Afferents of the anterior adductor muscle in the freshwater pelecypod Anodonta cygnea L.

Afferent signals evoked by electrical and mechanical stimulation of the muscle in the nerves of the anterior adductor muscle of the freshwater mussel (Anodonta cygnea L.) have been analyzed. On the basis of the findings, the existence of primary and secondary sensory neurones is suggested. Two types of primary neuron, one showing slow and another one showing quick adaptation, while at least three types of secondary sensory neurones, namely "on" and "on-off" ones with quick adaptation and a "phase-tonic" one with slow adaptation could be distinguished. The specific stimulus of the sensory neurones could be the tonicity of the muscle (stretch) rather than the touch or the velocity of pressure alteration.