An electrodiffusion model of the mammalian myelinated nerve fiber

A new model of the mammalian myelinated nerve fiber is presented which includes the representation of longitudinal electrodiffusion of component ions within the intra-axonal and periaxonal volumes. The model utilizes a non-uniform compartmental approximation to the detailed anatomy of the nodal and paranodal regions. The axonal membrane includes ionic pumps and multiple types of ionic channels whose spatial distribution and dynamics are derived from contemporary experimental studies. The model takes the form of a system of coupled non-linear parabolic partial differential equations with time-varying coefficients. A finite-difference approximation to this system is formed and solved utilizing an implicit numerical integration method. This model also includes a graphical user interface as well as a simulation management and optimization environment. The model reproduces conduction behavior seen in previous experimental and modeling efforts. Importantly, this model represents activity-dependent changes in ion concentration within the myelinated nerve fiber. In particular, significant changes can be seen in the concentration of potassium ions in the restricted periaxonal volume contained between the inner layer of the myelin sheath and the axon.