The Human Ear

    Humans and other animals have ears to detect sound waves.  In the most primitive sense, they are meant to alert us of predators or a possible meal.  Then we took advantage of our ears, and learned to communicate through speech and music.
    The human ear consists of three main parts; the outer ear, the middle ear, and the inner ear.  The outer ear consists of:  the pinna, the ear canal, and the eardrum.  The pinna is the cartilage flap that is visible, and acts as a funnel to chorale the sound waves through the ear canal to the eardrum.  To hear more sound, you can cup your hand over your ear in the shape of a larger funnel.

    Once the sound wave reaches the eardrum, it is transferred to the inner ear via the middle ear which consists of; the three smallest bones in the human body called the hammer, anvil, and stirrup, and also the eustachian tube which equalizes the pressure on the eardrum to compensate for atmospheric pressure. The eardrum vibrates, which causes the bones in the middle ear to vibrate. This action transmits the information to the inner ear.

    When the sound reaches the inner ear, it is changed from a longitudinal wave into electrical signals that can be processed by the brain.  To do this, the stirrup vibrates against a small tissue called the cochlea.  This is filled with an endolymph fluid.  The vibrating fluid causes tiny hairs, called cilia, to vibrate at the same frequency as the endolymph fluid.  The cilia are then able send that information to the brain using electrical signals through the auditory nerve..


So why do our ears ring after a prolonged period of loud noise?

    Like any other object, the cilia in the ear have resonant frequencies.  When the cilia resonate at their resonate frequency for a long period, the get damaged and die.  The ringing sensation is the signal that is produced from a dying cilia.  The cilia never grow back, so it is best to keep this from happening.   To prevent this from happening, it is best to reduce the amount of loud noise that enters the inner ear.  The most common way this is done is by using ear plugs when exposed to loud noises.

This animation shows how an incoming sound wave
interacts with the ear drum and causes it to vibrate.  
After this point, the sound wave is no longer in longitudinal form.
It is transferred to the brain using electrical signals.