Types of Muscle Tissue

In this video, we're going to begin our lesson on the types of muscle tissue. And so you may recall from our last lesson video that we briefly mentioned that there are three different types of muscle tissue. And so those three different types of muscle tissue are skeletal muscle tissue, cardiac muscle tissue, and smooth muscle tissue. And so moving forward in our course, we're going to talk about each of these three different types of muscle tissue in their own separate videos. And so in our next video, we'll get to start with skeletal muscle tissue. So I'll see you all there.

In this video, we're going to talk about the first type of muscle tissue in our lesson, which is skeletal muscle tissue. And so skeletal muscle tissue is also sometimes referred to as voluntary muscle tissue. And so the reason that skeletal muscle tissue is called skeletal muscle tissue is because it tends to be attached to the skeleton via tendons, which connects muscles to bone. And the reason that it's called voluntary muscle tissue is because it allows for voluntary or consciously controlled movements. And so really what we're saying here is that skeletal muscle tissue or voluntary muscle tissue is under our control. When we think about these muscles, we can actually consciously control the contraction of those muscles that allows us to control our body movements. And so, for example, when I think about the muscles in my hand, I can consciously control the contraction of those muscles in my hand to force my hand to contract as so and so that is going to be skeletal muscle or again, voluntary muscle issue. Now, this voluntary nature that allows for consciously controlled movements is actually unique to skeletal muscle tissue. And so the other two types of muscle tissue, including cardiac muscle tissue, and smooth muscle tissue do not allow for consciously controlled movements. And so they are actually considered involuntary muscle tissue. And so once again, any type of muscle that you can think about and consciously control the contraction of those muscles is going to consist of skeletal muscle tissue or again, voluntary muscle tissue. And so skeletal muscle tissue actually has several key features, including the ones that we're listing down below. And so, one notable feature of skeletal muscle tissue is that it contains striations in the tissue. And so these striations are really just a banded appearance or a banded pattern that appears in the tissue. And so these striations or this banded appearance is due to the alignment of protein myo filaments. And so you might recall from our last lesson video that all a common feature of all muscle tissue is that they contain protein myo filaments. However, the protein myo filaments in skeletal muscle tissue align themselves in such a way that it creates these striated or banded like. Now, another notable feature of skeletal muscle tissue is that it consists of long cylindrical cells that are also known as muscle fibers. And so you might recall in our last lesson video, we said that the term muscle fibers can refer to muscle cells. And so the skeletal muscle tissue cells are called muscle fibers. And once again, these are going to be long and cylindrical cells. And in some cases, these cells can be quite long, they can actually be over 1 ft in length, which is pretty long for a single cell. And so, because these cells are so long, one nucleus is not going to be enough to support the cell. And so this leads us to the next notable feature of skeletal muscle tissue, which is that it consists of multi nucleated cells, which of course means that the cells, these muscle fibers are going to have multiple nuclei. And so uh recall that uh a common feature of all muscle tissue is that they contain protein myo filaments. And these protein myo filaments allow for contractions. And so, in skeletal muscle tissue, which allows for voluntary contractions that we have control over, we are constantly controlling our uh skeletal muscle tissue all the time. So our skeletal muscle tissue is constantly contracting. And so they need a lot of protein myofilament to support all of those contractions. And so these muscle fibers and skeletal muscle tissue are going to have a very high protein demand. And so in order to meet the high protein demands of these skeletal muscle uh fibers, uh it's going to need lots of nuclei because recall that within the nuclei is the DNA and the DNA codes for protein. And so if you have high protein demands, you're going to need lots of DNA and therefore lots of nuclei. And so let's take a look at our image down below where we can start to piece things together and visualize some skeletal muscle tissue. And so, once again, skeletal muscle tissue is also known as a voluntary muscle tissue. So any muscle that you can think about and consciously control the contraction of that muscle is going to be skeletal muscle tissue. And so, for example, our biceps, we know that we can con consciously control the contraction of our bicep. And so it's going to consist of skeletal muscle tissue. And so what you'll notice is looking at this micrograph of skeletal muscle tissue, notice that the muscle fiber uh which again is the muscle cell is being indicated here with the brackets. And so this entire thing that I'm highlighting right here is going to be one muscle fiber, which is just one muscle cell up above right here, you'll see another muscle fiber, which is again, another muscle cell and then down below right here, you'll see yet another muscle fiber. And so this micrograph is showing us three muscle fibers or three muscle cells if you will. And what you'll notice about each of these muscle fibers is that they have this striated or banded appearance when you look really, really closely. And so this striated or banded appearance once again, is due to the alignment of protein myofilament. And these uh um banded appearance again, are referred to as striations. And so that is a feature of skeletal muscle tissue. And then once again, each of these muscle fibers are going to be multi nucleated. And so you can see that we are labeling m multiple nuclei here. In this one muscle fiber, you can see these purple uh circles here represent the nuclei. And so uh once again, each of these muscle fibers is going to be multi nucleated to support the high protein demands. And so this year concludes our brief lesson on skeletal muscle tissue and we'll be able to get some practice and learn about the other types of muscle tissue as we move forward. So I'll see you all in our next video.

