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Neurobiology I > Voltage-Dependent Membrane Permeability > Flashcards

Voltage-Dependent Membrane Permeability Flashcards

1
Q

Resting potential (Vrest)

A

Membrane potential before current is injected

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2
Q

Is Vrest usually negative or positive?

A

Negative

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3
Q

Vrest and membrane potential are measuring the charge ___ vs ___.

A

Inside vs outside

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4
Q

Depolarization

A

Changes in membrane potential such that Vm > Vrest

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5
Q

Hyperpolarization

A

Changes in membrane potential such that Vm < Vrest

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6
Q

A passive response occurs when?

A

Small changes in current cause small changes in membrane potential that are proportional to the change in stimulus

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7
Q

When enough depolarizing current is added to the neuron to cause it to go above its threshold, what occurs?

A

Action potential

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8
Q

How does an active response differ from a passive one?

A

A passive response is proportional to the change in stimulus, whereas an active response (action potential) does not

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9
Q

What happens when the neuron reaches threshold that enables an action potential to occur?

A

Voltage-gated ion channels open, enabling ion permeability

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10
Q

Why is the action potential called “all-or-none?”

A

With increasing depolarization above threshold, there is no change in action potential amplitude, but instead increased frequency of action potentials

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11
Q

Hyperpolarization always yields a _____ response, whereas depolarization can yield a ____ or ____ response depending on whether or not it raises membrane potential above threshold.

A

Passive

Passive or active

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12
Q

Inward current is synonymous with _______. Why?

A

Depolarization

Both bring membrane potential up

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13
Q

Outward current is synonymous with ______. Why?

A

Hyperpolarization

Both bring membrane potential down

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14
Q

Before the stimulus, the neuron’s membrane potential is considered to be _____.

A

Vrest

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15
Q

Action potential: rising phase

A

First phase of action potential

Neuron depolarizes and Vm increases above Vrest

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16
Q

Action potential: overshoot phase

A

Second phase of action potential

Vm goes above 0 mV (reaches its peak)

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17
Q

Action potential: falling phase

A

Third phase of action potential

Vm decreases and neuron repolarizes to Vrest

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18
Q

Action potential: undershoot phase

A

Fourth phase of action potential

Neuron is briefly hyperpolarized (Vm goes below Vrest)

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19
Q

Why did early neuroscientists use giant squid axons?

A

They could be seen by the naked eye and the neuroscientists could easily create wires the right size to insert into them

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20
Q

A voltage-clamp instrument holds ____ ____ constant in order to measure ___ generated when ion channels open

A

Membrane potential

Current

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21
Q

How does a voltage-clamp instrument hold membrane potential constant?

A

Injects equal and opposite current to that caused by opening of ion channels, which prevents membrane potential from changing

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22
Q

In early experiments, neuroscientists measured changes in membrane potential of resting neurons as outside K+ concentration was increased. What occurred as outside K+ concentration was increased, and what did that tell the neuroscientists?

A

For a resting neuron, when outside K+ concentration is increased, Vm increases
Neurons are permeable to K+ at rest

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23
Q

For a neuron at rest, what happens to membrane potential when you increase outside Na+ concentration? What does that suggest?

A

For a resting neuron, increasing outside Na+ concentration has little effect on Vm
At rest, the permeability of Na+ is low

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24
Q

If the neuron is only permeable to K+, then why isn’t Vm=E K+?

A

Slight permeability of Na+ and Cl- have a small effect on the Vm

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25
Q

During an action potential, changing the outside concentration of what ion causes the greatest change in amplitude? What does that suggest?

A

Na+

Na+ plays a major role in determining the amplitude of the action potential

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26
Q

The action potential max voltage is close to the equilibrium potential of ___.

A

Na+

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27
Q

During rising phase, there is an increase in ___ permeability.

A

Na+

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28
Q

During falling phase, there is an increase in ___ permeability and a decrease in ___ permeability.

