Understanding the Enteric Nervous System

Hi Ninja Nerds, in this video we're going to talk about the enteric nervous system. Now, if you guys watched our video on the introduction to the autonomic nervous system, that's great, because remember, some people, they don't even necessarily include the enteric nervous system as a part of the autonomic nervous system, but you have to remember the enteric nervous system is really, really special. Do you know all the neurons, all the neurons that are involved within the enteric nervous system, basically the gut brain, is equal to the amount of neurons located within the entire spinal cord? That's unbelievable when you think about it. So it technically is like a little gut brain. Now the enteric nervous system is super important and what we're going to do is we're going to talk about the myenteric nerve plexus and the submucosal nerve plexus and how they regulate motility and secretions, okay, intrinsically. And then after we do that, then we're going to talk about the extrinsic effect, in other words, the sympathetic nervous system, the parasympathetic nervous system, and how that can play a role in altering the intrinsic activity. So we'll talk about short reflex arcs and long reflex arcs. Alright, so let's go ahead and get started. So first things first, when we're looking at this, what we're doing with this part here, this diagram, is if we come over here to this little stomach and duodenum over here, all I'm doing is, is I'm taking a cut, I'm taking a section right here, onto the actual duodenum. So imagine I'm doing this, I'm cutting this, and I'm looking at the duodenum with the lumen. Going from the lumen all the way out to the serosa. If we're talking about the first part of the duodenum, technically that's serosa. The second, third, and fourth parts have adventitia. But again, for simplicity's sake, let's assume that we're talking about the first part. So all I'm doing is I'm zooming in on the mucosa all the way out to the outer serosa layer. Okay? So that's what you see here. So now let's get a good idea of the histology. We're not going to talk about this in great detail. We're going to keep it rather simplistic. But again, first layer here. There's four basic layers of the alimentary canal. So first one is your mucosa, okay? Now technically the mucosa is actually made up of three layers, okay? So what are those three layers? Technically it's made up of a epithelial tissue, okay, so an epithelium. Another one is called a lamina propria, which is basically areola connective tissue. And the last one is called a muscularis mucosa. Now, the epithelium is different from organ to organ. For example, just simplicity-wise, the esophagus, the stratified squamous epithelial tissue. But the stomach, the duodenum, and pretty much all the intestines are going to be simple columnar. If we take, for example, the trachea, the epithelial tissue there will be pseudostratified ciliated columnar epithelial tissue. It depends from organ to organ. But in general, these are the three parts of mucosa. epithelium, lamina propria, muscularis mucosa. Then, after that, you have a big space here. Okay, this whole space here. So let's assume that the mucosa ends right here, starts right here, right? So the end part of the mucosa is right here. It goes all the way up to this muscle layer here. So from here to here. That's the next one. This layer here is going to be a specific component. We call this the sub mucosa. The submucosa is actually kind of a mixture of areolar connective tissue and a little bit of dense connective tissue. But in the submucosa you have lots of glands in this area and you have this nerve plexus. This really really important nerve plexus. They call this bad boy the submucosal plexus. So simple right? So simple one. Another name for it if you don't want to remember the submucosal plexus. There is another name, they call this the Meissner's plexus. Okay, so you have the Meissner's plexus. So you have the submucosal plexus and the Meissner's plexus. Now, that's the submucosa. Again, it's some areola connective tissue and it's also going to be some dense fibrous connective tissue. And what else will you have out here? You could have some glands. So there could be certain types of glands in this area right here. And they can have different types of functions. Alright, next thing. If we got to the next part here, so we have mucosa, submucosa, then we have these two parts out here. So if you look here, from this circular structure here, all the way down here to this kind of like a longitudinal structure here, from here to here. This part here is called the muscularis externa. And generally, for most organs, It has an inner circular layer and over here it has a outer longitudinal layer. Okay, now there is an exception the stomach. The stomach actually does have a inner oblique, middle circular, and an outer longitudinal. But for the sake of its simplicity, we're going to just keep it to inner and outer. Okay, but do remember that the stomach does have a third one, inner oblique, middle circular, outer longitudinal. Okay, so this is the inner circular layer. This is the outer longitudinal layer. But these two together make up the muscularis externa. Now, in the muscularis externa, there is a nerve plexus of ascending and descending. fibers. This structure here is called the myenteric plexus. Another name for this plexus is called the Arbach plexus. Okay, just so that you hear them in different types, right? So you have two different types of plexes here. One is the submucosal plexus, located within the submucosa, also called the Miesner's plexus. And you have the myenteric plexus. And the myenteric plexus is also called the Arbach plexus, and it's located within the muscularis externa, but specifically in between the inner circular and the outer longitudinal. And it consists of ascending and descending fibers. Okay. Last part here for the histology, right, is going to be this outer layer here, which is called serosa. The serosa is basically mesothelium, which is simple squamous epithelial tissue with a little bit of areolar connected tissue mixed in. But you have to remember, if you haven't watched our embryology videos on the GI tract, go watch those. Because if something has serosa, it's intraperitoneal, meaning that it has a mesentery. If it doesn't have serosa, it's retroperitoneal, meaning that it could be either primary or secondary retroperitoneal. But they don't have serosa, they don't have a mesentery, so they're anchored to the posterior abdominal wall by what's called adventitia. So remember that. For this case, I'm saying that it's serosa, but depending upon the organ, it could be adventitia. Alright? So that covers our basic histology here. Now what we've got to do is, is we have to talk about how this intrinsic nervous system submucosal and my enteric plexus operate in response to different types of stimuli. Okay, so let's say you're hungry, right? You just housed a pizza, alright? Nice pepperoni pizza with some stuffed crust, alright? Mmm, good, good, right? What happens? Two things can happen. Let's say that this food bolus, right, we're gonna assume it's a food bolus, it starts accumulating this digestive tract lumen. This is our lumen right here. right? And let's just for simplicity's sake, let's say this is the oral side and this is the ab-oral side. Also if you want it for simplicity's sake, the anal side. Right? So the doodle hole side, the mouth side. Simple as that. What happens is, as it comes into this lumen here, it can actually cause distension, stretch basically. So it can actually stretch the walls of this actual basically digestive wall, this alimentary wall here. As it stretches it, let's say it stretches it, as it stretches there's specific types of receptors located in this actual muscularis externa within the muscular layers. This is called stretch receptors. Simple right? So let's say that there's a food bolus and it's causing distension. So distension is just a fancy word for Stretch. Alright? As it distends this actual