How Cochlear Implants Work
The ear processes sound through three main mechanisms: the outer ear, the middle ear and the inner ear.
Sound waves traveling through the air enter the outer ear - the visible outer part of the ear and the ear canal and pass into the middle ear. The middle ear contains the eardrum, and three tiny bones. When the sound waves reach the eardrum, it vibrates and, in turn, causes the tiny bones to move. The movement of the bones further generates motion of fluid in the snail shell-shaped cochlea in the inner ear.
The cochlea is lined with thousands of tiny sensory receptors called hair cells. When the fluid in the cochlea is set in motion, the hair cells convert the vibrations into electrical impulses, which are then delivered by the auditory nerve to the brain. The brain interprets these electrical impulses as sound.
In the profoundly deaf, hair cells are usually damaged or depleted so that they cannot generate the electrical charges that bring sound vibrations to the brain. However, despite the lack of hair cells, there are usually some surviving hearing nerve fibers, which are the key to how the cochlear implant works.
 A Clarion implant chip. |
1. Sound waves reach a small microphone worn on the head.
2. The sound is converted into an electrical signal which is sent to a speech processor by way of a tiny cord. The processor converts the signal into a code that is sent back up the cord.
3. The signal is transmitted through the skin to the implant by radio waves.
4. The implant decodes the signal and sends it to an array of electrodes placed within the cochlea.
5. The electrodes directly stimulate the hearing nerve fibers in the cochlea. The fibers cause electrical impulses to be carried by the auditory nerve to the brain, where they are interpreted as sound.
All images courtesy of Advanced Bionics