The Pectoral Girdle - Video Tutorials & Practice Problems
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1
concept
Pectoral Girdle
Video duration:
6m
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We're now gonna move from talking about the axial skeleton of those bones on the center of your body to the appendicular skeleton, the bones of your arms and your legs. And what links the two is gonna be the girdles. So we're gonna start by talking about the pectoral girdle and a girdle is just something that surrounds something else or binds something else. So the pectoral girdle surrounds the pectoral or the thoracic region, the region of your chest. So the pectoral girdle, we're also just gonna start by saying it's sometimes called the shoulder girdle because the bones of the pectoral girdle make up the shirt, the shoulder and its job is to attach the arms to the axial skeleton. Now, quickly, some people have a misconception that the shoulder girdle or the pectoral girdle is gonna be part of the axial skeleton because it's on the core of the body here. But it's really important to remember that technically, this is gonna be part of the appendicular skeleton. When we think of the girdles. When we think of the pectoral girdles, we wanna think of them sort of as parts of the arms and the legs All right. So the pictorial girl is gonna be made up of two bones and we're gonna go through those. Now, first up, we have the clavicle, the clavicle. It's very likely you've heard before it called the collar bone with the collar bones. And you can see the collar bone, you can see the clavicle. You can feel it very easily. You just start at your sternum here, you can touch it, you can walk your fingers across, it sort of comes out the sh uh curves around like the shape of your chest comes back and then it kind of swoops over to the tip of your shoulder there. So that medial side that we were just feeling that articulates with the sternum and then the lateral side out at the tip of your shoulder, there is gonna articulate with the scapula. And we can see that in this image here. So we have an image, it shows the thoracic cage here kind of grayed out. And then we see the clavicle and purple. We have the medial side articulating with the sternum there. We feel it sort of swoops around like the shape of the chest and then out and it articulates with the scapula here at the edges there. Now, I have a clavicle here and the word clavicle actually comes from the Latin meaning key. And I guess some people thought that it maybe looks like an old tiny key when I look at it I always think that it kind of looks like something I could use to butter my bread and you could sort of hold it like this and it has this flat part that you could spread butter or jam on your toast with. Now, I don't recommend using human bones to spread butter, but if you did choose the clavicle and when I look at this, I see that one end is really blunt and one end is really flat, that blunt end comes up and that's the end that meets the sternum and then it curves around and that flat end comes out and articulates with the scapula at the acromion process. And we're gonna talk all about that now. So we're gonna look over here, we have the scapula, the scapula, I'm sure you've heard before called the shoulder blades. And you can see the scapula really easily when you look at someone's back, especially when they move their arms because the scapula is really superficial, sort of stuck on the back there and it moves when you move your arms. So it's gonna articulate with the clavicle just as we said right up here at the tip of the shoulder. And it's also gonna articulate with the humerus or that upper arm bone. That's how the arm attaches to the body. So first off, let's look at this acromion process and that's gonna be where it articulates with the clavicle. So we have an image down here and we have two views. We have the anterior view here on the left and the posterior view looking at it from the back here on the right. And I also have a scapula here. So this anterior view, you can see the scapula is very flat. So this is the part that would sort of go up against your back there. And you can see that on the posterior view though, it has this sort of spine that comes up and this process that sticks out and you can see it on our image here. This is that, that spine that comes up in this process right here. And then you can see this process here labeled two A, that process is gonna make up the tip of your shoulder. And so that's called the acromion process. And remember when we learn the regions of the body acromial meant the top of the shoulder and it came from that same root as the acropolis. And the acropolis is the top of the hill in Greece and the Acromion process, that's the very top of the, your shoulder right here. And so if you touch that, you can feel, you can walk it back and you can feel the spine of the scapula there, you can feel the scapula, you can also walk it across the front and you'll start walking onto the clavicle and you can walk across right there. Now, the other thing that we wanna note on the clavicle for now is the glenoid cavity. This is gonna be the depression for the joint. It's gonna be the place where