00:00The cornea is the only part of your body with living cells that doesn't have blood vessels.
00:07It gets nutrients and oxygen directly from the tear fluid on the outside
00:11and the thick, watery substance you have between the cornea on the inside
00:15and also from the nerve fibers connected to the cornea.
00:20That's why contact lenses used to be a potential issue.
00:24The older ones were reducing oxygen supply
00:26since the cornea mostly gets oxygen from the outside.
00:30This problem was solved, or at least reduced, when silicone hydrogel lenses came to the market.
00:37Some other parts of your body with no blood vessels are your nails,
00:41hair, outer skin layers, and tooth enamel.
00:45Did you notice your sweat sometimes smells of onions after your workout?
00:50You have nothing to worry about.
00:51There are two types of sweat glands in your skin.
00:54The first kind of glands are located on certain areas of your body,
00:58like the groin region and the armpits.
01:02They produce a specific oily fluid, which is a response to certain emotional experiences.
01:08Another type of sweat gland is way more common.
01:11They're distributed all over your body
01:13and are responsible for the specific sweat you get after the workout.
01:17The sweat cools your body down as it evaporates from your skin.
01:21It's 99% water, so it's practically odorless.
01:26Well, at least when it first leaves the pores and comes to the surface of your skin.
01:31But there are many types of bacteria on the human skin,
01:34and they feed on the nutrients in that sweat, together with skin flakes.
01:38One of the byproducts of this is specific chemicals,
01:42and their smell can sometimes strongly remind you of onion.
01:46You may have noticed you produce more saliva when you go for a run,
01:50especially if it's a short jog in cold weather.
01:54But if you're running a marathon, and it's a nice warm day outside,
01:58you'll produce less saliva.
02:01It's your body trying to offset the drying effect,
02:04since you breathe through your mouth way more.
02:06But your body becomes more dehydrated over longer periods,
02:12which is why it's trying to conserve water by reducing saliva production.
02:17Every training you do, no matter how intensive it is,
02:20also makes you secrete more of a specific type of protein.
02:24It makes the saliva more viscous and sticky,
02:27which is why you may feel like your mouth is dry way more after your workout.
02:33Humans see the world 15 seconds out of date.
02:36Which means your brain constantly keeps you a little bit in the past.
02:41This way, it helps you stabilize your vision of the world around you.
02:45Your eyes receive a huge amount of visual information.
02:48Yep, literally millions of colors, shapes, and ever-changing motion, wherever you turn.
02:54It's not an easy task for your brain to process all that.
02:58The visual world alters all the time because of changes in viewpoint, light, and the rest of the outer factors.
03:06Your visual input changes because you need to blink.
03:10Plus, your head, eyes, and your entire body are always in some sort of motion.
03:15Your brain has to establish a mechanism that can create illusory stability.
03:21It automatically smooths your visual input.
03:24It doesn't analyze every little visual snapshot.
03:27It's like a time machine.
03:28You actually perceive an average of things you saw in the past 15 seconds at any given moment.
03:36The brain pulls together objects, so they appear more similar to each other.
03:40That's why it tricks you into believing you're in stable surroundings.
03:44If your brain kept you updated in real time, the world would feel like a very, very chaotic place.
03:50With constant changes in movement, light, and shadow.
03:53Your bones are really strong, but your teeth, which we also consider as part of the skeletal system, are even stronger.
04:07That's because of the enamel, the hard outer layer of your tooth.
04:11The enamel keeps the tissue and the delicate nerves inside your teeth safe.
04:17You're basically burning calories while you're thinking.
04:19When you rest and don't engage in any particular activity, except for the basics,
04:24which includes digesting, breathing, and keeping yourself warm,
04:29it's the stage where your brain uses up to 20-25% of the total energy of your body.
04:36That means your body will burn around 350-450 calories per day, while pretty much doing nothing.
04:43We're not the only ones in the animal kingdom with such a mechanism.
04:47Some small mammals, like the minuscule pygmy marmoset, and the tiny tree shrew,
04:53devote the same percentage of their total body energy to their brain.
