The long-term objective of the research described in this application is to elucidate structure-function relationships in inner ear sensors. These relationships are expected to be rich in implications regarding the physical mechanisms employed in signal processing. A thorough understanding of the relationship between sensor structure and function is necessary so that the underlying mechanisms of inner ear pathologies might be understood and rational measures undertaken to alleviate them. Inner ear sensors process a variety of incoming sensory signals including airborne auditory, substrate-borne seismic and internally generated signals concerning the position and movement of the head in space. The proposed study focuses on the structure and function of two of these sensors; the auditory sensor and the saccule. The animal model used in our studies is the red-eared turtle (Pseudemys scripta elegans). The structural and functional similarity between the turtle auditory sensor and that of other vertebrates including mammals has resulted in substantial contributions to the understanding of auditory sensory cell biophysics and signal processing. The research described in this proposal will take advantage of the proven utility of the turtle inner ear and extend its use to studies of seismic sensitivity. Two major questions will be addressed; 1) How are the various components of the peripheral auditory sensor in the turtle organized to provide signal frequency characteristics and source location?, and 2) What is the specific role of the saccule in this model system? Sensor morphology will be studied with light microscopy and scanning and transmission electron microscopy. Functional parameters of individual primary afferent nerve fibers will be identified electrophysiologically using microelectrodes advanced into the eighth cranial nerve. This approach allows the investigator to study information encoded in the activity of nerve fibers leaving the sensor: as it is normally received by the central nervous system. The principal investigator is trained in each of the experimental methods required to complete the goals of the proposed research.