Path of the vagus nerve (anatomy)

[Music] right come on in let's get to it um uh I've talked about the Vegas nerve before there's a lot to talk about with the Vegas nerve because it does so much stuff today I want to do a visual thing I want to start at the brain stem and follow the vagus nerve down the neck into the thorax through the thorax and into the abdomen I want you to see where the vagus nerve runs how it runs the major structures that it runs with so that you will always be able to remember how to find the vagus nerve I'm not going to talk about all of the minor branches I'm just going to talk about its major root um and I'm gonna try and avoid talking about function but you know what it's like we'll talk about some of the functions of the vagus nerve as we go through all right just a little bit a little bit okay uh if we're gonna describe the path of the vagus nerve we're going to have to start with the Brian uh the brain sorry because it is one of the cranial nerves why is the vagus nerve so interesting well right the vagus nerve carries a parasympathetic and motor fibers from the brain stem down into the neck chest and abdomen and the parasympathetic nervous system is the rest and digest side of the autonomic nervous system you know slows your heart rate kicks off digestion that sort of thing kind of works against the sympathetic division of the nervous system in many cases the sympathetic side being your fight or flight your adrenaline response so the vagus nerve is responsible for innovating these major organs right that's why it's root is so interesting it's also carrying some visceral afferents that is sensory fibers from the organs back to the brain because the brain is also monitoring what's going on down here and responding to that right so Brian uh cerebrum brain stem pons medulla and I quite like this model because the cranial nerves are clearly labeled which means they'll never use this in an exam but we can see in the medulla oblongata cranial nerve 10 the vagus nerve leaves the medulla oblongata just posterior to the olive here so by cranial nerve we mean peripheral nerves that come out of the brain stem spinal nerves are nerves that come out of the spinal cord they're all peripheral nerves this is a peripheral nerve that comes out of the brain stem and then it's going to leave the cranial cavity pretty immediately right skull skull take off the skull cap and I have chosen a painted skull so inside here the Dual venous sinuses have been painted blue and the r3s have been painted red and I'll show you the reason why I've done that so there's anterior I'm going to turn this around we're looking at the back of the head now the occipital region tilt that up the the big hole here is foreign Magnum and right next to it there is the jugular foramen you can see the blue paint going to that the vagus nerve leaves the cranial cavity by passing out through the jugular foramen it's called the jugular foramen because the internal jugular vein also starts here these Dural venous sinuses these sinuses collecting blood from inside the cranial cavity from the brain leave through that hole and at the other side of the skull then we see the internal jugular vein and that descends through the neck oh look the vagus nerve is right next to it the other thing we've got here is there's another hole and that hole is the Canal for the internal carotid artery and that is right next to the internal the jugular foramen for the internal jugular vein so the the the internal carotid artery and the internal jugular vein and the vagus nerve all enter and leave the skull very near to each other so what we see in the neck is we see a connective tissue tube forming attached to the base of the skull which then descends through the neck surrounding those blood vessels now the internal carotid artery is a branch of the common carotid artery so in the neck I'll see the Carotid sheath that's that fascial tube and if I open that up in there I will find the common carotid artery nice big blood vessel the internal jugular vein nice big blood vessel and I'll find the vagus nerve descending down here another model here we go the red structures here are the arteries so down here we've got the common carotid artery and this branch in here is the internal carotid artery that's going to supply blood to the brain and that yellow structure we can see running with it I can confidently identify as the vagus nerve because I know that's where the vagus nerve runs we just don't have the internal jugular vein on here but I do have another model that does we are swapping to the left side now because the right side is still covered by a muscle so you're aware of how deep we are and look internal jugular vein common carotid artery and it's not on this model but in there would be the vagus nerve it's the vagus nerve is a significant nerve but it is a lot smaller than the blood vessels here but it's running down here so it run down