The Bionic Ear

by Tim Jacob

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.

COCHLEAR IMPLANT
The cochlear implant is designed to stimulate the user's auditory nerve directly and it has been developed by Professor Graham Clark and his colleagues at the University of Melbourne. Whereas the conventional hearing aid uses sound vibrations, the implant converts sound vibrations into electrical stimuli which are picked up by the auditory nerve and transmitted to the brain.

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.

For additional information:

Ear structure, Radiology Museum, South Bank University - detailed info on structure

Special Senses Menu

Sue Archbold, Paediatric Cochlear Implant Programme, Nottingham General Hospital.

J. Martin, St John's School fot the Deaf, Boston Spa, near Leeds.

Further reading

• "Neurophysiology", R.H.S. Carpenter, pub. Edward Arnold, 2nd ed. 1990*, 3rd ed. 1995. ISBN 0 340 50634 2.
• "The Senses" by H.B. Barlow and J.D. Mollon, Cambridge University Press, 1982, ISBN (pbk) 0 5221 28714 6
• "An introduction to the physiology of hearing" by J.O. Pickles, Academic Press, 1988, ISBN 0 12 554754 (pbk).

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last update 8th May 1998