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1H06A > 06 - Skeletal Muscle Anatomy & Physiology > Flashcards

06 - Skeletal Muscle Anatomy & Physiology Flashcards

1
Q

What are the 3 types of muscles?

A

Smooth muscle
Cardiac muscle
Skeletal muscle

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2
Q

What jobs can muscle types perform?

A

Movement
Stabilization
Storing & moving substances
Generating heat

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3
Q

How do the types of muscles differ?

A

Morphology (how they look)
Body location
Funstion
Method of activation (contraction)

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4
Q

Put the different types of muscle cells in order from the smallest to the largest

A

Smooth muscle cell (smallest)
Cardiac muscle cell
Skeletal muscle cell (largest)

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5
Q

What are the key features of skeletal muscles?

A
  • Massive
  • Muscle fibre (one cell but very big)
  • Has a lot of nuclei in one cell
  • Voluntary
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6
Q

Where are skeletal muscle cells found?

A

MSK system

  • Musculoskeletal system
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7
Q

Where are cardiac muscle cells found?

A

Heart

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8
Q

Where are smooth muscle cells found?

A

Hollow organs

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9
Q

Morphology of skeletal muscle cells

A

Striated, multinucleated

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10
Q

Morphology of cardiac muscle cells

A

Striated, 1-2 nuclei, branched

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11
Q

Morphology of smooth muscle cells

A

No striations, single nucleus, spindle shaped

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12
Q

Gap junctions in skeletal muscle cells?

A

No

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13
Q

Gap junctions in cardiac muscle cells?

A

Yes

  • Intercalated disks
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14
Q

Gap junctions in smooth muscle cells?

A

Yes

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15
Q

Do cardiac muscle cells have autorhythmicity?

A

Yes

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15
Q

Do skeletal muscle cells have autorhythmicity?

A

No

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16
Q

Do smooth muscle cells have autorhythmicity?

A

Yes

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17
Q

What’s the speed of contraction of skeletal muscle cells (in comparison to the other 2 types of muscles)?

A

Fast

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18
Q

What’s the speed of contraction of cardiac muscle cells (in comparison to the other 2 types of muscles)?

A

Moderate

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19
Q

What’s the speed of contraction of smooth muscle cells (in comparison to the other 2 types of muscles)?

A

Slow

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20
Q

What is skeletal muscle regulated by?

A

Somatic nervous system

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21
Q

What is cardiac muscle regulated by?

A

Autonomic nervous system
Hormones
Pacemaker cells

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22
Q

What is smooth muscle regulated by?

A

ANS
Pacemaker cells
Hormones
Stretching

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23
Q

What nerve controls the contraction of skeletal muscles?

A

Peripheral nerves

  • Peripheral nerve axons originate from motor neuron cell bodies in the spinal cord (somatic)
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24
Q

Which muscle type contraction accounts for all voluntary body movements?

A

Skeletal muscle

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25
Q

Layers of connective tissue that wrap around skeletal muscle

A

Endomysium
Perimysium
- Fascicle
Epimysium

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26
Q

What does endomysium surround?

A

Endomysium: surrounds each individual muscle fibre/cell
- endo - in, within

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27
Q

What does perimysium surround?

A

Perimysium: surrounds a bundle of muscle fibres
- peri - around

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28
Q

What does epimysium surround?

A

Epimysium: surrounds the entire muscle
- epi - on, upon

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29
Q

What are fascicles?

A

Fascicle: a bundle of fibres wrapped in perimysium

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30
Q

What are skeletal muscle cells also known as?

A

Skeletal muscle fibre
Myocyte
- myo - muscle
- cyte - cell

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31
Q

Around 50% of the cells in muscle is ______ that makes up the matrix?

A

Fibroblast

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32
Q

What does the 3 layers of connective tissues that wraps around skeletal muscle become?

A

Tendon

  • All 3 layers contribute to the muscle sheath and become the tendon
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33
Q

What is the tendon continuous with?

A

The periosteum of bone
- pero - around
- osteum - bone

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34
Q

What is aponeurosis? Give an example

A

Broad flat tendon

eg. external obliques

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35
Q

What’s the order of the connective tissues (smallest to bigger) wrapping skeletal muscle?

A

Muscle fibre –> endomysium –> perimysium –> epimysium

  • These forms a tendon
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36
Q

What are muscle cells filled with?

