Understanding Brain and Spinal Cord Structure

So parenchyma, again, just means functional tissue of any organ. And when we think about functional tissue of the brain, we certainly think neurons. And that is going to be absolutely true. Neurons in this picture, we're walking our way through the room. Neurons here are pink. to be fed by several directly fed or interacting with several real cells and so but when we think about the prism of the brain it's not just neurons it is also the real cells and it's also the blood vessels and it's also the CSF area. The brain, probably no surprise, is a complicated organ. And here we can see it just by distilling down the brain to its most salient parts of the parenchyma. It is quite complicated. We've got multiple cell families that we're dealing with, two different fluid-filled areas. And we have to keep all of this more... It's separate because there's stuff in the blood that cannot possibly reach a neuron without killing it. There's stuff in the blood that does not belong in the CSF. So we're going to see these barrier cells, these pinnacle cells, that only reduce the CSF but prevent other things from getting in there. So it's a very busy area. I'll be starting in that upper left hand corner so if you're drawing and you just have time to draw that before I start yacking it's okay. I'm going to work my way around in sequence. We'll be starting in the upper right left hand corner. Right and left. What a trick today. I'm just going to provide some basic labels so that way if you're reviewing this, you're thinking, what the heck is that? You'll have that word here. This is going to be a blood vessel. This is a cross-section of a blood vessel. So it looks funny. This is also a blood vessel, probably what you're used to seeing. But blood vessels sometimes reveal more details if we examine them on the cross-section. So that's what we're doing here. So this is a capillary, just like this one down here. Cross-sectional capillary reveals kind of more details of the cells that make up the capillary wall, which is important here because we're about to talk about astrocytes. And it turns out to truly understand astrocytes, we kind of need to know a little bit of detail about the blood vessel wall because their little foot extensions become almost part of that blood vessel wall. It's a very strange relationship, and most a lot of other cells do that. So I've got a capillary there cut on the cross-section. I will label neurons here and these are neurons in the brain so these are going to be interneurons. So everything I got three of them here. Interneurons are the neurons of the brain. Three of those. This up and zoom in a little bit. Maybe focus, that'd be helpful. I'm also going to show an astrocyte and its physical relationships to other structures as well as an oligodendrocyte. So these numbers and colors match your chart above but you can't really see all that in this particular zoomed in view. Astrocyte number one, oligodendrocyte number two, and three in turnarounds, all pink. Alright, feel pretty comfortable with this. Again, you don't have time for this, but I'm just going to look at this. Just try to avoid having you draw details and talking at the same time. I say avoid. I'm not perfect at it. Alright, I'm going to talk about astrocytes. I'm seeing a lot of eyeballs. That's usually my cue. Astrocytes here, notice they have what's called a foot extension. So here's the soma or cell body. They have extensions coming out from that and they have these little processes. processes, end feet, there's a lot of different names for them, but they're just the end of the cell, and we can see they actually almost wiggle in between, almost seemingly find their way into or as part of this blood vessel wall. So the cells that you're looking at here, these are endothelial cells. Endothelial cells make up the inner lining of a blood vessel, so endothelial. Endothelial cells. make up the inner lining of all blood vessels, capillaries, arteries, veins, it doesn't matter. The very inner layer of cells and all of those vessels are endothelial cells. And we see the foot processes almost becoming part of that blood vessel wall. And that's sort of an important detail for understanding. These astrocytes take nutrients from the blood and help pass them to the interneuron. So that approximation, that close physical relationship makes sense there. So nurse cells, for example. astrocytes called nurse cells. But we also see these astrocytes, some of their foot processes extend in the opposite direction and they help reinforce this space right here which is called a synapse or synaptic cleft. And a synapse or synaptic cleft is the space between two neurons. And this space cannot be too wide. Too small and it can't contain debris because a synapse will see diffusion of neurotransmitters from one cell to another. And so we want that synapse to stay relatively free. clear of debris that's important for diffusion. We also need it to be pretty close because diffusion is a slow process, doesn't work very well with long distances. So these split processes come in and really help reinforce that synapse. So astrocytes do a lot as far as the direct health and function of neurons. We have also, though, sort of the spider-looking thing. That's an oligodendrocyte. Oligodendrocyte. And notice how it has a soma, a cell body. And it has these extensions that come out, and they myelinate. They can almost wrap around these axons. Notice they associate with different neurons. They can myelinate axons of many different neurons. and that is a space-saving feature. You get the speed of reaction potential conduction, but you don't have to have so many individual cells like a Schwann cell. So those two cells, astrocytes and oligodendrocytes, form a direct connection and association with our interneurons. So that's why they're sort of grouped together. Questions on this? Questions on the approximation, the function? Move over to the orange, the number three there. Number three. This is microglia. Microglia. So in this particular shape, microglia, that's what these are. In this particular shape, it's sort of looking. It's roaming. It would be able to move through the different areas of the brain parenchyma and survey. It does surveillance. And it's going to be looking for things that don't belong. Passogens, viruses, for example. cell debris, anything that could junk up our diffusional processes. So remember, microglia are shape shifters and we can glean a lot about what's happening by just looking at the angle, looking at it histologically and going... oh well this person maybe was suffering from some sort of infection based on the shapes of their microglia. So it's pretty interesting when microglia shape will tell you what is likely happening in the brain and then from there you would make different sort of diagnostic decisions for example. But this one, this particular shape is roaming or looking. Now if you look up in your chart we noted if it was activated, if it had found something that it didn't think would belong, it would change shape. processes there would not be so spiky or linear, they'd be more rounded. And that's a sort of a telltale sign of a cell, that's hard to say, that's a lot of alliteration, of a cell that has found something it doesn't like, its organelles