Modelling locust tympanal systems: understanding the link between biomechanics and neurophysiology
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1
University of Strathclyde, Department of Electronic and Electrical Engineering, United Kingdom
For over 50 years the auditory systems of insects have been of great interest to researchers in the field of acoustic systems. However, only recently have advances in technology allowed a more scrupulous approach to the study of the insect ear.
The locust hearing system consists of a stretched tympanal membrane backed by a tracheal air sac. The membrane has two distinct zones, the thin transparent membrane and anterior to this, the thick opaque membrane. At the internal boundary between these zones Müller’s organ, a mechanosensory receptor organ, innervates the membrane, attaching at two areas of sclerotised cuticle - the pyriform vesicle (PV) and folded body (FB). Neurophysiological studies of the locust ear have shown that receptor cells coupled to the FB region are tuned to low and medium frequency stimuli in the range 1-12 kHz. In contrast, those cells linked to the PV are tuned to sound of frequency from 12-30 kHz.
Scanning Laser Vibrometry (SLV) of the tympanum in response to relevant sounds within the locust hearing range of 1-30 kHz indicates that a travelling wave forms on the membrane. The origin of the wave is consistently in the posterior thin region of the membrane and at lower frequencies – those less than 12 kHz - the wave converges to a maximum at points on the FB. However at sound of a higher frequency range, the area of convergence is at the PV.
This new work investigates the interesting and potentially valuable characteristics of locust ears. The properties which define the system have been studied using SLV and Scanning Electron Microscopy. Thereafter virtual computer models, representing the auditory system, have been built and finite element analysis applied. The finite element analysis uses a combination of the examination of standard free-resonating eigenmodes, and a simulation of the interaction of the tympanal membrane structure with a sound field.
Eigenmode analysis of the membrane model highlights three major modes. Firstly, the fundamental mode with an amplitude maximum located in the thin region. Secondly a mode with two maxima at opposite phase, one in the thin region and the other situated at the location of the FB. Using acoustic-structure interaction simulations, with a load frequency between these two eigenfrequencies, our results show the formation of a travelling wave due to mode coupling. This travelling wave starts in the thin region and ends at the model FB location, as previously reported in the experimental SLV measurements. The third mode of importance has several maxima spanning smaller areas than the maxima associated with the other two modes mentioned. One of these maxima is located in the attachment region of the PV.
For a wide range of stimuli, the model and simulations enable us to predict the unique membrane behaviour. The results are analysed with a view to linking the biomechanical response and corresponding neurophysiological response of a locust. This allows us to understand the mechanical processes undergone by the ear structures, as well as the influence of the nervous system.
Keywords:
Locust,
modelling,
Tympanum
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for student poster award)
Topic:
Sensory: Audition
Citation:
Mackie
D,
Gordon
S and
Windmill
J
(2012). Modelling locust tympanal systems: understanding the link between biomechanics and neurophysiology.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00141
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Received:
27 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Mr. David Mackie, University of Strathclyde, Department of Electronic and Electrical Engineering, Glasgow, G1 1XW, United Kingdom, david.mackie@eee.strath.ac.uk