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From Flashcardlet > A&P Chapter 9 Part 2 > Flashcards

A&P Chapter 9 Part 2 Flashcards

1
Q

What are the charges of the resting membrane?

A

Inside is slightly negative, outside is slightly positive

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2
Q

How is end plate potential generated?

A
  • The binding of ACh opens ion channels for Na+ and K+
  • Na+ diffuses in faster than K+ exits the cell
  • The membrane charge becomes less negative (depolarization)
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3
Q

Where do Na+ and K+ travel?

A

Na+ travels into the cell

K+ travels out of the cell

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4
Q

Which travels faster, Na+ or K+?

A

Na+ moves into the cell faster than K+ moves out

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5
Q

What happens to membrane potential when depolarization occurs?

A

The membrane potential becomes less negative (closer to zero)

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6
Q

How does depolarization generate an action potential?

A
  • Depolarization causes an end plate potential
  • The end plate potential spreads to adjacent membrane areas, opening their ion channels for Na+
  • Once the threshold of membrane potential is reached, an action potential is generated
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7
Q

How is the membrane repolarized?

A

Na+ gates close and K+ gates open - K+ rapidly diffuses out of the cell because it has a high concentration inside the cell, which restores the negative inside charge of the cell

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8
Q

What is the refractory period?

A

During repolarization, the cell cannot be further stimulated until it restores its electrical conditions

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9
Q

How are the ionic conditions restored?

A

Na+K+ATPase pumps

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10
Q

What does action potential result in?

A

The contraction of a muscle

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11
Q

Which last longer, the electrical event or the contraction?

A

The contraction can far outlast the electrical even that triggered it

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12
Q

What is excitation contraction coupling?

A

A sequence of events by which transmission of an action potential along the sarcolemma causes the myofilaments to slide

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13
Q

Does the action potential directly cause the filaments to slide?

A

No, the action potential causes a rise in calcium which binds to filaments allowing them to slide

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14
Q

How does the action potential cause the release of calcium?

A

The action potential along the T tubules causes proteins to change shape. The conformational shape allows calcium channels to open in the terminal cistern of the SR

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15
Q

Where does calcium bind once released from the SR? What does this do?

A

To troponin on the thin filament, causing tropomyosin to rotate out of the way of the active site on actin

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16
Q

When does contraction begin?

A

When the myosin head binds to actin forming a cross bridge

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17
Q

What happens to the T tubule proteins when the action potential ceases?

A

The proteins change back to their original shape and no longer allow the passage of calcium

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18
Q

What happens once calcium is removed back into the SR?

A

The blocking ability of tropomyosin is restored and relaxation occurs

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19
Q

What position is the myosin head in when the cross bridge cycle is about to begin?

A

The high energy cocked position, so it is ready to attach to actin

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20
Q

Why do cross bridges form and break many times during contraction?

A

Because as the filaments slide across one another, the myosin head attaches and pulls the thin filament, then detaches and does it again

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21
Q

What happens if high calcium levels in the cytosol are sustained?

A

Apotosis (cell death)

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22
Q

What is the power (working) stroke?

A

ADP and P are released from the myosin head and myosin pivots and bends, changing to its bent, low energy state
*As a result, myosin pulls actin towards the M line

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23
Q

How does a cross bridge detach?

A

ATP binds to myosin and the link weakens between the myosin head and actin, eventually causing the head to detach

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24
Q

How does the myosin head return to its original cocked position?

A

ATP is hydrolyzed to ADP and P and the head returns to prestroke position

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25
Q

What two molecules continue the cross bridge cycle

A

ATP and calcium

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26
Q

What is rigor mortis?

A

Actin and myosin become irreversibly cross linked producing the stiffness in muscles right after death (until muscle starts to break down)

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27
Q

What is muscle tension?

A

The force exerted by a contracting muscle on an object

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28
Q

What is a load?

A

The opposing force exerted on the muscle by the weight of the object to be moved

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29
Q

What is an isometric contraction?

A

If the muscle tension develops but the load is not moved

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30
Q

What is an isotonic contraction?

A

If the muscle tension overcomes the load and the muscle shortens

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31
Q

What is a motor unit?

A

One motor neuron and all the muscle fibers it innervates (could be 4-100)

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32
Q

Which fibers contract when a motor unit fires?

A

All the fibers it innervates contract

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33
Q

What kind of muscles have a small motor unit?

A

Fine control muscles like the fingers

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34
Q

What kind of muscles have a large motor unit?

A

Weight bearing muscles like the hips

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35
Q

Stimulation of one nerve fiber of a motor unit would produce a strong/weak contraction of part/whole muscle?

A

Weak contraction of the whole muscle because the muscle fibers of a motor unit are spread throughout the muscle

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36
Q

What is a myogram?

A

A device that records contractile activity

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37
Q

What is a tracing?

A

The line recording from a myogram

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38
Q

What is muscle twitch?

A

The motor unit’s response to a single action potential of its motor neuron

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39
Q

What are the three twitch phases?

A
  1. Latent period
  2. Period of contraction
  3. Period of relaxation
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40
Q

What happens during the latent period?

