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Nervous System

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

The nervous system is a network of neurons that send signals to different parts of an organism's body to coordinate the actions of the organisms. Most animals have two parts to their nervous systems - the central nervous system includes the brain and spinal cord while the peripheral nervous system includes sensory neurons and nerves. The nervous system is different from the endocrine system because its messages travel more quickly and don't last as long.

One of my favorite systems to teach about is the Nervous System and this is because it's the voice talking inside your head it's what's watching me right now and the Nervous System is the one of the two major control systems of the body it works with the endocrine system to help control and regulate the activities of the body and maintain homeostasis. Now when studying the Nervous System you got to be kind of careful because it's been something that's been just inspiring scientists to dive into the research for years and years and so each scientist tries to organize it and they've organized it in many different ways and so sometimes kids get confused which ones is what? Well there's one way of organizing things based on essentially it's like Geography it's just where are they continent and that's saying the central nervous system versus the peripheral nervous system.

The central nervous system is the brain and spinal cord alright? The stuff in the middle, whereas the peripheral nervous system is all of the nerves coming off of the brain called cranial nerves and all the nerves coming out from the spinal column the spinal cord called the spinal nerves alright? Now within the peripheral nervous system they'll make the distinction between the somatic nervous system which is the part of your nervous system that controls your skeletal muscles in other words it's my somatic nervous system that I actually or activate in order to do this or that why I don't know but autonomic nervous system controls everything else now that's a really broad category because its really a lot of things. It's the autonomic nervous system that helps you regulate how open or close blood vessels are two different parts of your body your autonomic nervous system adjust the size of the pupil the hole in your eyelids that allows more or less lighting based on how much light you're looking at.

In general people think of this somatic nervous system as being the voluntary part the consciously controlled part while the autonomic is the unconsciously controlled stuff. Now again there's some blowing going on here, when you walk very rarely do you actively sit there and think "how I'm I balancing? How do I need to adjust the muscles of my trunk my abdomen to keep me from falling over" even though it's technically that would fall under the somatic nervous system and autonomic stuff well you can have some input into that if you start working under those Buddhist Monks who'll site there and they can learn how to control blood flow and other really bizarre things.

Now within the autonomic nervous system there's a further subdivision, there's the sympathetic nervous division or nervous system and the parasympathetic nervous system or nervous division. Now the sympathetic division in general you can lump that together as it controls the fight or flight type responses in other words getting you ready for action whereas the parasympathetic nervous division in general gets you ready for resting and repairing now usually most body parts are being given signals by both of these and they're usually some kind of balance your very rarely all the way sympathetic and no parasympathetic or vice versa and when you're going through your normal life, there are just sitting there adjusting based on input on what your body needs and even your conscious mind can influence this.

Now to help you think through what would the sympathetic nervous division control? What kinds of body parts would it send blood to? What kinds of actions or effects would it have on your body and versus the parasympathetic, let's start thinking about hmm close your eyes and just kind of relax a little bit and in your head imagine its 3:00 a.m. you're in your bed oh you're just sleeping you're just doing that kind of surfing between consciousness and rest and you just feel so wonderfully relaxed, the room is dark it's perfectly quiet and all of a sudden you hear 'pop' and somebody licks your ear. Now how would your body react? Your heart would start increasing as the sympathetic division says "whoa we need to run away or kill the killer clown" you would you would open up the blood vessels to the large muscles of your arms your legs getting ready to run away or engage in your Ninja battles with the killer clown. The opening of your lungs the bronchi's and bronchioles will spasm open to allow more air flow because engaging in Ninja battles with killer clown takes a lot of oxygen so you need to start to breathing faster and deeper. Now what parts of your body don't need blood at that moment well you don't need your immune system to fight off the killer clown now you may get some diseases later but right now you need to focus on fighting killer clown that's why long term stress can cause problems with your immune system.

What else don't you need? Well you had a nice dinner few hours ago but you don't need to digest it right then so you shut off blood supply to your digestive system slow it down because you don't really need it and sometimes that's maybe why you go hmm if you've got too much food in your stomach when you all of a sudden go ah ah ah I need to fight your stomach may go, I can't handle this and reverse the pumps. Now unless you've really got a thing for killer clowns what other system don't you need at that moment? The reproductive system so the blood supply to there gets shut down and you just are ready for fighting and flighting. Now, what's an opposite kind of situation, Thanksgiving, you eat Thanksgiving dinner, you have your portion of the turkey, you have about 3 pounds of turkey, you have mashed potatoes you have everything else and then you sit on the lazy boy recliner and then your body says, we do not need to have heart-rate racing, we do not need excess air in the lungs, we do not need your muscles to be pumping and using lots of energy and instead it shuts it down. Digestive system gets a lot and everything is good.

Weirdly enough the sympathetic division does activate one activity of the reproductive system and that's either orgasm or it can actually activate labor which is why that stereotype of the woman giving birth and when she gets trapped in the elevator there actually is some legitimate see to these this means that if a lady is walking around she is looking pretty pregnant don't just jump up behind her and go aah and attack her with her with the chains that's not just nice to do.