GI tract wall, it'll activate and stimulate this stretch receptor. What will happen as a response to this? If this stretch receptor is activated, it can do two things. One thing. You have these descending fibers. What does that mean that it's descending? It's going towards the aboral or anal side. So these are the descending fibers. This one is coming towards the oral side. So if it's coming towards the oral side, it's the ascending fibers. So these are the ascending fibers of the myenteric plexus. Now, here's what's very, very tricky for some people. The circular layer, when it contracts, it acts like a sphincter basically. It produces what's called a constriction ring behind the bolus and pushes the bolus forward. Alright? So remember, the circular layer constricts and forms a little constriction ring and pushes behind the bolus, propelling it forward. Here's what you gotta be careful of. The longitudinal layer is the really weird one. When it contracts, it actually opens up the lumen. front of it. We want the muscle right here, let's just say for simplicity's sake, these muscles right here to contract. Because we want to form a constriction ring here pushing it forward. We want these muscles to relax because if they're relaxing the lumen behind it isn't going to increase in size. We want to constrict it pushing it forward. So what's going to happen? This guy here, guess what's going to do? It's going to stimulate The ascending fibers, okay? It's going to stimulate the ascending fibers. When it stimulates the ascending fibers, look what these frickers do. They come over here and they give axons to this guy, the outer longitudinal layer. And then they give axons to the circular layer. What kind of chemicals do you think they're releasing here? Well, on this one, we're going to want it to release specific chemicals that are going to stimulate it. Well if you want to stimulate it, you need to release chemicals like acetylcholine and substance P. Okay? These two chemicals will stimulate this actual circular smooth muscle by increasing the cation influx and cause it to contract, pushing the balls forward. Alright? Back here, you're not going to want to stimulate the longitudinal muscle. You're going to want to inhibit the longitudinal muscle. You should inhibit it. So if you're going to inhibit the outer longitudinal layer, what kind of chemical substances would you want to be releasing to inhibit this muscle from contracting? Because again, you don't want to contract because if it contracts, remember it does that weird thing, it opens up the lumen behind the bolus. That's not going to help us propel it forward. So you want to inhibit it by releasing chemicals such as vasoactive intestinal peptide and nitric oxide. Sometimes they even say ATP. But what happens is this VIP and nitric oxide will act on these cells, basically causing potassium ions to leave the cell or causing the hyperpolarization of these cells. If you hyperpolarize them, they're not going to contract. So these will relax. So as a result, this will relax and this will contract. Now, what about these guys? What happens to these suckers? Here's where it gets even cooler, right? We want this side to push on the pizza, propelling it forward, right? The ultimate goal is to move this guy towards the doo-doo hole, right? That's the overall goal. So you want to squeeze behind it, but would you want this area to be squeezed and closed? No. You'd want to accept it. So you want this one to just open up and welcome it with open arms, right? So what would you want to do to this area? Now this is where these neurons come into play. So now, it's going to stimulate the descending neurons. So we stimulated the ascending, now we're going to stimulate the ascending. Now watch what happens here. We're going to come down here, let's say to about this area. Just suppose, right? About that area. These guys here, what are they going to do? Look what happens. They're going to give fibers that are going to go all the way over to this area, right? The circulus gluteus muscle downstream or in the ab-oral side of the pizza. Here, are you going to want to constrict this? No, because you're going to constrict here, constrict here, the balls isn't going to go anywhere. So, what do you need to do? You want this side to receptive or relax. What kind of things, chemicals should you be releasing here? You should be releasing vasoactive intestinal peptide and nitric oxide. This will relax it and by re-inhibiting this guy it's going to receptively open. Now same thing, bring this guy down here. Boom. With the longitudinal layer downstream on the aboral end of the pizza. What are you gonna want to do this guy? You're gonna want to stimulate him. If you stimulate him, what's it going to do? When you contract this muscle, it'll open up the lumen in front of the bolus, helping it to receptively relax and accept the food bolus. So it should be releasing chemicals such as acetylcholine and substance P. Woo! Alright. That is how the GI motility works for these guys. Okay? All right, it's getting hot in here guys. Getting excited for science. Okay, so now that we covered that, let's go over the next thing. So there's another receptor here, okay, and these stretch receptors, they can come and stimulate the submucosal plexus also. So we'll include that here, but the more powerful stimulator here for these guys is going to be some other structures. But realize the stretch receptors can give axons that can stimulate the submucosal plexus. And we'll talk about what these are for in a second, okay? Excuse me. Now, these next receptors here, these are called chemoreceptors. So this one right here is called a chemoreceptor. Now, you might be thinking, why the heck are there chemoreceptors out here? It depends upon certain chemicals. So let's say, for example, let's say that you eat this food, and this food gives off lots of fatty acids. Okay, so it has lots of fatty acids in it or it has lots of glucose in it or it has lots of Acidic residue, maybe you downed a Dr. Pepper right after that you get a lot of acidic residues out of that Maybe there's other things in there too. Maybe there's partially digested Peptides, okay, so there could be a whole bunch of different things here, but what is the whole purpose of this? Certain chemical substances can activate these chemoreceptors And as a result, when you stimulate these chemoreceptors, guess what you could do? These chemoreceptors can actually give connections over here to these submucosal plexus neurons here. If it stimulates, let's say that it stimulates this submucosal plexus here, right? So let's say that for whatever reason we respond to fatty acids. If we respond to this fatty chyme, which is what we're going to call it, which is basically the food paste, it's going to stimulate the submucosal plexus. Guess what this sucker could do? It could release certain chemicals that come over here and maybe stimulate some certain types of glands. Let's say that it stimulates this gland here, and these glands have little ducts, right? They have little ducts or tubes, basically, that carry whatever type of secretion it is towards the actual lumen. So let's say that it stimulates this duct and it actually increases the secretion of maybe some type of bicarbonate. rich secretion. Okay? Because let's say that whenever the substance is coming from the stomach into the duodenum, you want to have a lot of bicarbonate-rich secretions to neutralize the acidic substances. That's one situation. Another thing that you're going to want to have here, you know there's a lot of blood vessels in the vicinity here. So there's a lot of blood vessels. So let's say I put a blood vessel right here. Okay, so here's a blood vessel. And these blood vessels are important too because they can help with the absorption process. So let's say that I release certain chemicals that act on these blood vessels. I act on these blood vessels here and as I act on these blood vessels, I cause the blood vessels to dilate. So now as the blood vessels start dilating, I got a lot