Neurology | Sympathetic Nervous System

Iron innards. In this video, we're gonna talk about the sympathetic nervous system. Have you guys, if you haven't already, please you'll watch the video in the introduction to the autonomic nervous system. We discuss a little bit about a little brief introduction into talking about the different types of ganglia and a little bit on the sympathetic nervous and the parasympathetic.

In this video, we're gonna go into a little bit more detail on the actual specific splanchnic nerves, right? And there are target organs and then the functions of those target organs, okay? Before we do that, I want to talk about this, the thoracolumbar outflow, right? So let's go ahead and talk about that first. So if you remember, we talked about this in the autonomic intro video, that from T1 to L2, and again, taking a little bit of grain of salt, there's some variants in there that sometimes it can be to L3. This is called the thoracolumbar outflow. It's a sympathetic outflow.

Now, where are these? What are these blue things? These blue things, if you remember, are the cell bodies of the preganglionic motor neurons, which are located in the intermediate lateral column or the lateral gray horn. I think that one's easier to say, but either way, remember that you can find these blue guys here. These are the cell bodies of the preganglionic motor neurons of the sympathetic nervous system, about a lateral gray horn or the intermediate lateral column, all right?

Now, what we're going to do is I want to talk about the outflows of these target organs. So we have these things on the side here, right? These are called your ganglia. What is a gang? A gang is just a group of cell bodies in the peripheral nervous system, which is outside the CNS, which is made up of the brain and the spinal cord, right? So outside of the brain and the spinal cord, you have these groups of cell bodies. They're called ganglia. If they're located on the side, they're called chain ganglia. If they're located in front, you remember they were called prevertebral or pre-aortic or subdiaphragmatic, or collateral, a whole bunch of darn names for the same thing, right? Well, we're going to talk about, and a lot of this video is the collateral ganglia, okay, which we're gonna stick with collateral or prevertebral, right? But I want to talk about these chain ganglia first, these top ones, this one right here. Have you come up an extension up here? These chain going up lit to the cervical region, right? Around like C2, about this is actually you're gonna have what's called your superior cervical ganglion, which we're going to put SCG. You'll have another one at this level, which is the middle cervical ganglion, MCG, or the inferior cervical ganglion, which is the ICG. But again, there are some variants in different people. Sometimes the inferior cervical ganglion is fused with T1. They call it the stellate ganglion. Not necessarily super important, but again, one of you guys to understand the variance here.

What I want to do is I want to talk about the outflows of these target organs. So we have these things on the side here, right? These are called your ganglia. What is a gang? A gang is just a group of cell bodies in the peripheral nervous system, which is outside the CNS, which is made up of the brain and the spinal cord, right? So outside of the brain and the spinal cord, you have these groups of cell bodies. They're called ganglia. If they're located on the side, they're called chain ganglia. If they're located in front, you remember they were called prevertebral or pre-aortic or subdiaphragmatic, or collateral, a whole bunch of darn names for the same thing, right? Well, we're going to talk about, and a lot of this video is the collateral ganglia, okay, which we're gonna stick with collateral or prevertebral, right? But I want to talk about these chain ganglia first, these top ones, this one right here. Have you come up an extension up here? These chain going up lit to the cervical region, right? Around like C2, about this is actually you're gonna have what's called your superior cervical ganglion, which we're going to put SCG. You'll have another one at this level, which is the middle cervical ganglion, MCG, or the inferior cervical ganglion, which is the ICG. But again, there are some variants in different people. Sometimes the inferior cervical ganglion is fused with T1. They call it the stellate ganglion. Not necessarily super important, but again, one of you guys to understand the variance here.

What I want to do is I want to talk about the preganglionic flow to the superior cervical ganglion and then out, okay, via to the head and neck structures. That's what we're gonna start with first. So first things first, generally from anywhere from about T1 to T3, okay, about T1 to T3, these guys can come out, right? So here's well, here's what I'm I'm gonna bring this guy in here. It's not gonna synapse in that chain ganglia. It's gonna move upwards and it can synapse on the cell bodies and the superior cervical ganglion. And again, this can come from T1, it can come from T2, or it could even come from T3, all right? When these fibers move up, they can move up through the inferior cervical, middle cervical, up to the superior cervical ganglion and synapse on cell bodies here. From this point, they can then come out. When they come out, guess what these guys do? You know, there's a big artery right there? There's a big artery here. You know, your heart, you have the common carotid artery. The common carotid artery actually bifurcates into the external carotid artery and the internal carotid artery. What happens is you can have this nerve fiber kind of swirl around the internal carotid artery. And when it does that, it forms a special plexus. We call this the carotid plexus, and it can actually come off and go to different portions around the head and the neck. The main ones we're going to talk about is going to be first the, okay? So it's gonna supply a lot of different structures here, okay? The first one that we're going to talk about here is going to be the eye, all right?

