1 00:00:02,040 --> 00:00:06,600 Speaker 1: Welcome to brain Stuff from How Stuff Works. Hi, there, 2 00:00:06,640 --> 00:00:09,320 Speaker 1: brain Stuff. I'm Lauren voc Obama, and I've got another 3 00:00:09,360 --> 00:00:12,920 Speaker 1: classic episode for you today from our former host, Christian Sager. 4 00:00:13,480 --> 00:00:17,200 Speaker 1: This one explores some literal brain stuff. Why do some 5 00:00:17,239 --> 00:00:24,759 Speaker 1: people faint at the side of blood? Hey, welcome to 6 00:00:24,800 --> 00:00:27,640 Speaker 1: brain Stuff. I'm Christian Sager, and this is the episode 7 00:00:27,680 --> 00:00:30,240 Speaker 1: where I explain to you why some people faint at 8 00:00:30,240 --> 00:00:32,800 Speaker 1: the sight of their own blood. Fainting at the side 9 00:00:32,800 --> 00:00:36,440 Speaker 1: of blood, which is either a condition called neuro cardiovascular 10 00:00:36,520 --> 00:00:42,159 Speaker 1: syncope or vasovagil syncope, is actually related in some cases 11 00:00:42,240 --> 00:00:46,159 Speaker 1: to what's classified as a blood injury phobia. Something like 12 00:00:46,320 --> 00:00:49,440 Speaker 1: three to four percent of people have a blood injury phobia. 13 00:00:49,640 --> 00:00:53,519 Speaker 1: But what's really interesting is that of people faint at 14 00:00:53,520 --> 00:00:55,960 Speaker 1: the sight of blood, which means there's a lot of 15 00:00:56,000 --> 00:00:59,200 Speaker 1: people out there who really have no issue with cutting themselves, 16 00:00:59,240 --> 00:01:03,080 Speaker 1: but they still faint dead away any time they see 17 00:01:03,120 --> 00:01:07,080 Speaker 1: themselves bleeding. That's kind of weird, right. Well, when you 18 00:01:07,120 --> 00:01:10,240 Speaker 1: faint from anxiety, which is what researchers think is going on, 19 00:01:10,440 --> 00:01:12,319 Speaker 1: when you faint from the side of your own blood, 20 00:01:12,560 --> 00:01:16,760 Speaker 1: your blood pressure suddenly spikes, but then just as quickly 21 00:01:16,959 --> 00:01:20,720 Speaker 1: it decreases, and that decrease in blood pressure drains blood 22 00:01:20,760 --> 00:01:24,319 Speaker 1: away from your brain, causing you to lose consciousness. When 23 00:01:24,319 --> 00:01:26,880 Speaker 1: you're anxious or when you feel like you're in danger, 24 00:01:27,000 --> 00:01:30,000 Speaker 1: it's normal for your blood pressure to rise. It's part 25 00:01:30,120 --> 00:01:34,199 Speaker 1: of the sympathetic nervous systems fight or flight response. What's 26 00:01:34,319 --> 00:01:37,520 Speaker 1: unusual in this case is the sudden decrease in blood 27 00:01:37,560 --> 00:01:41,759 Speaker 1: pressure that causes you to lose consciousness. At the center 28 00:01:41,800 --> 00:01:44,880 Speaker 1: of all this oddness is the vagus nerve. It's a 29 00:01:44,920 --> 00:01:47,920 Speaker 1: major nerve that connects your brain to various regions of 30 00:01:47,920 --> 00:01:52,280 Speaker 1: your body that are involved in involuntary movement like your 31 00:01:52,320 --> 00:01:55,600 Speaker 1: heart beating, your throat swallowing, that kind of stuff. And 32 00:01:56,000 --> 00:01:58,560 Speaker 1: at the other end, your vagus nerve is connected to 33 00:01:58,600 --> 00:02:01,120 Speaker 1: a region of your brain called the nucleus of the 34 00:02:01,200 --> 00:02:05,480 Speaker 1: solitary tract, or the NST for short. The n s 35 00:02:05,520 --> 00:02:07,880 Speaker 1: T is kind of like a toggle switch that goes 36 00:02:07,960 --> 00:02:11,280 Speaker 1: back and forth between the sympathetic response that's your fight 37 00:02:11,360 --> 00:02:15,520 Speaker 1: or flight response, or the parasympathetic response, which is what 38 00:02:15,680 --> 00:02:19,240 Speaker 1: calms you down after danger has passed. And what researchers 39 00:02:19,280 --> 