Membrane Potentials

Question 1

What are the three things a cell needs to generate a membrane potential?

Answer 1

1. Ionic concentration gradient
2. Semi-permeable membrane
3. Membrane capacitance

Question 2

What are the two forces that are relevant to membrane potentials?

Answer 2

Concentration gradient vs. charge gradient

Question 3

What does the Nernst equation describe?

Answer 3

The electrical potential at concentration-electrical equilibrium with respect to one particular ion.

Question 4

What effect does ion permeability have on the resting membrane potential?

Answer 4

The membrane potential lies closest to the ion with the highest permeability.

Question 5

If an ion is bound to a protein and cannot cross the membrane does it contribute to the membrane potential?

Answer 5

Nope.

Question 6

What screws up the Nernst equation at very low K+ concentrations?

Answer 6

Na+ contributes to the resting membrane potential at low K+ concentrations.

Question 7

Is ATP used in action potential generation?

Answer 7

Nope.

Question 8

Would a Na+/K+ pump inhibitor change a cell’s ability to generate action potentials in the short term? Long term?

Answer 8

Not in the short term. In the long term the membrane potential would slowly dissipate and the cell would eventually be unable to generate an action potential.

Question 9

What fraction of ions present in/around a cell are involved in an action potential? What effect does this have on the overall electrical potential of the cell?

Answer 9

A tiny fraction is involved, so the overall electrical potential is essentially unchanged.