Lesson video

Hello, and welcome to today's lesson.

My name is Mr. Swaithes, and I'm looking forward to teaching you today.

We are going to be looking at synovial joints and some of the common structural features, as well as learning the function of those different features with particular reference to sporting performance.

Today's lesson is called synovial joint structure and function, and it comes from the anatomy and physiology, musculoskeletal system unit.

By the end of this lesson, you'll be able to identify and describe the features of synovial joint, and explain how they prevent injury.

I wonder if you can think of the names of any of the features that you have at joints.

For example, your knee joints or your elbow joint.

Do you know any of the correct anatomical terms for different structures that you have at joints? We will also be looking at what is the same and what is different at different joints, like the elbow, the shoulder, the hip, and the knee.

Knowing what these features are and how to keep them in good health will help you to prevent injury.

But this lesson will also help you to understand why the human body is built the way that it is.

The key words for today's lesson are synovial joint, synovial fluid, cartilage, ligaments, and tendons.

There are also a few more key terms we will share that you will want to be able to define.

You may want to pause the video now to make a note of them, but I will explain them fully as we come across them in the lesson.

As I mentioned just now, this whole lesson is about synovial joints, and they're a special type of joint that allows free movement.

This is possible thanks to the synovial fluid, which lubricates the joint.

It is a bit like oil in your car engine, so it works best when it's warm, and that makes it able to, I guess, lubricate that joint better.

It becomes less viscous.

So to stop the ends of bones from rubbing together, if this is an example of my knee joint here, to stop the ends of those bones rubbing together and grinding away on each other, we've got cartilage or articular cartilage covering the ends of the bones.

That helps absorb shock as we're perhaps jumping, but also to stop that constant wear and tear as we move.

And then ligaments connect bone to bone to help stabilise, whereas tendons are attached to the end of muscles and connect them to bones.

People often get those two confused.

So please be careful.

So in our lesson today, we will, first of all, identify the features that are common across all synovial joints.

We actually have some other types of joint in the human body, and if you go on to study perhaps A-level PE, or maybe you're gonna go and study sports science at university, you'll learn all about some other types of joints between, for example, the different plates of your cranium that don't really allow any movement at all once you stop growing during childhood, and also about cartilaginous joints, like those found between each of your vertebrae.

But at this stage, we are more interested in the joints that enable lots of movement for us to participate in physical activity and sport.

So we're narrowing our focus in on just synovial or freely movable joints.

We will then locate two different types of synovial joints with a focus on the elbow, the shoulder, the hip, and the knee, before explaining how different joint structures help to prevent injury.

I hope you're ready.

Let's get started.

As I said, we have lots of joints in the human body.

Some allow much more movement than others.

For example, the cranium is made up of a number of sutures that allow no movement once our skull has grown to its full size.

However, synovial or freely movable joints are of most interest to us in sport, as they allow us to do lots of movements thanks to that cavity filled with synovial fluid that allows free movement.

Articulation is a posh word for movement, and the way I like to remember that is you might have heard of articulated lorries.

So those are those massive, long lorries.

They've got kind of a joint in the middle of them that enables the back half of the lorry and the front half to move separately, and that enables them to go around bends.

So to be clear, synovial joints are freely movable, and have a cavity filled with synovial fluid.

All synovial joints have common features to help 'em support movement, or articulation as we know it now, and now we are going to look at some of those features in a bit more detail.

If you have a look at the seven key features of this joint, you might want to pause the video for a moment, and see if you can recall the names of any of these features from science or general knowledge, or things that I've mentioned already, and can you identify them on this example of a joint? Okay, so you can see here in the red colour, we've got the joint capsule that encloses the joint.

So its job is to provide some stability and protection.

It's almost like the bubble that contains that joint.

Next up, we've got the synomial, sorry, synovial membrane, and that's the lining within the joint capsule that secretes that all-important synovial fluid.

Then, as you can see here in almost a grey colour, we've got the synovial fluid that fills that joint cavity, and helps lubricate the joint, and also to allow free movement.