Which of the following would NOT require the use of skeletal muscle?

• A. Kicking a soccer ball.
• B. Your heart rate increasing after exercise.
• C. Chewing and swallowing food.
• D. Raising your eyebrows.

In this video, we're going to talk about the second type of muscle tissue in our lesson, which is cardiac muscle tissue. And so cardiac muscle tissue is going to be made of cells that are called cardiomyocyte. And so these cardiomyocyte that make up the cardiac muscle tissue are going to be located in the walls of the heart. And so what's really helpful to note is that the root cardi, which you can see in cardiac muscle tissue and cardiomyocyte is a root that means heart. Now, unlike skeletal muscle tissue, which we know is voluntary, cardiac muscle tissue is going to be involuntary, which means that its contractions are not going to be consciously controlled. And so recall from our last lesson video that skeletal muscle tissue is unique in its voluntary nature. And the other two types of tissue including cardiac muscle tissue and smooth muscle tissue are going to be involuntary in nature, which again means that they are not consciously controlled. We can't just think about the muscle tissue in our heart and cause our heart to increase in pace or decrease in pace voluntarily in a conscious manner. And so that's what makes it involuntary. Now, cardiac muscle tissue has several other key features that are notable, including the ones that we have listed down below. And so, like skeletal muscle tissue, cardiac muscle tissue contains striations due to the protein myofilament alignment. And so recall that this means that the cardiac muscle tissue is also going to have a banded or a striated appearance. And so it turns out that generally the striations in cardiac muscle tissue are going to be a little bit harder to see than the striations in skeletal muscle tissue. But nevertheless, those striations are still there. Now, another notable feature of cardiac muscle tissue that can make cardiac muscle tissue pretty easily identifiable is that the cardiomyocyte or the cells that make up the cardiac muscle tissue are going to be branching. And so it contains branching cells or cells that have a branched structure. Now, another notable feature of cardiac muscle tissue is that the cardiomyocyte are going to tend to be uni nucleate and note that the root uni is a root that means one. And so this means that the cardiac muscle cells or the cardiomyocyte, they often are going to have just one single nucleus. And so recall from our last lesson video, we said that skeletal muscle tissue cells or the muscle fibers can be pretty long over 1 ft in length in some cases. And so because those skeletal muscle fibers can be really, really long, they certainly need to be multinucleate. However, the heart is a pretty short or pretty small organ. And so the cardiomyocyte don't need to be nearly as long as many of those skeletal muscle fibers need to be. And so one nucleus is generally going to be enough for those relatively shorter cardiomyocyte. Now, the last notable feature of cardio of cardiac muscle tissue that we have listed here is that they contain structures known as inter collated discs. And so these are structures that are going to join the ends of the cardiomyocyte together and enable co coordination. And so with these inter collated discs, they are going to help these cardiomyocyte function as a unit, which is going to be critical for the heart to function as a pump and pump blood throughout our entire body. And so let's take a look at this image down below where we can start to piece these things together. And so, again, cardiac muscle tissue is going to be found in the heart. And so notice here, we're focusing in on the heart and we've got this micrograph here of cardiac muscle tissue. Now, the first thing that you should note is that cardiac muscle tissue is going to contain striations like skeletal muscle tissue. Now, those striations might be a little bit more difficult to see, but they are certainly present in the cardiac muscle tissue. Now, the next notable feature that you'll notice here is that it contains branching cells. The cardiomyocyte are branching And so you can see here that we're highlighting some of that branching nature, but you can also see these branches occurring in different areas, different parts here. Now again, the cardiomyocyte tend to be uni nucleate, which means that they tend to have just one nucleus and uh that is a tendency. So occasionally there may be a cardiomyocyte that is multinucleate. But for the most part, every time you see these darkened nuclei, you can assume that is a different cardiomyocyte. And then last but not least here, the inter collated discs are these structures that once again are going to join the ends of the cardiomyocyte together to enable coordination. And so here you can see that we've identified one of the inter collated discs, but there are more inter collated discs throughout this cardiac muscle tissue. And so this here concludes our brief lesson on cardiac muscle tissue and we'll be able to get some practice applying these concepts and talk about the last type of muscle tissue as we move forward in our course. So I'll see you all in our next video.

