JOAN CARTAN-HANSEN, Host: How do we interact with the world?

We use our five senses.

Seeing, hearing, smelling, tasting and touching.

But how do they all work?

And what do they have in common?

[MUSIC] CARTAN-HANSEN: So what are your five senses?

STUDENTS: Seeing, hearing, smelling, taste, and touch.

CARTAN-HANSEN: We all use our five senses to understand what's happening around us.

For some, that means not becoming somebody else's dinner.

So let's learn about our five senses.

STUDENT: We see with our eyes.

CARTAN-HANSEN: Your eyeball is about the size of a ping-pong ball.

It's covered by the sclera, a tough outer layer; that's the white part of your eye.

When you look at something light travels through the cornea, the front part of your eye.

It goes through the pupil, that's the round black hole in the center.

A muscle called the "iris," or the colored part of your eye, opens and closes the pupil to regulate the amount of light coming in.

Light travels through the lens which focuses the image on the back of your eye or the retina.

Nerve cells on the retina send the image to the optic nerve and then to your brain.

STUDENT: We hear with our ears.

(HARP) CARTAN-HANSEN: A sound creates energy.

Those sound waves enter your ears and travel down the ear canal to the eardrum.

This thin piece of skin is stretched very tight, and when the sound waves hit it, it begins to vibrate.

That makes three tiny bones, known as the hammer, anvil, and stirrup, move, too.

This moves or transmits those sound waves into a snail's shaped structure called the cochlea.

The cochlea is filled with fluid and 17,000 tiny hairlike tissues.

Sound waves move through the fluid and bend the hair.

Somehow the movement of the hair stimulates the fibers leading to the acoustic nerve, and that nerve takes the sound to the brain.

STUDENT: the sense of smell is probably our oldest sense.

CARTAN-HANSEN: Tiny particles too small to be seen with your eyes float into your nose when you breathe.

They drift to the top end of your nasal cavity.

Inside your nose are two small areas called the olfactory epithelium.

These are about the size of your thumbnail, but they contain about 20 million olfactory cells with tiny hairs or cilia.

Those scent particles stick to the cilia and trigger nerve cells.

Those nerve cells send a message to the brain which identifies the scent.

STUDENT: Your sense of taste begins your tongue.

CARTAN-HANSEN: Your tongue is covered with thousands of tiny bumps called papilla.

Inside those bumps, on the back part of the roof of your mouth, and in the very back of your throat are 10,000 tastebuds.

The tiny cells have little hairs.

Dissolved food particles seep into the hairs, and the taste buds sense whether the food is sweet, sour, bitter, or salt.

That information is sent to your brain, and then you decide if the food is good or bad.

STUDENT 1: Did you know most of your sense of taste comes from your sense of smell?

STUDENT 2: So let's share.

STUDENTS TOGETHER: Hey!

STUDENT: Your sense of touch is really a bunch of senses that work together, and you start with your skin.

CARTAN-HANSEN: Your skin is the largest organ in the body.

The layers of skin have at least seven different kinds of sensors.

And there are as many as a million of these microscopic touch sensors in a square inch of skin.

Some of these nerves respond to light pressure; others respond to heavy pressure.

Some are activated by heat, cold, or even vibrations.

So when you touch something all that information activates the nerves, and that information goes to your brain.

Your brain is really the most important part of your five senses.

The brain collects information from all these different sources, and that's how we make sense of the world.

You guys ready?

Let's eat.

STUDENTS: Yeah!

CARTAN-HANSEN: If you want to learn more about the five senses, check out the Science Trek website.

You'll find it at ScienceTrek.org [MUSIC] ANNOUNCER: Presentation of Science Trek on Idaho Public Television is made possible through the generous support of the Laura Moore Cunningham Foundation, committed to fulfilling the Moore and Bettis family legacy of building the great state of Idaho.

By the Idaho National Laboratory, mentoring talent and finding solutions for energy and security challenges.

By the Friends of Idaho Public Television and by the Corporation for Public Broadcasting.