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Physiology > Membrane & Muscle > Flashcards

Membrane & Muscle Flashcards

1
Q

What are 4 functions of the plasma membrane?

A

1) Separate ICF from ECF
2) Selective barrier to diffusion
3) Selective transporter of nutrients and ions
4) Interpret and carry signals

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2
Q

What do proteins function as in the plasma membrane?

A

Channels, carriers, receptors, and enzymes

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3
Q

What are important factors for passive transport?

A
  • Lipid solubility
  • Concentration gradient
  • Size
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4
Q

Does the rate of passive transport depend on temperature?

A

Nope

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5
Q

What are 4 characteristics of carrier-mediated transport?

A

1) Specificity
2) Saturation (waiting time)
3) Competition
4) Temperature-sensitivity

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6
Q

What are the 2 types of carrier-mediated transport?

A

1) Passive (facilitated diffusion)

2) Active (“pumps”)

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7
Q

What is primary active transport?

A

When the mechanism uses ATP directly

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8
Q

What is secondary active transport?

A

When the mechanism is powered by a mechanism that directly uses ATP

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9
Q

What is the relationship between solutes and water concentration?

A

Inverse – less solutes means a higher concentration of water

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10
Q

Define isotonic in regards to a cell

A
  • A solution in which the cell retains its original volume because it does not gain or lose water
  • Impermeable solutes = 300 mOsm
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11
Q

Define isosmotic

A

A solution in which the TOTAL solutes (impermeable and permeable) = 300 mOsm

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12
Q

Do permeable solutes contribute to the dilution of water?

A

Nope

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13
Q

What happens when concentration gradient equals electrical gradient?

A

The ion will stop moving down its concentration gradient

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14
Q

What is resting membrane potential?

A

A dynamic steady state in which inward current is exactly matched by outward current

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15
Q

What impact will increasing extracellular potassium have on Em?

A

It will raise Em, resulting in depolarization

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16
Q

What impact will increasing permeability of potassium have on Em?

A

It will decrease Em, resulting in hyperpolarization

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17
Q

What impact will increasing permeability of sodium have on Em?

A

Raise Em, resulting in depolarization

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18
Q

What impact will decreasing sodium potassium pumping have on Em?

A

Raise Em, resulting in depolarization

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19
Q

What impact will increasing the permeability of chlorine have on Em?

A

No impact

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20
Q

Uncharged and nonpolar molecules are highly ___ soluble

A

Lipid

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21
Q

Charge and polar molecules are highly ___ soluble

A

Water

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22
Q

What is equilibrium potential?

A

When the concentration gradient and the net electrical gradient become balanced

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23
Q

What direction is the sodium gradient?

A

Into the cell

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24
Q

What direction is the potassium gradient?

A

Outside of the cell

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25
Q

What causes Em to change?

A

Any change in ionic current

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26
Q

When do aquaporins close?

A

Never

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27
Q

When do voltage-gated sodium channels open?

A

Upon depolarization

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28
Q

What is the speed of the response from a voltage-gated sodium channel?

A

Very fast

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29
Q

How long does it take for voltage-gated sodium channels to self-inactivate?

A

Very short time

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30
Q

What happens when a cell becomes depolarized?

A

1) Potassium current increases through aquaporin channels, tending to repolarize
2) Voltage-gated sodium channels open, producing a sodium current
3) If the current of sodium is more than the potassium current an action potential starts

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31
Q

What does the peak of an action potential represent?

A

When the sodium current equals the potassium current

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32
Q

When do voltage-gated potassium channels open?

A

Upon depolarization

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33
Q

What is the speed of the response from a voltage-gated potassium channel?

A

Slow

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34
Q

How long do voltage-gated potassium channels stay open?

A

As long as depolarization persists

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35
Q

What is the membrane considered during the downstroke (repolarization)?

A

Refractory

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36
Q

What happens with progressive repolarization?

A
  • Sodium channels reset
  • Potassium current decreases as Em approaches Ek
  • Potassium channels begin to close
  • Excitability is restored
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37
Q

What is the absolute refractory period?

A

When not enough sodium channels are open to make the sodium current greater than the potassium current, results in total inexcitability

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38
Q

What is the relative refractory period?