A
  1. Cross bridges are beginning to form
  2. No measurable muscle tension generated
    Occurs during the first few ms after stimulation while EC coupling occurs
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41
Q

What happens during the period of contraction?

A
  1. Cross bridges are active
  2. Tracing rises to a peak
  3. If tension is great enough to overcome the resistance of the load, the muscle shortens
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42
Q

What happens during the period of relaxation?

A
  1. Contractile force is declining
  2. Muscle tension decreases
  3. Muscle returns to original length
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43
Q

What initiates the period of relaxation?

A

The reentry of calcium into the SR

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44
Q

Which takes longer, contraction or relaxation?

A

Relaxation

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45
Q

What kind of twitches are brief?

A

Eye

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46
Q

What kind of twitches are sustained?

A

Gastroc and soleus of the calf

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47
Q

Do healthy muscles twitch?

A

No, their contractions are smooth and sustained

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48
Q

What influences the strength of a contraction?

A

The demand placed on the muscle

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49
Q

What are two characteristics that influence the grade of contractions?

A
  1. Change in frequency of stimulation

2. Change in strength of stimulation

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50
Q

How does the nervous system increase its muscle force?

A

By increasing the firing rate of motor neurons

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51
Q

Why is the second twitch always stronger than the first?

A

Because the muscle has not yet relaxed

52
Q

What are two ways the frequency of a stimulation adds?

A

Temporal and wave summation

53
Q

What three things happen if stimulus strength holds and muscles are stimulated at an increasingly faster rate?

A
  1. Relaxation time between twitches is shorter
  2. The concentration of calcium rises
  3. The degree of wave summation becomes greater
54
Q

What terms are used when stimulus strength progresses to a sustained and quivering contraction?

A

Unfused or fused tetanus

55
Q

What does the graph of unfused tetanus look like?

A

Increasingly wavy pattern up to a peak

56
Q

What does the graph of fused tetanus look like?

A

Plateau

57
Q

How does the muscle relax during unfused tetanus?

A

Partial relaxation between stimuli

58
Q

How does the muscle relax during fused tetanus?

A

No relaxation

59
Q

What is the cut off point to where stimulation frequency can increase to?

A

When it reaches maximum muscle tension

60
Q

What happens quickly to a muscle during fused tetanus?

A

It fatigues quickly and tension drops to zero as the muscle can no longer contract

61
Q

What does recruitment refer to?

A

The force of contraction is more controlled and precise

62
Q

How does increasing the strength of stimulation affect muscle fibers?

A

Increase of voltage to muscle calls on more muscle fibers

63
Q

What is a subthreshold stimulus?

A

It produces no observable contractions

64
Q

What is the threshold stimulus?

A

It produces the first observable contraction

65
Q

What is the maximal stimulus?

A

The strongest stimulus that still increases contractile force - the point where all the muscle’s motor units are recruited

66
Q

What does the graph look like leading up to the maximal stimulus?

A

There is a small hump at the threshold stimulus, steadily increasing until it reaches a certain height where the force does not produce higher spikes in the graph (maximal stimulus)

67
Q

What happens when a stimulus is continued to increase beyond the maximal stimulus?

A

Stronger contractions are NOT produced

68
Q

What principle is the recruitment process organized by?

A

The size principle

69
Q

Which motor units are activated first and why?

A

The motor units with the smallest fibers because they are controlled by the most highly excitable neurons

70
Q

What happens to contractile strength as the motor units with larger fibers are excited?

A

Contractile strength increases

71
Q

What is the threshold of the motor unit with the largest fibers?

A

The maximal threshold - the least excitable neurons

72
Q

When is the motor unit with the largest fibers activated?

A

Only when the most powerful contractions are necessary

73
Q

Are all motor units recruited simultaneously? Why?

A

Usually not as some fibers are resting, helping prolong strong contraction by preventing fatigue

74
Q

What are two types of isotonic contractions?

A
  1. Concentric

2. Eccentric

75
Q

What is a concentric contraction?

A

The muscle shortens and does work

76
Q

What is an eccentric contraction?

A

The muscle lengthens while generating force

77
Q

Which isotonic contractions produce more force?

A

Eccentric contractions produce 50% more force

78
Q

Does an isometric contraction shorten or lengthen the muscle?

A

Neither, but tension still develops

79
Q

What are two functions of isometric contractions?

A
  1. Posture

2. Holding joints stationary while other moves (Quads isometric while the knee bends)

80
Q

Do cross bridges form in isometric contractions?

A

Yes, but the filaments don’t move

81
Q

What is muscle tone and why is it important?

A

Relaxed muscles are always slightly contracted which keeps muscles firm, healthy, and ready to respond

82
Q

What is the sole energy source for contraction, and what does is supply energy for (3)?

A

ATP supplies energy to move/detach cross bridges, operate calcium pumps in SR, and return Na+ and K+ to their original homes

83
Q

What three pathways are used for ATP regeneration?

A
  1. Direct phosphorylation
  2. Anaerobic respiration
  3. Aerobic respiration
84
Q

What is the high energy molecule that is stored in muscles?

