Neurology | Enteric Nervous System

I ninja nerds in this video we're going to talk about the enteric nervous system now if you guys watch our video on the introduction to the autonomic nervous system that's great because remember some people they don't need to 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 it's a gut brain it's 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 gonna do is we're gonna talk about the my enteric nervous and the submucosa 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 all right so let's go 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 on to 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 on serosa the second third and fourth parts have adventitia but again for simplicity 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 gonna talk about this in great detail we're gonna 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 area all the connective tissue and the last one is called a muscularis mucosa now the epithelium is different from organ dorgon's for example just simplicity wise the esophagus a stratified squamous epithelial tissue but the stomach the duodenum is pretty much all the intestines are gonna be simple columnar if we take for example the trachea the epithelial tissue there will be pseudo stratified 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 sabah new cosas 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 important nerve plexus they call this bad boy the submucosal plexus so simple right so simple one another name for if you don't want to remember the submucosal plexus there is another name they call this the Me's nurse plexus okay so you have the Me's nurse plexus so you have the submucosal plexus and the Me's nurse plexus now that's the submucosa again some areolar connective tissue and it's also gonna 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 all right next thing if we go out to the next party or 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 from 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 in an outer longitudinal but for the sake of its simplicity we're gonna just keep it to inner and outer okay but do remember that the stomach does have a third one inner oblique middle circular and 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 my enteric plexus another name for this plexus is called the arbok plexus okay just so that you have you've 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 meteor's plexus and you have the my enteric plexus and the my enteric plexus is also called the arbok plexus and it's located within the muscularis externa but specifically in between the inner circular and the outer longitudinal and this consists ascending and descending fibers okay last part here for the histology right is gonna 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 connective 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 its intraperitoneal meaning that it has a mesentery if it doesn't have serosa its 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 post here 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 all right so that covers our basic histology here now what we got to do is is we have to talk about how this intrinsic nervous system sub mucosal and my enteric plexus operate in response to different types of stimuli okay so let's say you're hungry right you just how is the pizza alright nice pepperoni pizza with some stuffed crust all right good good right what happens two things can happen let's say that this food bolus right we're going to assume it's a food balls 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 sake the anal side all right so the doodle whole 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 digestible this alimentary wall here as it stretches it let's say it stretches it as it stretches there 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 distention so distension is just a fancy word for stretch all right as it descends this actual GI tract wall it'll activate and stimulate this stretch receptor what will happen is 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 is going towards the AB oral 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 my enteric 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 all right so remember and the circular layer constricts and forms a little constriction ring and pushes behind the bowl is propelling it forward here's what you gotta be careful of a longitudinal layer is the really weird one when it contracts it actually opens up the lumen in front of it we want the muscle right here let's just say for simplicity 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 gonna happen this guy here I guess what's gonna do it's gonna stimulate the ascending fibers okay it's gonna stimulate the ascending fibers when it stimulates the sending fibers look what these Fricker's 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 gonna 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 gonna want to inhibit the longitudinal muscle you should inhibit it so if you're going to inhibit the avalancha - no 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 room or does that weird thing it opens up the lumen behind the bowls that's not gonna help us propel it forward so you want to inhibit it we're releasing chemicals such as vasoactive intestinal peptide and nitric oxide sometimes they even say ATP but what happens is this VIP a nitric oxide will act on these cells basically causing potassium ions to leave the cell or causing the hyperpolarization of these cells if you hyperpolarizes them they're not gonna contract so these will relax so as a result this will relax and this will contract now what about these guys what happens 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 dude hole right that's the overall goal so you want to squeeze behind it but what do you want this area to be squeezed and closed no you don't 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 gonna stimulate the descending neurons so we stimulated the ascending now we're gonna stimulate the ascending now watch what happens here we're gonna come down here let's say to about this area just suppose right about that area these guys here what