are becoming more active, they get more plump, the cell becomes more plump, and it basically just sort of goes from this linear smaller version to a more plumped up rounder version, and that is due to the inner cell working. That's what causes that shape chipping, is the inside of the cell is becoming very busy and that makes the rest of the cell look pretty plump. So microglia. I'm going to come in here to number four, talk about several things here. Are we good with sort of the top part of this image? Prankema, yes ma'am. What is this resting slash... It's just looking for... So it's homeostatic function. So it's got different labels. Some people call that a resting shape, some people call it a homeostatic shape. Just go with whatever makes most sense to you. Also the belonging. You can say it's looking for something that does not belong. Good question. Any other questions before we go down to the bottom? Taking a look at production of CSF and what is CSF? What produces it? Circulates it? Where does it go? So far so good? Alrighty. Let me come down here then and I'll give you a moment to draw this out. I've got several different things I want to talk about and you can kind of get a feel for where I want to go with this drawing based on some bulleted points there. Looking at covoid plexus. Let me give this particular area of the parenchyma a proper title, covoid plexus. The halfway that you're drawing looks probably more familiar, because longitudinally, um... I think there's a lot of value in understanding structures in the cross section and longitudinal section. You get a lot more detail if you understand both. So same structure as what you saw up there. So the lines that you're drawing, endothelial cells forming the walls of that capillary. A very special capillary. Thank you. ...things about the choroid plexus. This is described as a tuft of capillaries. It truly looks tufted, sort of bunched up, and it's a very special area in the brain, this tuft of capillaries, where we... see cerebrospinal fluid produced. So not all capillaries in the brain produce TSF. Only the capillaries that come very near a ventricle. You have four ventricles in the brain, two laterals, lateral ventricles. which are also called ventricle 1 and 2. They don't tell you that. They just say two ventral, two lateral, and then ventricle 3 and 4, and you're like, is there not 1 and 2? There is. Lateral ventricles are also ventricle 1 and 2. Ventricles are fluid-filled areas in the brain. So the choroid plexus, the specialized tuft of capillaries that approaches a ventricle. So I have some blood flow coming in this direction. Blood flow in this direction, we're bringing in fresh blood, so it would have oxygen, nutrients, should be fairly fresh. devoid of waste. So what we'll see is that blood passes through the special capillary, tuft of capillaries known as the choroid plexus. We'll see that that blood flow is able to deliver nutrients. So we'll have nutrients coming out as that blood flows past and then it will start to pick up waste products. So the diffusion works pretty well here because we're full of oxygen and glucose which we push out. We have fewer waste nutrients or waste nutrients waste products which we will change as we pick up those waste products as that blood continues to move through the choroid plexus. So first of all let's talk about getting nutrients out from the blood and into this particular area of the brain called the ventricle. So these are ependymal cells so number four corresponds to the fourth line in your chart above so ependymal cells and projecting from the apical surface here I'm going to do a little better job writing in cilia. So these cilia are hair-like projections, a lot of them, and the apical surface. So remember the apical surface just means the exaggerated surface usually faces some fluid-filled area. So we've got a lot of cilia. cilia coming off the apical surface and those cilia beat and that helps move this fluid. So it's not just enough to produce the fluid, you have to distribute the fluid and remember the blood moves because it has the force of the heart behind it. Pressurizes blood and moves. There's nothing pressurizing cerebrospinal fluid and indeed you don't want it to because it's a very delicate area of the brain. So something has to be developed that will help circulate this. We don't have a pressure generator like we would in the heart or blood capillaries for example. So we're gonna push these items out. So when we think about what is in the CSF. So first of all, what is CSF? It's pretty vague here. Nutrients, oxygen from the blood. The HSF is about 99% water. And then the 1% that's left, so you've got 1% protein, glucose. Ions, oxygen, but most of it is water. It is a really a distributing fluid that helps distribute the few ions and nutrients and reclaim the waste. So what we get here comes from the blood. So these ependymal cells are responsible for very carefully selecting items from the blood and dragging them into the CSF. they produce the CSF, but again it beats and helps that CSF circulate. So, epenemal cells are more than just a barrier function. They do a lot of jobs here. They have a lot of functions. We'll also see the epenemal cells are responsible for helping those waste products. What are some waste products we find here? CO2, lactate, Lactic acid, believe it or not, hydrogen ions, waste products that have accumulated from parts of the central nervous system, they cannot accumulate in CSF. That's a C, by the way. I don't know what this looks like. I can't read it. I don't know how you could. So CO2, carbon dioxide, lactic acid, hydrogen, all that's got to come out and go back into the blood for distribution to the kidneys, for example, or the lungs. You're that CO2 that cleans that blood. So the cori plexus is where this happens. And these ependymal cells in the cori plexus produce the CSF. Everywhere else where we find ependymal cells, they may just form sort of a barrier function. We only see cerebrospinal fluid being produced in the cori plexus. So the parenchyma of the brain, there is an awful lot going on here. And it all has to be sort of coordinated and timed just right. Or these cells just don't hold up too well. Questions? about this? Questions about parenchyma of the brain, cells of the brain. Questions you may expect on the exam from this would be, other than just be familiar with these things, what functions would be lost if oligodendrocytes were obliterating? What would happen if the microglia changed shape and was plumper? The flow to this area decreased. What would be lost? So those are things that I would expect you to be able, after studying something like this, thoroughly, to be able to have a level of comfort with answering. And these are transfer type questions. I've given you the pieces, and now the exam, I may be looking for you to put them together. Yes, sir. So are, like, the cilia changing, like, the concentration between, like, the two, or, like, is it physically, like, grabbing? Stuff from the CSF would take it out, from the blood into the CSF. So the cilia aren't really responsible for moving the composition items from one ear to the other. The cilia are responsible for beating and producing a current. So they would not be able to choose glucose or lactate from the mix. That's the cell membrane