Organization of the Nervous System: Study with Video Lessons, Practice Problems & Examples

The Nervous System

This video, we're going to be talking about the nervous system. So the nervous system is a complex network of neurons that conveys electrochemical information throughout the body and it has two divisions. First is the central nervous system, also known as the CNS, and then there's the peripheral nervous system, also known as the PNS for short. You can see the central nervous system is depicted in this image in blue and it is composed of the brain and spinal cord and this essentially functions as like a control center for the human body. You can think of it as like a literal headquarters up there.

Every single thought that you have, every emotion that you experience, memories, sensation, perceptions, motor commands, all of that is coming from your central nervous system. Now, we also have the peripheral nervous system and this is composed of nerves that are outside of or peripheral to the brain and spinal cord. Basically, parts of the nervous system that are outside of the CNS would be the PNS. The purpose of the PNS is essentially to connect the body to the brain and it is essential for both sensation and movement. You can see all these little purple nerves here in this image.

They're running down our arms into our hands, throughout our entire body, down our legs into our feet, and we're going to have sensory nerves that will basically convey sensory information up to our CNS basically saying, hey, there's some pain or pressure or whatever happening, and then your CNS can send a motor signal or a movement signal down the motor nerves of your arms and legs and say, hey. Let's pick up our foot. Let's move our hand, etc. So they kind of work together in that way. Now the central nervous system just is what it is, brain and spinal cord.

But the peripheral nervous system actually has several subdivisions, and we're going to talk about those in our next concept video. So I will see you there.

Organization of the Nervous System Example 1

Okay. So for this example, we're going to be filling out this Venn diagram, basically saying if these statements describe the CNS, the PNS, or both. So, for our first one, it says that it is composed of nerves outside the brain, so that would be our peripheral nervous system, which is composed of nerves that are outside of or peripheral to the brain and spinal cord. We'll put an a over here. Our next statement is acts as a control center for most functions, and that is going to be our central nervous system, which is central to our functioning, basically acting as a command center for everything that you do, feel, and think in your body.

Alright. The next one is uses electrochemical signals to communicate, and that is true of the nervous system broadly. So both the CNS and PNS use electrochemical signals in their communication. So we're going to put c under both, and then finally our last one is includes the spinal cord, and that is going to be our central nervous system which is comprised of both the brain and the spinal cord. Alright, I will see you guys in our next one.

Bye bye!

True or False: If false, choose the answer that best corrects the statement.

The peripheral nervous system is comprised of nerves outside the brain and the spinal cord.

• A. True.
• B. False; the peripheral nervous system includes nerves, the spinal cord, and the brain.
• C. False; the peripheral nervous system includes the brain and the spinal cord.
• D. False; the peripheral nervous system is a system of organs and muscles that coordinate with the brain.

Subdivisions of the PNS

Alright. So, the peripheral nervous system, or the PNS, can be divided into two major subsystems. First, over here in green, we have the somatic nervous system. The somatic nervous system controls voluntary movement and it does this by primarily innervating or connecting to skeletal muscles, which are just literally the muscles around your skeleton. So any kind of voluntary movement, like things that you're conscious of.

So, you know, I was writing a word just then. If I was to stir a pot of soup, pick up my dog, kick a ball, all of those things would be controlled by my somatic nervous system. Those are all voluntary movements that I am consciously enacting. Now, over here in purple we have the autonomic nervous system and the autonomic nervous system essentially does the opposite and it controls involuntary movements.

So things that you have no conscious awareness of, things that you have no voluntary control over. This nervous system primarily innervates things like organs, like the heart and lungs, as well as glands and blood vessels. It can tell your blood vessels to constrict or dilate, it can tell glands to release hormones, and it can tell your heart to, you know, pump faster or whatever. So, any kind of function that you have no voluntary control over is going to be controlled by your autonomic nervous system. Now, I always remember this because autonomic sounds a lot like automatic and it basically controls all of the automatic functions in your body.

Now, the somatic nervous system does not get divided any further; it just is what it is, but the autonomic nervous system actually has two subdivisions of its own and we're going to talk about those in our next concept video so I will see you there. Bye bye.

Organization of the Nervous System Example 2

Okay. In this example, we're going to read through these scenarios and decide which subdivision of the PNS seems to be in use. So we'll write an s for the somatic nervous system and an a for the autonomic nervous system. Alright. So a reads, "Your heart rate increases after walking up a flight of stairs while your heart is an organ and that is something that you have no voluntary control over, right?"

And so we're going to put an a, that would be your autonomic nervous system. b is "Your biceps contract to pick up your dog." Picking up your dog is a voluntary movement that involves skeletal muscle so we're going to put an s for somatic. c is "Your calf muscles contract to jump over a puddle." Jumping also involves that skeletal muscle, right?

That's probably going to be a voluntary action so we'll put an s there. d is "Salivary glands contract at the smell of fresh cookies." Glands are not something that we have voluntary control over so that would be our autonomic nervous system, and then finally e is "Your pupils dilate when walking into a bright room," and that is again something we have no voluntary control over so that would be our autonomic nervous system. And there you go.

Which of the following statements is true about the autonomic nervous system?

I) It is a division of the central nervous system.

II) It primarily innervates organs, glands, and vessels.

III) It controls involuntary movement.

• A. I & II only.
• B. I & III only.
• C. II & III only.
• D. I, II, & III.

