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Structure and Function Test 1 > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

1
Q

Represents the largest tissue mass responsible for blood glucose storage and post-prandial lipid oxidation

A

Skeletal muscle

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2
Q

Second only to the liver, skeletal muscle is also the predominant site of

A

Thermogenesis

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3
Q

Reduced skeletal muscle mass (such as what can occur with illness and aging) is associated with an increased risk for

A

Cardiovascular disease, diabetes, and obesity

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4
Q

What are the three types of muscle tissue?

A

Smooth, cardiac, and skeletal

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5
Q

Muscle contraction falls into what two general categories?

A

Isometric and Isotonic

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6
Q

The development of tension without force

A

Isometric contraction

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7
Q

The generation of force via moving a load over a distance

A

Isotonic contraction

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8
Q

Muscle fibers are surrounded by a specialized plasma membrane containing an additional tough outer coat of collagens and polysaccharides, called the

A

Sarcolemma

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9
Q

Within each muscle fiber are bundles of

A

Myofibrils

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10
Q

Repeating units of sarcomeres that are surrounded by the sarcoplasm

A

Myofibrils

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11
Q

The sarcoplasm contains mitochondria, ions, enzymes, and the main intracellular sink (storage site) for Ca2+, which is called the

A

Sarcoplasmic reticulum (SR)

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12
Q

An important SR protein which binds Ca2+ and maintains Ca2+ in the low energy state while it is housed within the SR

A

Calsequesterin

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13
Q

Each myofibril is comprised of sarcomeres. The sarcomere is comprised of interdigitating elements
of myofilaments which each contain what three things?

A
  1. ) Actin
  2. ) Myosin
  3. ) Anchoring Z disc
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14
Q

Histologically speaking, the sarcomere is characterized by specific bands and is capped on each side by a Z disc. What are the three bands?

A
  1. ) A band
  2. ) I band
  3. ) H band
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15
Q

An overlapping region of thick (myosin) and thin (actin) elements

A

A band

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16
Q

Contains only actin filaments

A

I band

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17
Q

A centrally located light area within each sarcomere, and contains myosin

A

H band

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18
Q

Actin is anchored to

A

Z discs

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19
Q

The myosin heads are in fact connected to the tail regions by a hinged arm; collectively, the head-arm region is referred to as the

A

Myosin cross-bridge

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20
Q

In skeletal muscle, actin is in the form of a double helix of F actin, which is made up of which three things?

A
  1. ) G actin
  2. ) Troponin
  3. ) Tropomyosin
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21
Q

Shields active, myosin binding, sites on actin

A

Troponin

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22
Q

The myosin binding domains within actin

A

Tropomyosin

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23
Q

Troponin contains which three subunits?

A
  1. ) I (actin attachment)
  2. ) T (tropomyosin attachment)
  3. ) C (calcium binding)
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24
Q

Prevents actin and myosin from interacting and inducing muscle contraction during relaxed (basal) conditions

A

Troponin/tropomyosin complex

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25
Q

The process of skeletal muscle contraction begins at the juncture between the motor neuron and the
muscle tissue. This region is referred to as the

A

Neuromuscular junction, motor endplate, or myoneural junction

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26
Q

The terminus of the efferent (motor) neuron is unmyelinated and branches into several troughs on surface of the

A

Muscle cell

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27
Q

The nerve terminus contains and abundance of mitochondira as well as vesicles that house neurotransmitters, most notably

A

Acetylcholine (ACh)

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28
Q

These α motor neurons cannot synthesize choline; they can however convert choline into

A

Acetylcholine (ACh)

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29
Q

In the neuromuscular junction, ACh is the neurotransmitter, and the post-synaptic membrane belongs to the

A

Sarcolemma

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30
Q

Acetylcholine diffuses across the synaptic cleft and binds to receptors located on the post synaptic membrane called

A

Cholinergic-nicotinic receptors

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31
Q

As depolarization propagates through the sarcolemma, the ACh signal is deactivated by degradation of ACh by

A

Acetylcholinesterase

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32
Q

To pallitatively treat syndromes where ACh release and/or binding to cholinergic/nicotinic receptors is impeded, i.e. myasthenia gravis, we want to use an

A

Acetylcholinesterase inhibitor (will result in prolonged muscle contraction)

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33
Q

Skeletal muscle ACh receptors are ligand-gated ion channels, more specifically, they are

A

ACh-gated Na+ channels

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34
Q

Na+ influx induces relatively minor membrane depolarizations within the motor endplate, and these sub-threshold membrane depolarizations are known as

A

Endplate potentials (EPP)

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35
Q

Within the sarcolemma, voltage-gated Na+ channels are activated to induce membrane threshold, by the

A

EPPs

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36
Q

The spread of signal is relayed from the sarcolemma via highly conductive specialized structures known as the

A

Transverse tubules (T tubules)

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37
Q

As the AP travels down the T tubules, a conformational change occurs in voltage-gated Ca2+ channels known as

A

Dihydropyridine receptors (DHPR)

