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Physiology > Smooth and cardiac muscle > Flashcards

Smooth and cardiac muscle Flashcards

1
Q

Where is smooth (visceral) muscle found?

A

In walls of hollow organs

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2
Q

What does smooth muscle produce? (contractions)

A

Continuous contractions of relatively low force

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3
Q

What is involuntary control influenced by?

A

By nervous system, hormones and local metabolites

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4
Q

How much muscle mass is contracted?

A

Contraction of whole muscle mass

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5
Q

Characteristics of smooth muscle cells

A

Smaller, spindle-shaped cells with a single nucleus, lack striations

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6
Q

Characteristics of smooth muscle fibres

A
  • Bound together
  • Irregular
  • Varying according to the organ
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7
Q

What is the type of nucleus in smooth muscle?

A

Elongated and centrally located nucleus

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8
Q

What is the activity of smooth muscle modulated by?

A

A.N.S input

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9
Q

What controls cross-bridging ?

A

Controlled via effect of alterations in [Ca2+] on regulatory myosin light chain rather than troponin

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10
Q

How are contractile proteins arranged?

A
  • Not in myofibrils

- Do not appear striated

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11
Q

Shape of smooth muscle cells

A

Spindle-shaped cells that taper at the end

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12
Q

What is the dense body anchored by?

A
  • Intermediate filaments (desmin)

- Thin filaments (actin)

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13
Q

What is the purpose of the thick and thin filaments?

A

Both stabilise and link the dense body to the plasma membrane

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14
Q

How are thin and thick filaments linked?

A

Thin filaments cross link to myosin thick filament

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15
Q

What does the dense body allow for?

A

Allows for shortening of cells in characteristic bulging pattern

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16
Q

Where is the dense body located? (line)

A

Analogous to Z-line

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17
Q

What is the shape of the lattice of smooth muscle?

A

Elongated-diamond shaped lattice

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18
Q

How many filaments are in the arrangement of smooth muscle?

A

10-15 actin filaments/myosin

filament

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19
Q

What do contractions do to cell?

A

Shorten it

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20
Q

What happens where bulging is present?

A

The filaments attaches to plasma membrane

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21
Q

What does the contraction require (and not)

A
  • Requires Ca2+

- Not troponin

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22
Q

How is actin pulled?

A

Along longer distances and in opposite directions

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23
Q

What is smooth muscle contraction induced by?

A

Calcium

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24
Q

What can be graded?

A
  • Calcium released
  • Stretch
  • Hormones
  • ANS input
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25
Q

Where does extracellular fluid-electrochemical gradient enter?

A

Via voltage gated and receptor regulated channels in plasma membrane

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26
Q

What is the extracellular fluid-electrochemical gradient dependent on?

A
  • Depolarisation

- Second messenger

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27
Q

Calcium release from internal stores (direct or indirect and via what?)

A

Mainly indirect

  • via activation of phospholipase C,
  • Production of inositol-3-phosphate (IP3)
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28
Q

Calcium release from internal stores

A
  • via activation of phospholipase C,

- Production of inositol-3-phosphate (IP3)

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29
Q

Is the calcium release from internal organs direct or indirect and why?

A

Mainly indirect as a result of receptor activation - can be modulated

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30
Q

How is the internal store calcium channel opened?

A

Via specific receptor

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31
Q

What is the process of smooth muscle contraction?

A
  1. Muscle excitation
  2. Rise in cytosolic Ca2+
  3. Series of biochemical events
  4. Phosphorylation of myosin cross bridges in thick filament
  5. Bind of actin and myosin at cross bridges
  6. Contraction
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32
Q

What is the process of skeletal muscle contraction?

A
  1. Muscle excitation
  2. Rise in cytosolic Ca2+
  3. Physical repositioning of troponin and tropomyosin
  4. Uncovering of cross-bridge binding sites on actin in thin filament
  5. Binding of actin and myosin at cross bridges
  6. Contraction
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33
Q

Where is the Ca2+ from in smooth muscle?

A

Mostly from extracellular fluid

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34
Q

Where is the Ca2+ from in skeletal muscle?

A

All from intracellular sarcoplasmic reticulum

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35
Q

How does phasic smooth muscle contraction

A

Contracts in bursts driven by action potentials

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36
Q

An example of where phasic smooth muscle present?

A

Digestive tract

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37
Q

What is the resting membrane potential of tonic smooth muscle?

A

-55mV to -40mV

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38
Q

How is tonic smooth muscle always contracted?

