| A cochlear implant can be a helpful aid for | | | | hearing aid, which amplifies the sounds that enter the |
| sensorineural hearing loss in children and adults. This | | | | outer ear. However, people with hair cell damage often |
| article describes how normal hearing and implants | | | | find it difficult to distinguish between different sounds |
| work. | | | | – including speech – and simply increasing the |
| What might seem like a simple process – the | | | | volume of those sounds does not solve the problem. |
| hearing of a sound – is dependent on the proper | | | | For these people, a cochlear implant (sometimes called |
| functioning of a complex sequence of events. A | | | | a 'bionic ear') may help. |
| problem with any step in this sequence can lead to | | | | How Does a Cochlear Implant Work?Cochlear |
| hearing loss. | | | | implants take the place of the damaged hair cells by |
| How Does the Ear Work?In the outer ear, sound is | | | | directly stimulating the cochlear nerve. |
| collected in the auricle (the external part of the ear) | | | | A microphone worn behind the ear picks up sounds, |
| and funnelled down the ear canal to the eardrum.In the | | | | converts them to an electrical signal and transmits this |
| middle ear, a chain of tiny bones (or ossicles) transmits | | | | to a processor. The processor may be also be |
| vibrations in the eardrum to the inner ear.In the inner | | | | positioned behind the ear, or may be carried in a |
| ear, the vibrations transmitted by the ossicles cause | | | | pocket or on a belt.The processor organizes and filters |
| movements in the fluid that fills a cavity called the | | | | the signal, then sends it to a transmitter in the form of |
| cochlea. The cochlea is lined with ‘hair cells' bearing | | | | radio waves. The transmitter is worn on the side of |
| flexible protein filaments, and movements in the fluid | | | | the head, held in place by a magnet.Under the skin, |
| cause the filaments to bend. The bending stimulates | | | | implanted into the bone directly beneath the transmitter, |
| the hair cells and this in turn stimulates the cochlear | | | | is a second magnet together with a receiver/stimulator. |
| nerve, which carries information about the sound that | | | | The receiver/stimulator picks up the radio signal from |
| was heard to the brain, for processing.Sensorineural | | | | the transmitter and passes this down a thin wire that |
| Hearing Loss and Cochlear ImplantsLoss of hearing | | | | has been threaded into the cochlea.Electrodes on the |
| can stem from problems at any point in this sequence. | | | | wire stimulate the cochlear nerve as would healthy hair |
| Sensorineural hearing loss is caused by abnormalities in | | | | cells.The patient can usually return home the same |
| the hair cells that prevent them transmitting normally to | | | | day, but the implant is not switched on for up to a |
| the cochlear nerve. These abnormalities can be | | | | month after the surgery. An extended period of |
| present at birth, or may be caused by drugs, infection | | | | training follows, during which the patient learns how to |
| or prolonged exposure to very loud noise. | | | | interpret the sounds that he or she hears through the |
| Sensorineural hearing loss may be overcome with a | | | | implant. |