English: The voltage v(t) (measured in millivolts) of the Hodgkin-Huxley model graphed over 50 milliseconds. The injected current varies from -5 nanoamps to 12 nanoamps. The graph passes through 3 stages, equilibrium, a single spike, and a repetitive spike train. The system is going through a Hopf bifurcation. The graph was generated in Mathematica version 9.0.1. Constants used to generate the graph can be found online for free at http:// www.math.pitt.edu/~bard/bardware/hh - c.ode.