Subdivisions of the Autonomic Nervous System

Okay, so the autonomic nervous system is further organized into two divisions and remember the autonomic nervous system handles those automatic functions though these two divisions are also going to be handling automatic things that we have no voluntary control over. So, these are the sympathetic and parasympathetic divisions of the ANS, also known as the sympathetic nervous system and the parasympathetic nervous system. What's cool about these is that they can actually become more active or more dominant depending on your environment and what's happening to you and how you are thinking and feeling about what is happening to you. Your sympathetic division is actually going to become more activated or more dominant when you are engaged with a stimulus, when you are threatened, or when you are stressed, and this is essentially your fight or flight response. Okay, so we'll talk about some of the specific effects that it can have on your body in a moment but I'm sure you're all familiar with that kind of fight or flight response, that rush of energy that you get, the tension in your muscles when you're really stressed or scared of something, that is basically your sympathetic division becoming activated.

And I do want to be clear that while this certainly would become activated in, like, a life or death situation, anything that makes you feel threatened or scared or stressed will activate this. So this could be like a biology test. It could be giving a big presentation in front of your entire lecture, you know, whatever it may be. So anything that makes you scared, stressed, or really engages you is going to activate that sympathetic division. Now, in contrast, we have the parasympathetic division, and this becomes more activated when we are relaxed and at rest.

And in contrast to the term fight or flight, this is sometimes known as, like, your rest and digest system. So, you know, if you just ate a really large meal and you're sitting down and relaxing watching some TV, this nervous system would become more active or more dominant, kind of giving you time to just return to homeostasis, getting that food moving through you, and just getting everything back to where it should be. What's cool about these divisions is that they connect to or innervate many of the same organs. So they both innervate the heart, the lungs, the eyes, etcetera. However, they usually have opposite effects on those organs.

So, this is sometimes known as having antagonistic effects, but basically what this means is that they really can't both be active at the same time because they're having opposite effects and that just really wouldn't work. So basically if one is active, the other is going to be more suppressed and vice versa. So, to give you some specific examples of effects that they can have on your body, let’s say I am being chased by a tiger. I am in full fight or flight mode. My sympathetic division is active, what's it going to do, right?

Well, if I am running really fast, I need blood pumping through my body, right? And so it's going to increase my heart rate, kind of, you know, really boost that, get blood flowing. If I'm running, I need oxygen. Right? And so this division is going to dilate the bronchioles of my lungs.

Okay, get more oxygen in my body. So we've got blood pumping, oxygen coming in. In terms of my gastrointestinal tract, that's not important right now. Right?

I am running for my life. I don’t have to be digesting food. So, that division is actually going to decrease activity in my gut temporarily, and if I'm running really fast, I need to be able to see really well. I need to be able to scan for predators. So it’s going to dilate the pupils of my eyes, let more light in, and make my vision a little bit sharper.

So those are all things that my sympathetic division would do to help me stay alive when I'm under threat. Now again, the parasympathetic division is basically going to have the opposite heart rate. Right? We're just relaxing. We don’t need our heart pumping.

We've got, well, it needs to be pumping just not super fast. Right? We're going to be constricting the bronchioles. We don’t have to be taking in a ton of extra oxygen right now. Again, this is our rest and digest system, so it’s going to increase the activity of our gastrointestinal tract, get food moving through us, and it’s going to constrict the pupils.

We don’t have to be taking in any, like, extra light into our eye. Our vision doesn't have to be particularly sharp in that moment. Right? So those are just some examples of effects on the body that these different nervous systems can have. Alright.

So those are the two divisions of the autonomic nervous system, and I will see you guys in our next video. Bye-bye.

Organization of the Nervous System Example 3

Okay. So the nervous system has a lot going on, right? A lot of divisions. So we have a nice little flowchart here where we're going to kind of map out how all of these divisions are organized.

So we have this kind of the general label of the nervous system up top, and we know that the nervous system has two main divisions, and I can see that this one over here has a bunch of little branches, and this one does not which tells me that this one must be the central nervous system. Remember that the central nervous system is just the brain and spinal cord? That one is super easy. And then the peripheral nervous system or the PNS, which is comprised of nerves outside the brain and spinal cord, has all those little divisions. So starting off with the peripheral nervous system, we have 2 main divisions, our somatic nervous system and our autonomic nervous system, and the somatic nervous system, remember, is going to be in charge of voluntary movement.

And in contrast, the autonomic nervous system is in charge of those automatic or involuntary movements, right? Reflexes, movement of your gut, things like that that you have no control over. And then the autonomic nervous system is further divided into 2 divisions. We have our parasympathetic division and our sympathetic division, and our sympathetic division is basically our fight or flight response.

That division will become more dominant when we are, you know, engaged with a stimulus or threatened or stressed, and in contrast, the parasympathetic division becomes more dominant when we are relaxed and at rest, and so we sometimes call this our rest and digest system. Alright. So that is the organization of the nervous system, and I will see you guys in the next one. Bye-bye.

The ________ system is likely active during a difficult exam while the _______ system is likely active while relaxing.

• A. Central; peripheral.
• B. Sympathetic; parasympathetic.
• C. Autonomic; somatic.
• D. Sympathetic; somatic.

Parasympathetic activation would _________ heart rate while sympathetic activation would ______ heart rate.

• A. Increase; decrease.
• B. Not affect; increase.
• C. Decrease; not affect.
• D. Decrease; increase.