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Kinesiology Term 1 > Muscle Structure and Function > Flashcards

Muscle Structure and Function Flashcards

1
Q

Composition of a Muscle Fiber

A

-Sarcolemma
-Myofibril
-Myofilaments

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2
Q

Sarcolemma

A

Cell membrane enclosing muscle fibers

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3
Q

Myofibril

A

-composed of numerous stacked myofilaments

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4
Q

Myofilaments

A

Myosin and actin

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5
Q

Which are the thick myofilaments?

A

Myosin

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6
Q

Which are the thin myofilaments?

A

Actin

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7
Q

What forms actin myofilaments?

A

-Two chainlike strings of actin molecules
-Troponin
-Tropomyosin molecules

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8
Q

What controls the binding of actin and myosin myofilaments?

A

-Troponin and tropomyosin molecules

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9
Q

What forms myosin myofilaments?

A

-Head groups that attach to specific binding sites on actin molecule

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10
Q

What is the critical role myosin head groups have?

A

-Muscle contraction and relaxation

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11
Q

Contractile Unit

A

-Sarcomere, distinguished by bands and zones

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12
Q

What portion of the myofibril is the sarcomere?

A

-Located between any two Z discs

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13
Q

What does the Z discs link together?

A

-The thin filaments

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14
Q

What is the A band?

A

-Portion of the sarcomere that extends over length of thick filaments and small portion of thin filaments

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15
Q

What is the I band?

A

-Areas that only include actin filaments

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16
Q

What is the H zone?

A

-A band area where there is no overlap with thin filaments

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17
Q

What is the M line?

A

-The center of the H zone; wide middle portion of thick filament

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18
Q

How is a muscle contraction initiated?

A

-By the interaction between thick and thin filaments within the sarcomere

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19
Q

Cross-Bridge Interaction

A
  1. Coupling
  2. Contraction
  3. Uncoupling
  4. Recharging
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20
Q

Coupling phase

A

-Calcium released makes troponin move to expose active sites of actin
-Myosin head will reach out + attach to actin forming the x-bridge

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21
Q

Contraction phase

A

-Cross-bridge will generate force (power stroke) to pull thin filament one notch to the Mline

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22
Q

Uncoupling phase

A

-Power stroke complete, myosin head will detach from actin and repeat cycle

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23
Q

Recharging phase

A

-ATP hydrolysis occurs, releasing ADP and Pi, bounding to myosin head, reattaching to actin binding site

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24
Q

Concentric (shortening) Contraction

A

-Sarcomere length is shorter (distance btw Z discs) than when fiber is at rest
-Closer to M line

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25
Q

Eccentric (lengthening) Contraction

A

-Sarcomere length is greater than a resting fiber

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26
Q

Isometric Contraction

A

-No change in length

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27
Q

What is happening in a Concentric contraction?

A

-Thin filaments overlap thick filaments
-Cross-bridge formed, broken, and re-formed

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28
Q

What happens in an Eccentric contraction?

A

-thin pulled away from thick filaments by an external force on muscle
-Cross-bridge broken, re-formed, and broken again

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29
Q

What happens to the Cros-bridge cycle when an eccentric contraction occurs?

A

-It is broken and re-formed as the muscle lengthens

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30
Q

What happens as the cross-bridge is re-formed?

A

-Tension is generated

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31
Q

What happens in an Isometric contraction?

A

-Active muscle fiber will not change length if the force created by the x-bridge cycling matches the external force

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32
Q

What initiates the muscle contraction?

A

Calcium influx

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33
Q

What fuels the cross-bridge cycle?

A

ATP hydrolysis

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34
Q

How is a Motor Unit organized?

A

-Cell body in Ventral Horn
-Motor axon extends to muscle
-Axon divides into a few or thousands of branches
-Each branch terminates in a motor endplate

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35
Q

Excitability

A

-Capacity of muscle fiber to react to stimulus

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36
Q

Contractibility

A

-Ability to create tension when stimulated from a motor neuron

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37
Q

Extensibility

A

-Capacity of a muscle tissue to stretch without damage

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38
Q

Elasticity

A

-Muscles tendency to return to original after being stretched

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39
Q

What affects the strength of the contraction?

A

-the changing # of motor units that are activated
-frequency at which they are activated

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40
Q

What affects the size of the motor unit?

A

-Depends of the function
-Controls fine movements
-Make small adjustments

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41
Q

How are motor neurons recruited?

A

-All or None Law
-Size Principle

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42
Q

All or None Law

A

-All muscle fiber will contract on the same stimulus

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43
Q

The Size Principle

A

-Small motor unit generate less tension than larger motor unit
-Will be stimulated first to save energy

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44
Q

When is the Size Principle in place?

