[SOUND] [MUSIC] So as you may recall. The central nervous system is surrounded by meninges, which are membranes. There are three layers. There's the dura, the arachnoid and the pia. The dura is the toughest. This is the dura and I don't know if you can see, but that is tough. I'm pulling on it. I couldn't pull it apart. okay. So, this is the dura. It wraps the entire central nervous system, not just the brain. But it also wraps the spinal cord. So here's the dura, and it's wrapping the entirety of the spinal cord. So, let, let, I just want to make sure everyone is oriented here in this brain. This is the front, this is the back, this is the top of the head and here is the bottom. And there's been parts removed the cerebellum in fact has been removed, but we'll get to that in another segment. So this meninges, this dura madre, tough mother, is, is the most outer layer of the meninges and inside of that layer is the aractnoid. And the arachnoid is this filmy like substance and what you can see is that it covers the entire surface of the brain. It doesn't invaginate with every hill and valley of the brain. The final layer of the meninges which we actually can't see, it's, it's too too fine for us to actually see. But I've peeled, here I just peeled away a little bit of arachnoid, so here's a, a one of these hills and valleys in the, in the brain and on this, this is covered by pia. Okay. Lets get back to the dura. The dura is separated by the brain, by a layer of fluid and we'll, we'll look at that in, in a, in a little bit but what that name, what that does is that it circles the brain and it, in cases the brain in this bag of fluid. So that as the brain moves around it's cushioned, it can't bang against the skull because it's cushioned by the fluid. And so there's going to be less harm done, there's going to be less injury. If in fact the brain is slammed against the, the skull. So, we can avoid concussions from a lot of head blows, of course. If the head is struck hard enough the brain will impact the skull. And that will harm it. Now there's an important difference between the dural covering in the cranium and in the vertebral column. Let's start in the cranium. In the cranium, the dura is right up against the skull. There's no separation. They can't be separated, except if there's a bleed. And that is a. A, very dangerous, that's a medical emergency. If there's a bleed between the skull and dura. If blood ge, if there's some injury and blood gets in there that's a medical emergency. But, un, under normal circumstances, these are plastered up against each other. And actually anthropologists use this because look at the inside of the skull. Can you see the imprint, imprints of the blood vessels? Do you see that? Let's point that out. Right here. See that imprint of the blood vessels? That's imprinted because the dura is stuck up against the the skull and it actually makes an impression on the skull. And, when we find old humanoid skeletons, we can actually discern what that blood, the course of those blood vessels. And that has lead to a lot of ideas in physical anthropology about how the brain evolved in recent human history. Okay. In contrast to the situation in the cranium, where the dura is right up against the bone, the dura in the spinal cord is not up against the vertebral column circles it like this, it circles it like this. So there's a lot of space. It's not up against the bone. And therefore, you can imagine that pressure, increasing pressure in the cranium is a much bigger deal. It's much mroe of an emergency. It's much more problematic. Than it is here where there's, there's space. If there's pressure, so the spinal cord moves over a little bit. Okay, so that's a very fundamental difference between the brain and the spinal cord. The brain has a very limited space, limited by the cranium, whereas the spinal cord exists in a much wider space. Let's look at one final thing with the dura. And that is that you can see it here and I'm just, I've also shown it here. This is another piece of dura. This dura sits like that and it has these folds. These are folds of dura, so if the dura is tough, these dural folds are doubly tough, because they are actual double, double folds. So this is the front, this is the back. This fold right here is called the Falx Cerebri, and it goes between these two parts of the brain, between the two hemispheres. This piece back here, right here, see that. That goes between the cerebrum and the cerebellum. We'll look at that in another moment, but in another segment, but most importantly the point of these folds, or one of the benefit of these folds, is that it separates problems, pressure problems, two, three compartments. The compartment on this side falx cerebri, the compartment on that, that side of the fax cerebri. And then the compartment that's below. This fold which is called the tentorium. In the next segment, we're going to look more closely at the brain.
