Appendicular System PDF

We're gonna get rolling here. All right. Onward and upward, right? Yeah, so thanks for being patient with the five-minute late start. I was running a Q&A for our webinar and trying to keep my child quiet. So we're gonna move on to the appendicular system. I am in the midst of recording the videos...

We're gonna get rolling here. All right. Onward and upward, right? Yeah, so thanks for being patient with the five-minute late start. I was running a Q&A for our webinar and trying to keep my child quiet. So we're gonna move on to the appendicular system. I am in the midst of recording the videos for that for next week's labs, right? So we're gonna switch. B is gonna go first, A is gonna go second. The ID manual and the lectures are posted. So since there's different learning styles, I am not going to require that you watch the videos, but you have to at least look at the presentation for next week because there's clinical scenarios and clinical correlations that are in there. So some of you are gonna do better with the videos, some of you are gonna be better looking at the presentation, but you have to do that before you come into lab. presentation, but you have to do that before you come into lab. So if you haven't ever taken anatomy yet, I highly recommend watching the videos. I'm not gonna name everything for you, but what I'm going to do is help you kind of relate what you're seeing to the entire body, look at things, kind of side things, how to know that they're looking lateral versus medial, which is really essential for the ribs, right? Because we're gonna have radial and ulnar side, that's gonna help you maintain the muscles, and basically everything else that we're gonna look at, look at them here on our nerves, our arteries, and veins, right? So if you haven't taken anatomy before, probably watch those videos. I'm gonna do them in shorter segments so you can take a break in between, okay? What you could do anyway is by pausing, but I'm gonna try to block them out. Does anybody have any questions on expectations for next week? questions on expectations for next week? All right, so B group will be in the lab on Tuesday, A group will be in the lab on Thursday, and we'll do kind of similar stuff. All right, so moving on to development of the musculoskeletal system. It's a lot, it's all in here, but we're gonna walk our way through it. Okay, these are wordy, but I really wanted to be specific in terms of what I wanted you to pull out because this is a complex system. So we're first gonna look at the development, how things come to be in terms of muscle, cartilage, and bones. So it's basically musculogenesis, chondrogenesis, and so forth, and then we're gonna move on to how things grow and then kind of timing of different events. All right, so in terms of myogenesis, the creation of muscle, right, you're going to have individual muscle fibers and cells called mesodermal cells, and these mesodermal cells are going to come from mesenchyme or that myoderm, right, or mesoderm, excuse me, right? So mesoderm, recall, creates bone, muscle, and connective tissue, so that's at the origin of these. These cells are going to elongate and kind of line up with one another, and then they're going to differentiate into these myoblasts. These myoblasts will then fuse, so myotubes. These myotubes will really then become these individual muscle fibers, right? So we look at muscle histologically, we have a lot of nuclei in one individual fiber. This is how it comes to be, right? So we have these nuclei along these fibers, so individual muscle fibers are going to extend the length of your muscle, so we have some really long ones, right? We have some additional cells that you can see that support these muscle fibers, and those are going to be called satellite cells. those are going to be called satellite cells. We also looked histologically at the different connective tissue layers surrounding these muscle fibers, then the fascicles, and then the entire muscle itself, right? And so those are the two of them, so our endoderm, and our endomysium is going to be formed by just the existing outside layer of these muscle fibers, right? So it kind of creates its own, okay? creates its own, okay? The perimysium and epimysium that come the middle and biggest coverings are going to be produced by fibroblasts. biggest coverings are going to be produced by fibroblasts. Everybody remember fibroblasts? Way from the beginning, right? They're going to be connective tissue cells, so they're going to form on their own while that endomysium is going to be really part of that actual muscle fiber, okay? Most of our muscles will be formed at birth, and they're going to just keep getting a little bit bigger each year, right? little bit bigger each year, right? Condrogenesis, pretty basic, but we have a lot of different cartilage in our body. We looked at all types of cartilage, we looked at hyaline cartilage, fiber cartilage, and so forth. So we're going to, this is going to really start in week five. Bone formation is going to start in week four, but in week five we'll have mesenchyme going into these different areas in our body, right? It's going to migrate to these locations. Once they're in these locations, it's going to condense, inform, chondrification centers, right? So they're told to go to specific locations in the body to build our cartilage. cartilage. Really, we're going to use very similar terminology, so chondroblasts are going to be those cells that are created, and they are going to mitotically divide, right? Because we have a little bit of tissue, now we need a lot more tissue. They're going to then, like we've seen way in the first block, secrete, create their extracellular matrix, right? right? These cells are going to, which are going to be fibroblasts, create the surrounding tissue. So when you think of that hyaline cartilage, we have those spaces with the cells. Hopefully that's been recording. We'll assume it has. So we have, if we think of that hyaline cartilage in our mind, that view of the slide, all that surrounding purplish stuff is created by these cells. And then, of course, we have our chondroblasts. We're going to be called chondrocytes, specifically, and they're going to sit in their little lakes, those spaces called the lacunae. So kind of a review. Now we're going to talk about chondroblasts. So the first thing is that this is the formation of bone. We are going to then look at the growth of bone, right? So this is the formation and then we'll have the growth of bone. There's two types of bone formation. It's that intramembranous bone formation and then the endochondrial. The one with chondrial in it, for cartilage, is going to differentiate