Now, if you remember, those are the preganglionic, the blue. The black are the postganglionic. They release norepinephrine. There's only one exception to it, and we'll talk about that, and it's gonna be the sweat glands. But we're here, what's gonna happen is this guy's gonna release norepinephrine. Now, what areas are gonna act on the eye? You know, there's around the iris, you have a specific muscle there. We talked about in the actual special senses videos. There's the iris, right? It has what's called the dilator pupillae, right? And think about these things logically. In a sympathetic situation, your fight, your flight, your fright situations, what are you gonna want to do? Let's pretend that I don't know, Chuck Liddell, he's getting ready to come at you, he's chasing you. What's gonna happen? Well, you want to be able to see all different types of options, right? So what would your pupils want to do in that situation? Would you want to only see things like very small amount of areas, or would you want to be able to see a lot of stuff? You want to see a lot of stuff. So what's gonna happen is it's gonna release norepinephrine on this muscle here called the dilator pupillae. So what can I do? It can act on what's called the dilator pupillae, and when it acts on the dilator pupillae, it causes pupillary dilation. If it acts on the dilator pupillae and causes pupillary dilation, what does it allow for? Primarily for far vision, okay? Allows more light to come in. You're gonna have a little bit more exception for the far vision.

What else? It's also gonna act on a muscle right here around the ciliary body. They call it the ciliary muscle. So it's also gonna act on the ciliary muscle called the ciliary. When that contracts, what it does is it actually helps the lens to become more flattened. When the lens becomes more flat, and it helps us to be able to see very, very far too. It's called accommodation. So the ciliary allows for what's called accommodation, and this accommodation can lead to the assistance in far vision, right? That's important.

Then it's also gonna act in the, remember I said the head and neck region? We got a lot of glands in this area. You know, we have the salivary glands, like the submandibular, the sublingual, the parotid salivary glands, right? And even other glands too, associated with this, but these are your main salivary glands, right? So the main thing is gonna be your salivary glands. So let's put here salivary glands. And again, remember submandibular, sublingual, parotid. What's going to happen is they're gonna release chemicals like norepinephrine, which can act in two places. One is that norepinephrine, remember this was norepinephrine, which is acting here. You can also release norepinephrine, which can act on two places. One is it could act directly on the blood vessel. It can act on the tunica media. You know, there's the tunica media, the smooth muscle within the vessel wall, which contracts. When it constricts, it decreases the blood flow to the salivary glands, which decreases the actual substances that you can take for these salivary glands to take from the blood and put into the saliva. That's one important thing. The next thing is that also is going to act on the salivary glands directly. There's different types of adrenergic receptors. We'll have another video on that. When it acts on the salivary glands, it actually causes them to switch their mucus production into producing more mucin, which is a glycoprotein, which helps the thick, thick in the mucus. So it's gonna cause two different effects. One, it's gonna cause a thick, viscous, thick and viscous mucus production, okay? So it's gonna cause a thick, viscous mucus production, all right?

Now, what about other glands? There's other glands besides salivary glands in this area. You know, there's another one, lacrimation, right? So you also have what's called these lacrimal glands. So that other ones here called lacrimal glands. Now, your lacrimal glands, what happens is norepinephrine can also act on the blood vessels in this area, constrict them, decrease the blood flow through there, which decreases the lacrimation, or it could act directly on the lacrimal glands and decrease lacrimation, right? So it's gonna try to decrease lacrimation, okay? So that pretty much covers this. Now, what was this thing here called, which comes off the superior cervical ganglion, that they pretty much call this the carotid plexus, okay? All right, that covers that part.

Now, the next thing here is I'm really important. Now, there's other things that can come from the superior cervical ganglion. Actually, can join on to some of the actual spinal nerves. And if it joins with some of the spinal nerves, that can go to supply your erector pili. It can go to supply the actual blood vessels, the vasomotor supply, or it can also do what, if you remember, it can also go to the sudoriferous sweat glands, okay, which are gonna be important for sudomotor control, which is sweat production, all right? But let's talk about these other ones here.

So now we're gonna have the middle cervical ganglion and the inferior cervical ganglion. These can give off branches too, but the most important branches for these guys are going to be specifically structures that are going to the heart, the lungs, and the esophagus, okay? So they're gonna give off fibers here, and these fibers here are gonna go specifically to the heart, the lungs, and the esophagus, okay?

