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Physiology > Muscle > Flashcards

Muscle Flashcards

1
Q

What is the method of excitation for skeletal muscle?

A

alpha motor-neurons

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2
Q

What is the method of excitation for cardiac muscle?

A

self-depolarization

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3
Q

The regular arrangement of ____ within the myofibrils gives them a striated appearance.

A

Proteins

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4
Q

Invaginations of the sarcolemma, called the____, extend into the cell itself.

A

Transverse-tubules (t-tubules)

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5
Q

The tunnels of the t-tubules provide a quick delivery system for the spread of ____ to the skeletal muscle cell.

A

Action potentials

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6
Q

Excitation of skeletal muscle requires the release of _____ from the sarcoplasmic reticulum.

A

intracellular calcium

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7
Q

The triad allows for a close coupling of what?

A

action potentials with intracellular calcium release

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8
Q

What is the contractile unit of a skeletal muscle cell?

A

sarcomere

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9
Q

Actin, thin filament, is composed of a globular protein called G-actin arranged into a double stranded helical structure called…

A

F-actin

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10
Q

What myosin light chain serves as a structural role?

A

alkali light chain

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11
Q

What myosin light chain is involved in regulating the ATPase capability of the myosin head?

A

regulatory myosin light chain

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12
Q

Filamentous protein that lies in the groove of the double-stranded actin.

A

Tropomyosin

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13
Q

What has a binding site for the myosin head, which is covered up by tropomyosin?

A

Each G-actin

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14
Q

Each tropomyosin extends over …

A

7 G-actin molecules

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15
Q

When calcium binds to the TnC subunit, this leads to …

A

a conformational change in troponin

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16
Q

The conformational change in troponin from calcium binding to TnC, allows ….

A

tropomyosin to move out of the actin groove

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17
Q

When tropomyosin moves out of the actin groove it …

A

exposes the actin active sites for myosin to bind to

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18
Q

What binds tropomyosin?

A

TnT

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19
Q

What is the function of TnI?

A

binds to actin, and inhibits actin and myosin from interacting

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20
Q

The central point of the sarcomere to which the thick filaments are anchored by associated proteins

A

M line

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21
Q

The anchor points for the thin filaments and the boundaries for the sarcomeres

A

Z-discs

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22
Q

A region that contains the entire length of the thick filaments

A

A band

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23
Q

A region that contains the portion of the thick filaments that does not overlap with the thin filaments

A

H zone

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24
Q

A region that contains the portion of the thin filaments that does not overlap with the thick filaments

A

I band

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25
Q

Structural proteins maintain a _____ of fibers within a sarcomere, with the thin filaments arranged around the thick filaments.

A

hexagonal cross-section

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26
Q

During a muscle contraction in which the sarcomere shortens, what will happen to the length from Z-disc to Z-disc?

A

decrease

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27
Q

During a muscle contraction in which the sarcomere shortens, what will happen to the length of the H zone?

A

decrease

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28
Q

During a muscle contraction in which the sarcomere shortens, what will happen to the length of the A band?

A

stays the same

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29
Q

During a muscle contraction in which the sarcomere shortens, what will happen to the length of the I band?

A

decrease

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30
Q

Converts the electrical signal of an action potential into the chemical signal of neurotransmitter.

A

Alpha motor neuron

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31
Q

The steps of excitation-contraction coupling occur where?

A

at the neuromuscular junction

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32
Q

In the first step of the ECC, the action potential spreads down the axon of the alpha motor neuron, leading to a …

A

depolarization of the end-bulb (fast-gated sodium channels)

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33
Q

In the ECC, the depolarization of the end-bulb leads to the opening of …

A

voltage-gated calcium channels, and calcium flows down its electrochemical gradient into the cell

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34
Q

In the ECC, the influx of calcium into the cell leads to the fusion of membrane-bound vesicles, which contain …

A

the neurotransmitter acetylcholine

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35
Q

The membrane bound vesicles containing acetylcholine, fuses with what?

A

The active zone of the plasma membrane

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36
Q

In ECC when the vesicles fuse with the plasma membrane, acetylcholine undergoes …

A

exocytosis and diffuses through the synaptic cleft

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37
Q

In the ECC, the neurotransmitter is released at an area of the muscle fiber called the …

A

motor end-plate

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38
Q

The binding of acetylcholine to its receptors on the motor end-plate leads to the opening of …

A

ligand-gated cation channels

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39
Q

What type of receptors does the acetylcholine bind to?

