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MUSCULOSKELETAL - BRS > Microstructure And Contraction > Flashcards

Microstructure And Contraction Flashcards

1
Q

What type of control is smooth muscle under?

A

Involuntary control

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2
Q

What part of the nervous system does smooth muscle act under?

A

Autonomic nervous system

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3
Q

What type of control is the skeletal muscle under?

A

Voluntary control

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4
Q

What does skeletal muscle do?

A

contract to bring about movement

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5
Q

What connects bone to muscle

A

A tendon

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6
Q

What are skeletal muscles usually attached to?

A

Bones

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7
Q

What is the microstructure of a muscle? - 5

A

Myofilaments => Myofibril => Myofibre => Fascicles => Muscle

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8
Q

What are muscle fasciculus surrounded by?

A

Perimysium

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9
Q

What are myofibres/muscle fibres surrounded by?

A

Endomysium

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10
Q

What surrounded the bundles of muscles fascicles to hold them together?

A

Epimysium

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11
Q

What is the nucleus state of muscle fibers?

A

Multinucleate

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12
Q

What is the plasma membrane that covers the myofibres called?

A

Sarcolemma

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13
Q

What is found in the sarcoplasm?

A

myoglobin and mitochondria

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14
Q

What is the sarcoplasmic reticulum?

A

Network of fluid filled tubules regulating intracellular calcium concentration for contraction and relaxation

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15
Q

What is one repeating unit of a myofibril called?

A

A sarcomere

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16
Q

What two proteins do myofibril consist of?

A

Actin and myosin

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17
Q

What is the thin filament called

A

Actin

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18
Q

Thick filaments are

A

Myosin

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19
Q

What makes up the dark portion of the light and dark bands?

A

Myosin

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20
Q

What separates sarcomere?

A

Dense Z protein discs

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21
Q

What is the I band?

A

The light bands with thin actin filaments

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22
Q

Do myofilaments extend the length of the myofibres?

A

No

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23
Q

What causes muscle contraction?

A

Movement of actin filaments over the myosin filaments, which shortens the length of the sarcomere

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24
Q

How many heads does myosin have?

A

Two globular heads

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25
Q

What forms the single tail of myosin?

A

Two alpha helices

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26
Q

What forms a myosin filament?

A

The tails of several hundred molecules

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27
Q

What two other molecules do actin filaments contain?

A

Troponin and tropomyosin

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28
Q

What shape are actin molecules twisted into?

A

Helix

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29
Q

What happens to the I band when the muscle contracts?

A

Shortens

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30
Q

What happens to the A band during contraction?

A

Stays the same length

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31
Q

What is the A band?

A

The dark band

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32
Q

What happens to the distance between the Z discs during muscle contraction?

A

Shortenes

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33
Q

Describe the initiation of muscle contraction - 7 steps

A
  1. Action potential arrives at end of motor neurone
  2. Voltage gated Ca2+ channels open
  3. Ca2+ enters pre-synaptic terminal
  4. Triggers the exosytosis is of vesicles
  5. ACh released into the cleft
  6. Binds to receptors => generates action potential
  7. local currents flow from depolarised region to adjacent region, allowing AP to spread along the surface of the muscle fibre membrane
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34
Q

How is ACh broken down?

A

Using acetylcholine esterase

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35
Q

Describe the activation of muscle contraction - 8 steps

A
  1. AP propagates along surface and into T tubules
  2. Dihydropyridine (DHP) receptors in T tubule membranes sense change in voltage and changes shape of the protein linked to ryanodine receptor
  3. Ryanodine receptor then opens and releases Ca2+ out into space around filaments
  4. Ca2+ binds to troponin => causes tropomyosin to move, exposing the myosin head binding site
  5. Ca2+ is then actively transported into the sarcoplasmic reticulum
  6. Charged myosin head binds to exposed site on actin filament => binding causes the myosin head to pivot pulling the actin filament towards centre of sarcomere
  7. ATP binds which causes the myosin head to be released
  8. ATP hydrolysis provides energy to recharge the myosin head
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36
Q

What receptor detects the change in voltage when an action potential arrives at the T tubule

A

Dihydropyridine

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37
Q

What is the DHP receptor bound to?