Now, another thing is the superior cervical ganglion can also give off some fibers too. It can also give off. So sometimes we call this the superior, middle, inferior cardiac nerve or plexus, right? And these are your sympathetic fibers. And what they're doing is they're going to three different targets. And what are these targets? One is it can go to the heart. If it goes to the heart, it acts mainly on two different areas. One is your nodal cells. Your nodal cells are important for heart rate. So what it's gonna do is it's gonna try to increase the heart rate. It's gonna try to cause positive chronotropic action. So what's the overall effect here is gonna try to, let's do a different color, let's say it increases heart rate. So one thing is it's gonna increase heart rate, when they call that positive chronotropic action, right? Another thing is to connect on the myocardium, the contractile muscle cells. If that happens, it can increase the action power. If that does that, if we increase contractility, we increase what's called cardiac output. And if you increase cardiac output, eventually that could increase your blood pressure, okay? That's a pretty cool thing there, right?

All right, what else? It can act in the esophagus. And now, generally, you don't, in every year, in this flight or flight situation, or you don't want to be able to worry about digesting food. No, you don't really care about that. So it's gonna try to decrease peristalsis of the esophagus. So for the esophagus, it's gonna decrease peristalsis of the esophagus and certain secretions of the esophagus from the within the serum. You because you have some tight certain types of glands within this area, the esophageal glands, okay?

The lungs, the respiratory system, the specific area that is affecting though is the bronchi. You know, the bronchial smooth muscle. There's bronchial smooth muscle here that actually control the diameter of the airway. They control the airway resistance. So if the sympathetic nervous system is gonna act here, think about that. What are you gonna do if Chuck Liddell's coming at me? One of the toughest UFC fighters in history, right? What's gonna happen? I'm gonna, I'm gonna hyperventilate. I'm gonna get really scared. So you're gonna want to be able to allow for the dilation of the respiratory bronchioles because you're gonna want to be able to run away, right? Have as much air getting into your, your blood as possible, as much oxygen, cuz you want to run away from that guy, all right? So what's gonna happen here? It's gonna dilate the bronchioles. So it's gonna cause dilation of the bronchioles.

Now, another thing it can do, remember that it actually does have the ability to go to the vascular smooth muscle, I'm sorry, the vascular smooth muscle within the blood vessels in this area. Now, why that's important is, is you don't want your blood vessels within the respiratory system to dilate, right? Because it allows for a lot of fluid to come into the area and leak out and make a lot of secretions. You don't want a lot of secretions within the lungs because you want to have open area, open airways, that you can get as much oxygen in and out. So what do you want to do to the secretions? You want to decrease it. So two things can also have what happened here is it's also gonna decrease secretions acting on the glands directly, and it's gonna cause vasoconstriction of bronchial arteries. Make sure that you understand I'm saying bronchial arteries. I am NOT talking about the pulmonary artery. These are completely different, okay? Those are more autoregulated, autoregulation type of control, okay? Cool.

Now, the next thing that we have to talk about is what do we call this? Well, specifically, if it's going to the heart, what do we connect? We call that we called it the cardiac plexus. If it's going through the esophagus, we're gonna call this the esophageal plexus. If it's going to the lungs, we're gonna call this the pulmonary plexus. But here's one more thing that we have to understand, right? So I said that it was mainly coming from the superior, middle, and inferior. That's not always the case. There's also other contributions. Remember I said here that there was T1, T2, T3, right? Well, guess what else? There's also gonna be. So you can have these fibers that can actually go straight up here, or they can come and synapse in this area. So let's say that it actually synapses here, or this guy comes over here. So let's say now that it comes here and synapses, or it comes here and synapses, comes here and synapses, mainly T1 to T4, but you can have some contributions here from T5, okay? So you can have T1 to about T4, but if you want, we'll throw in another one there, which is going to be T5.

Now, what can happen? Some of the fibers from T1 to T3 can go up, right? So here, let's show that kind of like this, or some of them can go to the actual cell bodies within the chain ganglia. Remember what I told you? They don't have to go out through the gray rami communicans. They can go out as their own nerve. What was that called? It's called a splanchnic nerve. And so some of these fibers here, so T1 to T2, T3, T4, and again, take it with a grain of salt, there's a lot of variability here, but even T5. And remember, I'm saying a lot of variability because sometimes you're gonna read in different books that certain nerves might go to different ganglia, and certain nerves might not go to this one, certain my nerves might go to the other one. So just remember, there's a lot of variability in these textbooks, okay? All right, so that's that. All right, so we talked about the cardiac plexus, esophageal, pulmonary, and the carotid.