A

Myofibrils

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37
Q

What are myofibrils?

A

Sarcomeres in series

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38
Q

What are sarcomeres?

A

The basic contractile unit of muscle

  • Responsible for muscle contraction
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39
Q

What is the smallest contractile unit in a skeletal muscle cell?

A

The sarcomere

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40
Q

What is the thick filament in a myocyte?

A

Myosin

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41
Q

What is the thin filament in a myocyte?

A

Actin

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42
Q

What has cross-bridges?

A

Myosin
- Thick filaments

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43
Q

What is from 1 z line to another z line?

A

Sacromere

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44
Q

What are the lines & bands & zones in a sacromere?

A

I band
A band
H zone
M line
Z line

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45
Q

What zone is shrinking during muscle contraction?

A

H zone
- Bring it closer to the center during muscle contraction

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46
Q

What are the lighter areas in a sarcomere?

A

I bands
- two 1/2 I bands

  • B/c there are very little proteins therefore light can pass through easily
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47
Q

What are the darker zones in a sarcomere?

A

A bands

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48
Q

What are the lighter regions in a sarcomere called?

A

Isotropic regions

49
Q

What are the darker regions in a sarcomere called?

A

Anisotropic regions
- an - without –> not letting light through

50
Q

Largest protein in the body

A

Titin filament

51
Q

What does the titin filament do (in a sarcomere)?

A

Attached to the M line
- Always ensure that the myosin filaments are always in the center of the sarcomere
- Keeping them there so they don’t go left or right

52
Q

Titin filament properties

A

Elastic
- Got coils
- Can be stretched and it will recoil back to its original position

53
Q

What is the M line in a sacromere?

A

A protein that bundles together the myosin filament

54
Q

What are the 2 ways to get bigger muscles?

A
  1. Increase the # of muscle cells
  2. Make the muscle cells bigger
55
Q

Can all muscles increase the number of cells?

A

No

Not possible with skeletal muscle (can not create new muscle cells)

Possible with smooth muscle - hyperplasia

56
Q

Why can you not make new skeletal muscle cells?

A

B/c who would control them?

  • Each muscle cell is controlled by a motor neuron that originates from your cerebral cortex
  • In order to do useful work, you can’t interrupt that connection therefore can not make new skeletal muscle cells
57
Q

How to make skeletal muscle bigger?

A

Make the muscle cell bigger

  • Do so by putting stress on the cells
    • Use those muscles –> it will grow
    • Don’t use those muscles –> you will lose it
58
Q

Why might you lose skeletal muscle cells if you don’t use them?

A

B/c skeletal muscle cells take a lot of energy to keep it going (even at rest)
- Consumes a lot of ATP and amino acids to make the proteins (the contractile filaments inside that muscle)

59
Q

How do muscles enlarge with use?

A

By adding sarcomeres

  • Exercise stimulates production of actin and myosin filaments
  • Increased number of myofilaments expands the fiber causing muscle enlargement and definition
60
Q

What is the process called when your muscles enlarge with use?

A

Hypertrophy
- hyper - increase
- trophy - food

A process where we get a lot of nutrients to the muscle and it’s getting bigger

61
Q

What causes fibre atrophy?

A
  • Decrease sarcomere
  • Immobilization (eg. cast)
  • Weightlessness (eg. space flight)
  • Denervation (eg. spinal cord injury)
62
Q

What causes fibre hypertrophy?

A
  • Increase sarcomere
  • Training (eg. resistance training)
63
Q

Atrophy

A

Losing muscle (not actually losing the muscle fibre but it’s shrinking)

Atrophy
- a - without
- trophy - food (nutrition)

64
Q

What is the term for growing muscle?

A

Hypertrophy

65
Q

What is the term for losing (shrinking of the) muscle?

A

Atrophy

66
Q

What is the sliding filament theory?

A

Filaments slide past one another = shortening

  • Thin actin filaments slide over the thick myosin filaments
  • Requires an increase in Ca2+
  • Repeated binding cycles between actin and myosin
67
Q

How do filaments shorten?

A

The Z lines gets closer (the sarcomere shortens)

68
Q

In a contraction what is shortening? What has no change?

A

Shortening: sarcomere, H & I bands

No change: A band

69
Q

Why does I band APPEAR to shorten?

