 Okay, so if you agree that the nervous system has this job of receiving information, processing it, and then sending out an order for action, then you have to have some sort of structures that are enabling this to happen. And this primary structure that is responsible for transmitting information like this is the neuron. So the neuron is a cell that is basically respond, it's a functional unit of the nervous system. Neuron, functional unit of the nervous system. And what we'll see as we progress, it's not the only cell in the nervous system by any stretch of the imagination. In fact, it's not the most common cell that you're going to find in the nervous system. However, it has the most obvious function because it's the one who's directly delivering information. How? How does it do this? Well, let's draw a picture of a neuron. What? Me? Draw a picture? Shocking. A neuron is a cell. So it has a cell body with a nucleus. Wow. Hmm. Brace yourself. I'm drawing, okay, what does it look like I'm drawing? Besides some rockin' punk hair on my neuron. Okay, yeah, it's true. You can think of these as punk hairs, but they're actually extensions of the neuron. So they aren't really hairs. And I'm going to tell you what they are. These guys are called dendrites. And we'll look in a second at what they do. So here's my cell body. We've got to make it a different color. Cell body. And let's just say this is my nucleus, right? Straight forward. Dendrites are extensions of the cell, kind of like microvilli, they're extensions of the epithelial cells lining the digestive system. The dendrites are extensions. And these extensions can be wholly long. Like they can be huge, long extensions of the cell, but they're filled with cytoplasm, and their cell membrane is surrounding them, as opposed to, say, a cilia, which is a structure of microtubules, which is like hair. So when I draw dendrites, they look like little hairs coming out of this cute little head of the neuron, but don't be confused, because they're not hairs. They're extensions of the cell themselves. We also have another extension. Now I'm drawing like the quintessential neuron here. It's so quintessential, like the most perfect neuron that you've ever seen, ever. But know that, of course, they don't all look like this. Most neurons, many neurons, have a very long extension from the cell body that's different from the dendrites. Talk about how. But this one is called the axon. And then a neuron has, again, more little, look at how I'm going to draw these guys. Wow, I'm amazing right now, if I do say so myself. I'm sure that's what you're thinking right now, right? Look, I even drew them. These are little synaptic knobs. Synaptic knobs. And watch and be amazed. Dendrites, the neuron as a whole, is essentially an electric structure. It can pass, that's the worst color I've ever picked, info in the form of, ready for this, electricity. Neurons are electrical cells. And how they do this is a topic that you will deal with in physiology. What you have to accept is that information in the form of electricity can pass from one end of the neuron to the other. And that's directional, okay? So information comes in electricity, comes in through the dendrites, and travels down through the axon, and out through the synaptic knobs. And that process, again, is not the important part. But by definition, dendrites deliver information toward the cell body. Axons deliver information away from the cell body. As soon as you accept that information can travel through this cell, as soon as you're like, oh, okay, I can accept that, that makes sense to me, the whole rest of the nervous system is going to be a lot easier. Because we're not going to go into the details of how that information is traveling. How does the cell do this? That's a topic for physiology. We're just going to accept that, indeed, it happens. So dendrites bring information into the cell body. That information passes through the axon toward the synaptic knobs. Now, dude, really, is that the end of the story? What happens to the information at the synaptic knobs? What happens at this point? You said that the information was electrical as it was passing through the neuron itself. True story, but guess what? It doesn't stay electrical for forever. Once the information passes to the synaptic knobs, it has to be passed on chemically. And these chemicals, again, this is, like we just are going to have to accept, we're not going into crazy detail here. These chemicals are called neurotransmitters. And the neurotransmitters can cross a synapse, what? And the synapse is a space and head to either another neuron or an effector. Okay, what effector did I just draw here? Of course you know. That's a skeletal muscle dog. Come on. You can have your effector be a skeletal muscle. So essentially, this neuron sent a message to my skeletal muscle to do something. What do skeletal muscles do? They contract. Watch out for the elecranon of this fella, yeah? Or we can pass the information on to another neuron. Passing it on to another neuron, we can send messages all over the place. We can send simultaneous messages to, like a shockingly, oh, it hurt your head, all the possibilities of places that we can send messages if we can send the message, if we can pass it on to another neuron. Okay, do all neurons look like this? No, of course not. And in fact, I'm going to draw you one more neuron. I'm going to draw you a neuron called a... I think it's a unipolar neuron. I kind of want to check really fast. That's what I'm talking about. It is a unipolar neuron. Oh my gosh, say that like 30 times fast. I'm not going to. I'm going to send a unipolar neuron. You have a cell body, just like normal, but look at this. You have these, okay, it's called unipolar because it's like one thing coming out of here and I'm not drawing it as... these are my synaptic knobs down here, right? And these are my dendrites up here. What, really? And here's the deal. And I know those were dendrites because the information passes toward my cell body. How did I know that this was my axon because the information passes away from my cell body to a synapse, which is going to do something, which it might be to an effect or most of the time this particular type of neuron isn't? Can you see your parts? Totally. If I didn't label anything, if I didn't have my little synaptic knobs, really you can't see those, at least not in our microscope slides. If I didn't have that, if I didn't have an effector out here, could you tell which direction the information is traveling in this neuron? You couldn't tell. So if you can't tell, then you can't decide which one is the dendrite and which one is the axon. In this case, since I drew arrows on, you know this is the axon and you know this is the dendrite. And here's what I want to tell you. That says dendrite. Your textbook says that it's... They have different names. Awesome. They're fighting about it. They're fighting about what we should call these different structures. I don't care. To me, a dendrite is taking information to the cell body. It's easy. Let's just call it good there. They can fight about it. The details, that's awesome. The axon is taking information away from the cell body. You can't tell the difference between them unless you can tell the direction that information is traveling. I think that's everything that you want to know about your neuron. One more thing. I'm so glad that I looked at my notes really fast to see this thing. I'm going to go back to... No, I can do it here. Sometimes axons are covered with fatty... Fatty, fatty, fatty, what, blobs? And these... this is myelin. And so they make up these myelin sheaths. So the axon can be covered with fat. Little fat blobs. And these myelin sheaths make the information go faster. They make info travel faster. And what was our info? Electricity. So it's like insulation. What? True story. So these are like little... like in a wire, like a copper wire. The information will travel faster and more efficiently through an insulated copper wire. The electricity will. Then through a non-insulated wire. And it's the same thing with your axons. If they have myelin around them and this fatty protective insulation, then the information will travel faster than if they do not have this sheath of myelin around them. Whoa, how's that for fun times? You're good? Okay, let's move on and we'll do the next thing of looking big picture once more on the concept of the neuron attached in.