A

Ryanodine receptor

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38
Q

What does Ca2+ bind to on the actin filament?

A

Troponin

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39
Q

What is covering the myosin binding site?

A

Tropomyosin

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40
Q

What is the power stroke?

A

The pivoting of the the myosin head to slide the actin chain over the myosin filament

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41
Q

What binds to the myosin head to charge the myosin head to move?

A

ATP

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42
Q

What is used to “recharge” the myosin head for more contraction?

A

ATP hydrolysis to make ADP + Pi

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43
Q

Where is neural control of muscle contraction - 2

A

Upper motor neurone in the brain to lower motor neurones in the brainstem or spinal cord

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44
Q

What is a motor unit?

A

A single motor neurone together with all the fibers that it innervates

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45
Q

How many muscle fibres do each motor neurone supply on average?

A

600

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46
Q

What happens when a single motor neurone is stimulated?

A

All the muscle fibers in that motor unit will contract

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47
Q

What is the best innervation ratio for high levels of fine control?

A

Neurones which innervate fewer muscle fibers

48
Q

What is a type one motor unit?

A

Slow

49
Q

What are type IIa muscle fibers?

A

Fast, fatigue resistant

50
Q

What are type IIB motor units?

A

Fast and fatiguable

51
Q

Which motor units have small cell body diameter?

A

Slow, type I

52
Q

Which motor unit type have thicker axons?

A

Type IIA and IIB

53
Q

What is the size difference in dendritic trees of the different motor units ?

A

Larger dendritic trees in Type IIA and Type IIB, smaller in type I

54
Q

How are muscle fibers distributed throughout the muscle?

A

Randomly

55
Q

Which muscle fiber type are rich in myoglobin?

A

Slow type I and type IIB (fast, fatiguable)

56
Q

Which type of muscle fibers are used for aerobic activity?

A

Slow twitch fibres

57
Q

Which muscle fibre type are used for anaerobic functions?

A

Fast and fatiguable muscle fibers

58
Q

Which muscles have a high proportion of slow twitch fibers?

A

Muscles involved in postural control

59
Q

What three factors are motor units classified by? - 3

A

Amount of tension, speed of contraction and fatiguability

60
Q

What are the 2 mechanisms by which the brain regulates the forces that a single muscle produces?

A

Recruitment and rate coding

61
Q

Describe the recruitment mechanism?

A

The more motor units that are recruited, the larger the size of the force

62
Q

What is the size principle?

A

The smaller motor units are recruited first, then as more force is required, more units are recruited

63
Q

What happens during recruitment when more forces is needed?

A

More muscle units are recruited

64
Q

Describe the rate coding principle?

A

The firing rate down the motor neurones to the motor unit changes as more force is needed to be produced

65
Q

What is ramp contraction?

A

When the force of contraction increases over time due to more recruitment

66
Q

How does recruitment regulate the stimulation of motor units?

A

By regulating the number of motor units that are recruited

67
Q

Which motor unit is the first to be derecruited?

A

The motor unit which was recruited last - therefore this motor unit will be the one largest in size

68
Q

What are neurotrophic factors?

A

Type of growth factor which prevent neuronal death and promote growth of neurones after injury

69
Q

What does the motor unit and fibre characteristics depend on?

A

The nerve which innervates them

70
Q

What happens to fast and slow twitch muscle fibers is they are cross innervated?

A

The fast becomes slow and slow becomes fast

71
Q

What are the three main types of muscle contraction?

A

Isometric
Concentric
Eccentric

72
Q

What is isometric contraction?

A

When the muscle unit produces forces but doesn’t change length

73
Q

What is a concentric muscle contraction?

A

When the muscle shortened in order to produce movement

74
Q

What is eccentric contraction?

A

When force is produced but the muscle fibers is getting longer

75
Q

What is an example of eccentric muscle contraction?

