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Autonomic nervous system (ANS) and physiologic markers of emotion

Created by Jeffrey Walsh.

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Video transcript

So if you've ever ridden a roller coaster, you've probably experienced the emotion of fear or excitement. And accompanying that feeling of fear and excitement, you probably felt your heart rate increasing. Maybe you were breathing a little bit quicker. And these physiologic changes that occurred while you were riding a roller coaster, they weren't under your conscious control and you didn't tell yourself to start breathing quicker. It just happened automatically. And these physiologic changes happen automatically through connections in your nervous system. And the branch of the nervous system responsible for these automatic reactions is called the autonomic nervous system. Sometimes autonomic nervous system is shortened as ANS. And the autonomic nervous system has two branches. It has a sympathetic branch, called the sympathetic nervous system. And the other branch is called the parasympathetic nervous system. And each of these arms of the autonomic nervous system cause different changes, oftentimes opposite changes, in different organs of your body. So the sympathetic nervous system, sometimes people refer to it as performing actions involving fight or flight. Whereas, people refer to the parasympathetic nervous system as rest and digest. So let's examine what we mean by this. The sympathetic nervous system causes changes in your body consistent with the feelings and changes you get when you might be afraid of something. So like when you're riding a roller coaster, there's some sort of fear response there. And all those sorts of changes in your body are often changed automatically by the sympathetic nervous system. So let's go over some parts of your body that are affected by the autonomic nervous system, especially when it comes to emotions. So here we see this gentleman or lady standing here, with so many organs exposed. You have an eye. This is a salivary gland, where your saliva comes from. You have several of them. But I'm just making one here as a representation. We have the lungs, the heart, which of course is not drawn anatomically, a liver. Here are two kidneys. And the reason I included them is because on top of the kidneys sits a gland called the adrenal gland, which I've drawn as yellow triangles. And the adrenal gland is responsible for releasing hormones, like adrenaline. Adrenal, adrenaline, that's where the name comes from. And here is your GI tract, known as the gastrointestinal tract. Now, I didn't draw the entire thing, which goes from top to bottom. But I just drew it here to represent that I'm talking about the GI tract. So let's go through this one at a time and see how they react and respond to the different arms of the autonomic nervous system. Here we see an eye. And when your sympathetic nervous system is activated, your pupils dilate. And the reason why you would want your pupils to dilate when they're activated by the sympathetic nervous system is if you think of it in the context of fight or flight. If a wild animal is chasing you, you want your eyes to be wide, so to speak, so that you can see them better and you can bring in more light to have better vision. So that's the idea of your pupils dilating. And as I said here, this is the salivary gland. And the sympathetic nervous system causes a decrease in salivation. An easy way to remember this is think of a time when you had to do a public speaking presentation. And if you felt really nervous speaking in public, you might notice that you get dry mouth and have to sip water a lot. And that's why people who give lectures sometimes have to drink a lot of water. And here we have the lungs. And the sympathetic nervous system causes your respiratory rate to increase. In other words, you breathe quicker. The sympathetic nervous system also makes your heart beat quicker, so you have an increased heart rate. And the reason for having an increased heart rate, as well as an increased respiratory rate, is so that your body has better oxygenation. So more blood can flow easier throughout your body. Now, here's your liver. And your liver is a major storage site for glucose. And glucose is sugar. And it's a sugar that your body can use to produce energy. And the idea behind wanting to increase glucose to be released is consistent with the other areas we talked about. Having increased glucose gives you more energy to fight or flight. Here, as I said earlier, are the adrenal glands. And the adrenal glands sit on top of each kidney. Now, your kidneys are actually closer to your back than towards your front. So I drew it kind of transparent, so you get the idea that they're farther away. And during a sympathetic response, the adrenal glands are stimulated through hormones to release epinephrine and norepinephrine. And another name for epinephrine is adrenaline. And adrenaline gives you a real boost of energy. And, of course, that energy is needed in a situation involving fight or flight. And here's the GI tract. And one of its main functions is to digest food. But digesting food takes up a lot of energy. And in a situation where a wild animal is chasing after you, you want to divert all your energy towards vital resources in areas of your body that can help you escape. So when it comes to the sympathetic nervous system, there's actually a decrease in digestion. And again, that's because the activity of digesting food takes up way too much energy in this sort of situation. So that some of the main effects of the sympathetic nervous system. So let's look at the parasympathetic nervous system. This is the arm of the autonomic nervous system that's involved with, well, you can say rest and digest. So this is a relaxed state. And the parasympathetic nervous system affects many of the same organs and parts of the body that the sympathetic nervous system effects. And oftentimes, it affects it in the opposite way. So when it comes to your pupils, this parasympathetic nervous system causes constriction of the pupils. So your pupils get smaller. And just as your pupils dilated during a sympathetic response so you could get more light in to see better, the parasympathetic nervous system causes pupil constriction, because you don't need as much light being brought in because you're not in a situation where you need to run or act quickly. Because again, you're resting and digesting. When it comes to salivation, you actually have an increase in salivation when it comes to the parasympathetic nervous system. And why do you have an increase of salivation? Well, again, the parasympathetic nervous system is involved with resting and digesting. So part of digestion involves saliva. Saliva helps break down certain carbohydrates. It also helps lubricate the bolus of food that you eat that later gets digested. So that's why there's an increase in salvation. In terms of your respiratory rate, it gets slower or goes back to your baseline. So to represent that, I'll put it down arrow. I'll put a down-pointing arrow. And what I mean by that is if you're sitting on the couch watching television, just relaxing, you're probably not hyperventilating. Or rather you just breathing at a normal, moderate pace. So in the parasympathetic nervous system, you're breathing at a moderate or decreased rate because you don't need the extra oxygenation. And the same goes for your heart rate. So your heart rate also goes back to normal or at least it decreases compared to when it's in a sympathetic state. So when the parasympathetic nervous system is activated, your heart rate decreases or slows. From the parasympathetic nervous system, since your resting and digesting you're trying to extract nutrients from your food. And one important component of nutrition is glucose, which as we said earlier, can be used for energy. So in a parasympathetic state, you don't have this glucose release from the liver. If anything, your body is working to increases its glucose store. So I'll just say there's an increased glucose storage because you're digesting your food to get the glucose. The bottom line is you don't have a huge release of glucose in the parasympathetic state. And the same goes for adrenalin when you look at the adrenal glands. Since you're not in such a high-strung, detrimental state, you don't need to have the adrenalin coursing through your veins. So again, there's a decrease in adrenalin release. And when it comes to digestion, you've probably guessed it. In a parasympathetic state your digestion increases because this is the time when you're not in imminent danger and you're able to spend your time digesting the food that you took in so you can extract the nutrients and get the energy from it, so your body can function properly and also you'll have plenty of stored energy. So when the time comes, you'll be able to escape should a predator come. So this is some of the basic functions of the parasympathetic nervous system. Of course, there are more functions than the ones we listed. But I think these are the most relevant when it comes to an emotional response.