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BRS (RF) > Muscular contraction > Flashcards

Muscular contraction Flashcards

1
Q

What are the three muscle types?

A

Smooth muscle
Cardiac muscle
Skeletal muscle

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2
Q

What type of control is smooth muscle under control by?

A

Involuntary control from the autonomic nervous system

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3
Q

Describe the nucleation of smooth muscle

A

Mononucleated

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4
Q

Describe the nucleation of cardiac muscle

A

Mononucleated

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5
Q

How are cardiac cells connected?

A

Physically and electrically connected, ensuring that contraction signals are transmitted through cells, and the entire heart contracts as a singe unit

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6
Q

What type of nervous control, controls cardiac muscles?

A

Autonomous (myogenic)

and under influence of autonomic nervous system (cardiac control centre)

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7
Q

What is the nucleation of skeletal muscles?

A

Multinucleate

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8
Q

Which type of control are skeletal muscles subjected to?

A

Voluntary control by the somatic nervous system

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9
Q

How are skeletal muscles attached to bone?

A

Attached via tendons, consequently facilitating movement of bone through contraction

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10
Q

What connective tissue sheath wraps muscle?

A

Epimysium

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11
Q

What is the purpose of the epimysium?

A

Enables muscle to contract and more powerfully while maintain structural integrity.

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12
Q

How are muscle fibres arranged?

A

Arranged in bundles, known as fascicles

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13
Q

Which connective tissue layer surrounds the fascicles?

A

Perimysium

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14
Q

How does the fascicular arrangement support muscular contraction?

A

Triggers specific movement of a muscle by activating a subset of muscle fibres within a fascicle of the muscle

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15
Q

What is contained within each fascicle?

A

Myofibres, encased in a thin layer of collagen and reticular fibres, the endomysium

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16
Q

Which layer surrounds the outer layer of each myofibre?

A

Endomysium

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17
Q

What does the endomysium contain?

A

Surrounds the extracellular matrix of cells, plays a role in transferring force produced by muscle fibres to tendons

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18
Q

What is the term used to describe the plasma membrane of myofibres?

A

Sarcolemma

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19
Q

What is the term used to define the cytoplasm of myofibres?

A

Sarcoplasm

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20
Q

Which proteins are spent in myofibrils?

A

Myosin and actin

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21
Q

What is the smallest functional unit of a skeletal muscle fibre?

A

Sarcomere

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22
Q

What are t tubules?

A

Extensions of the sarcolemma that penetrate into the centre of skeletal muscle cells, a conduit of action potentials

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23
Q

What is the role perfumed by the sarcoplasm?

A

Cytoplasm of myocyte consisting of greater proportion of glycogen granules, myoglobin and mitochondria

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24
Q

What is the sarcoplasmic reticulum?

A

Network of fluid-filled tubules, constitutes the main intracellular calcium store in striated muscle, cardinal role in the regulation of excitation-contraction coupling.

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25
Q

What is the line that defines the region of a micofibril contained between two cytoskeletal structures?

A

z lines

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26
Q

Why is there a strained appearance of skeletal muscle fibres?

A

This is due to the arrangements of the thick and thin myofilaments within each sarcomere.

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27
Q

What is the A band?

A

Composed of thick filaments, containing myosin, span the centre of the sarcomere, extending towards the Z-discs

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28
Q

Which protein comprises the thick filaments?

A

Myosin

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29
Q

What is the M-line?

A

Thick filaments are anchored at the middle of the sarcomere by myomesin

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30
Q

What is the I band?

A

Lighter regions contain thin actin filaments anchored at the z-discs by alpha-actinin. The thin filaments extend into the A band towards the M-line overlapping the regions of thick filaments.

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31
Q

Why is the A band darker?

A

Due to the thicker composition of myosin filaments, in addition to overlapping actin filaments

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32
Q

What is the H-zone?

A

Middle of the A band, thin filaments do not extend into this region, there is no actin present.

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33
Q

What does a single sarcomere contain?

A

Single dark A band, with half of the I band on either side

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34
Q

What effects does contraction have on the distance between z-discs?

A

Distance shortens

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35
Q

What effect does contraction have on the length of myofilaments?

A

The length of myofilametns are not altered, however slide across each other

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36
Q

How is the length of the A band affected during contraction?

A

Does not change (thick myosin filaments remain constant length)

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37
Q

Which zones and bands decreases during contraction?