Now, let's go to the next one. The next thing we're going to talk about is we're gonna go to this structure called the celiac ganglia. So we're gonna go from a specific portion now. We're gonna go because now we're getting ready to go into the abdomen, and we're gonna go from T5 to about T9. Now, that's what we're gonna focus on, okay? So we're gonna focus primarily here on T5 to T9. Let me get this kidney and you out of the way, okay? So first things first, remember I told you some of these fibers, they can go to a chain ganglia. So I'm hoping they don't have to. They can pass right through it, right? They can go into a collateral ganglia. So now that's what we're gonna talk about. So let's say that this T5 passes right through, T6 passes right through, T7 passes right through, T8 and T9 pass right through their chain ganglia. They don't synapse there, and they come out right as some type of splanchnic nerve. This splanchnic nerve right here, why do we call this bad boy? We call this nerve the greater splanchnic nerve. Now, the greater splanchnic nerve pretty much extends from T5 to T9. Now, what's the main ganglia that it's going to go to? The main ganglia here that it's going to go to is going to be right around here. You know, there's the aorta, right? You have the aorta, and right around the aorta, you have this paired ganglia. This paired ganglia is actually gonna be called the celiac ganglia. So let's actually show that guy right here. Here's the cell body. I'm just drawing one, but remember there's multiple cell bodies here. Synapses right there. There's the ganglion. What is this ganglion called? This ganglion is called the celiac ganglion. And remember, this is a prevertebral or collateral.

Now, from the celiac ganglia on, you remember what the artery was that actually moves right where the celiac ganglia, the nerves are gonna move in that same area? It's called the celiac trunk, right? So the celiac trunk gives off multiple branches, but we're gonna pick the main, the most common ones, right? So if we come up here, look what's gonna happen here. We're gonna have a heck of a supply here, okay? So what is this gonna be? So the celiac ganglia is gonna give branches off the celiac trunk again. And the celiac trunk, if you remember, it gives off multiple branches. We're gonna focus on the common ones, right? Big one right here, stomach. So it's gonna go to the stomach. And when it goes to the stomach, what do you think you're gonna want to do? You're gonna want to inhibit the actual peristalsis, inhibit the secretions. So two effects here for this guy: inhibit peristalsis because again, you don't want to be contracting your stomach and trying to focus a lot of that energy and muscles on, on basically focusing on digesting food. That's not your sole focus, right? So you want to try to inhibit the peristalsis. Another thing here is you're gonna want to try to inhibit some of the secretions there too. But the main thing that we're gonna try to do here is remember the blood flow, right? The splanchnic circulation. You don't really want a lot of blood flow going to the stomach during a sympathetic situation. So what are you gonna want to try to do to the actual blood flow to that area? You're gonna try to decrease it. So we're gonna do the vessels. You're gonna constrict the blood vessels. So you're gonna constrict the blood vessels going to the stomach. And if you do that, by default, it's gonna do two things. One is it, again, it's gonna decrease the absorption process, alright? Because there is certain things that do get absorbed across the gut, specifically in the stomach, like lipid-soluble substances like aspirin and alcohol. But another thing is it's gonna decrease some of the actual secretions, okay?

There is another exception here where it actually can, there's a sphincter muscle right here. It's actually called the pyloric sphincter. I'm not gonna talk too much about it, but if you really do want to remember what it can actually do here is it can act on the pyloric sphincter. And when it acts on the pyloric sphincter, it can constrict the pyloric sphincter to prevent chyme from moving from the stomach into the duodenum, basically slowing down the digestive process, basically. So if you do want to remember that, it is a different one where it actually can cause contraction of the pyloric sphincter. They call this whenever that happens, they call it the gastroenteric reflex, okay, which is basically inhibitory reflex. It's very common and happens normally within the actual GI tract processes. But anyway, the reason why that's a little bit different is you might believe, wait, how is it causing contraction? How is it inhibiting it here? It is dependent upon receptors. For example, this is alpha-1. This is usually beta-2, okay? But again, we'll make a video on that specifically.

All right, now we're gonna go to the liver. The liver, what is it gonna try to do? The liver, it's mainly gonna focus on trying to do a special thing here. One of the special things about the liver is that the liver can actually break down glycogen into glucose, which is important whenever our blood sugar levels and they need to be high so we can get our muscles contracting to be able to fight Chuck Liddell or run from Chuck Liddell, right? So what are we gonna do here? The big thing here is we're gonna do what's called glycogenolysis. That's gonna be the big thing here. We're gonna want to try to cause glycogenolysis to occur for the liver.

All right, now the biliary tree here, you're not gonna really want the actual gallbladder contractions to occur. You're not gonna want to be able to release bile. You're not really focusing on emulsifying fats and digesting and absorbing lipids, right? So you're gonna want to try to inhibit the biliary contractions, right? So you're gonna want to be able to decrease biliary tree contractions and flow. Yeah, I like that. I like that. But let's say decrease biliary tree flow, okay, biliary tree flow because again, you're not really focusing right now and trying to be able to get rid of the bile and help to cause the emulsification of fat. That's not really your focus at that point. All right?