A

ligand-gated cation channels; nicotine cholinergic receptors

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40
Q

Acetylcholine is enzymatically digested in the …

A

synaptic cleft

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41
Q

The enzyme that digests acetylcholine is called

A

acetylcholinesterase

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42
Q

What portion of the digested ACh is typically taken up by the alpha motor neuron and can then be recycled to create new molecules of acetylcholine?

A

Choline portion

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43
Q

The binding of acetylcholine to ligand-gated receptors at the motor end-plate opens what?

A

non-specific cation channels

44
Q

Both sodium and potassium pass through the non-specific cation channels, but because sodium influx is much greater than potassium efflux, …

A

the cell (motor end-plate) depolarizes

45
Q

Why is it impossible to generate an action potential in the motor end-plate region?

A

There are no fast voltage-gated sodium channels

46
Q

Instead of an action potential the motor end-plate generates an …

A

end-plate potential (EPP)

47
Q

What is an end-plate potential (EPP)?

A

A localized electrical signal; an example of the excitatory post-synaptic potentials (EPSPs)

48
Q

What sends electrical signals bidirectionally away from the motor end-plate to adjacent regions of the sarcolemma?

A

EPP

49
Q

The electrically stimulated adjacent regions of the sarcolemma do contain … that can open once threshold is reached. This allows an action potential to spread through out the sarcolemma and t-tubules.

A

voltage-gated sodium channels

50
Q

What occurs due to quantal release of ACh from the terminal button?

A

miniature end-plate potentials (MEPP)

51
Q

The motor end-plate lacks …

A

a stable RMP

52
Q

It is hypothesized that quantal release of ACh causing MEPPs occurs to maintain …

A

the integrity of the neuromuscular junction

53
Q

How does the production of MEPPs maintain the integrity of the neuromuscular junction?

A

the quantal release of ACh may keep the ACh receptors localized to the motor end-plate

54
Q

The depolarization from a MEPP is not of sufficient magnitude to …

A

depolarize adjacent regions of the sarcolemma to threshold

55
Q

What are the 3 “safety” factors to ensure neuromuscular transmission?

A
  1. More ACh is released than needed to depolarize the motor end-plate.
  2. The MEP contains 4-12 times more ACh receptors than needed to ensure neuromuscular transmission
  3. The EPP magnitude is 3-4 times greater than required to initiate depolarization of the sarcolemma
56
Q

Physostigmine is an anti-acetylcholinesterase, what is the direct effect on neuromuscular transmission?

A

Prolonged post-synaptic response to ACh

57
Q

w-Conotoxin blocks voltage-gated calcium channels in nerves, what is the direct effect on neuromuscular transmission?

A

Prevents exocytosis of ACh

58
Q

Dendrotoxin blocks voltage-gated K+ channels, what is the direct effect on neuromuscular transmission?

A

Prevents repolarization of presynaptic membrane and increases release of ACh

59
Q

Tetrodotoxin blocks voltage-gated Na+ channels, what is the direct effect on neuromuscular transmission?

A

Prevents nerve and muscle action potentials

60
Q

Tetanus blocks synaptic vesicle exocytosis in inhibitory interneurons, what is the direct effect on neuromuscular transmission?

A

Produces skeletal muscle spasms

61
Q

Curare blocks the acetylcholine receptor, what is the direct effect on neuromuscular transmission?

A

Produces flaccid paralysis

62
Q

In order for the action potential to initiate muscular contraction , …levels must rise.

A

intracellular calcium

63
Q

The main source for calcium influx is via an organelle called the …

A

Sarcoplasmic Reticulum (SR)

64
Q

The SR contains a calcium binding protein called …

A

calsequestrin

65
Q

Calsequestrin helps to maintain a …

A

lower concentration gradient in the SR for free calcium

66
Q

What serves as reservoirs of calcium within the cell?

A

Junctional SR regions/terminal cisterns

67
Q

As the action potential spreads down the t-tubules, … in the sarcolemma are activated.

A

“L-type” calcium channels - dihydropyridine receptors (DHPR)

68
Q

DHPRs serve as both … in skeletal muscle and voltage-gated calcium channels inn cardiac muscle.

A

voltage sensors

69
Q

In skeletal muscle, each DHPR is linked to a calcium release channel in the membrane of the SR, called a …

A

ryanodine receptor (RYR)

70
Q

As the wave of depolarization spreads along the sarcolemma and down the T-tubules, ____ are stimulated.

A

L-type calcium channels (DHPR)

71
Q

DHPR stimulates the … in the SR to open.

