Understanding the Ear

The ear can be divided into three areas, or regions.  These areas group the elements that physically and functionally similar.

  1. Outer Ear
  2. Middle Ear
  3. Inner Ear

The following discussion will describe these three areas and how they function to bring you sound.  Please refer to the diagram below as the various areas of the ear are discussed.

Diagram of the Outer and Inner Ear
Diagram of Ear Courtesy of NIDCD.NIH.GOV

The Outer Ear

The Outer Ear
Simple Depiction of the Outer Ear
The outer ear consists of what can be seen from the outside of the ear.  The external portion of the ear is also called the "Pinna".  The pinna acts like a collection dish to direct the sound waves towards the ear canal.

The ear canal, also called the "auditory canal", is the tube that connects the pinna to the eardrum.  Sound travels down the ear canal from the pinna like a funnel, bringing it to the eardrum.

The eardrum (also called the Tympanic Membrane) is the border or barrior betweent he outer ear and the middle ear.  When the sound waves hit the eardrum, they cause the eardrum to vibrate back and forth at different speeds (frequencies) and different strengths (loudnesses).

The Middle Ear

The Middle Ear
Depiction of the Middle Ear
The middle ear is a cavern with three tiny bones which connect the external ear to the inner ear.  These three bones, together, are called the Ossicles.  The three bones are called the hammer, anvil, and stirrup (also known as the Malleus, Incus, and Stapes).

These three bones transfer the vibrations of the eardrum to the interface with the inner ear.  The hammer is activated by the eardrum, and the stirrup pushes the oval window.  The oval window is a membrane interface to the Cochlea (or inner ear).

Because the Cochlea is filled with fluid, and the initial sound in air, there is a large impediance mismatch between the outer and inner ear.  Most of the sound energy would reflect off of the oval window of the inner ear, instead of being transferred to it.  The bones of the middle ear take the energy from the ear drum and act like a lever to amplify the sound and focus it on the oval window.  The oval window has about 20 times less surface area than the ear drum, and with the lever action of the Ossicles, the energy transmission is much more efficient.

The Inner Ear 

The inner ear consists mainly of the Cochlea and the Auditory Nerve.  The Cochlea looks like a snail shell, and is filled with liquid.  The energy from the sound waves were transferred to the Cochlea from the middle ear through the oval window.  The waves then travel through the Cochlea (back and forth) causing the hair receptor cells to become slightly electrically charged.

The Auditory Nerve (or eighth nerve) receives the signal from the Cochlea (receptor hairs) and transmits those signals to the brain.   

 
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