Again, the pancreas. The pancreas, you know that there are structures here within the pancreas. They called these guys the islets of Langerhans. And the islets of Langerhans have alpha cells and beta cells. Now, the beta cells are responsible for secreting insulin, all right? The alpha cells are responsible for secreting glucagon. Now, in this situation, insulin wants to be able to decrease your blood glucose levels. You don't want that. You want to increase them. So what do you think it's gonna do to the insulin production here? It's gonna focus on trying to decrease insulin production. And vice versa, I want the other hormone to even act synergistically with me to enhance the blood glucose levels. So I'm going to inhibit the beta cells, but stimulate the alpha cells. So I'm gonna want to try to increase glucagon production here, okay? All right.

And there is fibers that can go to the splenic capsule here, to the spleen. Not necessarily super important, to be honest with you, but it can cause the splenic capsule to have a slight contraction. So it can go to the spleen and cause like a splenic contraction. Again, not super important in this situation, not really significant to the sympathetic fight-or-flight response, okay? So the big thing here that we were able to grasp here is that from the celiac ganglia, it's gonna supply the stomach, cause the contraction of the pyloric sphincter, inhibit peristalsis, decrease absorption, secretions. It's caused like a glycogenolysis, decrease biliary tree flow, and it's gonna try to inhibit the insulin production, the glucagon production, and increase glucagon production. And again, it can cause the splenic contraction of the, the outer capsule. Also, there is, remember the celiac trunk does supply the proximal half of the duodenum. And again, if you remember that, it's going to decrease the absorption in the secretions of that area also, okay? So it's not just the stomach, but also remember the proximal half of the duodenum.

All right, so we deal now. The greater splanchnic nerve has another point that it goes to. And remember, I'm telling you guys this because you have to understand that there is so much variability here. Now, there is another part here, right? That the greater splanchnic nerve can have a branch that comes off here and goes to the adrenal medulla. Okay? Now, these are odd because you're gonna notice here, wait, where the frick is the ganglion? In this case, there isn't really any collateral ganglia. On this is a weird exception where we say that sympathetic preganglionic too short and sympathetic postganglionic so long. This is kind of like the opposite. In this case, so now the postganglionic are really short. They're actually called in this area. They call it the chromaffin cells. The chromaffin cells are really important because they're acting like the postganglionic fibers. And what happens is this is an example of what's called an intramural ganglion. You're like, oh, I thought that was just for the parasympathetic. This is just one of the exceptions of the sympathetic. And again, as a result, it can act on these chromaffin cells, which are very cool because they can release two different chemicals directly into the circulation. One is called norepinephrine, and the other one is called epinephrine. Okay? And these guys can go all rides, widespread. They can have that very, very widespread, diffuse effect, which is a very powerful effect as compared to parasympathetic, which is more localized, okay? All right, so that's that part. So we can go to the intramural and okay.

What else? There's another one. The greater splanchnic nerve can also give off another fiber here. And again, remember, take this with a grain of salt. It's not always the same thing. It's not always clear-cut here, but it can give off another one that goes to another ganglion, okay? There's another ganglion here, and this guy is called the superior mesenteric ganglion. So what are we gonna have right here? We should have it's right here below it, superior mesenteric ganglion, okay? And this one's really interesting also. Superior mesenteric ganglia, remember the blood supply, superior mesenteric artery. So the actual superior mesenteric artery specifically supplied a couple different structures. One is it can actually supply the cecum, and it can supply the colon. It can supply the actual transverse colon up to about around the actual left colic flexure, like the proximal two-thirds. And it can also supply the duodenum, the distal half, and it can supply the jejunum and the ileum, right? This is the easiest one to think about, honestly. If it's acting in this area, right? It's going to the duodenum, the jejunum, the ileum, the ascending colon. What do you think it's gonna do? Anything in the proximal two-thirds of the transverse colon, it's just gonna inhibit the digestive processes. So basically, the whole result out of all of this here is it's gonna basically try to, yeah, we'll write this one coming down. This right here, the result of this is it's gonna actually cause what? Decrease peristalsis. What else? Decrease in the absorption because it's gonna constrict the blood vessels. And if it constricts the blood vessels, it's not really relevant within the, the large intestine, but it is important within the jejunum and the ileum and the distal half of the duodenum. But it's gonna decrease the secretion processes also, okay? So again, you can just remember decreased peristalsis, decreases absorption, and decrease the secretion. If you really want to be specific though, the absorption of secretion is a little bit more important within a small intestine, not as important within the, the actual large intestine because they don't really play a big role in absorption. They really only absorb water and electrolytes, okay? Got that guy. And if you want, there is a little information that goes to the appendix, but we're not gonna talk about that. All right, so we got the greater splanchnic nerve.

