ABSTRACT
The isolated cardiac ganglion of the lobster is an autonomous, integrating system containing only nine neurons. Its physiology was first investigated by Welsh & Maynard (1951) and has been reviewed by Hagiwara (1961). Its component cells, when isolated from synaptic input, are usually either quiescent or fire nerve impulses at a uniform low frequency but, when connected normally in the ganglion, they periodically fire short, high-frequency trains of impulses. The periods of activity in all cells are approximately coincident, producing what is collectively termed the ‘burst’, which is followed by a quiescent period in all units (Maynard, 1955). Evidence so far accumulated indicates that the four posteriorly located ‘small cells’ or ‘pacemaker cells ‘control the burst timing, one of them initiating the normal burst. These interact strongly with the five anterior ‘large cells ‘or ‘follower cells ‘, producing firing in them. Output from these goes to the heart muscle, causing heart contraction. Pacemakerpacemaker interactions are presumed but not rigorously demonstrated; followerfollower interactions via impulses are present but weak (Otani & Bullock, 1959); long-lasting potential changes in followers affect pacemaker firing and intracellular potentials of other followers (Watanabe & Bullock, 1960). As a step toward the more exact determination of the means by which the over-all ganglionic behaviour derives from the synaptic interactions of its component cells, the paths of the axons of the large and small cells within the ganglion have been determined physiologically, and a means for identifying the nerve impulses produced by each during a burst has been developed.
