Speaker 1: Welcome to Brain Stuff from How Stuff Works. Hey, welcome
Speaker 1: to Brain Stuff. I'm Christian Sager, and this is the
Speaker 1: episode where I explain to you why some people faint
Speaker 1: at the sight of their own blood. Fainting at the
Speaker 1: side of blood, which is either a condition called neuro
Speaker 1: cardiovascular syncope or vasovagil syncope, is actually related in some
Speaker 1: cases to what's classified as a blood injury phobia. Something
Speaker 1: like three to four percent of people have a blood
Speaker 1: injury phobia. But what's really interesting is that percent of
Speaker 1: people faint at the sight of blood, which means there's
Speaker 1: a lot of people out there who really have no
Speaker 1: issue with cutting themselves, but they still faint dead away
Speaker 1: any time they see themselves bleeding. That's kind of weird, right. Well,
Speaker 1: when you faint from anxiety, which is what researchers think
Speaker 1: is going on, when you faint from the side of
Speaker 1: your own blood, your blood pressure suddenly spite, but then
Speaker 1: just as quickly it decreases, and that decrease in blood
Speaker 1: pressure drains blood away from your brain, causing you to
Speaker 1: lose consciousness. When you're anxious or when you feel like
Speaker 1: you're in danger, it's normal for your blood pressure to rise.
Speaker 1: It's part of the sympathetic nervous systems fight or flight response.
Speaker 1: What's unusual in this case is the sudden decrease in
Speaker 1: blood pressure that causes you to lose consciousness. At the
Speaker 1: center of all this oddness is the vagus nerve. It's
Speaker 1: a major nerve that connects your brain to various regions
Speaker 1: of your body that are involved in involuntary movement like
Speaker 1: your heart beating, your throat swallowing, that kind of stuff.
Speaker 1: And at the other end, your vagus nerve is connected
Speaker 1: to a region of your brain called the nucleus of
Speaker 1: the solitary tract or the NST for short. The n
Speaker 1: s T is kind of like a toggle switch that
Speaker 1: goes back and forth between the sympathetic response that's your
Speaker 1: fight or flight response, or the parasympathetic response, which is
Speaker 1: what calms you down after danger has passed. And what
Speaker 1: researchers think is going on is that the NST gets
Speaker 1: some sort of confused signal from the vagus nerve that
Speaker 1: causes it to decrease blood pressure as part of the
Speaker 1: parasympathetic response without deactivating the increase in your heart rate,
Speaker 1: which causes a lot of blood to suddenly be pumped
Speaker 1: away from your brain, hence making you pass out. Another
Speaker 1: explanation is that your NST simply toggles too quickly between
Speaker 1: the sympathetic and parasympathetic responses, like it's working like a
Speaker 1: joystick and it's going back up and down, and you
Speaker 1: your brain is saying what's going on? And then while
Speaker 1: you pass out on the floor. Then there's another parallel
Speaker 1: hypothesis that, because your NST is also in charge of
Speaker 1: mediating your disgust response, that there's some sort of mixture
Speaker 1: of fright and disgust that causes you to faint, because
Speaker 1: again the NST is confused. However you slice it, it
Speaker 1: seems that you can lay the fainting at the sight
Speaker 1: of blood thing at the feet of the NST. Evolutionarily speaking,
Speaker 1: passing out at the sight of your own blood doesn't
Speaker 1: make much sense, and researchers have bent over backwards to
Speaker 1: try to explain it. What they've come up with is
Speaker 1: that possibly when you faint at the sight of your
Speaker 1: own blood, say after being mauled by a bear, the
Speaker 1: bear will take you as being dead and maybe he'll
Speaker 1: lose interest. Well. Another more reasonable explanation is that this
Speaker 1: sudden decrease in blood pressure prevents us from bleeding out
Speaker 1: of some sort of wound, and the fainting is just
Speaker 1: an unfortunate byproduct of the whole thing. Either way, whatever
Speaker 1: the case, once you're on the floor, which is usually
Speaker 1: what happens when you faint, the blood flow to your
Speaker 1: brain can be restored fairly quickly because it's a lot
Speaker 1: easier for your heart to pump blood horizontally than upwards
Speaker 1: against graftic check out the brain stuff channel on YouTube,
Speaker 1: and for more on this and thousands of other topics,
Speaker 1: visit how stuff works dot com.