ROLE OF CARDIAC NEURONS IN COCKROACH HEARTBEAT

The paired lateral cardiac nerve cords of Periplaneta americana are composed of two physiologically distinct nervous components. Spontaneously active cardiac ganglion cells (GC) give rise to motor axons which innervate the heart and maintain nervous connexion throughout a single lateral cardiac cord. Spontaneously active neurosecretory nerve cells (NS) are located in the lateral cardiac cords near the segmental nerve junctions. The segmental nerves which arise from the ventral ganglia and join the lateral cardiac nerve cords contain neurosecretory axons which, with the intrinsic NS, comprise the cardioregulatory system. The paired lateral cardiac nerve cords are electrically independent with no impulses traversing caudal anastomosis. The heart muscle continues to beat when all GC and NS spontaneous activity has stopped; moreover, the heart movement regulates the GC activity specifically to fire at preferred times inducing burst groups which are correlated with the cardiac cycle. Some of the GC occasionally fire unidirectionally, with the preferred direction apparently not constant, whereas other GC fire both anteriorly and posteriorly. The classification of these GC as pacer and follower cells is premature. © 1968.