During normal hearing, sound waves travel through the ear canal and strike the eardrum causing it to vibrate. The eardrum is attached to three tiny bones in the middle ear. The last bone, the stapes, pushes on a fluid-filled chamber in the inner ear, called the cochlea. This fluid movement causes sensitive hair cells within the cochlea to bend.
When the hair cells bend, they generate an electrical signal that is sent to the brain. Age, disease, injury, or repeated exposure to loud noise can damage the various structures of the ear and interfere with hearing.
There are two specific types of hearing loss: conductive hearing loss, which is caused by a mechanical problem in the ear canal or middle ear that blocks the conduction of sound; or sensorineural hearing loss, which is caused by damage to the inner ear, auditory nerve, or auditory nerve pathways in the brain. Conductive hearing loss is often reversible; sensorineural hearing loss is not.