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HSC1007 > Muscle physiology Week 12 > Flashcards

Muscle physiology Week 12 Flashcards

1
Q

what are the different muscle types

A

skeletal muscle
- striated, voluntary

cardiac muscle
- striated, involuntary

smooth muscle
- unstriated, involuntary

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2
Q

where can skeletal muscle be foud

A

attached to bones of skeleton

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3
Q

where can cardiac muscle be found

A

wall of the heart

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4
Q

where can smooth muscle be found

A

walls of hollow organs and tubes such as stomach and blood vessels

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5
Q

what is the function of skeletal muscle

A

producing movement

maintain posture & body position

stabilize joints

protect organs

generate heat

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6
Q

what is the function of cardiac muscle

A

pump blood out of heart

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7
Q

what is the function of smooth muscle

A

movement of contents within hollow organs

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8
Q

what is the arrangement of muscle fibers

A

parallel to one another and bundled together by connective tissue (fascia)

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9
Q

what are muscle fibers composed of

A

myofibrils with each being made of regular arrangement of thick and thin filaments

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10
Q

What is the ion responsible for muscle contraction

A

Ca2+

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11
Q

what controls calcium levels

A

motor neurons

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12
Q

what is the film holding all the myofibrils together

A

sarcolemma

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13
Q

what is the repetitive sequence of myofibrils

A

I - band (Z- disc)
A - band (H- zone)

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14
Q

what is the triad found on myofibrils

A

T-tubule
2 x terminal cisternae of SR

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15
Q

What does SR mean

A

sarcoplasmic retinaculum

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16
Q

what are A bands

A

thick filaments along with portions of thin filaments that overlap

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17
Q

what are I bands

A

remaining portion of thin filaments that do not project into A band (only thin filaments)

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18
Q

what are cross bridges

A

project from each thick filament in 6 directions toward surrounding thin filament

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19
Q

where can sarcomeres be found

A

between Z-lines

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20
Q

what does 1 myosin protein consist of

A

2 identical golf club like subunits

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21
Q

what forms the cross bridges

A

heads of myson

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22
Q

what can be found at the heads of myosin

A

actin binding site and ATPase site

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23
Q

what is the length of the tail of myosin

A

100nm

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24
Q

what is the main structural component of thin filaments

A

actin which forms actin helix

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25
Q

what does actin do

A

interacts with myosin cross-bridges

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26
Q

what are the components of thin filaments

A

actin helix + tropomyosin + troponin

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27
Q

what happens during relaxed state of cross bridging

A

no cross bridging because cross bridge binding site on actin is physically blocked by tropnin-tropomyosin complex

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28
Q

what happens during excited state of cross bridging

A

Ca2+ is released and binds to troponin which moves it aside for myosin to bind to actin helix

triggers power stroke that pulls thin filament inward during contraction

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29
Q

what regultaes myosin actin binding

A

Ca2+

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30
Q

what happens during power strokes

A

binding > power stroke > detachment > cycle repeats
- stroking motion pulls thin filament towards centre of sarcomere

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31
Q

what causes the muscle to shorten

A

repeated cross bridge binding & power stroke

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32
Q

how is contraction accomplished

A

by pulling thin filaments from opposite sides of each sarcomere sliding closer together between thick filaments

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33
Q

what are the changes of sarcomeres during contraction

A

H- zone & I-band shortens
A-band remains the same (proportionally bigger)

HAI = thick, thick + thin, thin
Ai = A remains the same, i-band shortens, H band disappear

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34
Q

what is the main motor neurotransmitter

A

Acetylcholine (ACh)

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35
Q

what do T tubules contain

A

dihydropyridine receptor which are voltage gated Ca2+ channel

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36
Q

what do SR contain

A

Ca2+ releasing channels which have ryanodine receptors

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37
Q

are action potentials in skeletal muscle able to occur rapidly

A

no due to the refractory period

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38
Q

what happens during depolarization of a muscle

A

ACh binds to receptors which opens Na+ channels but close K+ channels

ultimately action potential generated

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39
Q

what happens during repolarization of a muscle

A

closed Na+ channel but open K+ channel

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40
Q

what are T tubules

A

transverse tubules

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41
Q

what is close to SR

A

T tubules

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42
Q

how are Ca2+ release channels opened

A

activation of dihydropyridine receptors by local APs in T tubules

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43
Q

what happens to Ca2+ after contraction

A

majority is re-absorbed back into SR, small amount is pumped outside

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44
Q

when does contraction occur after AP

A

much time after AP was generated and contraction outlasts AP due to Ca2+ reuptaking needing time

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45
Q

what is rigor mortis

A

stiffness of death

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46
Q

what is the role of ATP in cross bridge cycle

A

Once the Ca2+ binds is present and myosin is able to move, it bends but ADP & phosphate ion detach

