[MUSIC]. Okay. So, we have some spinal cords. I just wanted to show you a few more things. Once again, you see that the entire spinal cord is contained in a dural sheath. So it's, it's the same dural sheath that goes and surrounds the brain and even the same one that goes out to the eye. It's all one dural sheath. And it's still, it's tough. It's not, it's not a different dura, in the spinal cord than it is in the brain. It's the same dura, so it's very tough. Okay. So this is the dorsal side. This is towards the back of the spinal cord. And these roots, these are bunches of axons that group together. We call them fascicles or rootlets and they come out and they are going to gather. But they're going to exit this dural sheath to perform, to become the spinal nerve. But at this point they're roots and they are all sensory. So on the back side, all the roots are sensory. And then on the, on the bottom side, the ventral side, these roots are all motor. So within the dural sheath, the roots are either motor or sensory. And then once they get out to form the, the peripheral nerve which we see right here, these peripheral nerves are mixed. They're sensory and motor. Okay. >> And they mix outside or inside? >> They mix, they get mixed outside of the dural sheath. So inside of the dural sheath, they're roots and they're either a motor on the bottom side or sensory on the top side. They come out the same hole and join. And right at that hole is a structure called the dorsal ganglion, which are, there are these little hard things right here. And that's where the sensory neurons sit. So the sensory neurons sit outside of the dural sheath. They're part of peripheral nervous system and remember that herpes zoster, the thing that, the virus that causes chickenpox and, and also can cause an outbreak of zoster, that virus lives in these dorsal ganglion where the sensory nerves, sensory neurons sit. Okay? So, they live in, peripherally in the sensory ganglia. So here we have a view of the dorsal length of this spinal cord, which I think comes from a cow or a sheep. And you can see that it's really, it's actually wide up here. Do you see that it's wide up here, compared to it's less wide down here? This is thoracic cord, this is cervical cord, and then back down here it gets wider again for the limbo-sacral cord. But the other thing that you notice is that these, these fascicles, they are at a shallow slope. They're going down like that. See that? Yup, and then if we go a little bit farther down, they're going a little bit father more and if we still go down farther, look. Here, if we follow, if we follow these fascicles, they actually came from way up here. So they're traveling all the way down here. These are traveling all the way down there. And the, the, the roots have to actually travel for a long distance. And that is because the vertebral column and the spinal cord grew at different rates during as an embryo. And the vertebral column, the bones, grew way, way more than did the spinal cord. So the, but the spinal cord, these roots have to exit from the appropriate level of the vertebral column. They were once upon a time the same length. And so what has to happen is that as you get progressively lower, you have to, you have to travel farther and farther back. Now here, right here, is the end of the spinal cord, can you see that? That's the end. It ends in this little bunch of connective tissue, it's called the phylum terminale. And so, this is nothing, it's not, it's not spinal cord, it's a, it's a piece of, it's like a tendon. It's essentially a version of a tendon. And this is spinal cord. That's the end of the spinal cord. But below the end of the spinal cord are all of these roots. And these roots are going to exit the dural sac farther down, closer to the end of the vertebral column. So this structure here, where you, all you have is roots, the spinal cord is, is, has ended, that's the end of the spinal cord. So down here all you have is roots, that's called the cauda equina, which is some I think it's latin for horse's tail. And that looks like a horses tail. I think it really does. We'll just look at, here's another version of the horse's tail. It's been cut a little bit a little bit higher, so we're getting less of it. But you see here all these roots. They, they haven't exited yet. They're traveling in the dural sheath. Let's look at the one on this spinal cord. >> Where does the sheath end? >> The sheath ends at the base of the of the vertebral column. >> Where is its point of contact? >> The phylum terminale. >> So, that connective tissue travels. >> That, that connective tissue is going to, is going to attach to the bottom of the vertebral column. So here's the end of the the spinal cord and then all of this is cuada equina. And look they, they come off. Here I, here I am, I got to the right place, so out I go. Here I am. Got to the right place, out I go. But then, these guys still gotta travel to get to the right place. Everybody knows their, everybody knows their exit point in spinal cord land. Okay, so why does that matter? Well, besides that it's very pretty this end of the, of the spinal cord, the conus medullaris is right about here. It's the bottom of the, of the, just below the rib cage. So, if you wanted to, to find out, let's say you wanted to see whether there was an infection in this CSF. Or let's say you wanted to give a drug that was going to act centrally. Where's an easy access point? Well, the easiest access point is right here in the cauda equina. And so this is where people do what are commonly called spinal taps. But the medical term for that is a lumbar puncture. And why, why do we go there? Because if I put a needle in here, I am probably going to hit the spinal cord. And that's going to be disastrous. I might as well have been in a bad car accident. So very bad idea. But if I put a needle here there's no spinal cord, and these roots are just going to be nudged to the side by the, by the needle. And I'm not, I, I have much, much less >> Risk. >> Risk or a possibility of causing harm, okay? So that's where people go and do these spinal taps or lumbar punctures. And I think we're drawing to a close. [MUSIC]
