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Muscle Flashcards

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1
Q

What is the function of muscle?

A

To generate force and movement.

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2
Q

What can muscle function allow?

A

Expression and regulation- characterises people, regulates body functions, internal and external protection.

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3
Q

What are the 3 types of muscle?

A

Skeletal
Cardiac
Smooth

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4
Q

What does skeletal muscle allow?

A

Voluntary movement- controls body movement.

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5
Q

What does cardiac muscle allow?

A

Flow of blood through circulatory system.

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6
Q

What does smooth muscle allow?

A

Involuntary movement- influences movement of substances in body.

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7
Q

Is muscle excitable?

A

Yes- it can be electrically stimulated.

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8
Q

How is skeletal muscle characterised?

A

Large
Multinucleate
Striated

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9
Q

How is cardiac muscle characterised?

A

Smaller
Striated
Branched
Uninucleate

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10
Q

How is smooth muscle characterised?

A

Small
No striations
Uninucleate

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11
Q

What types of muscle are striated?

A

Skeletal

Cardiac

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12
Q

What type of muscle is not striated?

A

Smooth.

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13
Q

What type of muscle is multinucleate?

A

Skeletal.

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14
Q

How is skeletal muscle formed?

A

In utero by mononucleate myoblasts.

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15
Q

What are mononucleate myoblasts?

A

Precursor for in utero skeletal muscle development.

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16
Q

What happens to skeletal muscle fibres ing growth?

A

Skeletal muscle fibres can increase.

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17
Q

Can myoblasts replace skeletal muscle cells if damaged?

A

No- they cannot be replaced.

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18
Q

What are skeletal muscle fibres encased in?

A

Connective tissue sheath.

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19
Q

How is skeletal bone attached to bones?

A

Tendons.

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20
Q

How are skeletal muscle cells replaced after injury?

A

Satellite cells.

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21
Q

What do satellite cells do?

A

Replace skeletal muscle cells following injury- they differentiate to follow more muscle fibres.

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22
Q

Is the area between skeletal muscle and tendon clear?

A

No- there is no clear division but rather an area of hybrid cells.

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23
Q

Are satellite cells unlimited?

A

No- they are very limited which means that there is never full healing within skeletal muscle damage.

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24
Q

What happens to surrounding cells when skeletal muscle damage occurs?

A

Induced hypertrophy to try and compensate for the damaged muscle.

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25
Q

Is there ever complete recovery of skeletal muscle?

A

No- some cells will always form scar tissue.

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26
Q

Why is there large amounts of bleeding in skeletal muscle damage?

A

Very vascular structures with many blood vessels.

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27
Q

Why does skeletal muscle never fully recover from injury?

A

Myoblasts cannot replace cells and satellite cells are limited.

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28
Q

What are striations?

A

Stripes of protein bands- they start and finish at a molecular level.

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29
Q

What is the repeated unit between Z-lines in striations called?

A

Sacromere.

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30
Q

What is the sacromere?

A

Functional unit of muscle.

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31
Q

What is the functional unit of muscle?

A

Sacromere.

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32
Q

What are the 2 main proteins that give the sarcomere arrangement?

A

Actin and myosin.

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33
Q

How is myosin structured?

A

Thick filaments with myosin heads.

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34
Q

How is actin structured?

A

Thin filaments with binding sites for myosin head attachment.

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35
Q

What are actin and myosin major components of?

A

Sarcomere.

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36
Q

What does increased actin and myosin action lead to?

A

Increased generation of force.

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37
Q

What can actin and myosin action be altered by?

A

Chemical drugs / nutrients etc.

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38
Q

What cycle does actin and myosin act through?

A

Cross-bridge cycle.

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39
Q

How does the cross-bridge cycle work?

A

ADP + Pi are attached to myosin head.
Myosin head attaches to an exposed binding site on the actin filament.
The phosphate is released and the actin filament can slide along- the ADP is also released as it moves along.
The cross-bridge is broken again when ATP binds to the myosin head- it is broken back down to ADP + Pi and the structure is back at the beginning.

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40
Q

What are attached to the myosin head at the start of the cross-bridge cycle?

A

ADP + Pi.

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41
Q

What happens when a myosin head attaches to an exposed binding site on the actin filament?

A

Phosphate is released and actin filament can slide along- ADP is also released as it moves along.

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42
Q

How is the cross-bridge broken?

A

When ATP binds to the myosin head again.

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43
Q

What happens to ATP that breaks the cross-bridge cycle through binding to the myosin head?

A

Broken back down to ADP + Pi and the structure is back at the beginning again.

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44
Q

What 3 molecules regulate the cross-bridge cycle?

A

Calcium
Troponin
Tropomyosin

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45
Q

What does tropomyosin usually do?

A

Partially blocks myosin binding sites on actin filaments- it is held in position by troponin.

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46
Q

What does troponin do?

A

Holds the tropomyosin in place to block myosin binding sites on actin filaments.

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47
Q

What molecule partially blocks myosin binding sites on actin filaments?

A

Tropomyosin.

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48
Q

What molecule holds tropomyosin in place to block the myosin binding sites on actin filaments.