the arm comes in and makes the shoulder socket. So it's a ball and socket joint. This is the socket. You can see it here in uh labeled two B right here or also, it's that part there. And we can look at on this bone here. You can see as a socket, it's very shallow, it's almost shaped more like a golf tee than it is like a real socket. And when you take the humerus and take the ball of the humerus and put it in there, that means that this humerus can move around a ton because it doesn't actually fit deep deep into the joint. It just sort of has this shallow place to move around on. That's one of the things that makes your shoulder the most mobile joint in your body. Now, the other things that contribute to that is that this scapula, well, it doesn't articulate with very much at all. It has that shoulder joint, the, um, the, the socket here for the humor to go into. And then it arts also articulates with the clavicle appear at the achromia process, but that's it. And so when you move your shoulders, you can feel your scapula moving. When you move your shoulders forward, you feel them rounding around your back there. When you move your shoulders back, you can feel pinching in the back. If you raise your arm, you can feel it sort of moving out a little bit. All that movement really contributes to being able to move your arms a ton. And that's even the, the clavicle as you move your arm around. If you touch it, you can feel that that's moving too because on both ends of the clavicle are mobile joints. Now, that's gonna be very different than your pelvic girdle, your hip bones where it's got, you know, a pretty mobile joint where the, where the leg attaches, but those bones themselves really don't move again. The scapula moves a lot. All right, we're gonna be looking at that more in the example to follow. I'll see you there.
2
example
The Pectoral Girdle Example 1
Video duration:
2m
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Our example tells me that the shoulder joint is the most mobile joint in the body. And it wants me to describe how the structures of the pectoral girdle aid in making the shoulder so mobile. And what it wants me to talk about the glenoid cavity, the scapula and the clavicle. Now as a visual aid, it shows me the pectoral girdle right here. It also shows me the humerus and the thoracic cage as a reference. All right. So first off, let's talk about the glenoid cavity. You remember how the glenoid cavity contributes to shoulder mobility? Well, we said the glenoid cavity, that's the socket in the ball and socket joint. And when we look at the scapula, we see it's really shallow. I said it's more like a golf t than like a real socket. And when you take the humerus there, that means that it has a ton of mobility. It doesn't sit way in that, that socket itself doesn't bind the humerus. So the glenoid cavity, we're gonna start off just by saying that it is a shallow socket and it being sha sha shallow allows that humorous to move around a lot. Ok? Next though, we want to just talk about the scapula in general. What about the scapula in general? Aids to that shoulder mobility? Well, we said the scapula moves around a lot, right? It's only articulated to the axial skeleton directly through the clavicle and the attachment points way out here at the a chromium process. So when you move your arms, your scapula moves right, you can pinch it back, you can bring it forward. And when you're doing that, you're changing the angle of the glenoid cavity, which adds more mobility to that shoulder joint. So I'm gonna say the scapula itself, I'm just gonna sort of say that it is a mobile bone, it moves around a lot and as it moves, it changes the orientation of that shoulder so you can move your arm even more. Finally, it wants us to talk about the clavicle. So what about the clavicle aids in this mobility? Well, remember the clavicle as you move your shoulder around, if you have your arm on it, you can feel the clavicle moving. So the clavicle itself, we said it has two mobile joints and it again is gonna allow that shoulder to change its orientation to change the, the way that the glenoid cavity faces to allow you to move your arm a lot. Now, this is all gonna be in contrast to the pelvic girdle, which we haven't talked about yet, but the pelvic girdle where your legs attach, it's got a really deep socket and those bones aren't mobile, they don't move around. That's why you can swing your arm all around and you can't do it nearly as much with your leg. So next time you're raising your arm up above your head in class, remember, you can put it up that high because of the glenoid cavity, the scapula and the clavicle.
3
Problem
Problem
The medial end of the clavicle articulates with what structure?
A
Scapula.
B
Humerus.
C
Ribs.
D
Sternum.
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Problem
Problem
Which statement about the scapula is correct?
A
The scapula articulates with the ribs and the clavicle.
B
The acromion process is the most medial point of the scapula where it articulates with the clavicle.
C
The scapula is the largest bone of the axial skeleton.
D
The glenoid cavity of the scapula articulates with the humerus.
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