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38
Q

DHRP’s in the T tubule sit on clusters of

-embedded in the SR membrane

A

Ryanodine receptor Ca2+ channels (RyR)

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39
Q

The conformational change in DHPR alters the inhibitory interaction between DHPR and RyR, opening the pore in RyR that allows the flow of Ca2+ from

A

SR to the sarcoplasm

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40
Q

This rapid increase in sarcoplasm Ca2+ concentration, focused on the Z-disc due to the localization of the triad junction, signals

A

Contraction

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41
Q

Binds to troponin C and causes a conformational change of the troponin/tropomyosin complex

A

Calcium

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42
Q

The binding of calcium to troponin C causes a comformational change in the troponin/tropomyosin complex which reveals the

A

Active (myosin binding) domain in the actin molecule

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43
Q

The high energy myosin head/ADP + Pi complex is

maintained in

A

Resting Muscle

44
Q

When the myosin binding domain within actin is exposed in response to elevated sarcoplasmic Ca2+ levels, the high energy myosin head binds to

A

Actin

45
Q

The binding reaction induces a conformational change in the cocked (loaded) myosin head that drives the myosin head downward. This is called the

A

Power-stroke

46
Q

Pulls on the actin and attempts to draw actin towards the center of the sarcomere (Z-disc to Z-disc shortening)

A

Power-stroke

47
Q

Myosin light chains comprise the heads and contain the intrinsic

A

ATPase

48
Q

Significant sarcomere shortening does not occur during

A

Isometric contraction

49
Q

Muscle contraction always begins with an isometric contraction and can be followed by isotonic contraction if the muscle is more “powerful” than the

A

Opposing load

50
Q

Crossbridge cycling will be terminated as a result of decreased

A

Ca2+ or sarcoplasmic ATP concentration

51
Q

Experimental evidence has shown that excess extracellular Ca2+ (hypercalcemia) raises the membrane potential necessary to open motor neuron voltage-gated Na+ channels, thus inducing

A

Hypoexcitability

52
Q

Associated with an increase in nerve and muscle excitability, i.e. hyperexcitability

A

Hypocalcemia (low blood calcium)

53
Q

It appears that extracellular Ca2+ aids in somehow stabilizing membrane Na+channels within

A

Skeletal muscle and neurons

54
Q

Work in concert to maintain normal calcium levels, thus a disruption can raise concerns regarding calcium homeostasis

A

Parathyroid hormone, bone, and the kidneys

55
Q

Important for the activity of Na+/K+ ATPases, initial myosin activation, and the activity of SERCA pumps in the SR

-available for immediate use, but there is only enough for a couple seconds of contraction

A

Sarcoplasmic ATP

56
Q

A second source of ATP is derived from the sarcoplasmic stores of

A

Phosphocreatrine (pCr)

57
Q

Catalyzes the transfer of phosphate groups from pCr to ADP during muscle contraction

A

Creatine kinase

58
Q

During rest, and in active muscle, pCr is re-synthesized from ATP and creatine (Cr) via the catalytic actions of

A

pCr kinase

59
Q

During the more sustained muscle contractions, or numerous contractions over a longer period of time, ATP is produced via

A

Glycogen breakdown and subsequent glycolysis

-2 ATP per mole of glucose

60
Q

The ultimate source of ATP production, which can provide enough ATP to sustain muscle contraction for hours

A

Oxidative metabolism

61
Q

Has the capacity to promote the metabolism of fatty acids in order to provide the greatest proportion of ATP

A

Oxidative metabolism

62
Q

In oxidative metabolism, one mole of glucose can produce

A

38 ATP

63
Q

The use of fatty acids may also provide ATP during prolonged muscle activity. This mechanism is supported by the stimulatory effects of

A

Epinephrine and growth hormone (GH) in adipocytes

64
Q

In adipocytes, epinephrine and growth hormone stimulate the conversion of triglycerides into free fatty acids. Each mole of free fatty acid can generate

A

129 ATP

65
Q

Skeletal muscle fibers can only relax once the Ca2+ concentration in the sarcoplasm drops below the
minimal level required to allow Ca2+ to bind

A

Troponin C

66
Q

The principal mechanism that muscle fibers use to clear Ca2+ from the cytosol

-activated immediately after sarcoplasmic [Ca2+] begins to rise

A

Sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA)

67
Q

A highly abundant protein that sits in the SR membrane and pumps Ca2+ from the sarcoplasm into the lumen of the SR

A

SERCA

68
Q

Most of the Ca2+ is returned to the SR, however, some Ca2+ leaves the muscle fibers through Ca2+ leak channels or the

-expressed in skeletal muscle and cardiomycetes

A

Na+-Ca2+ exchanger (NCX) protein

69
Q

A blockade in NCX function would result in

A

Elevated sarcoplasmic Ca2+

70
Q

In muscle terms, mass means

A

Load

71
Q

In order for concentric contraction to occur, the force generated by the muscle must overcome the

A

Load

72
Q

Sometimes described as “lengthening contractions” since muscle fibers actually lengthen as they contract. These occur when the resistance against contraction is greater than the contractile force that can be generated by the muscle