more blood flow coming into this area. So now what's the overall result? If I stimulate this, I can dilate vessels. And if I'm dilating these vessels, I can increase the blood flow. By increasing the blood flow through this area, I can increase the absorption of certain substances that are trying to cross from here into the actual circulation. So remember, two important things here. When the chemoreceptors are stimulated, they can activate the submucosal plexi, which can cause them to release substances to stimulate certain types of glands. If these glands are stimulated, guess what they can do? They can release certain types of secretions. Maybe they might be rich in bicarbonate. It could also dilate blood vessels within the mucosa to increase the absorption, right? By increasing the blood flow. Here's where it gets really cool though. You know, specific type of substances, I mention these for a specific reason. Let's say that you're having food that's really, really rich in fatty acids and a lot of acid, okay? So protons and fatty acids. If that's the case, you know what these can do? They can stimulate these chemoreceptors. The chemoreceptors can stimulate specific nerve plexi, right, the submucosal. Guess what these guys can do? Let's suppose it secretes it onto a specific type of cell, specific cell in the area. And these cells here are gonna be called S cells. I'm just gonna mention a few of these. Let's say it stimulates these S cells, these enteroendocrine cells. Guess what these suckers can release? They can release secretin. And you know what secretin is important for? Secretin has two big functions. One is it's going to tell the liver to make more bile. Okay? So it's going to stimulate the synthesis of bile. That's one thing. Okay? So it'll stimulate the liver, the hepatocytes to cause more bile production. What else? It'll go to the pancreas, specifically the acini, and tell the acinar cells Specifically actually the duct cells within the SNI. You have the ductal cells there. It causes them to release pancreatic juice, which is rich in bicarbonate. So bicarbonate-rich pancreatic juice. Okay, so that's an example there. So the whole purpose is why would I have the bile? Because the bile can help to emulsify fats. Why do I need this bicarbonate-rich pancreatic juice? To neutralize some of the acids within the intestines. So that's an example. Just to give you two more real quick. Let's say that you have the chyme here. It's really rich in partially digested proteins and fats. That could also stimulate these chemoreceptors. These chemoreceptors could stimulate specific submucosal plexi. These specific submucosal plexi might release chemicals that'll stimulate other cells. For example, if it's response to the partially digested proteins and fats, it can stimulate what's called eye cells. in Taro endocrine cells causing them to secrete a chemical called cholecystokinin. Cholecystokinin is another hormone. This sucker can do so much it's insane. He can tell for example he can cause gallbladder contractions so he can cause the gallbladder to contract and expel bile into the ductal system the biliary tree. He can also enhance secretions action on the liver so we say that he can potentiate He can potentiate secretin's action on liver. Okay, so CZK can also stimulate the pancreas. Before I write this stuff down here, let's get this out of the way. Let's put aboral, we know that it's down at this end, right? The doodle hole end. So aboral or anal end. So it can act on the pancreas. Now in the pancreas it stimulates the acinar cells, while the secretin stimulates the actual ductal cells. This one is going to cause them to make lots of enzymes, like proteases. We'll talk about these in another video, like trypsin, chymotrypsin, carboxypeptidase. It can also secrete pancreatic, lipases, and then it can make even amylase, right? So all these enzymes that are designed to be able to break down the proteins, the lipids, the carbohydrates. One other thing, it also goes to what's called the, it's called the hepatopancreatic sphincter, but another name for it is called the sphincter of Odie. And it basically, when it acts on this guy, it relaxes it. Which basically, simply here, here's the pancreas. There's a very simple diagram here. And then let's say here's the common bile duct. The common bile duct here fuses with the main pancreatic duct. And when it does, it opens up into the duodenum. Through what's called the hepatopancreatic ampulla. What the actual... What CCK does is it acts on a sphincter, a muscle right here, that's keeping that opening closed. He will come over here, act on that opening, relax it, and then allow for the bile and all the pancreatic juices to get released out here into the duodenum to start breaking down things. So he's pretty cool. So that's important for that guy. And just for the last one, let's say that there's another one that responds to glucose, high amounts of glucose. maybe even fats and proteins, but primarily glucose, can stimulate chemoreceptors, activate the submucosal nerve plexus. What can you do? Activate glands, dilate blood vessels to increase absorption. Or we could activate another type of cell. Let's say that it activates one more and we'll say these are the K cells. And the K cells release a chemical called glucose, let's actually make it a different color, glucose insulinotropic peptide. They also call it G.I.P. It's easier that way, right? But what's the overall effect of G.I.P.? Big one is he goes to the pancreas. And since his primary stimulus is glucose in the actual kind, he'll tell the pancreas to make insulin. And insulin will actually help to get the glucose from the blood and put it into our cells. So that should make sense, right? And he can also inhibit gastric motility. A lot of these guys... C-Cretin, CCK, GIP, another one called VIP, they all basically inhibit gastric emptying. They're involved in what's called the enterogastric reflex. We'll talk about that in the GI. Okay, but the basic thing is that I want you... You guys dig it out of the intrinsic system as it can work autonomously. How? It can respond to stretch. It can respond to chemical sensations. Out of that what's the overall effect? If there's a chemical sensation it can cause glandular secretions. It can dilate the blood vessels to increase dilate the blood vessels to increase absorption. It can stimulate certain types of enteroendocrine cells like S cells, I cells, K cells which can have all these plethora of effects. Right? Or If there's chemoreceptor activation or stretch receptor activation, what can it do? The stretch receptors can activate the myenteric plexus. To do what? To enhance the gastric motility. How? Cause the circular layer on the oral side to contract, producing a constriction ring. Relax the longitudinal layer on the oral side so that the lumen doesn't open. Do what to the circular layer on the aboral side? Relax it so that it doesn't have a constriction ring and it opens up and accepts it. Contract the longitudinal layer on the aboral side so that it opens up the lumen to receptively accept it. So beautiful things that our enteric nervous system can do autonomously on its own. Now, how can the actual sympathetic and the parasympathetic nervous system modulate this activity? Okay, so now that we understand that, the intrinsic plexus, again, we have to talk about how the extrinsic, the sympathetic and the parasympathetic can modulate this activity. Okay, so... When we talk here, let's talk sympathetic first. And honestly, to keep it as simple as possible, remember that anything with the GI tract, the sympathetic is going to try to inhibit it. So any motility, any secretions, any blood flow, any absorption, it's going to oppose that. Simple as that. But if you remember, we're just taking parts of it, but the sympathetic nervous system, right? came from, let's just say here, T5 all the way down to L2. And if you want to be picky, some books say L3, right? And this was called the thoracolumbar outflow. But to even be more simple than that, again, I just