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PSIO 258: Elementary Physiology I > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

1
Q

Describe the structure of a skeletal muscle.

A
  • Connected to two or more bones by tendons
  • The tissue surrounding muscle (epimysium) and tendon connective tissue are continuous
  • Perimysium extends into the muscle body, dividing muscle into bundles (fascicles) of muscle cells
  • Fascicles contain 100s-1000s of muscle cells—muscle fibers, which extend the length of the muscle
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2
Q

What are the components of a muscle fibre?

A
  • Muscle fibers surrounded by connective tissue (endomysium)
  • sarcolemma (plasma membrane)
  • multinucleated
  • sarcoplasm (cytoplasm)
  • Contains many myofibrils
  • Sarcoplasmic reticulum (Smooth ER)
  • Contains many mitochondria—high energy
  • Transverse tubules (T Tubules)
  • Lateral sacs (terminal cisternae) (Ca2+)
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3
Q

What is a triad?

A

T tubule + 2 lateral sacs

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4
Q

What gives skeletal and cardiac muscle striated appearance?

A
  • myofibrils

- due to thick and thin filaments that run parallel to the long axis

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5
Q

What are the 2 types of filaments?

A
  • actin

- myosin

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6
Q

Filaments form ______.

A

sarcomeres

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7
Q

Components of a sarcomere include:

A
  • A band
  • H zone
  • M line
  • I band
  • Z line
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8
Q

What is the A band?

A
  • dark band

- thick filaments

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9
Q

What is the H zone?

A
  • thick filaments

- no overlap

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10
Q

What is the M line?

A

links thick filaments

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11
Q

What is the I band?

A
  • light band
  • thin filament
  • no overlapping
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12
Q

What is the Z line?

A

links thin filaments

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13
Q

What is the sarcomere?

A
  • functional unit

- Z line to Z line

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14
Q

Name the components of a thin filament.

A
  • actin
  • tropomyosin
  • troponin
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15
Q

Describe actin.

A
  • contractile protein

- each G actin has a binding site for myosin

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16
Q

Describe tropomyosin.

A
  • regulatory protein

- overlaps binding sites on actin for myosin

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17
Q

Describe troponin.

A
  • Regulatory protein
  • Complex of three proteins
  • Ca2+ binding to troponin regulates skeletal muscle contraction
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18
Q

The complex of three proteins of troponin attach to what?

A
  • Attaches to actin
  • Attaches to tropomyosin
  • Binds Ca2+ reversibly
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19
Q

In the thick myofilament, myosin tail is towards …

A

the M line

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20
Q

In the thick myofilament, myosin head is towards …

A

the I band

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21
Q

In the thick myofilament, myosin head has 2 binding sites:

A
  • actin binding site

- nucleotide binding site for ATP and ATPase

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22
Q

Describe titin.

A
  • Is a very elastic protein
  • Supports protein in muscle
  • Anchors thick filaments between the M line and the Z line
  • Provides structural support and elasticity
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23
Q

What is muscle contraction?

A

shortening of muscle

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24
Q

Describe the sliding filament model.

A
  • Thick and thin filaments overlap
  • Neither thick nor thin filaments shorten
  • Filaments slide past each other
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25
Q

What happens within a sarcomere during contraction?

A
  • A band stays the same length
  • I band shortens
  • H zone shortens
  • Sarcomere shortens
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26
Q

What is the cross bridge cycle?

A

Cyclical formation of links between actin and myosin, resulting in the sliding of thin filaments toward the M line of a sarcomere

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27
Q

_____ _____ undergoes conformation changes, swiveling back and forth.

A

Myosin head

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28
Q

What are the 2 energy forms of myosin during the cross bridge cycle?

A
  • high-energy form

- low-energy form

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29
Q

Describe high-energy form.

A

ADP and Pi bound to myosin

High affinity for actin

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30
Q

Describe low-energy form.

A

ATP bound to myosin

Low affinity for actin

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31
Q

The cross bridge cycle relies on…

A

hydrolysis of ATP

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32
Q

In a analogy of the cross bridge cycle to rowing a boat, the oar paddle is…

A

crossbridge

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33
Q

In a analogy of the cross bridge cycle to rowing a boat, oar contact with water is…

A

linking of thick filament to thin filament

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34
Q

In a analogy of the cross bridge cycle to rowing a boat, the power stroke (movement of oar propelling boat) is …

A

myosin head moves, propelling thin filament toward center of muscle

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35
Q

In a analogy of the cross bridge cycle to rowing a boat, the oar breaking contact with water is…

A

thick and thin filaments detach

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36
Q

In a analogy of the cross bridge cycle to rowing a boat, oar moved to new position is…

A

Myosin head returns to the initial position, cycle starts again

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37
Q

What is excitation-contraction coupling?

