Gravity and the human body - Jay Buckey

重力と人体 ― ジェイ・バッキー

翻訳: Teruhiko Kasai 校正: Tomoyuki Suzuki

Some of the issues that are important

人間が宇宙空間で

if you want to have people in space

長期間 過ごすには

for long periods of time.

重要な問題があります

One is that people will tend to lose

第一に人間は

bone and muscle mass.

骨や筋肉を失いがちです

We know this.

知っての通り

If you have to put a cast on your leg,

足にギプスをつけて

and you take the cast off after a few weeks,

数週間後に外すと

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

筋肉の大きさが縮みますね

And if you measured the bone strength,

そして骨の強さを測ると

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

少し弱っているとわかります

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

興味深いことに 我々の体は

to adapt to the loads that are put on it,

負荷への適応力があるため

so that bones and muscles aren't static,

骨や筋肉は不変ではなく

they're always changing.

常に変化します

While we think of bone as being a solid thing

骨は固いので あまり変化しないと

that doesn't change very much,

思いがちですが

it changes too.

骨も変化しているのです

And it turns out that in weightlessness,

また 無重力では 骨量が減少することが

you lose bone.

分かっています

And then you also cause the muscles

そして重力に対抗する

that work against gravity,

筋肉である

what are called the postural muscles,

姿勢筋が

they'll start to shrink and lose strength.

縮み始め 力を失います

There are other things in the cardiovascular system,

心臓血管系にも

the heart and blood vessels.

影響があります

And if you think about it,

考えてみてください

standing up in gravity

重力がある状態で 立っていると

means you have to work against gravity

重力に逆らって

in order to keep blood pumping to your head.

血液を頭に送り続ける 必要があります

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

頭に血を送り続けられなければ

you'd pass out every time you stood up

立つたびに気を失うでしょう

because when you're lying down,

寝ていれば

you don't have to push against gravity.

重力に逆らう必要はありません

But when you stand up,

でも立っていれば

you got to work against gravity

重力に逆らって

to keep blood flowing to your head.

頭に血を送り続けなければなりません

And your heart and blood vessels

心臓と血管は

have a really nicely worked-out system

本当に良くできたシステムで

to make that happen every time.

常にこれを行います

But that system can also change in weightlessness.

しかしこのシステムも 無重力では変化します

And then the other area that changes

他に変化するものは

is the system that has to do with balance.

平衡感覚に関する機能です

Again, maintaining your balance

平衡感覚を保つということは

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

重力に逆らうことですね？

If you didn't have gravity present,

重力が無ければ

you wouldn't have to worry about falling.

転ぶ心配はありませんが

But you obviously do have to worry about falling,

普段は当然 気をつけなければなりません

and we have a very highly developed sense of balance

だから我々には高度に発達した 平衡感覚があって

to keep us upright

真っすぐ立つことができ

and to prevent us from falling.

倒れることもないのです

And when you see what skaters do,

スケーターを見ると

you realize just how exquisite a system it is.

このシステムの 素晴らしさがわかります

But when you go into weightlessness,

でも無重力では

your balance system changes.

平衡機能が変化します

You don't really notice it

無重力の中では

while you are in weightlessness,

気づきませんが

but when you come back,

地上に戻った時に

you do notice it,

気づきます

that your balance has changed

and you have a little bit of trouble

平衡機能が変化し バランスを保つのに

maintaining your balance.

幾分 苦労します

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

宇宙にいる間

your brain is trying to allow you

脳は無重力でも体が 上手く動かせるように

to function in weightlessness.

調整しようとします

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

無重力に再適応させるのです

which you don't notice until you come back

このことは戻るまで気づきません

and find out that you're now back on Earth

地球に戻った時に

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

平衡機能が宇宙に適応した状態で 帰ってきたのだと気づきます

You know, all life developed here on Earth

ほら 地球上のすべての生命は

with gravity being present,

重力下で発達したのでしたね

so life evolved under the influence of gravity,

つまり 生命の進化は 重力の影響を受け

and then we grow up with gravity being present,

私たちも重力下で成長します

so we learn how to walk

だから歩き方も

and catch a ball

ボールを捕り方も

and ice skate

アイススケートの仕方も

or whatever,

何であれ

all with gravity being present.

すべては重力下で 身につけています

And what if you were to grow up without gravity?

では もし無重力環境で成長したら どうなるでしょう？

What about the systems that depend on gravity,

重力に依存するシステム

like your muscles

例えば筋肉や

or your balance system

平衡機能や

or the heart and blood vessels?

心臓や血管はどうなるでしょう？

Would they develop normally,

正常に発達するでしょうか？

or would they be different in some way?

それとも何か違いが出るでしょうか？

One reason why you might think

違ってくると考える

that it would go down a different pathway

理由の一つは

is from an experiment

ある実験に基きます

that was done some time ago

かなり前に

by two neuroscientists

２人の神経科学者

called Hubel and Wiesel.

ヒューベルとウィーセルが 行ったものです

And what they did is they had a kitten,

彼らは１匹の子猫の

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

片目を遮蔽しました

And then the kitten grew up to be a cat,

子猫は成長し

and they removed the patch.

遮蔽を外しました

And so, the question is,

そこで問題は

can the cat see out of that eye?

猫は遮蔽されていた目で 見ることができるか？です

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

遮蔽された目は 特に問題はありません

But it just hasn't seen anything,

ただ 何も見て来なかったので

there hasn't been any light coming in.

光が入ったことがないだけです

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

猫はその目で見ることができない これが答えです

because what happens is that the brain

何が起こっているかというと

goes down a different pathway when it develops

脳の発達は異なる経路をたどり

and the connections that would ordinarily develop

通常なら発達すべき その眼との連結が

to that eye don't develop.

発達しなかったのです

And that can't be undone,

これは取り返しできない

that's a permanent change.

恒久的な変化です

So, the brain of that cat

その猫の脳は

is fundamentally different from the brain of a cat

眼で見て成長した 普通の猫の脳とは

that grew up seeing out of that eye.

根本的に異なります

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

要するに その猫は違う脳で 成長したのです

So, then you wonder,

ここで疑問が生じます

well, what about gravity?

では 重力の場合はどうでしょう？

What if you don't have the forces

重力が無ければ

that gravity produces?

どうなるでしょう？

Is your balance organ going to develop

平衡器官は

in the same way,

普通に発達するでしょうか？

or will it be different?

それとも違いが出るでしょうか？

If somebody grew up in space,

もし宇宙で成長し

could they come back to Earth and function,

地球に戻ったら 正常に機能するでしょうか？

or would they really be a different person?

それとも全く違う人間に なってしまうのでしょうか？