A cochlear implant is an electronic system that stimulates the auditory nerve directly, bypassing the hair cells in the cochlea. The Cochlear Implant Programme at Great Ormond Street Hospital is one of around 20 in the UK and to date has carried out over 1000 cochlear implants.
Normal hearing occurs via a complex pathway. In people with normal hearing, sound waves are transmitted from the tympanic membrane (eardrum) across the middle ear to the cochlea (part of the inner ear) as a series of mechanical vibrations.
The cochlear (which is a spiral shape not dissimilar to a snail’s shell) has a membrane (organ of Corti), which is covered with lots of tiny hair cells. These hair cells act as transducers, changing the sound vibrations into electrical signals. Hair cells on different parts of the membrane respond to different frequencies of vibration (pitch). These signals from the hair cells then stimulate fibres in the acoustic (hearing) nerve and are then transferred to the brain where they are perceived as sound.
Sensorineural hearing impairment usually means that the hair cells have been permanently damaged or destroyed. For this reason, conventional hearing aids are not able to provide adequate benefit. A cochlear implant however bypasses the damage in the inner ear by using a series of tiny electrodes that stimulate the acoustic (hearing) nerve directly, producing signals that can then be interpreted by the brain as sound.