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  • KidsHealth presents "How the Body Works,"

  • with Chloe and the Nurb.

  • [MUSIC PLAYING]

  • [MUSIC PLAYING]

  • Nurb, just because eyeballs are the size

  • of ping pong balls doesn't mean they make good ping pong balls.

  • A nurb cannot be blamed for his love of scientific exploration,

  • my dear Chloe.

  • It is what makes him a nurb.

  • Then can we use the eyeballs to explore

  • how an eyeball works instead?

  • We could, but these are kind of small and--

  • Squished.

  • One might say that.

  • How about we take a look at him?

  • Most excellent idea.

  • Let's do.

  • The eyeball is a beautiful machine

  • with lots of different parts working together

  • to let you see.

  • Poets say the eyes are the window to the soul.

  • Well, the window to the eyeball is the cornea,

  • a dome of clear tissue up in front of the eye

  • that focuses light as it passes through.

  • Look at that beautiful green eye.

  • And brown eye.

  • And blue eye.

  • The colorful part is called the iris, right?

  • Yup.

  • It's right behind the cornea.

  • In the middle of the iris is a black circle called

  • the pupil, an opening that lets light into the eye.

  • The iris has muscles attached to it

  • that change its size, making the pupil bigger and smaller

  • to control how much light gets through.

  • So the pupil gets smaller when there's a lot of light

  • and bigger when it's dimmer.

  • Don't look now, but I think we're being watched.

  • Hmm.

  • Ha!

  • He blinked first.

  • Which is a good thing.

  • Blinking protects and moistens the eye.

  • Good point.

  • So what happens after the light has

  • passed through the cornea and the pupil?

  • The light passes through the lens.

  • Like the lens in a camera?

  • Precisely.

  • The lens focuses the light onto the back of the eye, where

  • seeing really starts to happen.

  • Can the lens in the eye focus on stuff

  • that's close and stuff that's far, like a camera lens would?

  • It sure can.

  • Let's head inside to see how.

  • Last one through the pupil's a rotten egg!

  • The lens is held in place by a bunch

  • of fibers, which are attached to this ciliary muscles.

  • (SINGING) Ciliary!

  • Ciliary!

  • Ciliary!

  • The ciliary muscles change the shape

  • of the lens to let the eye change its focus from something

  • close by to something far away.

  • What are you waiting for?

  • Let's get focusing!

  • To see something near, the ciliary muscle

  • makes the lens the thicker.

  • To see something far, the ciliary muscles

  • makes the lens thinner.

  • From the lens, we travel to the retina,

  • the back wall of the eyeball.

  • Right, because the lens focuses the light onto the retina.

  • The retina has millions of light sensitive cells called

  • rods and cones-- about 120 million rods and 7

  • million cones in each eye.

  • Whoa.

  • That's a lot of rods and cones.

  • What's the difference between them?

  • It's the difference between black and white and color!

  • The rods see in black, white, and shades of gray,

  • and help us see the shape and form of a thing.

  • Rods also help us see in the dark.

  • And the cones see color?

  • Cones are sensitive to one of three colors-- red, green,

  • or blue.

  • Together, they let us see millions of colors,

  • but cones need more light than rods to work with.

  • Hey, what's this thing behind the retina?

  • Hey, no bouncing on the optic nerve.

  • It carries messages to the brain about what you're seeing.

  • The rods and cones change the colors

  • and shapes you see into millions of nerve messages.

  • Then those messages are carried along the optic nerve

  • to the brain.

  • It's like your eye is sending the brain

  • a report on what you're seeing.

  • Then your brain translates the report

  • into cat, apple, or bicycle.

  • Or-- a ping pong ball!

  • Hm?

  • Keep your eye on the ball there, Nurb.

  • Oh!

  • Ha ha, it's on.

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KidsHealth presents "How the Body Works,"

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B1 US lens eye pupil eyeball retina cornea

How Your Eyes Work

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    Cristal Chen posted on 2017/05/10
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