Which of the following statements about cardiac muscle and skeletal muscle is true?

• A. They are both striated.
• B. They are both voluntary.
• C. They are both composed of long muscle fibers.
• D. They both have intercalated discs.

Intercalated discs allow cardiac muscle cells to coordinate. Why is this important?

• A. It increases the strength of the heart.
• B. It increases the endurance of the heart.
• C. It allows the heart to communicate with other organs.
• D. It allows the heart to contract as a unit and function as a pump.

In this video, we're going to talk about the third type of muscle tissue in our lesson, which is smooth muscle tissue and so smooth muscle tissue is actually named for its smooth appearance under the microscope. And so the smooth muscle tissue gets its smooth appearance due to the lack of striations and smooth muscle tissue. And so it turns out that the lack of striations is a feature that is unique to smooth muscle tissue. And so, recall from our previous lesson videos that the other two types of muscle tissue, skeletal muscle tissue and cardiac muscle tissue are both striated, meaning that they have a banded appearance. And again, smooth muscle tissue is going to be unique in that it lacks those striations. And that is what gives it the smooth appearance under the microscope. Now, in terms of the location of where smooth muscle tissue can be found within the body, we can pretty much say that any involuntary muscle tissue that's not part of the heart is going to be smooth muscle tissue. But more specifically here, we can see that smooth muscle tissue can be located in the walls of several hollow internal structures within the body. For example, smooth muscle tissue is found in the walls of blood vessels. They're also found in the walls of intestines that make up part of the digestive system and they're found in the walls around the bladder. And so the in terms of the function of smooth muscle tissue, we can say that it's going to control the diameter of these hollow internal structures and it can help propel the material through the organs. For example, we know that the smooth muscle tissue that is found in the intestines of the digestive system are going to contract in order to decrease the diameter of the intestines and to propel food through the digestive system in a specific direction. Also blood vessels, the smooth muscle tissue that is uh in the walls of the blood vessels can contract to decrease the diameter of the blood vessels to increase the blood pressure in those blood vessels. And also the smooth muscle tissue that surrounds the bladder can uh contract in order to help to release the urine from the bladder. Now, it is uh worthy of noting that the bladder does actually have some skeletal muscle tissue that is voluntary that allows us to control when uh we release the urine from the bladder. Now, smooth muscle tissue, as we already know is going to be involuntary in its nature, just like cardiac muscle tissue. And so this means that its contractions are not going to be consciously controlled. And so we can't really think about the smooth muscle tissue in our intestines and consciously control their contraction. And so this is what makes it involuntary. And again, skeletal muscle tissue is unique in its voluntary nature. Now, in terms of the shape of the smooth muscle tissue cells, it's notable that they are going to consist of short and spindle shape cells. And so uh the short and spindle shaped cells are going to be thin on the ends and thick in the middle, just like a spindle. And so notice over here on the far right, we're actually showing you an image of a spindle and thread in case you needed a better visualization of what this spindle shape looks like. And so we're focusing in on this green part here and that is the spindle shape. And again, you can notice that on the edges, it's going to be thinner, but then in the middle, it's going to be thicker. And that's exactly what we're describing right here now, uh because these smooth muscle tissue cells are relatively short, then one single nucleus per cell is usually sufficient. And that means that these cells are going to be uninucleate in nature, which again means that the smooth muscle cells are each going to have just one nucleus. And so let's take a look at our image down below where we can start to piece things together here. And so again, when it comes to smooth muscle tissue, it's going to have a smooth appearance under the microscope due to the lack of striation, a unique feature of smooth muscle tissue. And again, in terms of the locations, smooth muscle tissue is pretty much involuntary muscle tissue that is not found in the heart. And so um it can be found in many different locations. But we know once again from our lesson up above that they're found in the walls of several hollow internal structures, including the walls of the intestines of the digestive system. And so notice in our image down below, we're focusing in on the digestive system and walls of the intestines. And so notice we're showing you a micrograph here of smooth muscle tissue and notice that it does have a pretty smooth appearance. We don't really see these striations like what we saw in the skeletal muscle tissue and cardiac muscle tissue. So there is a lack of striations giving it a smooth appearance. Also notice that these cells are spindle shaped cells. And so notice that here, we are actually highlighting the shape of one of these smooth muscle tissue cells so that you can see that it is indeed spindle shape. And also notice that these cells are going to be relatively short. And so that means that they are going to be uni nucleate uh with just one single nucleus. And that is usually sufficient for these smooth muscle tissue cells. And so the nuclei are these darkened circles that you see here. And um each of these darkened circles would represent one muscle tissue cell, smooth muscle tissue cell. And so this here concludes our brief lesson on smooth muscle tissue and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