A

Sequence of events whereby an action potential in the sarcolemma causes contraction

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38
Q

Excitation-contraction coupling is dependent on…

A

neural input from the motor neuron

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39
Q

Excitation-contraction coupling requires…

A

Ca2+ release from the sarcoplasmic reticulum

40
Q

Describe the role of the neuromuscular junction in excitation-contraction coupling.

A
  • Each motor neuron innervates several muscle cells
  • Each muscle fiber receives input from a single motor neuron
  • Similar to ordinary synapse
  • Acetylcholine released
  • Motor end plate
  • End-plate potential
  • Motor neuron AP always creates a muscle cell AP
41
Q

Describe the motor end plate of the neuromuscular junction in excitation-contraction coupling.

A
  • High density of acetylcholine receptors

- Highly folded

42
Q

What happens in if there is no Ca2+?

A
  • troponin holds tropomyosin over myosin binding sites on actin
  • No crossbridges form between actin and myosin
  • Muscle relaxed
43
Q

What happens if there is Ca2+ present?

A
  • binds to troponin, causing movement of troponin, causing movement of tropomyosin, exposing binding sites for myosin on actin
  • Crossbridges form between actin and myosin
  • Cycle occurs; muscle contracts
44
Q

What are the steps of excitation-contraction coupling?

A
  1. Action potential in sarcolemma
  2. Action potential down T tubules
  3. DHP receptors of T tubules open Ca2+ channels (ryanodine receptors) in lateral sacs of SR
  4. Ca2+ increases in cytosol
  5. Ca2+ binds to troponin, shifting tropomyosin
  6. Crossbridge cycling occurs
45
Q

How does the termination of contraction occur?

A

Ca2+ must leave troponin, allowing tropomyosin to cover myosin binding sites on actin

46
Q

How is Ca2+ removed from cytosol?

A
  • Ca2+-ATPase in the sarcoplasmic reticulum

- Transports Ca2+ from cytosol into the sarcoplasmic reticulum

47
Q

ATP is required by _____ to generate work.

A

Muscle

48
Q

Production of ATP is dependent on:

A
  • intensity

- duration

49
Q

_____ drives cross bridge cycling.

A

ATP

50
Q

Name 3 sources of ATP.

A
  • Phosphorylation of ADP by creatine phosphate
  • Oxidative phosphorylation of ADP in mitochondria
  • Anaerobic glycolysis
51
Q

What energy source is used most in the first second of light to moderate exercise?

A

creatine phosphate

52
Q

What energy source is used most in seconds 1-2 of light to moderate exercise?

A

anaerobic glycolysis

53
Q

What energy source is used most from 2 seconds on of light to moderate exercise?

A

oxidative phosphorylation

54
Q

What is the role of the creatinine/creatine phosphate system?

A
  • At rest, small store of ATP

- Must quickly increase ATP synthesis

55
Q

Creatine phosphate + ADP =

A

Creatine + ATP

56
Q

How does the law of mass action play a role in the creatinine/creatine phosphate system?

A
  • Use of ATP drives the reaction to the right
  • Can supply up to 5 times the quantity of resting ATP
  • “On tap”
57
Q

How does muscle cell metabolism change with exercise intensity (light to moderate)?

A
  • Oxidative phosphorylation
  • Initially, glycogen stores supply glucose
  • Up to 30 min, glucose and fatty acids in blood
  • O2 supply must be kept adequate
  • Transient increase in GLUT4
58
Q

Why must O2 supplies be kept adequate during exercise?

A

Increases ventilation
Increases heart rate and contraction
Dilates vessels to muscle

59
Q

Describe what happens with exercise of heavy intensity.

A
  • Anaerobic glycolysis
  • Lactate
  • Only 2 ATP molecules per glucose molecule
60
Q

What energy source is used most in the first second of intense exercise?

A

creatine phosphate

61
Q

What energy source is used most in the first 3 seconds of intense exercise?

A

anaerobic glycolysis

62
Q

What energy source picks up in seconds 3-4 on of intense exercise?

A

oxidative phosphorylation

63
Q

How is skeletal muscle classified?

A
  • velocity of contraction

- energy source

64
Q

Describe how skeletal muscles are classified based on velocity of contraction.

A

fast vs slow

65
Q

Describe how skeletal muscles are classified based on energy source.

