Video 12.3a Endogenous Rhythm. The electrode enters around cells 6, 7, and 19. Resting potential is about −60 mV, with rhythmic dips to about −75 mV. Small postsynaptic potentials occur in the dips, but the hyperpolarizing dips may be endogenous, rather than driven by inhibitory input. Alternatively, the “dips” may be the normal resting potential, with bursts caused by rhythmic excitatory input.