The Four Classical Membrane Potential Treatments

It is assumed that only one ionic entity can diffuse through the membrane. A concentration gradient pulls the diffusing ion, and a potential gradient holds it back. Equilibrium is thus attained. Then, 

This is the best-known of the three classical treatments. It differs from the treatment of Nernst, in that it assumes that both cations and anions 

TABLE 1. Membrane Potentials for Some Biological Membranes 

If two ionic solutions are brought into contact via a permeable membrane, difference in concentration or type of ion will give rise to a liquid junction potential. This concept differs from the earlier ones in that it involves the Nemst-Planck equation which embraces a theory of the influence of both electrical and concentration gradients on the ionic distribution.  

By making a number of simplifications of these ideas, Goldmann showed that 

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