00:02:21,720 Speaker 1: think is going on is that the NST gets some 40 00:02:21,760 --> 00:02:24,960 Speaker 1: sort of confused signal from the vagus nerve that causes 41 00:02:25,000 --> 00:02:28,720 Speaker 1: it to decrease blood pressure as part of the parasympathetic 42 00:02:28,760 --> 00:02:33,040 Speaker 1: response without deactivating the increase in your heart rate, which 43 00:02:33,080 --> 00:02:36,120 Speaker 1: causes a lot of blood to suddenly be pumped away 44 00:02:36,120 --> 00:02:40,560 Speaker 1: from your brain, hence making you pass out. Another explanation 45 00:02:40,720 --> 00:02:44,440 Speaker 1: is that your NST simply toggles too quickly between the 46 00:02:44,440 --> 00:02:48,800 Speaker 1: sympathetic and parasympathetic responses, like it's working like a joystick 47 00:02:48,840 --> 00:02:51,440 Speaker 1: and it's going back up and down, and you your 48 00:02:51,480 --> 00:02:54,640 Speaker 1: brain is saying what's going on? And then while you 49 00:02:54,680 --> 00:02:58,639 Speaker 1: pass out on the floor. Then there's another parallel hypothesis 50 00:02:58,880 --> 00:03:01,560 Speaker 1: that because you're n s T is also in charge 51 00:03:01,600 --> 00:03:05,280 Speaker 1: of mediating your disgust response, that there's some sort of 52 00:03:05,360 --> 00:03:08,760 Speaker 1: mixture of fright and disgust that causes you to faint, 53 00:03:08,800 --> 00:03:13,079 Speaker 1: because again the NST is confused. However you slice it, 54 00:03:13,080 --> 00:03:15,280 Speaker 1: it seems that you can lay the fainting at the 55 00:03:15,280 --> 00:03:17,880 Speaker 1: sight of blood thing at the feet of the NST. 56 00:03:18,480 --> 00:03:21,720 Speaker 1: Evolutionarily speaking, passing out at the sight of your own 57 00:03:21,720 --> 00:03:25,639 Speaker 1: blood doesn't make much sense, and researchers have bent over 58 00:03:25,680 --> 00:03:28,320 Speaker 1: backwards to try to explain it. What they've come up 59 00:03:28,360 --> 00:03:30,520 Speaker 1: with is that possibly when you faint at the sight 60 00:03:30,600 --> 00:03:33,480 Speaker 1: of your own blood, say, after being mauled by a bear, 61 00:03:33,840 --> 00:03:36,840 Speaker 1: the bear will take you as being dead and maybe 62 00:03:36,840 --> 00:03:41,680 Speaker 1: he'll lose interest. Well. Another more reasonable explanation is that 63 00:03:41,760 --> 00:03:45,200 Speaker 1: this sudden decrease in blood pressure prevents us from bleeding 64 00:03:45,240 --> 00:03:48,560 Speaker 1: out of some sort of wound, and the fainting is 65 00:03:48,600 --> 00:03:52,520 Speaker 1: just an unfortunate byproduct of the whole thing. Either way, 66 00:03:52,800 --> 00:03:55,600 Speaker 1: whatever the case, once you're on the floor, which is 67 00:03:55,680 --> 00:03:58,320 Speaker 1: usually what happens when you faint, the blood flow to 68 00:03:58,360 --> 00:04:01,800 Speaker 1: your brain can be restored fair really quickly, because it's 69 00:04:01,840 --> 00:04:05,040 Speaker 1: a lot easier for your heart to pump blood horizontally 70 00:04:05,360 --> 00:04:13,400 Speaker 1: than upwards against grab. Today's episode was produced by Tyler 71 00:04:13,440 --> 00:04:16,279 Speaker 1: Clang and written by myself with style notes from Josh 72 00:04:16,279 --> 00:04:19,839 Speaker 1: Clark for brain Stuff's Erstwhile YouTube series. If you like 73 00:04:19,960 --> 00:04:22,680 Speaker 1: our show and also like not being naked, check out 74 00:04:22,680 --> 00:04:25,960 Speaker 1: our March shop at t public dot com, slash brain stuff, 75 00:04:26,279 --> 00:04:28,039 Speaker 1: and of course, for more on this and lots of 76 00:04:28,040 --> 00:04:31,400 Speaker 1: other topics that attempt to explain the unexplained, visit our 77 00:04:31,520 --> 00:04:45,000 Speaker 1: home planet how stuff Works dot com.