A distributed-parameter model of the myelinated nerve fiber

A model is presented that assumes a triaxial cable form, with separate nodal, paranodal, and internodal regions; a myelin sheath independent of the underlying internodal membrane; and a periaxonal conductance pathway. Unlike previous coaxial-cable-equivalent models, this triaxial form allows inclusion of ionic channels in the internodal membrane. The model uses ionic channel dynamics for the mammal and amphibian derived from recent experimental studies. It reproduces conduction behavior seen in experimental and previous modeling efforts, as well as the depolarizing afterpotential described by several investigators, which may have significance in determining the behavior of the nerve fiber as multiple action potentials are conducted or as multiple stimuli are imposed. This afterpotential cannot be produced by the previous coaxial models. The influence of the characteristics of the myelin sheath, underlying internodal membrane, and the periaxonal conductance pathway on the behavior of the nerve fiber is explored.<>