Sympathetic Nervous System - Video Tutorials & Practice Problems

Function of the Sympathetic Nervous System

In this video, we're going to be talking about the function of our sympathetic nervous system. So I'll be going over some of the effects that it has on our body. And I'll talk about how those effects may be helpful for us in a potential fight or flight situation. So as a reminder, this division becomes activated when we are engaged in physical activity or have to perform under some kind of stress or threat. So one major effect that we're going to see is an increase in heart rate and that of course will also increase blood pressure, that's going to have blood pumping faster through our body, delivering oxygen to our muscles much faster. We're also going to see a dilation of the bronchioles in the lungs which will increase airflow and increase oxygen intake. Our liver is going to begin releasing glucose into the blood and that will act as an energy source for our muscles. Should they need it? One kind of weird effect that we see is that um we're gonna see a contraction of the rector pilly muscles which are tiny muscles around your hair follicle. And when they contract, we get goose bumps. And if you're wondering like, why do we need goose bumps if we're under threat? The answer is we don't, but our evolutionary ancestors probably did. So we think it's just left over from evolution. So, you know how, like when a dog or a cat becomes threatened, they kind of puff up their fur to look bigger and scarier. We think that that's basically what this was. So, you know, way down the line, we had an ancestor that was covered in hair and they could kind of puff up to look scary when they were threatened. And over time we lost the hair, but we did not lose those goose bumps. So, kind of a fun fact. Right. All right. So next, we're gonna see a decrease in gastrointestinal activity. So that is considered a non-essential function when we're in kind of a stressful or threatening situation. So that gets kind of put on hold regarding our blood vessels. We're going to see a vasoconstriction in visceral vessels. So, vessels going to the stomach or intestines, that's all gonna get less blood flow. And we're gonna see vasodilation to our skeletal muscles. So those skeletal muscles are going to get more blood flow, more oxygen delivery, more nutrients, more glucose um to help them perform under stress, we're gonna have our pupils dilate, which will of course, allow more light to enter our eye and allow us to potentially scan our environment for threats. And then finally, we're going to have a stimulation of the sweat glands, everyone's favorite stress response rate. Um We think that this probably happens because many of these processes, for example, an increased heart rate do increase your body temperature. And so this kind of helps, of course cool you down. Um So not very fun, but it does have its purpose as all of these do. Um All right. So that is the function of our sympathetic nervous system and I will see you guys in our next video. Bye bye.

Sympathetic Nervous System Example 1

Ok. So for this one, we're looking at why does the sympathetic nervous system shunt blood to skeletal muscles? What is the purpose of that? And so thinking about it conceptually when we're shunting blood to skeletal muscles, what we're doing is delivering them oxygen, right? We're delivering oxygen and nutrients like glucose and those are going to help sustain our muscles if they have to engage in intense physical activity. So looking at our answer choices, it looks like b aligns the best with that. So to prepare the body for that intense physical activity by delivering oxygen and glucose and nutrients to our skeletal muscles, looking at these other choices here, I see a is to conserve energy, but that's not really what's happening here, right? Shunting blood to those skeletal muscles is a very effortful activity. We're delivering oxygen, we're delivering glucose, that's not conserving energy, right? And then c is to facilitate digestion and nutrient absorption, but that's the opposite of what's happening here, right? We are shunting blood away from our digestive system and putting that function on hold in order to deliver all of that oxygen and nutrients to our skeletal muscles. So C is of course not happening. And then D would be incorrect based on, you know, A and C being incorrect as well. So our answer here is B to prepare the body for intense physical activity and there you go.

Why does the sympathetic nervous system cause decreased activity in the digestive tract?

• A. Sympathetic activation stimulates the release of digestive hormones.
• B. Sympathetic activation reduces the sensitivity of the digestive tract.
• C. During sympathetic activation, energy is required elsewhere in the body for more 'essential' functions.
• D. The sympathetic nervous system does not innervate the digestive tract.

Which of the following statements is true?

• A. The sympathetic nervous system increases secretion from digestive glands.
• B. The parasympathetic system causes us to get goosebumps.
• C. Sympathetic tone controls the heart rate when we are at rest.
• D. None of the above are true.

