When sound waves reach the ear, they are gathered by the funnel-shaped outer ear and channeled into the middle ear. As sound passes to the middle ear, the sound waves hit the tympanic membrane, or ear drum. The vibrations then travel through the middle ear and reach the fluid-filled inner ear. The inner ear contains an important structure called the cochlea. Inside the cochlea, sound vibrations move tiny hairs that are attached to nerve fibers. In this way sounds are converted to signals that are sent to the brain via the auditory nerve. Disease, damage, or deformity of the cochlear hair cells is a common cause of hearing impairment or deafness. These malfunctioning hair cells may send intermittent or unclear signals to the auditory nerve, or send no signal at all. A device called a cochlear implant can restore hearing by replacing these damaged structures with a wire that is implanted in the cochlea. In order to stimulate the hearing process, sound waves are first received by a microphone unit that hangs over the back of the ear. The sounds are then passed via a thin wire to a speech processor that is often worn on the belt. This processor amplifies and filters sound before converting it into digital signals. These digital signals are sent back via the same wire to a transmitter located on the head. The transmitter then sends radio signals to a receiving unit embedded just under the scalp. The receiving unit then stimulates the wire implanted in the cochlea, enabling the cochlea to send clear signals to the auditory nerve. Although the surgery may permanently damages the cochlea, cochlear implants can greatly improve hearing, even in people who are profoundly deaf. There are several potential complications associated with this procedure that should be discussed with the doctor prior to surgery.