Hello everyone, welcome to chapter 15 where we're going to take a look at the autonomic nervous system. So this is part of the efferent portion of the nervous system where we have motor output going from the brain out to the body. Now this diagram here illustrates for us on, I got to change, there we go, and illustrates for us on the left side the somatic nervous system where we have upper motor neurons descending from the primary motor cortex, the precentral gyrus. They descend down through the cerebral peduncles and out through the cortical bulbar or corticospinal pathways, where they synapse the lower motor neurons, either at the ventral gray horn or in the cranial nerve nucleus, and they go out to skeletal muscle.
So the idea is the somatic nervous system, the effector organs are skeletal muscle. This is your voluntary nervous system. This is your intentional movements of your body. Great. So we've worked on that vocabulary.
Over here, when we look at the autonomic nervous system, we're looking at different effector organs. That's all. These are still motor neurons. These are still out. put efferent output from the central nervous system to effect a response to the environment it's just that we have different effector structures so what do we have for autonomic effectors we have smooth muscle we have cardiac muscle so we learned in amp1 about the three kinds of muscle you know skeletal muscle gets all the press but smooth muscle and cardiac these are targeted by autonomic motor neurons we also have glands and then adipocytes so adipose tissue so as the the difference here really is the effector organs all right what when you send out a motor command what is uh what's being impacted to create a response the other aspect is the physical structure here we had upper motor neurons and lower motor neurons in the somatic nervous system for skeletal muscle here We have some different vocabulary.
We talk about visceral motor neurons here in purple on this diagram. Now for the rest of this chapter, we're just not going to pay attention to that, okay? We're just not.
So in the central nervous system, we have visceral motor neurons, and look, they're coming from the hypothalamus, and then they descend down the spinal cord to either the lateral gray horn of the spinal cord. or in the cranial nerve nuclei, either way. And when they leave the central nervous system on nerves, what we have here is a new set of vocabulary because the key here with the autonomic nervous system is that between the central nervous system, the spinal cord of the brain, and the effector organ here are going to be two neurons. The first one is called the preganglionic neuron.
The second one is the postganglionic neuron, which they neglected to label on this, so I am going to do it. Look at this. Postganglionic neuron.
So we have, leaving the central nervous system, we have a preganglionic neuron, a synapse, and a postganglionic neuron. neuron and that is what synapses with the target tissue. There's always two neurons between the central nervous system and the target tissue with the autonomic nervous system.
Now why do we call them preganglionic and postganglionic? Because the synapse occurs in a ganglia. So what we need to do here for the autonomic nervous system is not only do we learn like the functionality of these pre and postganglionic neurons, we have to learn the ganglia.
Where are they? And then the other thing is we have to figure out how this pattern is different for the two divisions of the autonomic nervous system, the sympathetic and parasympathetic. So that's what we're going to do here in this chapter.
Along the way, we have to learn some new vocabulary for types of neurons and their receptors on the postsynaptic membrane. So buckle up and here we go and let's take a look at the details. of the autonomic nervous system.
All right, let's take a look at this diagram. So what this diagram is trying to show you is, again, some basic differences between the somatic nervous system, where we're sending motor neurons from the ventral gray horn out to the ventral root into the spinal nerve, where we have myelinated motor neurons, ending at the neuromuscular junction on skeletal muscles. And we know that from previous conversations, these motor neurons are cholinergic neurons. They release acetylcholine into the neuromuscular junction and cause ligand-gated sodium channels to open.
Okay, so that's somatic motor innervation. That's what we've already learned. Down here, we're seeing the two different divisions. of the autonomic nervous system.
Part B here is sympathetic and then part C here is parasympathetic. So let's look at the differences here physically between sympathetic and parasympathetic motor innervation in the autonomic nervous system. Let me zoom in here a little bit. Okay. let's look at what we got with the sympathetic motor innervation here what we see is here's that lateral gray horn so the lateral gray horn here is for sympathetic let me i'll put that in here so the lateral gray horn is for the sympathetic division of the autonomic nervous system.
That's where the nuclei of the motor neurons are. But they leave on the ventral root just like somatic motor neurons. And the antispinal nerves, we're going to look in detail at how these make it out of the spinal cord. And then they end up here. This yellow structure here is the ganglion.
We said there's a preganglionic, a synapse inside of a ganglion, and a postganglionic fiber neuron, right? They've color-coded them here. Here, they've color-coded it.
The preganglionic is green. The postganglionic is red. And then the postganglionic neuron goes to the target tissue, in this case, cardiac muscle, right? So there we go.
And then they just kind of give you a generic, yeah, I know the visceral effectors. Could be cardiac, could be smooth, could be the glands, you know, and so on and so forth. Don't worry about the neurotransmitters here.
This represents norepinephrine. This is acetylcholine. We're going to talk in detail about that later in the chapter. So this is the sympathetic pattern.
If we look down here at the parasympathetic pattern, now parasympathetic motor neurons have their cell bodies in a ventral gray horn, just like somatic, just like skeletal muscle motor neurons. So here we are, we're in our familiar territory of the ventral gray horn. You have a motor neuron going out the ventral root. It just happens to be a parasympathetic motor neuron. And what we'll also see is this could be a cranial nerve nucleus.
Heads out as a preganglionic nerve, neuron. It's a green, see the green up here? And it goes virtually all the way to the organ. And there in yellow is your ganglion.
So there's the ganglion. And then it synapses inside the ganglion and the postganglionic fiber goes to the target tissue. So here's our first big difference here in the comparing pre-ganglion or parasympathetic and sympathetic.
