For example a faulty/mutated nerve, that when stimulated allowed itself to flood with positive charged ions with no means of getting rid of them due to mutated ion channels. Or the neuron only has these channels which pump in positive ions and nothing else.

Edited May 2, 201510 yr by LisaLiel

After a while (if nothing else happened) there would be a positive charge in the cell that would repel any incoming ions to such an extent that the pump would "stall"