Types of Muscle Tissue - Online Tutor, Practice Problems & Exam Prep

Muscle tissue comprises three types: skeletal, cardiac, and smooth. Skeletal muscle, or voluntary muscle, allows conscious control and features striated, multinucleated fibers. Cardiac muscle, found in the heart, is involuntary, striated, and consists of branching, typically uninucleate cells connected by intercalated discs. Smooth muscle, also involuntary, lacks striations, has a smooth appearance, and consists of short, spindle-shaped, uninucleate cells. Each type plays a crucial role in bodily functions, from movement to circulation and digestion.

3 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 3 different types of muscle tissue. And so those 3 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 3 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.

Skeletal Muscle Tissue

In this video, we're going to talk about the first type of muscle tissue in our lesson, which is skeletal muscle tissue. Skeletal muscle tissue is also sometimes referred to as voluntary muscle tissue. The reason skeletal muscle tissue is called this is because it tends to be attached to the skeleton via tendons, which connect muscles to bone. It's called voluntary muscle tissue because it allows for voluntary or consciously controlled movements. Essentially, 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. For example, when I think about the muscles in my hand, I can consciously control the contraction of these muscles, reinforcing their voluntary nature that allows for consciously controlled movements. This characteristic is unique to skeletal muscle tissue, as the other two types of muscle tissue, including cardiac muscle tissue and smooth muscle tissue, do not allow for consciously controlled movements and are considered involuntary muscle tissues. Any type of muscle that you can think about and consciously control the contraction of those muscles is going to be skeletal muscle tissue.

Skeletal muscle tissue has several key features, including striations in the tissue. These striations are a banded appearance or pattern that appears due to the alignment of protein myofilaments. You might recall from our last lesson that a common feature of all muscle tissue is that they contain protein myofilaments. However, the protein myofilaments in skeletal muscle tissue align in such a way that they create these striated or banded appearances. Another notable feature of skeletal muscle tissue is that it consists of long, cylindrical cells known as muscle fibers or muscle cells, and these can be quite long, even over 1 foot in length. Because these cells are so long, one nucleus is not enough to support the cell, leading to another notable feature of skeletal muscle tissue: it consists of multinucleated cells. These muscle fibers have a high protein demand, necessitating many nuclei because DNA within the nuclei codes for protein. If you have high protein demands, you will need a lot of DNA and, therefore, many nuclei.

Let's take a look at our image down below where we can start to piece things together and visualize some skeletal muscle tissue. Once again, skeletal muscle tissue is also known as voluntary muscle tissue. For instance, our biceps are muscles that we know we can consciously control the contraction of, so they consist of skeletal muscle tissue. If you look at this micrograph of skeletal muscle tissue, notice that the muscle fiber, which is a muscle cell, is indicated with brackets. This highlighted section is one muscle fiber. Up above here, you'll see another muscle fiber, and down below another. This micrograph is showing us three muscle fibers, or three muscle cells. Notice about each of these muscle fibers is that they have a striated or banded appearance when looked at closely. This banded appearance is referred to as striations and is a feature of skeletal muscle tissue. Each of these muscle fibers is also multinucleated, which supports the high protein demands. This concludes our brief lesson on skeletal muscle tissue, and we'll get some practice and learn about the other types of muscle tissue as we move forward. 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.

Cardiac Muscle Tissue

In this video, we're going to talk about the second type of muscle tissue in our lesson, which is cardiac muscle tissue. Cardiac muscle tissue is made of cells called cardiomyocytes, which are located in the walls of the heart. It's helpful to note that the root 'cardi,' present in both cardiac muscle tissue and cardiomyocytes, means heart. Unlike skeletal muscle tissue, which is voluntary, cardiac muscle tissue is involuntary, meaning its contractions are not consciously controlled. Recall from our last lesson video that skeletal muscle tissue is unique in its voluntary nature, and the other types of tissue, including cardiac muscle tissue and smooth muscle tissue, are involuntary.

Cardiac muscle tissue has several other key features that are notable, including its striations due to protein myofilament alignment, giving it a banded or striated appearance. The striations in cardiac muscle tissue are generally a bit harder to see than those in skeletal muscle tissue, but they are still present. Another identifiable feature of cardiac muscle tissue is that cardiomyocytes are branching, containing branch-structured cells. Cardiomyocytes tend to be uninucleate, which means they typically have just one nucleus. This is in contrast to skeletal muscle cells, which can be over one foot in length and are often multinucleate. The heart is a relatively small organ, and thus, one nucleus is usually sufficient for the shorter cardiomyocytes.

