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  • [intro]

  • Summer is winding down here in the Northern Hemisphere,

  • which means we've started to reflect on our long days at the lake and all the times

  • we've jumped into swimming pools.

  • And there's one thing we've noticed:

  • Being immersed in water is really relaxing.

  • As it turns out, though,

  • this isn't just because of the warm weather or the sound of the waves.

  • There's something larger at play here, called the mammalian dive reflex.

  • And you can actually take advantage of it all year round, no pool required.

  • When you dunk yourself in water,

  • this reflex kicks in,

  • and your body does some pretty interesting things.

  • Mainly, as soon as your face makes contact with the water,

  • it triggers a reduction in your heart rate

  • called bradycardia.

  • The effect happens very quickly,

  • and studies have shown that the mammalian dive reflex can drop someone's heart rate

  • by ten to 25%!

  • This is what results in that nice, peaceful feeling.

  • Multiple studies have shown that when your heart rate slows down,

  • you feel calmer.

  • This is also why breathing exercises are so relaxing

  • although in that case,

  • you're slowing your heart rate through careful, slow breaths.

  • But while it's a nice bonus, this reflex doesn't exist to help you chill out.

  • Instead, research suggests it's an evolutionary adaptation

  • that allows us to stay underwater for an extended period of time.

  • After all, lowering your heart rate ultimately reduces the amount of oxygen entering your

  • bloodstream,

  • and it means your body can immediately start conserving oxygen.

  • Which makes sense because, you know, we kind of stop breathing when we're underwater.

  • Additionally, the mammalian dive reflex causes your body

  • to divert blood from your extremities.

  • Instead of getting pumped out to your fingers and toes,

  • the blood is redirected into your lungs and other vital organs.

  • This helps preserve your body's temperature in cold water,

  • and might even help protect you from the powerful crush of water pressure at deep depths.

  • This reflex exists in all kinds of mammals, from aquatic ones to terrestrial ones

  • including rodents and primates.

  • Even newborn babies exhibit it!

  • And what's really interesting about this reflex

  • is that it's triggered even when just your face comes in contact with water!

  • A big splash to the face activates receptors in your nose and sinus cavity,

  • and that triggers a physiological override via your trigeminal nerve,

  • which is the largest cranial nerve.

  • This sends an immediatehey-we're-underwater-water-nowmessage to the brain,

  • and these physiological changes start to kick in.

  • So next time you feel stressed out,

  • splash some water over your face, or go for a dip!

  • You can thank the mammalian dive reflex for the chill vibes that come along with a nice

  • soak.

  • If you want to learn more about underwater science,

  • you can check out our episode about whether humans could ever breathe underwater.

  • And as always, thanks for watching this episode of SciShow!

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Why Is Being Underwater So Peaceful?

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    Yuquan Ou posted on 2019/08/10
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