Diverse forms of activity in the somata of spontaneous and integrating ganglion cells

With the introduction of the lobster cardiac ganglion into the service of physiology by Welsh and Maynard (1951) and Maynard (1953a—c, 1954, 1955), an extremely valuable preparation for the analysis of the properties and mechanisms of organized groups of neurones became available. Maynard has studied particularly the organization of the normal burst which initiates each heart beat and the consequences of stimulation of the extrinsic inhibitor nerve from the central nervous system, which he found to contain a single inhibitory axon on each side. These studies with extracellular macro-electrodes, partly confirmed by Matsui (1955), have shown: (a) that the ganglion, consisting of nine cells of complex form (Fig. 1 and Alexandrowicz, 1932), is capable of initiating at regular intervals complex bursts consisting of several to many impulses in each cell; (b) that there is a distinct pattern in the whole complex as well as in the bursts of impulses in each unit; and (c) that there is a division of labour among the ganglion cells. Certain of the cells apparently normally initiate the burst which represents one heart beat, others, although capable of spontaneous firing, apparently normally follow. These latter certainly, and possibly also the former, are motoneurones to the myocardium. Both are probably sensitive, but to different degrees, to stretch or inflation of the heart, in the wall of which the ganglion lies (Bullock, Cohen & Maynard, 1954), and to the effects of the extrinsic inhibitor axon and the accelerator axons, of which Maynard (1954) reported there are two. The followers are integrative as indicated by the fact that their pattern of discharge is not the same as that of any antecedent cell.