Okay, well lets briefly talk a little about spinal cord just a few points that I want you to take away from this discussion of Spinal cord. One is that there is longitudinal organization to the spinal cord which is to say there are segments of spinal cord that could be recognized. By the attachment of 31 pairs of spinal nerves. So, in the cervical region of the spinal cord, we have eight pairs of nerves that attach. In the thoracic region of the spinal cord, we have 12 pairs of nerves that attach, one on either side, of course. And then both in the lumbar region And in the sacral region of the cord we have five nerves that attach, five lumbar and five sacral. And then finally there's a single coccygeal nerve that attaches at the very bottom of the spinal cord. So, when you add all those numbers up together we get the number 31. So there are 31 pairs of spinal nerves. eight cervical, 12 thoracic, five lumbar, five sacral, and one coccygeal. Now, that's one way of characterizing the long axis of the spinal cord. Another way is to note that there are, two regions where the diameter of the spinal cord is enlarged. One in the cervical region, and another in the lumbosacral region. Now, you can probably imagine what's going on here. There's an expansion of the numbers of neurons, and the circuitry of the spinal cord, that's related to these important locations, along the vertebral access of the body. namely, this is where our arms are attatching to the body axis and the legs. And in, and in these two regions of the spinal cord, these are way o, the, these regions are where we find the nerves that are providing motor output to the extremeties, as well as providing sensory input. So there are enlargements, or, a increase in diameter of the spinal cord. There in the sacral region. I'm sorry, in the cervical region. As well as in the lumbosacral region. And this thickening then, allows for an increase in the circuitry that is required to govern the activities of the arms and the legs. One other point to make before, we leave this view of the spinal cord. I want you to notice where we find the location of the, inferior end of the spinal cord. we find it not at the bo-, bottom of the vertebral column, but we actually find it at about the level of l One or L2. That is vertebral body levels L1 or L2. Well, of course, it didn't begin that way as the spinal cord was first developing. It was approximately the same length as the bones of the vertebral column. So the spinal cord filled up that space within the vertebral column. But as we grow in, especially in early life, the, the, non-neural structures grow at a faster rate so we end up with a longer vertebral column than spinal cord, and as a result the spinal nerves end up continuing to exit through the canals. where they first developed but now there is a long length of nerve root that develops as the vertebral column grows at a faster rate than the spinal cord. And what we end up with as a result of all of this is, beautiful structure. Called the horses tail, or the cauda equina. And so in the lumbosacral regions of the spinal cord what we see are these long nerve routes that extend like a horses tail. From the lumbosacral enlargement out through the canals between the vertebrae. space called the anterior vertebral foramina, that allow for the passage of the spinal nerve routes. So, I say all that to emphasize that I don't want you to be confused about, the nomenclature that we use to describe level within the spinal cord. if we're talking about, for example, the l two level. you need to understand are we talking about The spinal nerve. Are we talking about the vertebra or the vertebrae itself or are we referring to the segment of the spinal cord and always try to be clear about that as we're talking about these anatomical issues. So for example, the second, vertebral, body is found, right at this level here, and that's where we find the emergence of the second lumbar nerve. However, that nerve attaches to the spinal cord at some, significantly higher level. So when it comes to understanding the relationship of Lesions within the spinal cord to dormatomal levels of paresthesias or anesthesia it will be important to know these relationships between spinal cord segment, nerve and vertebrae. So I'd just like to make a few points as we look a little bit more closely here at the vertebral column. what I want you to notice is that the, dorsal or the posterior aspect of the vertebrae is off to the right, sort of coming at you. And the ventral or anterior aspect is to the left with the, dorsal/ventral axis running something like this through this illustration. Okay. So then it makes sense to recognize a ventral root that's coming out of the ventral horn of the spinal cord. This ventral root is going to send signals out to striated muscle. And these are motor signals leading to the contraction of those muscle fibers. Now That spinal nerve is also going to contain sensory axons that may be derived from special receptors in skin or some other kind of structure. And the course of the axons will run right that same spinal nerve so we call that a mixed spinal nerve. And then there's a cell body that sits in a ganlian right here, and the central process of that axon will enter through the spinal cord. So, we're talking about the spinal nerve itself I want you to understand that it is mixed with both motor and sensory components. But once we get down to the roots then we have a ventral motor root and a dorsal sensory root. Alright? Now we also have something called the sympathetic chain. Which is a chain of ganglia that runs in the long axis or the superior to inferior axis of the spinal cord on either side. And we'll talk about this when we get into a discussion of the autonomic nervous system. But within these sympathetic chain ganglia are the neurons that innervate viscera. innervate vascular, arterials. basically, where ever there is sympathetic innervation of smooth muscle, cardiac muscle, and glandular tissue. But that's where we find those kinds of motor neurons in the sympathetic chain. And notice that the sympathetic chain. Is connected by a series of small connecting rootlets that go back and forth between the spinal nerve and the sympathetic chain as that nerve emerges out of the canal fallen between the vertebrae of the vertebral column. All right. Well that's really all that I wanted to tell you today about cranial nerves and spinal nerves before having a chance to focus in on the brain stem and show you the cranial nerves in the lab. So, if you'll bear with me, we'll make a transition. And when you see me next, I'll be in the neuroanatomy lab with a brain in my hands. So I'll see you there.