Form and role of deformation in excitation of an insect mechanoreceptor.

Abstract

THE proprioceptive campaniform sensilla of insect legs are thought to sense strains developed in the cuticle of the leg in weight bearing and walking. Pringle1 proposed that a ridge in the cuticular cap of the sensillum bulges outward under compressional shear stress, thus stretching and exciting the underlying single bipolar sensory neurone. His main assumption was that the mechanical compliance of the cuticle should differ in at least two subregions of the cap. This hypothesis has been widely accepted and is probably substantially correct, but several essential details have not been tested directly. Until now, the structure of the cap has not been shown clearly in cockroach legs, although it has been in dipterous halteres2,3, and neither the mechanical properties of the cap cuticle nor the magnitude and direction of the excitatory deformation have been measured, although the fine structure of the bipolar neurone4,5 and its responses to punctate stimulation6,7 are known.