Alright, now I can go through the structures of the spinal column or the spinal cord but what most people want to know about is the brain, so let's take a look at the brain. There's 4 major regions of the brain; the brain stem, cerebellum, diencephalon and cerebrum. If we take a look at this diagram here, this portion here the light blue weirdly purple and light green thing there that is the brain stem. This the bottom of the brain and even though this is not quite accurate you could think of it as the part that evolved first and it deals with those basic needs this keeps your heart going your lungs breathing these are keeping you not dead kind of activities. Now there are some other things that are involved there besides just keeping you not dead there are some visually reflexes and some other things plus all the signals that are coming up the spinal column right at the bottom of this they're passing through the brain stem.

Now this weird lump the a reddish lump that's sitting behind the brain stem it's called the cerebellum which means little brain because it actually looks a lot like the bigger cerebrum that sits on top and you can even see it has it's white matter in this thing which means white or tree of life it's got its white matter on the inside just like the cerebrum has white matter in on the inside and grey matter on the outside. What does the cerebellum do? It does a number of things but some of the most important things that it does it helps regulate and coordinate motor control. Now when you wish to move your right or left arm you don't sit there and hope that your cerebellum does it that's what the cerebrum's involved with but the cerebellum is the thing that says "I wish" no the cerebellum says "I want lift my left arm" the cerebellum says "well okay but I know Newton's third law for every reaction there's an equal on opposite reaction if I lift this arm I'm going to fall forwards" so the cerebellum says, "tighten up trunk and keep me from flapping over" when the cerebrum carries out it's action and it does that kind of smoothing things out if this is the CEO of motor control, this is the middle management that makes the CEO's directives actually becomes a reality.

Now you may not realize how much of this actually regulates as I said it's involved a lot in balance and it helps coordinate actions and a lot times if it thinks the cerebrum's made a mistake it will override it this is why some times if you're trying to do a muscle activity like walking or climbing especially if there's something complicated if you start to think about what you're doing you may get screwed up. Now here's a weird little thing that you can do, stick out, sitting down stick out your right leg and start rotating it clockwise for you that we'd be rotating it like this then with your right hand in the air draw the number 6 what would happens to your leg? That's your cerebellum saying warning CEO stupid, stop that cerebrum and it overrides.

Alright sitting on top of the brain stem this weirdly yellow thing here is the diencephalon and its such a little property it's so important this is where a lot of relay relying of information starts happening. This part decides where things should go in the cerebrum plus it starts doing a lot of the initial analysis of the data that's coming in and out of the brain and it starts making some decisions. This is also where a lot of autonomic control the body is decided upon. You see this little dangly guy there that's the pituitary gland the master gland of the endocrine system and it's the diencephalon that controls the pituitary gland so this is involved in a wide range of things especially with this little part here called the hypothalamus you can be involved in deciding whether or not like something it's involved in thermoregulation lots of functions are located there.

Up here, is the cerebrum this is the perhaps most recently developed of the parts of the brain and this is what people think of as the brain. This is where your conscious thoughts probably mostly exists. Now it's divided into primarily 4 major lobes; the frontal lobe in the front, the parietal lobe here, in the back you have the occipital lobe and to the side this is a kind of a view of the brain you have the temporal lobe. I often think of it kind of like a boxing glove where the thumb is the temporal lobe the fingers are the frontal lobe, the back of the palm is the parietal lobe and then it breaks down occipital lobe is the back here, weirdly enough vision analysis happens on occipital lobe I don't know why its not the front it make lot more sense. The temporal lobe which is right by the ear hey! That makes sense it's involved in the analysis of sound its also involved in analyzing things like smell, there's a number of other functions that go on in there involving there's some language stuff that goes on in there and memory is actually helped out by the temporal lobe. The parietal lobe does a lot of analysis of touch which you think of us touch and in fact right where you go from parietal lobe to frontal lobe you have this ridge called the primary somatic motor, primary somatic sensory area where you have the individual neurons that are listening to signals from different parts of your body and they've actually done things where they run along with electrodes somebody's that little ridge there and you the person will say "I'm reporting tick lings sensation or something" and it seems to run along their body and they can map it out and so you'll have lots of that brain portion dedicated to analyzing information from your hand but not so much to analyzing information from your elbow. Similarly the frontal lobe has right by that has a ridge that controls those muscles and again if you run your electrode along it you'll see the person won't feel anything but their body will start to move and that's called the primarily somatic motor area. The rest of the frontal lobe is involved in things like executive function and conscious decision making and speech so this is where you start thinking hmm what do I really want for my birthday now other parts of the brain may want may come up with I'm hungry but you may be thinking yes birthday cake is nice but I think I want a leather jacket. These portions of it right here they're involved in very long term judgment and this is the part that right now as a teenager if you're watching this, this is the part that this is fascinating to me, it's growing and developing right now which is why everyday as you age you're getting smatter and wiser and assuming that you don't do things to impede it's development, you're going to be a very wise and smart individual especially after watching this video.