that's doing that. They're more like, I'm trying to think of a good, like imagine a bunch of people with brooms, and you all sweep at the same rate in the same direction. That's kind of what that would be like. I don't know if that metaphor works, but they... they sweep the fluid, which really just means it makes a current. Yeah, that's a good question. Other questions before we go into the spinal cord? Parenchyma of the spinal cord. Which we kind of already looked at. I'm going to be looking for not just placement of the few glial cells here, but, hey, can you still label this and understand the different parts of the gray H, for example? Any other questions on this before we go? Seeing none, I'm going to come over here and this is all you get. Great to the spinal cord. I'm giving you the central canal. And that's all we're going to do for now. Draw this is a just a cross section of the spinal cord and it doesn't matter really where in the spinal cord we're talking about just a cross section of the spinal cord. I also have some things extending from the spinal cord so be careful when you're drawing not to Think that everything here is spinal cord. We actually have a nice sort of fusion of CNS and PNS in this drawing. Emphasize where we find some other neural cells. Label dorsal and ventral. It's a challenge. See what you can come up with. Even if you're dead wrong, there's learning to do. Dorsal and ventral. And you can even, if you're feeling pretty good about that, label the parts of the horn. Or the gray H, or the different horns of the gray H. Hope you got that right. Dorsal back, posterior ventral front, anterior. Gray H in this picture is brown because I don't have a gray marker, but you get the idea. The gray H contains unmyelinated areas. Out here, these are myelinated areas. So the gray H, if you have the ability and you want to shade this in some light colored gray that may help. Out here this is white matter I can write that in and it's going to be highly myelinated. So anything so it's called gray because it's unmyelinated. Out here This is all white matter and that's because it's highly myelinated. So everything out here I'll just sort of lightly shade just to make some distinction between the gray H and the white matter which is ironically blue. There we go. Kind of makes that gray H stand out a little bit more. So everything outside of the gray H highly myelinated. Everything inside the gray H not myelinated. So we talked about horns and once you know dorsal and ventral, you know dorsal horns, ventral horns, and then we have some interneurons in the middle. We talked about that already. What I'm going to talk about first though on this drawing, some new stuff, kind of new stuff, central canal. And my question for you is what glial cells line the central canal? Look up in your chart, disinformation can be found there. Maybe the color coding is a little bit of a hint. What glial cells line the central canal? You probably know it, but you're like, I'm not quite sure how to say it. It's a weird word. Ependymal cells. Yeah, ependymal cells. If that's what you're thinking, there you go. This stuff just takes practice. It's not normal words we use every day. So the central command there, you see the little bit of CSF right here. It's pink cells. Here are appendimal cells and I can attempt to put some cilia in there. I feel like I'm going to regret this but you know Never know that till you try and they'll be like yeah, I regret that But here are some cilia projecting from that and they are they beat and they help move that cerebrospinal fluid So the cerebrospinal fluid will be this little tiny bit of fluid in that canal. So appendimal cells here It's a strange word to say. Ependymal cells, they don't produce the CSF. CSF is only produced in the lateral ventricles in the brain. But they do help distribute it because they have cilia that beat. So that's one glial cell we would find. in the spinal cord parenchyma. There are other glial cells though that I want to spend more time talking about. One of them we saw in our chart. What cell would we find? surrounding the soma of our primary sensory neuron.... beats by Dr. Dre. What's the name of that song? Satellite cells, yeah, so I'm going to put them on both sides because we are bilaterally symmetrical. So on the other side, we've got other primary sensory neurons. They too would have somas surrounded by satellite cells. So both of these that I just drew are examples of primary sensory neurons bringing information in at the same time from the right and left sides of the body. And it gets pretty small here, so hopefully you can see that. For some reason, this looks like a floppy-eared dog, but that's just as good. Surrounding the soma of our satellite cells, there we go, or soma of our sensory neurons are these satellite cells. This swelling here, do you remember what this is called, where we see all those somas housed? What is the name of this swelling? Dorsal root ganglion. Great job. So this swelling here, we'd see the somas with their satellite cells housed. This swelling here, one on both sides. This is a dorsal root. Ganglion. Ganglion defined as a collection of somas in the PNS. Ganglion is a collection of somas in the PNS. Dorsal root ganglion. So there's some of our peripheral nervous system satellite or glial cells. We also need to add in some Schwann cells. And it turns out the vast majority of neurons in the peripheral nervous system are myelinated. So I can add a few on our primary sensory neurons, but I will also add some more down here when we get to the ventral. root. So I think I use light green for this as well. So these are satellite cells. I'm going to use a similar color. I'm just going to myelinate as well as I can, always short of space. But I'm going to myelinate here areas of this axon that would have some Schwann cells. So the Schwann cells wrapping around those axons. Schwann cells again wrapping around, kind of draw it like a little tunnel. So there's a Schwann cell. So we've got satellite cells, got Schwann cells, both of these in this view. And then down here, if we were to look at motor neurons, if we were to move away from things in the dorsal area, things in the dorsal roots, dorsal root ganglions, and the dorsal horn of the gray H, everything here is dorsal, it's towards the back. could come down here and talk about motor neurons. So in the ventral roots, the ventral horns of the gray H, we have the somas of motor neurons, nice multipolar neurons, trying to take in as much information as possible. I'll do both sides, remember bilaterally symmetrical. And these are going to be somas or cell bodies of somatic motor neurons. What would they innervate? What effector? There's only one. What would these innervate? We follow them all around the peripheral. Skeletal muscle. So somatic motor neurons only innervate one type of defector, and that's skeletal muscle. So the axons here, right after we leave this spinal cord and into the ventral root, ventral ischemic, PNS, we would find a heavily myelinated axon. What glial cell would you want to put there? Heavily myelinated axon in the peripheral nervous system would be due to what glial cell? I'm about to say Schwann cell. So only Schwann cells can myelinate areas in the PNS. So I'm going to heavily myelinate these as well. And