Structural Class: Synovial Joints - Video Tutorials & Practice Problems
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1
concept
Synovial Joints
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8m
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In this video, we're going to talk about the third and final structural class of joint in our lesson, which is the synovial joints class. And so it turns out that most of the joints in the human body are actually classified as synovial joints. And so if you were to ask a random person on the street to point out a joint in the human body, they're probably going to point out a synovial joint such as for example, the shoulder, the elbow, the knees or the knuckles in our hand. And so these synovial joints are actually distinguished from other types of joints and that they actually have dynamic or a free range of movement. And therefore, these synovial joints are always functionally going to be classified as diarthrosis, which is why we have the symbol for diarthrosis here in our lesson. And so once again, notice that this symbol for diarthrosis has multiple movement arrows going around it, which can hopefully help remind you that these diarthrosis allow for dynamic movement. Now, it is important to note that different synovial joints can vary in the degree of movement that they allow for. And so some synovial joints allow for more free movement than other synovial joints. But in general, synovial joints allow for more movement than other types of joints. And recall that the mobility of a joint comes at the cost of the stability of a joint. And so because these synovial joints allow for dynamic and free movement, that also means that they are quite unstable and prone to injuries such as dislocations like a shoulder dislocation for example. And so this is why synovial joints have the following unique characteristics that you can see down below in the text to help reinforce them and make them a little bit more stable than they otherwise would be. And so notice that the text is very nicely color co ordinated to the image down below which we'll get to here very shortly. And so the first unique characteristic of synovial joints is the presence of a synovial cavity also sometimes referred to as a joint cavity. And really, this is just a space that exists between the bones of the synovial joint. And so this cavity or space actually stores synovial fluid and synovial fluid is actually a viscous or a thick liquid that has many functions including serving as a lubricant to ensure the smooth movements within the synovial joint and acting as a shock absorber to help protect the components of the synovial joint. Now, the next unique feature of synovial joints is the presence of articular cartilage. And so really this is just hyaline cartilage that covers the ends of the synovial joint bones. And so because it covers the ends of the bones where they meet, it actually creates a slippery and smooth surface that reduces friction between the bones when they move in the synovial joint. And the articular cartilage also serves as a shock absorber to help protect the components of the synovial joint. And the last unique feature of synovial joints is actually the presence of an articular capsule which actually surrounds the entire synovial joint as two layers, an inner layer and an outer layer. The inner layer is a synovial membrane which actually lines the synovial cavity and produces the synovial fluid. And the second layer is an outer fibrous layer that's made of fibrous connective tissue or connective tissue proper, specifically dense irregular connective tissue. And so, recall from our previous lesson videos that dense irregular connective tissue has fibers in its extracellular matrix that are really densely packed together and arranged in an irregular or a random pattern, which actually allows it to resist forces in multiple directions, which is really important for a synovial joint to be able to do when it has dynamic movement. And so really these unique characteristics help to make the synovial joint more stable than it otherwise would be without them. So let's take a look at our image down below where we can start to piece things together. And so notice over here on the left hand side we're showing you the bones of the hand. And we're focusing in specifically on one of the synovial joints of the pointer finger right over here. And so we know that our pointer finger has quite a lot of dynamic movement. And so this joint is considered a synovial joint. And so notice that here, we are highlighting the bones of the synovial joint and notice that the space that exists between this bones highlighted here in pink is the synovial cavity or the joint cavity. And so we can go ahead and label it as so over here and recall that the synovial cavity stores the synovial fluid, which recall is a very viscous or thick liquid that has many functions including acting as a lubricant to ensure the smooth movements of the synovial joint and also serving as a shock absorber to help protect the components of the synovial joint. Now, we can also really clearly see the articular cartilage which again is going to be the hyaline cartilage that covers the ends of the bones in the synovial joint highlighted here in blue. And so recall, the articular cartilage creates a very smooth and slippery surface that reduces friction when these bones are moving in the synovial joint. And it also acts as a shock absorber to help protect the components of the synovial joint. And then last but not least, we can also see the articular capsule over here, which again consists of two layers. The inner synovial membrane, which you can see highlighted in green uh which again is lining the synovial cavity. And it produces the synovial fluid that fills the synovial cavity. And then you can also see the outer fibrous layer uh which is immediately outside of the synovial membrane highlighted here. And it turns out that this outer fibrous layer is actually a thickened continuation of the periosteum, which recall is the outermost layer of the bone. And so this outer fibers layer is going to allow for the flexible movements of the synovial joints. But it's also going to help reinforce that synovial joint to make it more stable than it would be without it. Now, although ligaments are not a unique characteristic of synovial joints, ligaments are present in synovial joints. And again, they help to reinforce the synovial joints to make them more stable than they would be without them. And although it's not shown, it's really important to note that synovial joints are nourished by blood vessels. And so that's important for the synovial uh membrane to continuously produce synovial fluid. And uh synovial joints are also innervated by nerves, which is important for us to be able to sense pain and also to be able to sense the position and the movements of the synovial joints. And so, although those are not shown here, it's important to keep that in mind, they have blood vessels and they also are innervated with nerves. And so this year concludes our brief introduction to synovial joints. And as we move forward in our course, we'll be able to learn more and apply these concepts and practice problems. So I'll see you in our next video.