Which of the following movements requires smooth muscle contraction?

• A. Eyeballs rotating to look to the left.
• B. Heart pumping blood through blood vessels.
• C. Arm moving to lift a weight.
• D. Blood vessels constricting to restrict blood flow.

Arrector pilli are small muscles located in the connective tissue beneath the skin and are connected to the base of each hair. They are responsible for creating goosebumps when you get cold, an involuntary response to temperature. Based on this information, what type of muscle would you expect the arrector pilli to be?

• A. Skeletal muscle, as one function of skeletal muscle is to generate heat.
• B. Smooth muscle, as getting goosebumps is an involuntary reaction.
• C. Cardiac muscle, as blood flow helps control temperature.

In this video, we're going to do a review of the three types of muscle tissue. And so because this video is a review, that means that we're not going to introduce any new information in this video that we haven't already introduced in our previous lesson videos. And so because of that, if you're already feeling really good about these three types of muscle tissue, then you can feel free to skip this video if you'd like. But if you're looking for a review, then this video could be helpful for you. And so notice down below in this table, we're going to be reviewing the three types of muscle tissue, which are skeletal muscle tissue, cardiac muscle tissue, and smooth muscle tissue. And we're going to review the locations of where these tissues can be found, whether they are voluntary or involuntary, whether they are striated or not. And the number of nuclei per cell in terms of if the tissue cells are uninucleate with just one nucleus per cell or if they are multi nucleated with multiple nuclei per cell. And so let's start here with skeletal muscle tissue. Now, recall from our previous lesson videos that skeletal muscle tissue is also known as voluntary muscle tissue. And so what that means is, of course, skeletal muscle tissue is going to be voluntary. Now, recall that skeletal muscle tissue is unique in its voluntary nature. And the voluntary nature means that we're going to have conscious control over the contractions of this tissue. And so, uh what this means is that the other two types of tissue are going to be involuntary in nature. And so we can go ahead and fill those in as so. And so, uh one thing to keep in mind here is that if you can think about the muscle and then consciously control the contraction of that muscle, then it's going to be skeletal muscle tissue. But if you think about the muscle and you cannot not consciously control the contraction of that muscle, then it's going to be involuntary muscle tissue, either cardiac muscle or smooth muscle. If it's found in the heart, then we know it's going to be cardiac muscle tissue because recall that the root cardi is a root that means heart. And so cardiac muscle tissue is only found in the walls of the heart. So in terms of the location, we can put the heart over here. Now, smooth muscle tissue can be found in many different areas of the body. And so uh we talked about how it can be found in the internal hollow organs within the body. Uh and that is true but it can also be found in some other locations. So what we're going to put over here is just many locations. Now, in terms of skeletal muscle tissue, it can also be found in many locations. Again, any muscle tissue that you have voluntary control over is going to be skeletal muscle tissue. So that includes the skeletal muscle tissue that give us our facial expressions to the skeletal muscle tissues that allow for the movements of our torso and of our limbs, our arms and legs. Now, in terms of striations, uh recall that uh skeletal muscle tissue is going to be striated, which means that it has a banded appearance to it. So here we can say that it is strid and cardiac muscle tissue is also going to be striated as well. Although the striations in