So sympathetic here i'll keep my color coding sympathetic motor innervation we have short pre-ganglionic fibers we have long post ganglionic fibers all right the uh the ganglia are close to the central nervous system. They're right next to the spinal cord. They are not far away, and I will show you those maps. In the parasympathetic, we have the opposite here. We have long preganglionics, short postganglionic, and in fact, the ganglia are usually on the surface.
of the target tissue or inside the target tissue. So most of the distance traveled for the parasympathetic nervous system is preganglionic because the ganglion is right there at the organ or inside the organ. And that's the case with the digestive tract, for example. In the GI tract, you have what we call the myenteric plexus and the submucosal plexus. And inside the walls of the GI tract, you actually have these ganglia.
And if I zoom out here and look at it this way, If we have their, if they're inside the target tissue here, we call these intramural ganglia. So we're going to look at maps of, in the body, of where the autonomic ganglia are, the sympathetic and parasympathetic. Okay, but there's, here are some. Very real differences physically between the two divisions. Okay, and we're going to reinforce this as we go.
In general, I'm going to start with sympathetic, and we're going to take a look at innervation patterns and maps. And then we're going to jump to parasympathetic, and then we'll talk about some more global issues. So let's take a look.
So here's a map. that shows us kind of schematically here the physical distribution of the sympathetic nervous system so i'm going to write this out over here because it doesn't really say this on the diagram but this is the sympathetic division and you'll notice on your handout that i have in parentheses The sympathetic division is also called the thoracolumbar division. Thoracolumbar division.
Because if you look here, they're showing here the spinal cord, right? Cervical, thoracic, lumbar, and sacral. Color-coded here. Green, blue, I don't know, orange and yellow or whatever.
So here they have it color-coded. And what they're showing here... The green is preganglionic neurons, red is postganglionic neurons.
When the green preganglionic neurons leave the nervous system, they're leaving the nervous system in the thoracic region of the spinal cord and the lumbar region of the spinal cord. So all 12 thoracics plus three lumbars or two lumbars, T1 through L2. So it's the thoracolumbar division, which tells me, and it should tell you, that if we were to look at a cross-section of the spinal cord from T1 to L2, that is the region of the spinal cord where you will see a lateral gray horn in the gray matter, because the lateral gray horn is where sympathetic division neurons leave the spinal cord.
So the soma, the cell bodies. of these preganglionic neurons that are arising from the lateral gray horn. So this is showing us a map here, and in order to really understand this, we're going to look at this twice. I'll start here, just give you a brief overview. We have the spinal cord here.
We have the preganglionic neurons leaving the spinal cord, and look what we have here. This is the sympathetic chain. So we've learned this in lab and lecture, this idea that when the spinal nerves emerge from the spinal cord and the roots merge into the spinal nerves, you have the gray and white communicating rami going to the sympathetic.
chain ganglia. All right, they're there, and they're called the sympathetic chain ganglia, because that's where the pre-ganglionic neurons, they go to the ganglia here. Sometimes they're going to synapse in these ganglia, and sometimes not.
We're going to take a look at that, and then they go off to their target tissues, all right, and this shows us some of the various places that they go. So before we... get into depth on like the celiac ganglion superior and inferior mesenteric ganglia things like that i want us to focus in on the spinal cord and sympathetic chain and i can use a diagram here coming up that i can illustrate for you four basic patterns of sympathetic innervation right and then we're going to come back to this diagram and interpret that on a larger scale So bear with me while we switch back and forth here. Let's take a look. Okay, here we are.
So look what we got here. We have a spinal cord and we have the lateral gray horn and they're showing the soma preganglionic neurons, right? So these green neurons are preganglionic. They kind of keep this color coding throughout these diagrams for the most part.
We do have over here. they're showing somatic effectors right so on this side they're just showing skeletal muscle right here's your skeletal muscle motor neuron you know there's the cell body and the ventral gray horn goes out through the ventral root and out to the out to the muscles great it's a little more complicated over here with somatic or sympathetic motor neurons so what do we got here i'm gonna trace for you notice they've got one two two, and three here. They're showing on this diagram three different pathways by which sympathetic neurons make their way to their target tissue.
I'm going to use this in another diagram to show you actually four patterns, right? So pattern number four is not labeled on here. Let's start with number one, pattern number one.
So what we want to do here is we want to kind of do some some line tracing here so i'm going to i'll just start with black here all right so let's start with that so over here in this lateral gray horn i'm i'm outlining one of these pathways in black all right so i'm going to follow this here comes a preganglionic neuron and it's going to come out here through the Ventral root. So look at that. We just came out through the ventral root. Now we're in the spinal nerve, right? And we come out here in the spinal nerve and look what happens.
Everybody takes a hard right turn on the white ramus. So here's the white ramus communicans. that white communicating ramus and then we enter the sympathetic chain ganglion and here's how they indicate a synapse a little y shape there and look what we have next in line we have a post ganglionic neuron and that's in red here and then watch the post ganglionic neuron it leaves the ganglion and it goes back and gets back on the spinal nerve and heads back out on the spinal nerve.
So we took a little detour, right? We came out the ventral root into the spinal nerve, said, whoa, wait a minute, get off the exit into the ganglion. We'll synapse and we'll send the post ganglionic fiber out the spinal nerve instead. So this is pattern number one.
And it's like, well, what's the big deal about pattern number one? If you are going to do sympathetic innervation for sweat glands, piloerector muscles, and blood vessels of the skin, and skeletal muscles, then you're going to follow this pathway. So basically, any sympathetic innervation to the skin is coming through pathway number one. The postganglionic neurons are traveling in the spinal nerves.
