscle tension is transmitted to bone via what

A

The stretching and tightening of muscle connective tissue and tendon

60
Q

What are the 2 types of skeletal muscle contraction

A

Isotonic conraction and Isometric contraction

61
Q

Isotonic contraction is used for what?

A

body movements and for moving objects - muscle tension remains constant as the muscle length changes

62
Q

Isometric contraction is used fo what?

A

Supporting objects in foxed positions and for maintaining body posture
Muscle tension develops at constant muscle lenght

63
Q

How are isotonic and isometric contractions transmitted to bone

A

Via the elastic components of muscle

64
Q

Describe the relationship between velocity of muscle and load

A

As the load increases, the velocity of muscle shortening decreases

65
Q

What produces purposeful skeletal muscle activity

A

Input from a variety of sources influence the activity of motor unit to produce purposeful skeletal muscle activity

66
Q

Input to motor nerves could be excitatory or inhibitory. True or False

A

True

67
Q

What 4 things can cause impairment of skeletal muscle function

A

Intrinsic disease of muscle
Disease of NMJ
Disease of lower motor neurons which supply the muscle
Disruption of inputs to motor unit

68
Q

What are 3 types of genetically determined myopathies

A

Congenital
Degeneration (muscular Dystrophy)
Membraine ion channels (myotonia)

69
Q

What are 3 types of acquired myopatihes

A

Inflammatory (polymyosytis)
Endocrine (Cushing syndrome, thyroid disease)
Toxic (alcohol, statins)

70
Q

What is a reflex action

A

A stereotyped response to a specific stimulus

71
Q

Reflex actions are the simplest form of what?

A

coordinated movement

72
Q

What are important for localising lesions in the motor system

A

The neural pathaways for reflexes

73
Q

Where are pathways responsible fore reflex action located at?

A

Various levels of the motor system

74
Q

The stretch reflex is the simplest what?

A

Monosynaptic spinal reflex

75
Q

What does the stretch reflex serve as

A

A negative feedback that resists passive change in muscle lenghth to maintain optimal resting length of muscle

76
Q

What is the muscle spindle? and when is it activated?

A

The sensory receptor and By the muscle stretch

77
Q

By stretching the muscle spindle, what does this do to the afferent neurons

A

It increases firing in the afferent neurons

78
Q

Where do the afferent neurons synapse

A

In the spinal cord with the alpha motor neurons

79
Q

The stretch reflex is coordinated by what?

A

simultaneous relaxation of antagonist muscle

80
Q

How cant he stretch reflex be elicited

A

By tapping the muscle tendon with a rubber hammer

81
Q

What muscle is stretch in the patella tendon reflex (knee jerk)

A

Quadriceps fermoris

82
Q

Name 5 examples of reflexes that can be elicited by the rubber hammer

A

Knee, Ankle, Biceps, Triceps Jerk and the brachioradialis

83
Q

What spinal segment is effected in the biceps jerk and brachioradialis

A

C5-6

84
Q

What peripheral nerve is affected by the brachioradialis and triceps jerk

A

Radial nerve

85
Q

what spinal segment is affected by the

a) knee jerk
b) ankle jerk

A

a) L3,4

b) S1,2

86
Q

What spinal segment is affected in the triceps jerk

A

C6-7

87
Q

What peripheral nerve is affected by the knee jerk

A

Femoral nerve

88
Q

What peripheral nerve is affected in the ankle jerk

A

Tibial nerve

89
Q

What peripheral nerve is affected in the biceps jerk

A

Musculocutaneous Nerve

90
Q

What are the sensory receptors for the stretch reflex?

A

Muscle spindles

91
Q

What are muscle spindles

A

A collection of specialised muscle fibres

92
Q

What are muscle spindles also known as

A

intrafusal fibres

93
Q

What are ordinary muscle fibres referred to as?

A

extrafusal fibres

94
Q

Where are muscle spindles found and where do they run

A

Within the belly of muscles and they run parallel to ordinary muscle fibres

95
Q

Muscle spindles have sensory nerve endings. What are these known as?

A

Annulospiral fibres

96
Q

What are the efferent neurons that supply muscle spindles called

A

gamma motor neurons

97
Q

what do gamma motor neurons do?

A

adjust the level of tension in the muscle spindles to maintain their sensitivity when the muscle shortens during muscle contraction

98
Q

The contraction of intrafusal fibres contributes to the overal strength of the muscle contraction

A

False - it does not contribute

99
Q

What does the discharge from the muscle spindles sensory ending do?

A

increases as the muscle is stretched

100
Q

What are the 3 main differences between different types of skeletal muscle fibres

A

The enzymatic pathways for ATP synthesis

The resistance to fatigue - muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue

The activity of myosin ATPase - ths determines the speed at which energy is made available for cross bridge cycling ie. the speed of contraction

101
Q

What are 3 metabolic pathways that supply ATP in muscle fibres

A

Transfer of high energy phosphate from creatine Phosphate to ADP
Oxidative phosphorylation (main source when O2 is present)
Glycolysis (main source when O2 is not present)

102
Q

What are type 1 fibres used for

A

prolonged relatively low work aerobic activities - maintenance of posture, walking

103
Q

What are type 2a fibres used for

A

prolonged relatively moderate work activities - jogging

104
Q

What are type 2x fibres used for

A

short term high intensity activities - jumping

105
Q

What are 3 useful investigations in neuromuscular disease

A

Electromyography (EMG)
Nerve conduction studies
Muscle enzymes

MSK SM (42 decks)

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