 Hey everybody, Dr. O here. So we've talked about the wiring of the sympathetic nervous system. We've talked about its organization, the anatomy of it. Now we're going to cover the physiology. What does it actually do? So when you fully activate the sympathetic nervous system, that's the fight or flight response or better known as the fight, flight or freeze response. It's all about readying your body for a crisis that could require intense physical activity. And that's the big problem, right? Your sympathetic nervous system is only designed to respond to physical stressors and it knows how to do so by fighting or fleeing. But a big problem is this system is also kicked in by, you know, stress, you know, mental, emotional, chemical stressors can trigger this response system, which is why we get so. So think about these symptoms, what I'm mentioning here. Think about this happening to your body while you're studying or taking an exam. It's not designed to help you in those situations. It's designed to help you get food or not become food, basically. All right. So in general, when the sympathetic nervous system kicks in and when it fully kicks in, it's called sympathetic activation. When it kicks in, it's going to stimulate tissue metabolism and increased alertness. You're going to be dumping energy out into your circulatory system. You're going to be mobilizing every energy reserve you have and you're going to be preparing your mind and body for physical activity. So here's kind of the general pattern and then I'll look at some specific examples. So number one, heightened mental alertness. You're trying not to die, right? You're watching for predators. You're looking for prey, these kind of things. This is why people talk about like bank robberies and during really stressful situations, they talk about a time slows down. Time doesn't slow down. Their brain kicks it into high gear. So the perception of time might slow down. So that's going to be that heightened mental alertness. Number two, increased metabolic rate. You're going to fight. You're going to flee. You have to have your metabolism firing and all cylinders to do that. Number three would be reduced digestive and urinary function. If you're going to send all your blood to your muscles and your heart and your lungs, which you should, then you're not going to have as much blood going to your GI tract and your kidneys, et cetera. So you're going to kind of pause digestion and urination or urine production during this stressful time. Now there is something called the voiding reflex. Some people like athletes and stuff, some people will have the urge to urinate prior to an athletic event, these kind of things. So the voiding reflex is kind of separate. But generally speaking, when your sympathetic nervous system is under control, you will slow down digestion and urine production, which could be why stress might lead to constipation in some people. Number four, just activation of energy reserves. You're going to be dumping fat into the bloodstream. You're going to be releasing glycogen as glucose. You're just mobilizing energy to fight or flee. Number five, increased respiratory rate and dilation of respiratory passageways. You're going to be moving more air because it's going to take oxygen to power your metabolism and take oxygen to fight or flee. Number six would be an increase in heart rate and blood pressure. Same reason. You're going to pump this blood through your body so you can fight off that attacker or do what you have to do. And lastly, the activation of sweat glands. So you're going to have more blood flowing to your skin and more sweat gland activity because you cranked up your metabolism. Your body's going to get hot. So you need to be able to cool off as you're fighting or fleeing. All right, a few more examples here of this full sympathetic activation, just a little bit more detail here. Where does this increased mental alertness come from? It comes from what's called the reticular activating system in your brainstem that helps you maintain consciousness. So it's going to make sure you don't fall asleep while you're guarding a post or you're fighting, fleeing, whatever. This is also why when you're under stress, you're going to feel on edge. Your system is just hyper acutely aware of what's going on. You are going to get that boost of energy because of all the energy being mobilized, but also you might even feel like a sense of euphoria or like, you know, the endorphins being released are going to make it so maybe you're not going to feel pain as much. This is why you see people like getting shot and not even knowing it. So they were kind of impervious to pain for a short period of time. We talked about, so obviously your heart rate, blood pressure, all that, that makes perfect sense. You're going to, you're getting ready to fight or run. You're going to need your heart and lungs to work with you. Your muscles, so your muscles, there's going to be a general increase in muscle tone, which is great if you actually are fighting or fleeing. This is also why when you're stressed, you look tense. You can tell someone's cleansing their jaw. They look tense. They might even be so scared they start to shiver. That's because of this increase in muscle tone that comes with sympathetic activation. And then we talked about, you know, your liver and your muscles and your fat, everything's about mobilizing energy so you can fight or flee. So those are the responses. I think that, excuse me, I think it's worth noting that there's a lot of common sense here, right? If I said, do you need to have an increased heart rate when you're running or when you're resting on your couch or taking a nap, I think it's pretty clear. So if there's any questions about which of these two systems does, what? Just think about what's happening. Would you need it to fight or flee or would you need it to rest? And that'll be your answer. Okay, so that's the function of the sympathetic nervous system. I'll come and talk about the parasympathetic nervous system next. I hope this helps. Have a wonderful day. Be blessed.