One last notable feature of cardiac muscle tissue is that it contains structures known as intercalated discs, which join the ends of cardiomyocytes together to enable coordination. This is critical for the heart to function as a pump and to circulate blood throughout the body. The presence of branching cells and intercalated discs helps these cardiomyocytes function as a unit.

Now, focusing on the heart, let's look at this micrograph of cardiac muscle tissue. Note that it contains striations like skeletal muscle tissue, though these might be more difficult to see. The cardiomyocytes are branching, and you can observe these branches in various areas. While cardiomyocytes tend to be uninucleate, occasionally a cardiomyocyte might be multinucleate. Every time you see darkened nuclei, you can assume it is a different cardiomyocyte. Lastly, intercalated discs are structures that join the ends of the cardiomyocytes together to enable coordination, identifiable throughout this cardiac muscle tissue.

This concludes our brief lesson on cardiac muscle tissue. We'll be able to practice applying these concepts and discuss the last type of muscle tissue as we move forward in our course. 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.

Smooth Muscle Tissue

In this video, we're going to talk about the 3rd 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 in 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, 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 is 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, 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 contract in order to help to release the urine from the bladder. It is, worthy of noting that the bladder does actually have some skeletal muscle tissue that is voluntary that allows us to control when 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 contractions. 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-shaped cells. And so, 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, 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, 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 the 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 the 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-shaped. And also, notice that these cells are going to be relatively short. And so that means that they are going to be uninucleate, with just one single nucleus and that is usually sufficient for these smooth muscle tissue cells. 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.

Review of Types of Muscle Tissue

In this video, we're going to do a review of the 3 types of muscle tissue. Since this video is a review, it means that we're not going to introduce any new information that we haven't already covered in our previous lesson videos. If you're already feeling confident 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. Notice down below in this table, we're reviewing the 3 types of muscle tissue: skeletal muscle tissue, cardiac muscle tissue, and smooth muscle tissue. We'll 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, such as whether the tissue cells are uninucleate with just 1 nucleus per cell, or if they are multinucleate with multiple nuclei per cell.

Let's start here with skeletal muscle tissue. Recall from our previous lesson videos that skeletal muscle tissue is also known as voluntary muscle tissue. This means that skeletal muscle tissue is voluntary. The voluntary nature means that we have conscious control over the contractions of this tissue. This means that the other two types of tissue are involuntary. One important aspect to remember is that if you can think about the muscle and then consciously control its contraction, then it's skeletal muscle tissue. However, if you think about the muscle and you cannot consciously control its contraction, then it is involuntary muscle tissue, either cardiac muscle or smooth muscle. If found in the heart, then it is cardiac muscle tissue, as the root "cardi" signifies heart and is only found in the walls of the heart. Smooth muscle tissue can be found in many different areas of the body, including the internal hollow organs and others. Skeletal muscle tissue, which you have voluntary control over, is found in many locations, such as those that give us our facial expressions and movements of our torso and limbs.

Regarding striations, skeletal muscle tissue is striated, meaning it has a banded appearance. Cardiac muscle tissue is also striated, though the striations may be a bit harder to see than in skeletal muscle tissue. In contrast, smooth muscle tissue lacks striations, which contributes to its smooth appearance under the microscope. Regarding the number of nuclei per cell, skeletal muscle tissue cells, referred to as muscle fibers, can be quite long, sometimes over a foot. These long cells, due to their length and high protein demands, often need multiple nuclei and thus are multinucleate. Both cardiac muscle tissue cells and smooth muscle tissue cells are shorter, generally with one nucleus per cell, making them uninucleate.

In the images below, you'll notice skeletal muscle tissue represented by a bicep, highlighting the multinucleated nature of the cylindrical muscle fiber cells and their striated appearance. Also shown are cardiac muscle tissue cells (cardiomyocytes), which are branched, a unique identifying feature amongst the three muscle tissues, and tend to be uninucleate. Lastly, smooth muscle tissue micrograph shows a smooth appearance due to the lack of striations and spindle-shaped cells, typically uninucleate. This concludes our review of the 3 types of muscle tissue, and we’ll be able to get more practice moving forward. 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.