ATP then binds to myosin cross bridge and assumes original conformation

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47
Q

what happens to myosin upon death

A

myosin and actin remain bound in rigor complex

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48
Q

what are the 4 steps in excitation, contraction and relaxation

A
  1. splitting ATP by myosin ATPase
  2. binding ATP to myosin breaks cross bridge
  3. active transport of Ca2+ back into lateral sacs of SR during relaxation (SERCA)
  4. activity of Na+ & K+ pump during AP production
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49
Q

what does SERCA mean

A

Sacro/Endoplasmic Reticulum Ca2+ ATPase

50
Q

what are alternative pathways to form new ATP

A

creatine phosphate

glycolysis

oxidative phosphorylation

51
Q

what does creatine phosphate do

A

supports short burst of high intensity contraction

fast reaction requires only 1 enzyme but not efficient

52
Q

what are products of glycolysis

A

2 ATP & 2 Pyruvic acid

53
Q

what can glyolysis support

A

anaerobic high intensity exercise

54
Q

what happens to pyruvic acid with or without o2

A

with o2 = krebs cycle

w/o o2 = lactic acid

55
Q

what does oxidative phosphorylation do

A

supports aerobic or endurance exercise

1 glucose = 36 ATP

Mitochondria & O2 involved

56
Q

what happens when muscle fatigue occurs

A

when muscle can not respond to stimulation with same degree of contractile activity
- increase of phosphate
- Ca2+ leak
- depletion of glycogen

central fatigue occurs when CNS cannot adequately activate motor neurons

57
Q

what are the origins of fatigue

A

muscle or central origin

58
Q

what is needed to recover from exercise

A

increased o2 consumption
- excess post exercise o2 consumption

59
Q

what are the different types of skeletal muscle fibers

A

based on differences in ATP hydrolysis and synthesis
1. slow oxidative fibers (type I)
2. fast oxidative fibers (type iia)
3. fast glycolytic fibers (type iix)

60
Q

what are the colours of the different skeletal muscle fibers

A

type i = red
type iia = red
type iix = white

61
Q

what is the glycogen content in the different skeletal muscle fibers

A

type i = low
type iia = intermediate
type iix = high

62
Q

what is responsible for red colored meat

A

myoglobin

63
Q

what has been proven to minimise sarcopenia

A

weight training / resistance training

64
Q

what are the causes of sarcopenia

A

motor neuron death

changes in testosterone, activity, protein metabolism

mitochondria dysfunction

65
Q

what does a loss of muscle protein lead to

A

hinders immune system, insulin absorption

increased risk of type ii diabetes

66
Q

which muscle fiber is more affected than the other

A

type ii muscles are more severely affected than type i

67
Q

when does gradual muscle loss begin

A

after 40
- loss through inactivity is ~1% and more so after 50

68
Q

What are the differences between the skeletal muscle fibers

A

Fast vs slow fibers
- Myosin ATPase in Fast fibers > slow fibers

Oxidative vs glycolytic fibers
- fiber types differ in ATP synthesizing ability

Genetic endowment of muscle fiber types
- largely determined by type of activity for which muscle is specialized in

69
Q

How do muscle fibers adapt

A

improvement in oxidative capacity (aerobic endurance)

muscle hypertrophy (anaerobic high intensity training)

Testosterone influence

interconversion between fast and slow muscle types under training

type I to II conversion during spinal cord injury/low gravity

muscle atrophy

muscle repair

70
Q

What does anaerobic high intensity resistance training

A

increase myosin and actin filaments

71
Q

What happens to satellite cells when muscle damage occurs

A

They become myogenic precursor cells that repair muscles

72
Q

what causes muscle atrophy

A

disuse, denervation, aging

73
Q

What are the primary types of contraction

A

isotonic (constant tension) = load remains constant as muscle changes

isokinetic (constant motion) = velocity remains constant as muscle fibers shorten

isometric (constant length) = muscle length remains constant as tension increases

74
Q

What are secondary types of contractions

A

concentric contractions = muscle shortens

eccentric contractions = muscle lengthens

75
Q

Which muscle fibers are more susceptible to eccentric exercise induced damage

A

fast twitch fibers

76
Q

What are graded contractions

A

contractions of a whole muscle of varying strength

77
Q

what are the factors that can help produce graded contractions

A

number of muscle fibers contracting

tension developed by each contracting fiber

78
Q

what are the factors affecting contraction

A

no. of fibers contracting within muscle depending on extend of motor unit recruitment (stronger contraction = more motor units)

