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MSK Exam 2 > Membrane Potentials > Flashcards

Membrane Potentials Flashcards

1
Q

________ allows cells to establish a means of communicating to their own interior or to other cells.

A

Excitability

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2
Q

_______ ________ ________ establishes a starting point for a cell to potentially excited. Signal is required to activate and transmit the signal.

A

Resting membrane potential

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3
Q

Resting membrane potential will deviate from rest based on changes in charge across the membrane. What are the two ways to make the resting membrane potential change?

A

Different ions (anions vs. cations)

Direction of electrochemical gradient (positive or negative)

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4
Q

T/F. Nerves and muscles rely heavily on excitability.

A

True

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5
Q

What is the ion concentration of K+ inside and outside the cell?

A 
Inside = 150 mM
Outside = 5 mM
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6
Q

What is the ion concentration of Na+ inside and outside the cell?

A 
Inside = 15 mM
Outside = 150 mM
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7
Q

What is responsible for developing the concentration gradient for a cell with K+ and Na+?

A

Na+/K+ ATPase Pump

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8
Q

T/F. Na+ can freely diffuse down its concentration gradient and into the cell, but K+ cannot move so easily.

A

False. K+ can freely diffuse down its concentration gradient and into the cell, but Na+ cannot move so easily.

***Remember K+ goes through “windows with screens”, but because of the “screens” Na+ cannot move through. Na+ has its own means of transport.

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9
Q

As K+ cells move down their concentration gradient and out of the cell, the charge inside the cell is (POSITIVE/NEGATIVE) and the charge outside the cell is (POSITIVE/NEGATIVE).

A

Negative

Positive

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10
Q

Eventually, K+ will start getting repelled backwards into the cell and the concentration gradients will balance out. Ions stop moving and this is the point we establish our…

A

Resting Membrane Potential

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11
Q

Resting membrane potential is primarily due to permeability of the plasma membrane to _________ ions.

A

Potassium

***If Na+/K+ ATPase Pump is messed with, it won’t change the resting membrane potential much. But messing with the K+ channels will change it a lot!

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12
Q

What is the resting membrane potential for skeletal muscle?

A

-80 to -90 mV

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13
Q

What is the resting membrane potential for neurons?

A

-60 to -70 mV

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14
Q

Membrane is permeable to ______, but not as much to _____ or _____. Movement across the membrane is governed by various channels/pumps.

A

K+
Ca2+ (calcium)
Na+

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15
Q

Ion channels are integral membrane proteins that form gated pores. They are highly specific, and how ions interact with _______ decides the specificity for these channels.

A

Water

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16
Q

Channels involved in membrane potential are mostly _______, meaning they do not require energy.

A

Passive

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17
Q

Open channels (non-gated) are ions that move down their concentration gradient. What is an example of this?

A

Leak (non-gated) channels

***i.e., K+ leak channels

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18
Q

Gated channels restrict ion movement. What are examples of these channels?

A

Voltage-gated
Ligand-gated
Signal-gated
Mechanically-gated

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19
Q

T/F. Leak channels are always open.

A

True

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20
Q

This type of gated channel will open (transiently) in response to change in the membrane potential.

A

Voltage-gated channel

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21
Q

This type of gated channel will open and close in response to a specific extracellular neurotransmitter (i.e., ACh).

A

Ligand-gated channel

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22
Q

This type of gated channel will open and close in response to a specific intracellular molecule.

A

Signal-gated channel

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23
Q

Explain how the Na+/K+ ATPase Pump works.

A

Exchanges 3 Na+ ions to outside of cell in exchange for 2 K+ ions to the inside of cell (against concentration gradient). Requires ATP.

***Remember this pump is only responsible for maintaining concentration gradient, it does not affect the resting membrane potential very much!

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24
Q

Leak channels are open all the time and permit mostly unregulated passage of ions. K+ lead channels are present at a _______ ration compared to Na+ leak channels.

A

100:1

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25
Q

T/F. Overall, passively K+ is more likely to leave the cell than Na+ is to enter the cell.

A

True

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26
Q

What type of forces are chemical gradients or concentration gradients (move high to low down gradient)?

A

Diffusion forces

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27
Q

Why type of forces are electrical gradients (charge based, opposites attract)?

A

Electrostatic forces

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28
Q

During movement of ions across a plasma membrane, a charge will develop on either side. This charge opposes further diffusion. Give an example of this.

A

When K+ tries to exit the cell via its leak channels but it’s repelled back into the cell (this is when resting membrane potential is close to being reached).

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29
Q

What are Electrochemical Forces a combination of?

