Hearing Part 1: How We Hear

  An elementary explanation of how the human ear works:

–      sound waves travel down the ear canal to a thin membrane called the eardrum; 

–      the eardrum vibrates, and these vibrations pass through the three tiny bones of the middle ear into the cochlea;

–      the tiny hair cells that line the inside of the cochlea move in accordance with these vibrations;

–      this movement stimulates the auditory nerve;

–      the auditory nerve carries the signal to the brain.

A slightly more complex explanation:

1. Catching Sound  

The part of the ear that’s responsible for catching the sounds of the outside world is called the outer ear, and it is comprised of just two things, the ear (technically called the ear lobe), and the ear canal. The ear lobe captures vibrations in the air (sound waves) and directs these vibrations down the ear canal to the eardrum, a thin membrane stretched tightly across the entrance to the middle ear.

2. Amplifying Sound  

The middle ear is a small, air-filled cavity, with the eardrum on one side and the entrance to the inner ear on the other (called the oval window). The three tiny bones of the middle ear receive the vibrations from eardrum, amplify them, and deliver them to oval window, which is on the outside of the cochlea. 

3. Converting Sound

The cochlea is the actual organ of hearing. It begins at the oval window and curves around into a shape resembling a snail shell. There are three liquid filled canals inside of the cochlea, separated from one another by thin membranes, and inside one of these canals is the Organ of Corti.

Now this is where we get to the good stuff.

The Organ of Corti contains three things: inner hair cells (hairs that move when certain wave lengths hit them), outer hair cells (which inhibit the movement of the inner hairs), and something called the basilar membrane, which transmits the fluid vibrations to these hairs. (Yes, this will be important later. It will be on the test.)

4. Sending Sound

And finally, these hairs stimulate the auditory nerve, which sends the information to the brain.

* * *

Put far more succinctly:

“When sound waves from the world outside strike the eardrum, it vibrates. These vibrations from the eardrum pass through the three bones of the middle ear and into the inner ear through the oval window. Action of the oval window causes fluids in the cochlea to create waves where they disturb the basilar membrane. Inner hairs attached to the basilar membrane convert the waves into electrical impulses that are transmitted to the brain by the auditory nerve. The hair cells are critical to hearing; it is the inner hairs that move in the Organ of Corti fluids, and translate the fluid movements to chemical messengers that can in turn be converted to electrical impulses that the brain understands.”  

–– (http://www.hearingcentral.com/howtheearworks.asp)

Other websites from which I gathered information, as of June 17, 2012

http://www.ndt-ed.org/EducationResources/HighSchool/Sound/humanear.htm

http://www.medicinenet.com/script/main/art.asp?articlekey=21685