04:58Most of the energy the brain burns is to help its cells, the neurons, to communicate with each other.
05:04They do it via chemical signals the brain transmits across synapses, those special cell structures.
05:10So, the brain directs a lot of energy towards synapses in order to make them work.
05:15Your brain never really rests.
05:19Even when you're sleeping, certain parts are active.
05:22So, your brain needs its fuel to work, and you're basically burning calories in your sleep.
05:28The more demanding mental tasks you take throughout the day, the more calories you burn.
05:33So, if you skip today's workout, solve some Sudoku!
05:37Do you like to rush with your ice cream?
05:41Sometimes it pays off, but if you do it often, you must know the feeling of brain freeze pretty well.
05:48It's a pretty intense and uncomfortable feeling that comes from the front or sides of your head,
05:54right after you drink or eat something cold, such as a slushy drink, ice cream, or an ice pop.
05:59Some people even go through a similar sensation whenever they're exposed to cold air.
06:06Scientists are still not sure exactly why this happens, but one of the theories is the cold substance stimulates a cluster of nerves located at the back of the palate.
06:15Another theory says the blood vessels in the roof of the mouth and sinuses quickly constrict because the temperature in your mouth drops before they dilate again.
06:26Brain freeze is not something dangerous that you should be seriously worried about.
06:31And no, hanging over the table, groaning, or clasping your head in your hands won't help much.
06:36Some people like to sleep a lot. Hey, guilty as charged.
06:42But some have a certain condition called familiar natural short sleepers, which means they're kind of immune to sleep deprivation.
06:51About 1% of our population has it.
06:54They can fall short on sleep and feel pretty good about it.
06:58They're fine with sleeping for 6 hours per night.
07:01This amount would wreck the majority of people after a couple of nights.
07:04The human eye normally has 3 cones.
07:09That means we can recognize approximately a million different shades in the green, red, and blue spectrums of colors.
07:16But there are some people with a rare condition, so-called tetrachromats, that have 4 cones in their eyes.
07:22This allows them to see ultraviolet shades, which means they can distinguish 100 million distinct colors.
07:30Did you know your skeleton is all wet?
07:33I mean, your entire body mostly consists of water, up to 60%.
07:37That fluid is not only in your organs, muscles, and skin.
07:42It's in your skeleton, too.
07:44Your bone mass is almost one-third water.
07:48There's this amazing hidden network a human body holds inside.
07:52Blood vessels are really small.
07:54But if you could line them all up, you'd get something huge.
07:57Your entire body boasts a network of 60,000 miles of blood vessels.
08:02One of the ways to keep your network healthy is by eating right.
08:07Have you ever wondered why our distant relatives, the primates, are so much stronger than us?
08:12In many ways, our bodies are very similar.
08:16Look at the chimp's muscle structure, for example.
08:19But our closest primate relatives are approximately 1.35 times stronger than us.
08:24The human body developed more slow-twitch muscle fibers compared to the rest of the primates.
08:31This type of muscle fiber is a less powerful one.
08:34But it lets us endure more than other primates.
08:37And do things like foraging and hunting.
08:40Activities that helped our distant ancestors to survive.
08:43That's also the reason why we can run a marathon.
08:46A monkey could never do it.
08:48But we'd still lose in a strength competition.
08:52Laughter is contagious.
08:54It's not just a metaphor.
08:57Researchers have found that strong emotions can make the brain activity of different people sink.
09:02Laughter is something science usually links with social creatures.
09:07People are almost 30 times more likely to laugh when in some social situations,
09:12hanging out with their friends or people they feel relaxed with.
09:14One of the theories says that you're probably going to join when you see your friend laughing
09:19because humans are empathetic beings.
09:23Your brain will release endorphins when you're laughing.
09:25These are special chemicals that make you feel safe and at ease.
09:29So we're not sure why exactly our laughter is contagious.
09:32But it feels really good, so...
09:35Join us on the Bright Side of Life and Laugh Away!
09:44Thank you so much for joining us on the Bright Side of Life and Laugh Away!
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