Voltage-Dependent Membrane Permeability

Question 1

Resting potential (Vrest)

Answer 1

Membrane potential before current is injected

Question 2

Is Vrest usually negative or positive?

Answer 2

Negative

Question 3

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

Answer 3

Inside vs outside

Question 4

Depolarization

Answer 4

Changes in membrane potential such that Vm > Vrest

Question 5

Hyperpolarization

Answer 5

Changes in membrane potential such that Vm < Vrest

Question 6

A passive response occurs when?

Answer 6

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

Question 7

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

Answer 7

Action potential

Question 8

How does an active response differ from a passive one?

Answer 8

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

Question 9

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

Answer 9

Voltage-gated ion channels open, enabling ion permeability

Question 10

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

Answer 10

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

Question 11

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

Answer 11

Passive

Passive or active

Question 12

Inward current is synonymous with _______. Why?

Answer 12

Depolarization

Both bring membrane potential up

Question 13

Outward current is synonymous with ______. Why?

Answer 13

Hyperpolarization

Both bring membrane potential down

Question 14

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

Answer 14

Vrest

Question 15

Action potential: rising phase

Answer 15

First phase of action potential

Neuron depolarizes and Vm increases above Vrest

Question 16

Action potential: overshoot phase

Answer 16

Second phase of action potential

Vm goes above 0 mV (reaches its peak)

Question 17

Action potential: falling phase

Answer 17

Third phase of action potential

Vm decreases and neuron repolarizes to Vrest

Question 18

Action potential: undershoot phase

Answer 18

Fourth phase of action potential

Neuron is briefly hyperpolarized (Vm goes below Vrest)

Question 19

Why did early neuroscientists use giant squid axons?

Answer 19

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

Question 20

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

Answer 20

Membrane potential

Current

Question 21

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

Answer 21

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

Question 22

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?

Answer 22

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

Question 23

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

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

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

Question 26

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

Answer 26

Na+

Question 27

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

Answer 27

Na+

Question 28

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

Answer 28

K+ | Na+

Question 29

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

Answer 29

Cations (positive ions) | Anions (negative ions)

Question 30

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

Answer 30

Anions (negative ions) | Cations (positive ions)

Question 31

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

Answer 31

No

Question 32

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

Answer 32

Inward | Outward

Question 33

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

Answer 33

Early | Late/delayed

Question 34

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

Answer 34

Transmembrane | Pore

Question 35

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

Answer 35

Both- some are ion specific, some are more generalized

Question 36

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

Answer 36

Voltage-gated | Na+ and K+

Question 37

What does "gated" mean when referring to ion channels?

Answer 37

Opens and closes

Question 38

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

Answer 38

Depolarized

Question 39

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

Answer 39

They are voltage-gated

Question 40

Early transient current peaks around _____ mV.

Answer 40

0

Question 41

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

Answer 41

Na+ | K+

Question 42

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

Answer 42

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

Question 43

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

Answer 43

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

Question 44

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

Answer 44

Early (Na+ drives early current)

Question 45

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

Answer 45

Na+ channels | Early

Question 46

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

Answer 46

K+ channels | Late

Question 47

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

Answer 47

mSiemens | Amount of current that can go through an ion channel

Question 48

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

Answer 48

-40 mV

Question 49

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

Answer 49

Low Increases Plateaus

Question 50

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?

Answer 50

Na+ | Conductance for Na+ is transient

Question 51

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?

Answer 51

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

Question 52

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

Answer 52

0

Question 53

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.

Answer 53

Inward | Increase

Question 54

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.

Answer 54

Outward | Increase

Question 55

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

Answer 55

Driving force

Question 56

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

Answer 56

Threshold (-40 mV) | Increases

Question 57

Current equals _____ x _____.

Answer 57

Conductance | Driving force

Question 58

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

Answer 58

0 | Threshold (-40 mV)

Question 59

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

Answer 59

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

Question 60

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 ____ _____.

Answer 60

Less Equilibrium potential Driving force

Question 61

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

Answer 61

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

Question 62

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

Answer 62

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

Question 63

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

Answer 63

Open | Inactivate

Question 64

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

Answer 64

Slowly | Longer

Question 65

Conductance for Na ____ before action potential does.

Answer 65

Ends

Question 66

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?

Answer 66

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

Question 67

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.

Answer 67

Na K Rising Na

Question 68

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

Answer 68

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

Question 69

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

Answer 69

They open

Question 70

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

Answer 70

K Repolarizes Outward

Question 71

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

Answer 71

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

Question 72

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

Answer 72

No

Question 73

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

Answer 73

Threshold | Na

Question 74

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

Answer 74

Fire another action potential

Question 75

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

Answer 75

Action potential would last longer (peak would be broader)

Question 76

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

Answer 76

Closed | Open

Question 77

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

Answer 77

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

Question 78

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

Answer 78

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

Question 79

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

Answer 79

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

Question 80

What is the minimum inter-spike interval?

Answer 80

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

Question 81

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

Answer 81

No

Question 82

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?

Answer 82

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

Question 83

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

Answer 83

Absolute

Question 84

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

Answer 84

Interval between stimuli in ms | Action potential amplitude

Question 85

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

Answer 85

K channel

Question 86

Why does the neuron need to have a refractory period?

Answer 86

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

Question 87

How does passive propagation of an axon work?

Answer 87

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

Question 88

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

Answer 88

Electrons/charge

Question 89

How does active propagation of an axon work?

Answer 89

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

Question 90

An action potential requires both ____ diffusion and ____ propagation.

Answer 90

Passive | Active

Question 91

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

Answer 91

2- both toward distal and toward soma

Question 92

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?

Answer 92

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

Question 93

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

Answer 93

Synaptic Dendrites Threshold

Question 94

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

Answer 94

Initial segment | Voltage-gated channels

Question 95

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

Answer 95

Initial segment

Question 96

Inactivation of sodium channels is _____ dependent.

Answer 96

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

Question 97

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

Answer 97

Voltage gated Na and K channels

Question 98

Why can't action potentials occur in the soma?

Answer 98

No voltage gated channels in soma

Question 99

2 ways in which leakage of current can be overcome

Answer 99

Increasing axon diameter | Myelination of axons

Question 100

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

Answer 100

Rolls of fat | Insulate axon to prevent loss of current

Question 101

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

Answer 101

No

Question 102

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

Answer 102

Nodes of Ranvier

Question 103

Saltatory propagation: how does it work?

Answer 103

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

Question 104

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

Answer 104

Proprioceptive

Question 105

Increasing diameter increases _____.

Answer 105

Velocity

Question 106

Capacitance

Answer 106

Ability to store charge

Question 107

Resistance

Answer 107

Resisting charge from passing through

Question 108

Increasing axon diameter lowers _____. Why?

Answer 108

Resistance | Greater area for charge to escape through membrane

Question 109

Increasing axon diameter increases ____. Why?

Answer 109

Capacitance | More membrane is available to store charge

Question 110

Myelination increases _____ and decreases ______.

Answer 110

Resistance | Capacitance

Question 111

Resistance and capacitance are _____ related.

Answer 111

Inversely (raise one, lower the other)

Question 112

Slow inactivation of Na channel affects action potential how?

Answer 112

Prolonged action potential

Question 113

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

Answer 113

Deinactivation Closing Na