 Hey everybody, Dr. O here. So now I'm going to cover, in the next two videos, I'm going to cover the sympathetic nervous system. I'm going to cover its organization here and then its activation and its function in the next video. So generally, you know, real quickly the sympathetic nervous system, the fight, flight or freeze response system kicks in anytime there's any sort of emergency or stressor or some sort of physical exertion. So the other name for the sympathetic division is the thoracolumbar division because as you can see here, the spinal segments T1 to L2 are what control the entire system. As I mentioned in the overview video, the first nerves, the preganglinic nerves are very short. They synapse there and those ganglia very close to the spinal cord. So the preganglinic nerves are very short and they release the neurotransmitter acetylcholine. The postganglinic nerves are very long and the reason this is important is while these nerves are traveling, they diverge and they spread out. So one of these preganglinic neurons can actually do the stimulation of two dozen or more of these ganglinic neurons at the second half. And that means that one stimulus leads to a huge response all over the place, very complex coordinated responses. This just goes to show you that when the fight or flight system controls your entire body, whether it's test anxiety or exercise, your entire body responds when your sympathetic system kicks in. And it's because these nerves spread and diverge so much. So your entire body is going to see a heightened level of somatic activity. Your body's preparing to fight or to flee. So we'll cover what that means as far as its function in the next video. One other thing to talk about here that makes the sympathetic system unique is the sympathetic nervous system controls the adrenal medulla, the center of the adrenal gland. We'll cover the rest of the adrenal gland with the endocrine system. But the center of the adrenal gland is a modified sympathetic ganglion. So when your fight or flight system kicks in, it tells the center of the adrenal gland to dump neurotransmitters, but into the bloodstream, not into synapses. So they actually become hormones. And what the adrenal medulla releasing is about 75 to 80% is epinephrine or adrenaline. The other 20 to 25% is norepinephrine or noradrenaline. So that means that your nervous system is now dumping hormones into your blood, into your bloodstream. Why does this matter? This means that your entire body, any cell in your body that gets blood supplied to it is going to be controlled by your sympathetic nervous system. Even if there aren't sympathetic nerves there, if blood is showing up there, it's going to respond to the fight or flight response. Number two, it makes the effects last a whole lot longer. Neurotransmitters might only function for milliseconds, but once you've dumped these hormones into your blood, you're going to see elevated levels for 30 seconds or more and the response is going to last for several minutes. So think about like you almost get hit by a car. Just barely jump out of the way of a moving car or something. You're not over that in milliseconds. Your nervous system usually works very quickly. The response goes away quickly, but you've dumped adrenaline into your bloodstream. So now it might be minutes or longer before you can calm back down from that scary experience. Okay. So those are the key features of the organization of the sympathetic nervous system. I'll cover sympathetic activation and what actually happens when the system kicks in in the next video. I hope this helps. Have a wonderful day.