The Resting Membrane Potential

Question 1

Measuring the membrane potential

Answer 1

Using a very fine micropipette (a microelectrode) to penetrate the cell membrane
Expressed as the voltage inside the cell relative to the outside
Animal cells range from -20mV -> -90mV

Question 2

Selective permeability of the cell membrane

Answer 2

Membranes are selectively permeable to different ions
Ion channels are characterised by…
- Selectivity - Na+, K+, Ca2+, Cl- and non-selective cation channels
- Gating - can be open or closed by a conformational change in the protein molecule
- High rate of ion flow that is always down the electrochemical gradient for the ion

Question 3

Na+ concentration in a typical mammalian cell

Answer 3

Intracellular - 10 mM

Extracellular - 145 mM

Question 4

K+ concentration in a typical mammalian cell

Answer 4

Intracellular - 160 mM

Extracellular - 4.5 mM

Question 5

Cl- concentration in a typical mammalian cell

Answer 5

Intracellular - 3 mM

Extracellular - 114 mM

Question 6

Setting up the membrane potential

Answer 6

At rest the membrane has open K+ channels and so K+ will begin to diffuse out of the cell down its conc. gradient
Cell becomes negatively charged inside
Eventually the system comes to equilibrium as the membrane potential opposes the outward movement of K+

Question 7

Nernst equation

Answer 7

61 [ion] out
___ log10 ______

Z [ion] in

Z = valency (Cl- = -1, Na+ = 1 etc.)

Question 8

Why is the resting membrane potential not the same as the equilibrium potential for K+?

Answer 8

The membrane is not perfectly selective because other types of ion channel are open so RP is less negative than Ek
The dependence of the RP on Ek means that if [K+]out is increased -> Ek = more positive -> RP more positive

Question 9

Depolarisation

Answer 9

Decrease in membrane potential, inside of cell becomes less negative

Question 10

Hyperpolarisation

Answer 10

Increase in membrane potential, inside of cell becomes more negative

Question 11

Opening Na+ or Ca2+ channels

Answer 11

Depolarise the cell

Question 12

Opening Cl- or K+ channels

Answer 12

Hyperpolarise the cell

Question 13

Control of channel activity

Answer 13

• Ligand gating - channel is opened/closed by binding of chemical ligand (extracellular transmitter or intracellular messenger)
• Voltage gating - channel opens/closes in response to changes in membrane potential