This applet gives an introduction to the Hodgkin-Huxley model. It outlines the dynamics of the membrane voltage and membrane currents.

It was written by Thomas Pollinger.

See this website for more details

Try this:
set current clamp to 0.4; duration to 0.1, end 100
"show"
"run" current clamp of 0.4, 0.5, 0.6, 0.7
(in that order without clearing, to see all in the same graph)
notice how once over 0.5, we get similar action potentials, always of the same magnitude
note also the faster rise of n, and the symmetry of m and h