Mechanism of Hearing
The ear is comprised of three portions: an outer ear (external), a middle ear and inner ear. Each part performs an important function in the process of hearing.
The outer (external) ear consists of an auricle and ear canal. These structures gather the sound and direct it toward the ear drum (tympanic membrane).
The middle ear chamber lies between the external and inner ear. This chamber is connected to the back of the throat (pharynx) by the eustachian tube which serves as a pressure equalizing valve. The middle ear consists of an eardrum and three small ear bones (ossicles): malleus (hammer), incus (anvil) and stapes (stirrup). These structures transmit sound vibrations to the inner ear. In so doing, they act as a transformer, converting sound vibrations in the external ear canal into fluid waves in the inner ear. A disturbance of the eustachian tube, eardrum or the ear bones may result in a conductive hearing impairment. This type of impairment is usually corrected medically or surgically.
The inner ear (cochlea) contains the microscopic hearing nerve endings (hair cells) bathed in fluid. Inner ear fluid waves move the delicate nerve endings which in turn transmit sound energy to the brain by the hearing nerve, where it is interpreted into sound. A disturbance in the inner ear fluids or nerve endings may result in a sensorineural hearing impairment. Most often this type of hearing impairment is due to a hair cell loss. This type of impairment is not correctable with surgery.