Neurodynamics Teaching Demo
Explore threshold firing, sodium-potassium channel timing, refractory periods, and myelin-accelerated axon conduction in an interactive action potential propagation model.
A suprathreshold stimulus launches a fixed-size spike that travels segment by segment and cannot immediately reverse because of the refractory tail.
Watch a single location on the axon. Above threshold, excitable nodes produce full spikes, while internodes can show smaller coupled deflections in myelinated mode; below threshold, no propagated spike appears.
A stimulus below threshold produces only a local perturbation. Once threshold is crossed, voltage-gated sodium channels open in positive feedback and the spike reaches its characteristic full amplitude rather than scaling continuously with stimulus size.
After depolarization, sodium channels inactivate and potassium channels remain active for a short refractory interval. That tail of low excitability prevents the just-fired region from immediately re-exciting, so the wavefront moves forward instead of bouncing back.
Myelin reduces current loss along internodes, letting depolarization leap between nodes of Ranvier. In this simplified teaching model, nodes show the strongest spikes while internodes still display smaller passive voltage deflections and earlier arrival times.