Hi Niche Nerds, in this video we're going to talk about the autonomic nervous system. So the autonomic nervous system is extremely, extremely important, okay? So what we're going to do is, before we even start getting into the nitty-gritty, parasympathetic and sympathetic and enteric, I want to talk about what exactly the branches are that actually make up the autonomic nervous system. So for example, if we come over here real quick, when we talk about the divisions of the nervous system, you know there's the central nervous system, which is the brain and the spinal cord.
And then there's the peripheral nervous system. The peripheral nervous system is broken into two systems, right? A sensory system and a motor system, all right?
The motor system, what we can do is, is we can actually break that into two parts. One is called somatomotor, which is a part of your somatic nervous system, okay? And this one is under voluntary control. In other words, if I want to have my biceps brachii contract, I have voluntary control over that, right?
So we call that somatomotor. Whereas my heart, or my GI tract, or other different parts of my actual viscera, Those aren't under voluntary control. Thank goodness they're not.
They're under involuntary control. So the involuntary control is a part of your visceromotor. They call this the autonomic nervous system. The autonomic nervous system, which means it stands by itself.
Now the autonomic nervous system, there's three traditional branches of it. Most people know it by the sympathetic nervous system. The parasympathetic nervous system and the last one, most people don't consider it, they forget about this one, but the enteric nervous system. The enteric nervous system is another branch. We'll have a specific video focusing on this in the GI physiology, but for right now we're going to focus primarily on the sympathetic nervous system and the parasympathetic nervous system in this video.
Okay? Alright, so let's go ahead and talk about the differences real quick. between the autonomic nervous system and the somatic nervous system, just very, very briefly. All right, so somatic nervous system, one of the big, big differences when we're talking about this is this guy, the somatomotor fibers, it takes one motor neuron to reach its effector organ. So this right here is going to be representing the somatic nervous system.
So what do I mean? You see this motor neuron right here? They call this an alpha. Motor neuron.
It only takes one of these motor neurons to extend all the way from the spinal cord. You know what part of the spinal cord specifically? It's in with the anterior gray horn of the spinal cord.
Okay? So the anterior or ventral gray horn of the spinal cord, this alpha motor neuron comes out. And this alpha motor neuron will come to an effector organ, usually your skeletal muscles, and it will release a specific chemical that acts on this effector tissue. Do you know what that chemical is called?
It's called acetylcholine. Okay, and acetylcholine, whenever it's released on this target tissue, will act on specific receptors that we'll talk about in other videos, which is going to be called a nicotinic receptor. All right, nicotinic M receptors for muscular system.
So they're going to cause the contraction of that actual skeletal muscle. Now, differentiating the somatic versus the autonomic, we have to remember that the autonomic nervous system And again, we're only specifically in this video talking about the sympathetic and the parasympathetic. The autonomic nervous system takes two motor neurons to reach their effector.
We call the first one, the first one which is coming out from the spinal cord or coming from the brain stem, because you have cranial nerves that actually act as autonomic nerves. This first one is called a preganglionic. And this next one afterwards is going to be called a postganglionic motor neuron.
But we just want to, for right now, we're not going to go into the big, big differences here. I just want us to understand that the preganglionic motor neurons are going to be the ones that are coming out of the spinal cord, or they're going to be coming from the actual brainstem. The postganglionic motor neurons are usually going to be going to the effect organ.
And we'll talk about specific. ganglia afterwards, not right now. Okay, so now we have the basic difference between the somatic nervous system and the autonomic. Big difference is one motor neuron to reach the effector organ. The autonomic takes two motor neurons to reach the effector organ.
First one is the preganglionic, the next one is the postganglionic. We'll go into more detail on these after. Let's go ahead first and focus on the sympathetic, then we'll talk about the parasympathetic.
Okay? So the sympathetic nervous system, what is it for? What's its purpose? You probably might have heard it as the fight or flight or fright stage, right? It's designed to be able to use energy.
