This page is, for the most part, my notes on Chapter 3, "Ionic Basis of the Resting Potential" in From Neuron to Brain by Nicholls, Martin and Wallace.

Nernst Equation

This formula is used to calculate the equilibrium potential required to balance a ion concentration difference across a membrane.

             R T       Extra_Con_i
	E = ----- ln( ------------- )
         i   z F       Intra_Con_i

The Variable Definitions

Ei : The equilibrium potential for the ion i.
R : the thermodynamic gas constant
T : the absolute temperature
z : the charge/valence of the ion
F : the Faraday (96485.309 C/mol)
Extra_Con_i : the extracellular concentration of the ion i.
Intra_Con_i : the intracellular concentration of the ion i.

RT/F is defined in units of volts and
= about 25 mV at room temperature/20 degrees Celsius in log e units
= about 58 mV at room temperature/20 degrees Celsius in log 10 units
= about 61 mV at mammalian body temperature/37 degrees Celsius in log 10 units

Note that RT/Fz can be easily calculated by dividing by the ion's charge.

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