A

Creatine phosphate

85
Q

What is the formula for creating ATP using creatine phosphate?

A

CP + ADP –> Creatine + ATP

86
Q

What enzyme catalyzes the formation of ATP from creatine phosphate?

A

Creatine Kinase (CK or CPK)

87
Q

Do muscles store more CP or ATP?

A

2-3 times more CP stored in muscles

88
Q

Where is CP made?

A

The liver/kidney/pancreas, and is then transported to muscle

89
Q

How long of a muscle contraction is sustained when phosphate is transferred to ADP to create ATP?

A

15 seconds of sustained muscle contractions (100m dash)

90
Q

What is ATP generated from in anaerobic respiration?

A

The break down (glycolysis) of glucose or glycogen

91
Q

How is ATP brought into skeletal muscles after generated from anaerobic respiration?

A

Facilitated diffusion

92
Q

What is the net gain of ATP from anaerobic respiration?

A

2 ATP

93
Q

What is the product of the glycolysis of glucose?

A

Pyruvic acid

94
Q

What happens to pyruvic acid if oxygen is available?

A

It enters the mitochondria and undergoes aerobic respiration to continue to make ATP

95
Q

What happens to pyruvic acid if oxygen is NOT available?

A

Pyruvic acid yields lactic acid

96
Q

Why would oxygen not be available for aerobic respiration in the muscles?

A

If muscles are contracting vigorously, they compress the blood vessels impairing blood and oxygen flow

97
Q

Where does lactic acid flow to?

A

80% diffuses into the blood, the liver can convert it back to glucose, or the liver/heart/kidneys can use lactic acid as an energy source

98
Q

How does ATP production in anaerobic respiration compare to aerobic (amount and time)

A

It produces only 5% of what aerobic makes, but produces it 2.5 times faster

99
Q

When is anaerobic respiration used?

A

During periods of moderately strenuous activity (30-40 seconds of sustained maximal muscle contractions - 400m dash)

100
Q

What is the energy source of aerobic respiration?

A

CP is limited so muscles metabolize food to ATP

101
Q

What percentage of all ATP is made by aerobic respiration?

A

95% of ATP

102
Q

Where does aerobic respiration occur?

A

Mitochondria

103
Q

How is glucose broken down (partially/entirely)?

A

Entirely

104
Q

What is the formula of the aerobic metabolism of glucose?

A

Glucose + Oxygen –> CO2 + Water + ATP

105
Q

How many ATP does the aerobic respiration of glucose yield?

A

36 ATP

106
Q

What type of contraction is aerobic respiration able to supply?

A

Prolonged contractions

107
Q

What three substances can be sent to the mitochondria in aerobic respiration to be metabolized?

A

Pyruvic acid, amino acids, fatty acids

108
Q

What are some sources of ATP for short exercise?

A
  1. ATP stored in the muscle
  2. ATP generated from CP (direct phos)
  3. ATP generated from glycogen breakdown (anaerobic)
109
Q

What is the source of ATP for prolonged exercise?

A

ATP generated by the breakdown of glucose from food (aerobic)

110
Q

What is aerobic endurance?

A

The length of time a muscle can continue to contract using aerobic pathways

111
Q

What is anaerobic threshold?

A

The point at which muscle metabolism converts to anaerobic glycolysis

112
Q

Which pathway would produce a surge of energy?

A

direct phosphorylation of CP

113
Q

Which pathway would produce a burst of energy?

A

Anaerobic respiration

114
Q

Which pathway would produce a prolonged source of energy?

A

Aerobic

115
Q

What four factors influence the force of muscle contraction?

A
  1. Number of muscles stimulated
  2. Size of fibrils
  3. Frequency of stimulation
  4. Degree of stretch
116
Q

How does the number of muscles stimulated effect the force of muscle contraction?

A

The more motor units recruited, the greater the force produced

117
Q

How does the size of the fibrils effect the force of muscle contraction?

A

The bulkier the muscle, the greater the tension developed and the greater the strength

118
Q

What is internal tension?

A

The force generated by cross bridges - as a muscle contracts, the internal tension stretches the CT sheaths

119
Q

What is external tension

A

When the CT sheaths become taut, they transfer their tension to the load

120
Q

How does the frequency of stimulation effect the force of muscle contraction?

A

Rapid stimulation summates and the muscle tension becomes stronger

121
Q

Where is the optimal operating length of a muscle fiber (in general terms)?

A

Where is can generate maximal force

122
Q

Why should the muscle be slightly stretched to be at its optimal operating length?

A

The thin and thick filaments overlap allowing sliding along the entire length of the filament

123
Q

What happens if a muscle stretches past the thick and thin filaments overlapping?

A

The heads don’t have anything to attach to and the muscle can’t contract

124
Q

What happens if a muscle is so shorten that the thin filaments are touching one another?

A

The thin filaments begin to inhibit one another

125
Q

What four factors increase contractile force?

A
  1. Large number of fibers
  2. Large fiber size
  3. High frequency stimulation
  4. Muscle stretched slightly over 100% of its resting length

From Flashcardlet (133 decks)

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