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example
Structural Class: Synovial Joints Example 1
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2m
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So here we have an example problem that asks which of the following is not a unique characteristic of synovial joints. And we've got these four potential answer options down below. Now, option A says dynamic movement. And so recall from our last lesson video that synovial joints are always functionally classified as diarthrosis because they allow for dynamic or free movement. And so really this is a unique feature of synovial joints because the other structural classes of joints including the fibrous joints and cartilaginous joints do not allow for this dynamic movement. And so really synovial joints are the only ones classified as diarthrosis and they're the only ones that are going to allow for this dynamic movement. So, dynamic movement is a unique feature of synovial joints. And for that reason, we can cross this option off of our list because we're looking for the feature that is not unique to synovial joints. Now, moving on option B says ligaments and so again, ligaments can be found reinforcing synovial joints. However, ligaments are not unique to synovial joints because ligaments can also be found in the other structural classes of joints, including some five joints and some cartilaginous joints. And so for that reason, ligaments is a characteristic that is not unique to synovial joints. And for that reason, option B must be the option that we are looking for. So we can go ahead and indicate option B as the correct answer to this problem. But just in case, let's check the last two options here. Option C says articular capsule and recall that this consists of two layers, the inner synovial membrane and the outer fibrous layer. And so the articular capsule is a unique feature or a unique characteristic of synovial joints. So for that reason, we can cross it off this list. And then option D says synovial fluid which recall acts as a lubricant and a shock absorber in the synovial cavity. And so it is again a unique feature of synovial joints. So we can cross it off this list. And so option B ligaments is the only option here that is not unique to synovial joints. So that is the correct answer that concludes this example. And I'll see you all in our next video.
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Problem
Problem
Which of the following is a unique feature of synovial joints?
A
Presence of ligaments.
B
Joint movement.
C
Presence of a joint cavity.
D
Presence of hyaline cartilage.
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concept
Weeping Lubrication
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2m
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In this video, we're going to talk briefly about weeping, lubrication of synovial joints. So weeping lubrication is the name of a process where synovial fluid in articular cartilages is forced out of the articular cartilages upon compression of the synovial joint. And when pressure on that synovial joint is relieved, the synovial fluid that was forced out of the articular cartilages is actually soaked back into the articular cartilages, kind of like how water soaks into a sponge. And so really articular cartilage is analogous to a sponge in this weeping lubrication process. So let's take a look at our image to understand this a bit better. And so notice on the left hand side, we're focused then on a relaxed knee joint, since we can see this person relaxing on this beach chair over here, and we know that the knee joint is an example of a synovial joint due to its dynamic movement. And so zooming into this relaxed knee joint over here, notice that the articular cartilage which covers the ends of the bones serves as a sponge to absorb the synovial fluid. And so notice here, we have an image of a sponge where again the sponge is analogous to the articular cartilage. And we can see that the synovial fluid shown here in this reddish pinkish color is being absorbed into the sponge or the articular cartilages. And again, this happens during the relaxed state of the knee joint. And this allows the synovial fluid to nourish the cells or the chondrocytes found within the articular cartilage. Now, on the right hand side over here, we're focused in on a compressed knee joint. And so notice that the person no longer is laying down on a beach chair, relaxing the person is now running. And so you can see that their knee joint is being compressed in this fashion. And so zooming in on that compressed knee joint again, you can see the compression here with these arrows. Notice that the articular cartilage is also going to be compressed and that means that the synovial fluid is going to be forced out upon compression. And that allows the synovial fluid to serve as a lubricant and a shock absorber to help protect the articular cartilage during this compression and this movement and also protect the other components of the synovial joint as well. And so really, this is all uh we have on the weeping lubrication of synovial joints and we'll be able to get some practice applying these concepts and learn more about synovial joints as we move forward in our course. So I'll see you all in our next video
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example
Structural Class: Synovial Joints Example 2
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So here we have a pretty straightforward example problem that wants us to use the words in the word bank down below to fill in the blanks and complete the sentences. And so the first sentence says as a synovial joint blank, the pressure from the bones coming together squeezes the articular blank. And so we've got these four potential words, fluid cartilage, friction or compresses. And so as a synovial joint compresses is the first interactive blank here. So we can cross it off the pressure from the bones coming together, squeezes the articular cartilage. And so we can cross off cartilage from here. As this happens, the synovial blink is squeezed out into the synovial cavity lubricating the joint and reducing blank. And so, of course, as this happens, we know that the synovial fluid is going to be squeezed out into the synovial cavity lubricating the joint and reducing friction. And so we can cross these off. And this here concludes this example problem. So I'll see you all in our next video.
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Problem
Problem
Which of the following statements accurately describes weeping lubrication in synovial joints?