A

Partially contracted at all times

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39
Q

Give an example of where tonic smooth muscle is present

A

Walls of arterioles

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40
Q

Why is Ca2+ always present in cytosol in tonic smooth muscle?

A

As VDCCs are open at these potentials

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41
Q

Where is most Ca2+ from in phasic SM

A

From extracellular fliud

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42
Q

What does Dihydropyridine (DHP) receptors function as in phasic SM?

A

As Ca2+ channels

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43
Q

What does Ca2+ trigger in phasic SM?

A

Triggers opening of Ca2+ channels in the SR

open

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44
Q

How can IP3 be generated?

A

By G-protein linked receptors that engage noradrenaline

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45
Q

How can Ca2+ be boosted in tonic SM?

A

By sarcoplasmic reticulum

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46
Q

What does sarcoplasmic reticulum have?

A

IP3 receptors

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47
Q

What is the function of IP3 receptors?

A

They conduct Ca2+ release channels

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48
Q

What tubules & sarcoplasmic reticulum are in smooth muscle and sarcoplasmic reticulum?

A

No T-tubules and poorly developed sarcoplasmic reticulum

49
Q

Is there sufficient Ca2+ to enable cross-bridging throughout cell and why?

A

Yes as SM are small cells

50
Q

How do multiunits of smooth muscle function?

A

Independently

51
Q

What type of smooth muscle is multiunit?

A
  • Phasic

- Neurogenic

52
Q

Where is multiunit present?

A
  • walls of large blood vessels
  • small airways of lung
  • muscles of eye
  • base of hair follicles
53
Q

What type is a single unit?

A

Tonic or phasic and myogenic

54
Q

How does a single unit function?

A

Syncytia

55
Q

What does syncytia mean?

A

Linked by gap junctions

56
Q

Where is a single unit present?

A
  • Digestive
  • Reproductive
  • Urinary tracts
  • Small blood vessels
57
Q

What type of activation is multi-unit involved in?

A

A.N.S neurogenic activation

58
Q

What type of activation is single unit involved in?

A

Myogenic activation (ANS modulation)

59
Q

What are the two major categories of smooth muscle based on type of excitation?

A
  • Multi-unit

- Single unit

60
Q

How can depolarisation and extent of calcium elevation be modified?

A

Can be neurally and hormonally modified to grade frequency and force of activity

61
Q

Why is there depolarisation in pacemaker potential?

A

Due to shifts in passive ionic flux

62
Q

How is pacemaker potential initiated?

A

By non-contractile pacemaker cells

63
Q

How does the AP spread in pacemaker potential?

A

AP spreads via gap junctions

64
Q

Where is slow-wave potential present?

A

Only in smooth muscle of digestive tract (nonmuscle

pacemaker cells

65
Q

Slow-wave potential polaristaion

A

Alternating depolarisation and hyperpolarisation

66
Q

Is threshold always reached by depolarisation in slow-wave potential?

A

No

67
Q

What is the threshold of depolarisation of slow-wave potential influenced by?

A

By neural and local factors

68
Q

What is always present in slow-wave potential and why?

A

Always some Ca2+ present to maintain some level of tone

69
Q

What is the type of excitable tissue involved in end-plate potential?

A

Skeletal muscle

70
Q

What is the type of excitable tissue involved in receptor potential?

A

Afferent neurons

71
Q

What is the type of excitable tissue involved in summation of excitatory post-synaptic potentials?

A

Efferent neurons, interneurons

72
Q

What are the types of excitable tissue involved in pacemaker potential?

A
  • Smooth muscle

- Cardiac muscle

73
Q

What are the types of excitable tissue involved in slow-wave potential?

A

Smooth muscle (in digestive tract only)

74
Q

Give a description of the pacemaker potential event

A

Gradual depolarisation of the membrane on its own because of shifts in passive ionic fluxed accompanying automatic changes in channel permeability

75
Q

Give a description of the slow-wave potential event

A

Gradual alternating hyperpolarizing and depolarising swings in potential brought about by unknown mechanism; depolarizing swimg may or may not reach threshold.

76
Q

How is the portion of cross-bridges activated varied by ?

A

By varying cytosolic Ca2+

77
Q

In the graduation of single-unit smooth muscle contraction does ANS initiate contraction?

A

No but can modify rate

78
Q

In the graduation of single-unit smooth muscle contraction, what varies / remains the same regarding fibres?

A

Number of fibres contracting remains the same but amount of tension varies

79
Q

What does ANS express in single-unit smooth muscle?