A

When there are less sodium channels and/or more potassium channels open than normal, the threshold is higher than normal and can still be excited

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39
Q

What impact does increasing extracellular potassium have on an action potential?

A

Potassium from inside the cell with leak outside, inhibiting repolarization

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40
Q

What effect does decreasing temperature have on an action potential?

A

Stops the Na/K pump, which stops membranes from getting excited

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41
Q

What effect does increasing extracellular calcium have on an action potential?

A

Calcium stabilizes sodium channels, so more depolarization would be needed to excite

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42
Q

What effect does local anesthetic have on an action potential?

A

“Super calcium”; will cause threshold to increase dramatically

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43
Q

What are 3 characteristics of local circuits?

A

1) Depolarize adjacent membranes, causing an action potential
2) Decay with distance
3) Slow

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44
Q

What is the velocity of conduction determined by?

A

Spatial extent of local circuits

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45
Q

What is the relationship between threshold and velocity of conduction?

A

Inverse

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46
Q

What is the relationship between height and velocity of conduction?

A

Direct

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47
Q

What is the relationship between membrane resistance and velocity of conduction?

A

Direct

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48
Q

What is the relationship between fibre diameter and velocity of conduction?

A

Direct

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49
Q

Why does decreasing diameter result in a lower velocity?

A

Decreasing the diameter means an increase in axoplasmic resistance

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50
Q

What is the immediate effect of temperature on rate of activation of channels?

A

Cooling decreases fluidity of membranes which slows opening of sodium channels

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51
Q

What is the progressive effect of temperature on rate of activation of channels?

A

Cooling slows rate of Na/K pumping, which means a loss of sodium and potassium gradients, resulting in depolarization, which raises threshold, decrease action potential height, and decreases membrane resistance. These altogether decrease conduction velocity

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52
Q

Why can a “backward” current flow NOT reexcite old active areas?

A

Because these areas are in a refractory period

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53
Q

What are 5 events of neuromuscular transmission?

A

1) Release of acetylcholine
2) Acetylcholine diffuses across cleft
3) Acetylcholine binds to Ach receptors
4) End-plate potential spreads via local circuits to adjacent excitable sarcolemma
5) Hydrolysis of Ach

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54
Q

What causes acetylcholine to be released?

A

Motor action potential arrives at nerve terminal, depolarizes, activates voltage-gated calcium channels, causing a calcium influx, which causes packets of Ach to be released

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55
Q

What happens when Ach binds to receptors?

A

Permeability of sodium AND potassium increases

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56
Q

How much does end-plate potential depolarize to?

A

Threshold

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57
Q

What happens when voltage-gated calcium channels are blocked?

A

Voluntary muscles (lungs) will no longer work

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58
Q

Is a membrane more permeable to K or Na?

A

K

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59
Q

How does a membrane being more permeable to potassium impact Em?

A

Em will be affected more dramatically by changes in K permeability than by changes in Na permeability

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60
Q

Is the sodium/potassium needed to keep up concentration gradients after every action potential and why?

A

No because very few sodium and potassium ions are needed to cause an action potential

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61
Q

What is the charge of a cell that is experiencing an action potential?

A

Positive

62
Q

What is the charge of a cell that is at resting potential?

A

Negative

63
Q

Does the original action potential travel along a membrane?

A

No, it triggers an identical new action potential in the adjacent area

64
Q

What must happen for a sodium channel to be triggered a second time?

A

Resting potential must be restored and the channels must be reset to their original positions

65
Q

How are refractory period and action potentials related?

A

The longer the refractory period the greater delay between action potentials

66
Q

Describe the all-or-none fashion of an action potential

A

An excitable membrane responds to a triggering event with either a maximal AP, or it does not respond with an AP at all

67
Q

What is the effect of a stronger stimulus on an AP, and what will it not do?

A
  • It will produce a greater number of AP’s per second

- It will not produce a larger AP

68
Q

What causes striations?

A

Acto-myosin organization

69
Q

Between skeletal and cardiac muscle, which one controls voluntary movement and which one controls involuntary movement?

A
  • Skeletal – voluntary

- Cardiac – involuntary

70
Q

Which types of muscle have striations?

A

Skeletal & cardiac

71
Q

Does smooth muscle control voluntary or involuntary movement?