from the other one, intramembranous, because we're going to have mesenchyme come together in intramembranous, then that's going to form bone or bone's going to build on that mesenchyme. In the other one, we're actually going to have the development of hyaline cartilage models and then bone will replace that. So there's an extra step in that endochondrial. We're going to go through them, right? So they both are going to start out with this mesenchyme, which is, do you guys recall what mesenchyme is? Most of the time, they're right up here. Unorganized connective tissue, right? So when we hear that we think unorganized connective tissue, almost always, outside of a few special examples, it's going to come from that mesoderm. So let's take a look at these more specifically. these more specifically. So intramembranous ossification, right? We are going to have these certain centers around the body. Here, for example, we have an ossification center where our parietals are, the midline of the parietals, we'll have two right here because our frontal actually starts at its two bones and so forth. So throughout the body, certain groups of cells are going to congregate in these different locations, which are going to be these centers of ossification. We're first going to start to talk about our primary centers of ossification so that mesenchyme is going to condense and then blood vessels are going to come in. And that's important because we've got to bring in different types of cells and so forth. Some of those cells in that mesenchyme will become osteoblasts, right? mesenchyme will become osteoblasts, right? Bone building cells. They are going to distribute osteoid in that condensed mesenchyme. Osteoid is that flexible part of organic part of bone, which I told you it was going to be on the exam. The inorganic matrix is then going to be deposited on that kind of osteoid model. So not a cartilaginous model, but an osteoid model. And it's going to be put down as a really unorganized bone. And it's called woven bone. So you might be like, why in the world is there a pathological tibia up here? So this is what I used to do, is look at bones to see abnormal bone growth and abnormal bone loss. So when we are deposit bone abnormally and when we're growing, we'll see this type of bone right here. You can see how it's unorganized. It's porous compared to this mature bone right here. So this is what woven bone looks like, right? It's unorganized. unorganized. And this will eventually be kind of replaced and organized into those lamellae or into those osteons that we talked about last block in terms of our microscopic bone organization. So in that woven bone we'll have some trapped osteocytes, right? have some trapped osteocytes, right? Because they were osteo, we'll have osteocytes trapped. They were osteoblasts. And then we'll just kind of continue to replace that and further develop it and organize that bone. These are going to happen in places where we have flat bone primarily. So cranial vaults, our ribs, and other locations. vaults, our ribs, and other locations. If we think about how that bone looks when it's mature, we have two surface plates of that compact bone. And in between we have that spongy bone or cortical bone, right? have that spongy bone or cortical bone, right? And so the outside plates here are going to kind of form on either side and then we'll maintain this spongy bone through really osteoclasts. through really osteoclasts. They're going to kind of eat and maintain that bone. I'm keeping space in there because what's going to hang out in that bone, in that spongy bone, especially as we're growing? that spongy bone, especially as we're growing? Bone marrow. Bone marrow. Put your headphones back on. There we go. So bone marrow. So bone marrow is in different locations when we're growing and when we are adults, right? So when we're growing, it's really within our cranial vaults, bones. It's really cool. And sometimes if you have to, if you're anemic as a child, the bone marrow gets bigger and then your bone gets bigger and they have this really thick stuff called parotid hyperostosis that we can see in past populations anyways. called parotid hyperostosis that we can see in past populations anyways. So we have these two different kind of types of bone form. That's the more straightforward one. Lots of text, but let's talk through it, right? So this is a process that we're going to see here, but we're also going to see in other places. So during the fifth week of development we have in these places of ossification, primary ossification centers, we're going to have a dense, condensed mesenchyme that will have built these hyaline cartilage models, right? right? So a model is something that is going to be replaced basically. So that hyaline cartilage model, you can see right here we're making the long bone, most long bones. Basically everything outside the clavicle, which is intermembranous, is going to be made through this this type of ossification. So limbs are all endochondrial except the clavicle. Don't worry about that part. We have tissue surrounding this though, right? Some of those cells differentiate into that perichondrium, that outside connective tissue layer. outside connective tissue layer. If you recall, when we talked about periosteum, it has that cellular layer, right? right? This does too. So in our perichondrium, that surrounding connective tissue, we're going to have that innermost layer have cells in it, osteoprogenitor cells, which are going to turn into osteoblasts. cells, which are going to turn into osteoblasts. So around the diaphysis of this hyaline cartilage model, we're going to have a thin bone color develop. So a thin layer of bone is going to grow around this structure, specifically in the diaphysis, right? in the diaphysis, right? That long part. Inside that model, we're going to have our cartilaginous cells hypertrophy, which means they're going to increase in size. But because that bone color is forming, it's also going to cut off nutrients to those inside cells. nutrients to those inside cells. So they're going to hypertrophy, but then they're going to die. And what that leads to, or leaves behind, are these bubbles, right? These openings within that. And that is really the beginning of our bone marrow cavity, okay? So the bone collar is formed. Then the next really important step after that bone collar forms is the penetration of blood vessels into that periosteum now, right? vessels into that periosteum now, right? Because the periosteum would change names because now we have bone, into that bone collar. So you see that these blood vessels are going to grow into here. They're going to penetrate those two layers, grow into that