Publisher Summary A cochlear implant system is an electrical stimulator that discharges electrical current to spiral ganglia, giving rise to action potentials in the auditory nerve fibers. It is also a medical instrument that can measure intracochlear evoked potentials, electrical field potentials generated by the electrodes, and electrode impedance. It consists of three main components: an external sound processor, an implanted stimulator, and a programmer. When pressure waves move the footplate of the stapes inward against the fluid of the cochlea, the basilar membrane is set in motion. Different pressure wave frequencies have different patterns of transmission. When a pressure wave reaches the portion of the basilar membrane that has a natural resonant frequency equal to the input sound frequency, the basilar membrane vibrates at its maximum such that the wave energy dissipates and dies. Thus, sound frequencies from 20 Hz to 20 kHz become mapped by their physical distance of travel, or the distance from the stapes.