cardiac muscle tissue may be a little bit more difficult to see than the striations in skeletal muscle tissue, they're both still strided. Now, on the other hand, smooth muscle tissue is going to lack striations and that's where it gets its name from. It has a smooth appearance under the microscope because it lacks striations. And so what we can say here is that it lacks striation or no striations. Now, in terms of the number of nuclei per cell recall that skeletal muscle tissue cells are called muscle fibers. And sometimes these muscle fibers can be pretty long over a foot in length. And so a single cell that is over a foot in length is pretty long and one single nuclei is not going to be enough to support this those long cells. And so it's going to need multiple nuclei. Plus, it's going to need multiple nuclei to support its high protein demand. And so what we can say is that the skeletal muscle tissue is going to be multi nucleated. Now, on the other hand, the cardiac muscle tissue cells and the smooth muscle tissue cells are going to be much shorter in length. And so usually one nucleus per cell is sufficient for those muscle tissue cells. And so cardiac muscle tissue tends to be uninucleate, meaning it has just one nucleus per cell. And again, smooth muscle tissue also tends to be uninucleate as well. And so if we take a look at the images down below which you'll notice is on the far left, we are showing you skeletal muscle tissue. And uh we're uh specifically using the bicep here as an example of skeletal muscle tissue. Uh recall that the muscle fibers are the cells and they are long cylindrical cells. And so here I'm highlighting that there, the fact that there are three different muscle fiber cells that you can see in those regions. And what you'll notice is that they are multi nucleated. So you can see that these purple circles here are the nuclei and so there are multiple nuclei within a single muscle fiber. And you'll also notice that it, it has this striated appearance, this band like appearance. And you can also see those striations in the cardiac muscle tissue, which is right over here, again, found in the walls of the heart. And so it is also going to have these striations a little bit harder to see. But they are there uh notice that in the uh cardiomyocyte, which are the cells of the cardiac muscle tissue, uh they are going to be branched. And so you can see these branching uh cells over here. And that is a very helpful, unique identifying feature of cardiac muscle tissue amongst the three muscle tissues is the branching nature of the cells. And uh once again, it tends, they tend to be uninucleate. And so those nuclei are the darker circles that you see and usually they are going to be uninucleate meaning one nucleus per cell. And then last but not least over here on the far right, we have the smooth muscle tissue micrograph. And what you'll notice is that it has more of a smooth appearance because it lacks striations. And so this uh banded pattern is not really present here. Now, these cells, they do have a spindle shape to them, which recall means that they are narrow at the ends and kind of thicker in the middle. And again, they tend to be uninucleate meaning one nucleus per cell. And so this here concludes our review of the three types of muscle tissue and we'll be able to get some more practice as we move forward. So I'll see you all in our next video.

During an intense running session, you pull a leg muscle. Which type of muscle did you injure?

• A. Skeletal.
• B. Cardiac.
• C. Smooth.

Striations are a feature shared by skeletal and cardiac muscle, but they are not present in smooth muscle. Based on what you know about the functions of these three types of muscle, what do you think the presence of striations indicates about the muscle it is found in?

• A. It's a flexible muscle.
• B. It's a voluntary muscle.
• C. It can generate significant force when it contracts.
• D. It has a branched structure.