Our example tells us that the image below shows multiple sarcomeres, and then it asks us to draw arrows to label at least 2 myosin filaments, draw arrows to label at least 2 actin filaments. And then it asks us the question when the muscle contracts, which filament gets closer to the center of the sarcomere? So as I look at this image, I see this sort of long, drawing here showing all these protein filaments, and I see this repeating pattern, and that repeating pattern is the sarcomere. So the first thing I want to do, just to orient myself to this picture, I'm gonna draw the ends of the sarcomere in, so I can see the individual sarcomeres. So the ends of the sarcomere are these sort of zigzaggy lines here. I'm just gonna draw a straight line over it. Right? Here's another zigzaggy line. Those zigzaggy lines we haven't defined yet, but those are gonna be called the z discs, and those mark the ends of the sarcomere. So as I look here, I now have one, two, three, four sarcomeres, four spaces between those blue lines that I drew in. Now, again, just to simplify things, I think I'm just gonna try and look at one of them. So I'm gonna shade in and just sort of ignore the parts that I'm shading in, and let's just focus on this sarcomere number 3 right here. As I look at that and I look at the filaments I see, I see two major types of filaments here. I see the purple filaments right there, sort of in the center of the sarcomere, and those have those, sort of like many arms that are kind of reaching out or the heads that are reaching off of them. And then I have these yellow filaments that are attached to the ends of the sarcomere. Alright, so one of those the myosin, one is the actin. Do you remember which is which? All right. Well, the myosin was the thick filament. And we said in our story, right, that the myosin just wants to pull on a rope. And so it has all these hands to just sort of pull hand over hand on that rope. So when you look at this, the thicker filament with many sort of hands, they're called heads, but there are many hands coming off of it. That's that purple filament. So there's one. There's one. Said two, but I can keep going. There's another one. There's another one. Alright? Those horizontal purple filaments there, that's the myosin. That means the actin is those yellow filaments. Remember the yellow filaments? The actin? That's like the rope that the myosin is gonna pull on. So there's one. There's one. There's one. Said just label two. We got three. We're doing great. So that's the actin. Alright. Myosin, that's, located at the center of the sarcomere. The actin is attached to the ends of the sarcomere. So that means when we ask this question down here, which filament gets closer to the center of the sarcomere? Well, the center of the sarcomere is right here. The ends are out here. That myosin is gonna grab on that actin, it's gonna pull it in, and that actin is gonna slide closer to the center of the sarcomere. So my answer is the actin. Alright. Like always, we have more problems to follow, and then we're gonna go into the proteins in the sarcomere in a lot more detail coming up. And I'll see you there.
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9. Muscle Tissue
Sliding Filament Theory and the Sacromere
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