A

Diffusion Forces + Electrostatic Forces

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30
Q

This is the term for the membrane potential when electrical and chemical forces are equal, and no further movement occurs (does NOT equal resting membrane potential).

A

Equilibrium potential (E ion)

***i.e., K+ has one E ion, and Na+ has a E ion. You use all these different E ions to predict resting membrane potential (especially for K+)

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31
Q

What is the equilibrium potential for Na+?

A

60 to 66 mV

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32
Q

What is the equilibrium potential for K+?

A

-90 to -95 mV

***Close to skeletal muscle Resting Potential = -90 mV

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33
Q

If you subtract the Equilibrium Potential from the Resting Membrane Potential, what does that give you?

A

Driving Force

34
Q

Explain the Driving Force for K+.

A

-90 mV - (-91 mV) = +1 mV

+1 mV is the driving force for K+

This small positive driving force represents a net efflux (pushing out of cell).
Not pushing very hard because it’s a small number.

35
Q

Explain the Driving Force for Na+.

A
  • 90 mV - (61.5 mV) = -141.5 mV
  • 141.5 mV is the driving force for Na+

This driving force represents an influx (coming into cell). Pushing very hard because it’s a high number.

***This doesn’t happen because the membrane is mostly impermeable to Na+ at rest. The doors and windows are closed.

36
Q

This equation allows you to calculate resting membrane potential while taking into account different ion concentrations and permeability.

A

Goldman Equation

37
Q

What is the name of the equation used to calculate equilibrium potential?

A

Nernst Equation

38
Q

What is the equilibrium potential for Ca2+?

A

+123 mV

39
Q

What is the equilibrium potential for Cl-?

A

-66.4 mV

40
Q

What is the main contributor to resting membrane potential?

A

Contribution of K+ diffusion potential

41
Q

What is the contribution of Na+ diffusion for resting membrane potential?

A

Minimal contribution due to low permeability at rest

About 5 mV positive contribution (very little – due to sodium leak channels)

42
Q

What is the contribution of the Na+/K+ ATP pump for resting membrane potential?

A

Minimal direct contribution

About 4 mV negative contribution

Indirectly contributes to maintain ion concentration gradients

43
Q

What happens to resting membrane potential if you increase extracellular K+ concentration?

A

It will increase (become less negative)

***Hyperkalemia – higher than normal K+ in blood

44
Q

What happens to resting membrane potential if you decrease extracellular K+ concentration?

A

It will decrease (become more negative)

45
Q

A more (POSITIVE/NEGATIVE) resting membrane potential makes it easier to depolarize the cell (closer to threshold).

A

Positive

46
Q

A more (POSITIVE/NEGATIVE) resting membrane potential makes it more difficult to depolarize the cell (cell is hyperpolarized and further from threshold).

A

Negative

47
Q

For equilibrium potential, if the ION(in) > ION(out) then the log will be (POSITIVE/NEGATIVE).

A

Negative

48
Q

For equilibrium potential, if the ION(in) < ION(out) then the log will be (POSITIVE/NEGATIVE).

A

Positive

49
Q

This is the term for a deviation from 0 mV.

A

Polarization

50
Q

This is the term for when membrane potentials become less negative.

A

Depolarization

***Does not mean it’s an action potential!

51
Q

This is the term for when membrane potentials become more negative.

A

Hyperpolarization

52
Q

This is the term for when a membrane potential is returning towards the resting membrane potential.

A

Repolarization

53
Q

What are the basics of action potentials?

A

– Large depolarization causing a reversal of membrane potential across plasma membrane

– Caused by changes in permeability of membrane to different ions

– Deviation from resting membrane potential varies b/w cells

– Length of action potential varies b/w cells

54
Q

What are key properties of an action potential?

A

– All-or-none

– Propagating or self-reinforcing

– Non-decremental (strength and speed the same throughout)

55
Q

Changes in membrane potential can occur that are small and local. These do not create action potentials and are excitatory or inhibitory. These graded potentials dissipate with distance because…

A

K+ leak channels are always open

56
Q

T/F. The strength of an initial graded potential correlates with the strength of the triggering event. This means the stronger the triggering event, then the more channels will open to change polarity of the membrane.

A

True

57
Q

What are the phases of the action potential?

A

Phase 4 – Resting
Phase 0 – Depolarization
Phase 3 – Repolarization
Refractory Period – Hyperpolarization

58
Q

This is the membrane potential at which action potential will certainly occur.

A

Threshold

59
Q

What are the key players in action potentials?

