Video 12.3n Spontaneous Stimulated. The electrode enters around cell 17. After an initial volley of action potentials, the resting potential settles down at about −50 mV and fires action potentials in response to synaptic input. During hyperpolarizing stimuli, action potentials cease but syanptic potentials appear larger; afterwards, the firing rate increases above baseline. During depolarizing stimuli, firing rate increases; afterwards, the neuron is silent for several seconds.