developing bone marrow cavity. What does that bring in with it? What do you think? Or you could read the slide. Osteoprogenitor cells, right? So now bring in cells, osteoprogenitor cells, that are going to start to replace the cartilage. start to replace the cartilage. One minute. You're going to replace the cartilage with bone, right? cartilage with bone, right? So the hyaline cartilage doesn't turn into bone. It's not conjurification. It's osteo, ossify, ossification. There you go. So does that make sense? So we have really important things that happen. We're going to have a model. We're going to have bone grow around it because we have a nice layer that makes cells with osteoprogenitor cells in there. That's going to cut off nutrients to the inside of that model. Those cells are going to get big, but then die. You will wait. And then we will have from externally into the nutrient foramen that we talked about last time. We're going to have blood vessels come in and bring in osteoprogenitor cells to start to replace the cartilage with bone. bring in osteoprogenitor cells to start to replace the cartilage with bone. This is a process that we're going to see again in bone growth. Does that make sense? Any questions on that? Any questions on that? It's kind of a hard concept sometimes because it's symbiology. After birth in general, we're going to have these secondary centers of the long bones, right? These are going to be the epiphysis. This is the metaphysis. Excuse me. I said epiphysis earlier. The epiphysis here, the epiphysis, the ends of our long bones, like the head of our humerus, the head of our femur, our vertebra are in like five different pieces that haven't come together yet. We're going to have the same thing happen. Only we are going to maintain some of our long bones to lengthen and we'll talk about that process next, right? So we'll have these secondary centers of ossification that will continue this process to form the ends of our long bones, usually after birth. birth. And then also after birth, again, we're going to have our cartilage remain not only at this epiphysial plate, but also on the ends of our long bones to help with that smooth movement, right? Some of that will remain. All right. We will continue to maintain the medullary cavity. One second. I see your question. We'll continue to maintain that medullary cavity through osteoblasts and osteoclasts absorption and building of bone, right? of bone, right? So it's going to get bigger. What was your question? So in general, there are diseases where you have abnormal cartilage maintenance or growth. So yes, this would then impact the development of bone and so forth. So there's a number of different diseases like this. Sometimes you make too much of it. Sometimes your cartilage turns to bone, which is sometimes called stiff person syndrome. I think, um, what's that singer? Huh? Not share. Close. Titanic. Celine Dion. I think that's what she has. So the bone is turning into cartilage. So you can't move cartilage is turning to bone. So you can't move. All right. So bone growth, right? So this is similar, but different. So bone formation and then growth. We're going to grow in two different ways. Let me grow taller. So we also have to grow in our diameter because if you had, I mean, our bones started out really tiny. So if we don't grow in diameter, you're just going to crush. crush. Um, so parastio or oppositional growth is that, um, kind of growth and robust density, right? robust density, right? Um, diameter is going to occur in the compact bone from the outside. Okay. Endochondrial. We're going to see this word again. So don't confuse it with the bone formation or interstitial growth is that growth in length. We're going to cover the easier one first. So, uh, recall, we just talked about it that we have a connective tissue covering around these long bones. That innermost layer is that osteoprogenic layer, right? We're going to our cellular layer. to our cellular layer. It's got osteoprogenitor cells in there. Those cells are going to build bone on the outside, right? They're going to build bone. Some of them we've kind of encapsulated and some of them will return into osteocytes, right? So osteoblasts are building bone. Osteocytes get kind of hugged, right? Um, then on the inside of this bone, if we didn't remodel the inside, the medullary cavity, then we would just have a really thick bone. Bone's pretty heavy, especially when it's got all the juicy parts, right? Because skeletal material can be pretty light, but, um, we have to also remodel the inside and make it bigger. So that's going to primarily happen through that, um, osteoclast action, right? So we're going to take bone away from the inside, still trying to maintain, um, those bony spectrals that we see right here. Make sense? Make sense? Similar processes. All right. Endochondral or interstitial growth is going to happen on the ends of these long bones, right? So we're going to change in length. Um, and so we have this area of, of reserve cartilage, that hyaline cartilage that we started out with, it's going to proliferate a lot, especially when, I think my husband, he was really short in high school and then he grew like eight inches over the summer and that's a lot of work for those chondrocytes. a lot of work for those chondrocytes. Um, so, um, these are going to divide and push the older cells towards, further towards the ends or towards the atifices, really, right? atifices, really, right? So we have bone here, but here we have that hyaline cartilage, right? That, um, that cartilage is going to go through a similar process as, uh, chondrocytes. They are going to hypertrophy, then go through the program cell death, uh, apoptosis, and then they're going to do the same thing, leave these nice big open spaces, right? And we're going to see this. So in here we see, um, this reserve cartilage, the epiphyseal plate. We see cell proliferation. We see these stacked cells. They're stacked because they're building. they're building. Here we have the zone of hypertrophy. We know what that is. That resulting cartilage that's there will then, um, calcify, right? That resulting cartilage that's there will then, um, calcify, right? It's going to get hard. Then that calcified cartilage is going to ossify. going to ossify. So, being replaced by actual bone. And so it's similar to what we see in bone formation, but it's going to be this continuous process. We're pushing towards the boundaries, right? towards the boundaries, right? Growing in length. So, trampoline parts are known to break the epiphyseal plates of children, right? Because you're bouncing, sometimes you land weird. What's going to happen if we damage or break your epiphyseal