Why do we get Goose Bumps when it is cold?
[ 2006-03-29 09:13 ]
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Goose bumps are a vestige from the days when humans
were  covered with hair.
When it's hot and you need to cool down, little muscles at
the base of each hair relax. Your hair becomes relaxed. Your
sweat glands pump out body heat in sweat. Your blood
vessels get big to take more heat to the skin to get rid of
it. When it's cold, the arrector muscle pulls the hair
up. The duct to the sweat glands gets small to conserve
heat. Our blood vessels also get small to save heat.
Hair standing up doesn't make very good insulation
we don't have enough fur for that. Humans don't have very much
hair on their bodies anymore. Millions of years ago, humans
probably did. And that hair standing on end helped keep people
warmer. Those little muscles we have on the end of each hair
still work. They still make goose bumps.
Cold is not the only thing that can cause our hair to stand
on end. Fear or anger can cause the same reflex. The
same is true for other mammals. You'll notice that on a cat or
dog. Their fur gets bigger when they're angry or afraid.
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vestige: 殘余，痕跡
gland：腺
muscle：立毛肌
conserve：貯藏
insulation：隔熱
reflex：反應(yīng)
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