that myelination allows these motor neurons, these somatic motor neurons, to be very fast. And that's good because we don't want to waste time activating skeletal muscles. So I'm going to stop here because really once we enter that spinal cord, we wouldn't have Schwann cells anymore. So both of these are going to be myelinated heavily with Schwann cells that help these. Axons conduct action potentials very quickly, but they're Schwann cells because they're in the PNS. So here's another example of a Schwann cell. So the parenchyma of the spinal cord obviously looks different than the parenchyma of the brain. And here we can start to put together different sort of placements and functions of the glial cells. So that's when you study this chart, this is how you would study it. I would not memorize that chart. I just don't think it's very helpful. That's a waste of your brain power. Charts are for reference. Images and manipulation solving problems, that's a problem for the human brain. So let's talk about this question down here before we go, this particular drawing, before we leave this drawing. If a neuron, an interneuron to be specific, lost its astrocytes, I love this poor grammar here, my fault. What problems would this cause? Yikes. What problems would this cause other than poor grammar? Loss of astrocytes. What problems would it cause for neurons? It wouldn't be able to pull any nutrients from the blood. Lack of nutrients, absolutely. What else? That's a big one. That's what I would start with, lack of nutrients. Second problem would be? The synapses. Synapses, yeah. Probably not going to be able to maintain those synapses. Interneurons wouldn't have a lot of nutrients anyway, so they're probably not doing a lot of communication. But if they were, we'd have trouble with the communication. Astrocyte damage due to traumatic brain injury. concussion is what usually causes the residual remaining problems after the concussion has been assumed to be fine. It's the astrocytes that really determine how fine is that person. Now you can see when we look at what all... all astrocytes do, you lose those astrocytes, it doesn't really matter how intact your interneurons are, they don't function. So that's why it's sort of the next-gen helmet engineering. It's really aimed more at protecting the astrocytes compared to the previous generation of helmets. Questions on this? I'm just going to compare nerves and tracks before we end for the day. Questions on anything you see here? So nerves and tracts, we've actually drawn out part of nerves and tracts. You didn't know it, but that's why I wanted to sort of formally go through this. Just it's actually something to clarify, I hope, some of the things we looked at on here. So give me just a moment and I'll get setup and we'll take a look at nerves versus tracks they are different they are different we cannot use them interchangeably cannot use these words interchangeably so we're at least gonna get a good comparison and contrast of nerves and tracts. Let's take a look at what's a nerve. I've talked about nerves. I've talked about spinal nerves. I've talked about peripheral nerves. Very simple definition. A nerve is a bundle of neurons, specifically their axons. that are surrounded by different layers of connective tissue. Remember, CT stands for connective tissue. So a nerve is a bundle of axons surrounded by different layers of connective tissue. We only find nerves in the peripheral nervous system. We find a corollary in the central nervous system, and that's called a tract. They are different, so nerves, PNS, tract, CNS. we saw different glial cells for PNS and CNS. We see different anatomical structures in the CNS and PNS. Nerves also contain their own blood supply. Neurons need a lot of nutrients. They need waste removal. They need to be kept warm. That all comes from the blood. Nutrients, waste removal, warmth, all blood. Also confined, associated with nerves, adipose. What is adipose more commonly known as? Fat. It is. It is known as fat. We see some fat associated with the outside of neurons or nerves, and we see some fat associated with the inside of large nerves. We also see this cell called a fibroblast. Look at this suffix, blast. We talked about this suffix before when we talked about osteoarthritis. Osteoblast. What do you remember about that particular suffix? Provide some hints about the age of this cell and what it does. Blastamine. Is it mature or immature? Immature. Does it produce a lot of product or no? It does. So fibroblast, even if you've never seen a cell that's named something like that before, just look at it and go, wait, I think I do know something about this. You likely do. Fibroblast, suffix blast, means immature, produces a lot of product. Fibroblast, wherever we find them, produce collagen. And that collagen is the CT layer. So we find a lot of fibroblasts producing collagen. Collagen is what forms the connective tissue layers. Mention that nerves are just simply bundles of axons. And these axons of the neurons in the nerve are sensory or motor. They have sensory neurons, they have motor neurons, or the axons of sensory motor neurons. This means all nerves are mixed. Mixed means contains sensory and motor axons. Mixed means it contains sensory and motor axons. Nerves are not neurons. That's what that symbol means. The equal sign with the line. If you haven't seen that before. Nerves do not equate to neurons. Why? What's a neuron? How'd you define a neuron to someone who's never heard of it? Is it a cell? It is. That's probably the best way to start. It's a cell. Nerves are not cells. Nerves are collections of many different types of things. So it turns out a nerve is a collection of many items. And we've listed them. Nerves contain axons. They contain blood vessels. They contain fat or adipose. They contain fibroblasts, which make collagen. That's a lot of stuff. So this is a collection or an amalgam. ...of items. Neurons are cells, so they are not used interchangeably. And I'd just like to be very clear about that, because a lot of times you see, unfortunately, a lot of different bad vocab. Now, putting this together in a very simple schematic, nerves are not neurons. I'm going to draw a cross-section of a nerve. On the outside, we find a really thick connective tissue layer. This is a really thick connective tissue layer called epineurium. On the inside we find little bundles of axons and they're bundled up but we still find sensory and motor axons. And we find those sensory and motor axons in structures called fascicles. So I'm going to do red for motor. This is a cross-section of motor neurons, somatic motor neurons for example. And I will do green circles for sensory neurons because nerves are mixed. And if we cut a nerve on the cross section, we'd find sensory neurons. And we'd find motor neurons. So sensory neurons, specifically their axon. And over here, motor neurons, specifically their axons. So to say neurons are not nerves, now you know why. And that's where we will end for the nervous system portion. On Thursday, we'll take an introduction to the endocrine system. And then on Tuesday, we'll have your questions. Any questions about any of this, let me know. Any questions about your quiz grades, any questions about content, feel free to let us know. Otherwise, we'll see you Thursday.