A

oxidative vs glycolytic

66
Q

Skeletal muscle speed of contraction is dependent on..

A
  • Dependent on myosin ATPase activity
  • ATP hydrolysis
  • Higher rate = faster crossbridge cycling
67
Q

ATP hydrolysis =

A

rate-limiting step of cycle

68
Q

Describe fast skeletal muscle fibres.

A
  • Myosin with fast ATPase activity

- fast contraction speed

69
Q

Describe slow skeletal muscle fibres.

A
  • Myosin with slow ATPase activity

- long contraction duration

70
Q

What are the properties of slow oxidative fibres (type I)?

A
  • Low myosin ATPase
  • High oxidative capacity—aerobic
  • Small diameter
  • Fatigue slowly
71
Q

What does high oxidative capacity mean?

A
  • Mitochondria
  • Rich blood supply
  • Myoglobin (red)
72
Q

What does small diameter mean?

A
  • Little tension

- Small diffusion barrier

73
Q

What are the properties of fast oxidative fibres?

A
  • Intermediate myosin ATPase activity
  • High oxidative capacity—aerobic
  • Myoglobin
  • Slow to fatigue, but more rapid than slow oxidative fibers
  • Intermediate diameter
74
Q

What are the properties of fast glycolytic fibres?

A
  • High myosin ATPase activity
  • High glycolytic capacity
  • No myoglobin (so they appear white)
  • Large diameter
  • Fatigue rapidly
75
Q

What does high glycolytic capacity mean?

A
  • High glycogen stores

- Many glycolytic enzymes

76
Q

What does large diameter mean?

A

greater tension

77
Q

The response of the three muscle fibre types to exercise depends on ______.

A

function

78
Q

Postural muscles have higher counts of what type of muscle fibre?

A

type I

79
Q

1 muscular unit has …

A

the same fibre type

80
Q

What is the recruitment order for muscle fibres?

A
  1. Type I
  2. Type IIa
  3. Type IIx
81
Q

What are the 2 types of fibres in muscle spindles?

A
  • intrafusal fibres

- extrafusal fibres

82
Q

Describe intrafusal fibres.

A
  • Contractile cells of the muscle spindle
  • Adjust the sensitivity of the muscle to stretch
  • Innervated by gamma motor units
83
Q

Describe extrafusal fibres.

A
  • Contractile cells of the muscle
  • Responsible for skeletal muscle contraction
  • Innervated by alpha motor neurons
84
Q

Muscle spindles detect…

A

changes in muscle length

85
Q

What are the 2 types of sensory endings in muscle spindles?

A
  • annulospiral endings

- flower-spray endings

86
Q

Annulospiral endings are for…

A

type Ia afferent fibres

87
Q

Flower-spray endings are for…

A

type II afferent fibres

88
Q

Sensitivity of muscle spindles can be adjusted by…

A

action of intrafusal fibres

89
Q

What are Golgi tendon organs (GTOs)?

A
  • Sensory capsules within tendons

- Tendon stretch activates the GTO

90
Q

Describe how tendon stretch activates the GTO.

A
  • Reflex inhibition of muscle via type Ib afferent neurons

- Protection against overactivity of muscle

91
Q

Describe skeletal muscle fibre resistance to fatigue for high-intensity exercises.

A
  • Glycolytic fibers
  • Buildup of lactate
  • Strong contractions cause compression of blood vessels
  • Neuromuscular fatigue → depletion of acetylcholine
  • Altered enzyme activity
  • Recovery within minutes to hours
92
Q

Describe skeletal muscle fibre resistance to fatigue for low-intensity exercises.

A
  • Depletion of energy reserves (glycogen)

- Long time to recover

93
Q

Name the long term responses of muscles to aerobic exercise.

A
  • increased oxidative capacity
  • some fast glycolytic fibres can be converted to fast oxidative fibres
  • increase in size and number of mitochondria
  • decrease in fiber diameter
  • increase in number of capillaries surrounding muscle fibres
94
Q

Name the long term responses of muscles to high-intensity exercise.

A
  • decreased oxidative capacity
  • some fast oxidative fibres can be converted to fast glycolytic fibres
  • decrease in size and number of mitochondria
  • increase in fibre diameter
  • reduced resistance to fatigue
95
Q

What is disuse atrophy?

A
  • Decrease in size (lose myofibrils)

- Muscular dystrophy, sedentary-ism

96
Q

What is sarcopenia?

A

loss of muscle tissue as a natural part of the aging process

PSIO 258: Elementary Physiology I (14 decks)

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