The physiology of a coelenterate neuromuscular synapse

Postsynaptic potentials can be recorded intracellularly from epitheliomuscular cells overlying the inner nerve-ring in the medusa Polyorchis penicillatus (Cnidaria, Hydrozoa) These postsynaptic potentials lead to the generation of muscle action potentials which propagate through the swimming-muscle sheets. It is the swimming motor neuron network that innervates this epithelium. An alternative motor pathway is present that involves a network of small, multipolar neurons that is interpolated between swimming motor neurons and overlying epithelial cells. Action potentials in the motor network are brought into phase as they conduct around the margin. This leads to more synchronous activation of synapses and hence larger PSPs at regions distant from the initiation site of the motor spike. The resulting decrease in the latency of muscle APs at these distant sites will automatically compensate for the conduction delay of motor spikes.