A

K+

Na+

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29
Q

Inward current: flow of ____ into or _____ out of cell

A

Cations (positive ions)

Anions (negative ions)

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30
Q

Outward current: flow of ____ into or ____ out of cell

A

Anions (negative ions)

Cations (positive ions)

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31
Q

When clamping at a hyperpolarized voltage, ____ current change is seen.

A

No

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32
Q

When clamping at a depolarized voltage, transient ____ current and sustained _____ current is seen.

A

Inward

Outward

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33
Q

Transient inward current is called _____ current, whereas sustained outward current is called ____ or _____ current because of when they are seen.

A

Early

Late/delayed

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34
Q

An ion channel is a ____ protein with a ____ in the center.

A

Transmembrane

Pore

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35
Q

Can ion channels be ion specific, allow multiple ions through, or both?

A

Both- some are ion specific, some are more generalized

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36
Q

What type of channels for what 2 ions are responsible for the action potential?

A

Voltage-gated

Na+ and K+

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37
Q

What does “gated” mean when referring to ion channels?

A

Opens and closes

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38
Q

Voltage-gated ion channels are usually only open when the neuron is _____.

A

Depolarized

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39
Q

What about the ion channels causes action potentials to exhibit an all-or-none threshold?

A

They are voltage-gated

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40
Q

Early transient current peaks around _____ mV.

A

0

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41
Q

Early current is caused by ____ channels whereas late/delayed current is caused by ____ channels.

A

Na+

K+

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42
Q

In a voltage clamp experiment, as Vm increases, early inward current first ___, then ___ until it reverses. Why is that?

A

Increases
Decreases
Ex for Na is around 50 mV- driving force decreases as Vm nears ENa, then stops and switches direction when Vm equals ENa

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43
Q

In a voltage clamp experiment, as Vm increases, delayed/late outward current _____ linearly. Why is that?

A

Increases

Ex for K is around -80 mV- driving force increases as Vm goes farther away from EK (becomes more positive)

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44
Q

In an experiment where Na+ concentration is 0, which current would be affected, early or late?

A

Early (Na+ drives early current)

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45
Q

Tetrodotoxin (TTX): which channels blocked, which current affected (early or late)?

A

Na+ channels

Early

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46
Q

Tetraethyl-ammonium (TEA): which channels blocked, which current affected (early or late)?

A

K+ channels

Late

47
Q

Conductance is measured in what unit? What is this conductance specifically measuring?

A

mSiemens

Amount of current that can go through an ion channel

48
Q

What value in mV is considered to be the threshold for K+ and Na+?

A

-40 mV

49
Q

When plotting membrane potential vs conductance, below -40 mV conductance is ____. Past -40 mV, conductance ____ exponentially until it ____ out.

A

Low
Increases
Plateaus

50
Q

Which ion channel, K+ or Na+, opens faster? Because ion channels for Na+ don’t stay open for the whole action potential, what does this mean for Na+’s conductance?

A

Na+

Conductance for Na+ is transient

51
Q

Which ion channel, K+ or Na+, opens slower? ___’s conductance just begins to start as ____’s conductance is peaking. What does this mean for K+’s conductance?

A

K+
K+, Na+
Conductance for K+ is sustained (K+ channels stay open for the duration of the experiment)

52
Q

At a given ion’s equilibrium potential, the driving force on that ion equals ____.

A

0

53
Q

When the membrane potential is less than the equilibrium potential for an ion, current will be ____ and will _____ in magnitude the further away the membrane potential is from equilibrium potential.

A

Inward

Increase

54
Q

When the membrane potential is greater than the equilibrium potential for an ion, current will be ____ and will ____ in magnitude the further away the membrane potential is from equilibrium potential.

A

Outward

Increase

55
Q

Between driving force, current, and conductance, which will give a linear plot on a graph of membrane potential vs driving force/conductance?