A

Eccentric contraction

73
Q

The propensity for muscle damage is greater during

A

Eccentric contraction

74
Q

Determines the strength of muscle contraction, i.e. how much load a muscle can displace

A

Stress (stress = Force / cm^2)

75
Q

Tension, strength, and stress are all intended to describe the same property of a muscle, that is,

A

Strength

76
Q

Maximum muscle stress (i.e. greatest force generated) occurs in the range of optimal overlap between actin and myosin cross-bridges that is present only near

A

Normal resting length (Lo) of the sarcomere

77
Q

The resistance of muscle tissue to stretch

-increases as muscle is stretched beyond its Lo

A

Passive tension

78
Q

Tension (active and passive) is pretty high in resting muscle, and as resting muscle is stretched beyond its normal resting length (>Lo), passive tension

A

Increases

79
Q

Generated during muscle contraction and falls as a result of stretch from Lo

-the change in tension during muscle contraction

A

Active tension

80
Q

Peaks during the early phase of isotonic muscle contraction, when the velocity of muscle contraction is the greatest

A

Active tension

81
Q

Active tension in fact decreases as

A

Isotonic muscle contraction peaks

82
Q

Total tension increases somewhat within muscle fibers (increased passive tension); whereas, active tension is very low, during (remember, no displacement of load)

A

Isometric contraction

83
Q

Maximal active tension is generated at the very beginning of the contraction when muscle fibers are very near

A

Lo

84
Q

Is highest right near Lo, but declines if the muscle is stretched and also peaks and declines shortly after contraction begins as the muscle becomes much smaller than Lo

A

Active tension

85
Q

A muscle fiber has the greatest potential to develop force from L0, and force declines rapidly in response to

A

Sarcomere shortening (isotonic muscle contraction)

86
Q

A single rapid muscle contraction in response to a single action potential

A

Muscle twitch

87
Q

Results from the simultaneous contraction of many motor units and/or the increased frequency of contraction of a motor unit per unit time

A

Summation of twitches

88
Q

Responsible for muscle contraction as we know it

A

Summation of twitches

89
Q

Occurs when rapid successive twitches fuse

-represents the physiologic MAXIMUM strength of contraction (i.e. further summation will not result in increased strength of contraction)

A

Muscle Tetany

90
Q

The phenomenon whereby a stimulus is relayed to a small motor unit (more fatigue resistant), which recruits other smaller motor units until eventually large motor units are activated

A

Orderly recruitment principle

91
Q

What are the two main types of muscle fibers in adult humans?

A

Type 1 and Type 2 fibers

92
Q

Known as slow twitch, red, or oxidative fibers

-develop force at a slower rate but can sustain activity for longer periods of time

A

Type 1 fibers

93
Q

Known as fast twitch, white, or glycolytic fibers

-responsible for rapid generation of force sustained over short intervals

A

Type 2 fibers

94
Q

Type 2 fibers have been further divided into which two groups?

A
  1. ) Type 2a (low oxidative capacity)

2. ) Type 2b (almost no oxidative capacity)

95
Q

Changes in the net metabolism from an individual muscle may represent variance in the relative number of different fiber types being

A

Activated

96
Q

Physical training at high levels of resistance will result in

A

Hypertrophy of type 2 fibers w/ modest effect on aerobic capacity

97
Q

Results in an increase in the oxidative capacity of type 1 fibers associated with a proliferation of mitochondria and an increase in capillary density

A

Lower intensity endurance training

98
Q

Muscle protein synthesis is stimulated by resistance exercise; so long as net muscle protein synthesis
exceeds muscle protein breakdown (i.e. catabolism), the result will be

A

Hypertrophy

99
Q

Key hormones that stimulate the intracellular signaling motifs which promote myofibrillar protein synthesis

A

Anabolic androgens, IGF-1, and GH

100
Q

Prevent protein breakdown, increased amino acid uptake, increased lipolysis, and decreased glycogenolysis, which collectively support muscle function, growth, and repair

A

Growth hormone and IGF-1

101
Q

Anabolic androgens such as testosterone and its pharmacologic derivatives stimulate satellite cell activity and cause

A

Muscle cell hypertrophy

102
Q

Satellite cells are stimulated to differentiate into myoblasts, which then fuse with myotubules as part of the

A

Repair/hypertrophy process

103
Q

Satellite cells express androgen receptor and undergo proliferation in response to

A

IGF-1

104
Q

Blocks cell cycle progression within satellite cells, and loss-of-function is associated with enhanced muscle mass in humans and some other mammalian species

-member of TGFβ superfamily

A

Myostatin

105
Q

Regular resistance training results in hypertrophy primarily of

A

Fast twitch type 2 fibers

106
Q

Increases in strength result not only from muscle hypertrophy but from a better coordination of contracting

A

Motor units

107
Q

Stimulated and mediated by several intramuscular
growth factors that are secreted in response to load

-another cause of gain of muscle

A

Angiogenesis (synthesis of vascular tissue) in response to load

Structure and Function Test 1 (61 decks)

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