A
It involves the secretion of tears from the lacrimal glands into the synovial cavity.
B
It relies on the release of mucus from the goblet cells within the synovial membrane.
C
Synovial fluid is squeezed out of articular cartilage during compression & reabsorbed during decompression.
D
It occurs when blood vessels within the joint capsule deliver nutrients to the articular cartilage.
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Problem
Problem
What role does articular cartilage play in synovial joints?
A
It reduces stress on the joint.
B
It stores synovial fluid, allowing for weeping lubrication.
C
It lines bone ends, preventing them from coming into direct contact with each other.
D
All three answers above are correct.
8
concept
Additional Features
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4m
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In this video, we're going to talk about additional features that are found in just some synovial joints but not in all synovial joints. And the first are going to be bursae and so bursae are synovial fluid filled sacs that are strategically located in some synovial joints to reduce friction between ligaments or tendons and other tissues and by reducing friction, they also help to prevent damage. Now, a tendon sheath is really just an elongated bursa. So it's just a longer bursa that wraps around and protects a tendon as its name implies. And it therefore is going to help reduce friction and again prevent damage during the movement of some synovial joints. Now, next on our list are fatty pads, which as their name implies, are going to be made up of fat or adipose tissue. And these fatty pads are going to be present in the knee joint and the hip joints which are load bearing joints that need to bear the weight of our body. And so they do need these extra layers for cushioning. And so the fatty pads help to provide an extra layer of cushioning between the outer fibrous layer and the inner synovial membrane of the articular cartilage. Again, of some joints, specifically the knee and hip joints. Now, next on our list are articular discs which are also known as manic. And so these are disks of fibrocartilage or a fat that divide the synovial cavity into two spaces. And so these articular discs have many different functions including acting as shock absorbers to protect those joints. And so uh these articular discs are found in the knee and the jaw and in a few other joints as well. And so let's take a look at our image down below where we can start to visualize some of these additional features. And so notice on the left hand side, we're focusing in on the knee joint. And so you can see that this is this is a zoom in of the knee joint. And what you'll notice is that there are these purple structures throughout the knee joint and those purple structures are representing the bursa or bursa for the singular form. And what you'll notice is that the image on the right over here is a zoom in of the shoulder joint. And what you'll notice is that the shoulder joint also has a bursa strategically located right here in this position. And again, the bursa is just a flu a synovial fluid filled sac that's going to help to reduce friction within that synovial joint. Now notice that uh the shoulder joint has a tendon sheath which is just an elongated bursa that wraps around a tendon. And so you can see that there's a tendon here and uh the tendon sheath is wrapping around that tendon again to help reduce friction and prevent damage. Next over here, what we have is a fatty pad. And so you can see that this fatty pad is located right here in this position and it is strategically located in the knee joint to help uh provide an extra layer of cushioning. And then what we have are uh is an articular disc or a meniscus uh located right here in this position. And you'll notice that there's another one over here as well. And what it does is it separates the synovial cavity into two separate spaces which can help to relieve stress and redirect synovial fluid into specific regions to relieve the synovial joint of stress, provide stability and uh act as a shock absorber as well. And so this here concludes our brief lesson on these additional features that again are found in just some synovial joints, not in all synovial joints. And we'll be able to get some practice of finding these concepts moving forward. So I'll see you all in our next video.
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example
Structural Class: Synovial Joints Example 3
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1m
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So here we have an example problem that asks which of these statements about bursa and tendencies is false. And we've got these four potential answer options down below. Now, option A says that the primary function of both bursa and tendencies is to reduce friction at synovial joints. And so recall from our last lesson video that this is actually a true statement and because it's a true statement, it's not the false answer option that we're looking for. So we can cross off option A. Now moving on option B says that they are found in all synovial joints. But recall from our last lesson video, we said that those structures such as bursa and tendencies are only found in some synovial joints, not in all synovial joints. And so what this means is that option B is actually a false statement. And so that means that it is the false answer option that we're looking for. So we can indicate option B is the option uh the correct option for this problem. But let's check the other two just to be sure. Option C says that they can be found associated with some but not all synovial joints in the body. And again, we know that this is a true statement. So it's not a false answer. Option that we're looking for so we can cross it all. And then option D says that they are both fiber sacks filled with synovial fluid. And again, this is a true statement. Recall. Really, the uh most significant difference between bursa and tendencies is that the tendencies are uh much longer. There are elongated structures, but uh outside of that, they are both fiber sacks filled with synovial float. So again, because it's true, it's not the false answer option that we're looking for. So again, option B is the correct answer to this problem that concludes this problem and I'll see you all in our next video.
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Problem
Problem
Imagine you're a doctor and a patient comes to you because of pain in their knee joint. You find that there is not enough synovial fluid present in their knee's synovial cavity, leading to friction when the knee moves. Which of the following structures in the knee joint is not functioning correctly?
A
Bursae.
B
Articular cartilage.
C
Articular capsule.
D
Synovial membrane.
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