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EDKP-206 > Lecture 5 - Skeletal Muscle > Flashcards

Lecture 5 - Skeletal Muscle Flashcards

1
Q

What kind of muscle is the most abundant in the body?

A

skeletal muscle

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2
Q

How many muscle pairs are there?

A

<80

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3
Q

What are the 3 kinds of muscle?

A

cardiac, smooth and skeletal

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4
Q

Why striations in muscle happen?

A

due to repeating sequences of sarcomeres

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5
Q

What are the 3 primary functions of skeletal muscle?

A
  • Provide strength & protection to the skeleton by distributing
    loads & absorbing shock
  • Enable bones to move at the joints
  • Maintain body posture against force
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6
Q

What are the 3 basic performance parameters that describe skeletal
muscle function?

A
  • Movement production
  • Force production
  • Endurance
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7
Q

What kind of work does skeletal muscle do?

A

dynamic and static

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8
Q

What are the 2 functional units responsible for producing motion at a joint?

A

tendon and muscle belly

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9
Q

What comprises the muscle belly (2)?

A

muscle fibers and connective tissue

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10
Q

What are the levels of a whole muscle?

A
  1. muscle fascicle
  2. muscle fiber
  3. Myofibril
  4. Sarcomere
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11
Q

What is the basic function unit of muscle?

A

the sarcomere

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12
Q

What is related to a muscle’s contractile force?

A

the amount of actin and myosin

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13
Q

How does contraction occur?

A

from the formation of cross-bridges between the myosin and actin myofilaments

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14
Q

What are the 3 non-contractile elements?

A
  • Intracellular protein
  • Extracellular matrix (ECM)
  • Tendons
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15
Q

What is titin?

A

giant protein found in sarcomeres

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16
Q

What is the function of titin?

A

maintains architectural integrity

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17
Q

What is desmin?

A

protein that contributes to stability of myofilaments

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18
Q

What is costamere?

A

protein complexes found in the cytoplasm

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19
Q

What is the function of costameres?

A

link superficial sarcomeres to the cell wall and ECM and allow the force of contraction of one myofibril to be distributed laterally to adjacent myofibrils, the cell wall, and to the ECM

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20
Q

What are the 3 components of intracellular protein?

A

titin, desmin and costameres

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21
Q

What are the 3 systems of ECM?

A

endomysium, perimysium, epimysium

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22
Q

What does the endomysium surround?

A

each cell

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23
Q

What does the perimysium surround?

A

groups of cells (fascicles)

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24
Q

What does the epimysium surround?

A

the whole muscle

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25
Q

When does the ECM proliferate and accumulate?

A

in diseased, injured and spastic muscle

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26
Q

What is adipose tissue in the ECM associated with?

A

worse functional performance

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27
Q

How is the ECM compared to individual muscle fibers?

A

stiffer

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28
Q

What do tendons bind to?

A

muscle belly to bone

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29
Q

How does size of tendons vary? (3)

A
  • Muscle architecture
  • Size of the muscle
  • Size of the individual
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30
Q

What are the 2 factors that influence a muscle’s ability to produce motion?

A
  1. The length and orientation (architecture) of the fibers composing the muscle
  2. The length of the muscle’s moment arm
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31
Q

How is passive ROM achieved?

A

when an outside force causes joint movement

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32
Q

What does passive ROM depend on?

A

shape of articular surfaces and surrounding soft tissues

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33
Q

How is active ROM achieved?

A

when muscles contract resulting in joint movement

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34
Q

What does active ROM depend on?

A

a muscle’s ability to pull the limb through a joints available ROM

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35
Q

How much can each sarcomere shorten?

A

approximately the length of its myosin
molecules

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36
Q

How much can muscle fibers shorten?

A

approximately 50-60% of their length

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37
Q

When is contraction velocity greater?

A

in longer muscle fibers

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38
Q

Which kind of myofibrils can shorten more?

A

the ones with more sarcomeres

39
Q

Fibre arrangement can effect a muscle’s ability to:(2)

A
  • produce movement
  • generate force
40
Q

What are the 2 kinds of muscle architecture?

A

parallel and pennate

41
Q

What are the 2 kinds of parallel muscles?

A

fusiform and strap

42
Q

What are the 3 kinds of pennate muscles?

A

unipennate, bipennate and multipennate

43
Q

What are parallel fiber muscle parallel to?

A

the length of the whole muscle

44
Q

Fusiform muscles have ___ at both ends, so the muscle fibers taper to insert into the ___.

A

tendons

45
Q

Strap muscles have less prominent ___, and there, their fibers taper less.

A

tendons

46
Q

What are parallel fiber muscles composed of?

A

relatively long fibers, although these fibers still are shorter than the whole muscle

47
Q

Which muscle only contains fibers that are about 90% of its length?

