Sound!
What the heck is it? How do we hear? Why do we hear?
To explain what sound is, we have to talk about physics, biology, and your brain to really figure it out.
To make it easier, think about a pool.
If I throw a rock into it, it makes a ring of waves that spread out across the surface of the water.
Sound does the same thing, but in the air.
When you hear your favorite song on the radio, it starts out as vibrations in the air being pushed out of the speakers.
These vibrations make teeny, tiny air molecules bump into each other,
sending the vibration across the room as a wave.
The size and speed of the wave changes what it sounds like.
A long, slow wave makes a low sound, like a foghorn. A short, fast wave makes a high sound, like a bell ringing.
Okay, so we understand how sound travels, but how do we hear it?
When you hear your favorite song, the vibrations or waves in the air first hit the folds of your ear called the “pinna”.
These floppy parts of your ear are specially shaped to “catch” these vibrations and make sounds louder
so we can more easily tell where they are coming from.
The vibrations bounce into your ear canal, where they hit the ear drum.
The ear drum is called that because it has a membrane, which is just a thin layer,
like the plastic that covers a drum surface.
This next part is kind of crazy.
When the waves in the air hit the ear drum, they make the surface of the drum
vibrate by moving it back and forth.
Next time you have a piece of paper, hold it up and blow on it or tap it to see what I mean.
As the drum moves, the vibrations hit the three tiniest bones in your body:
the ossicles of the middle ear, called the malleus, incus, and stapes.
These bones act as levers to amplify the sound vibrations and pass them along to
another membrane called the “oval window”, which leads to the cochlea.
Inside the cochlea is a special fluid, called the perilymphatic fluid.
When the ossicles hit the oval window, the sound vibrations turn into sound waves again.
But this time, they are waves in the perilymphatic fluid.
As the waves are transferred through the oval window, it causes the perilymphatic fluid
to slosh across the surface of this, called the Organ of Corti.
All along that surface of the Organ of Corti are these funny little cells that look like flat top haircuts.
And in fact, they’re called hair cells!
These are a type of neuron, which are the cells used by your body to send messages from place to place.
As the perilymphatic fluid sloshes in waves, it pushes over these hair cells,
which tells them to send a message to the brain that a sound has been heard.
After wiggling your hair cells, the sound message is sent to different areas throughout your brain,
eventually reaching the primary auditory cortex found on the upper side of this bulge,
called the temporal lobe. This is where your brain first recognizes the sound.
From there, the information is passed on to other brain regions to better decode and understand the sound.
Some of those areas, like the middle temporal gyrus, have a specialized purpose.
They're important for learning, understanding, and creating language.
Human language is mostly sound-based, so it makes sense that our ability to hear sounds
is closely connected to our speech.
Other animals have special uses for sound, too.
Bats use sound to navigate in the dark through echolocation.
These animals have specialized vocal cords to let them create very high-pitched noises,
sending sound waves through the air in front of them.
When the waves hit an object, some of them bounce back toward the animal.
These are the “echo”.
Differences in the pitch and tone of the sound echo give them information about
the environment around them, letting them “see” using sound!
Owls don’t use echolocation, but they do rely on sound to help them find and track
their prey at night.
They have specialized ears to help them hear as much noise as possible.
For example, in some species, the ears are set at different heights to help them detect
where sounds are coming from.
Even the shape of the owl’s head can play a role
their round faces can act like a “radar dish” to collect sounds and send them back into the owl’s ears.
Scientists also think that whales use sound to communicate with each other.
Whales “sing” as they move through the water, creating very low-pitched tones that sound like this.
Low frequency sounds (sounds with long waves) travel farther than high frequency sounds.
So if whales are communicating with each other across great distances in the ocean,
using low sounds makes sense.
It’s obvious that sound is important for a lot of creatures in our world.
Now we know what sound is, how we hear it, and why it’s useful.
It’s kind of weird to think that we hear and communicate through moving air molecules.
But it’s also amazing how many steps sound has to go through just so we can hear it.
and think about how much you’ve just learned, through the power of sound!