It's used in stressful situations, right? or in many different types of situations. I like to think about it as like you're running away from some dangerous animal like an orangutan. All right, what's going to happen?
We'll talk about that in the individual video, but for right now we need an intro of where you're going to find the sympathetic nervous system within the spinal cord. So there's a specific part of the spinal cord and it extends all the way down from T1, from your T1 vertebrae. Down to about L2.
This is the part of the spinal cord from T1 all the way down to L2. There's a specific portion and this portion is primarily where the preganglionic cell bodies of the autonomic nervous system, specifically the sympathetic, are found. And we'll talk about where exactly after, but from T1 to L2.
They call this the thoracolumbar outflow. Okay, because this is where the sympathetic nervous system is coming out. This is where the preganglionic cell bodies are located, right here within the T1 to L2 region.
And they're going to come out, and they can go to different ganglia, and we'll talk about all that stuff afterwards, because we're going to talk about each different type of splenctic nerve in an individual video on the thoracic, on the sympathetic nervous system. Okay, because these guys will go to a postganglionic. motor neuron, and that'll go to the effector tissue.
Okay, but we'll talk about this afterwards. But I just want you to get the basic difference here is that the thoracolumbar outflow is going to be for the sympathetic nervous system from T1 to L2. Now, the parasympathetic nervous system, where would you find that one exactly? The parasympathetic has different parts within the spinal cord. One part is you're going to have to remember it's within the brainstem.
You know, within the brainstem, you have the third cranial nerve, oculomotor nerve. Well there's parasympathetic fibers that move with the third cranial nerve and it starts here at this nucleus called the Edinger Westphal nucleus and it comes out here and supply specific structures that we'll talk about individually in the parasympathetic videos but it'll come to some type of ganglion which we'll talk about and this is mainly going to go and supply parts of the eye alright but remember what nerve is this this is cranial nerve three it moves with And this is going to be parasympathetic fiber. So cranial nerve 3 has parasympathetic input.
Okay? What else? You know here, this blue nucleus, they call this the superior salivatory nucleus.
The superior salivatory nucleus is going to be where the preganglionic cell bodies are found. And they're going to come out here as a part of a specific nerve. And this is called the facial nerve or cranial nerve 7. So cranial nerve.
7 is actually going to have parasympathetic outflow and it'll go to many different structures. We're not going to talk about those target tissues now. What else?
Another one is going to be right here the inferior salivatory nucleus. That's going to be for the glossopharyngeal nerve. So the glossopharyngeal nerve is what nerve?
This is going to be cranial nerve 9 and this is going to go to specific tissues also. And what's the last one within the brainstem? Son of a gun. The last one within the brainstem is going to be the vagus.
And this is that big mambo-jumbo. This guy goes to so many different tissues. If you haven't watched them already, we've already made videos that go into super, super detail on all the branches of cranial nerve 3, 7, 9, and 10. I suggest you guys watch those because we're not going to go into a whole bunch of detail in these videos.
Okay, but this is going to be cranial nerve 10, the vagus nerve, and it goes into specific tissues. So we know cranial nerve 3, 7, 9, and 10 are parasympathetic nerves. What else? Down here.
Down here within the sacral region of the spinal cord. Now there is controversy in some textbooks. They say it's within the lateral horn of the spinal cord. They don't really say that it's there.
There is books that will say that there is technically no lateral gray horn of the spinal cord within the sacral region. But for right now, we're just going to say that it is within the lateral part of the spinal cord. But specifically what part, what level of the spinal cord?
Specifically around S2. S3 and S4. This is one heck of an ugly S.
Let me fix that. So S2, S3, and S4. This is going to be for our pelvic, the pelvic splenic nerves.
We'll talk about that. Okay, but these are going to be going to a bunch of target tissues also. So what we know is, is that the parasympathetic is made up of two portions. The cranial nerves, 3, 7, 9, and 10, and the sacral region, S2, S3, S4. So what do we call that?