A

the sartorius

48
Q

Where do the tendons extend in pennate fiber types?

A

most of the length of the whole muscle

49
Q

How do fibers run in pinnate fiber types?

A

obliquely

50
Q

What do the subcategories of pennate muscles depend on?

A

the number of tendons penetrating the muscle

51
Q

What does the muscle moment arm depend on (2)?

A
  • the location of the muscle attachment on
    the bone
  • angle of application
52
Q

What is the angle of application?

A

the angle formed between the line of pull of the muscle and the bone to which it attaches

53
Q

___ moment arm = movement through theta requires less shortening.

A

shorter

54
Q

___ movement arm = movement through theta requires more shortening.

A

longer

55
Q

What is the formula for strength?

A

M = r x F

56
Q

What are the primary factors influencing the muscle’s strength or ability to produce a moment? (3)

A
  • Muscle size
  • Muscle moment arm
  • Stretch of the muscle
57
Q

What is the most important determinant of tensile force generated by a muscle contraction?

A

muscle size

58
Q

What relationship does muscle architecture impact?

A

the relationship between muscle size and force of contraction

59
Q

What is the anatomical cross-sectional area?

A

the cross-sectional area (CSA) at the muscle’s widest point and perpendicular to the length of the whole muscle

60
Q

What is the physiological cross-sectional area?

A

the area of a slice or slices of muscle that pass through all the fibers of a muscle

61
Q

What is the overall tensile force of a muscle equal to?

A

the vector sum of the force of contraction of all the fibers (Ff)

62
Q

What is the angle of pennation?

A

the angle at which the fibers insert into the tendon

63
Q

What happens to PCSA when angle of pennation increases?

A

it increases

64
Q

Which kind of muscle have a larger PCSA?

A

pennate muscles

65
Q

What does PCSA respond to?

A

changes in activity level over time

66
Q

What is optimal length of a muscle?

A

when the full length of the actin strands at each end of the sarcomere is in contact with the myosin

67
Q

What does the length-tension relationship demonstrate?

A

the passive components generate an elastic recoil that begins at the muscle’s optimal length and increases as the muscle is stretch beyond the optimal length

68
Q

When are the length-tension effects amplified?

A

in a contracting muscle

69
Q

When does active insufficiency occur?

A

when a muscle is so short that it cannot generate enough contractile force to pull the limb through its available ROM

70
Q

The ___ the muscle’s moment arm, the ___ the moment the muscle produces with its contraction.

A

longer, greater

71
Q

When is the muscle’s moment arm at maximum?

A

when the muscle’s angle ofapplicationis90° I=dxsin90=d

72
Q

How is contractile velocity of a muscle determined?

A

by the
macroscopic changes in length per unit time

73
Q

What kind of contraction velocity does isometric contraction have?

A

zero

74
Q

What kind of contraction velocity does concentric contraction have?

A

positive

75
Q

As velocity increases, muscle force ___

A

decreases

76
Q

Velocity = 0 (isometric) = ___ force

A

maximum

77
Q

Velocity = large (concentric) = ___ force

A

minimum

78
Q

What do eccentric contractions produce?

A

more force than either isometric (FI) or concentric contractions

79
Q

What is the max eccentric strength estimated as?

A

1.5-2.0x max concentric strength

80
Q

Force of an ___ contraction > force of an ___ contraction > force of a ___ contraction regardless of joint position

A

eccentric, isometric, concentric

81
Q

What is a motor unit?

A

the individual muscle fibers innervated by a single motor nerve cell

82
Q

What does an electromyogram reflect?

A

the number of motor units active and the frequency of their activity

83
Q

In an isometric contraction, as force of contraction increases, what happens to EMG?

A

it increases

84
Q

What does EMG indicate in non isometric contraction?

A

the relative
activity of the muscle, not its force of contraction

85
Q

As a muscle’s mechanical advantage ___ ­, the level of recruitment needed (and hence the EMG) ___

A

increases, decreases

86
Q

When does activation failure happen?

A

on individuals who have pain or are chronically inactive

87
Q

A muscle lengthened or positioned with a large moment arm is said to be at a…

A

mechanical advantage

88
Q

What are slow motor units populated by?

A

slow-twitch fibers

89
Q

What are fast fatigue resistance motor units populated by?

A

medium-twitch fibers (IIa)

90
Q

What are fast fatiguable motor units populated by?

A

fast-twitch fibers

91
Q

What does prolonged stretch induce?

A

hypertrophy

92
Q

What does prolonged shortening induce?

A

possible atrophy, loss/gain of sarcomeres, and transition toward type II fibers

93
Q

How is hypertrophy increased?

A
  • Increase in cross-sectional area of both type I and type II fibers in animal studies
  • Possible transition from type II toward type I fibers

EDKP-206 (16 decks)

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