A

The proteins in there (actin and myosin) are not actually shortening
- There’s just an increase in their overlap

70
Q

Does the sliding filament theory happen in 2D or 3D?

A

3D

71
Q

What is the interaction between myosin and actin in 3D?

A

1 thick filament pulls on 6 thin filaments

1 thin filament can connect to 3 thick filament

  • Myosin has “little arms” (cross-bridges) that can reach out in many different directions
72
Q

How does the ATPase activity of myotin work?

A

Myosin has ATPase (an enzyme that breaks down ATP) activity

  • The enzyme transfers the energy from ATP into the myosin head to change its configuration and shape
  • Thus the myosin head can pull actin toward the center of the sarcomere
    • Transfering energy to movement
73
Q

Which direction does the myosin head point to?

A

Towards the center (both sides)

  • B/c both sides are pulling actin in towards the center of the sarcomere
74
Q

Where is the binding cite in thick filament?

A

Myosin heads

75
Q

What is the thick filament made of?

A

End to end myosin molecules

76
Q

What does a myosin consist of?

A

Myosin head
- Actin binding sites
- Myosin ATPase
Tail
Hinge

77
Q

What is the regulator of muscle contraction? Think in terms of the filaments

A

Thin filament
- Determines when the muscle contracts
- By Ca2+

78
Q

What does a thin filament consist of?

A

2 coiled chains of actin molecules

Tropomyosin

Troponin

79
Q

What does the tropomyosin molecule do?

A

Tropomyosin molecules run along actin, blocking cross bridge binding site

80
Q

What does troponin molecule do?

A

Troponin holds tropomyosin in place

81
Q

What binds to troponin?

A

Ca2+

82
Q

What happens when Ca2+ binds to troponin?

A

Ca2+ binds troponin, changes its confirmation which pulls tropomyosin away from the cross bridge binding site
- This allows for actin-myosin interaction to occur

When Ca2+ is removed, tropomyosin moves back to block cross bridge binding site (no actin-myosin interaction).

83
Q

Can sarcomere lengthen?

A

No, they can only shorten (can not lengthen)

  • can only pull not push
84
Q

Steps in the cross-bridge cycling

A
  1. Energizing myosin
    - ATP already bound to myosin
    - ATP breaks into ADP+Pi (energized myosin)
  2. Actin-myosin binding
    - Actin binds to myosin when Ca2+ is available
  3. Cross-bridge movement: POWER STROKE
    - Energy stored in myosin used
    - Cross-bridge moved
    - Sarcomere shortens
    • Thick pull thin filament
      • ADP & Pi released
  4. Breaking the cross-bridge
    - ATP binds to myosin
    - Breaks the actin-myosin bond

Cycle restarts

85
Q

What is the regulator of cross bridge cycling?

A

Ca2+

86
Q

What breaks the actin-myosin bond in the cross-bridge cycling?

A

ATP
- ATP present –> breaks the bond & release the thick from thin filament

  • If you’re alive this will happen
  • If you’re dead –> no ATP –> no release
87
Q

What is excitation-contraction coupling?

A

Electrical signal (excitation) from brain along motor neuron tells a muscle to move (contraction)

  • Anything that increases the amount of Ca2+ will cause a contraction
88
Q

What determine if muscle contracts or not?

A

Motor neuron

89
Q

Excitation

A

Action potential (AP) travels to the axon terminal (neuromuscular junction)

90
Q

Where are APs propagated down to in muscle fibres?

A

T-tubules

  • Muscle fibres are large, so to get deep into them, the AP is propagated down the T-tubules
91
Q

Steps of excitation contraction coupling

A

Neurotransmission
Action potential
T-tubules
Sarcoplasmic reticulum (terminal cisternae)
Release of Ca2+
Contraction

92
Q

What is the specialized area where Ca2+ are stored?

A

Terminal cisternae

93
Q

What are T-tubules?

A

T-tubules are invaginations of the membrane (allow APs to go deep inside the cell to deliver the message)

94
Q

What is a triad?

A

1 T-tubule & 2 terminal cisternae

95
Q

What proteins link the T-tubules and the sarcoplasmic reticulum?

A

DHP receptor
Ryanodine receptor

96
Q

When does relaxation occurs?

