Electrical processes involved in the encoding of nerve impulses.

A mechanism for impulse encoding is advanced for those neurones whose impulse trigger zone membrane is more excitable than the general axonal membrane. Electrical communication between an electrotonically small patch of highly excitable membrane and neighboring membrane places the control of membrane potential - in varying degree - to the larger membrane area throughout the interspike intervals. That control is relinquished to the trigger membrane near the time of action potential initiation in a natural fashion. Model calculations demonstrate that this mechanism can lead to a dramatic lowering of the minimum stable firing frequency of tonic neurons, and, additionally influence the shape of the stimulus - versus - impulse frequency curve. The results are compared with the behavior of the slowly adapting stretch receptor neuron of the crayfish.