want you guys to get the overall big picture of this thing. The sympathetic nervous system, what is it going to do here? Take anything that it would, you think here, motility, for example. Motility, what is it going to do? Decrease it. Secretions, what is it going to do? Decrease it. Absorption, what is it going to do? Decrease it. Okay, so the basic things here, motility, secretions, absorption, and like if you even want to put it here, blood flow. Right, the splenctic circulation, we talked about that before. It's going to decrease that blood flow by constricting the blood vessels to that area. Okay, so now how this happens is You remember, we're not going to mention all the ganglion, we've already done a video on this, but it can go to prevertebral ganglion. And these prevertebral ganglion could be like celiac, or superior mesenteric, or inferior mesenteric, superior hypogastric, inferior hypogastric, all these different types. And they can get different types of splenctic nerves. These guys are going to go where? They can go to the submucosal nerve plexus, the postganglionic fibers. Or they can go to the myenteric plexus. the ascending or the descending. Now, what will it do here? It'll inhibit it. It'll release norepinephrine, inhibiting these guys. And by inhibiting them, it'll inhibit the blood flow. It'll inhibit the secretions. It'll inhibit all these different hormonal substances here. It'll inhibit the actual motility in these areas. So it should make sense. One thing that I do want to mention, though, because this is the one thing I got to be careful of. For all this stuff here, there is one little exception. It will constrict sphincters. So do remember that. I do want you to remember that this is one of the weird exceptions where it can actually constrict certain sphincters. For example, the pyloric sphincter, the internal anal sphincter. There is certain areas, right? Okay, and what is this ganglia here called again? Just for the heck of it, this is a prevertebral ganglion. Okay, simple as that. That's it. Now, if you remember...... The parasympathetic for most of the GI tract is going to be vagus. Vagus, same thing, but here's what's really interesting. Here's the preganglionic fibers in the dorsal nucleus of vagus, which is in the medulla. These fibers, they can come and synapse directly on the submucosal nerve plexus or directly onto the myenteric plexus. What does that mean? That means that the submucosal plexus and the myenteric plexus are the actual postganglionic cell bodies. Means that this is the intramural ganglion. So technically right here, that is my intramural ganglion. Isn't that cool? I think it's cool. So this is our intramural ganglion because technically these two plexi are technically the cell bodies of the postganglionic motor neurons. So simple thing with the parasympathetic. It's the exact opposite. So let's come up here. Is that the parasympathetic nervous system here. Remember, what's the overall effects? Opposite of what sympathetic was. So it's going to increase the motility. It's going to increase the secretions. It's going to increase the absorption process. And what else? If you think about it, go opposite. Remember, opposite over here with the sphincters. It's going to relax. the sphincters. Okay, so just remember that I want us to be completely kind of clear here is that this one increases motility, secretions, absorption, and relaxes the sphincters. This guy here is going to decrease motility, secretions, absorptions, and constrict the splanchnic circulation and constrict the sphincters. So this is trying to put the, this is the brakes of the GI tract and this is the gas. Okay, no pun intended there. All right? So, now that we understand that, we get the basic thing here. But now I have one last thing I have to say, and I promise we're done. Remember how we said there's short reflexes and long reflexes? Short reflexes were those ones that I was talking about here, where the chemoreceptor or the stretch receptor activate the submucosal or the myenteric plexus and then produce an overall result. Because remember, with a reflex, it's receptor, integration center, and then you have an effector, basically, right? So you have like an afferent pathway, integration center, efferent pathway. That's the overall effect. So the receptor is the chemo or the stretch. The integration center is the myenteric or the submucosal plexus. And the effect is basically dilating, secretions, motility, all that stuff. But now we have to have a long reflex. So let's say here that I have some type of chemoreceptor or stretch receptor, whatever, doesn't matter. I just want you to get the point here that this receptor here can have an afferent fibers here. that it can come all the way directly to the vagus nerve, the nucleus there. You know what these fibers are? This is actually the vagus nerve. These are the GVA fibers of the vagus nerve. Because remember, the vagus nerve has afferent and efferent fibers, 70% of it, remember. It can come here, either stimulate or maybe inhibit the dorsal nucleus of vagus. But if it does that, it can come out and stimulate these submucosal or myenteric plexus. When it does this, Afferent vagal, efferent vagal, you know what they call that? They call that the vagal reflex where the afferent fibers of the vagus nerve whether it be stretch or chemoreceptors send impulses to the dorsal nucleus of vagus, activate the efferent fibers of the vagus nerve to go out and either innervate the submucosa or the myotaric. Last thing, same thing here. Let's say that these sensory neurons, chemoreceptors, stretch receptors, whatever. This is a little bit weird. These guys, instead of them going into the spinal cord, they can come right here, right to that prevertebral ganglion. And let's say that there's too much acid getting pushed from the stomach into the duodenum, or there's a lot of distension in the duodenum because the stomach's trying to empty the contents into the duodenum. We don't want that to happen really fast. So, If that happens, let's say that there is a lot of stretch, a lot of chemical substances, it can activate the stretch receptors or the chemoreceptors to send these signals to this prevertebral ganglion. Maybe it stimulates it. What does it do? It goes and inhibits the secretions. It inhibits the continual GI motility. Maybe it even constricts the pyloric sphincter. What do we call that? We call that the enterogastric reflex. That's the one where Whenever a lot of chyme is being dumped from the stomach into the duodenum, which is rich in protons, rich in a lot of different types of substances in the chyme, and it's stretching the duodenum, we don't want to unload all that stuff into the duodenum right away. So what does it do? It activates these fibers, which can go and stimulate the sympathetic nervous system at the prevertebral ganglion. They call these intestinofugal fibers, right? And if it does that, it can actually cause decrease in secretion, decrease in the absorption, decrease in the motility. but constrict the pyloric sphincter and prevent that kind from being released. Okay? And then what if it actually comes down here to the sacral? That's another exception here. We're not going to go all into depth on that, but again, it could actually come into the spinal cord, and maybe it comes here to S2, S3, S4. And if it does that, you know that these are the pelvic splenctic nerves, and they can come out here also and innervate the myenteric plexus, or they can innervate the submucosal plexus. And again produce the same overall response. Alright Ningeners, so I hope all this made sense. I really really do. I hope you guys enjoyed it. If you guys did like the video, please hit the like button. Comment down in the comment section. Please subscribe. Also check out our Facebook, Instagram, and Patreon account. If you guys did have any opportunity to be able to donate, even a dollar can make all the difference in us being able to make the most high quality videos possible for your enjoyment. Alright Ningeners, as always, until next time.