So parenchyma, again, just means functional tissue of any organ. And when we think about functional tissue of the brain, we certainly think neurons. And that is going to be absolutely true.

Neurons in this picture, we're walking our way through the room. Neurons here are pink. to be fed by several directly fed or interacting with several real cells and so but when we think about the prism of the brain it's not just neurons it is also the real cells and it's also the blood vessels and it's also the CSF area. The brain, probably no surprise, is a complicated organ. And here we can see it just by distilling down the brain to its most salient parts of the parenchyma.

It is quite complicated. We've got multiple cell families that we're dealing with, two different fluid-filled areas. And we have to keep all of this more... It's separate because there's stuff in the blood that cannot possibly reach a neuron without killing it.

There's stuff in the blood that does not belong in the CSF. So we're going to see these barrier cells, these pinnacle cells, that only reduce the CSF but prevent other things from getting in there. So it's a very busy area.

I'll be starting in that upper left hand corner so if you're drawing and you just have time to draw that before I start yacking it's okay. I'm going to work my way around in sequence. We'll be starting in the upper right left hand corner. Right and left.

What a trick today. I'm just going to provide some basic labels so that way if you're reviewing this, you're thinking, what the heck is that? You'll have that word here. This is going to be a blood vessel.

This is a cross-section of a blood vessel. So it looks funny. This is also a blood vessel, probably what you're used to seeing.

But blood vessels sometimes reveal more details if we examine them on the cross-section. So that's what we're doing here. So this is a capillary, just like this one down here. Cross-sectional capillary reveals kind of more details of the cells that make up the capillary wall, which is important here because we're about to talk about astrocytes. And it turns out to truly understand astrocytes, we kind of need to know a little bit of detail about the blood vessel wall because their little foot extensions become almost part of that blood vessel wall.

It's a very strange relationship, and most a lot of other cells do that. So I've got a capillary there cut on the cross-section. I will label neurons here and these are neurons in the brain so these are going to be interneurons. So everything I got three of them here. Interneurons are the neurons of the brain.

Three of those. This up and zoom in a little bit. Maybe focus, that'd be helpful. I'm also going to show an astrocyte and its physical relationships to other structures as well as an oligodendrocyte.

So these numbers and colors match your chart above but you can't really see all that in this particular zoomed in view. Astrocyte number one, oligodendrocyte number two, and three in turnarounds, all pink. Alright, feel pretty comfortable with this. Again, you don't have time for this, but I'm just going to look at this. Just try to avoid having you draw details and talking at the same time.

I say avoid. I'm not perfect at it. Alright, I'm going to talk about astrocytes.

I'm seeing a lot of eyeballs. That's usually my cue. Astrocytes here, notice they have what's called a foot extension.

So here's the soma or cell body. They have extensions coming out from that and they have these little processes. processes, end feet, there's a lot of different names for them, but they're just the end of the cell, and we can see they actually almost wiggle in between, almost seemingly find their way into or as part of this blood vessel wall.

So the cells that you're looking at here, these are endothelial cells. Endothelial cells make up the inner lining of a blood vessel, so endothelial. Endothelial cells.

make up the inner lining of all blood vessels, capillaries, arteries, veins, it doesn't matter. The very inner layer of cells and all of those vessels are endothelial cells. And we see the foot processes almost becoming part of that blood vessel wall. And that's sort of an important detail for understanding. These astrocytes take nutrients from the blood and help pass them to the interneuron.

So that approximation, that close physical relationship makes sense there. So nurse cells, for example. astrocytes called nurse cells.

But we also see these astrocytes, some of their foot processes extend in the opposite direction and they help reinforce this space right here which is called a synapse or synaptic cleft. And a synapse or synaptic cleft is the space between two neurons. And this space cannot be too wide.

Too small and it can't contain debris because a synapse will see diffusion of neurotransmitters from one cell to another. And so we want that synapse to stay relatively free. clear of debris that's important for diffusion. We also need it to be pretty close because diffusion is a slow process, doesn't work very well with long distances.

So these split processes come in and really help reinforce that synapse. So astrocytes do a lot as far as the direct health and function of neurons. We have also, though, sort of the spider-looking thing.

That's an oligodendrocyte. Oligodendrocyte. And notice how it has a soma, a cell body.

And it has these extensions that come out, and they myelinate. They can almost wrap around these axons. Notice they associate with different neurons. They can myelinate axons of many different neurons.

and that is a space-saving feature. You get the speed of reaction potential conduction, but you don't have to have so many individual cells like a Schwann cell. So those two cells, astrocytes and oligodendrocytes, form a direct connection and association with our interneurons.

So that's why they're sort of grouped together. Questions on this? Questions on the approximation, the function? Move over to the orange, the number three there. Number three.

This is microglia. Microglia. So in this particular shape, microglia, that's what these are. In this particular shape, it's sort of looking.

It's roaming. It would be able to move through the different areas of the brain parenchyma and survey. It does surveillance.

And it's going to be looking for things that don't belong. Passogens, viruses, for example. cell debris, anything that could junk up our diffusional processes.

So remember, microglia are shape shifters and we can glean a lot about what's happening by just looking at the angle, looking at it histologically and going... oh well this person maybe was suffering from some sort of infection based on the shapes of their microglia. So it's pretty interesting when microglia shape will tell you what is likely happening in the brain and then from there you would make different sort of diagnostic decisions for example. But this one, this particular shape is roaming or looking.

Now if you look up in your chart we noted if it was activated, if it had found something that it didn't think would belong, it would change shape. processes there would not be so spiky or linear, they'd be more rounded. And that's a sort of a telltale sign of a cell, that's hard to say, that's a lot of alliteration, of a cell that has found something it doesn't like, its organelles are becoming more active, they get more plump, the cell becomes more plump, and it basically just sort of goes from this linear smaller version to a more plumped up rounder version, and that is due to the inner cell working. That's what causes that shape chipping, is the inside of the cell is becoming very busy and that makes the rest of the cell look pretty plump.

So microglia. I'm going to come in here to number four, talk about several things here. Are we good with sort of the top part of this image? Prankema, yes ma'am. What is this resting slash...

