Skeletal Muscle Anatomy - Video Tutorials & Practice Problems
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Skeletal Muscle Anatomy
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In this video, we're going to begin talking about skeletal muscle anatomy. So, muscle are accomplished by molecular motor protein interactions and so the motor protein myosin is responsible for pulling on thin actin microfilaments during a muscle contraction. And muscle contractions in skeletal muscle tissue are one of the best understood mobility systems. And so for that reason, we're going to talk about the muscle contraction in skeletal muscles later in our course. But before we can talk about muscle contractions and skeletal muscles, we first need to understand skeletal muscle anatomy. And so in our next video, we'll talk more about skeletal muscle anatomy. So I'll see you guys in that video.
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Skeletal Muscle Anatomy
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In this video, we're going to talk about skeletal muscle anatomy. And so notice down below, we have an image showing you skeletal muscle structures and it ties together nicely with the text that we have up above and so we're going to start with the far left structure that we have highlighted here which are referred to as sarcomeres. So sarcomeres are complexes of thick myosin filaments and thin actin microfilaments that are in special arrangements. And so later in our course, in our next lesson video, we'll be able to talk more about the structure of the sarcomere and these special arrangements that these, thick and thin filaments are in. But for now, if we take a look down below at our image, we can see that these brackets that we see here in here are labeling the sarcomeres and so, this one bracket is labeling 1 sarcomere and this one is labeling another sarcomere and so there's actually another sarcomere here and here and here and so these repeating units of sarcomeres, are referred to as myofibrils. And so, these myofibrils again are repeating units of sarcomeres. And so if we take a look at our image down below, we can see that, this entire thing right here would be referred to as the myofibril. And notice that, here we have another myofibril. Here's another one. Here's another one. And here's another one. And so together, all of these myofibrils, which you'll notice, is that they are surrounded by what's known as a sarcoplasmic reticulum, which is a membranous structure. And so down below, notice that this yellow structure that we see here that's being labeled as the sarcoplasmic reticulum is, actually going to be very, very important when it comes to a muscle contraction. And so later in our course, when we're talking about muscle contractions, we are going to talk up, we are going to revisit this sarcoplasmic reticulum, which is going to be important for releasing calcium. But again, we'll talk more about the sarcoplasmic reticulum and the calcium that it releases later in our course when we're talking about the muscle contraction. But for now, we can see that the sarcoplasmic reticulum is, the yellow membranous structure that we see here. Now, what you'll notice is that these myofibrils that we see here are all packed in side of what's known as a muscle fiber and so a muscle fiber is just a long, multinucleated cell and so, multinucleated just means that it has multiple nuclei. So, instead of having just one nucleus like most cells, these muscle fibers have multiple nuclei, multiple nucleuses if you will. And so, what you'll see is that, here what we have is, the muscle fiber. And so you can see that this is all one really really long cell and so it is quite long and it it can actually run the length of the entire muscle. So that is quite long for 1 individual cell. And again, they are multinucleated. So you can see that each of these blue structures that we see here represent nuclei and they're going to repeat and, be within, this muscle fiber. Now, again, you can see that within the muscle fiber, the myofibrils are going to be packed inside and extend the length of the entire fiber. Now, notice that, this, entire muscle fiber that we see here is leading up to what's known as a muscle fascicle and so, This muscle fascicle, all it really is, what we can see here, it's just a bundle of muscle fibers. So it's just a bundle of individual cells, a bunch of, these long multinucleated cells packed together. And so, what you'll notice is that a bunch of these, here here we only have one muscle fascicle. But you'll notice here's another muscle fascicle. All of these are muscle fascicles and so a bunch of muscle fascicles are going to make up the skeletal muscle. And so the skeletal muscle are gonna be the voluntary muscles, the ones that we actually have control over, such as our biceps for instance, here. And, they are going to have a striated or striped appearance and, the striped appearance that you can see throughout here where you have a dark band followed by a light band, followed by dark band. This is the striated striped appearance and really, it all comes down to the structure of the sarcomere that gives the skeletal muscle this striated striped appearance. And again, the skeletal muscle is going to consist of muscle fascicles together. And so, you can see here we have the human body and you can see the skeletal muscle that's scattered throughout and so we can label this as the skeletal muscle. And so really this completes our lesson on skeletal muscle anatomy. And again, in our next lesson video, we'll be able to talk more about the structure of these sarcomeres and, later we'll be able to talk about the muscle skeletal muscle contraction. So I'll see you guys in our next video.
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Problem
Problem
Match the following parts of the muscle with the correct description:
a) Sarcomere. ______: voluntary muscles (i.e. triceps) that consist of muscle fascicles.
b) Myofibrils. ______: repeating units of sarcomeres.
c) Fascicles. ______: multinucleated cells that consist of a bundle of myofibrils.
d) Sarcoplasmic Reticulum. ______: membrane-bound structure found within muscle cells.
e) Skeletal Muscle. ______: complex of thin actin and thick myosin filaments.
f) Muscle Fiber. ______: a bundle of skeletal muscle fibers.
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Skeletal Muscle Anatomy
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Video transcript
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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Problem
Problem
Correctly label each part of the sarcomere in the electron micrograph below: