An expanding mechanical role for the tiny mammalian endolymphatic duct: 1. Modification of Békésy model is specifically needed to cope with ambient pressure variation—with weather, altitude or ocean depth

Abstract

von Békésy’s pioneering work and two-chamber model with basilar membrane (BM) separating the perilymph chambers was a first-pass assumption which worked to explain basic frequency-band analysis. Yet it did not cover psychoacoustical phenomena. Nor did it cover the repeated demonstrations by this author of baseline displacements of the BM, nor mysterious changes in the volume of the tiny endolymphatic duct—even in human ears with normal thresholds. Since 2009 the duct has been shown to possess all the necessary characteristics of a pressure vessel, viz., it is lined with aquaporins and tight junctions while the cells of the stria vascularis maintain a strict osmotic gradient. We submit that such evolutionary change was necessary because ambient pressure changes are too large to be corrected by passive equalization and need to be actively eliminated to preserve hearing sensitivity. Any theory must cover marine mammals which have adapted to ocean pressures measured in megapascals. In this case, infrasound is modelled as a varying pressure pedestal which must be cancelled. This video presentation covers one possible mechanical configuration for how such a cancelation might be achieved—a hypothesized feedback control system utilizing outer hair cell somatic motility plus our previously-modelled otolith-based pressure transducer.