A

Troponin.

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49
Q

What is the function of calcium?

A

Binds to troponin which allows release of tropomyosin and unblocks the myosin binding site on the actin filament.

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50
Q

Why is calcium required for muscular contraction?

A

Required to bind to troponin and unblock tropomyosin which uncovers the myosin binding sites on the actin filament.

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51
Q

What molecule binds to troponin?

A

Calcium- binds to troponin to move tropomyosin out of the way and unblock myosin binding sites on the actin filament.

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52
Q

What is the main function of the sarcoplasmic reticulum?

A

Storage of Ca2+ ions.

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53
Q

Where does the sarcoplasmic reticulum exist in muscle cells?

A

Extends all over the muscle cell for easy access during extensive contraction.

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54
Q

Where do mitochondria exist in muscle cells?

A

All over the muscle cell for easy access during extensive contraction.

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55
Q

Where is calcium stored in muscle cells?

A

Sarcoplasmic reticulum.

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56
Q

What does a motor unit consist of?

A

Motor neurones and muscle fibres it acts on.

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57
Q

Where can muscle fibres of a motor unit be scattered?

A

Throughout the muscle.

58
Q

What is the force exerted by a muscle called?

A

Tension.

59
Q

What is the force acting on a muscle called?

A

Load.

60
Q

What is tension?

A

Force exerted by a muscle.

61
Q

What is load?

A

Force acting on a muscle.

62
Q

What is a contraction with a constant length called?

A

Isometric.

63
Q

What is an isometric contraction?

A

A contraction with a constant length.

64
Q

Give an example of an isometric contraction.

A

Weightlifting.

65
Q

What is a contraction with shortened length called?

A

Isotonic.

66
Q

What is an isotonic contraction?

A

Contraction with a shortened length.

67
Q

Give an example of an isotonic contraction.

A

Running.

68
Q

What is a contraction with an increasing length called?

A

Lengthening contraction.

69
Q

What is a lengthening contraction?

A

A contraction with increasing length.

70
Q

Give an example of a lengthening contraction.

A

Sitting down.

71
Q

How does a twitch occur?

A

Action potential > Muscle fibre > Twitch

72
Q

What is the latent period?

A

Latent period is the time before the excitation contraction starts.

73
Q

When does contraction occur?

A

Between start of tension and peak tension.

74
Q

Do muscle fibres all have the same contraction time?

A

No- muscle fibres all have different contraction times.

75
Q

What molecule is muscular contraction time dependent on?

A

Ca2+ concentration.

76
Q

How are isometric contractions characterised?

A

Shorter latent periods but extended contraction event.

77
Q

What happens to muscle contraction as load increases?

A

Contraction velocity and distance shortened decrease.

78
Q

How can action potentials add up to give increased contraction?

A

Summation.

79
Q

Why is tetanic tension greater than twitch tension?

A

Calcium levels never get low enough to retain the tropomyosin covering of myosin binding sites on actin filaments.

80
Q

What does less overlap of filaments result in?

A

Less tension.

81
Q

What does too much overlap of filaments result in?

A

Filament interference with each other.

82
Q

What is the optimal length of muscle contraction?

A

The muscle length at which the greatest isomeric tension is seen.

83
Q

What systems are muscles arranged in?

A

Lever systems.

84
Q

What type of action between flexors/extensors does limb action require?

A

Antagonistic action of flexors and extensors.

85
Q

What do lever systems amplify?

A

Muscle shortening velocity which therefore increases manoeuvrability.

86
Q

Do muscles exert more force than the load they bear?

A

Yes.

87
Q

Where does the energy for muscular contraction come from?

A

ATP.

88
Q

How doe ATP power the cross-bridge cycle?

A

Hydrolysis of ATP energises cross-bridges as ATP binds to myosin and dissociates.

89
Q

How does ATP act with calcium?

A

Powers Calcium-ATPase in the sarcoplasmic reticulum which allows contraction to end.

90
Q

How does contraction end?

A

Pumping of calcium back into the sarcoplasmic reticulum through Calcium-ATPase.

91
Q

What leads to muscle fatigue?

A

Repeated muscle stimulation.

92
Q

What does muscle fatigue depend on?

A

Fibre type
Length of contraction
Fitness of individual

93
Q

What can enable fatigued muscle to contract again?

A

Rest periods.

94
Q

What does fatigue prevent?

A

Prevents muscles from using up vast amounts of ATP and not being able to generate new cross-bridge cycles.

95
Q

What factors could cause fatigue in high-intensity, short periods of exercise?

A

Conduction failure due to depolarisation issues
Lactic acid acidifying proteins
ADP/Pi inhibition of cross-bridge cycle

96
Q

What factors could cause fatigue in long-term, low intensity periods of exercise?

A

Decreased blood sugar
Decreased muscle glycogen
Dehydration

97
Q

What is central command fatigue?

A

Central command fatigue refers to a lack of ‘will to win’- the cerebral cortex cannot excite motor neurones.

98
Q

What is fatigue called when the cerebral cortex cannot excite motor neurones?

