How We Hear

The ear is comprised of three parts:  an outer ear (external), a middle ear, and an inner ear (containing hearing and balance chambers).  Each part performs an important function in the process of hearing and balance.

The Outer Ear

The outer (external) ear consists of the auricle and the ear canal.  These structures gather the sound waves and direct them towards the eardrum (tympanic membrane).

The Middle Ear

The middle ear chamber lies between the external ear and inner ear, behind the eardrum.  This air filled chamber receives air through the Eustachian tube.  It is a tubular structure connecting to the ear from the back of the throat (pharynx) and above the palate.  The Eustachian tube is responsible for equalizing the pressure in the middle ear with the atmospheric pressure.  The middle ear consists of an eardrum and three small bones (ossicles): the malleus, incus, and stapes.  These structures are connected to each other and 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.  The smallest bone in the human body (stapes) actually moves in and out of the inner ear opening, causing fluid waves to occur in the inner ear.  Any disturbance of the Eustachian tube, eardrum, or the ear bones may result in a conductive hearing loss, meaning impairment of sound conduction to the inner ear.  This type of impairment is usually correctable medically or surgically.

The Inner Ear

The inner ear contains microscopic hearing nerve endings (hair cells), which are bathed in fluid.  Inner ear fluid waves move the delicate sensory hair cells in the cochlea.  These hair cells in turn convert the sound energy into an electrical signal, and transmit this signal through the hearing nerve to the brain, where it is interpreted into sound.  A disturbance in the inner ear fluids, hair cells, nerve endings, or hearing nerve may result in a sensorineural hearing loss.  This type of impairment cannot be restored to normal with surgery.  The inner ear is also responsible for our balance.