runs down the neck now I know that the vagus nerve is going to have a role in innovating the muscles of the palate in innovating the muscles of the pharynx which involved in swallowing it's also going to innovate the whole of the larynx it's going to have a couple of different branches but it's going to be sensory from inside the larynx it's going to be motor to all the muscles of the larynx so as it's descending it's giving off branches that do things but it keeps on going down into the chest and I can't show you exactly where it goes but it it I find it uh posterior to the veins here and anterior to the artery I have another model we're almost into the thorax so we're still in the neck here look this is the laryngeal prominence the thyroid cartilage so this is the larynx here and oh I got a bunch of nerves hmm that's the brachial plexus going to the Upper Limb um but see this nerve here that's running with the artery the veins are here but they've been cut so that nerve there that's the left vagus nerve and then on the right this nerve here running with the blood vessel so this is the common carotid artery here that's the right vagus nerve so this nerve here and this nerve here which are a little more lateral well it helps if you can see where they go and then you can be confident in what they are but these are going to be the phrenic nerves I know they're going to come out of c345 spinal nerves they're anterior to the anterior scalene muscle they're going to run down to the diaphragm through the pericardium but we're not talking about the phrenic nerve today are we we're talking about the vagus nerve but those are the two nerves that you know those are the two major nerves here so those are the two options you have to pick between when you see a nerve running down here but remember that the vagus nerve is running with the blood vessel with the common carotid artery so all right um I'm going to take the lungs out [Applause] so the that that left vagus nerve well we have the arch of the aorta so the aorta comes out of the heart passes to the left arches posteriorly and that's the vagus nerve now so the next rule you have to remember is that when so the vagus nerve is going through the superior thoracic aperture to enter the thorax and it wants to get to the diaphragm and the way it's going to get through the diaphragm is by following the esophagus so once the vagus nerve enters the thorax it's going to try and get the esophagus pretty much as quickly as it can so on the left side it's going to run around the aortic Arch oh and we can see can we yeah and we can see it running with the esophagus down here to the diaphragm and then that's the left side on the right side is different because we're asymmetrical now hmm so there's the esophagus on the right yeah so that's the the vagus nerve on the right running down the right side of the esophagus and we're kind of missing a little bit here but yeah the the vagus nerve will descend with a common croted artery into the thorax and then once it gets down here it's going to dive down to the esophagus now what we're seeing another Branch here wrapping around there what's Happening Here is the recurrent laryngeal nerve so because of some fun embryology and the way all of this formed the recurrent laryngeal nerve branches from the vagus in the chest essentially and then it it loops around the subclavian artery on the right and runs up the posterior right corner of the trachea next to the esophagus and follows the trakia up and at the top of the trachea is the larynx so that's how the recurrent laryngeal nerve innovates the larynx on the right and then on the left um the vagus nerve runs around the arch of the aorta there and very there's the recurrent laryngeal nerve on that side so it's looping around lateral to the ligamental arteriosum um which gives a clue as to why it's being tied down and that recurrent laryngeal nerve will then run up with the Shakira on that side to the larynx but that there is the vagus nerve so if I take off the airway that's the vagus nerve there running down on either side of the thorax we have on either side of the esophagus now the vagus nerve has reached the gastrointestinal tract although the pharynx was really wasn't it so the vagus nerve will be innervating the muscles here and there is an esophageal plexus formed on the esophagus but the vagus nerve is also going to ascend and receive fibers from the lungs and also is going to send and receive fibers to the heart classic example of parasympathetic and sympathetic Innovation is that the heart beats at a regular rate because of the cells in the sinoatrial node depolarizing at a regular rate and triggering contractions of the Atria and the ventricles our sympathetic Innovation will then reduce that heart rate and the force of contraction or a sympathetic Innovation will increase the heart rate and the force of contraction and what happens is we have these are the sympathetic