Directional Sensitivity and Mechanical Coupling Dynamics of Campaniform Sensilla During Chordwise Deformations of the Fly Wing

Abstract

The complex morphology of an insect campaniform sensillum is responsible for transforming strains of the integument into a displacement of the campaniform dome and subsequently a deformation of the dendritic membrane. In this paper, the first step in this coupling process was investigated in identified campaniform sensilla on the wing of the blowfly by stimulating the sensilla with chord-wise deflections of the wing blade. Campaniform sensilla neurones were sensitive to both dorsal and ventral deflections of the wing, and thus exhibited no strong directional sensitivity to the chord-wise components of wing deformation. These results are consistent with a simplified mechanical model in which the wing veins act as cylinders that undergo bending and torsion during chord-wise wing deformation. By comparing the responses of campaniform neurones to chord-wise deflections of the wing with those evoked by direct punctate stimulation of the dome, it is possible to estimate the dynamic properties of the coupling process that links wing deformation to dome deformation. In the identified campaniform neurone examined, wing-dome coupling attenuates high frequencies and transforms the chord-wise deflections of the wing into dome deformation similar in degree of excitation to that caused by direct punctate indentions that are two or more orders of magnitude smaller in size.