Mechanics of the transduction of sound in the tympanal organ of adults and larvae of locusts

Abstract

The mechanical transmission of sound in the tympanal organ of adults and 5th instar larvae of Locusta migratoria and Schistocerca gregaria has been investigated by means of stroboscopic measurements within a frequency range from 1-20 kHz. Frequency dependent spatial distributions of amplitudes and phases of oscillation on the tympanal membrane and the Müller's organ could be demonstrated. Cuticular structures on the membrane may act as a lever arm (e.g. elevated process) and cause a transformation of the (unidimensional) membrane motion into components of displacements in the Müller's organ perpendicular, as well as even parallel, to the membrane. Sites of maximum relative displacements at distinct frequencies are found to be correlated to the course of the dendrites of the acoustic receptor cells. Differences in morphology of the tympanal organ between the two species as well as between adults and larvae always correspond to differences in the mechanical properties (resonances etc.). Consequently, differences or changes in the neurophysiological response characteristics of the different receptor cells have been found. Based upon these findings a correlation between the anatomical and physiological classification of the receptor cell groups is presented.

Input-Driven Components of Spike-Frequency Adaptation Can Be UnmaskedIn Vivo

“…Laser interferometry and stroboscopic illumination allow the observation of the tympanic oscillations under acoustic stimulation (Schiolten et al, 1981;Breckow and Sippel, 1985;Robert and Göpfert, 2002). Our results predict that a slight decrease in oscillation amplitude should be visible during the first…”

Sound signalling in orthoptera

“…So, there is a mismatch between the low frequency properties of the membrane and the frequency response of the d-cells. There is as yet no explanation for this observation, although it is probable that the frequency response of the ear is not solely related to movement of the tympanum and that the way in which Müller's organ responds may also have an influence (Stephen and Bennet-Clark, 1982;Brekkow and Sippel, 1985). When the tympanum vibrates, Müller's organ vibrates as well and the driving forces that act on it produce a twisting movement described by Stephen and Bennet-Clark (1982) as being similar to a Lissajous' figure.…”

Convergent evolution of insect hearing organs from a preadaptive structure

“…In particular, the CF is not represented as a peak in the spectra of the tympanal vibration. The mismatch can be explained either by an intrinsic tuning of sensory cells (as proposed for tympanal receptor cells of bushcrickets ;Old¢eld 1985) or by di¡er-ential movements of the sense organ in respect to the tympanic membrane (as seen in grasshoppers; Breckow & Sippel 1985;Meyer & Elsner 1995). (c) Convergent evolution of ears in Diptera…”