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Physiology 1 > Lecture 7: Basic physiology of muscles > Flashcards

Lecture 7: Basic physiology of muscles Flashcards

1
Q

Describe skeletal muscle

A

Large fibres, multinucleate cells

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2
Q

How do skeletal muscle cells appear beneath a microscope?

A

Stiped/striated

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3
Q

Describe cardiac muscle

A

Striated, smaller, branched, unicnucleate

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4
Q

How are cardiac muscle cells joined?

A

In series by junctions called intercalated disks

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5
Q

Describe smooth muscle fibers

A

Small, lack striations, spindle shaped cells

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6
Q

What is skeletal muscle attached to?

A

Bone

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7
Q

What muscle types are capable of generating spontaenous action potentials?

A

Smooth and cardiac

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8
Q

What is the diameter of a skeletal muscle fiber?

A

10-80micrometers

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9
Q

How long are skeletal muscle fibers extended?

A

The entire length of the muscle

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10
Q

What usually innervates a skeletal muscle fiber?

A

One nerve ending

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11
Q

What membrane encloses a skeletal muscle fiber?

A

Sarcolemma

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12
Q

What surrounds the myofibrils?

A

Sarcoplasm (intracellular fluid)

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13
Q

What does the sarcolemma consist of?

A

True cell membrane (plasma membrane) and an outer coat

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14
Q

What makes up the outercoat of the sarcolemma?

A

Thin layer of polysaccharide material containing numerous collagen fibrils

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15
Q

What happens to the sarcollema at the end of a muscle fiber?

A

The surface layer fuses with a tendon fiber

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16
Q

What do tendon fibers collect into?

A

Bundles to form muscle tendons

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17
Q

What do muscle tendons connect?

A

Muscles to bone

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18
Q

What does the sarcoplasm contain large quantities of?

A

K, Mg, Pi, enzymes

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19
Q

Why are mitochondria abundant in the sarcoplasm?

A

ATP synthesis

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20
Q

What stores and releases calcium in the sarcoplasm?

A

Sarcoplasmic reticulum (specialised endoplasmic reticulum of skeletal muscle)

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21
Q

How many myofibrils do muscle fibers contain?

A

Several hundred to several thousand

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22
Q

What are myofibrils composed of?

A

1500 adjacent myosin filaments

3000 actin filaments

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23
Q

What are thick and thin filaments composed of?

A

Thick: myosin
Thin: Actin

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24
Q

What protein attaches myosin to the Z disk?

A

Titin

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25
Q

What forms between overlapping mysoin and actin filaments?

A

Cross bridges

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26
Q

A sarcomere stretches from ____ to _____

A

Z disk

next z disk

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27
Q

The A band consist of…

A

The entire length of the myosin filament

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28
Q

The I band is…

A

Light filaments only

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29
Q

How is the sarcoplasmic reticulum arranged?

A

As a repeating series of networks around the myobrils from one A-I junction to the next

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30
Q

What is the name for where the sarcoplasmic reticulum meets at the A-I junction?

A

Terminal cisterna

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31
Q

What do cisterna act as reservoirs for?

A

Ca2+

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32
Q

What are T tubules?

A

The plasma membrane of the sarcoplasmic reticulum invaginates transverselty to form a tubular system

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33
Q

What is contained in T tubules?

A

Voltage-sensor proteins

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34
Q

When are voltage-sensor proteins activated?

A

When the membrane depolarizes inducing the sarcoplasmic reticulum to release Ca2+

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35
Q

What do T tubules and the adjacent cisternae form?

A

A triad

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36
Q

What else is present in the sarcoplasmic reticulum?

A

Mitochondria to provide energy

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37
Q

Describe resting stage of the sarcomere

A

Some interdigitation of thin and thick filaments

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38
Q

The contracted stage with increased interdigitation of thick and thin filaments is also called

A

Concentric contraction

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39
Q

What name is given to the stretched stage where thin and thick filaments do not interact?

A

Eccentric contraction

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40
Q

What name is given to the mechanism of contraction of the sarcomere?

A

Sliding filament mechanism

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41
Q

What does myosin consist of?