A 
Na+ ions
K+ ions
Voltage-gated Na+ channels
Voltage-gated K+ channels 
K+ leak channels

***Ca2+ ions are important for contraction, but don’t really have a part in the actual action potential component of skeletal muscle. They do in the heart!

60
Q

Describe what happens with Na+ during depolarization.

A

Threshold is reached and the activation gate opens, allowing Na+ to go into the cell. Shortly after, the inactivation gate closes and stops Na+ from coming into the cell.

***If the inactivation gate didn’t close, then overshoot would occur and repolarization would take much longer.

61
Q

What are the two voltage-gated Na+ channels?

A

Activation gate

Inactivation gate

62
Q

During rest, the Na+ activation gate is (OPEN/CLOSED) and the inactivation gate is (OPEN/CLOSED).

A

Closed

Open

63
Q

During activation, the Na+ activation gate is (OPEN/CLOSED) and the inactivation gate is (OPEN/CLOSED).

A

Open

Open

64
Q

During inactivation, the Na+ activation gate is (OPEN/CLOSED) and the inactivation gate is (OPEN/CLOSED).

A

Open

Closed

65
Q

T/F. To re-open the Na+ inactivation gate, you can apply another stimulus right away and it will open.

A

False. The gate won’t move until the membrane potential returns to near resting.

66
Q

Describe what happens during repolarization.

A

– Voltage gated Na+ channels are closed (specifically inactivation gate)

– K+ still leaks out via leak channels (“windows open”)

– Voltage gated K+ channels slowly open, increasing membrane K+ permeability (“doors open”)

67
Q

How are Voltage-Gated K+ Channels and K+ Leak Channels different?

A

Voltage-gated channels have the ability to close and have selectivity (via selectivity filter)

68
Q

Describe what happens during hyperpolarization.

A

– Voltage-gated K+ channels stay open a little too long

– K+ leak channels will get membrane potential back to resting

69
Q

During hyperpolarization, is it easier or more difficult to stimulate a subsequent action potential?

A

More difficult

***Refractory periods

70
Q

Review Slide 52 – Very good summary of steps in action potential!

A

Review 5 minutes

71
Q

During this type of refractory period, Na+ channels are either open or the inactivation gate is closed and cannot reopen. Another action potential cannot be generated no matter what!

A

Absolute refractory period

***Occurs during depolarization and repolarization

72
Q

During this type of refractory period, the inactivation gate is now open and the activation gate is closed. Action potential may be initiated but it requires a stronger stimulus!

A

Relative refractory period

***Occurs during hyperpolarization

73
Q

Put the following membrane permeabilities to ions in order of occurrence from start to end of the action potential:

A) Na+ permeability decreases rapidly
B) K+ permeability increases slowly
C) Na+ permeability increases rapidly
D) K+ permeability decreases slowly

A
  1. C
  2. B
  3. A
  4. D
74
Q

This is characterized by periodic dips in blood K+ levels and can trigger events.

A

Hypokalemia

75
Q

T/F. Hypokalemia causes a hyperpolarized membrane, making it harder to reach threshold and repolarization occurs more quickly.

A

True

76
Q

Describe the driving forces during hypokalemia.

A

The RMP is -100, so it’s further from threshold making it harder to create an action potential.

This causes driving force for Na+ to be larger at RMP and driving force for K+ to be larger at the peak.

***Phase 0 has increased slope

77
Q

This is characterized by excessive levels of K+ in the blood, making a person unable to compensate like a normal person would do.

A

Hyperkalemia

78
Q

Hyperkalemia causes action potentials and absolute refractory periods to be (LENGTHENED/SHORTENED).

A

Lengthened

79
Q

How can hyperkalemia attacks be managed?

A

Mild exercise
Potassium-wasting diuretics
Glucose consumption

***Reverse is true for hypokalemia (i.e., don’t consume a lot of sugar)

80
Q

Describe the driving forces during hyperkalemia.

A

RMP is -75 mV, which makes the driving force for Na+ smaller at the RMP and the driving force for K+ smaller at the peak.

***Phase 0 has less of a slope

81
Q

Briefly explain how hyperkalemia affects action potentials.

A

Hyperkalemia causes RMP to move closer to threshold. This allows a stimulus that would normally not create an action potential in normal people, to create an action potential in this person.

***Think HYPERkalemia = HYPERactive (overproducing action potentials)

82
Q

Briefly explain how hypokalemia affects action potentials.

A

Hypokalemia causes RMP to move farther from threshold (hyperpolarization). This makes it much more difficult to create an action potential, because a normal stimulus that would work in a normal person would not create a potential for this person. Requires a very strong stimulus.

MSK Exam 2 (26 decks)

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