A

Driving force

56
Q

When plotting membrane potential vs conductance, the conductance is basically 0 until what value? Past that value, conductance _____ exponentially until it reaches its maximum.

A

Threshold (-40 mV)

Increases

57
Q

Current equals _____ x _____.

A

Conductance

Driving force

58
Q

Plotting membrane voltage vs current, current is ____ until ____ is reached.

A

0

Threshold (-40 mV)

59
Q

When measuring current for sodium, past threshold it ____ in the _____ direction until it reaches the maximum value for ____. Why is this?

A

Increases in the inward direction
Conductance
I = g x DF: since DF is inward due to Vm being less than ENa, direction of I is inward

60
Q

When measuring current for sodium, past maximum conductance value in the inward direction, it becomes ___ inward as DF becomes less inward and changes from inward to outward at the ____ ____ for Na. During this time, current is proportional to ____ _____.

A

Less
Equilibrium potential
Driving force

61
Q

When measuring current for potassium, past threshold current for conductance, current will ____ consistently. Why is this?

A

Increase

I = g x DF: Driving force is increasing (outward current- EK is low), so I increases

62
Q

Why do the plots of conductance for K and Na look almost the same?

A

The conductance has similar kinetics for both ions: similar thresholds, reach max conductance with similar kinetics

63
Q

Na channels ___ and ____ fairly rapidly, making its conductance early but transient.

A

Open

Inactivate

64
Q

K channels open more ____ than Na channels and stay open much ____, making its conductance delayed and sustained.

A

Slowly

Longer

65
Q

Conductance for Na ____ before action potential does.

A

Ends

66
Q

Before the action potential begins and the neuron is at rest (Vm = ____), the ion channels for K and Na are ____. It is during this time that synaptic potential can be seen. What is synaptic potential, and what is it due to?

A

Vrest
Closed
Membrane potential increases while channels are still closed
Due to depolarization of synapses on dendrites

67
Q

As soon as threshold is reached in the action potential, the ____ channels open. Because the ___ channels are slow to open, they remain closed at this time. Thus, most of the ____ phase corresponds to the conductance of the ____ channels.

A

Na
K
Rising
Na

68
Q

Towards the peak of the action potential, what happens to the inactivation domain of the Na channels and why?

A

Change in charge/length of time passed causes conformational change in inactivation domain, which moves to block the pore of the Na channel so ions cannot flow through

69
Q

At the time that the Na channels are inactivating, what happens to the K channels?

A

They open

70
Q

During falling phase, the ___ channels are open, which ____ the cell because this ion’s current is ____.

A

K
Repolarizes
Outward

71
Q

Why does the hyperpolarization/undershoot phase of the action potential occur?

A

The K channels are open past when Vm reaches Vrest (they are slow to close)

72
Q

Do all the Na channels close at the same moment, and do all the K channels open at the same moment?

A

No

73
Q

At deinactivation, the Vm drops below ____ and all ___ channels close.

A

Threshold

Na

74
Q

Once both Na and K channels are closed, what can the neuron do?

A

Fire another action potential

75
Q

If Na channels took longer to inactivate than normal, what would happen to the shape of the action potential curve?

A

Action potential would last longer (peak would be broader)

76
Q

At rest, the Na channel is _____ and its inactivating domain is ____.

A

Closed

Open

77
Q

What is the absolute refractory period, and what does it correspond to in the action potential?

A

Interval during which a new action potential cannot be initiated
Corresponds to inactivation of Na channels

78
Q

What is the relative refractory period, and what does it correspond to in the action potential?

A

Interval during which initiation of a new action potential is inhibited, but not impossible
Corresponds to hyperpolarization/undershoot phase

79
Q

Why is firing an action potential more difficult during the relative refractory period?

A

Because the neuron is in undershoot phase, it requires more depolarization to bring it up to threshold

80
Q

What is the minimum inter-spike interval?