A
  • Cholinergic

- Adrenergic receptors

80
Q

Which type of muscle, smooth or skeletal has a wider range of lengths at which active tension can be generated?

A

Smooth muscle

81
Q

Is there a loss of cross-bridge potential in smooth muscle in stretched state and if not why?

A

No as actin-myosin overlap persists even in stretched state - no bare-zone of myosin

82
Q

Give an example of why the wider range of lengths at which active tension in smooth muscle can be generated important or it’s function?

A

Detrusor muscle adapts to bladder filling (stress -

relaxation response) and retains the ability to generate force for bladder emptying.

83
Q

How is the resting length for smooth muscle?

A

It’s below optimal length- more stretchable

84
Q

Speed of smooth muscle

A

Slow and economical

85
Q

What is the latch phenomenon?

A

Actin and myosin engagement and detachment takes a longer time

86
Q

What is an advantage of the smooth muscle length–tension relationship?

A

It inherently relaxes when stretched

87
Q

What is O2 delivery in smooth muscle sufficient for?

A

For low rate of oxidative phosphorylation

88
Q

What are the types of cells in cardiac muscle?

A

Striated cardiomyocytes

89
Q

What does excitation contraction coupling in cardiac muscle involve?

A

Troponin - same as skeletal muscle

90
Q

What is the calcium source from in cardiac muscles?

A

From ECF

91
Q

What type of modulation is in cardiac muscle?

A

A.N.S modulation

92
Q

What does ECF store?

A

Pacemaker

93
Q

What drives the syncitia in cardiac muscle?

A

Gap junction driven

94
Q

What is visible in cardiac muscle cells?

A
  • Abundant mitochondria

- Lipid droplets and glycogen granules

95
Q

Does skeletal or cardiac muscle have a more defined T tubule system and sarcoplasmuc Reticulum?

A

Skeletal

96
Q

What are cardiac muscle fibres interconnected by?

A

Intercalated discs

97
Q

What are the two types of membrane junctions that intercalated discs contain?

A
  • Mechanically important desmosomes

- Electrically important gap junctions

98
Q

How are bundles of cardiac muscles arranged?

A

Spirally around the ventricle.

99
Q

What happens when cardiac muscle fibres contract?

A

They ‘wring’ blood from the apex to the base where the major arteries exit.

100
Q

What do desmosomes provide and contribute to?

A
  • Provide strong adhesion between cells

- Contribute to mechanical strength

101
Q

Where is cardiac muscle excitation pacemaker potential controlled at?

A

At nodes in heart (SA and AV)

102
Q

What is the sympathetic nervous system’s effect on the cardiac muscle excitation curve?

A
  • Increases potential slope
    gradient
  • Decreases maximum
  • Negative potential
103
Q

What is the parasympathetic nervous system’s effect on the cardiac muscle excitation curve?

A
  • Flattens potential slope
  • Increases maximum
  • Negative potential.
104
Q

What is the heart innervated by?

A

The autonomic nervous system

105
Q

What is the cardiac muscle interconnected by?

A

By gap junctions found in intercalated discs that join

cells together

106
Q

What are the characteristics of cardiac muscle fibres?

A
  • Highly organised, striated, slender, and short fibres
107
Q

What is the classification of skeletal muscle?

A

Striated muscle, voluntary muscle

108
Q

Give a description of skeletal muscle?

A

Bundles of long, thick, cylindrical, striated, contractile, multinucleate cells that extend the length of the muscle

109
Q

What is a typical location of skeletal muscle?

A

Attached to bones of skeleton

110
Q

What is the function of skeletal muscle?

A

Movement of body in relation to external environment

111
Q

What is the classification of cardiac muscle?

A

Striated muscle, involuntary muscle

112
Q

Give a description of cardiac muscle

A

Interlinked net-work of short, slender, cylindrical,

striated, branched, contractile cells connected cell to cell by intercalated discs

113
Q

Give a location of cardiac muscle

A

Wall of heart

114
Q

Give a function of cardiac muscle

A

Pumping of blood out of heart

115
Q

What is the classification of smooth muscle?

A

Unstriated muscle, involuntary muscle

116
Q

Give a description of smooth muscle

A

Loose network of short, slender, spindle- shaped,

unstriated, contractile cells that are arranged in sheets

117
Q

Give typical locations of smooth muscle

A

Walls of hollow organs and tubes, such as stomach and blood vessels

118
Q

Give a function of smooth muscle

A

Movement of contents within hollow organs

Physiology (28 decks)

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