Sympathetic Nervous System Example 2

OK. So in the sympathetic nervous system, a ganglion is a place where what happens. So let's kind of think back to our train metaphor really quick. So imagine we have this kind of central track that's our spinal cord and that's where all of our trains originate from. And our trains are our neural impulses, right? And then in this metaphor, our ganglia act kind of like train stations. So if you have to, for example, change trains or catch a connector train that's going to happen in these ganglia and these like train stations. So I'm thinking about this more anatomical, we would have an impulse originate in our spinal cord and it's going to travel on a fiber right into that ganglia and then it's going to change trains or synapse there, right? So that impulse is now going to be carried by a different fiber. So here you can see ganglion are places where neurons can synapse with each other, which is also answer choice. C looking at these other ones quickly a reads, this is where impulses originate and that's not true. They're going to be originating in our spinal cord, right? And then B says that this is where impulses are integrated but integrated is not really an accurate word to talk about neural impulses integration implies some kind of like change or bringing different parts together. And that's not really how impulses work, right? They either stop or they continue. It's kind of simple. And then D reads where efferent fibers move fastest through the wording. There is tricky but efferent fibers don't actually move right impulses move through them. Um So that one would be incorrect. And our answer here is C this is a location where neurons can sit out. There you go.

Structure of the Sympathetic Nervous System

Now that we have that analogy in our tool belt, let's go through the structure of our sympathetic nervous system. So we're gonna be starting with our spinal cord, that kind of central terminal where all of our fibers originate from. And more specifically, our fibers will be arising from between spinal cord segments. T one through L two. That's why this is sometimes also called Ar Thora Columba division. And to help myself, remember T one through L two, I like to think of the phrase Lethal Tigers Lurking and I like that phrase because it has one word that starts with tt 12 words that start with LL two and a lethal tiger lurking is basically guaranteed to turn on your fight or flight response. So think of those lethal tigers lurking. Now, as I mentioned in that previous video, we're going to be working with a structure called the sympathetic trunk. And this is that kind of that parallel track that runs parallel to our spinal cord. And this structure is a bundle of nerve fibers that flanks both sides of the vertebral column. So it's technically one structure but it runs bilaterally. So you have one trunk on the left and one trunk on the right. And you may hear this referred to as the sympathetic chain or the ganglionic chain. So those all mean the same thing it's called that because it actually looks kind of like a chain of beads where each individual bead is a sympathetic trunk ganglion. So if we jump down to our image here, you can see on the left, we have a slightly more abstract image where we can see that vertebral column laid out very nicely. And you can see how we're working with nerve fibers that arise between spinal cord segments, T one through L two. There, we have these purple and green fibers. I'll explain that color coding in a moment and then running parallel to our spinal cord, we have that sympathetic trunk. And so each of these circles or beads is going to be a ganglia. And you can see how some of them have our little synapse symbol inside that triangle with the circle. So we're going to see some synapses happening within that structure. And we have here some of the major effectors of this division, those kind of ultimate destinations of our nerve impulses. And then here on the right, we have this more anatomical image. So you can see we have our spinal cord there and then flanking either side of the vertebral column, we have our sympathetic trunk. And then you can see how within that sympathetic trunk we have these kind of like bulbous oval structures, those are going to be our beads or our ganglia. So each of those is a ganglion. All right. So that's kind of what we're working with so far. Now, remember how I mentioned how every nerve impulse has to like change trains or synapse one time. And so every nerve impulse will go through two neurons. And that's a very unique feature of our autonomic nervous system. So we're going to be calling those two neurons, the preganglionic fiber and the postganglionic fiber. And the term fiber here is just referring specifically to their axons. And you can see how we have preganglionic here in purple and post ganglionic is highlighted in green and we're going to keep that convention consistent throughout the rest of this chapter, both in text and in images. So just keep that in mind. Now, what we often see in this division is that our preganglionic fibers tend to be short and our post ganglionic fibers are often long and I'll explain that whole short and long thing in just one second coming up, but just to kind of reorient you to our image here, you can see we have these preganglionic fibers and preganglionic literally means pre ganglia or before the ganglia or before the synapse is is a different way of thinking about that. So we have our preganglionic fiber before the ganglia and then our postganglionic fiber comes post ganglia or after the ganglia after that synapse. All right. So that is kind of what we're working with there. Now, we have two more structures to cover in this video. We're going to be talking about our white Ramus communic cans and our gray Ramus communic cans. And before I go over the definitions here, I'm going to jump down to our image and kind of show you where they are. So looking at our anatomical image, you can see we have our white ramus here and it's literally white because it's myelinated. And then we have our gray ramus here. And I bet you could already guess that this one is not myelinated. So another nice easy naming convention for you. Now, what we're looking at here. Um So the structure here, the structure here, those are our spinal nerves. And you guys remember spinal nerves, those are of course nerves that originate from our spinal cord and they run from our spinal cord out to our effectors, whether those are organs or glands or whatever they are. And so these nerves are going to be basically bundles of axons or fibers. Um They can be hundreds of axons all bundled together and encapsulated in a sheath. So that is our spinal nerve there. And then we have our sympathetic trunk here and you can see how the white and gray um Rey basically connect these two structures. So I'm gonna be talking a lot about these preganglionic and post ganglionic fibers in this chapter. But please keep in mind that whenever I'm talking about these fibers, they're going to be encapsulated in something. So they'll be encapsulated in a spinal nerve, encapsulated in the white and gray ramus encapsulated in that trunk. So they're always inside of something. So I like to think of the spinal nerves, the white and gray Ramy as kind of like tunnels that are um fibers actually travel through. So kind of keep that in the back of your head as we go through the rest of our chapter here. So what we see is that our white Ramus communic cans is going to carry our preganglionic fiber from our spinal nerve to our sympathetic ganglia. And then our gray ramus communic cans is going to carry our postganglionic fiber from our ganglia back out to our spinal nerves. So they kind of make like like a little loop, de loop almost. And I know that it's a very wordy definition here. So I'm gonna actually draw it out for you. So I'm gonna draw it using um purple for our preganglionic fiber and green for our postganglionic fiber. So if we're looking here, we're gonna have our, our purple preganglionic fiber start from our spinal cord and run through our spinal nerve and then it's going to go through the white ramus and then we'll have that axon terminal there within that sympathetic ganglia. And then our post ganglionic neuron is gonna have its cell body actually in that ganglia. So we're going to have the cell body and the dendrite there. And that's how we have that synapse. And then the post ganglionic fiber or the axon of that neuron is going to come out through our gray ramus and enter that spinal nerve. And then that spinal nerve will carry it all the way out to its effector organ. Let's just say it's the heart in this example. And then looking at that, you can see how this preganglionic fiber is going to be pretty short, right? Because it only has to go from our spinal cord to that sympathetic trunk and those structures are very close together. So that's why those fibers are often short. And then this post ganglionic fiber has to go all the way from the trunk, way out to its effector. So that's why those fibers tend to be very long. And if you're looking over at this image and you're like Hannah, some of those purple ones are looking a little long and some of those green ones are kind of short. You are totally on the right track. There is an exception to this and we're going to cover that in an upcoming video. So stick around. So that is kind of the basics of the structure of our sympathetic division. And I will see you guys in our upcoming videos to discuss some of this in a bit more detail. So I'll see you there.