A

The minimum amount of time between which a neuron can fire action potentials

81
Q

Can a neuron fire an action potential in less time than its minimum inter-spike interval?

A

No

82
Q

At or just above the minimum inter-spike interval for a cell, can the cell fire an action potential? How might its action potential be different than if the stimulus was applied a little bit later?

A

Yes
Action potential amplitude may be smaller- not all of the Na channels have gotten out of their absolute refractory period

83
Q

The ____ refractory period determines the minimum inter-spike interval.

A

Absolute

84
Q

A plot of what versus what reveals the minimum inter-spike interval?

A

Interval between stimuli in ms

Action potential amplitude

85
Q

The relative refractory period is due to the properties of the ____ _____.

A

K channel

86
Q

Why does the neuron need to have a refractory period?

A

Action potentials need to propagate away from the stimulus and in one direction

87
Q

How does passive propagation of an axon work?

A

Current diffuses along the axon, then gradually decays due to leakage

88
Q

In an action potential, what actually moves down the axon, ions or electrons/charge?

A

Electrons/charge

89
Q

How does active propagation of an axon work?

A

Current diffuses a short distance, then opens the next ion channels, which causes regeneration of the action potential

90
Q

An action potential requires both ____ diffusion and ____ propagation.

A

Passive

Active

91
Q

When ion channels open on a portion of axon, current passively spreads in how many directions?

A

2- both toward distal and toward soma

92
Q

When ion channels open on a portion of axon, why is it that an action potential doesn’t occur on the portion of axon that just had the action potential that caused the channels to open?

A

The part of the axon that initiated the current action potential is in absolute refractory period

93
Q

At the axon hillock, all _____ potentials of the ____ get added up. If the sum is above ____, then an action potential occurs.

A

Synaptic
Dendrites
Threshold

94
Q

The ____ ____ is the first part of the axon that is attached to the axon hillock and is enriched in what?

A

Initial segment

Voltage-gated channels

95
Q

If the summed inputs of the axon hillock bring Vm above threshold, then the action potential starts where?

A

Initial segment

96
Q

Inactivation of sodium channels is _____ dependent.

A

Time (inactivation occurs after a certain period of time- it is not voltage dependent)

97
Q

The axon initial segment and regions along the axon are enriched in what?

A

Voltage gated Na and K channels

98
Q

Why can’t action potentials occur in the soma?

A

No voltage gated channels in soma

99
Q

2 ways in which leakage of current can be overcome

A

Increasing axon diameter

Myelination of axons

100
Q

Myelination is due to ____ of ____ around segments of the axon. What is the purpose of myelination?

A

Rolls of fat

Insulate axon to prevent loss of current

101
Q

In general, are there voltage gated channels in myelinated areas?

A

No

102
Q

What are the areas of the axon called where there is no myelination but voltage gated channels are present?

A

Nodes of Ranvier

103
Q

Saltatory propagation: how does it work?

A

Passive current travels down the axon and regenerates action potential at nodes, making action potential appear to “hop” from node to node

104
Q

What type of axons have the biggest diameter and the most myelination?

A

Proprioceptive

105
Q

Increasing diameter increases _____.

A

Velocity

106
Q

Capacitance

A

Ability to store charge

107
Q

Resistance

A

Resisting charge from passing through

108
Q

Increasing axon diameter lowers _____. Why?

A

Resistance

Greater area for charge to escape through membrane

109
Q

Increasing axon diameter increases ____. Why?

A

Capacitance

More membrane is available to store charge

110
Q

Myelination increases _____ and decreases ______.

A

Resistance

Capacitance

111
Q

Resistance and capacitance are _____ related.

A

Inversely (raise one, lower the other)

112
Q

Slow inactivation of Na channel affects action potential how?

A

Prolonged action potential

113
Q

Short interspike interval is due to quick ____ and ____ of ____ channels.

A

Deinactivation
Closing
Na

Neurobiology I (18 decks)

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