Saltatory Conduction: A Cable-Equation Axon Model

This is the 2D counterpart to the 3D myelin g-ratio simulator, built on an entirely different computational core. Instead of plugging the axon's diameter and g-ratio into the classic Hursh diameter rule and Rushton g-ratio formula, this version discretizes each myelinated internode and solves the passive cable equation by finite differences, timing exactly when the depolarization reaches the next node of Ranvier. Where myelin is stripped away, the model switches to a Nagumo bistable reaction-diffusion equation — the standard description of continuous, non-saltatory conduction — and clocks the speed of the resulting traveling wavefront. Conduction velocity, the g-ratio at which conduction is fastest, and the severity of slowing under demyelination all emerge from these two solvers rather than being read off a formula, and the segment-by-segment bar chart shows exactly which internodes are bottlenecking the signal.