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Musculoskeletal Physiopathology > Muscle Structure & Physiology > Flashcards

Muscle Structure & Physiology Flashcards

1
Q

Mature muscle cells have multiple nuclei within a single cytoplasm with many mitochondria.
What are those muscle cells called?

A

Syncytia

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2
Q

Is skeletal muscle smooth or striated?

A

Striated

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3
Q

striated muscle

Which muscle filaments are aligned and connected to the Z line by nebulin?

A

Actin

thin filaments

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4
Q

Which muscle filaments are connected to the Z line by titin?

A

Myosin

thick filaments

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5
Q

Actin is the thin filament in striated muscle.
What aligns and connects actin to the Z line?

A

Nebulin

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6
Q

Myosin is the thick filament in striated muscle.
What connects myosin to the Z line?

A

Titin

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7
Q

Extrafusal fibers are responsible for ___, and have ___ neurons.

A

responsible for movement (contraction) and have motor neurons

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8
Q

Intrafusal fibers are responsible for ___, and have ___ neurons.

A

responsible for sensing stretch/pull with stretch receptors (muscle spindle organs) and motor and sensory neurons

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9
Q

Which muscle fibers are responsible for movement/contraction?

A

Extrafusal fibers

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10
Q

Which muscle fibers are responsible for sensing stretch?

A

Intrafusal fibers

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11
Q

What is the epimysium?

A

Fascia containing the whole muscle

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12
Q

What is the perimysium?

A

Fascia containing a fascicle of muscle fibers

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13
Q

What is endomysium?

A

Fascia containing myofiber/muscle cell

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14
Q

Which muscle fascia is involved in compartment syndrome?

A

Epimysium

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15
Q

The epimysium’s density needs to allow for swelling, otherwise there is risk of ___.

A

rhabdomyoma

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16
Q

Myofilament (actin and myosin) is found within bundles called ___ which make up myofibers.

A

myofibrils

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17
Q

Myofibers are comprised of ___ and ___ filaments.

A

thick (myosin) and thin (actin) filaments

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18
Q

When at rest, the binding site on thin filaments is ___ by the troponin-tropomyosin complex.

A

blocked

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19
Q

When at rest, the binding site on thin filaments is blocked by the ___.

A

troponin-tropomyosin complex

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20
Q

How are binding sites on actin unblocked?

A

Calcium binds to troponin to unblock the site

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21
Q

What is the function of titin in the myofiber?

A

Provides elasticity and stabilizes myosin

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22
Q

What is the function of nebulin in the myofiber?

A

Helps align actin

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23
Q

Troponin holds ___ in place.

A

tropomyosin

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24
Q

How does the muscle fiber react when motor neurons fire and release Ach?

A
  • Acetylcholine release opens Na+ channels
  • Na+ travels through T tubules
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25
Q

What is a sarcomere?

A

Functional myofibril unit (z-band to z-band)

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26
Q

The T tubule of a muscle is a channel for ___.

A

Na+ (sodium)

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27
Q

What is the function of the terminal cisterna of sarcoplasmic reticulum in the muscle?

A

Ca+ (calcium) storage

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28
Q

When the muscle is not contracting, there is active pumping of ___ from the muscle to ___.

A

pumping of Ca+ from muscle to sarcoplasmic reticulum

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29
Q

What is the Z-band?

A

Electron dense band that anchors thin actin filaments (end of sarcomere)

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30
Q

What is the I-band?

A

Zone where actin filaments extend from Z-band to A-band

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31
Q

What is the A-band?

A

Structure composed of myosin filaments.
Actin filaments overlap myosin filaments to a variable extent, depending on the degree of muscle contraction.

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32
Q

Within the A-band, thin filaments form a ___ around each thick filament.

A

hexagonal array

each thin filament is equidistant from three thick filaments

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33
Q

What is the H zone?

A

Pale region in the midportion of the A band where actin filaments end (only myosin present)

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34
Q

What is the M line?

A

Zone of intermolecular bridging and thickening of myosin filaments at the midline of the A-band, which forms a thin, slightly darker electron-dense bank

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35
Q

What is the name of the electron dense band that anchors thin actin filaments?

36
Q

What is the name of the zone where there is no myosin overlap in the sarcomere?

37
Q

What is the name of the structure within the sarcomere composed of myosin filaments with varying actin filament overlap?

38
Q

What is the name of the pale region in the midportion of the A-band where actin filaments end and there is only myosin?

39
Q

What is the name of the zone of intermolecular bridging and thickening of myosin filaments at the midline of the A-band, forming a thin, slightly darker electron-dense bank?

40
Q

Where in the structure of muscles is there only actin?

41
Q

Where in the structure of muscle is there only myosin?

42
Q

When a muscle contracts, is it the I-band or the A-band that shortens?

A

I-band shortens, A-band is the same

43
Q

Sarcoplasmic reticulum and transverse tubular systems regulate ___.

A

calcium distribution and storage

44
Q

Sarcoplasmic reticulum surrounds each ___.

45
Q

How does the sarcoplasmic reticulum immediately respond to depolarization during muscle contraction?

A

SR passively releases Ca2+ ions into the cell

via DHP and RyR receptors

follows diffusion gradient from high to low concentration

46
Q

How does the sarcoplasmic reticulum immediately respond to cessation of neural activity during muscle relaxation?

A

SR actively transports Ca2+ back into the cisternae

47
Q

How many lower motor neurons innervate a muscle fiber?

A

A fiber is innervated by a single lower motor neuron ending

48
Q

How many muscle fibers are innervated by a lower motor neuron?

