A cochlear implant is a surgically implanted device that helps overcome problems in the inner ear, or cochlea. The cochlea is a snail-shaped, curled tube located in the area of the ear where nerves are contained. Its function is to gather electrical signals from sound vibrations and transmit them to your auditory nerve (or hearing nerve). The hearing nerve then sends these signals to the brain, where they're translated into recognizable sounds.
If important parts of the cochlea aren't working properly and the hearing nerve isn't being stimulated, there's no way for the electrical signals to get to the brain. Therefore, hearing doesn't occur. (Sometimes referred to as nerve deafness, this is called sensorineural hearing loss.) By completely bypassing the damaged part of the cochlea, the cochlear implant uses its own electrical signals to stimulate the auditory nerve, allowing the person to hear.Article From: http://kidshealth.org