| The utricle is a vestibular end-organ that detects head movements in the horizontal plane. Hair cell bundles sit on top of the utricular epithelium and are covered by otoconial membranes. The hair cell bundles transform head movement into hair cell signals by mechanotransduction, which modulates afferent signals to the central nervous system. Utricular afferents differ in their morphophysiological properties and these differences are strongly correlated with the location of the afferent terminal on the utricular neuroepithelium. This raises the possibility that afferent differences originate in part from spatial differences in utricular peripheral mechanics, i.e., the otoconial membranes, and hair cell bundles. In this study, I quantified the dimensions of the otoconial membranes, bundle heights, and the coupling between them, using the utricle of a turtle, Trachemys scripta. I found that all of them change systematically as functions of location and cell type. The patterns I observed resemble spatial patterns in afferent physiology and may help explain them. This is the first study in any vertebrate to quantify the morphology of hair cell bundles, otoconial membranes and the coupling between them. My results provide an experimental foundation for models of utricular mechanics, and they should contribute to our understanding of signal processing in otoconial organs. |
