The Central Nervous Control of Complex Movements in the Uropods of Crayfish

Abstract

The control of postural uropod muscles in the crayfish has been investigated by stimulating ‘command’ interneurones isolated from central connectives. Reciprocity is preserved between exciters and inhibitors innervating the same muscle, and between motor axons serving antagonists. The control of combined movements, involving groups of muscles that are neither synergists nor antagonists, was analysed by simultaneous recording. Most command fibres affected several different motor pathways, and different command fibres produced different combinations of output. It is concluded that quite complex movements may be encoded in the connexions of a single central element. In several instances it was shown unequivocally that single central neurones were responsible for releasing the motor output. One identified command neurone produces a stereotyped, rhythmic pattern of activity in several motor pathways. This effect did not depend upon afferent feedback for its form or frequency. Command interneurones often produce asymmetrical responses in the appendages of the two sides. Some of these make connexions only to the ipsilateral motor neurones, others only to contralateral ones, and most make differential connexions on the two sides.