A

ryanodine calcium release channels

72
Q

Once _____ opens, calcium flows down its concentration gradient from the SR and into the cytosol (sarcoplasm)

A

Ryanodine Receptor (RYR)

73
Q

Because there is no influx of calcium from the ECF, the form of calcium release is called…

A

Calcium channel induced calcium release (CCICR)

74
Q

What form of calcium release is not essential in skeletal muscle, but used from cardiac muscle excitation?

A

Calcium induced calcium release (CICR)

75
Q

What type of calcium release does require the influx of calcium rom the ECF?

A

CICR

76
Q

In CICR, depolarization of the t-tubule stimulates the ____ to open, and calcium moves down its concentration gradient into the cell.

A

L-type voltage-gated calcium channels to open

77
Q

The calcium in the cell directly stimulates the RYR to release calcium from the …

A

SR stores

78
Q

T-tubules are located at the junction of the …

A

A and I bands

79
Q

In ECC, calcium flows down its electrochemical gradient, from the SR into the sarcoplasm, where it binds to the regulatory protein _____.

A

troponin

80
Q

The binding of calcium to TnC leads to a conformational change that moves _____ from the actin active sites.

A

tropomyosin

81
Q

When calcium binds to TnC & tropomyosin is removed from the actin active sites, the myosin head is free to bind to the thin actin filaments to …

A

initiate contraction

82
Q

In what state of the cross-bridge cycle does the myosin head use its ATPase capability to hydrolyze a bound ATP into ADP and phosphate?

A

Cocked state

83
Q

In the cross-bridge cycle the hydrolysis of ATP allows the myosin head to “cock” and move into an appropriate binding position ….

A

further away from the M-line

84
Q

With the ADP bound, the myosin head has a high affinity for ____

A

the actin filament

85
Q

Cross-bridge formation can only occur if there is a …

A

high intracellular concentration of calcium

86
Q

If there is a high intracellular concentration of calcium and tropomyosin has moved away from the actin groove, the myosin head …

A

binds to the actin filament, forming a bridge between the two filaments (cross-bridge state)

87
Q

In what state of the cross-bridge cycle does the myosin head release its bound ADP and inorganic phosphate?

A

Power-stroke state

88
Q

What powers the movement of the myosin head from a 90 degree angle to a 45 degree angle?

A

Energy from the ATP hydrolysis

89
Q

In what state of the cross-bridge cycle does the myosin head remain attached to the actin filament?

A

Attached state

90
Q

The binding of an ATP molecule to the myosin head allows the myosin to …

A

release its attachment to actin

91
Q

With ATP bound, the myosin has a ____ for the actin filament.

A

low affinity

92
Q

In what state of the cross-bridge cycle does the binding of ATP to the myosin head allow it to release from actin?

A

Released state

93
Q

If ATP levels become severely depleted, cross-bridges will remain in the attached state leading to …

A

sustained skeletal muscle contractions (rigor mortis)

94
Q

As long as ___ is present in the sarcoplasm, and ___ are plentiful, the contraction process will continue.

A

Calcium; ATP stores

95
Q

In order to terminate muscle contraction, the cell must resequester calcium into the SR, this occurs largely through use of a …

A

Sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) pump

96
Q

The SERCA pump moves calcium from the ____ into the ____

A

sarcoplasm into the SR

97
Q

What form of transport does the SERCA pump use?

A

moves calcium against its concentration gradient using primary active transport

98
Q

SERCA channels are also associated with a regulatory protein called …

A

phospholamban

99
Q

When ____, phospholamban produces an increase in the activity of the SERCA pump.

A

phosphorylated

100
Q

In the relaxation of skeletal muscle the regulatory protein phospholamban produces an increase in the activity of the SERCA pump, thus increasing the ….

A

Resequestration of calcium in the SR

101
Q

In the relaxation of skeletal muscle when calcium is pumped into the SR, it is subsequently bound to …

A

Calsequestrin

102
Q

Calsequestrin maintains a ____ concentration of calcium in the SR.

A

low free

103
Q

When calsequestrin maintains a low free concentration of calcium in the SR it provides a ____ for the SERCA channel to operate against.

A

lower concentration gradient

104
Q

Another function of calsequestrin, besides maintaining a low free concentration of calcium, is localizing calcium in the _____

A

Junctional SR

105
Q

By calsequestrin localizing calcium in the junctional SR, it makes it available for easy release during …

A

CICR or CCICR

106
Q

As SR calcium levels drop, calcium …., and tropomyosin ….; preventing further interaction between the myosin and actin filaments, until another excitation occurs.

A

calcium dissociates from TnC, & tropomyosin re-covers the actin active site

Physiology (16 decks)

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