A

Central command fatigue.

99
Q

How are the types of skeletal muscle fibres classed?

A

Based on them being fast/slow shortening, and the oxidative/glycolytic pathways to generate ATP used.

100
Q

Do fast-twitch fibres have high ATPase activity?

A

Yes.

101
Q

Do slow-twitch fibres have high ATPase activity?

A

No.

102
Q

What characterises oxidative muscle fibres?

A

Increased mitochondria, increased oxidative phosphorylation, increased vascularisation to deliver more oxygen and nutrients.

103
Q

Why do oxidative muscle fibres have increased vascularisation?

A

Delivery of more oxygen and nutrients.

104
Q

What molecule do oxidative muscle fibres include?

A

Myoglobin- increased oxygen delivery.

105
Q

What does myoglobin do in oxidative muscle fibres?

A

Increases delivery of oxygen for oxidative phosphorylation.

106
Q

What colour are oxidative fibres?

A

Red.

107
Q

What characterises glycolytic muscle fibres?

A

Decreased mitochondria, more glycogen and glycolytic enzymes, lower blood supply.

108
Q

What colour are glycolytic muscle fibres?

A

White.

109
Q

Why do glycolytic muscle fibres have reduced vascularisation?

A

Less oxygen needed as glycolytic processes occur rather than oxidative phosphorylation.

110
Q

What are the 3 types of skeletal muscle fibres?

A

Slow oxidative- resist fatigue
Fast oxidative- intermediate resistance to fatigue
Fast glycolytic- fatigue quickly

111
Q

How do slow oxidative muscle fibres respond to fatigue?

A

Resist it.

112
Q

How do fast oxidative skeletal muscle fibres respond to fatigue?

A

Intermediate resistance.

113
Q

How do fast glycolytic skeletal muscle fibres respond to fatigue?

A

Fatigue quickly.

114
Q

What is recruitment?

A

When an increased number of motor units is triggered.

115
Q

When are an increased number of motor units triggered?

A

When there is an increased load.

116
Q

What might an increased load lead to?

A

Increased recruitment of motor units.

117
Q

What types of skeletal muscle fibres are recruited first?

A

Slow oxidative, then fast oxidative then fast glycolytic.

118
Q

What is atrophy?

A

Decline in effectiveness.

119
Q

What is disuse atrophy?

A

Decline in effectiveness due to muscle not being used.

120
Q

What is denervation atrophy?

A

Decline in effectiveness due to nerve/NMJ destruction.

121
Q

What does atrophy cause?

A

Decreases in muscle mass.

122
Q

What effect does exercise have on muscle mass?

A

Hypertrophy (increased mass).

123
Q

How is smooth muscle described?

A

Small, mononucleate, no striation.

124
Q

What is smooth muscle innervated by?

A

Autonomic nervous system.

125
Q

What is different in smooth muscle?

A

Excitation-contraction coupling.

126
Q

How are actin/myosin filaments arranged in smooth muscle?

A

Diagonally.

127
Q

How does the cross-bridge cycle work in smooth muscle?

A

Calcium binds calmodulin.
Calcium-calmodulin complex binds to myosin light chain kinase.
Kinase phosphorylates myosin cross-bridges with ATP.
Phosphorylated cross-bridges bind to actin and contraction can occur.

128
Q

What does calcium bind to in smooth muscle?

A

Calmodulin.

129
Q

What does calcium form when it binds to calmodulin?

A

Calcium-Calmodulin complex.

130
Q

What does the calcium-calmodulin complex bind to?

A

Myosin light chain kinase.

131
Q

What does myosin light chain kinase do?

A

Phosphorylates myosin cross-bridges with ATP- these can bind to actin and contraction can occur.

132
Q

What enables contraction in smooth muscle cells?

A

Binding of phosphorylated myosin cross-bridges to actin- they are phosphorylated by myosin light chain kinase which is activated by the calcium-calmodulin complex.

133
Q

How does smooth muscle relax?

A

Action of myosin light chain phosphatase- dephosphorylates the cross-bridges.

134
Q

What does myosin light chain phosphatase do?

A

Dephosphorylates the cross-bridges to end contraction.

135
Q

Where is calcium sourced from?

A 
Sarcoplasmic reticulum 
Extracellular calcium (VG-channels)
136
Q

Is there the same amount of sarcoplasmic reticulum in smooth muscle as in skeletal muscle?

A

No- smooth muscle has less.

137
Q

In skeletal muscle, does one AP release enough calcium to saturate all troponin sites?

A

Yes.

138
Q

In smooth muscle, does one AP release enough calcium to stimulate contraction?

A

Not always- only some sites are activated and they are graded.

139
Q

What is smooth muscle tone?

A

Tone is a basal level of calcium in cells which means there is a constant state of tension.

140
Q

Is smooth muscle always single-unit?

A

No- it can be single-unit (GIT, BV), or multi-unit (Airways/large blood vessels etc).c

141
Q

Can an organ have different properties of single/multi-unit smooth muscle cells?

A

Yes- most organs have bits of both to add variation and increase ability to perform function.

Science for Medicine (19 decks)

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