The picture at left shows the device that was implanted into Chance's head. It consists of a magnet and a computer chip encased in silicon, the electrode array, and a ground wire. The magnet serves to allow the external parts to "stick" to it. The larger parts (the magnet and computer chip) are just under the skin in the skull, and the electrode array is the part that is actually placed into the cochlea.
Technically speaking, a cochlear implant is just the device that is implanted into the skull and cochlea. However, without something to tell the implant what to do, it is useless. The external parts of the implant are the microphone, speech processor, and transmitter coil, which also has a magnet to help it to attach to the implant.
The microphone, batteries, and processor are on an over-the-ear unit similar to a hearing aid. The processor converts sound into digital signals that it sends up through the wire to the telecoil.
The telecoil has a magnet in it to "stick" to the magnet in the implant. It also has a transmitter that transmits the signal across the skin to a receiver in the implant. The processor then interprets that signal to know which electrode to fire, at what rate and intensity, and for how long. (You can view an animation of this, as compared to natural hearing and hearing with a hearing aid, here.)
The magnet in the telecoil is replaceable, with more or less powerful magnets depending on the need.
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