The Process of Hearing
To summarize, hearing begins with pressure waves hitting the auditory canal and ends when the brain perceives sounds. Sound reception occurs at the ears where the pinna collects, reflects, attenuates, or amplifies sound waves. These waves travel along the auditory canal until they reach the ear drum, which vibrates in response to the change in pressure caused by the waves. The vibrations of the ear drum causes oscillations in the three bones in the middle ear, the last of which sets the fluid in the cochlea in motion. The cochlea separates sounds according to their spectrum. Hair cells in the cochlea perform the transduction of these sound waves into afferent electrical impulses. Auditory nerve fibers connected to the hair cells form the spiral ganglion which transmits the electrical signals along the auditory nerve and eventually on to the brain stem. The brain responds to these separate frequencies and composes a complete sound from them.