Sound waves are created when air vibrates. To hear, the ear must change sound into electrical signals which the brain can interpret. The outer part of the ear (the pinna) funnels sound waves into the ear canal. When sound waves reach the eardrum they make it vibrate. Vibrations of the eardrum make the tiny bones in the middle ear move too. The last of these bones (the stapes) passes on the vibrations to the fluid-filled chamber called the cochlea. When the vibrations reach the cochlea, the fluid inside it moves. As the fluid moves it vibrates the hairs on the cells that line the cochlea. Each cell is stimulated by a particular note (or frequency) of sound. The vibration of the hair cells is turned into an electrical signal by the organ of Corti, at their base. The organ of Corti then sends signals down the hearing (auditory) nerve to the brain. Special areas in the brain receive these signals and translate them into what we know as sound.
Your ears create electrical signals that represent an extraordinary variety of sounds. For example, the speed at which the eardrum vibrates varies with different types of sound. With low-pitched sounds the eardrum vibrates slowly. With high-pitched sounds it vibrates faster. This means that the special hair cells in the cochlea also vibrate at varying speeds. This causes different signals to be sent to the brain. This is one of the ways in which we are able to distinguish between a wide range of sounds.