Damaged inner ear hair cells. Scanning electron micrograph (SEM) of age-related degeneration of specialised hair cells and nerve cells within the inner ear. These are the outer hair cells (stereocilia) that line the organ of Corti (the auditory sense organ) inside the cochlea. Normally, sound waves enter the inner ear and displace the fluid surrounding the stereocilia, causing them to bend and trigger nerve impulses. Here, the stereocilia have become swollen and are unable to respond, resulting in deafness.