 Nervous system, part three. We're coming at you with more of exactly the same concepts, only we're going to fill in a few more details. So in the last lecture, we talked about the brain, which is part of the central nervous system. And we talked about different parts of the brain and primary integration or processing responsibilities. Today we're going to look at pathways that information travels. And we know, you know, because you guys are smarty smarts. We know that information comes into the central nervous system via afferent pathways. Afferent pathways have sensory receptors on the dendrites that receive some sort of stimulus, send the message to the central nervous system. While my central nervous system, my spinal cord is really skinny. It's going to be rather difficult to fit my processes in here. We know that the sensory information is going to come in. We know that the sensory information has two flavors. We could have somatic sensory. That's sensory information that we're aware of. We can have visceral sensory. And this is sensory information that you're not conscious of, like the pH of your blood. You have sensors in your blood vessels that are monitoring the pH of your blood. And you aren't even aware that that's happening. So this sensory information has to follow. It comes in through an axon and has to somehow hit a cell body and travel to the central nervous system. Once it gets to the central nervous system, we have a whole set of neurons. Okay, look at this tiny little neuron. Let's just send this information to the brain. These are inner neurons. These are neurons that are actually in the central nervous system. And then we might bounce that information around in the central nervous system. I'm just going to pass on through this just because why did I make this so skinny? Nobody knows. The central nervous system is going to decide based on the sensory information that came in it's going to decide on a course of action. And then it's going to send the message out to an effector. And we can have any number of flavors of effectors. What kind of motor neuron did I just draw? You know this is a somatic motor neuron. How did you know that? Because it's innervating skeletal muscle because I just drew that beautiful skeletal muscle. We have other flavors. We could have visceral motor pathways. And in fact, our next lecture is all about visceral motor pathways. This one, we're going to look at what are these pathways we speak of? What is? What is it? First of all, can you imagine sending all these guys out? We've got all the sensory information. Think about your skin. Every place on your skin actually can pick up information, which means there is a sensory structure in every bit of your skin that feels something. And so that sensory information, there's a neuron coming from there. Really? How crazy is that? If those neurons all traveled by themselves, if the axons and the dendrites traveled on their own, can you imagine that you would be nothing but little fibers? It's not very efficient. Probably pretty dangerous. Like damage could probably happen pretty easily. So let's all follow the same highway. And that's what a nerve is. It's a bundle. It's a bundle of axons in the peripheral nervous system that are all traveling the same direction. I say the same direction. Don't be confused by that. They're all traveling in the same location. Information in one of these pathways can travel both directions, which means we could actually have a motor neuron send information, okay, ready for this, out through that same nerve pathway. What? True story. So our nerves are combinations of all the different flavors of neurons, all the different flavors of their axons. Do you get the concept that our nerves are going to be highways in which all these axons pass, allowing information to go in and out? By the time we finish this lecture, hopefully that concept is crystal clear in your brain. Nerves are anatomical pathways for information to travel. And we might as well group things together to keep it efficient and clean. Even though you may wonder, like, dude, is that considered efficient and clean? Yes, it works. Before we dive into identifying and talking about specific nerves, we're going to look at a reflex pathway. We're going to map a pathway so that you, again, can visualize, okay, I can see how a nerve can carry different kinds of information, can be a path, can be a highway for different kinds of information. And the first reflex that we're going to look at is the patella reflex. I know all the anatomy of that. So let's look at how the patella reflex works and build from there.