Articular cartilage covers the ends of the bones.

As I said earlier, that acts as a shock absorber, but also to prevent friction and wear and tear of those bones rubbing against each other.

A bursae is a small fluid-filled sac located near joints to reduce friction and allow smooth movement.

And then we've got ligaments.

So their job is to connect bone to bone to help stabilise the joint, and tendons attach muscle to bone.

Okay, let's have a quick check.

Which of the following is the correct role of synovial fluid? I'll give you five seconds to decide.

Is it A, to protect the end of bones, B, to provide stability and structure to the joint, C, to lubricate the joint, allowing free movement, or D, to connect bone to bone? Hopefully, you'll have remembered that synovial fluid is that essential ingredient, a bit like engine oil, that works better when it's warm and is essential for lubricating the joint to allow free movement.

Let's try another one.

Which of the following connects bone to bone to stabilise a joint? Remember, this is the one that lots of people get confused.

I'll give you five seconds again to decide.

Hopefully, you have remembered that ligaments connect bone to bone.

If you're a meat eater, you might recall that sometimes when eating, for example, a chicken leg, there's that tough bit on the end of the meat that connects it to the bone.

So that is the tendon.

We tend not to eat that bit, whereas we do eat the muscle or the meat that connects to that tough fibrous cord.

So what I would like you to do now is label the diagram of the knee joint with those seven key features.

For part two of this task, I want you to briefly describe the role of each of those features.

For example, which one connects bone to bone to stabilise a joint? Pause the video now, and come back to me when you are ready.

Okay, let's look through some answers.

So hopefully, you've got the synovial membrane as that inside layer of that joint capsule, and that's where the synovial fluid gets released from.

Then, we've got the synovial fluid in that joint cavity.

Then, we've got the joint capsule, which is kind of the red colour, that bubble that holds that joint together.

We've got the bursae here, which is that fluid-filled sac that helps reduce friction when that muscle is moving, when it's contracting and relaxing.

We've got the cartilage on the end of those bones to help prevent wear and tear, and then we've got ligaments that are like those bands that help connect bone to bone, and tendons, which connect muscle to bone.

So for part two of that, hopefully, you've got something along these lines.

So synovial membrane secretes that synovial fluid, whereas the synovial fluid is what lubricates the joint and allows that free movement.

The joint capsule encloses the joint, and that provides some stability and protection.

It's almost like the bubble.

The bursae reduces friction to allow smooth movement, particularly against that muscle as it's contracting and relaxing.

Cartilage covers the ends of bones to absorb shock, and also to prevent friction to stop that wear and tear.

Ligaments connect bone to bone to help stabilise the joint.

And tendons attach muscle to bone to enable that movement to happen, and also to prevent injury by absorbing some of the impact.

Okay, let's move on to locate the different types of freely movable joints.

To understand what movement is possible at the hip, the shoulder, the knee, and the elbow joints, we need to identify the difference between hinge joints and ball-and-socket joints.

Which joints in the human body are hinge joints and what are their unique features, do you think? Okay, so hinge joints allow movement in one direction, like opening and closing a door.

When we bend at a joint, it is called flexion, whereas straightening at that joint, we call extension.

Here's a better illustration of what a hinge joint looks like.

As you can see, the joint moves in just one plane, opening and closing like the hinge on a door.

So the elbow, as I've just illustrated there, and if I just pull in this skeleton, we can see the elbow joint allows that flexion and extension.

So flexion, bending, extension, straightening.

So we can see here that elbow joint, but then also the knee joint, we can see here, allows that flexion and extension.

So bending and straightening.

Brilliant.

Whereas ball-and-socket joints, they allow movement in more directions due to the shape of the joint.

So we look at my shoulder here, this is a ball-and-socket joint.

Like hinge joints, they do allow flexion and extension, but they also allow abduction, adduction, and rotation and circumduction.

So abduction is movement away from the midline of the body, whereas adduction is movement back towards the midline of the body.

Rotation is almost like a twisting movement, and circumduction is like a circular movement.