That's unbelievable when you think about it. So it technically is like a little gut brain. Now the enteric nervous system is super important and what we're going to do is we're going to talk about the myenteric nerve plexus and the submucosal nerve plexus and how they regulate motility and secretions, okay, intrinsically.

And then after we do that, then we're going to talk about the extrinsic effect, in other words, the sympathetic nervous system, the parasympathetic nervous system, and how that can play a role in altering the intrinsic activity. So we'll talk about short reflex arcs and long reflex arcs. Alright, so let's go ahead and get started.

So first things first, when we're looking at this, what we're doing with this part here, this diagram, is if we come over here to this little stomach and duodenum over here, all I'm doing is, is I'm taking a cut, I'm taking a section right here, onto the actual duodenum. So imagine I'm doing this, I'm cutting this, and I'm looking at the duodenum with the lumen. Going from the lumen all the way out to the serosa. If we're talking about the first part of the duodenum, technically that's serosa.

The second, third, and fourth parts have adventitia. But again, for simplicity's sake, let's assume that we're talking about the first part. So all I'm doing is I'm zooming in on the mucosa all the way out to the outer serosa layer. Okay?

So that's what you see here. So now let's get a good idea of the histology. We're not going to talk about this in great detail. We're going to keep it rather simplistic. But again, first layer here.

There's four basic layers of the alimentary canal. So first one is your mucosa, okay? Now technically the mucosa is actually made up of three layers, okay?

So what are those three layers? Technically it's made up of a epithelial tissue, okay, so an epithelium. Another one is called a lamina propria, which is basically areola connective tissue.

And the last one is called a muscularis mucosa. Now, the epithelium is different from organ to organ. For example, just simplicity-wise, the esophagus, the stratified squamous epithelial tissue.

But the stomach, the duodenum, and pretty much all the intestines are going to be simple columnar. If we take, for example, the trachea, the epithelial tissue there will be pseudostratified ciliated columnar epithelial tissue. It depends from organ to organ.

But in general, these are the three parts of mucosa. epithelium, lamina propria, muscularis mucosa. Then, after that, you have a big space here.

Okay, this whole space here. So let's assume that the mucosa ends right here, starts right here, right? So the end part of the mucosa is right here.

It goes all the way up to this muscle layer here. So from here to here. That's the next one. This layer here is going to be a specific component. We call this the sub mucosa.

The submucosa is actually kind of a mixture of areolar connective tissue and a little bit of dense connective tissue. But in the submucosa you have lots of glands in this area and you have this nerve plexus. This really really important nerve plexus.

They call this bad boy the submucosal plexus. So simple right? So simple one. Another name for it if you don't want to remember the submucosal plexus.

There is another name, they call this the Meissner's plexus. Okay, so you have the Meissner's plexus. So you have the submucosal plexus and the Meissner's plexus.

Now, that's the submucosa. Again, it's some areola connective tissue and it's also going to be some dense fibrous connective tissue. And what else will you have out here?

You could have some glands. So there could be certain types of glands in this area right here. And they can have different types of functions. Alright, next thing. If we got to the next part here, so we have mucosa, submucosa, then we have these two parts out here.

So if you look here, from this circular structure here, all the way down here to this kind of like a longitudinal structure here, from here to here. This part here is called the muscularis externa. And generally, for most organs, It has an inner circular layer and over here it has a outer longitudinal layer.

Okay, now there is an exception the stomach. The stomach actually does have a inner oblique, middle circular, and an outer longitudinal. But for the sake of its simplicity, we're going to just keep it to inner and outer.

Okay, but do remember that the stomach does have a third one, inner oblique, middle circular, outer longitudinal. Okay, so this is the inner circular layer. This is the outer longitudinal layer. But these two together make up the muscularis externa.

Now, in the muscularis externa, there is a nerve plexus of ascending and descending. fibers. This structure here is called the myenteric plexus. Another name for this plexus is called the Arbach plexus.

Okay, just so that you hear them in different types, right? So you have two different types of plexes here. One is the submucosal plexus, located within the submucosa, also called the Miesner's plexus.

And you have the myenteric plexus. And the myenteric plexus is also called the Arbach plexus, and it's located within the muscularis externa, but specifically in between the inner circular and the outer longitudinal. And it consists of ascending and descending fibers.

Okay. Last part here for the histology, right, is going to be this outer layer here, which is called serosa. The serosa is basically mesothelium, which is simple squamous epithelial tissue with a little bit of areolar connected tissue mixed in.

But you have to remember, if you haven't watched our embryology videos on the GI tract, go watch those. Because if something has serosa, it's intraperitoneal, meaning that it has a mesentery. If it doesn't have serosa, it's retroperitoneal, meaning that it could be either primary or secondary retroperitoneal. But they don't have serosa, they don't have a mesentery, so they're anchored to the posterior abdominal wall by what's called adventitia.

So remember that. For this case, I'm saying that it's serosa, but depending upon the organ, it could be adventitia. Alright? So that covers our basic histology here. Now what we've got to do is, is we have to talk about how this intrinsic nervous system submucosal and my enteric plexus operate in response to different types of stimuli.

Okay, so let's say you're hungry, right? You just housed a pizza, alright? Nice pepperoni pizza with some stuffed crust, alright? Mmm, good, good, right?

What happens? Two things can happen. Let's say that this food bolus, right, we're gonna assume it's a food bolus, it starts accumulating this digestive tract lumen. This is our lumen right here.

right? And let's just for simplicity's sake, let's say this is the oral side and this is the ab-oral side. Also if you want it for simplicity's sake, the anal side.

Right? So the doodle hole side, the mouth side. Simple as that. What happens is, as it comes into this lumen here, it can actually cause distension, stretch basically. So it can actually stretch the walls of this actual basically digestive wall, this alimentary wall here.

As it stretches it, let's say it stretches it, as it stretches there's specific types of receptors located in this actual muscularis externa within the muscular layers. This is called stretch receptors. Simple right?

So let's say that there's a food bolus and it's causing distension. So distension is just a fancy word for Stretch. Alright? As it distends this actual GI tract wall, it'll activate and stimulate this stretch receptor.

What will happen as a response to this? If this stretch receptor is activated, it can do two things. One thing.

You have these descending fibers. What does that mean that it's descending? It's going towards the aboral or anal side.

So these are the descending fibers. This one is coming towards the oral side. So if it's coming towards the oral side, it's the ascending fibers. So these are the ascending fibers of the myenteric plexus. Now, here's what's very, very tricky for some people.