A

Involuntary

72
Q

How is skeletal muscle attached to the skeleton?

A

Tendons

73
Q

Define isometric

A

Force generated without change in length

74
Q

Define isotonic in regards to skeletal muscle

A

Length change at steady force

75
Q

What is concentric contraction?

A

Tension during shortening motion

76
Q

What is eccentric contraction?

A

Tension during lengthening motion

77
Q

What is each muscle cell/fiber innervated by and where?

A

By an alpha motor neuron in a neuromuscular junction or “end plate”

78
Q

Where is the efferent motor neuron cell body found?

A

Ventral horn of spinal cord

79
Q

Where is the afferent motor neuron found?

A

Dorsal horn

80
Q

How do neurons leave the spinal cord and what do they form?

A
  • By the ventral root

- Form mixed peripheral nerves

81
Q

What is a motor unit?

A

A motor nerve and all the muscle fibers it innervates

82
Q

What does it mean when a motor unit is described as a functional contractile unit?

A

All of the fibers contract synchrously

83
Q

How is motor unit size related to muscle function?

A
  • The motor unit gets larger as more fibers are needed

- Large motor units are needed for limbs that facilitate large movements with high force

84
Q

Where are neurotransmitters released?

A

Neuromuscular junctions

85
Q

What is epimysium and what does it do?

A

Epimysium is a mixture of elastin and collagen that surrounds muscle and prevents it from falling apart

86
Q

What is a fasciculus?

A

A bundle of muscle fibers

87
Q

What does perimysium surround?

A

Fasciculus’

88
Q

What does endomysium surround?

A

Muscle fibers

89
Q

What are myofibrils?

A

Bundles of actin and myosin filaments running along the long axis of cells

90
Q

What are the Z lines?

A

The beginning and ending of a sarcomere

91
Q

What is the I band composed of, and is it light or dark?

A
  • Actin filaments

- Light

92
Q

What is the A band composed of, and is it light or dark?

A
  • Myosin and actin filaments

- Dark

93
Q

What is the H band composed of and where is it found?

A
  • Only myosin

- Centre of sarcomere

94
Q

What does the M line do?

A

Organize and align thick filaments

95
Q

What are myofibrils surrounded by?

A

Calcium ion rich sarcoplasmic reticulum

96
Q

What is a T tubule?

A

Essentially the plasma membrane, hollow and filled with ECF

97
Q

What direction do actin filaments extend and from where?

A

Inward from the Z-disk

98
Q

What does it mean when myosin filaments are described as bipolar?

A

The heads are oriented in opposite directions at each end of the sarcomere

99
Q

Describe the organization of a thick filament

A
  • Hexamer with 2 heavy chains and 2 pairs of light chains

- Heavy chain has coiled tail with 2 globular heads

100
Q

What is a cross bridge?

A

The interaction between myosin heads with thin filaments

101
Q

Describe the troponin-tropomyosin complex

A
  • Tropomyosin binds actin and blocks myosin head binding
  • Troponin T binds tropomyosin
  • Troponin I facilitates inhibition myosin binding
  • Troponin C binds calcium ions, changes shape, and causes releases of troponin I and exposes myosin binding sites
102
Q

Describe the sliding filament theory

A

Muscle contraction is caused by the sliding of actin filaments past myosin filaments with no change in filament length

103
Q

What gets pulled together in the sliding filament theory?

A

Z-lines

104
Q

In the crossbridge cycle, does actin or myosin move?

A

Actin

105
Q

How does elevating cellular calcium enable cross bridge cycling?

A

Calcium binds troponin C, causing release of troponin I, and movement of tropomyosin to expose myosin binding sites

106
Q

Describe excitation-contraction coupling

A

1) Motor neuron releases synaptic vesicle at end plate
2) Ach from vesicles activates channels enriched on the facing sarcolemma
3) Short AP transmitted along the sarcolemma and down T tubules
4) AP changes conformation of DHPR leading to calcium release from SR terminal cisternae via RYR into myoplasm
5) Increased calcium promotes actin-myosin interaction (binds troponin C to move tropomyosin), thus inducing a twitch
6) Intracellular calcium re-sequestered to the SR via SERCA to cause relaxation

107
Q

What is DHPR?

A

A protein in the T tubule

108
Q

What is RYR?

