In a functioning ear, the outer ear collects the sound, funneling it to the eardrum, which vibrates. This vibration sets three tiny middle ear bones in motion, which causes fluid in the inner ear, or cochlea, to move. The movement of the inner ear fluid causes tiny hair cells inside the cochlea to bend, which in turn creates electrical impulses that are transmitted to the hearing nerve and then up to the brain.
It’s as if the cochlea and its tiny hairs were the translators of one language––vibration––to another––electrical impulses. The brain is the final translator, turning electrical impulses into recognizable words and sounds.
If hair cells in a cochlea are damaged, the electrical impulses cannot reach the auditory nerve, which in turn doesn’t send information to the brain. This is called nerve deafness, although the medical term is sensorineural hearing loss. Naveen came to us with this condition.
A hearing aid, which makes sound louder, will not help if the hair cells can’t transmit any impulses to the brain. A cochlear implant performs the function of the damaged or absent hair cells, using mini-computers to send the electrical impulses to the hearing nerve.
Internal and external parts
The implant body (pictured to the left in its packaging before surgery) is surgically placed under the skin in a shallow “bed” drilled in the bone behind the ear (see surgery pictures on the left). From this ”bed,” a hole is then drilled into the cochlea to allow for the insertion of an electrode array into it. This electrode array will do what the hair cells can’t do, transmit electrical energy.
Externally, a small directional microphone worn at ear-level picks up sound. The sound is then sent through a thin cord to a speech processor, worn either behind the ear or at belt level. The speech processor filters, analyzes and digitally converts the sound into coded signals, which are then sent to the transmitting coil, the telltale magnet attached to the skull of an implant user. The transmitting coil sends the coded signals as FM radio signals to the cochlear implant under the skin. The cochlear implant then delivers the electrical energy to the array of electrodes in the cochlea through a wire (visible in lower picture on left). The electrodes along the array stimulate the auditory nerve fibers in the cochlea, sending it to the brain for interpretation. The brain interprets it as sound or words.