plate? Where that cartilage is? Yeah, the other bone's not going to grow at least on one end. Yeah, the other bone's not going to grow at least on one end. Okay? Either turn that down or put your headphones on, okay? turn that down or put your headphones on, okay? Um, so, yeah, go ahead. They won't reach their potential height, right? So, sometimes you can go in there and fix it, right? Um, I know my, my, the other kid, um, fell off a, you know, the playground that thing that's like a half dome. Uh, he fell. He got a colleagues for actually broke both of these bones. Um, and he had to go to a specialist because they don't want to mess with those epiphyseal plates. People had to work with adults because they're so important, right? You don't want one arm, four arm shorter than the other. So, it's really important to maintain these, right? Okay. There you go, buddy. All right. So, we're going to look at this histologically because it's pretty cool and it's good to know. Um, so, we are looking at a phalanx, which is a single phalange. So, this is the part that's going to articulate with the next phalanx. going to articulate with the next phalanx. Um, the zone of reserved cartilage is going to be right here in this bone, okay? You can see here that is just that basic cartilage view. We got these chondrocytes that are sitting in lacunae, hyaline cartilage, right? hyaline cartilage, right? From this area, we have this view. have this view. See how these cells are stacked? That tells you you're looking at the zone of proliferation, right? You have these cartilage cells. When they start to multiply, they're going to stack up, okay? That's giving us more tissue for that growth, right? Then we come down here. We can see these big empty spaces. We can see these dying chondrocytes all over the place, right? chondrocytes all over the place, right? So, this is going to be the zone of hypertrophy, these big open spaces. Then we have these other two zones, which are pretty challenging because one's going to be that calcified cartilage and one's going to be bone. And they're going to have a bit of a different color. So, this is from this area right here. is from this area right here. This, um, condensed tissue, that's going to be your calcified cartilage, okay? calcified cartilage, okay? Down here, the more pink structure, and you might even recognize it from that trabecular bone histology that we looked at before, this is going to be bone down here, right? So, this cartilage, this calcified hardened cartilage, is then going to be replaced by bone by osteoblasts. So, this is pushing superiorly away, and this is going through the process. Does that make sense? Make sure you look at this because, oh, I see a question, one second. Make sure you look at this slide because there's another portion right here, but it's going to be flipped, right, because the end of the bone is right here, and right, so make sure you look at the histology slide. It's another example, but it's going to look backwards because it's the other bone. it's going to look backwards because it's the other bone. Okay, yes? How do you Yeah, so the calcified cartilage, yes, Teddy? Yes, I will open that for you. So, the, so, some of it is, why I start you guys on histology early on, right, is because there's subtle differences in what they look like, and so, our, right here, let me get a pen here, up here, if I find my pen, there you go, see how it's purplish? see how it's purplish? This should look similar to the hyaline cartilage that we're used to seeing, right? Coming down here, stating in a more pink way, and here, you can actually kind of see those lamellae that have form. This is bone down here. So, zone of calcified cartilage versus zone of ossification. Does that help, right, those subtle differences, but also, like, where they are. I also know that there was one picture on one slide on the exam. on one slide on the exam. I did replace it. ExamSoft decided not to replace it with the little thing. It was the muscle fibers. So, if you put anything miscium, you got a point. I also had two miscues. So, okay, so, musculoskeletal embryology. We're gonna now look at, like, the bigger processes altogether, not all together. All right, this is a slide you don't have to know, but hopefully it doesn't give you a long time ago, right? They're those cuboidal bodies that grow along the posterior dorsal aspect of the developing embryo, right? posterior dorsal aspect of the developing embryo, right? And they're made from mesoderm, specifically that paraxial mesoderm on either side. on either side. If you didn't watch, or I hope you have watched the pre-class activity video, I had you watch that to kind of contextualize all of this, right? So, we had different portions of these. We had the sclerotome, myotome, and dermatome. We're gonna work the dermatome in a little bit as well, even though it's not necessarily part of musculoskeletal. All right, so, we had the differentiation of the somites, meaning we're gonna separate into these different kind of different destinies, right? When you see dural myotome, that just means it hasn't further differentiated into the dermatome and the myotome yet, right? differentiated into the dermatome and the myotome yet, right? So, this is a representation of a cross-section of an embryo, got our neural cord, our neural tube, hasn't fully gone into the mesoderm yet, but here's a representation of our somites on either side. This is how they will differentiate. differentiate. Remember that this is happening at every level within each cuboidal body, right? And then finally, these cells with different destinies will go to different places and become different tissues, right? So, myotome, not surprising, is going to be muscle. Sclerotome is going to be bone and connective tissue, okay? okay? Notice how the sclerotome is moving really towards the midline of the embryo and it's going to actually hug this notochord, which will have a little bit of it left. little bit of it left. This is all going to lead to this pattern development, right? going to lead to this pattern development, right? We have patterns in right? When we cut a certain way, they're going to pull apart because that connective tissue organization. So, you're going to see this image again, but these are the somites and they are going to migrate anteriorly or dorsally or posteriorly. posteriorly. Taking with them muscle is going to form and nerves and arteries and veins, right? And so, this pattern development is going to lead to patterns in our body that we still see today, right? in our body that we still see today, right? If we look at our ribs, these patterns are there because of the somites. If we look at our vertebra, this