A

When Ca2+ is re-sequestered

97
Q

Steps in the release of Ca2+ to muscle contraction

A
  1. Muscle AP propagated down the Transverse tubule (T-tubule)
  2. Ca2+ released from terminal cisternae
    - The ryanodine receptor is like a plug to the terminal cisternae (where Ca2+ are stored)
    - AP triggers the movement of the DHP receptor which moves the ryanodine receptor
    - The “plug” is moved, thus Ca2+ are released
  3. Ca2+ binding to troponin removes blocking action of tropomyosin
  4. Cross bridge moves
  5. Ca2+ taken up to the terminal cisternae
  6. Ca2+ removal from tropin restores tropomyosin blocking action
98
Q

What is happening in the latent period in excitation-contraction coupling?

A

Sending AP to get Ca2+

  • Very short
99
Q

Factors regulating force production

A
  1. Muscle length
  2. Action potential frequency
  3. Number of fibres per motor unit and the cross-sectional area of those muscle fibres (how many fibres will active)
100
Q

What is a motor unit?

A

One motor neuron and all the muscle fibres it innervates

101
Q

How does muscle length regulate force production?

A

Too stretched or too compressed decreases force production

102
Q

How does AP frequency regulate force production?

A

Summation of stimulation
- Of Ca2+

  • Single twitch
  • Wave summation
  • Unfused tetanus
  • Fused tetanus
103
Q

What is tetanic force?

A

Multiple APs in a row
More Ca2+
Every cross bridge can be activated
Stronger contraction

104
Q

How does # of fibres per motor unit regulate force production?

A

The size of the motor unit determines the amount of force produced

  • 1 motor neuron branch to several muscle fibres
  • When it send signal, all muscle fibres connected will contract
105
Q

What are different types of motor units based on?

A

Muscle fibre types

  • Muscle fibre differ in size and ease of activation
106
Q

What are skeletal muscle fibre types based on?

A

Speed of contraction and/or metabolic profile

107
Q

What are the skeletal muscle fibre types?

A
  1. Slow and fast fibres
  2. Oxidative and glycolytic fibres
108
Q

Skeletal muscle fibre types:

Speed of contraction

A

Slow and fast fibres
- Dependent on the rate of myosin ATPase action
- Slow fibre types contract more slowly but are more fatigue resistant
- Fast fibres generate more power but fatigue more rapidly

109
Q

Skeletal muscle fibre types:

Metabolic profile

A

Oxidative and glycolytic fibres
- Oxidative fibres
- Glycolytic fibres

110
Q

What does oxidative fibres use?

A

Primarily use O2 for ATP production (aerobic)

111
Q

What does glycolytic fibres use?

A

High capacity for ATP production without O2 (anaerobic)

112
Q

What are the 3 skeletal muscle fibre types?

A

Slow oxidative
Fast oxidative glycolytic
Fast glycolytic

113
Q

Order the skeletal muscle fibre types in order from the most fatigue resistant to the most easily fatigued

A

Slow oxidative (fatigue resistant)
Fast oxidative glycolytic (less fatigue resistant)
Fast glycolytic (quickly fatigued)

114
Q

Order the skeletal muscle fibre types in order of the smallest diameter to the larger diameter

A

Slow oxidative (small diameter)

115
Q

Order the skeletal muscle fibre types in order of blood supply

A

Slow oxidative
- Rich blood supply

Fast oxidative glycolytic
- Rich blood supply

Fast glycolytic
- Few capillaries

116
Q

What respiration does each skeletal muscle fibre type use?

A

Slow oxidative
- Aerobic respiration

Fast oxidative glycolytic
- Aerobic & anaerobic respiration

Fast glycolytic
- Anaerobic respiration

117
Q

What are each skeletal muscle fibre types most used for?

A

Slow oxidative
- Posture & endurance

Fast oxidative glycolytic
- Walking & sprinting

Fast glycolytic
- Power movements

118
Q

Motor unit recruitment order

A
  1. Slow oxidative
  2. Fast oxidative glycolytic
  3. Fast glycolytic
  • Motor units are recruited in this order during EVERY task
  • Everytime start with the smallest one (slow-oxidative) then if need more then increase
119
Q

What does the motor unit recruitment depend on?

A

SIZE principle - motor units are recruited (activated) according to size (first to be recruited are Slow Oxidative, then Fast Oxidative Glycolytic then Fast Glycolytic)

  • In this way, fatigue resistant fibers are always first
  • The number of motor units recruited depends on the force required to perform the task

1H06A (8 decks)

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