So when you learned in lab the... radial nerve, the ulnar nerve, the median nerve, the anterior interosseous nerve, any sympathetic innervation to the skin of the forearm and hand are traveling. Those sympathetic postganglionic fibers are traveling out to the skin of your forearm and hand on those nerves. So they came out of the lateral horn and the ventral root. went into the sympathetic chain and synapsed and out of the ganglion comes the postganglion neuron and it goes out to those structures so that's the first pattern now i'm going to use this to illustrate something for you because there's a reason here why we call the incoming branch into the ganglion the white ramus the outgoing branch is the gray ramus so you learn these in lab there's a reason why we call them the white ramus and the gray ramus so I'm gonna come over here and do something really I should have talked about before but when we consider the autonomic nervous system and autonomic neurons All right, so write this down somewhere.
Preganglionic neurons are myelinated. I can write better than that. Hold on.
Myelinated. There we go. Preganglionic neurons are myelinated. Postganglionic.
neurons are unmyelinated. That, as long as you go ahead and write that down, we can come over here and look at this. And remember, myelination makes something white matter.
Unmyelinated makes a gray matter. The preganglionic fibers leaving the spinal cord are myelinated. They're white matter. And when they come into the sympathetic chain, they're white matter.
Always, always, always, that's the white ramus. When the postganglionics are leaving to go back into the spinal nerve, they're unmyelinated. This is the gray ramus because all of the postganglionic fibers traveling on that gray ramus are unmyelinated. That's why they're called white and gray rami.
So this is pattern number one. If you're heading out to the skin. basically sweat glands pilo-erector muscles are little bits of smooth muscle that raise the hairs on your skin blood vessels of the skin and skeletal muscles if you think about this skeletal muscles um like if you think of your arms and legs your arms and legs are solid tissue okay there's there's no soft tissue organ inside your arm there's there's skin muscle bone and connective tissue holding it all together. So basically we could also say arms and legs and in the trunk region, the torso, if you think about where the muscle is, it's all just under the skin.
So to have this pattern innervating arms and legs, skin, muscle right that's that's basically this pattern all right that's pattern number one let's take a look at pattern number two all right so let's do some more line tracing I'm going to I'm gonna choose a different color here darken up my blue a little bit and I'm gonna use blue here there we go All right, so pattern number two. Let's start here. All right, so here we come. We're going to come out here.
We are a pre-ganglionic fiber. See my blue line now. We're exiting the spinal cord.
We're coming out into the spinal nerve. Everybody takes a hard right and enters the sympathetic chain and the white ramus. Everybody. Now it's like monopoly do not pass go do not collect $200 you may not Pass up the white ramus you enter the chain if you're sympathetic Pregalonic fiber so here watch this we entered that Ganglion at that level, but we did not synapse in it We don't have to synapse at the level we enter in this case.
We're gonna go up. They only show going up a level here You could go up many, you see. You could keep going if you want. Sometimes you go four, five, six levels before you synapse.
But either way, we're synapsing in the chain. And we find ourselves a postsynaptic neuron or a postganglionic neuron. And that leaves the sympathetic chain. But we're not leaving the sympathetic chain on the gray ramus.
we are not re-entering the spinal nerve that's not happening we are leaving the sympathetic chain by a different route we are leaving by a sympathetic nerve not the spinal nerve all right so here's pattern number two these are sympathetic nerves where are we going Look at our targets here. The iris, salivary glands. So these are up in the head. Lungs, heart, thoracic blood vessels, and esophagus.
So what are we doing here? So pattern number two, we're going to the head. I'm going to get my blue pen back.
We're going to the head and we're going to the thoracic cavity. that's where we're going with pattern number two now they're showing pattern number two uh down below trust me it's the same pattern okay i'll i'll trace it in blue so we can see pattern number two is blue right here we go and we come out here we take a hard right on the white ramus into the chain we don't necessarily have to synapse the same level there's another example of pattern number two okay so i think the idea that the artist who made this diagram was trying to get to was that this one down here would be going out to say the thoracic cavity and this one up here is going up to the head i think that was the idea what they're trying to get to either way if you're going to the head or the thoracic cavity you're following number two on sympathetic nerves so the idea here is a sympathetic nerve is a nerve it's a physical structure remember fascicles epineurium perineurium endoneurium the whole thing you have a nerve leaving the chain and it's all gray matter because these are all post ganglionic neurons sympathetic nerves are gray matter let me write this in sympathetic nerves are gray matter because they're unmyelinated post ganglionic fibers pathway number three here uh i guess for lack of any better colors here i'll choose a dark red although i shouldn't because whatever here here's the third pattern i'm back in the lateral gray horn if you've missed that here we go we're leaving the lateral gray horn we're in the ventral root and now we're in the spinal nerve everybody takes a sharp right onto the white ramus and into the chain in this case we pass through the chain Now, we don't have to pass through the chain at the same level. We could pass through the chain at a different level. But either way, we pass through the chain, and we're going to synapse now in a different ganglion.
So the sympathetic chain represents a whole chain of ganglia from neck all the way to pelvic cavity. But they're not the only sympathetic ganglia. There are other ganglia out there.
In this case, they're called the collateral ganglia, right? They're called collateral ganglia. And on that map that we were looking at before, and we'll look at again, this is like the mesenteric ganglion, right? Superior and inferior mesenteric ganglia, the celiac ganglia, things like that. These are collateral ganglia.
So we... pass through the sympathetic chain completely untouched and out the other side. Now you might do it at a different level, but still you pass completely through without synapsing. What that means is these nerves that come out the sympathetic chain on the other side, these are preganglionic neurons.
They're myelinated. Splanchnic nerves here are white matter. So this is pattern number three, splanchnic nerves.
These are white matter. That's a major distinction between a sympathetic nerve up here, which is gray matter, postganglionic, versus a splanchnic nerve down here, which is white matter and myelinated. Look at where we're going. Liver, spleen, adrenal glands, stomach, intestines, kidneys, urinary, bladder, reproductive organs.
