The human ear is a vulnerable organ. It is divided into three parts the outer ear, the middle ear, which is made up of the ear drum (tympanic membrane) and a chain of tiny bones called ossicles, and the inner ear (the cochlea). The cochlea contains hair cells which, when stimulated, generate an electrical current in the auditory nerve which then transmits the signals to the hearing centres of teh brain.
Each region of the ear can suffer damage and even the most powerful hearing aids are ineffective if the function of both inner ears is impaired.
Sounds are collected by a microphone and are then converted into electrical signals by a speech processor. This processor passes on the signals to 22 electrodes surgically implanted inside the cochlea, which send the impulses to the brain via the auditory nerve. The microphone and transmitter are fitted behind the ear and are held in place by a magnet on the receiver which is buried under the skin.
Children who have been deafened since birth have been receiving the implant as a priority because they already have some experience of normal hearing. Even then, the implant is only used where the conventional hearing aid would be of no use. However, more recent developments have allowed congenitally deaf children to have the operation. But, because of the expense and the intensive rehabilitation period, implants have not been generally available to adults.
Adapted from an article in the Daily Telegraph by Emily Beardall.
For additional information:
Ear structure, Radiology Museum, South Bank University - detailed info on structure
Sue Archbold, Paediatric Cochlear Implant Programme, Nottingham General Hospital.
J. Martin, St John's School fot the Deaf, Boston Spa, near Leeds.
return to Teaching Menu or Tim Jacob homepage
last update 8th May 1998