Organization of the stomatogastric ganglion of the spiny lobster

Summary

As part of a study of the stomatogastric nervous system in the spiny lobsterPanulirus interruptus, the neural circuitry underlying movements of the medial tooth of the gastric mill was examined. These movements consist of a cyclic forward and backward motion which, together with opening and closing of the lateral teeth, chew the food which the animal has in its stomach. When the stomatogastric nervous system is isolated, the pattern of activity in the motor roots which supply the medial tooth muscles consists of alternate bursts in antagonist neurons. The timing of these bursts in the isolated system is approximately the same as that seen in intact lobsters.

The neural circuitry responsible for producing these alternate bursts consists of two interneurons and six motor neurons, all located in the stomatogastric ganglion. Four electrotonically coupled GM neurons fire together and activate muscles which pull the medial tooth forward. Firing in the GM neurons alternates with firing in two other motor neurons, DGN which innervates muscles which pull the medial tooth backward, and the AMN which innervates muscles which constrict the cardiac sac. These latter two neurons are also electrotonically coupled and usually fire together. The interneurons interact with these antagonistic groups in a way which provides periodic excitatory drive to one group while inhibiting the other and so causes alternation between them.