As the ossicles vibrate the oval window, the perilymph that fills the scala vestibuli transfers the pressure throughout the cochlea. The basilar membrane, which is wider and stiffer at the apex than at the base of the cochlear spiral, bends slightly in response to vibration. The auditory receptor cells are called hair cells because they possess stereocilia, which participate in the signal transduction process. The hair cells are located between the basilar membrane and the reticular lamina, a thin membrane that covers the hair cells. The stereocilia extend beyond the reticular lamina into the gelatinous substance of the tectorial membrane.
Hair cells synapse upon dendrites of neurons whose cell bodies are located in the spiral ganglion.
Vibrations are transduced by hair cells as the basilar membrane vibrates up and down. The movement of the basilar membrane relative to the tectorial membrane causes the cilia on hair cells to bend. Bending of the cilia causes the hair cells to either depolarize or hyperpolarize, depending upon the direction of the bend. The cilia directly regulate the flow of potassium from the endolymph into the hair cell. At rest, there is a small influx of potassium.