are they gonna do look what happens they're gonna give fibers that are gonna go all the way over to this area right the circular smooth muscle downstream or in the AB oral side of the pizza here are you gonna want to constrict this no because you're going to constrict here constrict here the balls isn't gonna go anywhere so what do you need to do you want this side too we receptively relax what kind of things chemical should you be releasing here you should be releasing vasoactive intestinal peptide and nitric oxide this will relax it and by we inhibit us guy it's going to receptively open now same thing bring this guy down here boom with the longitudinal layer downstream on the AB wall into the pizza what are you gonna want to do this guy you're gonna want to stimulate them if you stimulate him what's it going to do when you can track this muscle it'll open up the lumen in front of the bolus helping it to receptor v relax and accept the food balls so should be releasing chemicals such as acetylcholine and substance P whoa all right that is how the GI motility works for these guys okay all right let's get on 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 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 submucosa plexus and we'll talk about what these are for for in a second okay now these next receptors here these are called chemo receptors so this one right here is called a chemoreceptor now you might be thinking why the frak are there chemo receptors 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 down to dr. pepper right after that and you get a lot of siddik residues out of that maybe there's other things in there too maybe this 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 chemo receptors and as a result when you stimulate these chemo receptors guess what you could do these chemo receptors 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 where we're gonna 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 and 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 docks right they have little docks 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 substances 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 caused 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 okay so remember two important things here when the chemoreceptors are stimulated they can activate the submucosa flexy 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 mentioned 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 chemo receptors the chemo receptors can stimulate specific nerve plexy 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 going to be called as cell I'm just gonna mention a few of these let's say it stimulates these s cells these in Tarot endocrine cells guess what these suckers can release they can release C and you know what secreting is important for C has two big functions one is it's going to tell the liver to make more bile okay so it's gonna stimulate the synthesis of bile that's one thing okay so to stimulate the liver they have pata sites to cause more bile production what else it'll go to the pancreas specifically the Ascend eye until the Ascend our cells aren't specifically actually the duct cells within the sni if the the ductal cells there it causes them to release pancreatic juice which is rich and 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 bio 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 give you two more real quick right let's say that you have the chyme here is really rich in like partially digested proteins and fats that could also stimulate these chemo receptors these chemo receptors could stimulate specific sub mucosal plexi these specific submucosal plexus II might release chemicals that will stimulate other cells for example if it's response to the partially digested proteins and fats it can stimulate what's called I cells in taro endocrine cells causing them to see-cret a chemical called Coley cystic einen cholecystokinin is another hormone this sucker can do so much it's insane he can tell for example he can cause gall bladder contractions so he can cause the gall bladder to contract and expel bile into the the ductal system the biliary tree he can also enhance secrete ins action on the liver so we say that he can potentiate he can potentiate see cretins action on liver okay and 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 a plural we know that it's down at this end right do hole in so AB oral or anal end so it can act on the pancreas now in the pancreas it stimulates the Ascend are cells where the secreting stimate the actual ductal cells this one is going to cause them to make lots of enzymes like protease is we'll talk about these in another video like trips and chymotrypsin carboxy peptidase it can also secrete pancreatic lipase is 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 V I'm gonna it's called the apat of pancreatic sphincter but another name for it is called the sphincter of Oddi 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 right the common bile duct here fuses with the main pancreatic duct and when it does it opens up into the duodenum there was called the apat of pancreatic ampulla what the actual 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 an 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 and maybe Ewing 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 case and the K cells release a chemical called glucose let's actually making a different collar glucose insulin allotropic peptide they also call it G I P it's easier that way right but what's the overall effect of GIP big one is he goes to the pancreas and since his primary stimulus is glucose in the actual crime 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 cell such it makes sense right and he can also inhibit gastric motility a lot of these guys secreting CCK GIP another one called VIP they all basically inhibit gastric emptying they're involved in what's called the inteiro gastric reflux we'll talk about that in the GI okay but the basic thing is that I want you guys to get out the intrinsic system is 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 vessel and create dilate the blood vessels to increase absorption it can stimulate