Sympathetic Nervous System ( ESSAY )

So you're sound asleep, dreaming away, when suddenly the smoke alarm goes off. Before you even know it, you started to feel it, all the smoke and stuff. Those smoke alarms are loud - for a good reason. Your heart starts to race, your breathing picks up, you become sweaty all over your body. You are stressed. And I'm not talking about my-iPhone-is-about-to-die stress. I'm talking about maybe-I-am-going-to-die stress. Even though stress is often viewed as a dirty word, it, just like pain, isn't all bad, it's actually very useful if you're, y'know, trying to get off of a burning building and stuff. Your sympathetic nervous system is the part of your system responsible for stress, and it does it's job exceedingly well by focusing on what your body needs to do right now. Like if you are in a burning building. What you need to do is to run out of the building ASAP, not digesting the McDonald that you just eaten. That is stuff that you can deal later, when you are out of the life-threatening situation. So your sympathetic nervous system sweeps these suddenly trivial functions aside and focusing your blood and energy to the thing that needs to be done like, right now. So, pity on the guy that his sympathetic nervous system doesn't work well. But here is the problem: nowadays our bodies' stress responses are getting triggered all the time, even when you are not on a life-threatening situation, and that's not good. When you are stressed, you are basically overdriving your whole body, and that's a good thing if you are facing life-or-death ordeal. But if you are not, well, your body can get tired by being on overdrive for too long, and, well, "stressed". Like if you are late to an important meeting, but still stuck in a traffic jam, that kind of situation doesn't need your body being run on overdrive, but good luck explaining that to your nervous system. Because your physiological responses to non-immediate stress are largely the same as when you are fighting to stay alive. So that is why stress is sometimes - maybe most times, bad for you. Now I will tell about how your sympathetic nervous system takes over your body for several minutes. The stress signals includes two chemical : neurotransmitters and hormones. Neurotransmitters are made by and released by neurons themselves. While hormones are secreted by your glands. There are at least 50 different hormones in work in your body right now, and they do everything from regulating your sleep cycle, to making you retain water, so you don't get dehydrated. The understanding of neurotransmitters and hormones are 100% necessary for understanding how your sympathetic nervous system ultimately works. BUT! When you are trying to trace a single sympathetic signal, from the initial stimulus to the final response, that is a tough job, because the very same substances can have different effects, actually, sometimes, totally different effects depending solely on where it's being received in your body. And, fun fact, a compound can be considered both a hormone or a neurotransmitter without it changing a single bit, depending on where it is operating in your body. I know this is confusing, but bear with me. Ok, time to dive in. You are waken up by the smoke alarm. You need to move. Fast. Your brain sends action potentials down your spinal cord and preganglionic neuronal axons - I know, fancy words. Those signals flows all the way to their ganglia. When the signal reach the synapses inside the ganglia, the nerve fibers inside the ganglia then release a neurotransmitter, called acetylcholine, known to it's friend as ACh. In addition to working in sympathetic ganglia like this one, it's also what the rest of your peripheral nervous system and lots of your central nervous system uses to communicate. So when it comes to nervous communication, the ACh is basically the coin of the realm. The "Hermes" of your body. So the ACh crosses that synapse, and if there is enough of it, it can stimulate action potentials in several neurons at the other end. That's all it does. But it is important. It's basically a signal booster. Those actions potentials are then carried to the effector organs, in this case, let's say, your leg muscles, which are going to need an influx of blood if they are going to hustle you out of that house. And at the end of that second, the postganglionic neuron releases a different neurotransmitter. This one is called norepinephrine. It's what crosses that final synapse, and creates a response in the effector, like opening your blood vessel, so blood can flow more freely, providing your leg muscle the blood and oxygen it needed. So basically, the norepinephrine is the guy that "do" stuff, while the acetylcholine is, maybe kinda like the postman. Now the way the neurotransmitter/hormone like norepinephrine works, is a good example of another confusing aspect of your sympathetic nervous system. Because it works by both stimulating and inhibiting the same systems in your body at the same time. Like if you are in a life-or-death situation, norepinephrine your system releases causes an increase of blood flow in some parts of your body, and inhibiting blood to not flow to certain parts of your body where it's not needed right now, like to your stomach. That all depends on the organs. Several organs, like your stomach, have certain receptor that when triggered, will "prohibit" that organ. So it all depends also on what kind of receptor is getting triggered. Next, we will talk about the mellow-part of your autonomic nervous system, the one that tells you that it is now all right, the parasympathetic nervous system, so stay tuned.