Membrane Potential I

Question 1

Membrane Potential Generation?

Answer 1

By one thing only. Imbalance in # of cations and anions inside a cell.

Question 2

Nernst Equation

Answer 2

E (mv) = 60/Z log10 (Co/Ci)

Question 3

What does E= -40mV mean?

Answer 3

It means the INSIDE of the cell must be -40mV negative compared to the outside for the ion to be at equilibrium

Question 4

E stands for…

Answer 4

equilibrium potential. Electrical potential difference across the membrane that must exist if the ion is to be at equilibrium at the given concentrations.

Question 5

E=0 ?

Answer 5

The ion is at equal concentrations across a membrane

Question 6

Vm

Answer 6

Membrane potential. The real voltage (mV) (vs. E as electromotive force).

Question 7

Vm = E

Answer 7

Then ion is at electrochemical equilibrium and you don’t need a pump.
For example Cl- could be 10x more concentrated outside but the internal negativity balances it so there is equilibrium (strong electrical force!).

Question 8

When Vm does NOT equal E

Answer 8

Then the membrane is impermeable to the ion or you need to pump the ion across the membrane.

Question 9

How do I know which way an ion will be pumped?

Answer 9

Calculate Vm and E.
You want to make Vm move towards E, so for example is Vm was -40 and E was -60, you would have to make Vm MORE negative so inside of the cell has to become more negative… thus the negative ion will LEAK INTO the cell and have to be PUMPED OUT.