Now we're going to go to the next guy. Whoa. All right, next one is going to be from T10 to T11. So this was for the greater splanchnic nerve, right? This is going to be for what's called the LSN, the lesser splanchnic nerve, okay? So T10, T11, again, these preganglionic fibers come out. What can they do? They can either synapse, they become a part of the gray rami communicans and then go into the spinal nerve and supply pilomotor, sudomotor, vasomotor. Or they pass right through the frackers, boom, and boom. If these guys come out, what happens is, and if it does, it can go to a ganglion. Now, again, I'm gonna keep saying this because there's so much variance in these textbooks, but for the most part, this is what I was able to find is that the actual T10, T11, they come to a specific ganglion. And this ganglion is actually called the aorticorenal ganglion, right? So we got T10, T11, which is gonna pass right through. And then again, what is this nerve called? Lesser splanchnic nerve, okay? Getting a little lazy, sorry guys. Lesser splanchnic nerve. Now, that would go to the aorticorenal ganglia. The aorticorenal ganglion will take these postganglionic fibers out, and where are they gonna go? They're gonna go specifically to the good old kidney, all right? So here, let's have our kidney here, let's have a ureter, all right? So we're gonna have this guy here. So what they'll do is they'll synapse here in the aorticorenal ganglia. And the aorticorenal ganglia is gonna go to the kidney. And it's actually gonna go to the ureter. Now, when it goes to the kidney and the ureter, what are you gonna try to do? Are you gonna try to pee on Chuck Liddell? No, you don't want to pee on Chuck Liddell. That might happen, but that's not normal. But what you want to do is, is you don't want a lot of blood flow going to the kidneys, and you don't really want to make urine. So as a result, what are the two things that you would expect to happen here? One is I'm gonna decrease urine production, okay? That's one big thing. What's another big thing? Well, here's a little weird thing. There's actually these things in here in the actual kidney. We're not gonna zoom in on, but the JG cells, the juxtaglomerular cells. The juxtaglomerular cells are really important. Why? Because what they do is they respond by beta-1 adrenergic receptors. They can release a chemical called renin. And renin can set off the angiotensin II cascade, which can cause aldosterone, ADH, all these different hormones to get produced, which are trying to increase their blood pressure. So in that response, what else could I have? I could have what's called renin release, okay? But again, remember the urine production, it's usually due to what? Remember I said it's decreasing the blood flow. So it's gonna decrease the blood flow mainly by causing vasoconstriction to the blood vessels going to the kidney, diverting that blood away from the kidney so we can send it to more important vital organs. That's the same thing with the stomach again. You're decreasing absorption or secretion or the entire GI tract. If you're doing that, you're constricting the blood flow to it so you can divert the blood away from those organs so you can send it to the muscles or the brain or other different organs needed for you to do the flight or fright situations, okay? All right, so we got that one.

T12 is pretty easy also. This one's actually a lot easier. It can pass right through T12. I mean, it can go right through the chain ganglia. And again, I'm gonna keep saying it, take this with a grain of salt. There is these weird type of cells, diffuse ganglion cells, and they're kind of like found like they're kind of diffuse and kind of widespread around this area here. I'm gonna kind of represent it like this. These diffuse ganglion cells are important because when T12, the preganglionic fibers didn't come and synapse in some of these diffuse ganglion cells, when they do, these guys can enter into the kidney as a part of what's called the renal plexus, right? So what do we technically call this? It can synapse. Technically, we call this the renal plexus, okay, which again can help to support the fibers from the aorticorenal ganglia by causing renin release, decreasing urine production. But again, more of it is trying to be able to decrease urine production. Another thing that can happen with the urine production is if you don't want the actual ureter to contract, what are you gonna want to do? What you want to do to the ureter? You want to be able to decrease the peristalsis of the ureter because that's another effect that you can get out of the renal plexus and the fibers from the aorticorenal ganglia. You're not gonna want the actual ureter to be contracting. You don't want to focus on making urine, right? All right, my darn knees. All right, so we got here T12. I guess I should tell you what this guy's called. This is called the least splanchnic nerve, okay? So this fiber right here, I'm gonna denote it with LA, actually, one have two right here because I was the same thing here. This is called the least splanchnic nerve, okay? Okay, we are so close, guys.