Where are we going here with number three? We are going to the abdominal pelvic viscera, the soft organs. of the abdominal and pelvic cavities liver spleen stomach intestines kidneys urinary bladder all these things you've been learning about that's where they're going so these are three out of the four major innervation patterns and what i want to do here is i want to then take you back to the diagram we were on before and show you these patterns on that diagram and then i'll show you number four let's take a look Okay, here we are.
Let's take a look now. We've got all four patterns here, three that we've just talked about, plus one new one. So I'm going to go in order.
We'll start with pattern number one that we were talking about before, and that's going to be over here on the left side. So here's pattern number one. Look what we got here.
We have preganglionic fibers leaving the spinal cord. entering the chain. Now they don't show the white and gray rami here. They just show them entering the sympathetic chain and synapsing. And then they show them leaving the sympathetic chain and going to the skin.
Pylorector muscles, blood vessels of the skin, muscles. So this is pattern number one, right? So this is skin, arms, legs, muscle. etc.
This is number one. And they are traveling on the spinal nerves. Remember we said, you know, radial nerve, ulnar nerve, median nerve, interosseous nerves, femoral nerves, saphenous nerves, obturator nerves.
You tell me what a nerve is, where a nerve is, you've learned in lab. I'll show you inside there. There are fascicles inside that nerve carrying sympathetic postganglionic fibers to their destinations in the skin or the muscle. All right, so there's pattern number one, traveling on spinal nerves. Pattern number two, look up here.
We've got leaving. The spinal cord entering the chain but maybe going up or down, not synapsing quite yet, but take a look here. We finally synapse and we leave the sympathetic chain as postganglionic neurons. Remember, green is preganglionic myelinated, red is postganglionic unmyelinated. And look where we're going.
We're going up to the salivary glands under the jaw. We're going up to the eyes. So we had talked about pattern number two, right, the head. And we're going out to the heart and lung, the thoracic cavity. Don't worry about plexuses yet.
We'll talk about plexuses. So I'm going to draw a little dotted line here, and then I'll zoom out here. So dot, dot, dot, dot, dot, dot, dot, dot, dot, dot. Draw a dotted line. So this is above.
diaphragm and what you have here are sympathetic nerves these are sympathetic nerves that's what they are their post ganglionic nerves that are leaving the sympathetic chain going to the head or thoracic cavity So that's pattern number two. Pattern number three here, let's see here. What color did I use for that? I used red, I guess, right?
So pattern number three, we talk about below diaphragm. Diaphragm. There, below the diaphragm. So look, we had the abdominal, pelvic, viscera. They should all look familiar some way, right?
So look what we had here. We had preganglionic neurons leaving the spinal cord, passing through the chain. They're not synapsing in the chain.
They're passing through it. They could go up and down levels, but they're going to pass through it. And so the nerves leaving the sympathetic chain here.
Our myelinated white matter, we call these splanchnic nerves. I'm going to draw an arrow in here. Splanchnic nerves. And they're going to different ganglia now.
These are the sympathetic chain ganglia. These are collateral ganglia. We have the celiac ganglion, superior mesenteric ganglion, inferior mesenteric ganglion.
There's even a fourth one. I'm going to put it in here because I can because I'm in charge and I'm no one talking, right? So what I need is to get a kind of a dark yellow to try and match that.
There's a ganglion right And this is the, let me draw this in here, this is the hypogastric ganglion right there. So there are a bunch of these collateral ganglia and they have names. So the splanchnic nerves, these are abdominal.
splanchnic nerves. These are white myelinated axons and they head out to the ganglia and that's where they synapse because that's what ganglia are for. And then the postganglionic fibers go to their target tissues.
And there you go. There's number three. Now, there's another pattern here that I want to show that sticks out.
Let me see. How am I going to do this? I'm going to zoom in here real quick. And what I want you to pay attention to here is the adrenal medulla.
So let me get a new color. I'm going to use purple. for this pattern the adrenal medulla so as we focus here right i want you to watch this and follow it back as i zoom back out here we go look at that that's kind of new it's like one of those little logic tests which of these things don't fit right it's that one that doesn't fit And remember our color coding, green here is preganglionic.
So if we follow this all the way back to the spinal cord, we've got a situation where a preganglionic neuron leaves the spinal cord, passes through the sympathetic chain as a splanchnic nerve fiber, passes through the collateral ganglia without synapsing. It's like, dude, you're supposed to synapse somewhere. But we keep going.
and we go all the way to the adrenal medulla. Now, if we take a look at that adrenal medulla and come out here, and let's take a look at the adrenal medulla. Remember, we had this adrenal gland.
It was kind of this triangular thing here, and you had the cortex out here. and you had the medulla in here you know so you saw that on the kidney models in lab right okay if we follow this pre-ganglionic sympathetic fiber it penetrates through the cortex and all the way into the medulla and that's where it synapses with a post ganglionic fiber so in this case we have a special case, a singular pattern for the adrenal medulla. This is pattern number four, the adrenal medulla. And so we have direct sympathetic innervation of the adrenal medulla.
That's a pattern for the sympathetic nervous system. Now, you might have noticed down here in the region of this hypogastric ganglion here that we had a situation where we've got preganglionic fibers entering the sympathetic chain, descending, synapsing, and exiting as a postganglionic fiber down here in the pelvic cavity. Look, you've got your uterus and your ovaries, penis and scrotum, bladder, kidneys. But all of this stuff is down in the pelvic cavity. pelvic cavity so we have post ganglionic fibers gray matter nerve fibers exiting the sympathetic chain and going down to the sex organs and the bladder down in the pelvic cavity and if you look this is the same pattern as number two okay so it's uh pretty much the same idea but For whatever vagary of historical naming and this and that, these nerves that leave the sympathetic chain as postganglionic gray fibers and go to the pelvic cavity, they're not called sympathetic nerves.