The circular layer, when it contracts, it acts like a sphincter basically. It produces what's called a constriction ring behind the bolus and pushes the bolus forward. Alright?

So remember, the circular layer constricts and forms a little constriction ring and pushes behind the bolus, propelling it forward. Here's what you gotta be careful of. The longitudinal layer is the really weird one. When it contracts, it actually opens up the lumen.

front of it. We want the muscle right here, let's just say for simplicity's sake, these muscles right here to contract. Because we want to form a constriction ring here pushing it forward. We want these muscles to relax because if they're relaxing the lumen behind it isn't going to increase in size.

We want to constrict it pushing it forward. So what's going to happen? This guy here, guess what's going to do?

It's going to stimulate The ascending fibers, okay? It's going to stimulate the ascending fibers. When it stimulates the ascending fibers, look what these frickers do. They come over here and they give axons to this guy, the outer longitudinal layer. And then they give axons to the circular layer.

What kind of chemicals do you think they're releasing here? Well, on this one, we're going to want it to release specific chemicals that are going to stimulate it. Well if you want to stimulate it, you need to release chemicals like acetylcholine and substance P. Okay? These two chemicals will stimulate this actual circular smooth muscle by increasing the cation influx and cause it to contract, pushing the balls forward.

Alright? Back here, you're not going to want to stimulate the longitudinal muscle. You're going to want to inhibit the longitudinal muscle.

You should inhibit it. So if you're going to inhibit the outer longitudinal layer, what kind of chemical substances would you want to be releasing to inhibit this muscle from contracting? Because again, you don't want to contract because if it contracts, remember it does that weird thing, it opens up the lumen behind the bolus. That's not going to help us propel it forward.

So you want to inhibit it by releasing chemicals such as vasoactive intestinal peptide and nitric oxide. Sometimes they even say ATP. But what happens is this VIP and nitric oxide will act on these cells, basically causing potassium ions to leave the cell or causing the hyperpolarization of these cells.

If you hyperpolarize them, they're not going to contract. So these will relax. So as a result, this will relax and this will contract. Now, what about these guys?

What happens to these suckers? Here's where it gets even cooler, right? We want this side to push on the pizza, propelling it forward, right?

The ultimate goal is to move this guy towards the doo-doo hole, right? That's the overall goal. So you want to squeeze behind it, but would you want this area to be squeezed and closed? No.

You'd want to accept it. So you want this one to just open up and welcome it with open arms, right? So what would you want to do to this area?

Now this is where these neurons come into play. So now, it's going to stimulate the descending neurons. So we stimulated the ascending, now we're going to stimulate the ascending.

Now watch what happens here. We're going to come down here, let's say to about this area. Just suppose, right?

About that area. These guys here, what are they going to do? Look what happens.

They're going to give fibers that are going to go all the way over to this area, right? The circulus gluteus muscle downstream or in the ab-oral side of the pizza. Here, are you going to want to constrict this? No, because you're going to constrict here, constrict here, the balls isn't going to go anywhere.

So, what do you need to do? You want this side to receptive or relax. What kind of things, chemicals should you be releasing here?

You should be releasing vasoactive intestinal peptide and nitric oxide. This will relax it and by re-inhibiting this guy it's going to receptively open. Now same thing, bring this guy down here.

Boom. With the longitudinal layer downstream on the aboral end of the pizza. What are you gonna want to do this guy? You're gonna want to stimulate him.

If you stimulate him, what's it going to do? When you contract this muscle, it'll open up the lumen in front of the bolus, helping it to receptively relax and accept the food bolus. So it should be releasing chemicals such as acetylcholine and substance P. Woo!

Alright. That is how the GI motility works for these guys. Okay? All right, it's getting hot in here guys.

Getting excited for science. Okay, so now that we covered that, let's go over the next thing. So there's another receptor here, okay, and these stretch receptors, they can come and stimulate the submucosal plexus also. So we'll include that here, but the more powerful stimulator here for these guys is going to be some other structures. But realize the stretch receptors can give axons that can stimulate the submucosal plexus.

And we'll talk about what these are for in a second, okay? Excuse me. Now, these next receptors here, these are called chemoreceptors. So this one right here is called a chemoreceptor.

Now, you might be thinking, why the heck are there chemoreceptors out here? It depends upon certain chemicals. So let's say, for example, let's say that you eat this food, and this food gives off lots of fatty acids.

Okay, so it has lots of fatty acids in it or it has lots of glucose in it or it has lots of Acidic residue, maybe you downed a Dr. Pepper right after that you get a lot of acidic residues out of that Maybe there's other things in there too. Maybe there's partially digested Peptides, okay, so there could be a whole bunch of different things here, but what is the whole purpose of this? Certain chemical substances can activate these chemoreceptors And as a result, when you stimulate these chemoreceptors, guess what you could do? These chemoreceptors can actually give connections over here to these submucosal plexus neurons here.

If it stimulates, let's say that it stimulates this submucosal plexus here, right? So let's say that for whatever reason we respond to fatty acids. If we respond to this fatty chyme, which is what we're going to call it, which is basically the food paste, it's going to stimulate the submucosal plexus. Guess what this sucker could do? It could release certain chemicals that come over here and maybe stimulate some certain types of glands.

Let's say that it stimulates this gland here, and these glands have little ducts, right? They have little ducts or tubes, basically, that carry whatever type of secretion it is towards the actual lumen. So let's say that it stimulates this duct and it actually increases the secretion of maybe some type of bicarbonate. rich secretion. Okay?

Because let's say that whenever the substance is coming from the stomach into the duodenum, you want to have a lot of bicarbonate-rich secretions to neutralize the acidic substances. That's one situation. Another thing that you're going to want to have here, you know there's a lot of blood vessels in the vicinity here. So there's a lot of blood vessels. So let's say I put a blood vessel right here.

Okay, so here's a blood vessel. And these blood vessels are important too because they can help with the absorption process. So let's say that I release certain chemicals that act on these blood vessels.

I act on these blood vessels here and as I act on these blood vessels, I cause the blood vessels to dilate. So now as the blood vessels start dilating, I got a lot more blood flow coming into this area. So now what's the overall result? If I stimulate this, I can dilate vessels.

And if I'm dilating these vessels, I can increase the blood flow. By increasing the blood flow through this area, I can increase the absorption of certain substances that are trying to cross from here into the actual circulation. So remember, two important things here.

