Sensory Systems in the Swimmerets of the Crayfish Cherax Destructor and their Effectiveness in Entraining the Swimmeret Rhythm

Abstract

ABSTRACT The branching patterns and profiles of the main sensory nerves of the swimmerets of Cher ax destructor are described. The innervation is generally similar to that in Pacifastacus but there are important differences that may be due to species variation or that may explain apparent differences in the physiology of the two species. The two large axons from the long strand of the stretch-receptor complex in Cherax give rise to non-spiking signals whereas those from the short strand are not active during passive protraction and retraction of the swimmeret. The rhythmic movements of one swimmeret are sufficient to entrain the fictive swimmeret rhythm of an otherwise deafferented ventral nerve cord. The parameters of this entrainment match those of the known reflexes associated with swimmeret movement. Ablation experiments show that the stretch-receptor complex is necessary and sufficient for this entrainment and that input from the pleural plate hairs and swimmeret hairs is not required. Sinusoidal current injection into the non-spiking stretch receptors can also entrain the fictive rhythm of the deafferented cord. From these results it is argued that the non-spiking stretch receptors play an important part in stabilizing and adjusting the frequency of the swimmeret rhythm. The swimmeret system is therefore another example of patterned motor output generated by a distributed, multicomponent network and this may be a general feature of cyclically rhythmic systems.