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  • Some of the issues that are important

  • if you want to have people in space

  • for long periods of time.

  • One is that people will tend to lose

  • bone and muscle mass.

  • We know this.

  • If you have to put a cast on your leg,

  • and you take the cast off after a few weeks,

  • you'll see that your muscles have shrunk in size.

  • And if you measured the bone strength,

  • you'd also see that might have gone down a little bit, too.

  • And so, it's very interesting that our body has that ability

  • to adapt to the loads that are put on it,

  • so that bones and muscles aren't static,

  • they're always changing.

  • While we think of bone as being a solid thing

  • that doesn't change very much,

  • it changes too.

  • And it turns out that in weightlessness,

  • you lose bone.

  • And then you also cause the muscles

  • that work against gravity,

  • what are called the postural muscles,

  • they'll start to shrink and lose strength.

  • There are other things in the cardiovascular system,

  • the heart and blood vessels.

  • And if you think about it,

  • standing up in gravity

  • means you have to work against gravity

  • in order to keep blood pumping to your head.

  • So, if you couldn't keep blood pumping in the head,

  • you'd pass out every time you stood up

  • because when you're lying down,

  • you don't have to push against gravity.

  • But when you stand up,

  • you got to work against gravity

  • to keep blood flowing to your head.

  • And your heart and blood vessels

  • have a really nicely worked-out system

  • to make that happen every time.

  • But that system can also change in weightlessness.

  • And then the other area that changes

  • is the system that has to do with balance.

  • Again, maintaining your balance

  • is something that you're doing against gravity, right?

  • If you didn't have gravity present,

  • you wouldn't have to worry about falling.

  • But you obviously do have to worry about falling,

  • and we have a very highly developed sense of balance

  • to keep us upright

  • and to prevent us from falling.

  • And when you see what skaters do,

  • you realize just how exquisite a system it is.

  • But when you go into weightlessness,

  • your balance system changes.

  • You don't really notice it

  • while you are in weightlessness,

  • but when you come back,

  • you do notice it,

  • that your balance has changed

  • and you have a little bit of trouble

  • maintaining your balance.

  • And what it shows is that while you're in space,

  • your brain is trying to allow you

  • to function in weightlessness.

  • And so, it re-adapts you to be weightless,

  • which you don't notice until you come back

  • and find out that you're now back on Earth

  • with a balance system that's been adapted to space.

  • You know, all life developed here on Earth

  • with gravity being present,

  • so life evolved under the influence of gravity,

  • and then we grow up with gravity being present,

  • so we learn how to walk

  • and catch a ball

  • and ice skate

  • or whatever,

  • all with gravity being present.

  • And what if you were to grow up without gravity?

  • What about the systems that depend on gravity,

  • like your muscles

  • or your balance system

  • or the heart and blood vessels?

  • Would they develop normally,

  • or would they be different in some way?

  • One reason why you might think

  • that it would go down a different pathway

  • is from an experiment

  • that was done some time ago

  • by two neuroscientists

  • called Hubel and Wiesel.

  • And what they did is they had a kitten,

  • and they put a patch over the eye of the kitten.

  • And then the kitten grew up to be a cat,

  • and they removed the patch.

  • And so, the question is,

  • can the cat see out of that eye?

  • Now, there's nothing wrong with the eye, right?

  • But it just hasn't seen anything,

  • there hasn't been any light coming in.

  • And the answer is that the cat can't see out of that eye

  • because what happens is that the brain

  • goes down a different pathway when it develops

  • and the connections that would ordinarily develop

  • to that eye don't develop.

  • And that can't be undone,

  • that's a permanent change.

  • So, the brain of that cat

  • is fundamentally different from the brain of a cat

  • that grew up seeing out of that eye.

  • That cat grew up with a different brain, in essence.

  • So, then you wonder,

  • well, what about gravity?

  • What if you don't have the forces

  • that gravity produces?

  • Is your balance organ going to develop

  • in the same way,

  • or will it be different?

  • If somebody grew up in space,

  • could they come back to Earth and function,

  • or would they really be a different person?

Some of the issues that are important

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B1 中級

TED-ED】重力と人体 - ジェイ・バッキー (【TED-Ed】Gravity and the human body - Jay Buckey)

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    Kevin Tan に公開 2021 年 01 月 14 日
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