How we hear ?

The outer ear:

consists of the visible part of the ear, also called the auricle, and the ear canal. What we call ‘noises’ are actually just ‘sound waves’, which are transmitted by the air. Sound waves are collected and guided through the ear canal to the eardrum. The eardrum is a flexible, circular membrane that vibrates when sound waves strike it.

The middle ear:

is an air-filled space separated from the outer ear by the eardrum, or the tympanic (pronounced: tim-`pa-nik) membrane. In the middle ear are three tiny bones: malleus, incus, and stapes, often referred to as the hammer, the anvil, and the stirrup. They are collectively known as the ossicles. These form a bridge from the eardrum to the inner ear. The ossicles also vibrate in response to movements of the eardrum and in doing so, amplify and relay the sound to the inner ear via the oval window.

The inner ear:

referred to as the cochlea (pronounced: kohk-le-a), is similar in shape to a snail shell. It contains several membranous sections filled with fluids. When the ossicles conduct sound to the oval window, the fluid begins to move, thus stimulating the minute hearing nerve cells, called hair cells, inside the cochlea. These hair cells in turn send electrical impulses via the auditory nerve to the brain where it will be interpreted as sound.