The organ of Corti is lined with rows of auditory hair cells. As sound waves move deep into the ear (outer to middle to inner), they cause vibrations in the perilymph. Thousands of hair cells sense the liquid motion through projecting bundles of hairlike cilia. The hair cells convert the cilia motion into electrical signals that are transmitted to primary auditory neurons, which in turn transform the signals into electrochemical impulses dispatched to the brain for further translation and interpretation.
In other words, we hear something. It’s a remarkably fast and understandably delicate.
With age, hearing acuity naturally diminishes, but excessive exposure to noise or overly loud sounds can speed the process by damaging the fragile cilia. The problem has become particularly worrisome among teens, particularly with the advent of devices like the MP3 player and iPod and the widespread use of earbuds, which channel more, louder sound deeper into the ear. (adapted from UCSD Health sciences)
The cochlea is the working part of the inner ear, a tiny spiral-shaped cavity filled with a watery liquid called perilymph and lined with a strip of sensory tissue known as the organ of Corti (colored red in this image of a cochlea produced by M’hamed Grati and Bechara Kachar at the National Institute on Deafness and other Communication Disorders). (link)