THE CENTRAL CONNECTIONS AND ACTIONS DURING WALKING OF TIBIAL CAMPANIFORM SENSILLA IN THE LOCUST

Strain acting on the exoskeleton of insects is monitored by campanifor m sensilla. On the tibia of a mesothoracic leg of the locust (Schistoc erca gregaria) there are three groups of campaniform sensilla on the p roximo-dorsal surface. This study analyses the responses of the affere nts from one group, their connections with central neurones and their actions during walking. The afferents of the campaniform sensilla make direct excitatory connections with flexor tibiae motor neurones. They also make direct connections with particular spiking local interneuro nes that make direct inhibitory output connections with the slow exten sor tibiae motor neurone. During walking extension movements of the ti biae during stance produce longitudinal tensile forces on the dorsal t ibia that peak during mid stance before returning to zero prior to swi ng. This decline in tension can activate the campaniform sensilla. In turn this would lead to an inhibition of the extensor tibiae motor neu rone and an excitation of the flexor tibiae motor neurones. This, ther efore, aids the transition from stance to swing. During turning moveme nts, the tibia is flexed and the dorsal surface is put under compressi on. This can also activate some of campaniform sensilla whose effect o n the flexor motor neurones will reinforce the flexion of the tibia.