Physiological Anatomy, Burst Formation, and Burst Frequency of the Cardiac Ganglion of Crustaceans

Abstract

The crustacean cardiac ganglion consists of a small number of neurons that drive contractions of heart muscle. In isopods, cardiac neurons are similar in size and spontaneity. They all couple electrically and produce synchronous bursts of impulses to activate the muscle. In stomatopods, cardiac neurons are divided into pacemakers and followers, although all are motoneurons and are electrically connected. In decapods, cardiac neurons are differentiated into large motoneurons and small interneurons. The large and small neurons interact mutually via electrical and chemical synaptic connections to produce synchronous burst discharges. These neurons exhibit overlapping innervation fields. Synchronization of their output is dominated by electrical interaction in the short crab ganglia and by chemical interaction in the longer lobster ganglia. When the lobster heart is exposed to high filling pressure, heart rate usually follows the bursting of the large neurons. Under the influence of serotonin, which selectively activates small cardiac neurons, heart rate follows the bursting of small neurons, even at high filling pressures. Therefore, the maximum rates of decapod hearts may vary as afunction of activation of the large and/or small neurons.