The Process of Hearing
The ear is divided into three parts: the outer or external ear, the middle ear, and the inner ear.
The external ear, which is the visible portion of the ear collects sound and sends it to the ear drum (tympanic membrane). The eardrum is a small membrane that separates the external ear from the middle ear.
The middle ear houses a chain of three tiny bones (ossicles) that are connected together. The first bone is attached to the eardrum. These bones are set into vibration by movement of the eardrum which continues the transmission of sound through the pathway of hearing. The third ossicle in the chain is attached to the inner ear by another small membrane called the oval window.
The inner ear contains the tiny nerve endings for balance and hearing. It also contains a special fluid that becomes set in motion by movement (or displacement) of the oval window. The tiny nerve endings are then stimulated and each one sends a unique message or impulse to the brain.
The brain is separated into two distinct hemispheres. The left hemisphere receives the majority of information collected by the right ear, while the right hemisphere of the brain receives the majority of information collected by the left ear. The brain interprets the information received and the sensation of hearing occurs. The small differences in the intensity (or loudness) of the sound reaching our ears, along with the time it takes for sound to reach our ears, plays an important role in our brain's ability to filter noise, interpret or understand speech, and localize or determine the direction from which sound is coming.
When sound is processed through only one ear, the brain is deprived of this very complex information, and its efficiency in interpreting sound is significantly reduced. Therefore, both ears play a significant role in the process of hearing.
Types of Hearing Impairment
There are three types of hearing impairment: conductive, sensorineural and mixed.
The outer ear and middle ear are involved in the conduction of sound, therefore, a problem located in these areas is considered a conductive hearing impairment. It may be corrected or partially corrected with surgery and/or medication. The use of hearing aids may also be an option.
Pathology associated with the inner ear is considered a sensorineural hearing impairment. Generally, this type of hearing impairment is the result of damage or degeneration to the tiny nerve endings. It is typically not correctable with surgery or medication. The use of hearing aids is usually the treatment of choice.
If both of these types of impairment occur at the same time, the result is a mixed hearing impairment.