Sound waves entering the ear travel through the external auditory canal before striking the eardrum and causing it to vibrate.

The eardrum is connected to the malleus, one of three small bones of the middle ear. Also called the hammer, it transmits sound vibrations to the incus, which passes them to the stapes. The stapes pushes in and out against a structure called the oval window. This action is passed onto the cochlea, a fluid-filled snail-like structure that contains the organ of Corti, the organ for hearing. It consists of tiny hair cells that line the cochlea. These cells translate vibrations into electrical impulses that are carried to the brain by sensory nerves.

In this cut-view, you can see the organ of Corti with its four rows of hair cells. There is an inner row on the left and three outer rows on the right.

Let's watch this process in action.First, the stapes rocks against the oval window. This transmits waves of sound through the cochlear fluid, sending the organ of Corti into motion.

Fibers near the upper end of the cochlea resonate to lower frequency sound. Those near the oval window respond to higher frequencies.