These are called the sacral splanchnic nerves. So I'm going to zoom in here and I'm going to write that in for you. So these are the sacral splanchnic nerves.
So basically this is a variation. Actually let me, here let me do it this way. This is a pelvic.
Variant of pathway number two, okay, but they don't call them synthetic nerves. They call them the sacral splanchnic nerves as opposed to the abdominal Splanchnic nerves up here, which are myelinated so We have, I guess you could say there are four and a half different patterns. Pattern number one here on spinal nerves. Pattern number two above the diaphragm with sympathetic nerves.
Pattern number three below the diaphragm with abdominal splenic nerves. Pattern number four, the special case of the adrenal medulla. And pattern number four and a half here, this pelvic variant. of pathway number two which is the sacral splanchnic nerves All right, and the other thing here is with these sacral splanchnic nerves, I drew in the hypogastroganglion.
The author or the illustrator of this diagram, they show synapsing in the chain, the sympathetic chain, and these are postganglionic fibers coming out in sacral splanchnic nerves. That's not entirely true. It's not accurate.
The sacral splanchnic nerves here. are a mixture of preganglionic and postganglionic fibers. Some of the fibers in these nerves have not synapsed yet.
So if I were to kind of take another green nerve, there's going to be some travel in these sacral splanchnic nerves of fibers that are not. have not synapsed yet and they actually synapse in the hypogastric ganglion and then leave and go to their target tissues so the sacral splanchnic nerves are mixed nerves they're not completely gray matter they're not completely white real life is messy right sometimes things don't follow clean rules like we would like them to This is just the way it is. So here's our basic patterns in the sympathetic division for how we deliver innervations sympathetically around the body. All right.
Here is a map of the parasympathetic nervous system. So here is the parasympathetic. division here and you'll notice if you look at your handout your lecture guide outline you'll notice in parentheses this is also called the craniosacral division so the sympathetic was called the thoracolumbar division The parasympathetic is called the craniosacral division because you have parasympathetic neurons leaving the brain on cranial nerves or they leave the spinal cord from the sacral nerves.
Okay, so craniosacral. There are anywhere from C1, there's C1. From C1 all the way down through L5, there's no parasympathetic innervation that comes off the central nervous system in that region. It's only four cranial nerves, 3, 7, 9, and 10, and three sacral nerves.
That takes care of all of the parasympathetic innervation throughout the body. So what do we see here? Let's take the cranial. portion first. And we'll take three out of the four cranial nerves.
Cranial nerves three, seven, and nine. So the oculomotor, facial, and glossopharyngeal nerves have parasympathetic functioning. So they have parasympathetic motor neurons traveling in those nerves. Firstly, if we look here so let's for example let's look at the oculomotor nerve cranial nerve 3 it has parasympathetic function and if you look here's the green preganglionic myelinated fiber and it makes its way to a ganglion so in this case if you remember at the beginning here we said with parasympathetic pathways the Preganglionic fiber is long and the ganglion is either on the surface of the organ or inside the organ. And we said if it was inside the organ, we called it an intramural ganglion.
Here, with these three cranial nerves and their innervations of the salivary glands and the eye, their ganglia are... on the surfaces or very near the surfaces of their target tissues. And so we have a term for that, and if you look in your lecture outline, we call these terminal ganglia.
So I'm going to do this up here. Watch this. These are terminal ganglia. So these are very near, near, yeah, there's no T on near, near to or on the surface.
of the organ. These are terminal ganglia. The artist has drawn them separate just for clarity, but they're very close to those salivary glands or the lacrimal gland or the back of the eyeball. Those are terminal ganglia. So there are four of them, pterygopalatine, ciliary, submandibular, and otic.
So let's take a look here. at the pattern. So we have the oculomotor nerve, cranial nerve 3. It innervates the ciliary ganglion and then the postganglionic fibers go to the muscles of the pupillary sphincter and the ciliary ring of the lens.
This is something you will have learned in the lab. Facial nerve, cranial nerve 7, there's two branches, right? One branch of the facial nerve goes up to the pterygopalatine ganglion. And its postganglionic fibers innervate the lacrimal gland, the tear glands that wash tears over your eyes.
The other branch goes to the submandibular ganglion. And its postganglionic fibers then go to the submandibular salivary gland. Cranial nerve 9, the glossopharyngeal nerve, it targets the otic ganglion. and its postganglionic fibers innervate the parotid salivary gland. So there's, you know, part of our parasympathetic patterning.
We have cranial nerve outputs to terminal ganglia. So I would like you to know for each cranial nerve, which ganglion, or in the case of number 7, which ganglia it innervates. and what the target tissue is.
So you'd say glossopharyngeal nerve goes to the otoganglion and innervates the parotid salivary gland. So I would like you to have a handle on that, okay? If we look here at the fourth cranial nerve involved, that's the vagus nerve, cranial nerve 10. Now, Look at where cranial nerve 10 goes. It leaves the base of the brain. So this is on the side of the medulla oblongata, right about the level of the medullary olive.
Comes out and down and innervates the heart, the lungs, the esophagus and trachea, stomach, liver, spleen, pancreas, kidney, colon, small intestine. So the vagus nerve here travels from, or emerges from the brain, the base of the brain, and goes all the way down to the pelvic cavity. That's a pretty big nerve, right? Physically, it's the biggest nerve in your body, right?
