Insect visceral muscle: Neural relations of the proctodeal muscles of the cockroach

Abstract

The muscles of the proctodeum and their innervation are described for the cockroach, Periplaneta americana. The proctodeal nerve arises bilaterally as a small branch of nerve XI. Two populations of efferent nerve fibres were distinguished by ‘fast’ and ‘slow’ nerve spikes. Fast spikes (0·5 m/sec) evoked muscle PSP's and, thus, were conducted by motor axons. Motor axons were stained characteristically with methylene blue; they originated in the sixth abdominal ganglion and terminated in fine, varicose endings; associated ganglion cells were not observed. Slow, efferent nerve spikes (0·2 m/sec) did not evoke a muscle response; the nature of the slow axon is uncertain. Afferent activity was recorded from the proctodeal nerve and sensory nerve cells were present below the circular muscle layer. The proctodeum was enveloped by a ‘periproctodeal net’, a syncytium of polynucleated fibres that is innervated by motor axons; it does not appear to constitute a peripheral nerve net.