In the picture here, we can see these four directions of movement, but also when you combine those movements, that's what creates rotation or circumduction.

So the hip and the shoulder examples of those ball-and-socket joints, again, if we just looked at the skeleton, we've got the hip joint here, where you can see that the ball of the femur fits into the socket of the pelvis, and that allows flexion, that movement up in front, extension, the movement back down, abduction, movement away, and adduction, movement back together.

It allows a little bit of rotation, and it also allows circumduction to an extent.

Whereas if we now move up to the shoulder joint, because of the much shallower cavity that we've got here, we can get yes, flexion, that movement of the arm up in front, extension, movement back down to the body, abduction, movement away from the midlines and out to the side, adduction, rotation, we need to use that to perhaps apply spin on a tennis ball or a cricket ball, and then circumduction, that bowling action as we come all the way round, or I'm watching the Olympics at the moment, we can see that in butterfly, in swimming, for example, where we can see that circumduction at the shoulder joint.

Let's just quickly check.

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

It's A, where you can see the ball of the humerus in the arm, or the femur in the leg fitting into the socket cavity of the shoulder girdle or the pelvis of the hip.

Whereas B is a hinge joint, and C is a pivot joint, like that one that you get at the top of the spine, so connecting the neck to the head, and that allows rotation, and it's happening in what we call the atlas and axis.

And a second quick check on the terminology.

Which of the following movements are possible at ball-and-socket joints? Is it A, flexion, extension, B, abduction, adduction, rotation, and circumduction, C, flexion, extension, abduction, and adduction, or D, flexion, extension, abduction, adduction, rotation, and circumduction? Hopefully, you have correctly identified D.

Ball-and-sockets allow all six of these movements, and we have those ball-and-socket joints at the hip and at the shoulder.

So what I would like you to do now is note down whether each of the shoulder, the elbow, the hip, and the knee are hinge or ball-and-socket joints.

Then, you need to label the skeleton with those joints, and maybe you even want to remind yourself of the bones that articulate to each of those joints too.

Pause the video now, and come back to me when you are ready.

Here we go then with the answers.

So the shoulder is a ball-and-socket joint, allowing that full rotation.

The elbow, as we've got here, is a hinge joint.

The hip is a ball-and-socket joint.

You can almost see that ball-and-socket there.

And then the knee, again, is a hinge joint, allowing that flexion and extension.

And if we try to identify those on the skeleton, got your shoulder, ball-and-socket, elbow is a hinge, hip, ball-and-socket, and the knee is another hinge joint.

Okay, for the final part of this lesson, it's important to understand how the different joint structures help prevent injury, and also how they are helpful to us as sports performers.

Articular cartilage lines the, or covers the ends of all bones that meet at joints to help stop wear and tear from repeated rubbing.

You'll probably know older people who have had problems with excessive wear and tear at their joints.

For example, I'm a squash player, so the cartilage in my knees has had quite a pounding over the years.

But interestingly, we need to do weight-bearing exercise.

So exercises where we're weight-bearing, we're on our feet, whereas perhaps swimming is an example of a non-weight-bearing activity.

We actually have to do those weight-bearing exercises to help nourish and stimulate cartilage growth, but perhaps not too much.

Meanwhile, ligaments are those tough bands of connective tissue that help stabilise a joint.

If you've ever had a sprained ankle, then that is the ligaments that you have damaged through an excessive force, taking them beyond their normal range of movement.

So ligaments help prevent dislocation, for example, at the shoulder joint, and that's really susceptible to dislocation during perhaps a rugby tackle, as the ball-and-socket, the cavity there is actually quite shallow compared with the hip.

So we're more likely to dislocate the shoulder than we are the hip because of the shape of those bones.

And footballers can struggle with knee dislocations as well, when their studs get wedged into the ground, and excessive rotational force is experienced.

You may have heard of cruciate ligaments as one particular type of ligaments, and these are the ones in the knee joint that are like a crisscross within there to try and help stop that rotational movement.