And it parasympathetically innervates all of the soft tissues all the way down. And these are all intramural ganglia. intramural ganglia these are inside the organ now they're inside the organ intramural ganglia so for the cranial portion you've got the terminal ganglia up here plus the vagus nerve uh doing all of the rest now it's like what else is there well we have the pelvic cavity cranial sacral so off the sacral portion of the spinal cord we have three bundles of parasympathetic innervation leaving the spinal cord and these are the pelvic splanchnic nerves they pass through the hypogastric plexus here and we haven't talked about the plexuses but i will that that's coming up next and on to the sex organs in the bladder So, again, these are all intramural ganglia. right they're uh they're inside the walls of the various organ and tissues so there's your parasympathetic map okay so let's um look at a concept of the plexuses because you'll notice here look we got some things we're familiar with from lab cardiac plexus we didn't do pulmonary plexus in lab but we did the esophageal plexus okay So I'm going to show you a plexus map and talk to you about what these plexuses kind of physically are there for. And then we'll talk about how the sympathetic and parasympathetic systems interplay back and forth in the body.
So here are two diagrams showing pretty much the same thing. The diagram on the left here is a little more comprehensive because it shows both the thoracic and abdominal pelvic cavities separated by the diaphragm here. And if we take a look, what do we have here?
We have the spinal cord and vertebral column itself is not here, but we have the sympathetic chain. which travels left and right side of the spinal cord. And then what you see here is that basically if you were to put the heart, you know, back in right here, and maybe I'll draw a heart here, like there, see, there's your heart. If you put that back in, what you're going to notice is that if you follow the aortic arch and then follow the thoracic aorta through the diaphragm and the abdominal aorta, all the way down to the pelvic brim, and you break off into the common iliacs, into the internal and external iliacs, what you find is that all the way down, which is basically mirroring the spinal cord's passage with these organs, you find this nerve network. And let me get rid of this in here.
You have this nerve network in here of plexuses. to these mesh networks of nerves and those are called the plexus. There's one around the lungs, that's the pulmonary plexus. There's one around the aortic arch, the cardiac plexus, sometimes called the aortic plexus.
You have the esophageal plexus that you learned in lab. We have below the diaphragm, we even have, if you look, there's a celiac plexus. Here, there is a inferior mesenteric plexus.
There's going to be a superior mesenteric plexus. They don't show it here. There's a hypogastric plexus.
And I'm going to fill in here. Not only do you have a hypergastric plexus, you have a hypergastric ganglion. So these ganglia, the collateral ganglia for the sympathetic nervous system, are intimately associated with these plexuses.
If we look over here, it's a little more anatomically correct, so to speak, a little more detailed. Look at what happens as we pass through the diaphragm here. Look, we have the celiac ganglia, right?
Sometimes there's one, sometimes there's two, and then this is right next to the celiac trunk. That's where it gets its name from. Look, here we have a superior mesenteric ganglion, and then we have an inferior mesenteric ganglion here, for example, and then down in here we'd have a hypogastric ganglion.
All the way down through here we have plexuses that mirror the positions of these collateral ganglia and so what i want you to do is follow along with me as we go through the next couple of slides i want to show you the first the notion here of dual innervation with the autonomic nervous system and then once you understand that can begin to fully understand the nature of the plexuses. All right, so keep this, keep these maps in mind and we'll come back. All right, first let's look at a specific example and then we'll go to a more general map. What are we looking at here?
We're looking at the concept of dual innervation. Dual innervation. So when we look at these autonomic effectors in the body, smooth muscle, cardiac muscle, glands, and adipose tissue.
What we find is the vast majority of them, for example, the smooth muscle in the iris of the eye, the vast majority of them are dually innervated by both parasympathetic and sympathetic motor neurons. So there are efferent motor neurons to that same smooth muscle tissue from both divisions. That's dual innervation. So let's look what happens here. So here we have the iris of the eye.
We have the parasympathetic fibers from the oculomotor nerve, cranial nerve 3, going to the ciliary ganglion, synapsing, and a postganglionic neuron goes to the smooth muscle of the iris. Here we have the sympathetic side leaving the spinal cord. Entering the sympathetic chain, synapsing, and leaving the superior cervical ganglion, we have a postganglionic sympathetic nerve. Remember, sympathetic nerves go to the head and neck, and then we enter here the smooth muscle of the iris.
So we have motor neurons from both divisions in that same muscle. So look what happens. If we... innervate sympathetically, that causes the pupil to dilate. If we hit it with motor neuron action potentials from the parasympathetic side, causes the pupil to constrict.
So what we have here with dual innervation is typically, typically, typically the sympathetic and parasympathetic cause opposite actions in the same tissue. So they're almost like playing tug-of-war on the tissue that they're innervating, back and forth. Each one of them can cause an opposite effect.
within that tissue this is one specific example of dual innervation please don't pay attention yet to this idea of cholinergic stimulation versus adrenergic stimulation we're going to get there okay let's not let's not worry about the neurotransmitters at this point let's just concentrate on the general idea of dual innervation so what i want to do is i want to show you a larger map showing the concept of dual innervation across the body. And here is that diagram showing a wider relationship. And this is a really nice diagram because what do we got?
We got both divisions. This side is the sympathetic division. This side is the parasympathetic division.
This side is the thoracolumbar. Remember thoracic and lumbar vertebrae leading to the pre-gained glionic motor neurons. The parasympathetic is the craniosacral, cranial nerves and sacral nerves. Let me zoom in a little bit here and look here at the sympathetic.
We see a lot of things that we've been learning. So we've got, look up here, You've got preganglionic fibers. They're showing preganglionic and solid lines, postganglionic and dotted lines on this diagram. Preganglionics leave the spinal cord under the sympathetic chain and they leave as postganglionic fibers. These are sympathetic nerve fibers.
