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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 they called?

A

Syncytia

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2
Q

Is skeletal muscle smooth or striated?

A

Striated

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3
Q

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

A

Actin

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4
Q

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

A

Myosin

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5
Q

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

A

Nebulin

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6
Q

Myosin is a thick filament in striated muscle
What connects it to the Z line?

A

Titin

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7
Q

Muscles consist of fibers:
Extrafusal fibers are responsible for ___ and have ___ neurons

A

responsible for movement (contraction) and have motor neurons

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8
Q

Muscles consist of fibers:
Intrafusal fibers have ___, and ___ neurons

A

have 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

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

A

myofibril

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16
Q

Myofibers are comprised of ___ and ___ filaments

A

thick (myosin) and thin (actin) filaments

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17
Q

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

A

blocked

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18
Q

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

A

troponin-tropomyosin complex

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19
Q

How are binding sites on actin unblocked?

A

Calcium binds to troponin to unblock the site

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20
Q

What is the function of titin in the myofiber?

A

Provides elasticity and stabilizes myosin

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21
Q

What is the function of nebulin in the myofiber?

A

Helps align actin

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22
Q

Troponin holds ___ in place

A

tropomyosin

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23
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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24
Q

What is a sarcomere?

A

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

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25
Q

The T tubule of a muscle is a channel for ___

A

Na+ (sodium)

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26
Q

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

A

Ca+ (calcium) storage

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27
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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28
Q

What is the Z-band?

A

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

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29
Q

What is the I-band?

A

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

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30
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.
Thin filaments form a hexagonal array around each thick filament.

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31
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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32
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

33
Q

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

34
Q

What is the name of the zone where actin filaments extend from Z-band to A-band?

35
Q

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

36
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?

37
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?

38
Q

Where in the structure of muscles is there only actin?

39
Q

Where in the structure of muscle is there only myosin?

40
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

41
Q

At the outer edge of the A-band, the thin filaments form a ___ around each thick filament.

A

hexagonal array
(each thin filament is equidistant from three thick filaments)

42
Q

Sarcoplasmic reticulum and transverse tubular systems regulate ___

A

calcium distribution and storage

43
Q

Sarcoplasmic reticulum surrounds each ___

44
Q

What happens with depolarization of the sarcoplasmic reticulum?

A

SR passively releases Ca2+ ions (via DHP and RyR receptors) into the cell

45
Q

What happens with cessation of neural activity of the sarcoplasmic reticulum?

A

SR actively transports Ca2+ back into the cisternae

46
Q

How many lower motor neurons innervate a muscle fiber?

A

A fiber is innervated by a single lower motor neuron ending

47
Q

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

A

Can include hundreds of myofibers (a motor unit)

48
Q

What is a motor unit?

A

Multiple muscle fibers innervated by one motor neuron

49
Q

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

A

Conduction speed

50
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)
51
Q

In humans, all muscles consist of which fiber types?

A

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

52
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

53
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

54
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

55
Q

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

A

They don’t hypertrophy, number of mitochondria increases

56
Q

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

A

Hypertrophy

57
Q

Which structure is responsible for calcium ion regulation in sarcomeres?

A

Sarcoplasmic reticulum

58
Q

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

A

Lower motor neuron conduction velocity

59
Q

What is the sliding filament theory?

A

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

60
Q

sliding filament theory

Each cross-bridge cycle consists of the following steps:

A
  1. Rest
  2. Excitation
  3. Contraction
  4. Relaxation
61
Q

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

A

Excitation

62
Q

What occurs during the contraction phase of sliding filament theory?

A

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

63
Q

sliding filament theory

What is required for the myosin head to release actin?

A

ATP binds to myosin head

64
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
65
Q

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

A

Relaxation phase

66
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
67
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)

68
Q

sliding filament theory

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

A

Rest phase

69
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)

70
Q

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

A

Contraction phase

71
Q

sliding filament theory

How long can the contraction phase continue?

A

As long as action potential is sustained, ATP bind to myosin head and detaches then starts again

72
Q

sliding filament theory

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

A

Sequestered in sarcoplasmic reticulum

73
Q

length-tension curve

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

A

Sarcomere length

74
Q

force velocity curve

Velocity depends on which feature of the muscle?

A

Number of sarcomeres in a cell and force applied

75
Q

force velocity curve

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

76
Q

force velocity curve

As load increases, the contractile system ___

A

yields, and lengthening occurs

77
Q

What is tetanus?

A

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

78
Q

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

Musculoskeletal Physiopathology (32 decks)

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