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MED221A/B Lectures > MSK 15 - Skeletal muscle 2 > Flashcards

MSK 15 - Skeletal muscle 2 Flashcards

1
Q

what does skeletal muscle rely on to activate it

A

nerve AP travelling across the neuromuscular junction

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2
Q

what is the sequence of events that occur in the modulation of a muscle contraction - 3 steps

A

nerve AP travels across the neuromuscular junction

AP in nerve is sensed by muscle and gets a muscle AP

results in a twitch

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3
Q

in the modulation of a muscle contraction what is the time frame between the nerve AP and the muscle AP, what causes this

A

bit of a delay between the nerve AP and the muscle AP - this is because it takes time for neuromuscular transmission (a few milliseconds)

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4
Q

how long is the muscle AP and the muscle twitch

A

muscle AP = around 2-3milliseconds

muscle twitch is up to 200msec in duration

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5
Q

what are the conditions of the stimuli that creates unfused tetanus

A

stimuli far enough apart to allow for muscle relaxation slightly between stimuli

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6
Q

what are the conditions of the stimuli that creates summation

A

stimuli closer together such that they do not allow the muscle to relax fully before another stimuli causes another release of Ca2+ from the cytosol of that muscle fibre

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7
Q

what happens when muscle reaches a steady tension

A

summation has led to complete tetanus

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8
Q

if you continue stimuli at complete tetanus what happens over time

A

fatigue causes muscle to lose tension despite continuing stimuli

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9
Q

what do the Na+/Cl-/K+ channels across the sarcolemma do

A

balance ions across the membrane

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10
Q

what are the two things that the adrenaline receptor (B2 adrenoceptor) on the surface sarcolemma of a muscle cell can respond to

A

adrenaline or a B agonist

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11
Q

where are the adrenaline receptors found on the muscle cell

A

on the surface sarcolemma

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12
Q

what are the adrenaline receptors found on the muscle cell sarcolemma called

A

B2 adrenoceptor

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13
Q

when adrenaline or a B agonist binds to the B2 adrenoceptor what series of events happens and what is the end result

A

increased CAMP -> increased PKA -> react with DHPR and RyR1 and other targets like phospholamban (PLB)

overall it speeds up relaxation as phosphorylated PLB increases Ca2+ uptake by circa ATP-ase back into the SR and also increases force by increasing SR Ca2+ release via phosphorylation of RyR1

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14
Q

what is cAMP

A

cyclic AMP

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15
Q

what is PKA

A

protein kinase A

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16
Q

what is PLB

A

phospholamban

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17
Q

what does PLB do

A

controls/slows calcium ion uptake by SERCA (ATPase) back into SR

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18
Q

what is SERCA

A

sarcoplasmic reticulum Ca-ATPase

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19
Q

what happens when PLB is phosphorylated

A

speeds up the reuptake of Ca2+ into the SR = speeds up relaxation

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20
Q

what causes PLB to become phosphorylated

A

in response to B adrenergic reaction

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21
Q

increased B-adrenergic/adrenal activation will have what effect on force and contractions in fast twitch fibres

A

increase force and make it a faster and stronger contraction

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22
Q

does increased B-adrenergic/adrenal activation have the same effect on force and contractions in slow twitch fibres as they do in fast twitch fibres

A

no

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23
Q

increased adrenaline has what effect on skeletal muscle performance

A

increases performance

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24
Q

what is isometric contraction

A

contraction where no external shortening takes place so tension/force is developed but muscle length does not change

no movement generated

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25
Q

what is the force of weight relative to force developed by muscles in isometric contraction

A

force of weight = force developed by muscles

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26
Q

what is internal shortening of a muscle

A

cross bridge cycling and sarcomere shortening

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27
Q

what are the two types of muscle contractions

A

isotonic and isometric

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28
Q

what is isotonic contraction

A

contraction where movement takes place and external shortening of muscle fibres occurs (muscle length changes)

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29
Q

what is the force of weight relative to force developed by muscles in isotonic contraction

A

produces more force than the objects weight

mismatch between tension force generated by the contracting muscle and the constant load on the muscle

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30
Q

what are the two types of isotonic contraction

A

eccentric and concentric

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31
Q

what is concentric isotonic contractions

A

muscles shortens while generating force and overcomes resistance

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32
Q

what is an example of isotonic concentric contractions

A

Lifting a heavy weight, where the biceps contract to bend the arm at the elbow.