pattern is a somite. Even within our muscle tissue, think about our intercostal muscles. So, we have a lot of, especially in that axis, this pattern. So, I'm reminding you of this because knowing how we got where we are will help. reminding you of this because knowing how we got where we are will help. Okay, we're going to start with the axial musculoskeletal system. We know that quite a bit already, right? We are going to have those mesodermal cells from the mesoderm, specifically from the sclerotome migrate and condense really at that midline. At that midline, though, there's three different areas, right? They're going to condense around the notochord. They're going to condense around the neural tube and some are going to migrate to that lateral body wall. Remember how we fold and we have that body wall, the somatopore? They're going to condense and form the different segments of our vertebra and also our ribs, right? ribs, right? So, the ones that go around the notochord are going to be our vertebral bodies. The ones that go around our neural tube will form our neural arches, right, because they're going to surround the neural arch. And then the costoprocesses, the ones that are in the lateral wall, are going to form our ribs. So, in each of these layers, this is going to happen, okay? All right. So, we're kind of, we looked at a cross-section. Now we're thinking about a longitudinal section, right? This is our developing neural tube, specifically the spinal cord, right? This is a really cool process. So, we're going to have these portions of sclerotome. These are the ones that are going to become the vertebral bodies. They are going to have this fissure, this kind of indentation, and it's going to be called the von Ebner's fissure. But, the way they're organized right now, they're in the way of these developing spinal nerves, right? So, our spinal nerves, kind of in this way, don't forget that we had neural crust cells actually doing this, are going to branch out and reach towards this growing muscle surrounding it, right? That's going to be the myotome. So, from here, we got to get through these vertebral bodies, and the way we do that is by dividing each of these cuboidal sclerotomes. So, each of your vertebral bodies is made up of two different somites. vertebral bodies is made up of two different somites. So, we have a cranial portion, a caudal portion, I should say, one somite joining with the cranial portion of the one below it, right? cranial portion of the one below it, right? So, our vertebral bodies are actually divided and put back together to make way for our spinal nerves, which are going to be our peripheral nerves as they grow. So, super complex process, but it has to happen so we can have our spinal nerves grow out to reach, and these are just our axons, our motor and sensory axons, to reach our muscle. reach our muscle. We're back to a cross section, right? back to a cross section, right? Here is our, oh, it's our ALR plates, right there, right? And our basal plate, right there. So, we know basal plate is going to have motor and sensory, dorsal cord ganglia. motor and sensory, dorsal cord ganglia. So, recall again, at each of these different segments, it's patterned, right? We're going to have those myotomes now, kind of, I think, on the outside of the developing spinal cord or vertebral column, and they are going to further divide. They're going to take two different paths. One path is going to be towards the back, the dorsal path. The other one is going to be towards the front, right? So, this is going to divide our muscles and our trunk into one's anterior to the vertebral column and one's posterior to the vertebral column, right? one's posterior to the vertebral column, right? We're going to further call these and hypomere. So, our epaxial muscles are going to go posteriorly. They are fairly limited. Everything else anteriorly is going to be hypaxial. Our hypaxial muscles help us hug. And our epaxial muscles don't. All right, so here we can see this myotome right here, right? The hypaxial division is going to go posterior, taking with it specific nerves. going to go posterior, taking with it specific nerves. The epaxial is going to go ventrally, again, taking with it specific nerves or divisions of our nerves, okay? okay? So, epaxial muscles, dorsal to the vertebral column, epaxial muscles, dorsal, hypaxial, ventral. So, that's going to be forming these muscles of the trunk that we learned. Most go on and will help form things that aren't organized in that really nice way. But some will go on to form, like our intercostal muscles, that still have that really nice organized setup. still have that really nice organized setup. You guys have questions right now about this? about this? So, the epaxial division, we've seen all these, most of them at least, are posterior. are posterior. These are primarily our extensor muscles. So, our epaxial is extensor muscles of the trunk, right? We're going to extend our back, or laterally flex if we're only using one, with those erector spinae muscles primarily, right? That's what we think about. So, here we have our erector spinae. But we also have the ones that extend our head and our neck, right? So, what are some examples of neck or vertebral extensors? I already told you the erector spinae groups, right? What's one that is going to extend our head or neck? Spinae's capitis is a good one. Yeah, what else? Anything else? Yeah, so see how we're linking previous materials back in? Okay. Epaxial, it's going to be the flexor muscles in general, right? Everything in front of our vertebral column. So, flexor muscles, not only of the torso here, but also of our neck, right? also of our neck, right? These are going to be further divided into these different areas and build different parts of it. So, remember, our glottis muscles, and our suprain for hyalae muscles, and our abdominal muscles. So, these epaxial muscles, again, are going to be further divided into specific myotomes together, cervical myotomes. They are going to do our flexors of the head and neck. They are also going to do our infra-hyoid muscles, and then one weird superhyoid muscle, the geniohyoid. weird superhyoid muscle, the geniohyoid. We're going to see why this is. It's the weird one out, right? This is the one you want to pay attention to because it's the weird one. Everything else, hopefully, will make sense. Thoracic myotomes, they're going to be in our rib area, right? rib area, right? Are going to be our lateral and ventral flexors of the vertebral column, right? Internal intercostals, external intercostals, transversus abdominis, things like that. Rumbar myotomes, we haven't gotten there yet, but it will form the quadratus