When the chemoreceptors are stimulated, they can activate the submucosal plexi, which can cause them to release substances to stimulate certain types of glands. If these glands are stimulated, guess what they can do? They can release certain types of secretions. Maybe they might be rich in bicarbonate.

It could also dilate blood vessels within the mucosa to increase the absorption, right? By increasing the blood flow. Here's where it gets really cool though.

You know, specific type of substances, I mention these for a specific reason. Let's say that you're having food that's really, really rich in fatty acids and a lot of acid, okay? So protons and fatty acids.

If that's the case, you know what these can do? They can stimulate these chemoreceptors. The chemoreceptors can stimulate specific nerve plexi, right, the submucosal. Guess what these guys can do?

Let's suppose it secretes it onto a specific type of cell, specific cell in the area. And these cells here are gonna be called S cells. I'm just gonna mention a few of these. Let's say it stimulates these S cells, these enteroendocrine cells.

Guess what these suckers can release? They can release secretin. And you know what secretin is important for?

Secretin has two big functions. One is it's going to tell the liver to make more bile. Okay? So it's going to stimulate the synthesis of bile. That's one thing.

Okay? So it'll stimulate the liver, the hepatocytes to cause more bile production. What else?

It'll go to the pancreas, specifically the acini, and tell the acinar cells Specifically actually the duct cells within the SNI. You have the ductal cells there. It causes them to release pancreatic juice, which is rich in bicarbonate. So bicarbonate-rich pancreatic juice.

Okay, so that's an example there. So the whole purpose is why would I have the bile? Because the bile can help to emulsify fats. Why do I need this bicarbonate-rich pancreatic juice? To neutralize some of the acids within the intestines.

So that's an example. Just to give you two more real quick. Let's say that you have the chyme here.

It's really rich in partially digested proteins and fats. That could also stimulate these chemoreceptors. These chemoreceptors could stimulate specific submucosal plexi.

These specific submucosal plexi might release chemicals that'll stimulate other cells. For example, if it's response to the partially digested proteins and fats, it can stimulate what's called eye cells. in Taro endocrine cells causing them to secrete a chemical called cholecystokinin. Cholecystokinin is another hormone. This sucker can do so much it's insane.

He can tell for example he can cause gallbladder contractions so he can cause the gallbladder to contract and expel bile into the ductal system the biliary tree. He can also enhance secretions action on the liver so we say that he can potentiate He can potentiate secretin's action on liver. Okay, so CZK can also stimulate the pancreas.

Before I write this stuff down here, let's get this out of the way. Let's put aboral, we know that it's down at this end, right? The doodle hole end. So aboral or anal end. So it can act on the pancreas.

Now in the pancreas it stimulates the acinar cells, while the secretin stimulates the actual ductal cells. This one is going to cause them to make lots of enzymes, like proteases. We'll talk about these in another video, like trypsin, chymotrypsin, carboxypeptidase.

It can also secrete pancreatic, lipases, and then it can make even amylase, right? So all these enzymes that are designed to be able to break down the proteins, the lipids, the carbohydrates. One other thing, it also goes to what's called the, it's called the hepatopancreatic sphincter, but another name for it is called the sphincter of Odie. And it basically, when it acts on this guy, it relaxes it. Which basically, simply here, here's the pancreas.

There's a very simple diagram here. And then let's say here's the common bile duct. The common bile duct here fuses with the main pancreatic duct.

And when it does, it opens up into the duodenum. Through what's called the hepatopancreatic ampulla. What the actual...

What CCK does is it acts on a sphincter, a muscle right here, that's keeping that opening closed. He will come over here, act on that opening, relax it, and then allow for the bile and all the pancreatic juices to get released out here into the duodenum to start breaking down things. So he's pretty cool. So that's important for that guy.

And just for the last one, let's say that there's another one that responds to glucose, high amounts of glucose. maybe even fats and proteins, but primarily glucose, can stimulate chemoreceptors, activate the submucosal nerve plexus. What can you do? Activate glands, dilate blood vessels to increase absorption.

Or we could activate another type of cell. Let's say that it activates one more and we'll say these are the K cells. And the K cells release a chemical called glucose, let's actually make it a different color, glucose insulinotropic peptide.

They also call it G.I.P. It's easier that way, right? But what's the overall effect of G.I.P.? Big one is he goes to the pancreas.

And since his primary stimulus is glucose in the actual kind, he'll tell the pancreas to make insulin. And insulin will actually help to get the glucose from the blood and put it into our cells. So that should make sense, right?

And he can also inhibit gastric motility. A lot of these guys... C-Cretin, CCK, GIP, another one called VIP, they all basically inhibit gastric emptying. They're involved in what's called the enterogastric reflex.

We'll talk about that in the GI. Okay, but the basic thing is that I want you... You guys dig it out of the intrinsic system as it can work autonomously.

How? It can respond to stretch. It can respond to chemical sensations. Out of that what's the overall effect?

If there's a chemical sensation it can cause glandular secretions. It can dilate the blood vessels to increase dilate the blood vessels to increase absorption. It can stimulate certain types of enteroendocrine cells like S cells, I cells, K cells which can have all these plethora of effects.

Right? Or If there's chemoreceptor activation or stretch receptor activation, what can it do? The stretch receptors can activate the myenteric plexus. To do what? To enhance the gastric motility.

How? Cause the circular layer on the oral side to contract, producing a constriction ring. Relax the longitudinal layer on the oral side so that the lumen doesn't open. Do what to the circular layer on the aboral side? Relax it so that it doesn't have a constriction ring and it opens up and accepts it.

Contract the longitudinal layer on the aboral side so that it opens up the lumen to receptively accept it. So beautiful things that our enteric nervous system can do autonomously on its own. Now, how can the actual sympathetic and the parasympathetic nervous system modulate this activity? Okay, so now that we understand that, the intrinsic plexus, again, we have to talk about how the extrinsic, the sympathetic and the parasympathetic can modulate this activity. Okay, so...

When we talk here, let's talk sympathetic first. And honestly, to keep it as simple as possible, remember that anything with the GI tract, the sympathetic is going to try to inhibit it. So any motility, any secretions, any blood flow, any absorption, it's going to oppose that.

Simple as that. But if you remember, we're just taking parts of it, but the sympathetic nervous system, right? came from, let's just say here, T5 all the way down to L2. And if you want to be picky, some books say L3, right? And this was called the thoracolumbar outflow.

But to even be more simple than that, again, I just want you guys to get the overall big picture of this thing. The sympathetic nervous system, what is it going to do here? Take anything that it would, you think here, motility, for example.

