The spinal cord is part of the central nervous system and so like the brain and spinal cord, they are both covered with all three meningeal layers. This includes the dura on the outside, the next layer in which is the arachnoid and the pia mater which is just up against the spinal cord and very difficult to peel off as we talked about when we talked about gross anatomy and the nervous system in general. So all three of these layers exist. We have the subarachnoid space. Just like we did around the brain, we have a subarachnoid space around the spinal cord. The dura fuses with the spinal nerves out here and eventually the nerves are going to be covered by something called epineurium which is a connective tissue layer which helps the nerves maintain their integrity and keeps them from getting squished or pulled too hard. So there's a fusion of those but the initial part of that spinal nerve is covered actually by the dura mater itself. In the next couple of slides, we'll see some actual cadaveric images of these layers around the spinal cord within the vertebral column. So this is an image then of the actual spinal cord in C2 with our dura on the outside, and then you can see the arachnoid in this area with some of the nerve roots and blood vessels, and then the pia again it's so adherent to the spinal cord that we can't even peel it off. You can also start to see, which is really cool, some of these nerve rootlets in this area. These little guys are nerve rootlets. Then here is the spinal cord in the vertebral column. So, within the spinal cord and in the vertebral column, the dura is just a little bit different than it is in the brain. Around the brain, the dura acts as periosteum and forming a meningeal layer. So it's right up against the bone, and there's no basically hardly any space between the brain and the bone except for that kind of that subarachnoid space, so it's very tight. Within the spinal column, as you know from going over the musculoskeletal lectures, the vertebra bend a little bit. You've got a little bit of flexibility in your vertebral column because it's not one solid bony structure. It's individual vertebra that articulate with one another. So with regard to the dura in the vertebral column itself, there's a space. So the dura kind of comes down here and then all of the bones are out here. So in this zone, we have what's called the epidural fat because the dura is not right up against the bone, and there's some ligaments involved here too that hold the bones together. The reason is because the vertebral column is flexible. So, if you think about it, the skull doesn't move. So the dura can be right up against it because it's never going to budge, and it wouldn't stretch or pull on the dura within the vertebral column because the bones move and you want the dura to protect your spinal cord. It's going to form a sleeve around the spinal cord, but it's not going to be attached to the bones because the bones are moving. So you need space for that movement to take place and you don't want your dura stretched or pulled in any of these directions when the vertebral column moves. So that's why there's a space and some epidural fat above the dura and in between that and the vertebral bodies. The dura then continues down beyond the spinal cord itself into the base of your sacrum, and it covers around group of nerve fibers called the cauda equina. So, the basic explanation is that when you are an infant, your spinal cord and your vertebral column are about the same length, but as you grow, your vertebral column becomes dramatically longer but your spinal cord doesn't. It becomes a little bit longer but not dramatically longer. So, the bottom line is that all those nerves that are attached and exiting out between the vertebral bodies eventually have to get to their targets which are farther away. So the nerves just keep growing. It's not like you stretch them like a rubber band, they just keep adding more membrane and the axons keep growing. But the result is this bundle of nerve fibers that now extends because it's got to still make it out between the correct vertebral bodies, and so we end up with this big bundle of fibers called the cauda equina or horse's tail, equina, horse. The end of the spinal cord right here, this little pointy end is called the conus medullaris and that's basically your coccygeal levels of your spinal cord. Similar basic things about the spinal cord before we get into any of the details of the gray and white matter is if you draw a line across it, the dorsal part of the spinal cord is sensory, the ventral part of the spinal cord is motor. Just general organization of the spinal cord. You also have a blood supply for your spinal cord. You have one ventral artery that runs here in this kind of the sulcus and it sends out branches, kind of a corona of branches that then come in and feed the spinal cord, and you have two dorsal arteries. Again, these are going to come in and branch and feed areas of the spinal cord. So, theoretically, you could have a stroke in your spinal cord just like you could have a stroke in your brain if any of these branches of these arteries are occluded. In summary, what I want you to know for the assessment, how many regions is the spinal cord divided into? So if you know that, that's a good thing. What meninges are associated with the spinal cord? Can you remember what a spinal cord enlargement is all about? Then what are the general functions of the dorsal horns and the ventral horns? Can you explain to me what is the cauda equina? If you understand these concepts, then you'll do very well in the assessment.