lumborum. Our posterior abdominal cavity, we have this nice square muscle. It's back there, by the lumbar vertebra. And then our sacral coccygeal myotomes will form our pelvic diaphragm. This is our last section of our last block of the year, but pelvic. And then we have a tail. If you're Kevin Strezzo, who was my friend in high school, you might still have your tail. Apparently, he got it removed, but, I mean, I kind of want, I would have liked to see his tail, but I said I didn't want to see his ****, so. said I didn't want to see his ****, so. Anyways, sometimes your tail doesn't go away. Okay, so think pear-share. Take a minute. Think about why, why am I teaching you this? Why do we care about this pattern development? How can it help you when you're practicing medicine, or going on to become whatever you are, right? How does this help us? So, talk to your friends, and I'm going to ask someone. All right, so why, why give a hoot about dermatomes and myotomes and sclerotomes? If you don't volunteer, I'm going to ask someone, probably from the back, because you guys kind of hide out back there, and I forget to ask you things. Actually, I do that all the time. Every year, I should say. Why do we care about these? What can they do to help us? Yeah, so if we have like one specific segment of somites or sclerotome, myotome, and dermatome, it's not going to form properly, right? We can kind of go back to that origin of what happened. What else do we got? do we got? Shingles, right? So, shingles affects the nervous system, which is going to be reflected in the dermatome and myotome. Shingles is going to affect specific dermatomes. So, those nerves that are infected are going to show symptoms of those same dermatomes. So, it actually follows that pattern development in our skin. development in our skin. Crazy, right? Has anyone ever been to the doctor and got your patellar ligament whacked, and then you kick? Yeah? Does anyone have an infant in their lives somehow, and you run your finger down their foot, and it goes, yeah, right? Those are reflexes, right? So, one, we can test your nerves, and we know which nerves, because of this pattern development, we can make sure they're functioning by hitting certain things on your body. That's so cool. So, there's like a cute little one, and like the knee one, the patellar ligament, and the toe one. So, we're gonna cover those when we talk about nerves. So, one, we can assess our neurological functioning because of these reflexes, because of the dermatome and myotomes, because we know what is being innervated by what. We can look at different types of integument diseases and lesions and so forth, and we can also assess movement of muscles, say, in our flexor, our extensors, and our legs, and upper limbs, and lower limbs, even our tongue muscles, and so forth, and because we know what level is innervating them, we can assess what happened at that level, where a damage might have occurred, right? occurred, right? So, it's important, and it's why we can do what we can do from the outside looking in. Okay. Development of the crania. It's really complex. I've simplified it quite a bit. So, if you go on to learn more details, it's just because it's a lot. Okay. So, we have two different parts of the crania. We didn't really talk about them yet, but we have the neurocranium, everything that touches the brain, and then the visceral cranium, our face, right? And they're going to develop a little bit differently. differently. So, we're gonna have, recall, two different types of formation, the endochondral and then intramembranous, right? They're both are gonna play a role, and where the cells that make them come from, right? and where the cells that make them come from, right? So, the neurocranium is going to develop kind of like the rest of our body through a sclerotome, right? Different portions of that occipital sclerotome. The visceral crania is going to be from ectoderm that comes in and separates off a neural tube. Remember our neural crest cells. So, the bones of your face are the same origin of your central nervous system, which is pretty cool, because they're pretty special. They're going to migrate into these things called pharyngeal arches. Sometimes they're called brachial arches as well, but we'll see these here in a minute. So, neurocranium, paraxial mesoderm, somite, sclerotome, that's where the stuff's coming from. coming from. The base of the crania, so this is going to include the occipital, which reaches under the sphenoid, the ethmoid, kind of weird, and a little bit of the temporal. Those are going to form through endochondral bone formation. We have models for these complex bones, especially sphenoid, ethmoid, before we build them into bone, right? We're going to make a cartilage model to make sure we got it right, and then bone is going to come in. Intramembranous is going to be those flat bones, right? those flat bones, right? Where we have ossification centers, going to have clumps of connective tissue come in, condensations, and then we're just going to build bone right there. No model. So, frontal, parietal, and the squamma are the temporal here, right? That flat part, which hopefully will make sense. So, pretty straightforward. Then we look at the face. Again, they're going to cut this. These cells are coming from neural crest cells. This is the mesenchyme that isn't mesoderm. It's like the weird thing, right? So, we had mesenchyme, an organized connective tissue from our neural crest cells that are. These are going to form almost entirely from intramembranous bone formation, maxilla, mandible, our nasal bones, and our zygomatic. Intramembranous, we just have condensations here, bone is going to come in and grow, and it's neural crest cells. General themes. General themes. Okay. Talking about the muscles now, right? The ones that we already know, they're going to come from specifically those occipital myotomes, right? So, occipital myotomes are right here. These cells, the myotomes from those individual somites, those cuboidal bodies, are going to migrate into these pharyngeal arches, which are, which, if you're a fish, is going to develop into your gills. So, right here, you can see that. Each pharyngeal arch is going to contribute different things. We're not going to know those individually yet, but when we do, like, our digestive and respiratory system, we're going to talk about these again, which muscles come from where, right? So, cells are going to migrate into here from those myotomes, and they are going to then form specifically the muscles of facial expression, of mastication, and then our pharyngeal, which is our swallowing ones, and our laryngeal talking and breathing ones, right? right? So, don't