Fig. 8. Interaction between the cardiac ganglion (CG) neurons and the heart muscle. (A) A schematic drawing of the membrane potential activity in the CG neurons and the heart muscle tension. A burst discharge of the CG neurons induces tension of the heart muscle via the excitatory neuromuscular transmission (a). The muscle tension has a hyperpolarizing effect on the CG neuron (b^-), which may assist the termination of the burst and enhance the after-burst hyperpolarization in the CG neuron. Relaxation of the heart muscle causes the postinhibitory rebound excitation (b⁺), which may advance the following burst discharge. See text for details. (B) A single neuron reflex arc formed by the CG neurons in the Ligia heart. The CG neurons function as endogenous oscillators by generating rhythmical burst discharges. They produce rhythmic motor output that is sent to the heart muscle via the neuromuscular junctions (a). They are also sensitive to the muscle tension (b), so that the heart muscle activity can entrain the ganglionic bursting activity under specific conditions such as when `a' is artificially blocked by Joro spider toxin (JSTX).