Sympathetic Nervous System Example 3

OK. So which of the following most accurately describes the pathway for an impulse in the sympathetic nervous system. So let's just kind of draw it out before we're looking over these answer choices. So we're gonna start with a spinal cord, we're gonna draw the sympathetic trunk with the sympathetic trunk, ganglia and then we'll draw an effector organ, we'll just make it the heart to be fun. All right. So we're gonna have our impulse start in our spinal cord. That is where our impulses originate and then it's gonna travel on a fiber to the ganglia. Now, that is our preganglionic fiber, right? Because it comes before the ganglia and then that impulse can hitch a ride on this post ganglionic fiber right post because it comes after that ganglia. And that was where or that is what will deliver that impulse to our effector organ. So looking here, we are starting in the spinal cord, we are then traveling through that preganglionic fiber. We're going to go to that ganglion, either passing through it or synapses through it or synapses in it like we have here and then we're going to be traveling on that post ganglionic fiber and then we'll get to that effect or organ. So looking at the answer choices, it looks like b um aligns with that perfectly. So our answer here is going to be B and there you go.

Why are many preganglionic fibers in the sympathetic nervous system short?

• A. Many preganglionic fibers in the sympathetic division synapse at the sympathetic trunk, which is close to the spinal cord.
• B. Many preganglionic fibers cannot carry signals long distances.
• C. Preganglionic fibers carry norepinephrine, which gets diminished over long distances.
• D. None of the above are true.

Efferent neurons in the sympathetic nervous system will always arise in the __________________. Then, they will pass through the sympathetic ____________, where they will either synapse with another neuron, or continue towards the effector and synapse later on.

• A. Spinal cord, trunk.
• B. Spinal cord, fiber.
• C. Trunk, fiber.
• D. Spinal cord, communicans.

