8. Protein Function
Skeletal Muscle Anatomy
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In this video, we're going to focus on sarcomeres. So, sarcomeres are important because a muscle contraction is actually the result of a sarcomere contraction. And so later in our course, we're going to talk about sarcomere and muscle contractions, but before we can do that, we need to understand the of a sarcomere. And so a single sarcomere actually has several different regions and components and we're gonna talk about all of those regions and components down below here in our text. Now, notice that the text is actually color coordinated to match the regions and components down below in our image. And so notice up above here, what we have is the same exact visual representation of the sarcomere that we had in our last lesson video. And so really what we're doing here is we're zooming in on this specific region of, the sarcomere and we're blowing it up and, visually representing it in this, representation that we have here. And so if we go up to our text, we can focus on the first region here, which is right here and this is going to be the H zone. And so what helps me remember what the h zone is is I know that the letter h is quite a thick letter. It extends a lot horizontally from side to side. And so because the letter h is such a thick letter, the h zone is only going to contain thick myosin filaments, and it will have no overlaps with thin actin microfilaments at all. And so if we take a look down below at the image of our sarcomere, notice that the thick myosin filaments are in red right here. And of course, the thin actin microfilaments are in green at these positions on either side. And so, of course, the H zone, because H is such a thick letter, that reminds us that, the h zone is only going to contain thick myosin filaments. And so notice that this region here highlighted with a blue background, contains only thick myosin filaments and no overlap with any of the thin actin microfilaments. And so, because that's the case, that makes it the h zone. And so we can label this region, down below indicated by this bracket right here as, the h zone. And so, now, we can move on to the next region and so, the next region is going to be the eye bands and so because the letter I, what helps me remember what the I Bands are is that because the letter I is such a thin letter, that reminds me, that the since I is such a thin letter, that the eye band is only going to contain thin actin microfilaments and it will have no overlaps with thick myosin filaments at all. And so if we take a look down below at our image, notice that the region that only contains thin actin micro filaments. So the thin letter I, reminds us that this is gonna be the I band. So from this region to this region over here and, over here from this region to this region over here. Now, the next region that we have is referred to as the A band and so what helps me remember what the A band is is that the letter A is actually mostly a thick letter but towards the top, it's actually quite thin. And so because the letter a is mostly thick but has a little bit of thin, this means that it's gonna contain all of the thick myosin filaments, and some actin filaments as well. And so if we take a look down below at our image, the a band, again, because a is mostly a thick letter and, something. It's gonna contain the entire length of the thick myosin filaments. But notice that there's also going to be some overlap with thin actin microfilaments as well. And so the a band is really just going to be this entire region that we see here, really just defined by the length of, the thick myosin filaments. And so you can see that this yellowish background that we have, that extends from here to here indicated by this bracket down below is going to represent our A band. So, now, we can move on to the next component and so, the next component that we have is the M disk or the m line for that matter. And so, sometimes they'll be referred to as the m disks, other times they'll be referred to as the 'm' line. But what helps me remember what the 'm' disc or 'm' line is, is that the letter 'm' is for the middle. And so this is going to be a vertical anchor to myosin in the middle of the entire sarcomere in terms of being in the middle of the h zone and the a band. And so, down below, what you can see is that the m disc is this disc shaped structure that we see here in the center. So, we can go ahead and label it as the m disc and notice that the m disc is in the middle of the entire sarcomere. Present in the middle of the h zone and the middle of the a band. And it's also a vertical ink anchor to the thick myacin filament. So, you can think M Disc for anchoring the myosin filament. So then last but not not least, what we have are the z discs. Also known as the z lines. And so what helps me remember what the z discs or the z lines are is that because z is the last letter of the alphabet, the z disc is going to mark the end of a sarcomere. But because these sarcomeres are repeating units, the end of a sarcomere also marks the beginning or the start of another sarcomere. And so z discs mark both the start and the end of a sarcomere. And really, what you can see down below is that these purple structures that we see on either end, these purple discs represent, the z discs. And so one single sarcomere actually has 2 z discs on either end. And a sarcomere can be defined from, the region from z disc to z disc. And so, the z discs are important because they are vertical anchors to the actin, thin microfilaments. And the z discs are going to be centered on the I band. And so what you'll notice is that, here what we have is the I band and, this is one sarcomere here. But, if we had a neighboring sarcomere, there would be, another I band over here. And so, the z disc, here would be centered on the I band. And the same goes for over here. There would be another I band here. And so, the Z Disk would be centered, between the I band. Now, again, the z disc are vertical anchors to the actin. So the actin, microfilaments that we see here are anchored, to the z discs. And so that's important to keep in mind. And so really this is the structure of a sarcomere and, we'll be able to get some practice utilizing the concepts that we've learned here in our next video. So I'll see you guys there.
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