certain types of entero endocrine cells like s cells eye cells k cells which can have all these plethora of effects all right or if there's chemo receptor activation or stretch receptor activation what can it do the stretch receptors can activate the my enteric 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 they longitudinal layer on the oral side so that the lumen doesn't open do what to the circular layer on the AB oral 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 AB Laurel sides with it opens up the lumen to receptively accepted 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 extras 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 of men again I just want you guys to get the overall big picture of this thing the sympathetic nervous system what is it gonna do here take anything that it would treat you think here motility for example motility what is gonna do decrease it secrets what is gonna do decrease it absorption what is it gonna do decrease it okay so the basic things here motility secretions absorption and like if you either want to put here blood flow right the splanchnic circulation we talked about that before it's gonna 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 pre vertebral ganglia and these pre vertebral ganglia could be like celiac or superior mesenteric inferior mesenteric super hypogastric inferior epigastric all these different types and they can get different types of splenic tariffs these guys are going to go where they can go to the submucosal nerve plexus the postganglionic fibers or they can go to the my enteric plexus of the ascending or the descending now what will it do here it'll inhibit it and release norepinephrine inhibiting these guys and by inhibiting the middle hibbity blood flow it'll inhibit the secretions it will inhibit all these different hormonal substances here it'll inhibit the actual motility in this areas so it should make sense one thing I do want to mention though because this is the one thing I gotta be careful of for all the 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 does this ganglia here called again just for the heck of it this is a pre vertebral ganglion okay simple as that that's it now if you remember the parasympathetic for most of the GI tract is going to be Vegas Vegas same thing but here's what's really interesting here's the preganglionic fibers in the dorsal nucleus of Vegas which is in the medulla these fibers they can come in synapse directly on the submucosal nerve plexus or directly on to the my intact plexus what does that mean that means that the submucosal plexus and the my enteric plexus are the actual postganglionic cell bodies that means that this is the intramural ganglia so technically right here that is my intramural ganglia isn't it cool I think it's cool so this is our intramural ganglion because technically these two plaques that 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 a 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 what they can put the sphincters alright thinkers okay 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 alright so now that we understand that we get the basic thing here but now I have one last thing I have to say 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 her where this the chemoreceptor and the stretch receptor activate the submucosa or the my enteric plexus and then produce an overall result because remember with a reflex its receptor integration Center and then you have an effector basically right so we have like an a fare pathway integration Center efair pathway that's the overall effect so the receptor is the chemo or the stretch the integration Center is the my enteric 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 chemo receptor or stretch receptor whatever it doesn't matter I just want you to get the point here that this receptor here can have an eighth parent 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 a fair and efferent fibers seventy percent of it remember it can come here either stimulate or maybe inhibit the dorsal nucleus of Vegas but if it does that it can come out and stimulate these submucosal or my enteric plexus when it does this a ferret vagal efferent vagal you know what they call that they call that the vago vagal reflex where the a fan fibers of the vagus nerve whether it be stretch or chemo receptors send impulses to the dorsal nucleus of Vegas activate the efferent fibers of the vagus nerve to go out and either and innervate the southern coast or the my enteric 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 pre vertebral ganglia 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 extry and empty this guy 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 chemo receptors to send these signals to this pre vertebral ganglion maybe it stimulates it what does it do it goes and inhibits the secretions it inhibits the in continual GI motility maybe it even constricts the pyloric sphincter what do we call that we call that B entero gastric reflux that's the one where whenever a lot of time 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 kind and it's stretching the duodenum we don't want to unload all that stuff into Dewan them right away so what does it do it activates these fibers which can go and stimulate the sympathetic nervous system at the pre vertebra ganglion they call these intestinal fuel fibers right and if it does that it can actually cause decrease in secretion decreasing the absorption decreasing 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 as 3's for and if it does that you know that these are the pelvic splanchnic nerves and they can come out here also and innervate the my enteric plexus or they can innervate the submucosal plexus and again produced the same overall response all right ninja tears 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 on 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 iron engine airs as always until next time [Music] you [Music]

Channel: Ninja Nerd

Views: 148,264

Rating: 4.9761138 out of 5

Keywords: enteric nervous system, neurology, myenteric plexus, submucosal plexus

Id: OMQY9t9eC4g

Length: 36min 6sec (2166 seconds)

Published: Sat Dec 23 2017