Bio-Electricity.

Membrane potential (Vm)

The voltage difference across the cell membrane; defined as the potential inside the cell relative to outside (reference = ~0). Typically negative at rest.

Nernst potential

The membrane potential at which a given ion's net flux is zero; also called equilibrium potential or reversal potential.

Equilibrium potential

The Vm at which an ion's diffusional flow (concentration gradient) is exactly balanced by electrostatic attraction, so net flux = 0.

Reversal potential

The Vm at which the flux of a given ion switches direction (from net influx to net efflux, or vice versa).

-93 mV

EK

61 mV

ENa

-75 mV

ECl

130mV

ECa

Nernst equation

Equation used to calculate an ion's equilibrium potential from its concentration gradient and charge: Ex = (RT/zF) ln([X]o/[X]i)

Gas Constant R

TRUE constant in the Nernst equation; 8.31 J/mol·K

Farday’s Constant F

TRUE constant in the Nernst equation; 96,485 C/mol

Temperature in Kelvin

CAN vary in the Nernst equation; fixed at 310 K (37°C) for these problems, but not truly constant

ionic charge z

CAN vary in the Nernst equation; depends on the ion (+1 for K+/Na+, +2 for Ca2+, −1 for Cl-)

Diffusional force

The force driving an ion to move down its concentration gradient (high to low concentration).

Electrostatic force

The force of attraction/repulsion between charges (opposite charges attract, like charges repel) that can oppose or reinforce diffusional flow.