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Have you ever wondered why we cry? In today's episode of SciShow, Hank gives us the answer, covering different types of tears and whether we are the only species to get all teary eyed during the final scene of a good movie.
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Sources:
http://www.psychologytoday.com/blog/animal-emotions/201309/do-elephants-weep-emotional-response
http://www.epjournal.net/wp-content/uploads/ep07363370.pdf
http://www.theglobeandmail.com/life/health-and-fitness/health/conditions/why-do-we-cry-when-were-happy/article599605/
http://epjournal.wpengine.com/wp-content/uploads/EP075256.pdf
http://www.huffingtonpost.com/2013/02/04/why-do-we-cry-when-were-sad_n_2583885.html
http://www.brainpickings.org/index.php/2012/09/07/curious-behvaior-provine/
http://io9.com/do-tears-of-grief-look-different-from-onion-tears-under-1470513468
http://www.sharecare.com/health/eye-vision-health/different-types-of-tears
http://chemistry.about.com/od/chemistryfaqs/f/onionscry.htm
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It happens to all of us! Maybe you're walking on a beach in a windstorm or chopping onions or just had a bad breakup, got fired, lost your dog, broke your tailbone, reading a young adult novel by a particular author I could name. Waterworks.

Everybody does it, some rarely, others all the time. But why do we cry? Beyond destroying mascara, puffing up eyes, keeping Kleenex in business, what purpose do our tears serve?!
 
(intro music)

First off, you should know that not all tears are the same. There's the 'just got poked in the eye' tears. They are not the same as the tears of the broken heart. In fact, we humans are lucky enough to have three different kinds of tears: basal, reflex, and emotional.

Basal tears are always there, they're just helping keep your eyeballs lubed up and protected so they don't get all dry and crusty. Reflex tears are our defense against irritants. When you're getting abraded by wind, smoke, dust, sand, cat hair, suicidal gnats, reflex tears start flowing. They're also what come to the rescue when you get weepy chopping onions.

Since you're wondering, let's explain about that. Okay, so sliced onions release sulfenic acids. They mingle with enzymes to create a sulfur compound that then can become gaseous and comes in contact with your moist eyeballs and turns into sulphuric acid. And acid in your eyeballs is gonna burn, it burns, so it stimulates your sensory nerves in your eyes to tell your brain to send some hormones to the lacrimal glands in your eyelids, which floods your tear ducts and eyeballs with reflex tears to wash the burning away.

But! Even more interesting, the third type: emotional tears. Many researchers maintain that humans are the only animal capable of producing this kind of tear. But, others disagree, so the jury is out on whether we're the only ones who cry when we're sad. But we definitely do! And if it cheers you up any, the chemistry behind it is kind of awesome. 

Say you're reading Deathly Hallows and - spoiler alert - like, everybody dies. You're taking the news kind of hard, the emotional part of your brain is registering sadness and telling your endocrine system all about it, which then releases hormones that activate those tear glands. And the blubbering begins. The process is actually similar to the release of reflex tears, but these emotional tears actually have a different chemical content than the other tears, which are mostly just water. 

Several studies suggest that emo tears are actually loaded with protein, specifically hormones like prolactin, which is associated with the creation of breast milk in pregnant women, but also stress hormones, as well as an endorphin that's known to help relieve pain. So this has some scientists thinking that crying is an effective way to help get rid of stress, because, let's face it, you usually do feel better after, at least temporarily, after a good cry. Maybe that has something to do with the release of those extra stress hormones.

Another theory behind the purpose of humans' emotional tears suggests that they act as a symbol to others that you are distressed. Yeah, you could say, "Hey, I'm really sad," but if you say it with an ugly cry-face anyone within range is gonna be clear on your emotion. Evolutionarily speaking emotional crying is a good form of communication that may increase attachment, compassion, and empathy, and even tears of joy can act as poignant social signals that promote group bonding, something important to human survival and well-being. And there is no shame in that!

Thanks for watching this Sci Show dose. I hope it didn't break you up too much. And a special heartfelt thanks to our Subbable subscribers who make this channel possible. Makes me wanna cry with joy.  

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