[MUSIC] So, the difference between the peripheral and the central nervous system, is important. It's incredibly important because the diseases. That affect the nervous system, affect either peripheral or central nervous system. They don't tend to affect both. They're very few. And the meninges form a very effective barrier against. Toxins, against viruses, against all sorts of damage, so that the peripheral nervous system tends to be far more vulnerable, than is the central nervous system. In addition, the two regions have very different capacities for repair. If you cut a, an axon in the peripheral nervous system, it can repair itself. It will reconnect. If there's a traumatic injury to the central nervous system that does not happen. So, the ability to repair is far, far greater in the periphery than in, in the central nervous system. And ever since I was a graduate student in the early 80s, this has been a topic that people have been very interested in. They've been trying to make the central environment more hospitable to repair, more like the peripheral environment. This is something that, this is a, a, a research area that's had some successes but is, presents an ongoing challenge. And the truth is that today we still have not achieved the ability to regenerate or repair within the central nervous system. So let's, let's look at some of the Ways in which the peripheral nervous system is vulnerable. So, it's vulnerable to say a, large molecules such as botulinum toxin. So, botulinum toxin which comes from spoiled food can get in and it primarily will effect these peripheral, it will only effect these peripheral neurons. It will not get past the meninges. Let's take another example which is viruses and so. When there is a, one of the viruses is polio. And polio virus, actually gets in right here at this synapse between the motor neuron and the voluntary muscle, and it goes back. It travels back and see, it did a clever thing. It got through the meninges. But it got through the meninges by getting in through this the axon of this motor neuron. And what does it do in return? For thanks, it actually kills this motor neuron. So now, this motor neuron is going to die. And there, therefore, there is going to be weakness or an inability to move that muscle that was infected with the polio virus. Let's look at another virus herpes zoster, and herpes zoster is a virus that, that produces what's commonly called as shingles. And in herpes zoster, the, the virus gets in here, it gets transported back inside the cell, inside the axon in these sensory neurons, and then it goes and lives in here. And if all is great, all is well. It lives in there and then it never talks again. But, under some circumstances, the virus can decide to reproduce and blossom, and it will make so many copies of itself that it actually sends it back out that way, and what you get is. A virus all throughout the sensory territory, and what you get is a rash. So this is the skin, the sensory neuron has a process that ends in the skin, it takes up this herpes zoster. This zoster lives in the cell body, but if there's an outbreak, it will send all these virus particles back out to the skin and you'll get a rash. And here is an example of somebody who has a rash. Now, let's notice a couple things about it. First of all, it's only on one side. Because the infection is only on one side and,and these sensory neurons, are, are going to obey the midline perfectly, so it, the other half of the face is completely unaffected. The other thing that you notice, is that it's, it's in this distribution, and this distribution is one of the most common places to have shingles. The common place is in the thoracic region right about here. So and this is a distribution that has an anatomical basis. This is the ophthalmic division of the trigeminal nerve. Luckily, this does go away. And, it did go away for this individual. So, another, another example that's more like botulinum toxin is sarin. Sarin is a big molecule. And it's only going to affect the periphery. It's not going to affect the central nervous system. In the next segment, we're going to talk about brain tumors. [MUSIC]