Postganglionic or gray matter, right? Going up to the head and thoracic viscerae, the heart, lungs, esophagus, trachea. So that's sympathetic innervation to the thoracic cavity, remember, above the diaphragm, head, and thoracic cavity. We had, that was pattern number two, remember?
We had pattern number three here, leaving the spinal cord passing through the chain. as myelinated preganglionic nerve bundles. We call these splanchnic nerves, abdominal splanchnic nerves, traveling to the collateral ganglia. Celiac ganglion, superior mesenteric ganglion, inferior mesenteric ganglion, hypogastric ganglion. So this diagram actually shows the hypogastric ganglion.
The postganglionic fibers then go to the tissues, go to their target organs. Abdominal splanchnic nerves, we have three of them. The greater splanchnic nerve, lesser splanchnic nerve, and lumbar splanchnic nerve. We even have those sacral splanchnic nerves that we talked about. On the previous diagram, they showed these as being postganglionic gray matter fibers, and I said that's not really true.
This diagram shows them as preganglionic fibers. That's not really true. the sacral splanchnic nerves are carrying both and they target the hypogastric ganglion and then off to the pelvic cavity so here's your sympathetic size like well what about pattern number one pattern number one going to the skin the piloerector muscles the sweat glands the skeletal muscle fibers That is one of the examples where those tissues don't have parasympathetic innervation. So pattern number one does not equal dual innervation.
This map in front of you is mostly about dual innervation. So they didn't show pattern number one. So we won't worry about it.
We look on the right side here. This is the parasympathetic side. Let's see what we got.
We got cranial nerve three going to the ciliary ganglion. Cranial nerve seven going to pterygopalatine and submandibular ganglia. And we have cranial nerve nine going to the otic ganglion.
These are your terminal ganglia. keeping in mind remember that the parasympathetic the preganglionic fibers are very long and the terminal ganglia are near or on the surface of their target tissues cranial nerve 10 here the vagus nerve look starts in the brain goes all the way down to the pelvic cavity and innervates all the soft tissues in between and then we have the pelvic splenic nerves as opposed to the sacral splanchnic nerves. The pelvic splanchnic nerves are parasympathetic. S2, S3, S4, and they target the pelvic cavity.
So each one of these tissues you see here is dually innervated, every one of them. And the only variant here is that adrenal medulla. Remember that?
That was pattern number four. It's a special case where it gets directly innervated. Now here's something to think about. We learned here, let's take a look at cranial nerve 10, coming down and it comes into the stomach wall.
So we learned that intramural ganglia in the parasympathetic system are inside the walls or inside the tissue of the organ you're innervating. Well, that looks a lot like the adrenal medulla pattern number four on the sympathetic side. You have a preganglionic myelinated fiber entering the walls of the organ before it synapses.
That's exactly what you see here. So pattern number four in the sympathetic system is really a parasympathetic pattern, physically anyways. So...
Look for commonalities there. Look for patterns. So this is dual innervation. And what we said before was that typically dual innervation causes opposite effects in the target tissue.
If you sympathetically stimulate the SA node of the heart, then the heart rate speeds up. If you parasympathetically innervate the SA node, the heart rate slows down. Doesn't have to be that pattern though. For example, if you sympathetically innervate the walls of the small intestine or really any portion of the GI tract.
parasympathetically innervate the GI tract, this speeds it up. If you sympathetically innervate it, it slows it down. So sometimes it's one speeds it up, the other slows it down, sometimes it's reversed.
But either way, they're going to have opposite effects. That's the idea of dual innervation. Now, what about these plexuses? Now that we can see kind of this physical relationship between sympathetic and parasympathetic dual innervation to a particular target organ.
Let's say we have a target organ. Okay, you know, pick an organ, any organ. And let's say that it is innervated. I'll use the same colors as we have over here.
Let's say there's a sympathetic innervation and a parasympathetic innervation. So P and S. So, dually innervated.
Kind of like what this diagram over here, this diagram on the left here, shows the one coming in from one side and one coming in from another. Well, that's ridiculous. They just draw it that way to help you visualize it. This is not how it's done, okay?
So, how do we do it? Well, let's figure this out. Let me get rid of that yellow X there.
All right, that's kind of a handy little eraser. Let me erase some more here. I need this eraser. There we go.
So let's start over. I got to fix my target organ. It has some issues there. Okay, let's start over.
So we have parasympathetic coming in from one side. We have sympathetic coming in from the other. I probably reversed those. It's okay.
What happens is they mix together first. in the plexus. And so in here, we have the plexus, right?
It's a physical mesh network of nerve fibers. And what happens is the sympathetic comes in from wherever it's going to come in from. Who knows where it came in from?
The parasympathetic is going to come in from wherever it came in from, right? It doesn't matter. But what's going to happen then? is that they are going to exit the plexus together and travel to their target tissue together.
So it doesn't matter where they came in from, they're going to end up traveling together to reach their target organ. Okay, that's the idea of these plexuses. They can enter from any any angle, any any, you know, up or down, you know, position, doesn't matter.
they're going to meet up with their dual innervation buddies and they're going to travel together to the target organ this allows you to kind of coalesce the different fibers together right and there's a there's one more aspect to this but i'll wait to discuss it until we can talk about alpha and beta receptors later on The last thing to talk about on this diagram, I'll put it down here just to put it down in writing, is a concept called sympathetic activation. When we look at, you know, look at all these tissues that are innervated by both sides, the dual innervated tissues. If we look at the tissue sets, the organs and such, that are upregulated by the sympathetic division, that are activated by the sympathetic division, that are when the sympathetic division fires its action potentials, it speeds up or otherwise elevates the metabolic activities of those tissues. What do we look for?
for here let me make a little list here for us so tissues that have their metabolic activities elevated by sympathetic innovation. This would be cardiovascular, musculoskeletal, respiratory. All right, we'll just take those three.