A

6 polypeptide chains: 2 heavy, 4 light (tail and head)

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42
Q

What do thin filaments consist of?

A

Actin, tropomyosin, troponin

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43
Q

What makes up the backbone of the thin filment?

A

F-actin (2 in a helix), troponin intermittently attached

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44
Q

What are the loosely bound protein subunits of troponin?

A

T, I, C

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45
Q

What comprises the motor unit?

A

A motor neuron and the muscle fibers it innervates

46
Q

What is between the motor neuron and the muscle fibers it innervates?

A

The neuromuscular junction

47
Q

What is the transmitter responsible for generating an end plate potential in muscle fibers?

A

Acetylcholine

48
Q

What happens when acetylcholine is released at the neuromuscular junction?

A

Opens Ach gated cation channels

49
Q

What happens once Ach gated cation channels open at the neuromuscular junction?

A

Large quantities of sodium ions diffuse into the interior of the muscle fiber membrane, causing depolarisation

50
Q

What happens once the action potential has depolarized the muscle membrane?

A

The sarcoplasmic reticulum releases large amounts of Ca2+

51
Q

What happens once Ca2+ is released into the sarcoplasm?

A

It binds to troponin complex, allowing, causing changes in tropomyosin, allowing myosin heads to attach (contraction is initiated)

52
Q

What is the first stage of the contraction cycle?

A

Attachment (myosin head is tightly bound to actin molecule) Rigor state

53
Q

What is the second stage of the contraction cycle, after attachment.

A

Release

54
Q

What happens during the release stage of the contraction cycle?

A

ATP binds to the myosin head, inducing release of actin (muscle is relaxed)

55
Q

What happens after the release stage of the contraction cycle?

A

Bending

56
Q

What happens during the bending stage of the contraction cycle?

A

ATP causes further changes to myosin head, causing it to bend, this initiates breakdown of ATP to ADP which remain in the myosin head

57
Q

After the myosin head binds to the new site, the inorganic phosphate is released. What does this do?

A

Increases binding affinity for the myosin to the actin

Myosin head generates a force to straighten up, power stroke shortens sarcomere

58
Q

What else happens during the power stroke?

A

ADP is lost from the myosin head

59
Q

What happens when ADP is released?

A

Reattachment of the myosin head to the actin filament, rigor stage is re-established

60
Q

What happens to Ach during skeletal muscle relaxation?

A

It is recycled by being reabsorbed into the synaptic knob

61
Q

What happens to calcium ions to cause relaxation?

A

Active transport pumps in the SR pump it from the cytosol back into cisternae

62
Q

What happens when Ca2+ concentration decreases during relaxation?

A

Ca2+ unbinds from troponin, tropomyosin recovers the binding sites, tension is no longer produced/maintained

63
Q

What name is given to process by which skeletal muscle contracts after receiving an action potential?

A

Excitation-contraction coupling

64
Q

What are the two types of smooth muscle?

A

Multiunit smooth muscle

Unitary (single unit) smooth muscle

65
Q

Describe multiunit smooth muscle?

A

Each fibre behaves as a separate unit

Dense innervation

66
Q

Describe unitary smooth muscle.

A

Cells are linked by gap junctions

Chacterized by spontaneous pacemaker activity

67
Q

What is smooth muscle important in maintaining?

A

Homeostasis

68
Q

Where is smooth muscle found?

A

Blood vessels, GI tract and gallbladder, Ureter and urinary bladder, uterus, respiratory system, eye

69
Q

What is the diameter of a smooth muscle cell?

A

5 micrometers

70
Q

What is the length of a smooth muscle cell?

A

20-500 micrometers

71
Q

What surrounds each smooth muscle cell?

A

Basal lamina, small amount of connective tissue

72
Q

Why is there some connective tissue between smooth muscle cells?

A

Allow for passage of nerve tracts and blood vessels

73
Q

What are the two main types patterns of contraction of smooth muscle?

A

Phasic and tonic

74
Q

Give an example of phasic contraction

A

Oesophagus: contracts only when food enters

75
Q

When is tonic contraction seen?

A

Sphincters: relax to open to allow material to pass through

76
Q

What pattern of contraction is seen in vascular smooth muscle?

