Picture courtesy of Cochlear Ltd.

Here is how the ear works normally:

1. Sound is transmitted as sound waves from the environment. The sound waves are gathered by the outer ear and sent down the ear canal to the eardrum.
2. The sound waves cause the eardrum to vibrate, which sets the three tiny bones in the middle ear into motion.
3. The motion of the bones causes the fluid in the inner ear or cochlea to move.
4. The movement of the inner ear fluid causes the hair cells in the cochlea to bend. The hair cells change the movement into electrical pluses.
5. These electrical impulses are transmitted to the hearing (auditory) nerve and up to the brain, where they are interpreted as sound.