Membrane Potential

Question 1

membrane potential

Answer 1

• all living cells have this

- difference in charge inside and outside the cell membrane

Question 2

electrical potential

Answer 2

when electrical charges of opposite sign are separated they have the potential to do work if allowed to come together
- measured in mV

Question 3

inside cell

Answer 3

negative

Question 4

outside cell

Answer 4

positive

Question 5

resting membrane potential

Answer 5

-70 mV

Question 6

resistance

Answer 6

• opposition to passage of current

- phospholipid bilayer had a high electrical _____

Question 7

phospholipid bilayer

Answer 7

increase this = increase resistance = insulator

Question 8

current

Answer 8

• movement of charges (ions)
• proportional to voltage
• inversely proportional to resistance

Question 9

conduction

Answer 9

when ion channels are open, this is high and resistance is low; opposite of resistance

Question 10

Ohm’s law

Answer 10

I=V/R

Question 11

magnitude of RMP depends on:

Answer 11

1. difference in ion concentration between ECF and ICF
2. permeability of membrane to various ions
   - -> reflects the number of open channels for the different ions

Question 12

membrane only permeable to K+

Answer 12

1. K+ flows out of because the concentration gradient
2. K+ out creates imbalance
3. negative charge inside attracts K+ back in

Question 13

membrane only permeable to Na+

Answer 13

1. Na+ flows in because of concentration gradient
2. Na+ in creates electrical imbalance
3. negative charge outside attracts Na+ back out

Question 14

equilibrium potential (Eion)

Answer 14

voltage (at given concentration) at which there is no net movement of ion
- 2 forces are equal in magnitude but opposite in direction

Question 15

Nernst equation

Answer 15

used to determine equilibrium potential for a single permeable ion
- electrical gradient concentration gradient

Question 16

resting membrane potential #1

Answer 16

Na+ / K+ ATPase sets up concentration gradient

• Na+ / K+ ATPase pump is slightly electrogenic: about -4 mV
• –> pump moves net charge across membrane (+3/+2) and contributes directly to membrane potential

Question 17

K+ “leak channels” open

Answer 17

• permeability increased

- K+ can easily cross membrane

Question 18

Tiny number of Na+ channels open

Answer 18

• permeability decreased

- Not much Na+ can cross

Question 19

some Cl- channels open

Answer 19

special cases

Question 20

Vm

Answer 20

membrane potential is not equal to equilibrium potential so there is always a small but steady leak of Na+ into cell and K+ out of the cell
– Na+ / K+ ATPase balances leak

Question 21

equilibrium

Answer 21

• no net flux of ion
• concentration may be different
• no energy required to maintain

Question 22

steady-state

Answer 22

• no net flux of ion (pump balances leak)
• concentrations are different
• energy is required – not at Eion of either ion

Question 23

If cell does not have Cl- pumps

Answer 23

No Cl- pumps to change concentration gradient

Question 24

Goldman-Hodgkin-Katz (GHK) equation

Answer 24

expanded Nernst equation that takes into account the relative permeabilities of all ions

Question 25

K+ typical permeability

Answer 25

1

Question 26

Na+ typical permeability

Answer 26

0.04

Question 27

Cl- typical permeability

Answer 27

0.45

Question 28

current flow at RMP

Answer 28

• at resting Vm Na+ is moving in and K+ is moving out
• the influx of Na+ is roughly equal to the efflux of K+
• –> I k = I Na
• K+ is 100x more permeable than Na+