be memorizing which muscle comes from different pharyngeal arches. We'll get there. Eventually, we'll do them a little bit separate. Cells migrating from the occipital division are also going to form our tongue muscles. Take a little bit of a different route, which is, and this is why, the genial at glossus, our genial highlight is, how is it different? It's going to be from this occipital myotome with the muscles of facial expression. Anyways, it's cool. Do you need a break, or do you want to power through? Do you want to, who wants to break? Raise your hand. Okay, thank you. I need to get this day over with. to get this day over with. He's been really good. It's just like, musculoskeletal limb development. All right, so we talked about all this lovely pattern development, and then we have the limbs, which is like a lot of our body, but we haven't talked about yet, right? Okay, so in that weeks four through eight, anybody remember what that also is inside of us? What happens in weeks four through eight during development? Yeah, we do that, and then, yeah, organogenesis, right? So we're folding, and we have organogenesis, right? That really, when most of our organs are like forming, organ systems, right? At this point, we also have these little limb buds appear. The upper limbs are going to mature a little bit more quickly than the lower limbs, so when we look at this, we'll see things happening up in the upper limb first, and then the lower limb will follow, hopefully, right? will follow, hopefully, right? We're going to start out as these little limb buds, and we have folded. That folding is that lateral plate mesoderm. Remember, we had that lateral plate mesoderm. It's going to get a sealant in it, and it's going to fold. The innermost part is going to be our splantino floor. The outer is going to be our somatopoleur body wall. our somatopoleur body wall. From that, from the somatopoleur, that lateral plate mesoderm, we're going to **** out, right? So not really from somites, right? We have a different process, okay? So we're going to have these myogenic precursor cells in the limb buds, right? They're going to differentiate and become that, which means muscle creator cells, right? which means muscle creator cells, right? Myogenic. They're going to migrate into the limb buds. Some of these are going to come from that dermal myotome. myotome. Yeah, so somites, but yeah, more complex. And then, this is so cool, they're So basically, they are going to be induced and told what to become in a very specific way. This is part of that process, right? This is part of that process, right? Epithelial mesenchymal transformation. And then those cells will proliferate. We're going to look more specifically at how they proliferate, because it's got all these little zones that are going to be important, right? Okay, so this is a limb bud. This would be the axis of our body, right? So we're looking at this little guy, but kind of like, boop, like that, okay? All right, so our limb buds are going to grow on three axes. These are slightly different than the anatomical position axes. position axes. There's one particular that's going to be different and a little confusing, okay? So proximodistally, that's going to be the same. So growing out, right? From midline out, so growing in length. This is going to be led or done through the apical ectodermal ridge, right? So this red part here at the very tip of our limb buds is going to induce how the underlying mesenchym to proliferate and grow outwards, right? proliferate and grow outwards, right? So we've got our length done, but we also have more patterns in our limbs. Anterior to posterior is the one that's different. So anterior is really going to be our thumb side, and posterior is our pinky side. I don't know why they did this, because it still doesn't make sense. Well, I guess it does. No, it doesn't. So this is a one that's weird, but this is a terminology that they use. This is going to be really the difference between our lateral and medial aspects. So radial, brad radius in onar, or big toe tibial versus the little toe is on the fibular side, okay? So the differentiation between these sites. That's going to happen due to the zone of polarizing activity. That's purple here. It's kind of like in the armpit of the embryo. And that's going to tell the underlying tissue, you're going to become radius stuff. You're going to become onar stuff. You're going to become tibial-fibular. I use those. Our thighs and arms are involved, but this is the easiest way to kind of visualize it, I think. Then we have dorsal ventral, which is what we think, right? So ventral is going to be the anterior part. Dorsal is posterior And importantly, these are going to become our flexors and extensors. This is where we talk about flexors and extensors for forever, okay? So fortunately, we have these patterns in our, Teddy, stop. We have this pattern in our limbs. And it's really helpful because a lot of our muscles are named for flexing or extending, right? So flexor side is this side, anterior, in our upper limbs. in our upper limbs. Outside of our hip flexors, our flexors are posterior in our lower limbs. We'll see why in a minute, right? We'll see why in a minute, right? So flexors, flexors, flexors, flexors, flexors, hip is weird. So it is our epidermis. So it is our epidermis. Our epidermis tells our flexors and extensors where to form. It's crazy, right? It's crazy, right? Do that induction. Don't you dare. dare. Don't press any buttons. I'm not going to do that. So we have these three different ways to induce and tell the underlying tissue to become what it needs to become because we're really complex in this, right? So when something goes wrong in here, that's when we see people without limbs fully developed. That's when we see people with additional fingers, additional digits or missing digits or fused digits, right? digits or fused digits, right? So this is what is going to be involved in that. I would like you to know weeks four through seven here, the major things that happen. So four, getting our limb buds. Week five, we have the limb buds are fully present on upper limb and lower limb. Six through seven is when we have these plates formed. So kind of a widening at the distal end. AER, right? Apical ectodermal ridge. And then we'll have our bones form within that, or at least cardiolaginous models. And then we'll have our digits separate. So the tissue in between each of our fingers will die off. Okay. And then our cardiolaginous models, this is when they're really, they have formed, right? We're ready to start building our bone on these models. Week seven, limb rotation. Limb rotation. This is why we have flexors in the posterior aspect