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Hey, welcome to another numerade video.
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This video is about the structure basically of a muscle fiber.
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More specifically, the structure of a sarcomere, which will explain exactly what that is.
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And it's important to understand the structure so that you can understand how the muscle works.
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So this will be the first step in really grasping how muscles do their jobs.
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A couple of terms, when we say muscle fiber, we're talking about one cell.
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One muscle cell is called a muscle fiber.
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And it has all the parts that you would expect a cell to have.
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One big difference is it has multiple nuclei.
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There's not just one nucleus in a muscle cell, but many.
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And then that cell, that fiber is made up of smaller parts.
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Called myofibrils.
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Myofibrils are made of two types of filamentous proteins, actin, the thin filament, which i represented here in red, and myosin, the thicker filament, which i'll use green for.
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So muscle fiber, one cell, myofibril, smaller part of the muscle cell made up of two proteins, actin and myosin.
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They overlap one another.
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And so, you may have heard a skeletal muscle referred to as striated muscle.
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It's because it looks striped.
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When you see it, you slice a section of it lengthwise and look at it under a microscope, it looks striped because you're seeing some different bands.
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And we'll see, as we look at the picture, we'll see why those bands are like they are.
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So i'm going to draw in here some, the myos and filaments.
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The thicker filaments.
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And so they're thicker, so i'm going to have to do this to make them look thicker than the red lines.
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Notice that i'm not making them thick in the very middle.
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There's a reason for that.
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I'll get to that in just a second.
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Okay.
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Excuse me.
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So let's start over on the left side and look at the places where actin filaments are connected.
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You see here that looks like a z, right, as we go down.
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So this place where all the actin filaments are connected is referred to as the z line.
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And you can see that there is another z line over to the right where the actin filaments again on that side are connected.
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So when you look at the structure from one z -line, line to the next, that is called a sarcomere.
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Sarcomere is the structure from one z line to the next on a myofibro, in a myofibro.
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And that is the actual unit that contracts.
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And when multiple sarcomeres contract, then the whole muscle contracts.
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Okay, so sarcomere from z line to z line...