is nonzero, there are other pumps in the membrane, e.g. Na+/K+-ATPase, not considered here which serve to balance each individual ion's current, so that the ion concentrations on either side of the membrane do not change over time in equilibrium.) If all the ions are monovalent—that is, if all the nA equal either +1 or -1—this equation can be written whose solution is the Goldman equation where If divalent ions such as calcium are considered, terms such as e2μ appear, which is the square of e''μ; in this case, the formula for the Goldman equation can be solved using the quadratic formula. See also Bioelectronics Cable theory GHK current equation Hindmarsh–Rose model Hodgkin–Huxley model Morris–Lecar model Nernst equation Saltatory conduction References External links Subthreshold membrane phenomena Includes a well-explained derivation of the Goldman-Hodgkin-Katz equation Nernst/Goldman Equation Simulator Goldman-Hodgkin-Katz Equation Calculator Nernst/Goldman interactive Java applet The membrane voltage is calculated interactively as the number of ions are changed between the inside and outside of the cell. Potential, Impedance, and Rectification in Membranes by Goldman (1943) Physical chemistry Electrochemical equations