It's just looking for... So it's homeostatic function. So it's got different labels.

Some people call that a resting shape, some people call it a homeostatic shape. Just go with whatever makes most sense to you. Also the belonging.

You can say it's looking for something that does not belong. Good question. Any other questions before we go down to the bottom?

Taking a look at production of CSF and what is CSF? What produces it? Circulates it? Where does it go? So far so good?

Alrighty. Let me come down here then and I'll give you a moment to draw this out. I've got several different things I want to talk about and you can kind of get a feel for where I want to go with this drawing based on some bulleted points there. Looking at covoid plexus.

Let me give this particular area of the parenchyma a proper title, covoid plexus. The halfway that you're drawing looks probably more familiar, because longitudinally, um... I think there's a lot of value in understanding structures in the cross section and longitudinal section. You get a lot more detail if you understand both.

So same structure as what you saw up there. So the lines that you're drawing, endothelial cells forming the walls of that capillary. A very special capillary.

Thank you. ...things about the choroid plexus. This is described as a tuft of capillaries.

It truly looks tufted, sort of bunched up, and it's a very special area in the brain, this tuft of capillaries, where we... see cerebrospinal fluid produced. So not all capillaries in the brain produce TSF.

Only the capillaries that come very near a ventricle. You have four ventricles in the brain, two laterals, lateral ventricles. which are also called ventricle 1 and 2. They don't tell you that.

They just say two ventral, two lateral, and then ventricle 3 and 4, and you're like, is there not 1 and 2? There is. Lateral ventricles are also ventricle 1 and 2. Ventricles are fluid-filled areas in the brain.

So the choroid plexus, the specialized tuft of capillaries that approaches a ventricle. So I have some blood flow coming in this direction. Blood flow in this direction, we're bringing in fresh blood, so it would have oxygen, nutrients, should be fairly fresh. devoid of waste.

So what we'll see is that blood passes through the special capillary, tuft of capillaries known as the choroid plexus. We'll see that that blood flow is able to deliver nutrients. So we'll have nutrients coming out as that blood flows past and then it will start to pick up waste products. So the diffusion works pretty well here because we're full of oxygen and glucose which we push out.

We have fewer waste nutrients or waste nutrients waste products which we will change as we pick up those waste products as that blood continues to move through the choroid plexus. So first of all let's talk about getting nutrients out from the blood and into this particular area of the brain called the ventricle. So these are ependymal cells so number four corresponds to the fourth line in your chart above so ependymal cells and projecting from the apical surface here I'm going to do a little better job writing in cilia.

So these cilia are hair-like projections, a lot of them, and the apical surface. So remember the apical surface just means the exaggerated surface usually faces some fluid-filled area. So we've got a lot of cilia.

cilia coming off the apical surface and those cilia beat and that helps move this fluid. So it's not just enough to produce the fluid, you have to distribute the fluid and remember the blood moves because it has the force of the heart behind it. Pressurizes blood and moves.

There's nothing pressurizing cerebrospinal fluid and indeed you don't want it to because it's a very delicate area of the brain. So something has to be developed that will help circulate this. We don't have a pressure generator like we would in the heart or blood capillaries for example.

So we're gonna push these items out. So when we think about what is in the CSF. So first of all, what is CSF?

It's pretty vague here. Nutrients, oxygen from the blood. The HSF is about 99% water.

And then the 1% that's left, so you've got 1% protein, glucose. Ions, oxygen, but most of it is water. It is a really a distributing fluid that helps distribute the few ions and nutrients and reclaim the waste.

So what we get here comes from the blood. So these ependymal cells are responsible for very carefully selecting items from the blood and dragging them into the CSF. they produce the CSF, but again it beats and helps that CSF circulate. So, epenemal cells are more than just a barrier function. They do a lot of jobs here.

They have a lot of functions. We'll also see the epenemal cells are responsible for helping those waste products. What are some waste products we find here?

CO2, lactate, Lactic acid, believe it or not, hydrogen ions, waste products that have accumulated from parts of the central nervous system, they cannot accumulate in CSF. That's a C, by the way. I don't know what this looks like.

I can't read it. I don't know how you could. So CO2, carbon dioxide, lactic acid, hydrogen, all that's got to come out and go back into the blood for distribution to the kidneys, for example, or the lungs. You're that CO2 that cleans that blood. So the cori plexus is where this happens.

And these ependymal cells in the cori plexus produce the CSF. Everywhere else where we find ependymal cells, they may just form sort of a barrier function. We only see cerebrospinal fluid being produced in the cori plexus. So the parenchyma of the brain, there is an awful lot going on here.

And it all has to be sort of coordinated and timed just right. Or these cells just don't hold up too well. Questions?

about this? Questions about parenchyma of the brain, cells of the brain. Questions you may expect on the exam from this would be, other than just be familiar with these things, what functions would be lost if oligodendrocytes were obliterating? What would happen if the microglia changed shape and was plumper? The flow to this area decreased.

What would be lost? So those are things that I would expect you to be able, after studying something like this, thoroughly, to be able to have a level of comfort with answering. And these are transfer type questions. I've given you the pieces, and now the exam, I may be looking for you to put them together.

Yes, sir. So are, like, the cilia changing, like, the concentration between, like, the two, or, like, is it physically, like, grabbing? Stuff from the CSF would take it out, from the blood into the CSF.

So the cilia aren't really responsible for moving the composition items from one ear to the other. The cilia are responsible for beating and producing a current. So they would not be able to choose glucose or lactate from the mix. That's the cell membrane that's doing that. They're more like, I'm trying to think of a good, like imagine a bunch of people with brooms, and you all sweep at the same rate in the same direction.

That's kind of what that would be like. I don't know if that metaphor works, but they... they sweep the fluid, which really just means it makes a current. Yeah, that's a good question.

