## Research Method

|K+ ions diffuse out of the neuron creating a negative potential across the plasma membrane.

The resulting negative potential tends to pull K+ back into the cell. The diffusional force causing K+ to leave the neuron is

The resulting electrical force is EzF.

The diffusional force causing K+ to leave the neuron is

The resulting electrical force is EzF.

R = universal gas constant T = absolute temperature E = voltage difference across membrane zF = number of electric charges carried by a mole of K+ [K+] natural logarithm of the ratio ln n^+i°ut = of K+ concentrations on the two sides of the membrane

Deriving the Nernst equation:

At equilibrium the electrical force equals the diffusional force, or

The equilibrium potential is that membrane potential that counteracts the tendency of the K+ ions to diffuse out.

Rearranging this equality, we get an expression of the Nernst equation for the potassium equilibrium potential:

zF [K+]ta The equation can be made simpler by combining the constants, assuming the temperature is 20°C, and converting the natural logarithm to base 10 logarithm:

mV 0 