Muscle Physiology Flashcards Preview

Structure and Function Test 1 > Muscle Physiology > Flashcards

Flashcards in Muscle Physiology Deck (107):
1

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

Skeletal muscle

2

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

Thermogenesis

3

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

Cardiovascular disease, diabetes, and obesity

4

What are the three types of muscle tissue?

Smooth, cardiac, and skeletal

5

Muscle contraction falls into what two general categories?

Isometric and Isotonic

6

The development of tension without force

Isometric contraction

7

The generation of force via moving a load over a distance

Isotonic contraction

8

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

Sarcolemma

9

Within each muscle fiber are bundles of

Myofibrils

10

Repeating units of sarcomeres that are surrounded by the sarcoplasm

Myofibrils

11

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

Sarcoplasmic reticulum (SR)

12

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

Calsequesterin

13

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

1.) Actin
2.) Myosin
3.) Anchoring Z disc

14

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

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

15

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

A band

16

Contains only actin filaments

I band

17

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

H band

18

Actin is anchored to

Z discs

19

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

Myosin cross-bridge

20

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

1.) G actin
2.) Troponin
3.) Tropomyosin

21

Shields active, myosin binding, sites on actin

Troponin

22

The myosin binding domains within actin

Tropomyosin

23

Troponin contains which three subunits?

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

24

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

Troponin/tropomyosin complex

25

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

Neuromuscular junction, motor endplate, or myoneural junction

26

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

Muscle cell

27

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

Acetylcholine (ACh)

28

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

Acetylcholine (ACh)

29

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

Sarcolemma

30

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

Cholinergic-nicotinic receptors

31

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

Acetylcholinesterase

32

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

Acetylcholinesterase inhibitor (will result in prolonged muscle contraction)

33

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

ACh-gated Na+ channels

34

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

Endplate potentials (EPP)

35

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

EPPs

36

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

Transverse tubules (T tubules)

37

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

Dihydropyridine receptors (DHPR)

38

DHRP's in the T tubule sit on clusters of

-embedded in the SR membrane

Ryanodine receptor Ca2+ channels (RyR)

39

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

SR to the sarcoplasm

40

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

Contraction

41

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

Calcium

42

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

Active (myosin binding) domain in the actin molecule

43

The high energy myosin head/ADP + Pi complex is
maintained in

Resting Muscle

44

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

Actin

45

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

Power-stroke

46

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

Power-stroke

47

Myosin light chains comprise the heads and contain the intrinsic

ATPase

48

Significant sarcomere shortening does not occur during

Isometric contraction

49

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

Opposing load

50

Crossbridge cycling will be terminated as a result of decreased

Ca2+ or sarcoplasmic ATP concentration

51

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

Hypoexcitability

52

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

Hypocalcemia (low blood calcium)

53

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

Skeletal muscle and neurons

54

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

Parathyroid hormone, bone, and the kidneys

55

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

Sarcoplasmic ATP

56

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

Phosphocreatrine (pCr)

57

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

Creatine kinase

58

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

pCr kinase

59

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

Glycogen breakdown and subsequent glycolysis

-2 ATP per mole of glucose

60

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

Oxidative metabolism

61

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

Oxidative metabolism

62

In oxidative metabolism, one mole of glucose can produce

38 ATP

63

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

Epinephrine and growth hormone (GH) in adipocytes

64

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

129 ATP

65

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

Troponin C

66

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

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

Sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA)

67

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

SERCA

68

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

Na+-Ca2+ exchanger (NCX) protein

69

A blockade in NCX function would result in

Elevated sarcoplasmic Ca2+

70

In muscle terms, mass means

Load

71

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

Load

72

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

Eccentric contraction

73

The propensity for muscle damage is greater during

Eccentric contraction

74

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

Stress (stress = Force / cm^2)

75

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

Strength

76

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

Normal resting length (Lo) of the sarcomere

77

The resistance of muscle tissue to stretch

-increases as muscle is stretched beyond its Lo

Passive tension

78

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

Increases

79

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

-the change in tension during muscle contraction

Active tension

80

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

Active tension

81

Active tension in fact decreases as

Isotonic muscle contraction peaks

82

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

Isometric contraction

83

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

Lo

84

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

Active tension

85

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

Sarcomere shortening (isotonic muscle contraction)

86

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

Muscle twitch

87

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

Summation of twitches

88

Responsible for muscle contraction as we know it

Summation of twitches

89

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)

Muscle Tetany

90

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

Orderly recruitment principle

91

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

Type 1 and Type 2 fibers

92

Known as slow twitch, red, or oxidative fibers

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

Type 1 fibers

93

Known as fast twitch, white, or glycolytic fibers

-responsible for rapid generation of force sustained over short intervals

Type 2 fibers

94

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

1.) Type 2a (low oxidative capacity)
2.) Type 2b (almost no oxidative capacity)

95

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

Activated

96

Physical training at high levels of resistance will result in

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

97

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

Lower intensity endurance training

98

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

Hypertrophy

99

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

Anabolic androgens, IGF-1, and GH

100

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

Growth hormone and IGF-1

101

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

Muscle cell hypertrophy

102

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

Repair/hypertrophy process

103

Satellite cells express androgen receptor and undergo proliferation in response to

IGF-1

104

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

Myostatin

105

Regular resistance training results in hypertrophy primarily of

Fast twitch type 2 fibers

106

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

Motor units

107

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

-another cause of gain of muscle

Angiogenesis (synthesis of vascular tissue) in response to load

Decks in Structure and Function Test 1 Class (61):