Lesson video

Hi there and welcome to today's lesson.

My name's Mr. Swaithes and I'm really looking forward to working with you today.

So today's lesson is called Classification of joints, and it comes from the unit: Anatomy and physiology: the musculoskeletal system.

Okay, so by the end of today's lesson, you're gonna be able to identify and describe the features of a synovial joint and explain how they prevent injury.

In terms of keywords, we're gonna be looking at synovial joint, synovial fluid, cartilage, ligaments, and tendons, alongside a couple more keywords that are really important today around ball and socket and hinge and pivot joints.

You might wanna pause the video now while you make a note of these different definitions, but we will revisit them throughout the lesson.

Okay, so the lesson's gonna be split up into three parts.

First part of today's lesson we're gonna be identifying the features of synovial joints.

Then we're gonna locate the different types of freely movable joints.

Freely movable is another way of describing a synovial joint.

And then thirdly, we're going to be explaining how joint structures help prevent injury.

So I'm ready, are you? Let's get going.

Okay, so here we've got an example of a synovial joint, and this picture is actually of the knee joint.

We can see the femur at the top there and the tibia below it.

And synovial joints are the most common type of joint found in the human body and the one that we study the most, because as sports performers or sports scientists, we have a real interest in these ones, because they're freely movable, and they're freely movable because they've got this cavity filled with synovial fluid, the grey matter in that picture that allows you to keep moving in lots of different directions.

So they've got some common features that help support movement.

And a fancy word for movement is articulation.

So two or more bones meet at a joint which allows articulation or movement.

Okay, then, so let's have a little look.

We've got first up, the joint capsule.

So that encloses the joint and provides some stability and protection.

It's highlighted there in the kind of reddy colour.

Inside that we've got the synovial membrane.

So that's the lining within the joint capsule that secretes synovial fluid.

Then we've got, as I said earlier, the grey matter, the synovial fluid that fills the joint cavity.

And the synovial fluid's job is to help lubricate the joint to allow free movement.

So it's a little bit like engine oil in a car.

And actually, a bit like engine oil, it prefers to be warm.

So sometimes our joints feel a bit stiff if we've been sat still, but when we warm them up, their synovial fluid warms up and enables a bit more free movement.

What other features have we got? Well, we've got cartilage, or by its full name, articular cartilage, which covers the ends of bones and helps prevent wear and tear.

And you want a thick layer of that cartilage on the end of your bones to prevent them wearing on each other.

And then we've got a bursae, which is a small, fluid-filled sac located near joints to reduce friction and that allows smooth movement.

So that bursae on the front there, the browny colour, is kind of enabling that quadricep muscle that's stretching over the top of the knee joint to move without getting caught up in that joint.

So a bursae is really important to allow that free movement.

And then we've got ligaments.

So they are these bands of strong connective tissue that connect bone to bone.

Again, if I use this as the example of my femur, and this as the example of my tibia, we've got ligaments down either side that are connecting and holding that joint together to help stabilise it.

And that stops that kind of twisting movement, for example.

And then we've got tendons, of course, which connect muscle to bone.

So on the end of that quadriceps muscle, we've got a tendon connecting it to the tibia, which is why it's able to extend at the knee joint, there I am extending my illustration of a knee joint.

Okay, so let's do a quick check.

Which of the following is the correct role of synovial fluid? Is it A: to protect the ends of bones? Is it B: to provide stability and structure to the joint? Is it C: to lubricate the joint and allow free movement? Or is it D: to connect bone to bone? So what does synovial fluid do? That's right, it lubricates the joint to help allow free movement.

Let's do another one.

Which of the following connects bone to bone to help stabilise a joint? Is it A: cartilage, B: ligaments, C: tendons, or D: synovial membrane? That's right, so connecting bone to bone, we've got ligaments.

And I illustrated that there with my fingers on the outside here as if they're ligaments.

They're a bit like elastic bands, really, that help stabilise that joint.

Okay, so the first task I'd like you to do for this lesson is I'd like you to label this diagram of the knee joint with the following features: I want you to cover off synovial membrane, synovial fluid, joint capsule, bursae, cartilage, ligaments, and tendons.

So we've got seven features there that I want you to illustrate on the diagram.

And then next to each one, I want you to add a brief description of the role of that feature.

So you wanna pause the video now and come back to me as soon as you are ready.

Good luck with this one.

Okay, let's see what you came up with.

So synovial membrane there, the kind of pinky colour on the inside of the joint capsule.

The grey matter.

Sometimes I dot this to show that it's fluid.

So the grey matter in the middle there.

The joint capsule is kind of the reddy colour.

And we've got the bursae, which is a browny colour.

Don't get that confused with the patella, which is obviously a bone.

And then we've got the cartilage or articular cartilage, which is lining the ends of the bones.

We want that quite thick and well-nourished.

Then we've got ligaments that connect the bone to bone to help stabilise the joint, and tendons that connect the end of the muscle onto the bone to allow that articulation or movement to happen.

So the slightly harder part of this task was to be adding your description of each.