We call this craniosacral outflow. Okay, so what are we going to put it up here, here? Here, here. Alright, so it's going to be called the craniosacral outflow. Okay, and this is again made up of cranial nerves 3, 7, 9, 10, and S2 to S4.
Okay, this is the craniosacral outflow. So we know what levels of the spinal cord you're going to be seeing this coming from. Thoracolumbar, T1 to L2, sympathetic.
Parasympathetic, cranial nerve 3, 7, 9, 10, S2 to S4. Okay, so we covered that. We know what regions of the spinal cord and brain stem. What I want to do now is I want to zoom in on this thing that we talked about, the ganglia.
Alright, so now if we come down here, I want to talk a little bit more about these autonomic neurons. Okay, I know we talked about preganglionic and postganglionic, but I want to get a little bit more into that. So now, let's say that this top one up here, this one here, this nice blue color, this is going to be, or baby blue, this is the sympathetic nervous system.
We're going to represent this one. Now, there's structural differences between the parasympathetic and the sympathetic nervous system. They're axons, they're neurons.
The ones that are coming out of the spinal cord. This preganglionic, they're very short. Okay? So these preganglionic motor neurons within the sympathetic nervous system, they are short.
Okay? These ones over here, the postganglionic that we already termed, in the sympathetic nervous system, they're going to be long. So they're short in the preganglionic and long in the postganglionic. Okay? But in the parasympathetic nervous system, here in this darker blue, these are the preganglionics.
We already know that. It's just flipped. So now the preganglionic motor neurons are long. And the postganglionic motor neurons are short. Okay?
There's a reason why for this. So parasympathetic nervous system, these long preganglionic motor neurons, they travel and travel and travel until they reach very, very close to a target organ. Sometimes even within the target organ.
So when we talk about these ganglia, first off, how do we define a ganglia? A ganglia is just a group of cell bodies that are located within the peripheral nervous system. That's all they are.
So if you look, I'm only drawing one of these cell bodies, but there's multiple of them. Okay? Multiple cell bodies within that ganglia.
It's just a group of them. Now, there's only one specific type of ganglia. in the parasympathetic nervous system. Because these preganglionics are so long, they pretty much reach their effect organ. Sometimes they go in their effect organ.
So they call that terminal. So they sometimes refer to this one as a terminal. Sometimes you might even hear another synonym.
A terminal or you might even hear the word intramural ganglion. Okay, so for the parasympathetic nervous system, You're going to hear two different terms. One is you can find what's called a terminal ganglion, or you can find an intramural ganglion. It just means that they're either at the target organ or inside of the target organ.
That's why these have to be long. Now, for the sympathetic, it's a lot more complicated, unfortunately. These, you have so many different types of ganglia, and that's what we're gonna go ahead and talk about now because there is so many of these, okay? But before we do that, actually, Let's actually say one more thing about these pre-ganglionic and post-ganglionic interaction. When we look at the sympathetic, I want to zoom in real quick on that synapse.
Just zoom in real quick on it. So let's say that I zoom in on this, and I look at, here's the axon terminal, and here's the cell body of this post-ganglionic motor neuron. I want to know what type of chemical is being released here at this ganglion, this presynaptic to postsynaptic interaction.
Generally, this chemical that's going to be released is going to be acetylcholine. And acetylcholine will come over and stimulate this postganglionic motor nerve. Okay, so therefore we call this fiber the preganglionic sympathetic, the preganglionic sympathetic fibers, we call these cholinergic fibers because they're releasing acetylcholine.
Then, if I zoom in here, I look at the actual effector tissue. So now the postganglionic motor neurons are going to release a specific neurotransmitter onto their target tissue. What's that chemical that they release? It's not acetylcholine.
Instead, it's called neuro. epinephrine. So norepinephrine is released which will act on the target tissue. So preganglionic sympathetic release acetylcholine so they're cholinergic. Postganglionic sympathetic release norepinephrine so they're referred to as adrenergic neurons.
