 Shall we talk about the structural categories for classifying joints? We have three types. Oh, just like we had three categories for function, we have three categories for structure. Ready? The first category is called a fibrous joint. The second category is called a cartilaginous joint. And the third category is called the famous synovial joint. We're going to spend, I mean, check out our plan over here. We're actually going to spend most of the conversation talking about synovial joints. So we'll save that for later. We're going to focus instead on cartilaginous joints and fibrous joints. And this may make you a little bit sad? No. But the fact is that there are multiple types of fibrous joints. So let me tell you what unites all fibrous joints. All fibrous joints are, they're joints created. They're connections between bones that are created by or fused or, I don't know, linked by ready, dense, regular, connective tissue. Okay? So all of these joints have dense, regular, connective tissue spanning two bones. And connecting, I mean, creating a connection between those two bones. What do you suppose all cartilaginous joints have in common? I know it's really tricky. They are created. Cartilage might be different flavors of cartilage, but cartilage connects cartilaginous joints. And two bones that are connected by cartilage of some flavor are cartilaginous joints. And again, synovial joints, we'll deal with that in a second. So what are some examples of fibrous joints that are actually joints that are connected by dense, regular, connective tissue? Ready? Maybe I'll show you a picture of them. I think I will. Here are three examples of fibrous joints. I would have ever thought that the connection between a tooth and the, like, skull bone, the mandible or the maxilla that the tooth is actually embedded in, that is considered a joint. And it's a specific kind of joint called a, ready for this one, gomphosis. Your mouth is full of gomphosies. If you want to really insult somebody, tell them that, they'll be like, why you got to be so mean? So what is holding the tooth in to your mandible or your maxilla? Dog bounce. That would be dense, regular, connective tissue, right? Look at it. There it is. Aw. That is a gomphosis. You've got however many teeth you have left. That's how many gomphoses you have in your mouth right now. And you tell me, just out of curiosity, how would you classify the functional, what functional category would you apply to a tooth? Push pause and answer that question. Hopefully you, hopefully your teeth, unless you are a small human watching this video, most of the humans who are watching this video, I would imagine, do not have movement in their gomphoses. And it's true. They are classified as a synarthrosis. The exception to that is when the little slimes lose their teeth, no offense to the little slime that might possibly be watching this video. All right. What's another one? Another fibrous joint is called a suture. And you tell me, again, so a suture, an example of a suture is in your skull, connecting your skull bones. Because your skull, I think I've already told you this, is made up of 22 different bones and most of them have been fused together. And so the fusions are sutures and they're still considered joints, even though they, can you wiggle your skull? Wouldn't that be weird if we could like wiggle around and like, ha, that'd be really cool. But no, we can't do that. And so what kind of functional category are you going to assign to a suture? It is also a synarthrosis. Okay, so this is the one. The next one is one that you probably don't think of as a joint or you've never really maybe even been aware of. But this guy is called a syndesmosis. Really? It's true. It is called a syndesmosis. And do you see my connective tissue that is connecting? Oh, and can you identify my bones that I'm looking at right here? This is my friend, the radius and the ulna. Yes, and so between the radius and the ulna, there actually is a dense regular connective tissue like net, web, membrane, ethylene bouncer that is made out of what? Dense regular connective tissue. And you might not think, I mean, can you move that joint? Can you move between these two bones? You actually can. It's not a synarthrosis. It's an amphiarthrosis. Roses, keyword, amphi. Great. These are my fibrous joints. Okay, let's go take a look at my cartilaginous joints because I think I've got, oh, there they are, some examples of cartilaginous joints. Okay, we've got two types. We have one type of cartilaginous joint that is called a symphysis. Vessus, that's what I meant. These guys are what were they called again? Vess, cartilaginous, cartilaginous joints. And cartilaginous joints form between two bones and are made by cartilage. So check this out. Our symphysis joints are actually, do you remember what kind of cartilage we found in these locations? It's made by fibrocartilage. It's a fibrocartilage pad between two bones and that's what creates the symphysis joint. And these guys are amphiarthrosis. There's a slight amount of movement, probably a little bit more, actually I'm not sure if they're probably similar amounts of movement. The disc between the bodies of your vertebrae that we already know was a fibrocartilage pad, that actually is a symphysis joint. Your vertebral column has more than just symphysis joints in it. It also has synovial joints at these locations and we'll talk about that in a second. But here the pubic symphysis is another example and this is between your two pubis bones and apparently if I looked up the plural of pubis pubis bones, your pubis, that just sounds really weird to me. Are you ready? What? What is that? You already know what that is, right? That's your epithysioplate and technically because your epithysioplate is hyaline cartilage, it is considered a type of cartilaginous joint called a synchondrosis. Now, there are a lot of syn words in joint structures. Syn stuck together. Conde cartilage, drosis and the epithysioplate is an example. Now, you tell me. Amphiarthrosis? Diarthrosis? Can you go around wiggling your bones at the epithysioplate? No, my friends. These joints are synchondrosis. Synarthrosis. And there are also synchondrosis. Synchondrosis are synarthrosis. There's a lot of words that we are talking about here. So make sure that you write them all down and sort them into piles because there's lots of sorting possibilities here. Let's look at a synovial joint. Hopefully, these structural categories, you're like, uh, wasn't really aware or not at the top of my brain in possible joints. So how do you think we classify our shoulders, our elbows, our fingers? Those are synovial joints. So we're going to look at the structure of a synovial joint next.