A

H-zone

I band

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38
Q

Why does the H-zone and I band decrease?

A

These regions represent areas where filaments do not overlap, however during contraction area of filament overlap increases

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39
Q

Which protein comprises the thin filaments?

A

Actin

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40
Q

Which site does myosin bind upon on each globular actin monomer?

A

Myosin binding site

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41
Q

Which two regulatory proteins are associated with the myosin binding site?

A

Troponin

Tropomyosin

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42
Q

Which troponin binds to actin?

A

Tn1

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43
Q

Which troponin binds to tropomyosin?

A

TnT

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44
Q

Which troponin binds to calcium ions?

A

TnC

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45
Q

Describe the structure the thick myofilaments:

A

Myosin protein complexes: 6 polypeptides: Two myosin heavy chains, four light chain molecules.

Heavy chains consist of a tail region, flexible hinge region, and globular head which contains an actin binding site, and a binding site for ATP

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46
Q

Which chain interacts with actin?

A

Globular heavy chain head (comprises of actin binding site)

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47
Q

How are myosin protein filaments arranged in respect to M-lines and Z-discs? (Direction)

A

Tails towards M-line, head extending towards the Z-discs

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48
Q

What is the function of Titin?

A

Align thick filaments, adds elastic element to sarcomere, titan anchored at M-line

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49
Q

Briefly describe the sliding filament theory:

A

Arrangement and interactions between thin and thick filaments enable for shortening of the sarcomeres, subsequently generating force.

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50
Q

In which direction are actin filaments pulled during sarcomere contraction?

A

Pulled towards the M-lines, sliding passed the thick myosin filaments within the sarcomere

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51
Q

Which cation influence is responsible for sarcomere contraction?

A

Calcium ions

52
Q

What does tropomyosin do?

A

Tropomyosin is wound around actin filaments, and encapsulates the myosin-binding sites, preventing actin binding to myosin.

53
Q

Where are calcium ions released upon stimulation in muscle cells?

A

Sarcoplasmic reticulum

54
Q

At a presynaptic membrane, action potentials cause which voltage gated ion channels to open?

A

Calcium ion voltage gated ion channels

55
Q

The influx of calcium into the pre-synaptic knob results in what occurring?

A

Vesicles fusing with the presynaptic membrane, and releasing acetylcholine into the synaptic cleft by exocytosis

56
Q

What is the fate of acetylcholine during a synapse within the neuromuscular junction?

A

ACh diffuses across synaptic cleft, binding to ACh receptors on the post-synaptic membrane within the motor end plate of the sarcolemma.
Inducing an action potentials
Voltage gated sodium channels open to depolarise membrane

Acetylcholinesterase regulate ACh activity

57
Q

What type of coupling is induces by action potentials?

A

Excitation-contraction coupling

58
Q

Which enzyme hydrolyses acetylcholine in the synaptic cleft?

A

Acetylcholinesterase

59
Q

Which structure propagates action potentials along the sarcolemma into the muscle cell?

A

T-tubules

60
Q

Which voltage-sensitive receptors are present on the sarcolemma respond to action potential propagation via t tubules?

A

Dihydropyridine receptors (DHPR)

61
Q

Which receptors are mechanically linked with DHPR?

A

Ryanodine receptors

62
Q

What are ryanodine receptors?

A

Calcium channel in sarcoplasmic reticulum membrane

63
Q

What effect is induced by action potential stimulation of DHPR?

A

DHPR undergoes conformational change by detecting potential difference, triggers opening of RyR, enabling calcium ion efflux from SR into the sarcoplasm.

64
Q

Which channels do calcium ions efflux from the SR into the sarcoplasm?

A

Ryanodine receptors

65
Q

Upon calcium binding to TnC, what effect is induced?

A

Causes tropomyosin to exposure the myosin binding sites of actin filament

66
Q

How do the myosin globular heads bind to the myosin binding site?

A

Actin binding site of myosin globular head forms cross bridge with myosin binding site

67
Q

How are calcium ions removed from the sarcoplasm?

A

Actively transported into the sarcoplasmic reticulum continuously whilst action potential continue

ATP driven pump, uptake > release rate

68
Q

When does muscle contact stop?