All right, let's do L1 and L2, and sometimes L3. Okay, these are gonna be your lumbar splanchnic nerves, okay? Lumbar splanchnic nerves. So again, L1, you can have this guy pass through. L2, pass through. L3, pass through, right? Now, if they pass right through, they don't go to the chain ganglia. This is kind of important here. They can continue to keep passing through here. And here's where it gets kind of interesting. We're gonna kind of come up over here, all right? And there's gonna be a ganglion over here, okay? There's gonna be a ganglion right over here. We're gonna kind of finish what we didn't get to over here. So now there's gonna be a ganglion over here where these lumbar splanchnic nerves can actually come to and innervate. This ganglion is called the inferior mesenteric ganglion, okay? Now, from the inferior mesenteric ganglia, remember the inferior mesenteric arteries, okay? The inferior mesenteric artery, what happens with the inferior mesenteric artery? It supplies the descending colon, sigmoid colon, upper rectum, and the distal 1/3 of the transverse colon. Now, what do you think you're gonna try to do here? The overall result, you're gonna want to try to decrease peristalsis. You're gonna want to try to be able to, the main function, to be honest with you, is decrease the peristalsis here, okay? So as a result here, the main function for this one is you're gonna want to try to decrease the peristalsis, all right? You're not gonna want to try to poop or defecate in that type of situation. That's for parasympathetic when you're calm and you're resting, you're digesting, defecating, urinating, all right? So that's gonna be for that part.

All right, so now we're gonna start with the innervation to the bladder and the internal urethral sphincter. So we've talked about how L1, L2, and L3 can go out here. Now, sometimes what can happen is something even from T12, they can actually kind of come down here. And so can L1 and L2, and even L3 here can actually, what happens is sometimes they can even pass down to L4. But either way, nonetheless, some of these fibers all the way down from about T12, sometimes even T11, down to about L2, L3, they can pass through, right? And they can come to an area right over here. There's two plexi over here. One, it's actually draw it like this. There's actually two plexi over here. One is called the superior hypogastric plexus, and the other one is actually going to be what's called the intermesenteric plexus. So again, L1, L2, L3, and even T12, sometimes even T11, they can come down right through these actual chain ganglia, come out, and they can go to two ganglia over. One can be called the superior hypogastric ganglion, or we can have over here this weird sucker called the intermesenteric plexus. This is actually in between, as you can hear, between the superior and inferior mesenteric arteries. So it's kind of extending between these and allows for things to go up and go down around that area. But again, what can happen is we're not going to talk about the things from the intermesenteric because as I said, things can go up into the superior mesenteric ganglion, they can go down into the inferior mesenteric area. So they can go and follow the superior mesenteric artery or inferior mesenteric artery. Some of them can even follow some of the actual hypogastric nerves. There are so many different areas that can come from this point. So what I'm just gonna do here is I'll show that it can either go this way, you can go that way. Some of the fibers can actually even go over here, okay?

So the superior hypogastric ganglion gives these fibers here that can go to the internal urethral sphincter and can go to what's called the detrusor muscle, okay? So this big, big muscle here, which is basically the muscularis externa of this bladder, is called the detrusor muscle. If you watched our video on micturition reflex, this will also give you a little bit more detail if you want. But there's beta-2 and beta-3 adrenergic receptors in the detrusor muscle. Whenever it acts on that muscle, it relaxes the muscle, it inhibits it from undergoing contraction. So what is that going to do to this guy? It's gonna decrease contractions, basically trying to prevent the process of voiding or micturition. All right, down here you have the internal urethral sphincter. Now, this one's different. Now, this one actually, what happened? It did contract. Guess what's gonna happen here? The sucker's gonna constrict, prevent you from peeing your pants, right? So we're actually almost peeing your pants. So there's actually alpha-1 adrenergic receptors in this guy, but it's gonna act on this guy, the internal urethral sphincter, and actually cause constriction or contraction of the sphincter. But remember, this is the internal urethral sphincter, not the external. External is under voluntary somatic control.

