The amphibian ear has been extensively studied and used as a general model of the vertebrate auditory system, but much remains to be understood of an important component of the amphibian middle ear, the opercularis system. The opercularis system consists of an opercularis muscle that connects the suprascapula of the shoulder girdle to the operculum, a movable element in the oval window of the otic capsule. The system can function as a seismic sensory system. Ground vibrations produce movements of the forelimbs and shoulder, and the opercularis muscle transmits this motion to the operculum. Movements of the operculum in turn produce waves within the inner ear fluids that stimulate appropriate sensory areas. Research is proposed to further examine the mechanics of vibration transmission through the opercularis system, and to test if the system can provide directional cues about the source of vibrations. The opercularis system also appears to function in sound reception. In many amphibians, it is the only middle ear system, and probably acts as an alternate route of sound transmission to the inner ear. In species with tympanic ear structures, the opercularis system either may act as an alternate route for sound transmission or may modulate the responsiveness of the tympanum-stapes complex. Experiments are proposed to examine how the opercularis system functions in sound reception, including work on the mechanics of sound transmission through the system and functional effects of the system on sound transmission via the tympanic ear. Lastly, laser vibrometric studies will be made to precisely measure how the operculum moves in the oval window in response to sound and vibration. The proposed research will add to our understanding of the amphibian auditory system as a model system, and will further explore mechanisms of sound and vibration transmission through body tissues to the inner ear. This work is relevant to understanding pathways of vibratory and auditory stimulation of the inner ear that bypass the tympanum and auditory ossicular chain, such as those involved in the phenomenon of bone conduction hearing in humans.
| Kim, J; Hetherington, T E (1993) Distribution and morphology of motoneurons innervating different muscle fiber types in an amphibian muscle complex. J Morphol 216:327-38 |
| Hetherington, T E (1992) The effects of body size on functional properties of middle ear systems of anuran amphibians. Brain Behav Evol 39:133-42 |
