Hello everyone. Welcome to this tutorial on the embryological subdivisions of the human central nervous system. This tutorial pertains to our first core concept in the field of neuroscience: that the brain is the body's most complex organ. Although given the brevity and the, relative simplicity of today's tutorial, as well as your progress in the course thus far the complexity of the human brain won't exactly be front and center in our consideration. Really, what I'd like for you to be able to accomplish in this tutorial, is to really refresh your appreciation and your understanding of the basic parts of the adult form of the human brain. And so doing, what I want you to be able to do is to identify each of the major subdivisions of the adult nervous system. But now I want you to be able to relate them back to the embryological precursors and associated ventricular spaces. Well, after all we're entering unit 5 of medical neuroscience and our goal is to understand the changing brain. And that story, of course begins in embryological life. With the first formation of the central nervous system that occurs, really, beginning in about the third week of the gestation of human life. And ultimately what we want to be able to do is understand, where did this marvelous form come from in the process of building the human organism. Well, I hope to simply review some of the parts that we see in the adult human brain with you in this session, and relate them back to the terminology that we used to describe the developing brain in embryological life. So this will be largely review. And I hope that you'll appreciate this bit of a pivot as we turn from our studies of the adult form, to a consideration of the mechanisms that are responsible for building the human brain, the body's most complex organ. So, we will return to the lab, and have a chance to once again, review the anatomy of an actual human brain specimen. So I'll see you there. The lab lesson today is to recognize the embryological forms that are viewable in the adult brain. So let me reach into my bin and get a whole adult brain specimen. So when we look at the brain in its adult form, it's really amazing to think that this structure in front of me is derived from a simple tube. But as we just learned at about the third week of gestation the nervous system is in fact a simple tube, and that tube begins to form, a very prominent bulge in the front part and then two smaller bulges, one in the middle and one towards the back. And what we're looking at in front of us is mostly what has become of that forward bulge in that tube. And this is the cerebral hemispheres. This is the left hemisphere. This is the right. So that forward bulge divides into two parts. So most of what we see when we look at the adult brain is, in fact, this forward bulge. And we call this the Prosencephalon. Or forebrain, for short. Pro meaning fore, and encephalon meaning brain. So now we're looking at the posterior or the back side of the brain. And we can see a portion of the hind brain, or the rhombencephalon. And the major structure that's visible here is called the cerebellum. The cerebellum is a large part of the brain which expands into two prominent hemispheres, a left hemisphere and a right hemisphere. And then if I just pick the brain up just a small amount, we can see the additional part of the hind brain that's visible from the posterior surface, and that is the brain stem. But to get a really get a good look at the hindbrain, the rhombencephalon, we need to look at the ventral surface of the brain. So now we're looking at the underside or the ventral surface of the brain. And we'll have another lab lesson on many of the features that we see. For today I want to focus on the embryological divisions. So again all of these cerebral cortex that we see in the hemispheres this is part of the forebrain or the prosencephalon. Now on the ventral side, we can see a small division of the prosencephalon that form structures that we call in the adult form the thalamus and the hypothalamus. Together this is called the diencephalon, and we can see that, just behind this optic nerve and its crossing, there is a surface of the diencephalon here. That is the hypothalamus. And I believe we can see these two small bulges. These are called the mammillary bodies, and that is one surface landmark that tells us that we're looking at the floor of the diencephalon. The mammillary bodies being part of the hypothalamus. Well, just behind the mammillary bodies, we see, the midbrain. And from this view what we can see are two broad columns. These are called the cerebral peduncles. Peduncle is a word that means stalk, and these are two broad stalks that seem to support the cerebral hemispheres. That's the midbrain. Now just below the cerebral peduncle is this broad surface here, this is called the Pons. The Pons is that part of the hindbrain that is intimately connected to the cerebellum. In fact, I think you can appreciate how the pons seems to stream out laterally right into the cerebellum on either side. So that's the pons, together with the cerebellum, this is called the Metencephalon, which is a sub-division of the hind-brain. And then finally, just below the pons, is a complex part of the brain stem called the medulla oblongata, or just the medulla for short. And the medulla is that part of the brain stem that connects to the spinal cord. Now, from a different specimen, I'd like to show you what the human spinal cord looks like, and it would attach to this cut surface of the medulla. Now, attached to the bottom of the brain stem, of course, is the spinal cord. And I have several segments of spinal cord to show you. This is the upper third of the spinal cord that attaches to the bottom of the brain at the brain stem, but this has been removed so I'll go ahead and set this brain down and we'll turn our attention to the spinal cord. This is the upper third, which includes the cervical enlargement. And then this is the middle third of the spinal cord that is the part that's in the region of the thorax. We call that, the thoracic spinal cord. And then down below, is the lumbosacral enlargement. The cervical enlargement is concerned mainly with our arms and our hands. And the lumbar enlargement is concerned mainly with our legs and our feet. And just below the lumbar enlargement is the most inferior segment of the spinal cord and its called the cauda equina. And as we get a close look at the cauda equina you can see why it has its name. Couda equina means horses tail. And what we see is the terminus of the spinal cord with a set of spinal nerves that extend for several vertebral segments out from the vertebral column to serve the lower part of the body.