Well, the answer to that question can get quite complicated, but I will do my best to explain it.
First, sound is picked up by the microphone (worn either behind the ear or as a clip on clothing), which as I explained in my last post, is one of the external components of the implant. Then, the sound waves are transmitted by cable to the speech processor, also an external component. In the past, the speech processor has looked like a small box that the patient has to carry in a pocket (see previous post for picture). With newer technology, however, the processors are small enough to fit on the earpiece with the microphone. The speech processor sorts and digitizes the sound into a code of electrical signals, which travels to the transmitting coil. This is the circular shaped part of the device that attaches to the skull behind the ear via magnet (illustrated on the left).
|This is a picture of the electrode array.|
This part is inserted into the cochlea,
which is why the array has a spiral shape.
At this point, the sound moves to the internal components of the cochlear implant via the skin by means of FM radio signal, at which point it reaches the receiver/stimulator. The receiver/stimulator is the part that contains the internal magnet (it sits directly beneath the transmitting coil). From there, the sound is distributed to the electrode array. By definition, an electrode is a conductor which allows electricity to transfer across items that are nonmetallic (i.e. skin). The electrode array is a collection of tiny electrodes (current cochlear implants can have up to 24), each of which stimulates an area of the auditory nerve fiber inside the cochlea. Finally, the nerve notifies the brain that sound occurred. The more active electrodes that stimulate the nerve, the better the sound quality for the patient.
As technology advances, changes occur with cochlear implants. They are becoming much easier to use and are significantly more cosmetically appealing that they were ten years ago. The third and final post about cochlear implants will be about the latest design/features of cochlear implants--stay tuned!