All right, now remember the superior hypogastric ganglion or plexus, they call it. This one's interesting. And the reason why is, is it actually gives off things called hypogastric nerves, the right hypogastric nerve and the left hypogastric nerve. And those are pretty much the main contribution into this last thing and we're gonna talk about called the inferior hypogastric plexus. So I didn't want you to remember that the main input going down into the actual gonads, the ovaries and the testes, is going to be the contributions from the superior hypogastric plexus. The right hypogastric nerve, left hypogastric nerve will eventually become the inferior hypogastric plexus. But before we finish that off, there's a part down here, right? So what happens is, remember I said here, remember I said from going to the bladder, it could be from like L1, L2, L3, and it can even go out to the ganglion around L4. It can even be up to T12, T11. Well, same thing for the gonads. The gonads can actually extend from T10 to. So T10 can actually give extensions, and so can T11. So you can have extensions from T10 to 11, L1, L2, mainly from T10 to L2, okay? So it's pretty much going to go to about L2 here. What they do is they can come into these chain ganglia, right? And they can come out around the sacral region of these actual chain ganglia, around the sacral region. And what happens with these guys is they're going to go and supply the gonads, okay? So it's gonna go and supply the gonads. So for that, you remember that there's the uterus for the female, there's the vagina, right? There's also some of other tissues around that area like the actual oviducts, the ovary. For the male, it's gonna be like the penis, the scrotum, right? So around that area there. So this is important. So what is it gonna do? Okay, for the male, well, what kind of effect would it have in the male? Specifically, it's designed to initiate ejaculation. So you can remember this by parasympathetic point for the erection and sympathetic shoot for the ejaculation. And then for the female, this one, it actually is kind of interesting. It can act on the uterus, right? And generally wants to cause the contractions of the uterus. So it actually can cause uterine contractions. But whenever a woman is pregnant, what happens is it switches receptors, okay, from alpha-1 to beta-2, so that the uterus doesn't contract. You don't want to pop a baby out whenever you're pregnant, right? So it can change the, remember, uterine contractions is for non-pregnant women, but it does actually change when they're pregnant, right? It switches the receptors from alpha-1 to beta-2. Budding and causes uterine contractions or ejaculation within the male. There's also other structures called the prostate gland within the male, right? The prostate gland, the seminal vesicles that can actually cause those guys to produce what's called seminal fluid, all right? Not as super important for these guys, but again, what is these? These nerves here called? These ones here, son of a gun, these are called your sacral splanchnics. So this area here is called your sacral splanchnic nerves. And remember this one here going to the inferior mesenteric ganglion and the intermesenteric plexus and the superior hypogastric is called the lumbar splanchnics. And remember, like I told you, superior hypogastric ganglion can give off things called right and left hypogastric nerves. So these can be what's called your hypogastric nerves. And again, the hypogastric nerves are the main contributor to this structure down here because what happens is the sacral splanchnics, they come out to some diffuse ganglion cells out here also. And what happens is the main, main contributor that caught innervates the gonads, the main one, let's actually put this one in pink so that we can brighten it up here, is called the inferior hypogastric plexus, okay? So the inferior hypogastric plexus is the main nerves they're gonna supply the gonads, right? And it can get two contributions. Very little of it, very minute amounts, come from the sacral splanchnic nerves from T10 and L2. But a good, good, good portion of them, the more significant contributor is going to be from the superior hypogastric ganglion, which splits it into right hypogastric nerves and left hypogastric nerves will eventually become and merge with the sacral splanchnics and form what's called the inferior hypogastric plexus, which again will supply the gonads.

All right, so before we finish this off on the sympathetic outflow, you talk about one last thing, I promise. And this is gonna be some of the control. So, you know, there's a tissue of gray matter which is a part of the diencephalon, right here. It's called the hypothalamus. There's also other structures in here, like for example, you can have what's called limbic nuclei, all right? And even parts of your cortex. But here's the important thing. And the sympathetic nervous system actually has contributions from the hypothalamus and has contributions from the limbic nuclei. In certain situations, it can even have cortical control also. So sometimes it might even have cortical control, not very much though, but it can sometimes have some cortical control. But for the most part, the main ones is the limbic nuclei have a big effect on the sympathetic nervous system and the hypothalamus, okay? The only reason I say cortical control is that there's things called biofeedback techniques where you actually can, like on your own, control your heart rate. So there is some weird situations in which there can be cortical controls. But mainly the limbic nuclei and the hypothalamus are some of the big, big structures, tissues of gray matter within the cerebrum that actually can contribute to innervating or stimulating the sympathetic nervous system because you can have these things like these presynaptic fibers that can come down and stimulate these cell bodies right here. So again, these presynaptic fibers, they can come out and stimulate these cell bodies here and activate these preganglionic motor neurons to come out and stimulate the postganglionic and go and innervate the target organ. So remember, this sympathetic control can have kind of higher brain functioning control, right? Hypothalamus has sympathetic tissue that can actually have presynaptic fibers and come down and stimulate the cell bodies in the lateral gray horn or the intermediate lateral column. And so can the limbic nuclei. In certain situations where people can have biofeedback techniques, they might even have a little bit of cortical control, all right? All right, ninja nerds, I want to thank you guys so much for watching this video. If you guys did watch this video, if you got through the whole thing, man, you guys are awesome. I hope you guys like this video. I hope that you guys really learned something. If you did, please hit the like button, comment on the comment section, and please subscribe. Also, check out our Instagram, our Facebook, and our Patreon account. Please guys, every dollar counts. It helps us to make the highest quality videos for your guys' enjoyment. Fine, enginearies, as always, until next time. [Music] You [Music]