Pathways of Sympathetic Innervation

In this video, we're going to be talking about the different pathways of sympathetic innervation. So in our sympathetic division, a preganglionic fiber can synapse with a postganglionic fiber in one of three ways. So first, it can synapse in a trunk ganglion at the same level. And I'll show you what I mean by same level in just one second. So we're going to follow along with this blue fiber here, I'm gonna highlight it in a nice dark gray as we talk about it. So our preganglionic fiber is going to start in the spinal cord and it's going to travel through the spinal nerve like this, it's going to enter the trunk through the white ramus. And then in that same level that it entered it, it's going to synapse with a post ganglionic fiber. And then that postganglionic fiber will leave through the gray ramus, travel through the spinal nerve and head out to its effector organ. So the preganglionic fiber will enter at that level and then synapse at that same level. That's what I mean by the same level, right? So that's the first method pretty straightforward. What we can also have is that the preganglionic fiber and post ganglionic fiber will synapse in a trunk ganglion at a lower level or at a higher level. So, following along with this red nerve fiber, now we're again going to start in the spinal cord with that preganglionic fiber. It's going to travel through the spinal nerve, enter the trunk through the white ramus. But now it's going to travel down to a lower level trunk ganglion. And that is where we're gonna have that synapse. And then that post ganglionic fiber will exit through that gray ramus, travel through the spinal nerve and head out to the effector. So basically that preganglionic fiber will either travel up or it's going to travel down before synapses in a lower or higher level ganglion. That's that second one. So the 1st and 2nd are pretty similar. We're just talking if they're gonna be synapses at the same or a lower or higher level. The third one is quite different. So for this third one, what's gonna be happening is our preganglionic fiber is going to pass through our sympathetic trunk without ever synapses. So it's gonna pass through the trunk and instead it's gonna synapse in what's called a collateral ganglion. So that's what we have depicted right there. So following along with this purple fiber, our preganglionic fiber again will start in the spinal cord. Like always, it's gonna travel through that spinal nerve, enter the trunk, through the white ramus. So that's always the same, it's gonna travel right on through that separate a trunk, never stopping, never synapses and head all the way out to this collateral ganglion, which will or ganglion which will be closer to the effector organ and then it's going to synapse right in there. And then from there, our post ganglionic fiber will head out to the affect. So that one is quite different. And when this happens, the preganglionic fiber is actually called a splenic nerve. And that is going to be the topic of our next video. So I hope to see you there. Bye bye.

Sympathetic Nervous System Example 4

All right. So this one's asking us which of the following statements about pathways of sympathetic innovation is false. So we're gonna kind of run through these and draw them as we go just to kind of help us visualize it. So we're gonna draw a spinal cord over here. We'll draw our sympathetic trunk with our ganglia over here. So it's not gonna be anatomically accurate and just gonna kind of visualize what we're talking about and I'll draw a collateral ganglion over there as well in case we need it later. All right. So a reads a preganglionic and post ganglionic neuron can synapse in trunk ganglion at the same level. So that would look like this. We'd have our impulse happen in that spinal cord, preganglionic fiber going to the same level of the sympathetic trunk and then a synapse happening right there in that same level. And that's totally possible, right? So A is true and A can stay B reads a preganglionic and post ganglionic neuron can synapse in trunk ganglion at a higher level. So that would look like this. We have our impulse start in the spinal cord, our pre ganglionic fiber going to that sympathetic trunk and then traveling up to a higher ganglia, it could also go lower, right and then synapses and then that uh postganglionic fiber would extend out. And that is also possible. So B is true B can stay C reads a preganglionic and post ganglionic neuron can synapse in the ventral horn of the spinal cord. And no, it's not looking so good, right? Just think about how these fibers are named, right? Preganglionic and postganglionic for them to synapse in the spinal cord, they would both have to exist over here in that preganglionic space. So that doesn't make any sense. Huh? So our answer is indeed going to be CC is false. That cannot happen. All right, just to kind of finish out the example here D reads a preganglionic and post ganglionic neuron can synapse in a collateral ganglion and that can also happen, right? So our impulse would start in the spinal cord that preganglionic fiber would travel through the sympathetic trunk to a collateral ganglia. And our synapse would take place there, right? So our answer here is going to be C is false. These neurons cannot synapse in the spinal cord and there you go.

A preganglionic fiber arriving at the sympathetic trunk could do any of the following EXCEPT:

• A. Synapsing with a postganglionic fiber at the same level of the sympathetic trunk.
• B. Synapsing with a postganglionic fiber at a different level of the sympathetic trunk.
• C. Pass through the sympathetic trunk without synapsing.
• D. Synapse with a parasympathetic fiber at the same level of the sympathetic trunk.