That's a big set of stuff. So cardiovascular, heart rate, cardiac output. the vasodilation or constriction of blood vessels, musculoskeletal, your skeletal muscles, respiratory, your breathing rate. These have their metabolic activities elevated by sympathetic innervation. So when we talk about sympathetic activation here, that's a different thing.
Let me do this. Sympathetic activation. All right, this is a situation that we call the fight or flight response. So sympathetic activation means that you completely and utterly activate and elevate the metabolic output of these systems, cardiovascular, musculoskeletal, respiratory. Why and when do you do this?
You do this when you are in danger. That's the fight or flight response. When you are faced with imminent danger, your body does this. It does sympathetic activation.
And what that means is, if you look up here, this side takes over. We sympathetically take charge of the body. There's two ways to do this.
One is just what we saw down here. We activate these tissues. The second thing that happens is that the sympathetic division shuts down the parasympathetic neurons, takes them out of the game, says, get out of our way.
We have a life to save here. Once we're done fighting or fleeing, you can get back in the game. So what we do here is in these plexuses, in this, I'm going to show you later how these sympathetic neurons, because they're traveling together with the parasympathetic neurons, they can inhibit the parasympathetic neurons at will.
So that's actually kind of neat. So basically the sympathetic. Division of the autonomic nervous system takes over your body and puts all of your biochemical and metabolic dice on the table with these systems so that you can escape or overcome this imminent danger to yourself.
Okay, that's the fight or flight response. We call it sympathetic activation. And it's a misnomer because part of it is activating the sympathetic, but part of it is shutting down the parasympathetic. And I'll show you how we do that when we talk about receptor types. So keep an eye out for that later.
Here's a diagram for us. This is a little bit off topic, I guess, from what we've just been doing. But this is kind of where they put it in the chapter. And this is an important little side conversation.
In chapter 13, we learned about reflexes, but they were spinal reflexes. And this map should look familiar, right? What do we got?
We have a sensory neuron coming in the dorsal root. There's a dorsal root ganglion with a sensory cell neuron body. And comes into the dorsal gray horn. Here, look, we're synapsing with an interneuron, right? They don't say whether it's inhibitory or excitatory, but, you know, you're synapsing with an interneuron.
And then we have a motor neuron leaving the spinal cord and going back out. All right. So that should look familiar. I mean, you've gotten some practice reading these reflex arcs.
So we have reflexes in the autonomic nervous system, too. We have reflexes that are sympathetic reflexes and parasympathetic reflexes. But we have some different rules now because we have some different options. What you're used to thinking about with spinal reflexes are in the autonomic nervous system, what we are going to call long reflexes.
And a long reflex means we go all the way back to the spinal cord. We go all the way back to the spinal cord. So watch what happens. We have a sensory neuron.
It goes all the way back to the spinal cord. Hooks up with an inner neuron, and then now we have an outgoing motor neuron. Well, this is a preganglionic neuron. Come on, we're in the autonomic nervous system. This is going to leave the spinal cord and go to a ganglion.
Could be sympathetic, could be parasympathetic, doesn't matter, right? If it's parasympathetic, it's going to be leaving on the ventral. A grey horn, if it's sympathetic, it'll be coming off the lateral, but that's the only big deal. It's going to go to a ganglion. Then we have a synapse with a postganglionic neuron.
It's going to go to the effector organ. There's your reflex. Now, with a long reflex, you might have an inner neuron here, so you've got a synapse and a synapse, but you're always going to have a synapse and a ganglion because that's how it works. and then you go back out.
That's a long reflex. We have short reflexes though. This is important. In the autonomic nervous system, we could have a sensory neuron that doesn't go back to the spinal cord. It goes to the ganglion.
It bypasses the central nervous system altogether, synapses maybe with an inner neuron in the ganglion maybe not but then goes right back out to the effector organ this is a much shorter loop and it's going to be faster long reflexes go all the way back to the spinal cord and out short reflexes they only go to the ganglion and back right so they only go to the ganglion they only go to the ganglion so that's an important aspect we see this in the digestive system so this is part and parcel of local control of activities in the digestive system so when for example food enters a portion of the gi tract and expands the walls that expansion is detected kicks in short reflexes through the myenteric or submucosal plexus inside the gi tract wall and if they're parasympathetic ganglia intramural ganglion there they go through that ganglion back out as opposed to long reflexes like gastro ileal and gastrocolic reflexes those are long reflexes And then if you take a look at the diagrams for the micturition reflex or the defecation reflex, they talk about short reflexes and long reflexes there too. Those are autonomic reflexes. So it's a fairly important little point to be made that not all reflexes go through the spinal cord. When we look at how, especially in the sympathetic...
nervous you know the division how we do synapsing with the target tissues is very different from what you've learned from a synapse before so I'm gonna get my little pencil out here and get me something to draw with here and what I want us to look at are these little nodules here and these are called sympathetic varicosities And they show a smooth muscle bundle as a target tissue. And if you take a look at a couple of these sympathetic varicosities here, what you see is this region right here represents, for all practical purposes, the synaptic terminal, where you have vesicles containing neurotransmitter. that upon exponential stimulation are going to release neurotransmitter into a synaptic cleft. Well, what you've got with this down here...
These chains, we get a better color than this, these chains of varicosities, as an action potential comes down the axon of the postganglionic fiber, and it hits all of these varicosities and cascades through them. If we look up here, each one of them is going to then release neurotransmitter. from synaptic vesicles.
So you're going to have the neurotransmitter being released all over the surface of these target tissue cells all at once. And so it's a much more distributed release of neurotransmitter all across the surfaces of those target cells instead of at one specific spot. So this is a little bit of a different way to think about how a synapse works.