nerves here the sympathetic chain sympathetic trunk there is a cardiac plexus between um the aorta and the trachea essentially then that plexus a plexus is [Music] um you know I always describe it as you know um cable tidying organizing your wiring so these are sympathetic fibers and parasympathetic fibers coming together and then running to the heart there's a cardiac plexus uh which the Vegas nerve contributes to and will innovate the heart and then that is kind of continuous with the pulmonary plexus which we find around the the hilum the root of each lung and the vagus nerve is also contributing to the pulmonary plexus on either side and the pulmonary plexus is also a mixed mixed nerve so there are sensory information coming back from the lungs there is smooth muscle in the lungs as well um now look so if the vagus nerve runs with the esophagus [Music] that's it in a inner but also send fibers to the cardiac plexus and the pulmonary plexus look we have the the esophagus the airway is anterior to the esophagus and then we have the heart anterior to that here's a fun thing in the arch of the aorta are aortic bodies these are chemoreceptors they are looking at the dissolved CO2 in the blood the partial pressure of oxygen the pH of the blood that sort of thing and they're sending that information back to the brain you've guessed it through the Vegas nerve because look it runs right around here so aortic Arch aortic bodies Vegas nerve so as the vagus nerve descends either side of the esophagus it also innervates the organs of the thorax then the esophagus passes through the diaphragm so there's an opening in the diaphragm called the esophageal Hiatus and the esophagus esophagus the esophagus passes through the diaphragm into the abdomen and the vagus nerve with it another model here is a model of the stomach there's the esophagus passing through the diaphragm and the esophagus then passes to the stomach the stomach then continues as the duodenum the yellow we can see here this is the vagus nerve but whereas in the abdomen sorry whereas in the thorax we had a left vagus nerve and a right vagus nerve either side of the the esophagus what happens in the embryo is that the the tube that's forming the gastrointestinal tract at the level of the stomach it rotates like that which brings the left vagus nerve to the anterior surface of the stomach and the right vagus nerve to the posterior surface of the stomach so in the abdomen the vagus nerve often gets referred to as the anterior vagal trunk and the posterior vagal trunk and that's why now we're at the gastrointestinal tract sorted we're innovating the stomach we're now sending the parasympathetic Innovation to the gastrointestinal tract for rest and digest there's a little bit more back to the torso model save the liver out here's the stomach take the stomach out I'll take out the whole the organs of the of the abdomen and now we can see the aorta now what we would see if we were looking at a cadaver and we looked carefully is we'd see another plexus this is the Celiac trunk this an artery the first anterior Branch from the aorta and this is the superior mesenteric artery and we'd see another plexus the Celiac plexus and when that would be continuous with the mesenteric plexus and again those plexuses are mixed sympathetic and parasympathetic fibers and visceralafras running through as well so that posterior vagal trunk contributes to the Celiac plexus and the superior mesenteric plexus does the anterior vagatron get involved as well maybe who knows but that's the typical description and then the arteries go off and Supply blood to the structures of the forget and the that is they Supply blood to the gas the small intestine and then the large intestine as far as the transverse colon about this far away along and the um the parasympathetic fibers from the vagus nerve follow the same Roots as the blood vessels so the textbook description is that the vagus will innovate the gastrointestinal tract as far as about two-thirds of the way along the transverse colon and then there are pelvic nerves that send parasympathetic fibers from the pelvis and they will supply the descending colon the remainder of the colon but certainly now we have lost sight of the the vagus nerve it's off innovating the gastrointestinal tract how far does it go we may yet find out more things um that's the nature of science right but there you go hopefully that was useful that was a visual run-through of the root of the vagus nerve so hopefully um you've got a clearer idea of how it runs down the neck how it enters the thorax how it runs with these arteries how it runs with the esophagus gets through here uh gets down into the abdomen does your thing down there the path of the vagus nerve awesome right see [Music]

Channel: Sam Webster

Views: 108,941

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Id: rFZcW-KrRuU

Length: 19min 24sec (1164 seconds)

Published: Thu Nov 17 2022