Control of abdominal extension in the freely moving intact crayfish cherax destructor. I. Activity Of the tonic stretch receptor

Electrical recordings were made from the sensory neurone of the tonic muscle receptor organ in the abdomen of the intact, freely behaving crayfish Cherax destructor. Slow extensions of the abdomen were evoked by lowering a platform from beneath the suspended crayfish, and the movements and tonic sensory neurone activity were video-recorded simultaneously. The recordings showed that the tonic sensory neurone was active when the abdomen was fully flexed prior to the extension. When the extension began, however, the sensory neurone ceased firing shortly after movement was detected, irrespective of the load applied to the abdomen. When the abdomen was physically blocked from extending fully, the sensory neurone did not fire. The tonic muscle receptor organ is considered to be the length-detecting sensor for a load-compensating servo-loop, but the results demonstrate that its activity pattern during extensions evoked by a platform-drop in C. destructor are not consistent with that role.