Membrane Potentials and Action Potentials

Question 1

What is a typical membrane potential in a cell?

Answer 1

-60 to -90 mV

Question 2

Why is the resting potential negative?

Answer 2

• ion concentration differences
• ion permeability (ion channels)
• Na/K and other pumps
• Negatively charged proteins (anions) inside the cell

Question 3

What is the E_ion (Equilibrium potential) for each ion:

1. Na⁺
2. K⁺
3. Ca²⁺
4. Cl^-

Answer 3

1. Na⁺ = +70 mV (60-70)
2. K⁺ = -95 mV (-90 –95)
3. Ca²⁺ = +134 mV (120-135)
4. Cl^- = -86 mV (-65 –88)

Question 4

What is the equilibrium potential tell you?

Answer 4

The electrical potential difference that balances an ionic concentration gradient

Question 5

Nernst Equation

Answer 5

Equilibrium potential for a single ion

E_ion=2.303 (RT/zF) log ([ion]_o/[ion]_i)

R=gas constant

T=absolute temperature

z=charge of the ion

F=Faraday’s constant

E_ion= (61/z) log ([ion]_o/[ion]_i)

or

E_ion= (61/z) log ([ion]_i/[ion]_o)