Control of abdominal extension in the freely moving intact crayfish cherax destructor. II. Activity Of the superficial extensor motor neurones.

The activity of the superficial extensor motor neurones was recorded during slow abdominal extension in the crayfish Cherax destructor. Postural extensions were evoked by lowering a platform from beneath the suspended crayfish. During extensions where the abdomen was physically blocked from achieving full extension, the largest superficial extensor motor neurone (SEMN6) fired at a higher rate than during unhindered extensions. Blocking a segment neighbouring that being examined also increased SEMN6 activity, demonstrating an intersegmental spread of the reflex. The increase in SEMN6 firing rate occurred in the absence of activity in the sensory neurone of the tonic muscle receptor organ, demonstrating that the tonic sensory neurone is not necessary for load compensation during these abdominal extensions in C. destructor. The findings support earlier evidence suggesting that other receptor systems can mediate load compensation in the abdomen of the crayfish.