A

-In an isometric contraction

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45
Q

Which affects the magnitude of the response to a stimulus?

A

-# of muscle fibers in a motor unit

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46
Q

Which determines the conduction velocity of the nerve impulse?

A

-The diameter of the axon innervating a motor unit

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47
Q

Which affects the total force response of the muscle?

A

-# of motor units that are firing at any one time

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48
Q

Which affects the total response of the muscle?

A

-The frequency of motor unit firing

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49
Q

Wave summation

A

-Pace at which nerve signals are fired through the motor unit

50
Q

What does the wave summation say?

A

-In sighting a motor unit before fully relaxing, the second contraction won’t reach a stronger force compared to the first one

51
Q

What are the characteristics of muscle fibers?

A

-Diameter
-Muscle color
-Capillarity
-Myoglobin content
-Speed of contraction
-Rate of fatigue

52
Q

Type I (slow) fiber

A

-Small
Slow contraction but greater efficiency
-Longer duration/ endurance

53
Q

What activity will the Type I fiber be ideal for?

A

-Sustained activities
-Example: Marathon running

54
Q

Type IIA (intermediate) Fiber

A

-Larger
-Faster contraction
-Recover slowly
-Fatigue rapidly

55
Q

What activity will the Type IIA fiber be ideal for?

A

-High intensity workouts

56
Q

Type IIX or Type IIB (Fast) Fibers

A

-Large and powerful
-Fatigues the quickest
-Longer periods of rest to recover and replenish energy

57
Q

What activity will the Type IIX/B fiber be ideal for?

A

-Heavy lifting

58
Q

Postural / Stability

A

-High proportion of Type I fibers in relationship to Type II fibers
-Sustained activity due to slow fatigue
-Ex: Soleus

59
Q

Nonpostural / Mobility

A

-High proportion of Type II fibers
-Produce large ROM
-More force, able to contract faster, higher power output
-Ex: Hamstrings and Gastroc.

60
Q

Muscle Architecture

A

-arrangement of the fibers in relation to the axis of force
-size, arrangement, and length

61
Q

Muscle Fiber Length

A

-Determined by the # of sarcomeres along the fiber

62
Q

The more __________, the more a fiber can shorten.

A

-Sarcomeres

63
Q

Muscle Length

A

-The longer the muscle, the more sarcomeres, shortening more

64
Q

What is the advantage of having a long muscle?

A

-Able to move bony lever to which it is attached through a greater distance

65
Q

Physiological Cross-Sectional Area (PCSA)

A

-a measure of the cross-sectional area of the muscle perpendicular to the orientation of the muscle fibers

66
Q

Fusiform (strap) Muscles

A

-Parallel fibers to the long axis of the muscle and to e/other
-Ex: sternocleidomastoid/sartorius

67
Q

Pennate Muscles

A

-Fiber arrangement oblique to muscle’s long axis
-shorter and numerous fascicles

68
Q

Unipennate Muscles

A

-Oblique fascicles fan out on only one side of a central muscle tendon
-Ex: Flexor pollicis longus

69
Q

Bipennate Muscle

A

-Fascicles are obliquely set on both sides of a central tendon
-Ex: Biceps femoris/tibialis anterior

70
Q

Multipennate Muscle

A

-Oblique fascicles converge on several tendons
-Ex: Soleus/subscapularis

71
Q

Building a Muscle

A

-Endomysium surrounds individual fibers and their sarcolemmas
-Perimysium surrounds groups of fibers (fascicles)
-Epimysium on the outer layer of connective tissue

72
Q

Superficial Fasciae

A

-Loose tissue, located directly under dermis (skin)

73
Q

What does the Superficial fascia zone help with?

A

-mobility of the skin, insulator

74
Q

Deep Fascia

A

-Compacted and regularly arranged collagenous fibers

75
Q

What do Deep fasciae form?

A

-Tracts, bands, or retinaculae

76
Q

What does the Retinaculae help with?

A

-Maintains relationship between tendon and their respective joints and joint axes

77
Q

Passive Elastic Components

A

-Include the Parallel and Series Components

78
Q

Parallel Elastic Components

A

-Function in parallel with the muscle contractile unit; when a muscle lengthens or shortens, the tissues do the same

79
Q

Series Elastic Component

A

-Tendon functions in series with the contractile elements; when at rest, tendon relaxed and may be crimped (slack)
-tendon under tension when muscle actively produces tension

80
Q

Total Tension

A

-includes both active or passive components

81
Q

Passive tension

A

-tension created by lengthening the muscle beyond the slack length of the tissues (stretching muscle) at rest

