Lesson video

Hi there and welcome to today's lesson.

My name is Mr. Swayze and I'm really looking forward to teaching you today.

So today's lesson is all about synovial or synovial joints and their structure.

This lesson comes from the unit anatomy and physiology and the muscular system and the lesson tied to the Structure of a Synovial Joint.

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.

So we're gonna delve at detail into those different joints of the body and how, you know, similarities between the different joints and what some of the different features are that exist there.

So I'm wondering, do you already know what some of those features are at all synovial or freely movable joints? Yeah, well, as we go into the keywords, hopefully you'd already thought of a few of these.

So synovial joint, synovial fluid, cartilage, ligaments and tendons are really important keywords that we will be visiting throughout today's lesson.

You might want to pause the video now to get down a description of each, but I will revisit each of them as we go.

So in today's lesson we're gonna split it up into three parts.

Firstly, we'll be identifying the features of synovial joints, and secondly we're gonna be locating the different types of freely movable or synovial joint.

And then thirdly, we're gonna be explaining how those joint structures help prevent injury, particularly in sports people.

So it's looking like another cracker.

Let's get going.

Okay, so here we've got an example of a synovial joint.

This one is actually the knee joint.

And we're able to talk about how synovial joints are the most common joint in the human body.

They are freely movable and have a cavity filled with synovial fluid.

So that's what gives them their name.

All synovial joints have common features to help them support movement.

And another word for movement is articulation.

So we talk about how at joints, that's the place where two or more bones meet to enable articulation or movement, bending and straightening.

So we've got here the illustration and we can pick up how that kind of red line there illustrates the joint capsule, which encloses the joint.

And then inside of that we've got the synovial membrane, which is the lining of the joint capsule.

And that secretes synovial fluid, then bubbling around all in the middle of that kind of grey section is the synovial fluid.

Now the synovial fluid fills the joint cavity and it lubricates it to allow free movement.

So synovial fluid is a bit like engine oil and actually it likes to be warmed up to become less viscous and able to do a better job of feeling mobile.

So if you have, perhaps you go on a long haul flight or you're stuck still for a really long period of time, your joints kind of seize up and stiffen up a little bit.

And that's because of this synovial fluid needs warming and mobilising to operate at its best.

And then we've also got here on the lining of the bones.

So that's the femur lining.

And also on the tibia lining we've got what's called articular cartilage, which covers the ends of bones and its job is to absorb shock and prevent friction of those bones rubbing on each other.

And then we've got in kind of a brownish colour on the front there, a bursae or a bursae.

And that is a small fluid filled sack and it's located at joints to reduce friction and allow smooth movement.

If you imagine there that quadricep muscle which is stretching over the bursae, well if that bursa wasn't there, it restrict its movement a little bit.

So it provides almost like a cushion for it to sit on.

And then we've got ligaments.

Now the ligaments are connecting if this is my femur, this is my tibia, the ligaments are stretching down each side, holding that joint together.

So they connect bone to bone to help stabilise the joint.

And in fact, in the knee joint we've got these crossover ligaments in the middle of them called cruciate ligaments that help prevent that twisting rotation that we don't want.

And then we've got tendons and their job is to connect muscle to bone.

So a lot of people get confused with the difference between ligaments and tendons.

So ligaments connect bone to bone to provide stability.

If ever you've sprained your ankle, you have overstretched the ligaments at your ankle joint and if ever you've got kind of an overuse injury, maybe tennis elbow is where that tendon that stretches over the elbow joint has just had too much repetitive strain.

It happens a lot with musicians actually, repetitive strain injuries.

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 end 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's C, it lubricates to join a bit like engine oil and the more it's warmed up, the better it lubricates.

Another check, which of the following connects bone to bone to help stabilise a joint? Is it a cartilage, B ligament, C tendon, or D synovial membrane? That's right, it's ligaments.

So ligaments provide that connection of bone to bone to help stabilise the joint.

And we've got the example of the cruciate ligament in the knee.

Okay, that brings us into our first practise task of today's lesson then.

So I'd like you to label the diagram here of the knee joint with the following features, the synovial membrane, the synovial fluid, the joint capsule, the bursae, the cartilage, the ligaments and the tendon.

And then I'd like you to add to your diagram or maybe you want to write a sentence underneath for each that describes the role of each feature, pause the video now whilst you do that and then come back to me when you're ready.

