Unit Activity in the Abdominal Nerve Cord of a Dragonfly Nymph

Abstract

1. Electrical activity of single units has been studied in small bundles of nerve fibres split off from the connectives between abdominal ganglia of the dragonfly nymph. Many units showed a resting discharge but activity of other units was only found when the insect was stimulated mechanically. 2. In some fibres the resting discharge was unaffected by mechanical stimulation and such spontaneous activity showed different patterns. These units were identified as interneurones and a prominent feature of their discharge was an irregular firing over long periods and the formation of characteristic intermittent bursts. 3. Responses to tactile or proprioceptive stimulation were investigated in primary sensory fibres and interneurones. The latter showed excitatory and inhibitory effects which were often related to the site of the peripheral stimulus. 4. Primary sensory fibres generally gave action potentials of smaller amplitude and were excited by stimulation of more localized areas. Many fibres traverse at least one connective after they enter a segmental ganglion and most ascend or descend ipsilaterally, but some crossing-over of sensory fibres occurs in the ganglia. 5. Interneurones were classified according to the nature of the peripheral areas from which they received their input. Ipsilateral, contralateral, and bilateral fibres have all been found but so far there is no evidence for any asymmetric fibres. Fibres responding to stimulation of a single segment or of many segments were found. Some of the latter extended over the whole length of the body and it is clear that spikes may be initiated in many of the ganglia through which an interneurone passes. 6. It is evident from this work that a given peripheral area is represented centrally by many interneurones and a great deal of convergence from different areas may occur on individual interneurones.