Other questions before we go into the spinal cord? Parenchyma of the spinal cord. Which we kind of already looked at. I'm going to be looking for not just placement of the few glial cells here, but, hey, can you still label this and understand the different parts of the gray H, for example? Any other questions on this before we go?

Seeing none, I'm going to come over here and this is all you get. Great to the spinal cord. I'm giving you the central canal.

And that's all we're going to do for now. Draw this is a just a cross section of the spinal cord and it doesn't matter really where in the spinal cord we're talking about just a cross section of the spinal cord. I also have some things extending from the spinal cord so be careful when you're drawing not to Think that everything here is spinal cord. We actually have a nice sort of fusion of CNS and PNS in this drawing. Emphasize where we find some other neural cells.

Label dorsal and ventral. It's a challenge. See what you can come up with. Even if you're dead wrong, there's learning to do.

Dorsal and ventral. And you can even, if you're feeling pretty good about that, label the parts of the horn. Or the gray H, or the different horns of the gray H. Hope you got that right.

Dorsal back, posterior ventral front, anterior. Gray H in this picture is brown because I don't have a gray marker, but you get the idea. The gray H contains unmyelinated areas. Out here, these are myelinated areas.

So the gray H, if you have the ability and you want to shade this in some light colored gray that may help. Out here this is white matter I can write that in and it's going to be highly myelinated. So anything so it's called gray because it's unmyelinated.

Out here This is all white matter and that's because it's highly myelinated. So everything out here I'll just sort of lightly shade just to make some distinction between the gray H and the white matter which is ironically blue. There we go.

Kind of makes that gray H stand out a little bit more. So everything outside of the gray H highly myelinated. Everything inside the gray H not myelinated.

So we talked about horns and once you know dorsal and ventral, you know dorsal horns, ventral horns, and then we have some interneurons in the middle. We talked about that already. What I'm going to talk about first though on this drawing, some new stuff, kind of new stuff, central canal. And my question for you is what glial cells line the central canal?

Look up in your chart, disinformation can be found there. Maybe the color coding is a little bit of a hint. What glial cells line the central canal?

You probably know it, but you're like, I'm not quite sure how to say it. It's a weird word. Ependymal cells.

Yeah, ependymal cells. If that's what you're thinking, there you go. This stuff just takes practice.

It's not normal words we use every day. So the central command there, you see the little bit of CSF right here. It's pink cells. Here are appendimal cells and I can attempt to put some cilia in there.

I feel like I'm going to regret this but you know Never know that till you try and they'll be like yeah, I regret that But here are some cilia projecting from that and they are they beat and they help move that cerebrospinal fluid So the cerebrospinal fluid will be this little tiny bit of fluid in that canal. So appendimal cells here It's a strange word to say. Ependymal cells, they don't produce the CSF.

CSF is only produced in the lateral ventricles in the brain. But they do help distribute it because they have cilia that beat. So that's one glial cell we would find. in the spinal cord parenchyma. There are other glial cells though that I want to spend more time talking about.

One of them we saw in our chart. What cell would we find? surrounding the soma of our primary sensory neuron....

beats by Dr. Dre. What's the name of that song? Satellite cells, yeah, so I'm going to put them on both sides because we are bilaterally symmetrical.

So on the other side, we've got other primary sensory neurons. They too would have somas surrounded by satellite cells. So both of these that I just drew are examples of primary sensory neurons bringing information in at the same time from the right and left sides of the body. And it gets pretty small here, so hopefully you can see that.

For some reason, this looks like a floppy-eared dog, but that's just as good. Surrounding the soma of our satellite cells, there we go, or soma of our sensory neurons are these satellite cells. This swelling here, do you remember what this is called, where we see all those somas housed?

What is the name of this swelling? Dorsal root ganglion. Great job. So this swelling here, we'd see the somas with their satellite cells housed.

This swelling here, one on both sides. This is a dorsal root. Ganglion. Ganglion defined as a collection of somas in the PNS. Ganglion is a collection of somas in the PNS.

Dorsal root ganglion. So there's some of our peripheral nervous system satellite or glial cells. We also need to add in some Schwann cells.

And it turns out the vast majority of neurons in the peripheral nervous system are myelinated. So I can add a few on our primary sensory neurons, but I will also add some more down here when we get to the ventral. root. So I think I use light green for this as well. So these are satellite cells.

I'm going to use a similar color. I'm just going to myelinate as well as I can, always short of space. But I'm going to myelinate here areas of this axon that would have some Schwann cells.

So the Schwann cells wrapping around those axons. Schwann cells again wrapping around, kind of draw it like a little tunnel. So there's a Schwann cell. So we've got satellite cells, got Schwann cells, both of these in this view.

And then down here, if we were to look at motor neurons, if we were to move away from things in the dorsal area, things in the dorsal roots, dorsal root ganglions, and the dorsal horn of the gray H, everything here is dorsal, it's towards the back. could come down here and talk about motor neurons. So in the ventral roots, the ventral horns of the gray H, we have the somas of motor neurons, nice multipolar neurons, trying to take in as much information as possible. I'll do both sides, remember bilaterally symmetrical.

And these are going to be somas or cell bodies of somatic motor neurons. What would they innervate? What effector?

There's only one. What would these innervate? We follow them all around the peripheral.

Skeletal muscle. So somatic motor neurons only innervate one type of defector, and that's skeletal muscle. So the axons here, right after we leave this spinal cord and into the ventral root, ventral ischemic, PNS, we would find a heavily myelinated axon. What glial cell would you want to put there?

Heavily myelinated axon in the peripheral nervous system would be due to what glial cell? I'm about to say Schwann cell. So only Schwann cells can myelinate areas in the PNS.

So I'm going to heavily myelinate these as well. And that myelination allows these motor neurons, these somatic motor neurons, to be very fast. And that's good because we don't want to waste time activating skeletal muscles. So I'm going to stop here because really once we enter that spinal cord, we wouldn't have Schwann cells anymore. So both of these are going to be myelinated heavily with Schwann cells that help these.