Okay, let's see what you've come up with.

So first up, we've got the synovial membrane, which is that, I guess it's the lighter pinky colour on the inside of the joint capsule.

Then we've got the synovial fluid, like the grey liquid in the middle there we've got the joint capsule, which is more the the red-y colour connected next to the synovial membrane.

Got the bursae, which is that brownish colour on the front there, got cartilage, which is lining the ends of the bones.

We've got ligaments on both sides, but the most obvious ones are those there on the right hand side connecting bone to bone.

And then we've got the tendon, which is connecting the quadricep muscle to the tibia.

So the slightly harder part of that task was to briefly describe the role of each.

So synovial membrane, the job of the synovial membrane is to secrete synovial fluid.

Synovial fluid's job is to lubricate the joint to allow that free movement, is why they're called freely movable joints.

The joint capsule is what encloses that joint and provides some stability and holds it all together.

The bursa reduces friction to allow smooth movement of that quadricep muscle across the front of the bones there, cartilage covers the ends of bones to absorb shock and prevent friction.

Ligaments connect bone to bone to help stabilise the joint and then the tendons attach muscle to bone to enable movement and to help prevent injuries by absorbing some of the impact.

Okay, that takes us through into the second part of today's lesson where we're gonna locate different types of sorry, freely movable or synovial joints around the body.

So to enable us to understand what movement is possible at the hip, the shoulder, the knee, the elbow and the ankle joints in particular, 'cause those joints are really interesting to us as sports performers.

We need to identify the difference between hinge joints and ball and socket joints.

So which joints in the human body are hinge joints and which are ball and socket joints? But first of all, let's think in this question from Andeep.

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

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

Nice little illustration there of a hinge joint.

You can see how it's gonna allow that movement in one plane, in one direction.

Okay, so the elbow, the knee and the ankle are all examples of hinge joints.

And in fact, the ankle is a slightly complex hinge joint, but it is still a hinge joint.

Well what about this type of joint then? Well, this is a ball and socket joint.

So we've got the femur here and the ball of the femur fitting into the cavity of the pelvis.

And that movement allows lots of movement in different directions.

So we can see forwards and backwards, side to side and a bit of rotation.

So like hinge joints, they allow flexion and extension, but they also allow abduction, which is a fancy word for movement, away from midline of the body.

Adduction, another fancy word for moving, adding back together.

So here I am abducted at the shoulders and then adducted to bring my shoulders back in line close to the midline of my body.

Rotation is kind of this movement.

And then circumduction is this big circular movement at my shoulder joint, which is a ball and socket.

So we've got two types of ball and socket joint in the body, got the hip, and we've got the shoulder very similar in shape, although actually the the hip has got a deeper cavity and that means it's much better for weight bearing.

Whereas our shoulder has got a more shallow cavity, which you great for movement, but there is more risk of dislocation at the shoulder than there is at the hip.

Okay, let's a quick check then.

So which of the following is an illustration of a ball and socket joint? Is it A, B, or C? That's right, it's A, so that diagram of the ball fitting into the socket at the pelvis or at the shoulder girdle.

Let's do another quick check.

Which of the following movements are possible at ball and socket joints? A, flexion and extension, B, abduction, adduction, rotation and circumduction, C, flexion, extension, abduction and adduction or D, flexion, extension, abduction, adduction, rotation and circumduction.

Have a little think.

That's right.

It allows all of those six movements.

Okay, so that brings us into our second task of today's lesson where I'd like you to state whether each of the following joints is a hinge or a ball and socket joint.

So the shoulder of the elbow, the hip, the knee and the ankle, what type of joint are they? And then identify and label each of those joints on that diagram of a skeleton.

So if you pause the video now, come back to me when you are ready.

Well done.

Okay, I'm sure you've got these, but let's just quickly run through.

So we've got the shoulder, which is a ball and socket joint.

We've got the elbow, which is a hinge joint.

We've got the hip, which is another ball and socket joint, the knee which is a hinge joint.

And then the ankle, which is a complex type of hinge joint.

And then we wanted you to identify and label each of them on the diagram.

So here we've got the shoulder, ball and socket up there, the elbow, which is a hinge, the hip, which is the ball and socket, the knee, which is another hinge joint.

