cochlea

The cochlea, that spiral-shaped structure in the inner ear, is filled with fluid. In this fluid, tiny hair cells called stereocilia are positioned in bundles along the length of the structure. These bundles sense vibrations transmitted into the fluid from the bony levers of the inner ear. The vibrations picked up by the hair cell bundles, each tuned to its own frequency, mechanically transduce the sound impulses by opening ion channels that set up electrical impulses in the auditory nerve, that travel to the brain. But motion in fluid creates friction known as viscous drag. How do the hair cell bundles overcome it? Scientists have figured out that the hair cells in the bundles are not only finely tuned to reduce viscous drag, but actually to employ it for even higher sensitivity to sound.