Control of the Pacemaker System of the Nervenet in the Sea Anemone Calliactis Parasitica

The rhythm of spontaneous nerve-net pulses is reset by intercalated evoked nerve-net pulses. The origin of spontaneous nerve-net pulses can shift during a burst. There seem to be many potential pacemakers, widely distributed throughout the body, but apparently absent from the tentacles. If a spontaneous or evoked pulse in the endodermal slow conduction system (SS 2) occurs during a burst, the nerve-net pulse intervals are increased during a 15–30 sec period following the SS 2 pulse. Additional SS 2 pulses cause a further increase in pulse intervals. Nerve-net bursts are followed by a sequence of muscular contractions. The size of the contraction shown by any muscle group depends on nerve-net pulse number and frequency, the optimum frequency being different for different muscles. It is suggested that the SS 2 pulse action on nerve-net pulse frequency can significantly alter the behavioural output of nerve-net bursts. The SS 2 activity may represent sensory feedback on to the nervous pacemakers.