Motility, what is it going to do? Decrease it. Secretions, what is it going to do?

Decrease it. Absorption, what is it going to do? Decrease it. Okay, so the basic things here, motility, secretions, absorption, and like if you even want to put it here, blood flow.

Right, the splenctic circulation, we talked about that before. It's going to decrease that blood flow by constricting the blood vessels to that area. Okay, so now how this happens is You remember, we're not going to mention all the ganglion, we've already done a video on this, but it can go to prevertebral ganglion. And these prevertebral ganglion could be like celiac, or superior mesenteric, or inferior mesenteric, superior hypogastric, inferior hypogastric, all these different types. And they can get different types of splenctic nerves.

These guys are going to go where? They can go to the submucosal nerve plexus, the postganglionic fibers. Or they can go to the myenteric plexus. the ascending or the descending.

Now, what will it do here? It'll inhibit it. It'll release norepinephrine, inhibiting these guys.

And by inhibiting them, it'll inhibit the blood flow. It'll inhibit the secretions. It'll inhibit all these different hormonal substances here.

It'll inhibit the actual motility in these areas. So it should make sense. One thing that I do want to mention, though, because this is the one thing I got to be careful of.

For all this stuff here, there is one little exception. It will constrict sphincters. So do remember that.

I do want you to remember that this is one of the weird exceptions where it can actually constrict certain sphincters. For example, the pyloric sphincter, the internal anal sphincter. There is certain areas, right?

Okay, and what is this ganglia here called again? Just for the heck of it, this is a prevertebral ganglion. Okay, simple as that. That's it.

Now, if you remember...... The parasympathetic for most of the GI tract is going to be vagus. Vagus, same thing, but here's what's really interesting. Here's the preganglionic fibers in the dorsal nucleus of vagus, which is in the medulla. These fibers, they can come and synapse directly on the submucosal nerve plexus or directly onto the myenteric plexus.

What does that mean? That means that the submucosal plexus and the myenteric plexus are the actual postganglionic cell bodies. Means that this is the intramural ganglion. So technically right here, that is my intramural ganglion.

Isn't that cool? I think it's cool. So this is our intramural ganglion because technically these two plexi are technically the cell bodies of the postganglionic motor neurons. So simple thing with the parasympathetic. It's the exact opposite.

So let's come up here. Is that the parasympathetic nervous system here. Remember, what's the overall effects?

Opposite of what sympathetic was. So it's going to increase the motility. It's going to increase the secretions.

It's going to increase the absorption process. And what else? If you think about it, go opposite. Remember, opposite over here with the sphincters.

It's going to relax. the sphincters. Okay, so just remember that I want us to be completely kind of clear here is that this one increases motility, secretions, absorption, and relaxes the sphincters. This guy here is going to decrease motility, secretions, absorptions, and constrict the splanchnic circulation and constrict the sphincters.

So this is trying to put the, this is the brakes of the GI tract and this is the gas. Okay, no pun intended there. All right? So, now that we understand that, we get the basic thing here. But now I have one last thing I have to say, and I promise we're done.

Remember how we said there's short reflexes and long reflexes? Short reflexes were those ones that I was talking about here, where the chemoreceptor or the stretch receptor activate the submucosal or the myenteric plexus and then produce an overall result. Because remember, with a reflex, it's receptor, integration center, and then you have an effector, basically, right? So you have like an afferent pathway, integration center, efferent pathway.

That's the overall effect. So the receptor is the chemo or the stretch. The integration center is the myenteric or the submucosal plexus.

And the effect is basically dilating, secretions, motility, all that stuff. But now we have to have a long reflex. So let's say here that I have some type of chemoreceptor or stretch receptor, whatever, doesn't matter.

I just want you to get the point here that this receptor here can have an afferent fibers here. that it can come all the way directly to the vagus nerve, the nucleus there. You know what these fibers are? This is actually the vagus nerve.

These are the GVA fibers of the vagus nerve. Because remember, the vagus nerve has afferent and efferent fibers, 70% of it, remember. It can come here, either stimulate or maybe inhibit the dorsal nucleus of vagus.

But if it does that, it can come out and stimulate these submucosal or myenteric plexus. When it does this, Afferent vagal, efferent vagal, you know what they call that? They call that the vagal reflex where the afferent fibers of the vagus nerve whether it be stretch or chemoreceptors send impulses to the dorsal nucleus of vagus, activate the efferent fibers of the vagus nerve to go out and either innervate the submucosa or the myotaric. Last thing, same thing here.

Let's say that these sensory neurons, chemoreceptors, stretch receptors, whatever. This is a little bit weird. These guys, instead of them going into the spinal cord, they can come right here, right to that prevertebral ganglion.

And let's say that there's too much acid getting pushed from the stomach into the duodenum, or there's a lot of distension in the duodenum because the stomach's trying to empty the contents into the duodenum. We don't want that to happen really fast. So, If that happens, let's say that there is a lot of stretch, a lot of chemical substances, it can activate the stretch receptors or the chemoreceptors to send these signals to this prevertebral ganglion.

Maybe it stimulates it. What does it do? It goes and inhibits the secretions.

It inhibits the continual GI motility. Maybe it even constricts the pyloric sphincter. What do we call that? We call that the enterogastric reflex.

That's the one where Whenever a lot of chyme is being dumped from the stomach into the duodenum, which is rich in protons, rich in a lot of different types of substances in the chyme, and it's stretching the duodenum, we don't want to unload all that stuff into the duodenum right away. So what does it do? It activates these fibers, which can go and stimulate the sympathetic nervous system at the prevertebral ganglion. They call these intestinofugal fibers, right?

And if it does that, it can actually cause decrease in secretion, decrease in the absorption, decrease in the motility. but constrict the pyloric sphincter and prevent that kind from being released. Okay?

And then what if it actually comes down here to the sacral? That's another exception here. We're not going to go all into depth on that, but again, it could actually come into the spinal cord, and maybe it comes here to S2, S3, S4. And if it does that, you know that these are the pelvic splenctic nerves, and they can come out here also and innervate the myenteric plexus, or they can innervate the submucosal plexus.

And again produce the same overall response. Alright Ningeners, so I hope all this made sense. I really really do.

I hope you guys enjoyed it. If you guys did like the video, please hit the like button. Comment down in the comment section. Please subscribe. Also check out our Facebook, Instagram, and Patreon account.

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Transcript for:Understanding the Enteric Nervous System

Transcript for:
Understanding the Enteric Nervous System