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33
Q

what is an example of isotonic eccentric contractions

A

Lowering a weight slowly during a bicep curl.

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34
Q

what is eccentric isotonic contractions

A

Muscles elongate/lengthen while still generating force.

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35
Q

what is eccentric isotonic contractions in terms of the forces generated

A

Eccentric contractions occur when the opposing force (resistance) is greater than the force generated by the muscle.

force of weight > force developed by muscles

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36
Q

what is the common form of muscle contraction that damages skeletal muscle

A

eccentric isotonic contractions

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37
Q

what is concentric isotonic contractions in terms of forces

A

force of weight < force developed by muscles

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38
Q

what condition is associated with eccentric contractions

A

delayed onset muscle soreness

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39
Q

can skeletal muscle heal and why is this

A

yes

skeletal muscle have satellite cells around its muscle fibres so when there’s damage myoblasts can be assembled and repair fibres

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40
Q

what can be aided by eccentric contractions why is this

A

muscle growth as a result of the eccentric muscle damage causing release of cytokines

41
Q

what happens to the force when sarcomeres are stretched beyond their optimal length

A

the force developed is alot less

42
Q

what is the popping sarcomere theory

A

weakest sarcomeres in series will always lengthen first giving rise to the popping sarcomere

43
Q

what is the combination of conditions that causes DOMS

A

muscle and connective tissue microtrauma followed by inflammatory processes and oedema

44
Q

is the lactic acid theory still supported and why is this

A

lactic acid theory has been rejected

concentric contractions that produces lactic acid does not cause DOMS, lactic acid also returns to normal levels within one hour of exercise so therefore cannot cause the pain that occurs hours afterward

45
Q

what kind of force increases with increased length

A

passive force

46
Q

at what length do skeletal muscles generate the greatest force

A

at their resting/ideal length

47
Q

when muscles are shortened or elongated what happens to the force they generate and why is this

A

force decreases

for stretched muscles it is because you increased the passive force of the muscle

48
Q

explain in terms of the sarcomeres myosin and actin filament arrangements why lengthening the muscle beyond optimal length will decrease the force generated

A

very few cross bridges can form between actin and myosin as there is less overlap so force generated decreases

49
Q

the force that muscles generate is directly proportional to what factor

A

to the number of cross bridges that can form - ie the number of myosin that can bind to actin binding site to develop force

50
Q

explain in terms of the sarcomeres myosin and actin filament arrangements why shortening the muscle beyond optimal length will decrease the force generated

A

sarcomeres will buckle and twist at short lengths and lose their orientations

causes interference with actin filaments that blocks cross bridges from forming (some cross bridges might be working in the opposite direction because of sarcomere shortening)

51
Q

what is the passive force

A

force on muscle depending on length you have isolated muscle at

52
Q

what is the preload

A

the load experienced by the muscle in a relaxed state (muscle length)

putting force on muscle and muscle adjusts to this set length (sets sarcomere length)

53
Q

what is the afterload

A

load a muscle works against during contraction

54
Q

what contractions are involved to lift afterload

A

isotonic contractions

55
Q

what is the total load

A

load experienced by the muscle during contraction

its the sum of preload plus afterload

56
Q

as the load opposing contraction is increasing then the velocity of the shortening should ___

why is this

A

decrease

external shortening of muscle during isotonic contraction is going to be decreased if you shortening against a heavier load

57
Q

in isotonic contractions what is the relationship between load on muscle and speed of shortening

A

if the load on the muscle is constant then the speed of shortening should be constant

58
Q

isometric contraction occurs when maximum force developed by cross bridges is balanced with what

A

balanced with the load

59
Q

what happens if in isometric contraction even more force is applied to the muscle beyond the maximal force developed by the cross bridges (ie if afterload is too heavy)

A

then the muscle will stretch leading to eccentric contraction - negative shortening

60
Q

what is the SI unit for force

A

Newtons

(kgms^-2)

61
Q

what is the SI unit for work

A

Joule

62
Q

what is the SI unit for power

A

Watt

63
Q

what is the most important property of muscle that limits maximum sprinting speed

A

force velocity relationship

64
Q

power of a muscle depends on what

A

depends on the rate of muscle shortening

65
Q

is power generated in isometric contraction - why or why not

A

no

because there is no movement generated in isometric contractions meaning that though you are developing force there is no work done and therefore no power

66
Q

where is the maximum power generated in skeletal muscle (ie contractions are most efficient at what length of shortening)

