Department of Physiology, Development and Neuroscience

Dr. Matthew Mason: Further Information...

University Physiologist Tel: +44 (0)1223 333829, Fax: +44 (0)1223 333840, E-mail: mjm68@cam.ac.uk

Mason, M.J. & Narins, P.M. (2002a) Vibrometric studies of the middle ear of the bullfrog Rana catesbeiana I. The extrastapes. Journal of Experimental Biology 205: 3153-3165.

In this study, we used a laser Doppler interferometer to measure the vibration of the tympanic membrane and stapes footplate in male and female bullfrogs, in response to airborne sound. Having confirmed previous observations made in another frog species of an out-of-phase movement of the two structures, indicative of a rocking motion, we went on to measure from the cartilaginous extrastapes. We found evidence to suggest that there is a bending movement between the extrastapes and stapes shaft (pars media), which increases the velocity ratio between the tympanic membrane and stapes footplate. Furthermore, we showed that the ascending process of the extrastapes, a thin, strap-like piece of cartilage which has been almost completely ignored in previous accounts of middle ear mechanics, is literally pivotal in converting extrastapedial movement into movement at the oval window. Rather than the one-ossicle system of textbooks, the extrastapes and stapes of the frog actually behave as if they are two! The flexibility between the two structures may confer a protective advantage if the ear is exposed to high-amplitude pressures.

Comparing our experimental results, we found a significantly greater velocity ratio in male frogs than in females, which we believe is due to increased flexion between extrastapes and stapes. We explored the implications of this further in a later paper, which also considered anatomical sexual dimorphism in the bullfrog ear (Mason et al., 2003). In the sister-paper to this one (Mason & Narins, 2002b), we demonstrate that the stapes footplate is coupled to the operculum, and that movement of the eardrum in response to airborne sound results in opercular movement too.

To access this paper via the JEB website, please click here.

Please note the following correction:

On page 3162, the right-hand side of Equation 9 should read "dA/dB".

Please contact me if you would like to be sent a reprint copy of this paper.