Measuring Sound-Induced Motions of the Alligator Lizard Cochlea

by A.J. Aranyosi

This page briefly documents my PhD thesis, which I defended on March 21, 2002, and submitted as a final document shortly after. In brief, the thesis describes using an in vitro preparation of a vertebrate cochlea to study the mechanical response of the cochlea to sound stimulation. To summarize the basic results:

  • Maintaining an endolymphatic fluid apically can contribute significantly to the longevity of an in vitro prep;
  • Under the conditions used in this study, the computer microvision imaging system allows measurements of motions as small as 2 nanometers in the plane of microscope focus and 20 nanometers in the direction of the microscope axis;
  • The basilar papilla exhibits two modes of motion - one translational and one rotational - and this combination of modes makes the sensitivity of different hair cells more uniform;
  • In the tectorial region of this cochlea, the mechanical properties appear to be stiffness-dominated over the frequency range of interest;
  • In the free-standing region, the mechanical properties of hair bundles and their interaction with cochlear fluids can account for much of the frequency selectivity seen in hair cell receptor potentials.
  • MIT has made scanned, PDF, and hardcopy versions of my thesis available. The scanned version is freely available, but the images are terrible - some even appear solid black! I can't vouch for the quality of the PDF ($29 to non-MIT users) or hardcopy ($59 to non-MIT users, $74 overseas) versions. I'm currently checking with the MIT libraries to find out if I'm legally allowed to send out hardcopy and/or electronic reprints of my thesis, or at least copies of the figures.