In addition to synaptically induced potentials, low-frequency,
spontaneous potential fluctuations have been observed in many neurons
(2), (7), (9), (10), (11). These fluctuations, generally referred to
as pacemaker potentials, are usually rhythmic and may be undulatory
or more nearly saw-toothed in form. The depolarizing phase may be
accompanied by a spike, a volley of spikes, or no spikes at all.
Pacemaker frequencies have been noted from ten or more cycles per
second down to one cycle every ten seconds or more. Some idealized
pacemaker wave forms are shown in Figure 3.
[Illustration: A. PERIODIC BURSTS]
[Illustration: B. PACEMAKER POTENTIALS WITHOUT SPIKES]
[Illustration: C. PACEMAKER POTENTIALS WITH SINGLE SPIKES ON
DEPOLARIZING PHASE