English: A. Schematic of an electrophysiological recording of an action potential showing the various phases which occur as the wave passes a point on a cell membrane. B. An actual action potential (blue trace) recorded from a mouse hippocampal pyramidal neuron. In this case, the action potential was stimulated by a prolonged pulse of current (brown trace; approx. 2 micro Amps) passed into the cell through the recording electrode. This method of stimulation distorts the AP compared to the schematic, in that the "real" action potential is sitting atop a voltage offset caused by the current pulse. Thus, for example, the "undershoot" is offset from the resting potential, although it would dip below rest if the offset were not present. The slow decline of the membrane potential back toward rest upon the termination of the current pulse reflects the long time constant of the neuronal membrane.