A

A protein in the terminal cisternae

109
Q

What does an AP in the T tubule cause?

A

A conformational change in DHPR

110
Q

What does a DHPR shape change cause?

A

The RYR to open and allow SR calcium to be released

111
Q

What is SERCA?

A

A calcium-ATPase pump that re-sequesters intracellular calcium

112
Q

What is passive tension?

A

Resistance to stretch of a muscle at rest

113
Q

What is active tension?

A

New tension is developed after the muscle is stimulated

114
Q

What is Lo?

A

The optimal length to develop active tension

115
Q

What is the ideal Lo?

A

2.0 - 2.2 micrometers

116
Q

What is Vo (maximum shortening velocity)?

A

Velocity in the absence of a load

117
Q

What is Po (maximum isometric tension)?

A

Load at which stimulated muscle no longer shortens

118
Q

What is the relationship between load and shortening?

A

Inverse – increasing load decreases shortening

119
Q

What type of skeletal muscle is considered type 2?

A

Fast twitch

120
Q

How is a fiber determined to be fast or slow?

A

Innervation

121
Q

What type of activity is high for fast fibers?

A

Glycolytic

122
Q

What type of activity is high for slow fibers?

A

Oxidative

123
Q

Between fast and slow fibers, which has more mitochondria?

A

Slow

124
Q

Between fast and slow fibers, which has more capillaries?

A

Slow

125
Q

Between fast and slow fibers, which has a more extensive SR?

A

Fast

126
Q

Between fast and slow fibers, which is innervated by alpha 1 motor neurons?

A

Fast

127
Q

Between fast and slow fibers, which is innervated by alpha 2 motor neurons?

A

Slow

128
Q

Describe the diameter, excitability, and conduction velocity of alpha 1 motor neurons

A
  • Large diameter
  • Low excitability
  • Very fast conduction velocity
129
Q

Describe the diameter, excitability, and conduction velocity of alpha 2 motor neurons

A
  • Small diameter
  • High excitability
  • Fast conduction velocity
130
Q

Between fast and slow fibers, which fatigues faster?

A

Fast

131
Q

Between fast and slow fibers, which is used for sustained activities?

A

Slow

132
Q

What are 3 energy sources used during contraction?

A

1) ATP
2) Creatine phosphate
3) Glycogen & glucose

133
Q

What is oxygen debt?

A

When rate of energy use exceeds rate of production by oxidative metabolism

134
Q

How is oxygen debt payed back?

A

Increased respiration and cardiac work during recovery

135
Q

Can the ATP pool ever be reduced to zero?

A

No

136
Q

How is the force of contraction increased?

A

Recruiting more fibers

137
Q

How are cardiac muscle cells connected?

A

End-to-end

138
Q

Do smooth muscle cells have sarcomeres?

A

Nope

139
Q

Do smooth muscle cells have neuromuscular junctions?

A

No

140
Q

What are the 2 types of smooth muscle cells?

A

1) Phasic (single unit)

2) Tonic (multi-unit)

141
Q

Describe phasic smooth muscle cells

A
  • Cells contract together and are normally relaxed

- Cells coupled for free flow of ions and AP

142
Q

Describe tonic smooth muscle cells

A
  • Cells operate independently, normally contracted
  • Each cell innervated by a nerve ending
  • Little cell-cell communication
143
Q

What are muscle fibres made up of?

A

Myofibrils

144
Q

What are the outer limits of the A band determined by?

A

The 2 ends of the thick filaments

145
Q

What make up cross bridges?

A

Myosin heads

146
Q

What happens when troponin is not bound to calcium?

A

It stabilizes tropomyosin in its blocking position over actin’s cross-bridge binding sites

147
Q

What happens when troponin is bound to calcium?

A

The calcium’s shape changes, which allows tropomyosin to slip away from it’s blocking position

148
Q

When the sarcomere shortens, do the thick and thin filaments decrease in length?

A

No

149
Q

Where are T tubules found?

A

Every junction of an A band and I band

150
Q

What do terminal cisternae store?

A

Calcium

151
Q

How many muscle fibres does one axon terminal supply?

A

One

152
Q

As a motor unit increases in size, what happens to its ability to become activated?

A

The ability decreases (gets harder to activate)

Physiology (7 decks)

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