title: Hair-bundle stiffness dominates the elastic reactance to otolithic-membrane shear.
abstract: Efficient transduction by acousticolateralis organs requires that a stimulus force principally deflect hair bundles, rather than flex other structural elements. Hair bundles might therefore be expected to provide a large fraction of the impedence to shear motions of otolithic membranes and other accessory structures. We measured the stiffness for shear motions of the bullfrog's saccular otolithic membrane, and determined the stiffness due to a single hair bundle and its associated extracellular filaments; this component is termed the elemental stiffness. Stiffness measurements were made by displacing the base of a flexible probe whose tip was coupled to the otolithic membrane, and simultaneously measuring the flexion of the probe and the displacement of the membrane. The average elemental stiffness, about 1350 microN.m-1, only modestly exceeded the stiffness of individual hair bundles. The hair bundles therefore provide the dominant component of stiffness in the bullfrog's sacculus, and thus account for a significant component of impedance to otolithic-membrane shear. As a corollary, stiffness changes or active movements in hair bundles should influence the mechanical responses of this and other receptor organs.
authors.affiliation: Center for Basic Neuroscience Research, University of Texas Southwestern Medical Center, Dallas 75235-9039.
authors.forename: M E
authors.initials: ME
authors.lastname: Benser
authors.forename: N P
authors.initials: NP
authors.lastname: Issa
authors.forename: A J
authors.initials: AJ
authors.lastname: Hudspeth
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D004558:Electric Stimulation; D006198:Hair Cells, Auditory / Q000502:physiology* / Q000648:ultrastructure; D008433:Mathematics; D008854:Microscopy, Electron; D010037:Otolithic Membrane / Q000502:physiology* / Q000648:ultrastructure; D011892:Rana catesbeiana