So did you come up with something like this? Synovial membrane secretes the synovial fluid.

The synovial fluid is what lubricates the joint to allow free movement, a bit like engine oil in a car.

The joint capsule is what encloses or encapsulates that joint, providing stability and protection to it.

The bursae is what reduces friction to allow smooth movement.

So it's like that pad of, again, it's made up of some synovial fluid and it sits where the quadricep muscle and its tendons stretch over the front of that knee joint, and it sits there to help that movement to occur without getting all caught up with the joint.

And then cartilage or articular cartilage covers the ends of bones to absorb shock and prevent wear and tear or friction.

Ligaments connect bone to bone to help stabilise the joint.

So one of our most important ligaments in the body is around the ankle joint.

We've got ligaments that help stop us from spraining our ankle.

And then tendons attach muscle to bone and they help enable the movement to happen.

And you probably have heard of the achilles tendon is the tendon in the back of the leg that connects your calf or your gastrocnemius muscle to your heel.

And its job is to enable that movement and also to prevent injury by absorbing some of the impact.

Okay, so let's move into the second part of today's lesson, and I'd like you to locate the different types of freely movable joints in the body.

Okay, so if we want to understand what movement is possible at the hip, shoulder, knee, elbow and ankle joints, then we need to identify the difference between hinge joints and ball and socket joints.

So Andeep is wondering, "Which joints in the human body are hinge joints and what are their unique features?" Can you help him? What do you think? Okay, well, hinge joints allow movement in one direction, like opening and closing of a door.

So they have hinges on them, don't they? And they only allow movement in one plane or one direction.

So when we bend at a joint, it's called flexion, whereas straightening at a joint is called extension.

And I'm doing that here with my bicep, flexing my elbow joint and then my tricep extending my elbow joint.

And actually those joints, they look a little bit more like this to enable that movement to happen.

So the elbow, as I've just illustrated, but also the knee and the ankle are all examples of hinge joints, although actually the ankle is a slightly more complex hinge joint.

But to all intents and purposes, the elbow, knee and ankle are all hinge joints.

In contrast, what sort of joint do you think this is? That's right.

It's a ball and socket joint.

So it allows movement in more directions, because if we imagine this is the femur with the ball on the end of it, the socket of the pelvis encapsulates that, and a bit like a hinge joint, it allows flexion and extension, but it also allows some more movements there.

And those movements are called abduction, which is a posh word for movement away from the midline of the body.

So if I use my shoulder joint, which is another ball and socket joint, abduction is that movement away from the midline, adduction is movement or adding your arms back together close to your body.

Rotation is this movement here, and circumduction is drawing a big circle.

So ball and socket joints allow a lot of movement.

And we've got those ball and socket joints at the hip and at the shoulder.

And then we've also got another type of joint in the human body.

So the top two vertebrae are called the atlas and the axis.

And at the atlas and the axis, they enable rotation of the head, as you look to the left, to the right.

And that's an example of a pivot joint.

So we've got a pivot joint at the neck and then we've also got a slightly different joint at the wrist.

So it's a special kind of joint, this one at the wrist, and it allows movement in all directions.

So a little bit like a ball and socket joint.

You can see the illustration there.

It looks a little bit similar, except for the shape of that sort of the bone at the top.

So instead of it going into this kind of deep cavity, we've got this kind of ovoid surface that fits into an elliptical cavity and that enables that wrist joint to move.

And they're called condyloid joints.

So a condyloid joint is what we've got at the wrist to allow all these movements.

Okay, let's do a quick check.

Which of the following is an illustration of a ball and socket joint? Is it A, or B, or C? That's right.

A is the ball and socket joint, whereas B is a hinge joint, and C is that illustration of a pivot joint at the atlas in axis, the top two vertebrae at your head and neck.

Let's do another quick check.

Which of the following movements are possible at ball and socket joints? Is it A: flexion and extension? B: abduction, adduction, rotation, and circumduction? Is it C: flexion, extension, abduction, adduction? Or is it D: flexion, extension, abduction, adduction, rotation and circumduction? What do you think? That's right, it's D.

All six of those movements are possible at a ball and socket joint, which is why the shoulder and the hip are so important to us for movement.

Okay, so the task I'd like you to do now is I'd like you to state which of the following joints is a hinge joint and which is a ball and socket, out of the list of shoulder, elbow, hip, knee and ankle.

And then I'd like you to identify and label each joint on a diagram of the skeleton.

Pause the video now whilst you do that and come back to me when you are ready.

Okay, so hopefully, quite quick and easy for you to jot down that the shoulder is a ball and socket joint.

Elbow is a hinge, hip is a ball and socket, the knee is a hinge, the ankle is a hinge.

And then of course we haven't covered them here, but we've got the wrist, which is a condyloid joint.

There's my condyloid joint waving at you, and the neck, which is a pivot joint, allowing rotation.

And then as we label those first five up, we've got the shoulder, up here, elbow joint, which is a hinge, hip joint, which is a ball and socket, knee joint, which is another hinge, and then the ankle joint, which is your third type of hinge joint in the body, a more complex hinge joint at the ankle.

