WEBVTT

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(SCIENCE TREK MUSIC)

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JOAN CARTAN-HANSEN, HOST: All
living creatures have circadian

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rhythms, that is a sort of
biological clock.

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These rhythms are controlled by
a consistent and essential

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force: Light (Sound of a Click)
And dark.

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A human has a group of nerves
called the SCN.

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It's located between and behind
the eyes.

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It picks up light or dark and
send signals to parts of the

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brain that coordinate the timing
of tasks like eating and

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sleeping.

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When it gets dark, the SCN
signals your brain and the brain

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releases a hormone called
melatonin.

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That makes you feel drowsy.

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When the SCN detects light, it
signals your brain to release a

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hormone called cortisol .

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And that helps wake you up.

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When you travel across time
zones, you can get what's called

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jet lag.

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Jet lag happens when the time at
your new destination doesn't

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match the time your body is
thinks it's in.

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You may get sleepy or have an
upset stomach.

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It takes about a day for each
time zone you traveled for your

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body to re-adjust to your new
location.

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For more information about
sleep, check out the Science

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Trek website.

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You'll find it at
Sciencetrek.org