A

at around 1/3 of maximum load that you can put on a muscle for it to be producing isotonic concentric contraction

around 1/3 of the max rate of shortening

67
Q

in order to sustain contractile activity what must skeletal muscle do in terms of muscle metabolism

A

must produce molecules of ATP as rapidly as their breakdown

68
Q

what the 3 sources of ATP

A

creatine phosphate

oxidative phosphorylation

glycolysis

69
Q

where does creatine phosphate target for ATP production

A

targets phosphate delivery to where ATP is consumed

70
Q

does lactic acid exist in skeletal muscle - explain why

A

no

lactic acid is transported to plasma and is converted to lactate and protons

71
Q

what timeframe can glycolysis supply skeletal muscles with ATP

A

short term energy supply

around 1-2mins

72
Q

what timeframe can ATP-CP supply skeletal muscles with ATP

A

immediate energy supply

depletes quite rapidly

73
Q

what timeframe can aerobic respiration supply skeletal muscles with ATP

A

long term energy supply for system

74
Q

how many isoforms does actin have

A

2

75
Q

how many isoforms does tropomyosin have

A

2

76
Q

how many isoforms does myosin have

A

at least 7

77
Q

what is the differences in sarcomere filament isoforms

A

some isoforms have different rates of which they need energy

78
Q

do muscles only have fast/slow fibres or a mix of both

A

a mix of both depending on function

79
Q

what are the 2 types of skeletal muscle fibre types

A

type IIB = fast glycolytic
type I = slow oxidative

80
Q

what kinds of muscles does Type 1 fibres tend to be

A

postural muscles

81
Q

what are 3 possible causes of muscle weakness

A

muscle fatigue

muscular dystrophy

sarcopenia

82
Q

what is the definiton of muscle fatigue

A

failure to maintain the required/expected power output leading to reduced muscle performance

83
Q

what is the possible theory of why muscle fatigue happens

A

accumulation of metabolites

depletion of muscle energy supplies such as glycogen

84
Q

what are the 2 types of muscle fatigue

A

central and peripheral fatigue

85
Q

what is central fatigue in terms of what causes it

A

decreased activation from CNS = decreased number of motor units recruited

86
Q

what is peripheral fatigue in terms of what they affect

A

affecting the cellular mechanisms that control force such as smaller Ca2+ transient, reduced Ca2+ sensitivity of myofilaments and slower cross bridge cycling

87
Q

does muscle fatigue occur in fast twitch fibres, slow twitch fibres or both

A

mostly in fast twitch fibres

slow twitch fibres are much more fatigue resistant than fast twitch muscles

88
Q

describe T tubular K+ ‘s role in the metabolite accumulation theory of fatigue

A

decreases membrane excitability

everytime you have an AP the K+ conc increases outside builds up in T tubule so that the membrane is depolarised partially such that it is less excitable

89
Q

describe NH4+’s role in the metabolite accumulation theory of fatigue

A

decreases membrane polarity and excitability and also inhibits myosin ATPase

90
Q

describe Pi’s role in the metabolite accumulation theory of fatigue

A

build up of inorganic phosphate within SR causes precipitate that inhibits Ca2+ release, decreases Ca2+ uptake, decreases myofilament Ca2+ sensitivity and inhibits the power stroke

91
Q

describe reactive oxidative species’ role in the metabolite accumulation theory of fatigue

A

increases protein damage

92
Q

what are the clinical features of Duchennes muscular dystrophy

A

muscles normal at birth but increasing skeletal muscle weakness and degeneration

93
Q

what is Duchennes muscular dystrophy caused by

A

mutation in dystrophin gene which causes loss of dystrophin

94
Q

what is the early stages of Duchennes muscular dystrophy characterised by

give examples of what can happen due to this

A

increased cell membrane permeability such that soluble enzymes like creatine kinase leak out and ions like Ca2+ enter

95
Q

what does dystrophin do within muscle cells

A

link to contractile proteins with sarcolemma in some way so that force developed by contractile proteins during cross bridge cycling can be transmitted across the cell membrane

96
Q

what is sarcopenia mainly caused by

A

aging

97
Q

what happens in sarcopenia to the muscle and what does this mean in terms of strength

A

muscle mass/body mass ratio decreased

significant loss of muscle strength

98
Q

in terms of nerves and fibres what happens in sarcopenia

A

denervation of fast fatigable fibres and motor units and motor unit remodelling

99
Q

in sarcopenia there is a ____ in the capillary:fire ratio

A

decrease

MED221A/B Lectures (23 decks)

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