And then, finally, as I've just mentioned, rolling your ankle is a major risk for lots of sports performers, including games players.

And if we didn't have ligaments, then that would happen all of the time.

And then we've got synovial fluid.

So we said that reduces wear and tear, and also helps lubricate that joint.

The bursae are those small bags of synovial fluid that also surround the joint to reduce friction created by the tendon as it moves across the surface of the joint.

As I mentioned just now, the shape of different joints carefully considers the balance of maximum mobility versus stability.

Increasing one comes at the expense of the other.

So you either have much greater mobility, but with that comes a reduction in stability, or maybe you've increased the stability, the strength of a joint, and then that often comes with less mobility.

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

There is also a difference in the amount of movement available at the shoulder compared to the hip joint.

So at the hip, as I said earlier, that ball of the femur fits really deeply into the socket of the pelvis, and there's also bigger and stronger ligaments and muscles around that, big, strong muscles that help hold that in place, and actually it's very rare, other than perhaps in old age, that we see people getting a dislocated hip, whereas we perhaps see that happen more often at the shoulder.

So consequently, a hip is built for stability, and that's really important 'cause it's weight-bearing, isn't it? It's not as mobile as the shoulder joints, but it helps hold us upright and run around and move.

In contrast, the humerus fits into a far shallower socket at the shoulder joint.

This is great for increased range of movement, but comes with a higher risk of dislocation.

Okay, let's do a couple of quick checks.

This is a true or false question.

Ligaments help prevent injury by stabilising the joint.

True or false? Hopefully, you selected true.

So as we said earlier, ligaments connect bone to bone across a joint, and hence help prevent excessive movement or movement in the wrong direction, but they can still be forced out of position with enough force.

And another one.

Which feature is it that prevents wear and tear on the ends of bones? Is it cartilage, tendons, or ligaments? That's right.

It's cartilage or articular cartilage that lines the ends of bones and prevents wear and tear.

Time for the last task of this lesson.

I want you to pick a games player of your choice, and explain how these four features help prevent injury using specific examples to help you.

Press pause while you do this.

Okay, let's check our work and explore a few examples, but, of course, you will have come up with your own.

So here, we've got the cartilage or articular cartilage that prevents the ends of bones, including the femur and the tibia as we talked about earlier, at that knee joint from rubbing against each other.

An example there might be this basketballer.

As they're running up and down the court, to stop that femur and tibia from rubbing against each other and grinding away, they've got that cartilage lining the ends of bones to help provide some cushioning.

And then we've got ligaments.

So they help stabilise the joint by connecting bone to bone and keeping the joint together.

For example, again, that basketballer, the knee joint, as I'm perhaps twisting to receive a pass from the side, the job of the ligaments is to stop that upper body from turning right round and leaving the lower body behind.

You may have come up with an example from perhaps football or rugby or netball.

Then, we've got synovial fluid, as we've said earlier, that's like the engine oil that lubricates and reduces friction within the joint.

So as I warm up, ready for my basketball game, and start running around, that synovial fluid loosens up and lubricates better and better to reduce friction.

And then we've got the bursae.

So that helps prevent bones, tendons, muscles, and ligaments from rubbing against each other as we move.

Let's summarise what we have learned about synovial joint structure and function.

So movement occurs at synovial joints.

These joints have common features, including a joint capsule, which encloses the joint, and has a lining called the synovial membrane, which secretes the fluid.

Then, we've got synovial fluid, which fills that joint cavity to lubricate it.

We've got the bursae that helps reduce friction and ensure smooth movement, particularly stopping that muscle from rubbing against it as it contracts, you know, flexes and extends.

Then, we've got cartilage to absorb the shock and prevent friction on the ends of bones.

And finally, ligaments, which connect bone to bone and stabilise the joint, whereas a tendon connects muscle to bone.

The elbow, the knee, and the ankle are examples of hinge joints, whereas the hip and the shoulder are ball-and-socket joints.

Thanks for joining me in this lesson today, and I really look forward to seeing you again.

See you next time.