Ions, Permeability and the Resting Membrane Potential

Question 1

What are the three most important factors which determine the ‘passive’ movement of an ion across the membrane?

Answer 1

+ Electrical gradient

+ Concentration gradient

+ Membrane permeability

Question 2

What is equilibrium potential?

Answer 2

When the electrical potential precisely offsets the tendency for K+ to diffuse down its concentration gradient (chemical potential difference)

Question 3

What is the magnitude of the equilibrium potential?

Answer 3

The greater the chemical potential gradient ( conc. gradient) across a membrane, the greater the electrical gradient required to offset it

Question 4

In the Nernst equation, what is R?

Answer 4

R = gas constant

Question 5

In the Nernst equation, what is T?

Answer 5

T = absolute temperature

Question 6

In the Nernst equation, what is F?

Answer 6

F = Faraday constant

Question 7

In the Nernst equation, what is z?

Answer 7

z = valency

Question 8

What does the Nernst equation prove?

Answer 8

That the equilibrium potential is proportional to the logarithm of the ratio of the concentrations in the two compartments.

Question 9

What is the Nernst equation for a monovalent ion at 37°C?

Answer 9

Ex = 61 x log base10 x conc. of chamber 1 / conc. of chamber 2

Question 10

What is the Nernst equation for a divalent ion at 37°C?

Answer 10

Ex = 30.5 x log base10 x conc. of chamber 1 (outside) / conc. of chamber 2 (inside)

Question 11

What is the net difference between the distribution of Cl- ions and that of Na+ and K+ ions?

Answer 11

+ Cl- ions are passively distributed

+ According to the value of the membrane potential - intracellular Cl- ions concentration is set by the membrane potential

+ Na+ and K+ ion concentrations are maintained by the sodium pump and set the membrane potential

Question 12

Why is the resting membrane potential a negative value?

Answer 12

Because K+ ions are not accompanied by anions, charge separation occurs and the electrical potential of the cell interior becomes negative with respect to the extracellular solution.

Question 13

Why is the resting membrane potential a negative value? Explain the phenomenon with reference to differences in membrane permeability to sodium and potassium ions.

Answer 13

Because the resting membrane potential is much closer to EK+ than to ENa+, the membrane must be much more permeable to K+ than to Na+