 Hey everybody, Dr. Rowe here. So in this video we're going to cover the anatomical differences between the sympathetic and parasympathetic nervous systems. I want to do this because I know like pre-ganglionic, post-ganglionic, this stuff gets a little messy. But if you understand these differences, I think it will help you understand how they function and why these two divisions are so different in the end, okay? So let's go ahead and start here with the length of the nerves. So you see here that on the right side, your sympathetic nervous system, the pre-ganglionic neurons, the first neurons are short and the post-ganglionic neurons are long. And that's the opposite on the parasympathetic nervous system. The pre-ganglionic neurons are long with your parasympathetic system and the post-ganglionic nerves are short. So why does this matter? This means that the nerve that's actually controlling a structure or an organ is really close to its target with the parasympathetic nervous system and a long way away from its target in the sympathetic nervous system. So why does that matter? That means that when your parasympathetic nervous system is triggered, it's going to send a response to a very specific location so that the responses are usually going to be localized. Your sympathetic nervous system is all about huge, broad, massive changes occurring all over the place. So this long post-ganglionic neuron is going to have a lot of divergence and a lot of branches. So one signal, instead of controlling one organ or less, one signal can actually have an impact on multiple organs. So this isn't gibberish. The reason that you need to understand the lengths of the pre-ganglionics and post-ganglionic neurons is so you understand why the sympathetic nervous system has huge, broad effects, whereas the parasympathetic system has these small, local effects. The other thing to note here is which neurotransmitters are being used. It's something you just have to know. So with the parasympathetic nervous system, it's almost always acetylcholine. So unless you hear of an exception, it's always acetylcholine, which means that the pre-ganglionic neurons release acetylcholine and the post-ganglionic neurons also release acetylcholine. So some of them do release nitric oxide, which is an interesting vasodilator, but not worth noting. So the parasympathetic system just think acetylcholine is the only real key neurotransmitter being used. With your sympathetic nervous system, that isn't true. Your pre-ganglionic neurons, they release acetylcholine. But the post-ganglionic neurons, they're going to release primarily norepinephrine. So norepinephrine is the other name for it is noradrenaline. So this is going to be adrenaline's cousin. Adrenaline is more important as a hormone in the bloodstream, but as a neurotransmitter we use more norepinephrine. So the post-ganglionic neurons of the sympathetic nervous system are going to release primarily norepinephrine. Now some will also release epinephrine or adrenaline, and even other ones will release other things, but I want to muddy the water. So think sympathetic's releasing adrenaline or it's cousin. So what do you think the sympathetic system does? Fight or flight? So if you remember the neurotransmitters, hopefully that'll help you. All right, another thing here, just looking at the basic differences as far as where the names come from, the parasympathetic division is called the craniosacral division because it's controlled by cranial nerves 3, 7, 9 and 10, which you can see there at the top of that image on the right, and controlled by the sacral segments S2 to S4. So that's why it's called the craniosacral division. The sympathetic nervous system is called the thoracolumbar division because it's controlled by spinal segments T1 to L2. So there's another key anatomical difference is where this information is coming from. And the last thing that I haven't noted yet, which ties into even the last slide, is the adrenal medulla, sorry, apologize, the adrenal medulla. So the center of the adrenal gland, which releases the hormone epinephrine primarily, is a modified sympathetic ganglion. So your sympathetic nervous system actually controls the center of the adrenal glands. That's a special exception. We can cover that later, but that's also another reason. So since when your sympathetic system kicks in, all that nerve divergence is one reason you have real big broad effects, sorry about that. But the fact that your adrenal gland dumps hormones into the bloodstream is another reason why the sympathetic nervous system has much broader reaching effects and also they last a lot longer. Hormones stay in your bloodstream a lot longer than neurotransmitters stay in the synapse. Okay, so I hope that explaining these differences before we dive too deep in will help you understand why these systems operate so differently. Okay, I hope this helps. Have a wonderful day. Be blessed.