[MUSIC] So, we're going to talk now about the difference between the Central Nervous System and the Peripheral Nervous System. There's a barrier,there's a fence, and that fence is the demarcation between central and peripheral. And that fence is made up of three membranes, and those three membranes are the meninges. There are three meningeal layers, and the three layers go from very weak, very tender, the pia, to very tough, the dura and, in between, there's a spidery thing called the arachnoid, a spidery layer called the arachnoid. So, let's just look at what that looks like. We're only going to see the arachnoid in, in this next picture. So here, this is the brain, and what's covering the brain here, up here is pia and you can't see it, it's so thin, and so tender that we don't see it. But in this view, the dura has been removed and now we're looking down on this film, it's a, it's an actual membrane, and that membrane is the arachnoid. So, the different meningeal layers have different purposes, different functions. The dura is the, is a tough sack, and that is what's going to keep us from having concussions all the time. All right, so it's going to float our brain in in fluid and prevent it from banging about, and, and actually getting bruised. It takes a hard hit to actually injure the brain, and hopefully we, we don't have, we don't incur that. Okay, so the meninges go from, pia is closest to the central nervous system, is closest to the brain and spinal cord, and then dura is farthest away. And their, all the neurons, almost all of the neurons in the central nervous system, 200 billion minus something less than 100,000 are contained completely within the central neurons. The only neurons that leave the central nervous system, are these neurons that, that serve a motor function. They actually go out the meninges and they go into the periphery. In the periphery, there's the peripheral nervous system, and there's also every, the rest of the body. So there are motor neurons, they go to skeletal muscle, the voluntary muscle, so that we can move our arms and our legs. And these are motor neurons. And then there are Motor neurons that go to Autonomic Neurons that control our glands, that controls the cardiac muscle, they control our gut, smooth muscle. So for instance, these are going to be, these neurons are what is going to be active when you see food and you start to salivate. Well, somebody's got to tell that gland to start salivating and it's the brain and it does it through this two neuron chain. So, those are Autonomic Neurons. In addition to the motor neurons that carry information from the central nervous system to the peripheral nervous system, there are sensory neurons. And these sensory neurons are peripheral. They are located peripherally, and they carry information into the central nervous system. What you'll note is we call a neuron either or sensorial or peripheral based on where the cell body is not based on where its axon is or its dendrites, but based on where the cell body is. So these Peripheral Neurons include Sensory Neurons and Autonomic Neurons, these are in the autonomic ganglia. The consequence of that is that these neurons share vulnerabilities. The, the, they share with each other but not with the central neurons. So, for example, there's a disease called Congenital insensitivity to pain. People with this disease suffered a mutation in one of a number of developmental, developmentally important genes. And what it did was it, it, prevented a group of sensory neurons from developing, those sensory neurons that respond to injury. So, these people are insensitive, they never feel pain, because they can't, they don't have the sensory neurons that will respond to noxious stimulation which is what usually brings us pain. But in addition, there's a group of the Autonomic Neurons that also developmentally got knocked out, and these are the neurons that lead you to be able to sweat. And so, people with Congenital insensitivity to pa, to pain often have what's called anhydrous, meaning they can't sweat. Those seem like two completely weird symptoms to put together, but they're not weird because they make complete sense. Both of them are due to a developmental abnormality in the peripheral nervous system. So, in the next segment what we're going to do is, is look again, look a little bit more closely at other diseases that preferentially affect either the periphery or the central nervous system. [MUSIC]