Okay now parasympathetic. If we zoom in on that synapse there. If we zoom in on this synapse, it's the exact same as the sympathetic preganglionic.
So here's the axon, terminal. Here's the cell body. When they release a chemical, they release acetylcholine.
And acetylcholine stimulates this postganglionic motor neuron to fire. If we zoom in on this one here, the postganglionic motor neuron to the target tissue, it still releases the same thing, acetylcholine. So, how would we define this? We would say that the preganglionic sympathetic neurons are cholinergic.
The sympathetic postganglionic neurons are adrenergic. The parasympathetic preganglionic motor neurons are cholinergic. And the parasympathetic postganglionic motor neurons are cholinergic.
Okay? So cholinergic, cholinergic, cholinergic, adrenergic. Now that we've done that, let's go ahead and zoom in now on the different types of sympathetic ganglion. Alright, here's a nice big beast of a diagram here, right? So we have to talk about the different types of ganglia within the sympathetic nervous system.
Okay, before we do that, I want to talk about where you're going to find the cell bodies of those preganglionic motor neurons. So we have a cross-section of a spinal cord, right? Within the cross-section, you have the anterior gray horn or the ventral gray horn, and you have the posterior gray horn or the dorsal gray horn.
Within the thoracolumbar region, remember T1 to L2, you have an intermediate lateral gray horn, okay? An intermediate lateral gray horn. And right here is where you're going to find the cell bodies of the preganglionic sympathetic motor neurons.
So, for example here, let's zoom in on this guy. That cell body is the preganglionic sympathetic motor neuron. It can come out here, right? So here's the preganglionic.
It can move out along with the somatic fibers from the anterior gray horn. And it can move through the ventral root. When it goes to the ventral root, it can go out into the ventral ramus, where the spinal nerves will eventually form, right? But there's something really cool here. What can happen is these preganglionic sympathetic motor neurons can actually move.
in to this little like little sack of cell bodies here. It can move into this little like sack of cell bodies. What do they call that when there's a group of cell bodies in the PNS? It's a ganglia. So there's going to be a whole bunch of cell bodies here.
So it's called a ganglia. But what is this one here? That's a ganglia. Oh, what's this one down here?
That's a ganglia. What's this one up there? That's a ganglia.
All the ganglias are connected in like a chain. So what do you think they call these ganglia? They call them chain ganglia. So this ganglia right here is specifically called, there's many names for these sons of guns. You can call this one a paravertebral.
You can also call them, if you don't want to call them paravertebral, you can also call them a chain ganglia. So you can call them paravertebral ganglia, or you can call them the chain ganglia. So whichever one you guys prefer. But again, these preganglionic sympathetic motor neurons are coming out through the ventral root, all right? And then as they do that, they go into the ventral ramus.
They come through to this changanglia. But how? What's this little tube right here called that they move into it through?
It's actually, you know these preganglionic motor neurons are very, very myelinated? So because they're very, very, very myelinated, they show up as a white matter, okay? So this is, when you look at this, it's going to look like a lot of white matter.
So they call this the White Rami Communicants. Okay, the white rami communicants. Now, that's just the actual pre-ganglionic sympathetic motor neurons. They're axons, myelinated.
Comes into this chain ganglia where there's going to be a whole bunch of cell bodies. Let's just draw a bunch of cell bodies in here. Actually, let's just draw one for them. There's going to be the cell bodies of the post-ganglionic motor neurons.
Now, from here, we're going to go through the three scenarios of where they can go, right? If it comes here, synapses on... that cell body, that postganglionic motor on that cell body.
And when it does, it exits out through this next little tube. It goes out through this other tube and then through the ventral ramus with the spinal nerve. So it goes with the ventral ramus as a part of the spinal nerve and goes to three different types of locations.
Okay, if it does, that tube right there, this one here, is called the gray rami communicans. Now the question is why is it gray? It's because it's not myelinated.
