Re: how does a sound wave get received?

Sound is received in the ear in a few steps.  It seems like you know a 
little about what sound is, but I'm going to explain it for those who may 
not know.  Sound is a series of waves in the air, which if you could see 
them, would look like ripples in a pond.  When you throw a pebble into the 
water, the water rushes away from it in a series of small waves.  Air does 
the same thing when you make a sound.  Your vocal cords make the air 
vibrate, and the vibrations move through the air away from you in waves.  
So your voice is like the pebble, creating waves.

These sound waves reach the outside of your ear first.  The outside part of 
your ear is called the "auricle".  The ridges and hollows of your auricle 
help focus the sound.  Try putting your fingers behind your ears and making 
them stick out.  Can you hear better when you do that?  Why do you think 
that is?

The sound then goes into your ear canal.  The official name for this is the 
"external auditory meatus".  Your ear canal doesn't do much except protect 
your eardrum.  Then the sounds reach your eardrum, officially called the 
"tympanic membrane".  Your eardrum really does work like a drum.  It is a 
thin piece of skin that vibrates when sound hits it.

The job of the eardrum is to move three bones that sit behind your eardrum 
in your ear.  These three bones are very small - they are the smallest 
bones in your body, and each one is smaller than a grain of rice!  They are 
called the "ossicles", and each one has a name - the malleus (or hammer), 
incus (or anvil), and stapes (or stirrup).  They got these names because 
that's really what they look like.  When your eardrum vibrates, it makes 
these three little bones vibrate.

The last step is a big one.  The stapes, or the last bone in your ear, is 
attached to another membrane, very much like your eardrum.  On the other 
side of this membrane is the real place where hearing happens.  This place 
is called the "cochlea", and it looks just like a snail shell.  The cochlea 
is filled with fluid (it's basically salt water).  When the stapes vibrates 
this eardrum-like membrane, it makes the fluid inside the cochlea move.  
Inside the cochlea are also little hairs.  These hairs can tell when the 
fluid inside the cochlea is moving, and they send that information to the 
brain.

The brain sorts it all out, and then you decide how to react to the sound. 
 Was it a danger sound?  Was it someone talking?  Should I run away, or 
should I answer a question?  The most important part of hearing a sound is 
what it means to you.  The voice of your mom makes you feel completely 
different from the voice of the boy who was mean to you last week, even 
though the sounds they make are almost the same.

There are some good web sites which explain this and other related topics. 
See http://hyperion.advanced.org/19537/, or  http://faculty.washington.edu/chudler/bigear.html.  
There are also lots of books appropriate for the K-3 grade level at the library 
or bookstore which do a great job of explaining the brain and senses.

Please contact me if you have any other questions!