frequency of stimulus can influence tension develop by each muscle fiber

79
Q

what is twitch summation

A

increase in tension accompanying repetitive stimulation of muscle fiber

80
Q

what is tetanus contraction

A

smooth, sustained contraction of maximal strength

81
Q

What is the primary drive of twitch summation

A

sustained elevation in cytosolic Ca2+

82
Q

when does maximal tension occur

A

optimal muscle length

83
Q

what is the difference between whole muscles and tendons

A

whole muscles are groups of muscle fibers bundled together & attach to bones

tendons attach muscle to bones

84
Q

where is tension formed during muscle tension

A

produced internally in sarcomeres

85
Q

what are the differences between type I and II fibers

A

Z-disk, Titin, Nebulin, dystrophin sizes
- Type I > Type II

Membrane strain
- Type I < Type II

86
Q

For effective control of motor output, what does CNS continuously monitor

A

changes muscle length and tension

87
Q

what monitors changes in muscle length & tension

A

muscle spindles = monitor muscle length
golgi tendon organs = monitor tension changes

88
Q

what is the interactive system of skeletal muscles, bones and joints

A

Lever system
- bones are levers
- joints are fulcrum
- skeletal muscles provide force to move bones

89
Q

what is stretch feedback

A

local negative feedback mechanism to sense and resist changes in muscle length when additional load is applied

90
Q

what does the muscle spindle structure consist of

A

collection of specialized muscle fibers such as intrafusal fibers

91
Q

what does alpha gamma coactivation lead to

A

contracts both intra- and extra- fusal muscle fibers

92
Q

what do cardiac muscle feature

A

blends both skeletal and smooth muscle features

93
Q

where can cardiac muscles be found

A

only in the heart

94
Q

what are the fibers of cardiac muscles like

A

highly organized, striated, slender and short fibers

innervated by ANS

95
Q

What is the advantage of smooth muscle

A

can develop tension and yet be relaxed when stretched as part of stress relaxation response

96
Q

what are smooth muscles like

A

slow and economical based on latch phenomenon which allows them to stay attached longer

97
Q

What is the Ca2+ dependent phosphorylation of myosin like

A

Ca2+ + Calmodulin = Ca2+ - Calmodulin > activates myosin light chain kinase > phosphorylates myosin cross bridge to bind with actin

98
Q

Is troponin found in smooth muscle

A

no

99
Q

does tropomyosin cover actin in smooth muscle

A

no

100
Q

is smooth muscle myogenic

A

yes, they are pacemakers with slow wave potentials

101
Q

What are 3 forms of ATP production

A

Creatine phosphate

Glycolysis

Oxidative phosphorylation

102
Q

What is an example of a muscle that does not attach to bones at either ends but still produce movement

A

tongue

103
Q

what are the factors affecting contraction

A
  • frequency of stimulation
  • fiber length at contraction onset
  • fatigue extent
  • fiber thickness
104
Q

what are the neurons that assist with reflex

A
  • excitatory neurons which stimulate flexion
  • inhibitory neurons which inhibit extension
105
Q

what controls motor contraction in NS

A
  • motor cortex
  • brain stem
  • spinal cord
  • cerebellum
  • somatic & autonomous NS
106
Q

For the myofibrillar domain to remain constant, what needs to change

A

changes in myofibrillar proteins and cross sectional area either increase or decrease in hypertrophy or atrophy respectively

107
Q

Which component of the sarcomere acts as an ATPase?

A

myosin

108
Q

Which of the following describe the characteristics of slow muscle fiber?

A
  • small diameter, rich in myoglobin and very vascular
109
Q

What are the two membranous structures within the muscle fiber that play important roles in linking excitation to contraction?

A
  • transverse tubules and sarcoplasmic reticulum
110
Q

Which of the following describes the neuromuscular junction?

A

special intercellular connection between axon branches and a skeletal muscle fiber

111
Q

What happens to a muscle during an isometric contraction

A

prevented from shortening

112
Q

During muscle contraction, what becomes smaller?

A

H-zone

113
Q

What happens when two or more overlapping action potentials are “added” together within a muscle?

A

twitch summation

114
Q

How would a drug that blocks acetylcholine (ACh) release affect muscle contraction?

A

contraction prevented

115
Q

What two molecules participate in cross-bridge interactions?

A

actin & myosin

116
Q

In skeletal muscles, action potentials travel down the _____ to initiate calcium release.

A

T-tubules

117
Q

___ released from the lateral sacs of the sacroplasmic reticulum, binds to ___, which
induces contraction.

A

Ca2+, troponin

118
Q

if u sever the tendon attached to a muscle, how would it affect the muscle’s ability to move a bod part

A

no movement possible without muscle - bone connection

119
Q

what aspect of creatine phosphate allows it to supply energy to muscle

A

phosphate bonds

120
Q

what molecule forms the thick filaments within muscle

A

myosin

HSC1007 (18 decks)

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