HBS - The Resting Membrane Potential - Topic 3

Question 1

Define resting membrane potential (RMP) & give a typical value using the appropriate units.

Answer 1

The membrane potential refers to the SEPARATION of opposite charge that exists across the cell membrane.

-A typical value of RMP is -70mV with reference to inside the cell

Question 2

Explain the 3 reasons why a separation of charge exists across the cell membrane?

Answer 2

• an unequal distribution of key ions
• the selective permeability of the membrane
• the Na+K+ ATPase pump
-pumps 2K+ into the cell for every 3Na+ out of the cell

Question 3

What does polarised mean, with e.g.?

Answer 3

Polarized means charged

e.g. RMP = -70mV

Question 4

What does depolarised mean, with example?

Answer 4

Depolarized means reduction in charge

e.g. -70mV goes to -30mV

Question 5

What does Hyperpolarised mean, with example?

Answer 5

Hyperpolarized means an increase in charge

e.g. -70mv goes to -90mV

Question 6

What’s actually responsible for the membrane potential?

Answer 6

Separated Charges in the membrane

Question 7

If the membrane has (10+,10-) and (10+,10-) charges, is there any potential?

Answer 7

Membrane has no potential

Question 8

If the membrane has (15+,10-) and (5+,10-), does it have a potential?

Answer 8

Membrane has potential

Question 9

in a typical mammalian cell, what is the Concentration & permeability of the Na +
responsible for the RMP?

Answer 9

Ext= 150mM, Int=15mM,

Relative Permeability= 1

Question 10

in a typical mammalian cell, what is the Concentration & permeability of the K+,
responsible for the RMP?

Answer 10

Ext= 5mM, Int= 150mM,

Relative Permeability= 25-30

Question 11

in a typical mammalian cell, what is the Concentration & permeability of the A-
responsible for the RMP?

Answer 11

Ext= 0mM, Int= 65mM,

Relative Permeability= 0

Question 12

in a typical mammalian cell, what is the Concentration & permeability of the Cl-
responsible for the RMP?

Answer 12

Ext= 70mM, Int= 5mM,

Relative Permeability= 50

Question 13

When is equilibrium reached?

Answer 13

Equilibrium is reached when there is no net flux or ion.

Question 14

What is voltage measured across the membrane at equilibrium called?

Answer 14

The equilibrium potential for that ion

Question 15

How do you calculate the equilibrium potential for an ion?

Answer 15

Using the Nernst Equation;

Ex = 61/z x log (Co/Ci)

– (Ex = equilibrium potential for ion (x) in mV)

– Co is the EXTRAcellular concentration of ion(mM)

– Ci is the INTRAcellular concentration of ion(mM)

– the ion’s valence (z), IS ALWAYS 1.

– 61 is a constant

Question 16

If the Equilibrium potential for an ion is more negative than the RMP, what direction is the driving force?

Answer 16

Outward

Question 17

If the Equilibrium potential for an ion is more positive than the RMP, what direction is the driving force?

Answer 17

Inward

Question 18

If the Equilibrium potential for an ion is almost equal to the RMP, what direction is the driving force?

Answer 18

There is no driving force as it is at equilibrium

Question 19

How do you calculate the membrane potential?

Answer 19

using the GHK equation:

Vm= 61 log PK+ [K+] + PNa+ [Na+]o /
PK+ [K+]i + PNa+ [Na+]i

Where:
Vm = membrane potential in mV
61 = a constant representing RT/zF; where z = 1 for K+ and Na+

PK+, PNa+ = permeabilities for K+ and Na+, respectively
[K+]o, [Na+]o = concentration of K+ and Na+ outside the cell in mV, respectively
[K+]i, [Na+]i = concentration of K+ and Na+ inside the cell in mV, respectively

Question 20

what does mM stand for?

Answer 20

millimolar= 1 mM = 10−3 mol/L

Question 21

What is the equilibrium potential for a particular ion?

Answer 21

it’s the voltage at which there is no net movement of that ion

Question 22

Why is The RMP is closer to EK

, rather then ENa ?

Answer 22

The RMP is closer to EK , rather then ENa, because the resting membrane is more permeable to K

Question 23

At RMP neither K+ or Na+ ions are at equilibrium, so can they still diffuse out?

Answer 23

No because passive diffusion of these ions is prevented by the action of NaK ATPase