A

Can include hundreds of myofibers

motor unit

49
Q

What is a motor unit?

A

Multiple muscle fibers innervated by one motor neuron

50
Q

What characteristic of a lower motor neuron influences muscle fiber type?

A

Conduction speed

51
Q

All muscle fibers in a motor unit are the same fiber type.
What are the two fiber types?

A
  • Type I (slow twitch, red, dark meat)
  • Type II (fast twitch, white, white meat)
52
Q

In humans, all muscles consist of which fiber type(s)?

A

All muscles consist of a mix of Type I (slow) and Type II (fast)

53
Q

Type I/slow twitch muscle fibers function predominantly for ___ muscles.
Type II/fast twitch muscle fibers function predominantly for ___ muscles.

A

Type I: postural
Type II: major movers

54
Q

Fill in the following for type I fiber:

Contraction speed:
Color:
Motor neuron:
Metabolism:
Endurance:

A

Contraction speed: slow (postural)
Color: red
Motor neuron: alpha 2 (lower threshold, slower conduction velocity)
Metabolism: aerobic (higher myoglobin, mitochondria)
Endurance: high

55
Q

Fill in the following for type II fiber:

Contraction speed:
Color:
Motor neuron:
Metabolism:
Endurance:

A

Contraction speed: fast
Color: white
Motor neuron: alpha 1 (higher threshold, faster conduction velocity)
Metabolism: anaerobic (less myoglobin)
Endurance: low

56
Q

Why could type I fibers transform into type II fibers and vice versa in the Buller et al. study?

A

Innervation determines fiber type

57
Q

How do type I muscle fibers (slow twitch/postural) respond to endurance training?

A

They don’t hypertrophy, number of mitochondria increases

58
Q

How do type II muscle fibers (fast twitch) respond to strength training?

A

Hypertrophy

59
Q

Which structure is responsible for calcium ion regulation in sarcomeres?

A

Sarcoplasmic reticulum

60
Q

What is the most important factor in determining muscle fiber type?

A

Lower motor neuron conduction velocity

61
Q

What is the sliding filament theory?

A

During muscle contraction, actin filaments slide past myosin filaments in a series of cross-bridge cycles

62
Q

sliding filament theory

Each cross-bridge cycle consists of what four steps?

A
  1. Rest
  2. Excitation
  3. Contraction
  4. Relaxation
63
Q

Which phase of sliding filament theory involves Ca2+ binding to troponin, exposing binding sites for myosin?

A

Excitation

64
Q

What occurs during the contraction phase of sliding filament theory?

A

Bound myosin rotates its head, producing a “power stroke”

65
Q

sliding filament theory

What is required for the myosin head to release actin?

A

ATP binds to myosin head

66
Q

sliding filament theory

What is the result of ATP binding to the myosin head?

A
  • Ca2+ moves back into the sarcolemma
  • Troponin-tropomyosin complex moves to block interaction between actin and myosin
67
Q

In which phase of sliding filament theory does the myosin head bind to ATP and detach from actin?

A

Relaxation

68
Q

sliding filament theory

What occurs between the relaxation and rest phases?

A
  • Actin binding sites physically blocked
  • ATP is hydrolyzed, adding ADP to myosin head
69
Q

sliding filament theory

What is required for the myosin head to be ready to bind to actin (again)?

A

ADP must be bound to myosin head (rest phase)

70
Q

sliding filament theory

At which phase does myosin have the highest affinity for actin?

A

Rest phase

71
Q

sliding filament theory

What allows for calcium to be released before it binds to troponin-tropomyosin complex?

A

Action potential changes DHP and RyR receptors (allowing calcium release)

72
Q

During which phase of sliding filament theory will myosin heads bind with actin?

A

Contraction

73
Q

sliding filament theory

How long can the contraction phase continue?

A

As long as action potential is sustained

ATP binds to myosin head, detaches, then starts again

74
Q

sliding filament theory

After the relaxation phase, and the action potential ending, where will calcium go?

A

Sequestered in sarcoplasmic reticulum

by active transport

75
Q

recruitment

Graded contractions are built by ___.

A

repeated contraction

76
Q

length-tension curve

Tension produced during contraction is related to which feature of the muscle?

A

Sarcomere length

77
Q

length-tension curve

What is meant by “functional length” of a sarcomere?

A

Strength at mid range of motion

78
Q

length-tension curve

The greatest strength of a muscle occurs in the ___ of its arc of motion.

79
Q

length-tension curve

The greatest strength of a muscle occurs in the middle of its arc of motion.
What would happen if you were to work only in this area?

A

Muscle contracture and decreased range of motion/function

80
Q

force velocity curve

Velocity depends on which features of the muscle?

A

Number of sarcomeres in a cell and force applied

81
Q

force velocity curve

There is an ___ relationship between force applied and muscle contraction velocity.

82
Q

force velocity curve

As load on a muscle increases, the contractile system ___, and ___ occurs.

A

contractile system yields, and lengthening occurs

83
Q

force velocity curve

As load on a muscle increases, shortening velocity ___.

84
Q

force velocity curve

A muscle has developed maximum force and reached a velocity of 0.
What is the term for this point?

A

Isometric load/isometric contraction

point between safe exercise and overload

85
Q

Where in the force velocity curve does most muscle failure happen?

A

After isometric load, during eccentric loading/overload

muscle is now lengthening instead of shortening

86
Q

What is tetanus?

A

The fusion of individual contractions or twitches to form a continuous contraction

87
Q

What is the term for the fusion of individual contractions or twitches to form a continuous contraction?

Musculoskeletal Physiopathology (34 decks)

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