So if it's not myelinated, it's not going to have that myelin sheath. So that's why they call it gray rami communicans, because it's unmyelinated axons. So now, if this preganglion goes through the white rami communicans, synapses on the cell bodies in this chain ganglia, or perivertebral ganglia, goes... out through the gray rami communicans and enters into this ventral ramus with the spinal nerve. This is going to go to three different types of tissues.
Okay, so now if it comes out and goes to this actual smooth muscle tissue that's actually found within the skin and it can contract it and pull our hairs up, it's called the erector pili muscle. So these fibers are called pylomotor fibers because it's going to the erector pili throughout our entire body, throughout the entire level of the thoracolumbar output. Okay, it can also go to other different regions.
It can go to the actual blood vessels. So it can actually go to our blood vessels and cause the vasoconstriction of our blood vessels. So if that's the case, they call this vasomotor fibers.
So it can go to our blood vessels, which are going to be called vasomotor fibers, or It could go to certain glands, like sweat glands, throughout our entire body. So they call that pseudomotor, okay? So it can go to sweat glands.
And this is one of the, I didn't mention it over there, but there is a couple exceptions to the sympathetic postganglionic motor neurons. One of them is that sweat glands, the postganglionic sympathetic, they don't release norepinephrine, they actually release acetylcholine, which is one of the exceptions. There's many exceptions, but this is one of them, okay? They'll talk about another one which is actually, it doesn't actually act as a chain ganglia, it doesn't act as a collateral ganglia, it actually goes straight to the adrenal medulla, which is actually going to be an example of an intramural ganglia.
We'll talk about that, that's one more exception. Okay, so one type of ganglia is the chain ganglia or the paravertebral ganglia. They go through the white, out through the gray, and they go a part of a spinal nerve to the pylomotor fibers, vasomotor fibers, or pseudomotor fibers.
Okay, what's the next example? Let's say that we take again. What is this over here? Our intermedial lateral gray column right here.
And again, what are we going to have here? We're going to have the cell bodies of the preganglionic sympathetic motor neurons. They can come out. Again, these fibers are still going to be the same. They're going to come out through the ventral root.
When they go out through the ventral root, the only thing that's going to be a little different is they're still going to go through the white rami communicans. They're still going to go through this white rami communicans. And they can go in here. And two things can happen, right?
So let's say that it decides that these fibers, when they come in, it decides, you know what, I'm not going to actually go through the gray ray of my communicants. I want to go down to another level. So guess what it does?
It says, you know what, I'm going to take and just go down another level of the spinal cord. So it decides to descend down. Isn't that crazy?
So it can descend down. As it descends down, it goes into another ganglia. It didn't synapse here.
It just goes straight through the chain ganglia and down to a level below that part of the spinal cord. When it does that, it then can go to an actual chain ganglia. And then when it goes to this chain ganglia, it can synapse.
And then what can happen here is it can actually still move out through the gray rami communicans and become a part of the spinal nerve, right? And then go to the erector pili. Again, the pylomotor, vasomotor, or pseudomotor.
Or, you know what else can happen? It can actually directly leave. on its own. It doesn't even have to become a part of the spinal nerve. It just leaves its own nerve.
You know what they call that? When things leave as their own nerve, it doesn't even go through any type of nerve part. It goes through its own. This right here is called a splanchnic nerve.
Okay, so what have we seen here? If they can go through the white ray of my communicants to a chain ganglia at that same level, then what can happen is it can go a level down. Go to their synapse on these cell bodies and maybe go out through the gray ray of my communicants and go to pylomotor, pseudomotor, vasomotor.
Or it can synapse on the cell bodies there, these postganglion motor neurons, and come out as its own nerve. That is called a splanctic nerve. These are going to be a good example of the ones in the thoracic viscera that go to the heart, the lungs, and the esophagus. Okay.
Following off with the splenic nerve, some of you might be like, oh I thought splenic nerves have to go to a collateral ganglia. They do, but those are the ones that are going to more of your abdominal viscera. So for example, let's say I take these fibers here.
