"Frequency-dependent acoustic pathways in the amphibian ear: Evidence from models, measurements and microseismic stimulation" PM Narins, UCLA, Depts. of Physiological Science and OBEE Biology, Los Angeles, CA 90095
ABSTRACT. The frog inner ear consists of a complex of fluid-filled membranous sacs and canals containing eight distinct clusters of sensory hair cells. In this talk, I shall attempt to delineate the potential pathways for acoustic energy flow toward two of these clusters located within the amphibian papilla (AP) and the basilar papilla (BP). In addition, laser Doppler velocimetry was used to record the velocity responses of the contact membranes of the AP and BP. Acoustic energy flow through these two structures is frequency-dependent such that the AP contact membrane displays a peak velocity amplitude at frequencies less than 500 Hz whereas the BP contact membrane velocity response exhibits a maximum above 1100 Hz. Our data advocate for a mechanical substrate underlying the frequency segregation in the auditory nerve fibers innervating the AP and the BP. A quantitative mathematical model that explains the main features of the empirical data obtained from direct measurements of the AP and BP contact membranes will be discussed. Finally, intracellular eighth nerve recording from bimodal fibers in response to simultaneous microseismic and auditory stimuli provides a first approach to characterizing the tympanic and extratympanic pathways for acoustic energy flow to the inner ear. The frog inner ear thus provides a rich substrate for the examination of the mechanics, neural function and transduction subserving vertebrate hearing.