Okay, so that moves into the final part of today's lesson then.

Let's see if we can explain how joint structures help prevent injury.

So, we've got articular cartilage and that lines the ends of the bones.

So we had this example, didn't we? Of the femur and the tibia, and cushioning them almost like a bit of jelly on the end of each of those is that articular cartilage that lines the end of those bones and helps prevent them from wearing away on each other or from that repeated movement.

And then we've got ligaments.

I sometimes illustrate that with almost these two fingers.

So they're connecting bone to bone and they help that movement happen but try and stop dislocation from happening.

However, if a lot of force goes through one of your joints, particularly sort of games players, perhaps, we can suffer from ligament damage at the knees and ankles.

So for example, if you really try and change direction quickly and you've not got control properly, there is a risk of that turning over of your ankle, resulting in a sprained ankle, which is the ligaments getting damaged.

But if those ligaments weren't there at all, there'd be nothing to stop that from rolling right over.

So the ligaments are really important at preventing dislocation and the cartilage is really important at stopping the ends of bones from rubbing away on each other.

Meanwhile, we've got that synovial fluid and that prevents the wear and tear inside the joint by helping lubricate it.

So a bit like engine oil that we mentioned earlier.

And then we've got the bursae, which is that small bag of synovial fluid that also is located at that joint to help reduce friction created by that tendon as it's moving across the surface of the joint.

And then we've got an interesting one here where the shape of different joints helps them either be better for mobility or better for stability.

And if we increase mobility, we will reduce stability.

If I work through an example with you to help understand that.

So, ball and socket joints allow movement in more directions than hinge joints.

And there's also a difference in the amount of movement available at the shoulder joint, which is a ball and socket, compared to the hip joint, which is a ball and socket.

So at the hip, the ball of the femur fits into a really deep socket at the pelvis.

There's big, strong muscles and big, strong ligaments around that and they help hold that in place.

So that is really built for stability, and it's because we're, you know, weightbearing, aren't we? We're walking on our legs all the time, so we won't want them dislocating regularly.

So we've really got that pelvis wrapping round the femur and keeping that as stable as possible.

But because it's really stable, it's not as mobile as the shoulder joint, which if we bring that up in contrast, you can see that here, the bone of the humerus is sitting in quite a shallow cavity at the shoulder, and that means we've got a massive amount of movement.

You know, the flexion extension, abduction, adduction, circumduction, rotation, all those movements are really huge range of movements of the shoulder.

But because of that shallower cavity, there's an increased risk of dislocation at your shoulder joint, a particular problem in contact sports like rugby.

Okay, let's do a quick check.

True or false? Ligaments help prevent injury by stabilising the joint.

What do you think? That's right, it's true.

But can you tell me why? That's right.

So ligaments connect bone to bone across a joint and hence help prevent excessive movements or movement in the wrong direction.

But they can still be forced out of position with enough force which would lead to ligament damage, for example, a sprained ankle.

Second quick check.

Which of the following structures helps prevent wear and tear at the ends of bones? Is it A: cartilage, B: tendons, or C ligaments? That's right.

It's cartilage that prevents the wear and tear at the end of bones.

Okay, that brings us into our last task for the lesson, and I want you to have a go explaining the following synovial joint features and how they help prevent injury to a games player of your choice.

For example, you might wanna pick a basketballer.

So think about cartilage, think about ligaments, think about synovial fluid, and think about bursae.

So what do those things do to help prevent injury? Pause the video now and come back to me when you're ready to compare answers.

Okay, so here's what I came up with.

So the cartilage prevents the ends of bones, for example, the femur and the tibia, from rubbing against each other as the basketballer runs up and down the court.

So they help prevent wear and tear on the ends of the bones.

Meanwhile, we've got the ligaments that help stabilise the joint and they'll connect bone to bone, keeping that joint together.

So for example, at the knee, they help stop that twisting movement from happening.

Then we've got synovial fluid and that lubricates the joint to help reduce friction so that we are able to move more freely.

And then the bursae helps prevent the bones, the tendons, the muscles, and the ligaments from rubbing against each other as we are moving.

Well done with that one, and that just leaves us a couple of moments to summarise today's lesson.

So we've been looking at the classification of joints and we've learned that movement occurs at all synovial joints.

And those joints have a number of common features.

So they've got synovial fluid and it's the synovial fluid that lubricates the joint and allows free movement.

We've got cartilage, and that's that shock absorber on the end of your bones that prevents friction and then wearing away against each other.

We've got ligaments, so they connect bone to bone to help stabilise the joint.

Don't confuse them with tendons which connect muscle to bone.

So there we've got the tendons connecting muscle to bone.

And then we talked it through some example joints, didn't we? So we looked at the elbow, knee and ankle as all examples of hinge joints, whereas the hip and shoulder are examples of ball and socket joints.

And then we also touched on the neck, which is a pivot joint and the wrist, which is a condyloid joint.

Thanks very much for listening.

Goodbye for now.