in our lower limbs, flexors on the anterior aspect in our upper limbs. So pretty important, but it also explains why we're, why we blame embryology for most things. It's going to happen in the seventh week. It's going to happen in the seventh week. Flexor, we have, so essentially when we are developing, think that your, this embryo is going like this or like hoarding a beach ball, right? So I have my flexors here and I have my flexors here, right? So I have my flexors here and I have my flexors here, right? I have my extensors here and extensors here. So it makes sense. Then we're going to take our thumbs and put them out. So 90 degree rotation out, knees in. So while we start like this and we have this pattern, thumbs out, knees in, that's how we get them on opposite sides. It is also going to impact the dermatomes, which are going to play a really big role when we talk about spinal nerves. Because if you hold your arms out like this, cervical spinal nerve seven is going to do your middle finger. And that makes sense. I mean, it would go another, so four, five, six, seven, eight, and then two, one, two, right? The spinal nerve is coming from those different levels. That makes sense. But when we're like this, it doesn't make sense, right? So we get this complex relationship between our dermatomes and what we see. So this is going to be a pattern in terms of when we lose feeling, when we lose motor, when we lose other aspects. After this, week nine is when our synovial joints are going to form. So those are particular capsules and so forth. So those are particular capsules and so forth. Twelve, really in the osteogenesis portion, right? right? We're having our endochondral ossification occurring, continuing. occurring, continuing. We're starting to have bones replaced. We're going to grow in size, right? right? Length and diameter. So basically we're just growing. growing. And then as our long bones and our upper and lower limbs form, we will have these masses of myoblasts coming together, elongating, fusing together as myotubes, and becoming our muscle fibers in these different locations, right? And they're going to go, okay, do I need to be a flexor? Well, not do I need to be a flexor. Am I going on the flexor side or extensor side, pinky side or ulnar side, right? ulnar side, right? And then really the last portion here, before I make you think a little bit in a second. Just the development of the joints. I want you to kind of recognize these general processes. It's all very similar, right? So between the bones that will have a joint pubic synthesis or even our humerus and our scapula, which you'll see soon, we're going to have interzonal mesenchyme right between it. That's going to go on to form these different structures. Fibrous joints, hopefully it kind of already relating our connective tissue or dense connective tissue with that. Cartilaginous joints are going to have highly cartilage and fiber cartilage develop. So we're just linking these. And then synovial joints, it's a little bit more complex. They're going to form this solid structure first, and then we'll have apoptosis occur within that to create the cavity. that to create the cavity. The cells that line that cavity will go on to become our synovial membranes, which again are really important to keep healthy because our high link cartilage on the ends of our bones are avascular, right? We want to maintain the nutrition there. Any questions on that stuff? Any questions on that stuff? Quickly. Not quickly. Okay. When our bones break, there's all kinds of different ways. So this is what happened to the other kid, the colleagues fracture only. We broke both of them. So I get a call from daycare and they're like, something, Finn's had an accident and we think he needs to see a physician. So I'm like, okay. And I rush to get there. It was summer camp. And he's sitting with a bag of ice on his arm and the camp person lifts up the bag of the ice and his arms like this. And it's like, oh my God. That's when like that mom gear kicks in or our parental gear. And you're like, stay calm. We are going to get you in the car. And the best thing of it, he was, it was dressed as your occupation that you want to be day. And he was in an astronaut suit. So there he is with this weird looking arm. is with this weird looking arm. Oh man, that was awful. And then they said it like, well, he was awake and it was like, oh my God. Then he got a cute little pink cast, but we thought it was going to be this one that broke his bone first. It was not. Okay. There's different types of fractures, right? Some are more complex than the others. Some are kind of expected after certain faults, like fall and catch yourself, collies fracture. So using, I know you have that slide, but pretend you don't. So using the information provided on bone development, bone formation, what steps do you think are involved in the healing of bone, right? What we've already talked about, right? What we've already talked about, right? So it's pretty neat. These steps are going to be, first we're going to come in and we're going to use osteoclasts to eat up the fragments of bone. We've got to clean it up first, right? We've got to get that extra stuff out. Then we're going to have our osteoblasts come in and conger blasts as well. We're going to first form a cartilaginous connected tissue callus, right? It's basically, we're going to do that condensation of mesenchymal tissue, connective tissue first, and we're going to kind of sing things together in a superficial way. things together in a superficial way. And then that cartilaginous, our callus is then going to be eventually replaced by bone, right? be eventually replaced by bone, right? So it's a similar process that happens when we break bone. This is also, well, it's going to also continue kind of just in terms of that general maintenance as well. So when you're told to stay off a broken bone for so many weeks, it's because you're going to get a kind of a patch first of connective tissue that then will be replaced by bone. I broke my collarbone once, collarbone, my clavicle. I still have a bump. Anyways, so applying this to other things in terms of medicine. There you go. I can't believe we ended early on musculoskeletal system development. I'm pretty impressed. Any questions? All right. So I'm going to do my best to record the content for lab. It'll definitely be out by tomorrow. Again, watch it if you need to. It's going to help you contextualize what we're seeing or go through the slides, but we are going to bring in those clinical connections into the exam to kind of tie things together. All right, cool. Thank you for your patience. That's what happens when you don't have any family around.