There are four parts to the ear that work together to help you hear and interpret sound. The outer ear collects the sound waves and by means of the ear canal, sends the sound to the eardrum. The eardrum (tympanic membrane) is a thin membrane, almost like the skin on a drum, which serves as a seal between the outer and middle ear.  Once sound waves reach the eardrum, it vibrates and set a chain reaction off.  As the eardrum vibrates, the vibrations are sent to three bones: the malleus (hammer), incus (anvil) and stapes (stirrup).  These bones work together to send the vibrations from your eardrum to a snail-shaped part in the inner ear, called the cochlea.  Inside the cochlea, there are thousands of haircells of which the top portion moves when the cochlea vibrates.  These movements lead to the production of nerve impulses, which are carried to the brain via the auditory (acoustic) nerve.  It is in the brain where the signal is interpreted as sound.

The haircells will move differently according to different incoming sounds, thus allowing the brain to distinguish between a variety of sounds in terms of pitch (frequency) and loudness (intensity).