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Summer is winding down here in the Northern Hemisphere,
北半球的夏天慢慢退去，
which means we've started to reflect on our long days at the lake and all the times we've jumped into swimming pools.
这意味着我们开始回想在湖边悠长的日子以及我们跳进游泳池的所有时间。
And there's one thing we've noticed: Being immersed in water is really relaxing.
我们注意到了一件事：沉浸在水中真的很放松。
As it turns out, though, this isn't just because of the warm weather or the sound of the waves.
然而，事实证明，这不仅仅是因为温暖的天气或海浪的声音。
There's something larger at play here, called the mammalian dive reflex.
还有更重要的原因—哺乳动物潜水反射。
And you can take advantage of it all year round, no pool required.
并且全年都可利用它且无需任何游泳池。
When you dunk yourself in water, this reflex kicks in, and your body does some pretty interesting things.
当你潜入水中，这种反射开始起作用，你的身体会做一些非常有趣的事情。
Mainly, as soon as your face makes contact with the water, it triggers a reduction in your heart rate called bradycardia.
你的脸一旦和水接触，你的心率就会减慢，这被称为心动过缓。
The effect happens very quickly, and studies have shown that the mammalian dive reflex can drop someone's heart rate by 10 to 25%!
这种效果很迅速，并且研究已经表明哺乳动物潜水反射可以将一个人的心率减少10%至25%。
This is what results in that nice, peaceful feeling.
这会让你有一种美好平静的感觉。
Multiple studies have shown that when your heart rate slows down, you feel calmer.
多种研究已经表明当你的心率放缓，你会感觉更平静。
This is also why breathing exercises are so relaxing
这也是为什么呼吸练习是如此放松
although in that case, you're slowing your heart rate through careful, slow breaths.
虽然在这种情况下，你是在通过小心缓慢的呼吸来减慢你的心率。
But while it's a nice bonus, this reflex doesn't exist to help you chill out.
虽然这是一个很好的奖励，但这种反射的存在并不是为了帮助你冷静下来。
Instead, research suggests it's an evolutionary adaptation that allows us to stay underwater for an extended period of time.
相反，研究表明是一种进化适应让我们能够在水下呆很长一段时间。
After all, lowering your heart rate ultimately reduces the amount of oxygen entering your bloodstream,
毕竟，心率放缓最终会减少进入血液中的氧气量
and it means your body can immediately start conserving oxygen.
并且这意味着你的身体可以立即开始储存氧气。
Which makes sense because, you know, we kind of stop breathing when we're underwater.
这也有道理，因为我们在水下时会停止呼吸。
Additionally, the mammalian dive reflex causes your body to divert blood from your extremities.
此外，哺乳动物潜水反射会让你的身体体从四肢分流血液。
Instead of getting pumped out to your fingers and toes, the blood is redirected into your lungs and other vital organs.
血液没有流入你的手指和脚趾，而是流入了你的肺部和其他关键器官。
This helps preserve your body's temperature in cold water,
这可以帮助在冷水保存体温，
and might even help protect you from the powerful crush of water pressure at deep depths.
甚至还帮助保护你免受深海水压的强烈挤压。
This reflex exists in all kinds of mammals, from aquatic ones to terrestrial ones including rodents and primates.
所有哺乳动物都存在这种反射，从水生到陆生动物，包括啮齿动物和灵长类动物。
Even newborn babies exhibit it!
甚至新生儿也会有！
And what's really interesting about this reflex is that it's triggered even when just your face comes in contact with water!
关于这种反射最有趣的是，即使只是你的脸接触到水，它也会被触发！
A big splash to the face activates receptors in your nose and sinus cavity,
溅到脸上的大水花会激活你鼻子和鼻窦腔的感受器
and that triggers a physiological override via your trigeminal nerve, which is the largest cranial nerve.
并通过你的三叉神经（最大的脑神经）触发一种生理覆盖。
This sends an immediate "hey-we're-underwater-water-now" message to the brain,
这会立即向大脑发送“嗨，我们现在在水下”的信息，
and these physiological changes start to kick in.
并且这些生理变化开始起作用。
So next time you feel stressed out, splash some water over your face, or go for a dip!
所以下次你觉得压力大时，往脸上泼点水，或者去泡个澡！
You can thank the mammalian dive reflex for the chill vibes that come along with a nice soak.
你可以感谢哺乳动物潜水反射带来的寒冷的感觉，随之而来的是一个很好的沉浸。
If you want to learn more about underwater science,
如果你想了解更多关于水下科学的知识，
you can check out our episode about whether humans could ever breathe underwater.
你可以观看我们关于人类是否可以在水下呼吸的视频。
And as always, thanks for watching this episode of SciShow!
感谢收看！
