Morphology of inner hair cell stereocilia in C57BL/6J mice as studied by scanning electron microscopy.

The observation that hair cell tuning curves exhibit frequency selectivity as sharply tuned as that seen in auditory nerve fibers has prompted closer examination of the sensory hairs or stereocilia. The present study was designed to examine the morphologic organization of inner hair cell stereocilia in a mammalian species, the neonatal C57BL/6J mouse. The cochleae of mice were fixed in OSO4, dehydrated, dissected, and prepared for scanning electron microscopy. An examination of the number of stereocilia per inner hair cell revealed an orderly decrease from base to apex. Conversely, there was a 300% increase in the height of the tallest stereocilia, a 100% increase in the height of the middle row stereocilia, and a 30% increase in shortest stereocilia from base to apex. The total surface area of the stereocilia, per hair cell, was shown to increase by approximately 250% from the base to the apex of the cochlea.