Berlin 2012 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 32: Physics of Cells III
BP 32.8: Vortrag
Freitag, 30. März 2012, 11:30–11:45, H 1028
The Hair Bundle’s Viscous Losses in Response to Tip-Link Forces — •Johannes Baumgart — Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Str. 38, 01187 Dresden
The ear can sense air vibrations smaller than the Bohr radius. One important step of this highly sensitive process is the mechanotransduction, which takes place in the hair bundle. Therein active forces along the tip links can amplify the motion. Here we investigate which viscous forces counteract this active forces.
One individual bundle consists of closely apposed stereocilia surrounded by a viscous liquid, which are coupled by stiff horizontal top connectors and softer tip links. This configuration ensures a highly coherent motion over broad frequency ranges, as was shown by experimental data in conjunction with a detailed three-dimensional finite-element model incorporating the fluid-structure interaction1.
We investigate with the same numerical model how the bundle responds to a force at all tip links with the same phase and amplitude. This forces can displace the free standing bundle coherently, if the stiff horizontal top connectors below the tip links ensures the coupling. For this mode of motion the assigned viscous drag coefficient is similar to the one for displacing the bundle at the kinociliary bulb, which is mainly due to the external liquid. If the horizontal top connectors are removed, the bundle splays and the related drag coefficient increases by up to thirtytimes for frequencies below a few Hertz.
1 A.S. Kozlov, J. Baumgart, T. Risler, C.P.C. Versteegh & A.J. Hudspeth, Nature, 2011, 474, 376–379.