A

Signal termination from the motor neurone, depolarisation of sarcolemma and t-tubules
Ryanodine receptors close, and tropomyosin occupies the myosin binding sites on the actin filaments

69
Q

What is the first stage of excitation-contraction coupling? (Calcium)

A

In the presence of calcium, movement of troponin from tropomyosin chain, movement exposed the myosin binding site on the surface of actin chain.

70
Q

How does the myosin head bind to the myosin binding sites on actin filaments?

A

Charged myosin head is attracted to actin, binding actin at its respective actin-binding site forming the cross bridge.
Cross bridge formation occurs when myosin head attaches to actin, ADP and Pi bound to myosin.

71
Q

What happens to ADP and Pi upon myosin head binding to actin?

A

Released, resulting in myosin to form a stronger attachment to the actin, myosin head retracts towards the M-line, consequently pulling the actin filament inwards tinpot the A band
Movement is defined as power stroke.

72
Q

What is the power stroke?

A

Movement of thin actin filament

73
Q

What molecule is required for myosin head detachment?

A

ATP

74
Q

Where does ATP bind to the myosin head?

A

ATP binding site on myosin globular head

75
Q

How is ATP hydrolysed upon binding to the ATP-binding site on myosin globular head?

A

Intrinsic ATPase activity on myosin into ADP and Pi

76
Q

Why is ATP hydrolysed by intrinsic ATPase enzymes on the myosin globular head?

A

The energy released from ATP hydrolysis changes the angle of the myosin head into a cocked position, position for further movement.

77
Q

What is the cocked position?

A

Myosin is in a high energy configuration.
Energy is expended during the power stroke, end of power stroke, myosin head is in a low energy stage. ADP is released during the power stroke, however the cross bridge is intact, actin and myosin are bound
ATP readily attaches to myosin globular head, detachment enables cross bridge cycle to recur.

78
Q

Where are the upper motor neurones located?

A

The primary motor cortex, provides the descending corticospinal tract, decussating at the medullary pyramids within the medulla oblongata

79
Q

What is a motor unit?

A

Term used to describe a lower motor neurone, and all the muscle fibres it innervates

80
Q

What is an innervation ratio?

A

Defines the number of muscle fibres innervated by a single motor neurone,

81
Q

What is the relationship between innervation ratio and level of control?

A

The innervation ratio is inversely proportional to the level of control.

82
Q

What expected innervation ratios enable fine control and delicate movements?

A

Innervation ratios will tend to be small, enabling nuances of movement of the entire movement.

83
Q

What effect does a high innervation ratio have on muscular movements?

A

Coarse movements
No necessity for individual muscle fibres to undergo highly coordinated, differentiated contractions to produce a fine movement.

84
Q

Which type of motor fibres are fast, fatigue resistant?

A

FR type IIa

85
Q

Which muscle fibre type is oxidative?

A

Type IIa

86
Q

Why are type IIa fibres fast?

A

ATP hydrolysis is faster, resulting in a faster cross-bridge cycling
Actin filaments are pulled to the M-line of the sarcomere at a faster rate
Oxidative fibres are more resistant to fatigue considering that ATP is primarily produced through acerbic pathways

87
Q

What is the structure of type IIA fibres?

A

Large diameter cell bodies, large dendritic tress, thicker axons and faster conduction velocity

88
Q

Which type of fast fibres are glycolytic?

A

Type IIb

89
Q

Which type of muscle fibres are fast and fatiguable?

A

Type IIb

90
Q

Why are TypeIIb fibres fast and fatiguable?

A

Primarily generate ATP through anaerobic glycolysis, produce less ATP per cycle, thus fatigue at a quicker rate, permitting them to be used for short periods
Rapid forceful contractions associated with quick powerful movements

91
Q

What is the structure of FF typeIIb fibres?

A

Large diameter, and volume of glycogen

Do not posses substantial numbers of mitochondria, limited capillary supply, insignificant amounts of myoglobin.

92
Q

Which type of fibre is type 1?

A

Slow oxidative

93
Q

Why are slow type 1 fibres oxidative?

A

Maximises ability to generate ATP through aerobic metabolism
High presence of mitochondria increases sites of oxidative phosphorylation to synthesis ATP
Enabling slow oxidation fibres to contract for longer periods due to ATP supply

94
Q

How are type 1 fibres supplied in accordance to their respective ability?