82
Q

Isometric Length-Tension Relationship

A

-direct relationship between isometric tension + length of the sarcomeres in muscle fibers

83
Q

Optimal Sarcomere Length

A

Plateau of active tension curve

84
Q

Decrease of active tension

A

-when muscle is lengthened because fewer x-bridges can be formed

85
Q

Decrease of active tension

A

-when muscle is shortened; x-bridges already connected, losing capacity to shorten any further

86
Q

Passive tension Increases

A

-with elongation of the muscles as it continues to be stretched

87
Q

Active Insufficiency

A

-2 joint muscles have been maximally SHORTENED across 2 joints and can no longer generate additional or maximal torque

88
Q

Passive Insufficiency

A

-2 joint muscles have been maximally LENGTHENED across 2 joints and can no longer generate maximal torque in that position

89
Q

Force-Velocity Relationship

A

-the ability of a muscle to generate force is affected by the speed at which a concentric / eccentric contraction happens

90
Q

Maximum velocity of muscle shortening (concentric contraction)

A

-No force is produced; only when there is no load on the muscle

91
Q

Shortening velocity decreases

A

-force during concentric contraction increases

92
Q

Zero velocity

A

-isometric contraction

93
Q

Force increases dramatically and then plateaus

A

-Muscle is lengthened actively (eccentric contraction)

94
Q

The greater the # of cross-bridges that are formed,

A

-the greater the tension

95
Q

Are large or small cross-sections better in the capacity of producing more tension?

A

-Large cross sections

96
Q

When does tension increase?

A

-When velocity of active shortening decreases and velocity of active lengthening increases

97
Q

Recruitment order of the motor units

A

-Units with slow conduction velocities are generally recruited first

98
Q

Type of muscle fibers in the motor units

A

-Type II muscle fibers develop maximum tension more rapidly than Type I; rate of cross-bridge formation, breaking, and re-formation may vary

99
Q

Length of the muscle fibers

A

-Long fibers have a higher shortening velocity than shorter fibers

100
Q

Magnitude of the resistance

A

-A given muscle force production, greater resistance to the muscle action will result in a slower contraction

101
Q

Size of motor units

A

-Larger units produce greater tension

102
Q

and Size of muscle fibers in cross section of muscle

A

-Larger cross section, greater amount of tension produced

103
Q

Frequency of firing of motor units

A

-Higher the frequency of firing, greater tension

104
Q

Fiber arrangement

A

-Pennate fiber = > # muscle fibers = large x-sectional area = > tension

105
Q

Type of muscle contraction

A

Greater Tension:
Isometric > concentric
Eccentric > isometric

106
Q

Velocity

A

-Speed of short increases < tension in concentric
-Speed of active length increases > tension in eccentric

107
Q

Golgi Tendon Organ (GTO)

A

-sensitive to tension and may be activated either by an active muscle contraction or by an excessive passive stretch

108
Q

Muscle Spindle

A

-sensitive to length and the velocity of lengthening of the muscle fibers

109
Q

What does the GTO adjust?

A

-Muscle tension by sending message to the CNS via Ib afferent neurons when excited

110
Q

What are muscle spindles concerned about?

A

-State of stretch of a muscle; message sent to spinal cord and CNS via the group Ia afferent neurons
-movement will be affected

111
Q

Immobilization Effects

A

-Depend on immobilization position (short or lengthened), % of fiber types w/in muscle, length of immobilization period

112
Q

Shortened Position Changes

A

-Decrease in # of sarcomeres, increase length
-increase in perimysium
-Thick endomysium
-Collagen fibril orientation more circumferential
-increase in ratio of connective tissue to muscle fiber tissue
-decreased muscle mass and muscle atrophy

113
Q

Lengthened Position Changes

A

-Increase in # sarcomeres, decrease in length
-increased endomyseal + perimyseal connective tissue
-muscle hypertrophy, can be followed by atrophy

114
Q

Overuse

A

-causes injury to tendons, ligaments, bursae, nerves, cartilage, and muscle

115
Q

What causes overuse?

A

-repetitive trauma that does not allow time for complete repair of tissue

116
Q

Muscle Strain

A

-Injuries from single high-force contraction of the muscle while the muscle is lengthened by external forces

117
Q

What does the muscle fail at during Muscle Strain?

A

-The interface between muscle and tendon

118
Q

Eccentric Exercise-Induced

A

-injuries may occur with a single bout of eccentric exercise

119
Q

Sarcopenia

A

loss of muscle mass with age due to loss of fibers and decrease in size of existing fibers

120
Q

Connective Tissue Changes with Age

A

-Increases within a muscle; causes decreased ROM and increased muscle stiffness

Kinesiology Term 1 (16 decks)

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