Axons conduct action potentials very quickly, but they're Schwann cells because they're in the PNS. So here's another example of a Schwann cell. So the parenchyma of the spinal cord obviously looks different than the parenchyma of the brain. And here we can start to put together different sort of placements and functions of the glial cells. So that's when you study this chart, this is how you would study it.

I would not memorize that chart. I just don't think it's very helpful. That's a waste of your brain power. Charts are for reference.

Images and manipulation solving problems, that's a problem for the human brain. So let's talk about this question down here before we go, this particular drawing, before we leave this drawing. If a neuron, an interneuron to be specific, lost its astrocytes, I love this poor grammar here, my fault.

What problems would this cause? Yikes. What problems would this cause other than poor grammar? Loss of astrocytes.

What problems would it cause for neurons? It wouldn't be able to pull any nutrients from the blood. Lack of nutrients, absolutely. What else?

That's a big one. That's what I would start with, lack of nutrients. Second problem would be?

The synapses. Synapses, yeah. Probably not going to be able to maintain those synapses.

Interneurons wouldn't have a lot of nutrients anyway, so they're probably not doing a lot of communication. But if they were, we'd have trouble with the communication. Astrocyte damage due to traumatic brain injury. concussion is what usually causes the residual remaining problems after the concussion has been assumed to be fine.

It's the astrocytes that really determine how fine is that person. Now you can see when we look at what all... all astrocytes do, you lose those astrocytes, it doesn't really matter how intact your interneurons are, they don't function.

So that's why it's sort of the next-gen helmet engineering. It's really aimed more at protecting the astrocytes compared to the previous generation of helmets. Questions on this?

I'm just going to compare nerves and tracks before we end for the day. Questions on anything you see here? So nerves and tracts, we've actually drawn out part of nerves and tracts. You didn't know it, but that's why I wanted to sort of formally go through this. Just it's actually something to clarify, I hope, some of the things we looked at on here.

So give me just a moment and I'll get setup and we'll take a look at nerves versus tracks they are different they are different we cannot use them interchangeably cannot use these words interchangeably so we're at least gonna get a good comparison and contrast of nerves and tracts. Let's take a look at what's a nerve. I've talked about nerves.

I've talked about spinal nerves. I've talked about peripheral nerves. Very simple definition.

A nerve is a bundle of neurons, specifically their axons. that are surrounded by different layers of connective tissue. Remember, CT stands for connective tissue. So a nerve is a bundle of axons surrounded by different layers of connective tissue. We only find nerves in the peripheral nervous system.

We find a corollary in the central nervous system, and that's called a tract. They are different, so nerves, PNS, tract, CNS. we saw different glial cells for PNS and CNS.

We see different anatomical structures in the CNS and PNS. Nerves also contain their own blood supply. Neurons need a lot of nutrients. They need waste removal.

They need to be kept warm. That all comes from the blood. Nutrients, waste removal, warmth, all blood.

Also confined, associated with nerves, adipose. What is adipose more commonly known as? Fat. It is. It is known as fat.

We see some fat associated with the outside of neurons or nerves, and we see some fat associated with the inside of large nerves. We also see this cell called a fibroblast. Look at this suffix, blast.

We talked about this suffix before when we talked about osteoarthritis. Osteoblast. What do you remember about that particular suffix? Provide some hints about the age of this cell and what it does. Blastamine.

Is it mature or immature? Immature. Does it produce a lot of product or no?

It does. So fibroblast, even if you've never seen a cell that's named something like that before, just look at it and go, wait, I think I do know something about this. You likely do. Fibroblast, suffix blast, means immature, produces a lot of product. Fibroblast, wherever we find them, produce collagen.

And that collagen is the CT layer. So we find a lot of fibroblasts producing collagen. Collagen is what forms the connective tissue layers. Mention that nerves are just simply bundles of axons. And these axons of the neurons in the nerve are sensory or motor.

They have sensory neurons, they have motor neurons, or the axons of sensory motor neurons. This means all nerves are mixed. Mixed means contains sensory and motor axons.

Mixed means it contains sensory and motor axons. Nerves are not neurons. That's what that symbol means. The equal sign with the line.

If you haven't seen that before. Nerves do not equate to neurons. Why?

What's a neuron? How'd you define a neuron to someone who's never heard of it? Is it a cell? It is. That's probably the best way to start.

It's a cell. Nerves are not cells. Nerves are collections of many different types of things.

So it turns out a nerve is a collection of many items. And we've listed them. Nerves contain axons.

They contain blood vessels. They contain fat or adipose. They contain fibroblasts, which make collagen. That's a lot of stuff.

So this is a collection or an amalgam. ...of items. Neurons are cells, so they are not used interchangeably. And I'd just like to be very clear about that, because a lot of times you see, unfortunately, a lot of different bad vocab.

Now, putting this together in a very simple schematic, nerves are not neurons. I'm going to draw a cross-section of a nerve. On the outside, we find a really thick connective tissue layer. This is a really thick connective tissue layer called epineurium.

On the inside we find little bundles of axons and they're bundled up but we still find sensory and motor axons. And we find those sensory and motor axons in structures called fascicles. So I'm going to do red for motor. This is a cross-section of motor neurons, somatic motor neurons for example.

And I will do green circles for sensory neurons because nerves are mixed. And if we cut a nerve on the cross section, we'd find sensory neurons. And we'd find motor neurons. So sensory neurons, specifically their axon. And over here, motor neurons, specifically their axons.

So to say neurons are not nerves, now you know why. And that's where we will end for the nervous system portion. On Thursday, we'll take an introduction to the endocrine system. And then on Tuesday, we'll have your questions. Any questions about any of this, let me know.

Any questions about your quiz grades, any questions about content, feel free to let us know. Otherwise, we'll see you Thursday.

Transcript for:Understanding Brain and Spinal Cord Structure

Transcript for:
Understanding Brain and Spinal Cord Structure