How We Hear

Ear

The ear is made up of three main parts: the outer, middle, and inner ear.

outer ear The visible part of the outer ear is called the auricle or pinna (1).  It collects sound waves and channels them into the ear canal (2) where the sound is amplified.  The sound waves then travel toward a flexible membrane at the end of the ear canal.  This is the eardrum (3).  When the sound waves reach the eardrum, they make it vibrate - just like when you hit a real drum.
middle ear The vibrations from the eardrum (1) then pass into the middle ear, which contains three tiny bones:  the hammer (2), the anvil (3), and the stirrup (4).  These bones are the tiniest in the human body.  The sound vibrations then pass through a memebrane called the oval window into the fluid of the inner ear.  A tube at the bottom of the middle ear, call the Eustachian tube connects to the back of the nose to control the air pressure.
inner ear When the sound waves reach the inner ear, they enter the cochlea (1), a system of tubes shaped like a snailshell.  the cochlea is filled with a watery liquid which moves in response to the virations within the oval window.  As the fluid vibrates, 25,000 tiny nerve endings are set in motion.  These movements are converted into electrical impulses along the auditory nerve (2) to the brain.  The brain then interprets these signals as sound.