[MUSIC] We could approach the neuronatomy of the entire neuro system from either end. You could start at the brain, go out to the periphery or you could start to the periphery and come up to the brain. And I have always been a periphery to brain person, for reasons I do not know. So we are going to start with the nerves. And the nerves are in the periphery. They're outside of the central nervous system. They're outside of the dural covering. And they are, what nerves are, are bundles of axons that are in the periphery, that's all it means. And these bundles of axons are either sensory, which means they're carrying information in or they are motor in which they are carrying information out. So into the central nervous system are sensory out of the central nervous system are motor. Great, so there are two different types of nerves and they are defined by where they exit from the skeleton. So if nerves that exit from the cranium are called cranial nerves, nerves that exit from the spinal cord are called spinal nerves. It's as simple as that. Let's talk for a moment about the spinal nerves. These spinal nerves come out at every spinal segment. At every segment of the vertebral column, there's a spinal nerve that comes out on each side. And where they come out from? They come out from a hole. Here's the spinal cord we are looking. Let me orient you, this is the sacrum down here. This is where your tail would be if you had a tail. And up there would be your head somewhere. So this is the small of your back. And each one of these is a bone in the vertebral column and running down the middle of this vertebral column is the spinal cord. So if we just take one of these bones and we look at it, we look down on it, we isolate it, we can see that the spinal cord is running here right in the middle. And the nerves go out on either side through a little hole. And one of the things that happen over time is that this compresses. As a person get's older this compress and this hole get's smaller and that can have unfortunate consequences. It can produce some either weakness or some pain or both. The important point about these nerves in the spinal nerves is that they all are very stereotyped. They all have a both a sensory and a motor component. So in every spinal level, the nerves that go out from every vertebral level, there is information coming in, sensory information coming in and motor information going out. And the nervous system is set up sort of logically so if you look at a person and here are the legs and here are the arms. This is the spinal cord, this part of the spinal cord is going to enervate the neck. And then below that is going to be where it innervates the arms. And then it's going to be the sake of, or I'm sorry, the trunk. And then it's going to be the legs. There's not going to be a situation where this, the top of the spinal cord, innervates something out of order. So it's all topographic. [COUGH] Okay, now the situation in the cranium is a little bit different. We're looking down, again, this is the front, this is the back, this is where the brain connects to the spinal cord. These are the front of the temple lobes and this piece right here at convexity is where the top of the eye globe. The globe the orbit is bulging into the cranium, so the eyes are going to be right there. And you can see that there are a few little holes here and there and each of these holes has a name. And these are holes through which the cranial nerves pass. The cranial, there are 12 cranial nerves, they are named and numbered in Roman numerals. So it's I through XII and some of them are only motor, some of them are only sensory and some of them are mixed. So we'll look at two nerves in particular which are illustrative. One is the cranial nerve XI. So cranial nerve XI is called the spinal accessory nerve and it allows you to do two things. It's a motor nerve. It has only motor information. It allows you to do this. So it allows you to raise your shoulders and it allows you to turn your head. So it's a couple of neck muscles turns out that you raise you shoulder by contracting a muscle. [COUGH] What's interesting about cranial nerve XI is that if you look at, say, the spinal cord going into the hind brain and here is the skull. The motoneurons that enervate, that form the spinal accessory nerve are in the spinal cord. And the axons come out but they don't leave from the vertebral column and that's why they're not a spinal nerves they do a very weird thing. So they go in to the skull and then come out of the skull. And because they come out of the skull they're a cranial nerve, okay? [COUGH] Just to show you another example of another cranial nerve. This cranial nerve I, this is the olfactory nerve and remember that the eyes, this is a blow up of right here, and the eyes are sitting right here. So right down past this area, is the nasal sinuses. And the nose is in the front and so the nose sends little axons that come up through all of these little holes. You see all these little holes right there? That's called the cribiform plate and that's where the cranial nerve one enters through. So what's interesting about that is this is a delicate operation, these are tiny little unmyelinated axons, they're very vulnerable and they're coming up through this little tiny holes. So as you may imagine [COUGH] if one has this type of an action with some force going forward and then backwards. It's very possible that the axons that are threading their way through the cryptoform plate can break and this does happen. It happens with a whiplash type of injury. So if the head goes back forward and back the brain can move within the cranium and these axons can break. The bad news is that a person suffering this injury can lose the sense of smell and that is a very devastating thing to not be able to smell particularly after you've been able to smell. It makes life a little less vibrant. It really has a profound emotional effect to not be able to smell. But the good news is that these axons in some cases, not always, but in some cases can grow back. Okay, so finally, I just want to show you what this looks, how this looks. This is the bottom of the skull. It's a human skull. This is the front and this is the back. Again, this the foramen magnum where the spinal cord comes in. Here obviously is the mouth. And this is looking again into the inside of a skull. Here's the spinal cord, the dura is still inside the skull. So you're not looking at skull, you're looking at the inside of that dural envelope that contains the whole brain. But these things right here, this and this and this, these are all nerves. So just to name a couple, this is the optic nerve that's going out to the orbits and these are the oculomotor nerves that move the eyes. So there are 12 pairs of nerves and each of them have something to do. But this gives you now an idea of what they, how they look inside the skull, great. [MUSIC]