A

When a person is lifting up a dumbbell which is too heavy for them

76
Q

Which type of muscle contraction produces the most force?

A

Eccentric

77
Q

Which type of muscle contraction can damage and tear muscle fibers?

A

Eccentric

78
Q

Following training, what is the most common type of muscle fiber change?

A

Type IIB to IIA (FAST FATIGUABLE TO FATIGUE RESISTANT)

79
Q

What can cause a change from type 1 to type 2 muscle fibers?

A

Severe deconditioning or spinal cord injury

80
Q

What type of fibers are found in aged muscle and why?

A

Larger proportion of type 1 fibers, due to loss of type II fibres

81
Q

What provides evidence for the larger proportion of type 1 fibers in aged muscle?

A

Slower contraction time

82
Q

What shift in muscle fibers type is associated with microgravity!

A

Slow to fast

83
Q

Why is there a slow to fast shift in microgravity?

A

Less need for postural muscle innervation (slow)

84
Q

Where is the sarcolemma in relation to the endomysium?

A

The sarcolemma lies under the endomysium which surrounds the muscle fibre

85
Q

What is meant by a pennate arrangement of muscle fibres?

A

When muscle fibres are placed at angles to the tendon

86
Q

What is a unipennate arrangement of muscle fibres?

A

When the muscle is going in the same direction as the tendon

87
Q

What is a bipennate arrangement of muscle fibres?

A

When the muscle fibres are spread out in two direction from the tendon

88
Q

What is a multipennate arrangement of muscle fibres?

A

When there are many tendons and many fibres

89
Q

What is a parallel muscle fibre?

A

When the muscle fibre is straight across

90
Q

What is meant by a fusiform muscle fibre?

A

When the middle of the fibre is thicker and larger in size than the two outer edges

91
Q

What are the three shapes of muscle fibres?

A

parallel
fusiform
triangular

92
Q

what part of the nervous system does skeletal muscles act under?

A

somatic nervous system

93
Q

what is a triangular arrangement of muscle fibre?

A

converge at one end (typically at a tendon) and spread over a broad area at the other end in a fan-shape

94
Q

Label A

A

bone

95
Q

Label B

A

tendon

96
Q

label C

A

muscle

97
Q

label D

A

Fascicles

98
Q

label E

A

Myofibre

99
Q

label F

A

myofilaments

100
Q

label G

A

myofibril

101
Q

do myofibrils extend along the entire length of myofibres?

A

yes

102
Q

what two myofilaments overlap

A

actin and myosin

103
Q

what is the dark band also called

A

A-band

104
Q

what is the light bands also called

A

I band

105
Q

What happens to the H zone when the muscle contracts?

A

narrowed or disappears

106
Q

What theory is used to describe muscle contraction?

A

sliding filament theory

107
Q

When acetylcholine is broken down by acetylcholine esterase, what happens to the muscle fibre response?

A

ceases contraction

108
Q

during muscle contraction, when action potentials continue where is Ca2+ actively transported?

A

into the SR

108
Q

during muscle contraction, when action potentials continue where is Ca2+ actively transported?

A

into the SR

109
Q

during muscle contraction, when action potentials continue where is Ca2+ actively transported?

A

into the SR

110
Q

what neurones supply muscle contraction for voluntary neural control?

A

upper and lower motor neurones

111
Q

Which motor unit has the slowest conduction velocity?

A

Type I

112
Q

Which motor unit has the FASTEST conduction velocity?

A

Type IIB

113
Q

Which motor unit has the thinnest axons

A

Type I

114
Q

when does summation occur?

A

when units fire at frequency too fast to allow the muscle to relax between arriving action potentials

115
Q

what is the relationship between muscle force regulation and number of motor units?

A

muscle force is regulated by the no of motor units recruited

115
Q

what is the relationship between muscle force regulation and number of motor units?

A

muscle force is regulated by the no of motor units recruited

MUSCULOSKELETAL - BRS (13 decks)

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