Membrane Potentials

Question 1

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

Answer 1

Excitability

Question 2

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

Answer 2

Resting membrane potential

Question 3

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?

Answer 3

Different ions (anions vs. cations)

Direction of electrochemical gradient (positive or negative)

Question 4

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

Answer 4

True

Question 5

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

Answer 5

Inside = 150 mM
Outside = 5 mM

Question 6

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

Answer 6

Inside = 15 mM
Outside = 150 mM

Question 7

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

Answer 7

Na+/K+ ATPase Pump

Question 8

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

Answer 8

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.

Question 9

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).

Answer 9

Negative

Positive

Question 10

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…

Answer 10

Resting Membrane Potential

Question 11

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

Answer 11

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!

Question 12

What is the resting membrane potential for skeletal muscle?

Answer 12

-80 to -90 mV

Question 13

What is the resting membrane potential for neurons?

Answer 13

-60 to -70 mV

Question 14

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

Answer 14

K+
Ca2+ (calcium)
Na+

Question 15

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.

Answer 15

Water

Question 16

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

Answer 16

Passive

Question 17

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

Answer 17

Leak (non-gated) channels

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

Question 18

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

Answer 18

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

Question 19

T/F. Leak channels are always open.

Answer 19

True

Question 20

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

Answer 20

Voltage-gated channel

Question 21

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

Answer 21

Ligand-gated channel

Question 22

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

Answer 22

Signal-gated channel

Question 23

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

Answer 23

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!

Question 24

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.

Answer 24

100:1

Question 25

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

Answer 25

True

Question 26

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

Answer 26

Diffusion forces

Question 27

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

Answer 27

Electrostatic forces

Question 28

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.

Answer 28

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).

Question 29

What are Electrochemical Forces a combination of?

Answer 29

Diffusion Forces + Electrostatic Forces

Question 30

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).

Answer 30

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+)

Question 31

What is the equilibrium potential for Na+?

Answer 31

60 to 66 mV

Question 32

What is the equilibrium potential for K+?

Answer 32

-90 to -95 mV ***Close to skeletal muscle Resting Potential = -90 mV

Question 33

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

Answer 33

Driving Force

Question 34

Explain the Driving Force for K+.

Answer 34

-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.

Question 35

Explain the Driving Force for Na+.

Answer 35

- 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.

Question 36

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

Answer 36

Goldman Equation

Question 37

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

Answer 37

Nernst Equation

Question 38

What is the equilibrium potential for Ca2+?

Answer 38

+123 mV

Question 39

What is the equilibrium potential for Cl-?

Answer 39

-66.4 mV

Question 40

What is the main contributor to resting membrane potential?

Answer 40

Contribution of K+ diffusion potential

Question 41

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

Answer 41

Minimal contribution due to low permeability at rest About 5 mV positive contribution (very little -- due to sodium leak channels)

Question 42

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

Answer 42

Minimal direct contribution About 4 mV negative contribution Indirectly contributes to maintain ion concentration gradients

Question 43

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

Answer 43

It will increase (become less negative) ***Hyperkalemia -- higher than normal K+ in blood

Question 44

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

Answer 44

It will decrease (become more negative)

Question 45

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

Answer 45

Positive

Question 46

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

Answer 46

Negative

Question 47

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

Answer 47

Negative

Question 48

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

Answer 48

Positive

Question 49

This is the term for a deviation from 0 mV.

Answer 49

Polarization

Question 50

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

Answer 50

Depolarization ***Does not mean it's an action potential!

Question 51

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

Answer 51

Hyperpolarization

Question 52

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

Answer 52

Repolarization

Question 53

What are the basics of action potentials?

Answer 53

-- 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

Question 54

What are key properties of an action potential?

Answer 54

-- All-or-none -- Propagating or self-reinforcing -- Non-decremental (strength and speed the same throughout)

Question 55

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...

Answer 55

K+ leak channels are always open

Question 56

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.

Answer 56

True

Question 57

What are the phases of the action potential?

Answer 57

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

Question 58

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

Answer 58

Threshold

Question 59

What are the key players in action potentials?

Answer 59

``` 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!

Question 60

Describe what happens with Na+ during depolarization.

Answer 60

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.

Question 61

What are the two voltage-gated Na+ channels?

Answer 61

Activation gate | Inactivation gate

Question 62

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

Answer 62

Closed | Open

Question 63

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

Answer 63

Open | Open

Question 64

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

Answer 64

Open | Closed

Question 65

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

Answer 65

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

Question 66

Describe what happens during repolarization.

Answer 66

-- 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")

Question 67

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

Answer 67

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

Question 68

Describe what happens during hyperpolarization.

Answer 68

-- Voltage-gated K+ channels stay open a little too long -- K+ leak channels will get membrane potential back to resting

Question 69

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

Answer 69

More difficult ***Refractory periods

Question 70

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

Answer 70

Review 5 minutes

Question 71

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!

Answer 71

Absolute refractory period ***Occurs during depolarization and repolarization

Question 72

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!

Answer 72

Relative refractory period ***Occurs during hyperpolarization

Question 73

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

Answer 73

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

Question 74

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

Answer 74

Hypokalemia

Question 75

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

Answer 75

True

Question 76

Describe the driving forces during hypokalemia.

Answer 76

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

Question 77

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

Answer 77

Hyperkalemia

Question 78

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

Answer 78

Lengthened

Question 79

How can hyperkalemia attacks be managed?

Answer 79

Mild exercise Potassium-wasting diuretics Glucose consumption ***Reverse is true for hypokalemia (i.e., don't consume a lot of sugar)

Question 80

Describe the driving forces during hyperkalemia.

Answer 80

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

Question 81

Briefly explain how hyperkalemia affects action potentials.

Answer 81

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)

Question 82

Briefly explain how hypokalemia affects action potentials.

Answer 82

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.