A new membrane model for mammalian nerve fibers has been developed. The membrane model utilizes new characterizations for delayed-rectifier currents, and adds an inwardly-rectifying potassium channel as well as a sodium-potassium pump current. Fits are shown to action potential and I-V data at two different temperatures. The Nernst-Planck electrodiffusion equation was then utilized to derive a linked compartmental model of the unmyelinated mammalian nerve fiber with lumped parameter values. The results from this unmyelinated fiber model were presented and compared to data in the literature. A myelinated nerve axon model is also developed and issues of numerical implementation are discussed.