They come through the white rami communicans. They go into the chain ganglia. They don't synapse there, just like the ones that went down. Instead they say, you know what? I'm going to go through this alternate tunnel.
I'm going to go down through this alternate tunnel here. And I'm going to come here to this ganglia that's located in front of the vertebral column. Even in front of that, actually right around the aorta.
So they actually call these ones, because they're in front of the aorta, they're in front of the vertebral column, there's so many names for these sons of guns. If you would look at these ones, let's write down all the different types. They can call them pre-aortic.
You know what else they can call them? Pre-vertebral. They can even call these guys collateral ganglia. And then for the last one, you can even call them, because they're beneath the diaphragm, they're going to a lot of the abdominal pelvic viscera, they're called sub-diaphragmatic ganglia. Isn't that crazy?
So there's so many names for all of these darn ganglia here. Okay, so these are going to be the ganglia. of the autonomic nervous system that are going to be going to a lot of your abdominal pelvic viscera. The splanctic nerves down there, those are the ones that are going down to the thorax.
So if it does do this, if it does synapse here, it can actually go through its own little nerve. Again, this little nerve that's coming from the collateral ganglia and going on its own, this is a splanctic nerve. But it's the splanctic nerves that are supplying the abdominal visceral area. So this is still a splanctic nerve.
And we'll talk about the thoracic, the lumbar, and the sacral splanchnics in the sympathetic videos. Okay, so what do we have so far? We have ones that can go out at the level. We can have ones that descend at a level. We have them either go, if they go down a level, they can go through the gray ray line, or they can come out as their own splanchnic nerve.
We have ones that can actually pass right through the chain ganglia and go to a collateral, a prevertebral, a preaortic, a subdiaphragmatic ganglia. and go in their own nerve called a splanctic nerve. What else?
Well, if it can go down, it can go up. All right, so guess what? These fibers, let's say that we take here. This one was at this level here.
It went down. Let's say it goes up. So if it goes up, it can go and ascend to a level. And then from that level, it could either synapse on the cell bodies here. It might even go up another level too.
Sometimes you can go up more than one level. But it can ascend, and let's say that it ascends to this level here, and it synapses on cell bodies right in this area. What can happen?
It can either go out as its own splanchnic nerve. It could either do what? Go here, out through the gray rami communicans, and become a part of the pylomotor, pseudomotor, vasomotor fibers.
So many different things that can happen here. Okay? So what we know about the sympathetic ganglia is we have paravertebra or chain. They're the same thing.
They're these trunks basically, all the way up and down. And this can allow for them to ascend, descend, or go out at the same level. Preaortic, prevertebral, collateral, subdiaphragmatic means that they go through the white rami communicants. They pass straight through the chain ganglia and go to another ganglia. These collateral, preaortic, subdiaphragmatic, or prevertebral, and then go out as their own splanctic nerve.
And then the last exception was the one that supplies the thorax. which is going to be thorax and even some parts of the head and the neck, is it can actually come through the white rami communicants, right? Like if it happened at this level, I didn't show it here, but it could too.
So for example, if I come down here to this last part, let's say here is the intermedial lateral gray column that comes over here, comes out through the ventral root, through the ventral ramus, comes through the white rami communicants and synapses. on the cell bodies here. The cell bodies can either go out at that level or they can come as their own splenic nerve. Alright?
So I think that pretty much explains what we need to know about the chain ganglia. Okay guys, so I hope you guys enjoyed this video on the intro to the autonomic nervous system. What we're going to do in our next couple videos is we're going to talk a little bit more in detail on the craniosacral outflow, talking a little bit more about those ganglia and muscarinic and nicotinic receptors.
And then we'll have one more video which is going to focus on a little bit more detail on the sympathetic nervous system, talking about those splanctic nerves, the different ganglia in a little bit more detail, and then talking about the adrenergic receptors, okay? All right, Ninjas, until next time.