MIRACLE OF THE SMALLEST THREE BONES IN HUMAN

This is the job of the ossicles, a group of tiny bones in the middle ear. The ossicles are actually the smallest bones in your body. They include:

• The malleus, commonly called the hammer
• The incus, commonly called the anvil
• The stapes, commonly called the stirrup

Sound waves vibrate the eardrum, which moves the malleus, incus and stapes.

The malleus is connected to the center of the eardrum, on the inner side. When the eardrum vibrates, it moves the malleus from side to side like a lever. The other end of the malleus is connected to the incus, which is attached to the stapes. The other end of the stapes -- its faceplate -- rests against the cochlea, through the oval window.

When air-pressure compression pushes in on the eardrum, the ossicles move so that the faceplate of the stapes pushes in on the cochlear fluid. When air-pressure rarefaction pulls out on the eardrum, the ossicles move so that the faceplate of the stapes pulls in on the fluid. Essentially, the stapes acts as a piston, creating waves in the inner-ear fluid to represent the air-pressure fluctuations of the sound wave.

The ossicles amplify the force from the eardrum in two ways. The main amplification comes from the size difference between the eardrum and the stirrup. The eardrum has a surface area of approximately 55 square millimeters, while the faceplate of the stapes has a surface area of about 3.2 square millimeters. Sound waves apply force to every square inch of the eardrum, and the eardrum transfers all this energy to the stapes. When you concentrate this energy over a smaller surface area, the pressure (force per unit of volume) is much greater.

The configuration of ossicles provides additional amplification. The malleus is longer than the incus, forming a basic lever between the eardrum and the stapes. The malleus moves a greater distance, and the incus moves with greater force (energy = force x distance).

This amplification system is extremely effective. The pressure applied to the cochlear fluid is about 22 times the pressure felt at the eardrum. This pressure amplification is enough to pass the sound information on to the inner ear, where it is translated into nerve impulses the brain can understand.

Reference of this article

Haris, Tom.  "Life Science :Human Biology".How Hearing Works.how stuff works Date of Electronic Publication or other Date, such as Last Updated. Day Month Year of acces http://science.howstuffworks.com/environmental/life/human-biology/hearing3.htm.

Let also see the videos, ho do we hear?

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Video2

Practice to write the pathway of hearing mechanism by using flowchart.