Splanchnic Nerves and the Adrenal Medulla

We're gonna finish up this section by talking about those flank nick nerves as well as the adrenal medulla. So as we talked about in our sympathetic division, the preganglionic fibers arise from spinal cord segments, T one through L two. What we find is that from T five down, the majority of those preganglionic fibers are going to be these splanchnic nerves, which are nerves that synapse in a collateral ganglion rather than in that trunk. So these collateral ganglion are just ganglia that are further out closer to the effector organs. So these um nerves basically bypass the sympathetic trunk. So they pass through it without ever synapses and instead they synapse in these collateral ganglia. Now, these nerves mainly innervate um the visceral structures of our abdomen. So things like our stomach, our intestines, our liver, our spleen. And what we find with these nerves is that the preganglionic fibers tend to be long and the post ganglionic fibers tend to be short. So it's the opposite pattern that we saw in the fibers above teeth. So if we look down here, we have our um our spinal cord again, we're working from T five and down with these flank neck nerves. And you can see how these purple preganglionic fibers now have to extend all the way from the spinal cord, all the way out to these collateral ganglia, which we have depicted here is these yellow balls and then they will synapse in those ganglia. And then these now relatively shorter um post ganglionic fibers just go from the collateral ganglia out to the effector. OK. So that is what that looks like. And again, it's that opposite pattern from what we saw above T five. Now, next, we're gonna kind of switch gears and just talk about the adrenal medulla, which is a very important structure for our sympathetic division. Now, to understand why this is so important, we have to recall something called dual innervation. And so we've been talking about how our sympathetic nervous system obviously innervates all of these organs. But what we haven't talked about in detail is how most organs are actually innervated by both the sympathetic and parasympathetic divisions. And that is called dual innervation. But there are exceptions to that. And one of those exceptions is the adrenal medulla, which is only innervated by our sympathetic nervous system. And for a very good reason. So the adrenal medulla when it gets stimulated, um secretes epinephrine and norepinephrine, which are also known as adrenaline and noradrenaline. And as I'm sure you can imagine, those are very important for that fight or flight response to kick in and get your body really going. And so that's why this structure is only innervated by our sympathetic nervous system. That parasympathetic division does not want any extra epinephrine or norepinephrine kicking around in your body, right? That's not gonna help you rest and digest. So this is very much a sympathetic structure. So the adrenal medulla is located um in the adrenal gland, which is located right on top of the kidney, kind of like a little hat on top of the kidney. And what's really cool about this structure is that it can actually be considered a modified sympathetic ganglion. So if we look down here at our image, we have our adrenal medulla right here and you can see that the way that it's innervated, this is just a preganglionic fiber going all the way to this structure. And that's because the um the synapses is actually going to happen within that adrenal medulla. Again, it's acting kind of like a modern side gang Leon itself. Um So it is very unique in that way as well, but again, very important for this division because it's gonna be releasing that epinephrine and norepinephrine, which are essential for that fight or flight response. All right. So that was our sympathetic nervous system. Thanks for sticking around and I'll see you guys in the next one. Bye bye.

Sympathetic Nervous System Example 5

OK. So collateral ganglia contain which type of cell bodies. And looking here, we have a combination of preganglionic, postganglionic, parasympathetic and sympathetic. Now, we can very easily eliminate A and B because we're talking about the sympathetic division here, right? And we'll get to this in an upcoming video, but the parasympathetic division does not use collateral ganglia, it uses something called terminal ganglia. Um So a little sneak peek for you there. So A and B are out and we're left with C and D. So thinking about this kind of conceptually if we have our spinal cord, we have a collateral ganglia say, you know, it's way out here kind of close to the effector organ. Let's just say that it's the heart, for example. All right. So we're gonna have our impulse originate here in the spinal cord. So that is the cell body of our preganglionic fiber, right, where that impulse is being generated and it's going to come into our collateral ganglia and synapse, which means that that message is being received by the dendrites of the post ganglionic neuron inside of this collateral ganglia. So that is where the cell body of our post ganglionic fiber is. So looking at our answer choices, it looks like d would be correct. Our collateral ganglia contain the cell bodies of our post ganglionic fibers in our sympathetic division. And there you go.

Which of the following structures would not be innervated by splanchnic nerves?

• A. Liver.
• B. Spleen.
• C. Heart.
• D. Adrenal Medulla.