A

Extensibly supplied with blood capillaries to continuously supply oxygen.
High presence of myoglobin, oxygen binding molecules (high affinity); stores oxygen within fibre, results in dark red pallor

95
Q

What colour are slow type 1 fibres?

A

Red

96
Q

Why are slow type 1 fibres red?

A

High proportion of myoglobin content

97
Q

Describe the aerobic capacity of slow type 1 fibres?

A

Aerobic capacity is high

98
Q

What functions are performed by slow type 1 fibres?

A

Posture, isometric contractions and stabilising bones & joints.

Do not produce high tension, thus not used for powerful fast movements that require high amounts of energy and rapid cross bridge cycling

99
Q

Describe the structure of slow type 1 fibres:

A

Small soma diameter, small dendritic tress, thin axons, slowest conduction velocity.

100
Q

Describe the proportion & distribution of slow and fast twitch muscles:

A

Random distribution and proportions

101
Q

What colour are fast fatigue resistant type IIa fibres?

A

Pink

102
Q

What colour are FF IIb fibres?

A

White

103
Q

Describe the aerobic capacity of FF Type IIB fibres:

A

Low

104
Q

Describe the anaerobic capacity of FF TypeIIA/B fibres:

A

High

105
Q

Which fibres produce high tension?

A

Type IIb

106
Q

Which fibre produce low tension?

A

Type I

107
Q

What are the two methods of regulating muscle contraction and activation of motor units?

A

Recruitment and rate coding

108
Q

What is recruitment of motor units?

A

Refers to the activation of additional motor units to accomplish an increase in contractile strength in a muscle.

Activation of motor neurone will subsequently result in the respective muscle fibres being stimulated.

Multiple activated motor neurones will result in further muscle fibre activation, thus stronger muscle contraction.

Higher recruitment = stronger contractile force

109
Q

In which order premotor units recruited?

A

In order of smallest to largest (Slow to fast twitch), as contraction increased, governed by size principle

110
Q

Under low levels of required force, how is fine control adopted?

A

Activation of low innervation ratio motor units.

111
Q

What is rate coding?

A

Force produced by a single motor unit is determined by the number of muscle fibres it innervates
Determinant of force is the frequency in which the muscle fibres are stimulated by their inneverating axon.

Motor units fire range of frequencies = slow units fire at a lower frequency

112
Q

How does motor unit firing rate influence force produced?

A

Increasing firing rate increases the force produced by the unit

Summation occurs when units fire at frequency too fast, allows mucle to relax between arriving action potentials.

113
Q

What are neurotrophic factors?

A

Peptides that support the growth, survival and differentiation of developing and mature neurones

Prevents neuronal death and promotes growth post injury ]

Motor unit and fibre characteristics depends on the nerve that innervates them

114
Q

What happens to slow muscles when cross innervated with fast twitch nerves?

A

Exhibits characteristics functions and properties of that to fast muscle
Muscle emulates the properties of the innervating nerve

115
Q

What are the two main types muscular contractions?

A

Isometric and isotonic

116
Q

What is an isometric contraction?

A

Tension in the muscle is constant
Tension is produced, however muscle length does not change (Sarcomere shortening)
increasing muscle tensioN Though the force produced cannot overcome resistance provided by load

117
Q

What is a concentric contraction?

A

Involves the muscle shortening to move a load

118
Q

What is an eccentric contraction?

A

Muscle tension diminishes, and the muscle lengthens.

119
Q

What is muscle plasticity?

A

Muscle plasticity is defined as the ability of a given muscle to alter its structural and functional properties in accordance with the environmental conditions imposed on it.

120
Q

During conditions of severe conditions, muscle fibres are converted into which type?

A

Type 1 fibres to II

121
Q

What effect does microgravity have on muscle fibre types?

A

Promotes shift from slow to fast muscle fibre types

122
Q

Which system senses gravity?

A

Vestibular system

123
Q

How does microgravity cause deconditioning?

A

Results in diminished land on the msk system and hydrostatic pressure difference, contributes towards muscular atrophy

124
Q

How does ageing influence the types of fibres present?

A

Associated with loss of type 1 and 2 fibres

Preferential loss of type II fibres

Results in a larger proportion of type 1 fibres in aged muscle

(Evidence = slower contraction time)

125
Q

How does muscle training influence muscle fibre types?

A

Conversion from IIb to IIa

BRS (RF) (38 decks)

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