Sound waves enter the outer ear through the pinna and travel through the ear canal. The sound hits the eardrum and makes it vibrate. The sound waves then travel throught the middle ear bones - malleus (hammer), incus (anvil), and stapes (stirrup). The vibrations from the stirrup cause the fluid in the cochlea to move. The vibrations are picked up by nerve fibers which send the sound signal to the brain through the auditory nerve.