Medical Health Encyclopedia

Cochlear implant

HOW IT WORKS

In a normal ear, sounds are transmitted through the air, causing the eardrum and then the ossicles (middle ear bones) to vibrate. This sends a vibratory wave into the cochlea (inner ear). These waves are then converted by the cochlea into electrical signals, which are sent along the auditory nerve to the brain.

A deaf person does not have a functioning inner ear. A cochlear implant attempts to replace the function of the inner ear by transforming mechanical energy (sound) into electrical energy, which can then be used to stimulate the cochlear nerve (the nerve for hearing), sending "sound" signals to the brain.

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Most cochlear implants operate using several similar components. Sound is picked up by a microphone worn near the ear. This sound is then transmitted to a speech processor worn on the body, usually on a belt. The sound is then analyzed and converted into electrical signals -- which are transmitted to a surgically implanted receiver behind the ear. This receiver then sends the signal through an electrode array (wire) into the inner ear, where the electrical impulses are transmitted to the brain.

HOW IT IS IMPLANTED

Surgery for inserting a cochlear implant is performed with the patient fully asleep. An incision is made behind the ear, sometimes after shaving a portion of the hair behind the ear. A microscope and bone drill are used to open the bone behind the ear (mastoid bone) to allow the internal part of the implant to be inserted.

The electrode array is then passed into the cochlea (inner ear). The receiver is placed into a "well" created behind the ear to help keep it in place, and to make sure it is close enough to the skin to allow transmission of electrical information from the external portion of the device.

After surgery, there will be stitches behind the ear, and you may be able to feel the receiver in its "well" behind the ear. Any shaved hair should grow back. The external portion of the device will be placed about 3-4 weeks after surgery, to give the incision time to heal.