Nernst Equation in Biophysics
An equation calculating the exact electrical equilibrium potential across a membrane permeable to a single ion species.
Governing formula
E_ion = (R T / (z F)) ln([Ion]_out / [Ion]_in)
SI unit
mV (Equilibrium Potential)
In depth
Equates the electrical force driving an ion across the membrane to the equal and opposite chemical concentration gradient force. At 37 °C, E_K⁺ ≈ -90 mV, E_Na⁺ ≈ +60 mV, and E_Cl⁻ ≈ -70 mV.
Examples in the real world
Calculating the potassium equilibrium potential E_K = -90 mV in human skeletal muscle cells.