A

Variable tonic contraction

77
Q

Why does vascular smooth muscle have variable tonic contraction?

A

To control pressure and quantity of blood in a particular tissue

78
Q

What is smooth muscle capable to do to a greater degree then skeletal muscle?

A

Greater degree of contraction

79
Q

How are contractile units different in smooth muscles vs skeletal?

A

Less regular in smooth

80
Q

How else is smooth muscle contraction different to that of skeletal?

A

Slow onset and relaxation, prolonged contraction and slower cross-bridge cycling

81
Q

What happens when calcium ions enter a smooth muscle cell?

A

Induces the release of Calcium ions from the sarcoplasmic reticulum

82
Q

What does calcium bind to in smooth muscle cells that is different from cardiac muscle?

A

Calmodulin (CaM)

83
Q

What once calcium is bound to calmodulin in a smooth muscle cell?

A

Calmodulin activates myosin light chain kinase (MLCK) resulting in phosphorylation

84
Q

What happens once the mysosin light chain kinase phosphorylates the myosin?

A

the head attaches to actin. In the presence of ATP, the myosin head bends to produce contraction

85
Q

What is required to bring about relaxation in smooth muscle?

A

A calcium pump

86
Q

How is the calcium pump in smooth muscle different to that in skeletal muscle?

A

It acts on a slower timescale

87
Q

Other than the calcium pump, what else is important in cessation of smooth muscle contraction?

A

Myosin phosphatase

88
Q

What determines the time to relaxation in smooth muscle cells?

A

Myosin phosphatase

89
Q

What does myosin phosphatase do?

A

Removes phosphate from the myosin light chain, causing detachment of the myosin head from actin

90
Q

How are muscle fibres arranged in cardiac muslce?

A

Spiral arrangement

91
Q

What is the result of spiral arrangement of cardiac muscle fibres during ventricular contraction?

A

Upward squeezing of ventricular blood from apex

92
Q

What is found between myocaridal cells?

A

Intercalated discs

93
Q

What do intercalated discs contain?

A

Desmosomes (formed of protein plaques)

94
Q

What do desmosomes in the intercalated discs do?

A

Transfer the force from cell to cell

95
Q

What allows for the passage of electrical signals in cardiac mucles?

A

Gap junction in the intercalated dics

96
Q

What is the size of cardiac muslce?

A

Smaller than skeletal
10-20 micrometer diameter
50-100 micrometer long

97
Q

How are the nucleus/’s arranged in cardiac muscle?

A

Single, centrally placed

98
Q

How are T tubules different in cardiac muscle compared to skeletal muscle?

A

Short and broad (larger than skeletal muslce’s)

No triads

99
Q

How is the sarcoplasmic reticulum of cardiac muscle arranged differently to that of skeletal muscle?

A

It is organised as an anastomosing network (not expanded cisterna)

100
Q

Why does cardiac muscle contain large numbers of mitochondria?

A

It is completely dependent on aerobic metabolism

101
Q

What else is found in cardiac muscle?

A

Glycogen and lipid inclusions which store energy, myoglobin stores oxygen

102
Q

Cardiac muslce contracts without _____ stimulation

A

Neural

103
Q

What are pacemakers?

A

Specialised cardiac muslce cells, more excitable than others and thus contract first

104
Q

How are pacemaker cells regulated?

A

Innervated by cells of the nervous system

105
Q

In cardiac cells, T tubules form…

A

Diads

106
Q

How does cardiac muscle resist stretching as the heart fills with blood?

A

Desmosomes in intercalated discs link adjacent cells forming a physical bond

107
Q

How does action potential enter a cardiac muscle cell?

A

From an adjacent cell opening

108
Q

What happens when calcium ions enter the cardiac muscle cell?

A

The bind to troponin to initiate contraction

109
Q

When does relaxation occur in cardiac muslce?

A

When Ca2+ unbinds from troponin and is pumped back into the sarcoplasmic reticulum

110
Q

Thin filament attachment occurs where in each muscle type?

A

Skeletal: Z disc
Cardiac: Z disc
Smooth: Dense bodies

Physiology 1 (9 decks)

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