Reflex Control of Abdominal Flexor Muscles in the Crayfish

Abstract

In the crayfish abdomen most of the power for the flexor twitches employed in swimming is supplied by the massive oblique muscles which are innervated by large motor axons from the third root. All of the delicate flexor control of the abdomen is vested in a thin, superficial sheet of muscle fibres which have the histological characteristics of ‘slow’ muscle and are innervated by a special, independent supply of small motor nerves (Kennedy & Takeda, 1965). These forty or so muscle fibres and half-dozen axons comprise a reflex apparatus of exquisite complexity, both with respect to innervation pattern (which ranges from single to sextuple for single muscle fibres) and to central modulation of efferent discharge.