So the knee and the elbow are very similar in shape and structure and the movements they're allowing.

And then we've got the ankle joint, which is also a hinge joint.

Well done with that one.

Okay, so let's move into the third and final part of today's lesson where we're gonna have a little look at how those different joint structures help prevent injury.

Well, here we've got someone playing football and somebody playing tennis.

I wonder what injuries could occur.

Well, if we didn't have cartilage lining the ends of all of our bones, then we'd have a bone in contact with another bone and they would just rub away at each other, wearing away the ends of those bones.

It'd be really painful.

So we this articular cartilage on the ends of bones that helps cushion and prevent them from rubbing away at each other.

So cartilage is really important.

And then we also have ligaments and they help prevent dislocation.

However, those ligaments, again, if we've got the femur here and the tibia below and those ligaments connecting it, they protect, sorry, connect bone to bone and help prevent dislocation.

But it can, with a lot of force, they can be ruptured.

Or if they're just slightly torn, we call that a sprain.

And that can happen when we're changing direction.

I could really see it in both of these examples of the footballer and the tennis player.

If they quickly change direction, they've got a risk of a sprained ankle, which is overstretching of those ligaments.

So games that require the ligaments to work really hard are games that require the knees and the ankles and that changing of direction in particular that we can see here in these illustrations.

And then what about synovial fluid then? Well, that we said fills that cavity, doesn't it? And its job is to prevent wear and tear in that joint by lubricating.

So again, we've got the cartilage, but we've also got this added bit of cushioning.

The gel if you like, that's in that cavity, the synovial fluid.

And then we've got the bursae, which are those small bags of synovial fluid that also surround the joint to reduce friction.

And they reduce the friction between the tendon and the joint itself.

So you can see there how the tendon of the quadricep is stretching over the top of the kneecap and there'll be a bursae there to stop that from rubbing as we move, as we bend and straighten our leg.

Okay, so important to know that the shape of different joints has implications on our mobility versus our stability.

And if we increase stability, then we will reduce our mobility.

And this is really true at ball and socket joint.

So they allow movement in multiple directions.

Here I am at my shoulder joint allowing lots of different movement, whereas my hinge joint only allows flexion and extension of my elbow.

But this ball in socket joint allows an awful lot of movement, but it's less stable because of that.

It's because of that shallow cavity.

Whereas at the hip joint we've got the ball of the femur.

It fits really deeply into a socket of the pelvis so that because of that and big strong muscles and ligaments around it, it's far more stable.

It can cope with the fact that we're walking on our feet all the day, not on hands.

So it's more stable but less mobile.

I've got much more movement in my shoulder joint than I do in my hip joint.

So as a consequence, my hip joint is more built for stability and weight bearing, whereas my shoulder is more built for mobility.

Okay, as I said in contrast, the humerus fits into that shallow socket at the shoulder, which allows a great amount of movement, but comes at that higher risk of dislocation.

So in contact sports like rugby, there's a real risk isn't there of that dislocated shoulder.

Okay, let's do a quick check.

So true or false, ligaments help prevent injury by stabilising the joint.

What do you think? That's right, it's true, can you tell me why? Yeah, so ligaments connect bone to bone across a joint and then hence they're able to help prevent excessive movements or movement in the wrong direction.

But they can still be forced sometimes outta that position if enough force is applied.

So that might happen in game of football if you've got a tackle to the side and that might cause a dislocation at your knee joint or if you stud stuck in the ground as you twisted your knee, you can overstretch those ligaments.

But they do a great job of trying to stabilise the joint unless there's excessive force.

Let's do another 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 A, cartilage.

So they're on the ends of our bones providing that extra bit of cushioning to prevent wear and tear.

Okay, into the last task of today's lesson then, I'd like you to explain how the following synovial joint features help prevent injury to a games player of your choice.

So for example, you might choose a basketballer or a footballer.

So someone who plays a game, maybe a tennis player, and I want you to talk about cartilage, ligaments, synovial fluid, and bursae.

So how do they prevent injury? Pause the video now and come back to me when you're ready.

Okay, let's see if your answers were similar to mine.

So for cartilage I've said that it prevents the ends of bones.

For example, the femur and the tibia from rubbing against each other as the player runs up and down the court, so that basketball is running up and down.

And if they didn't have cartilage, the femur and the tibia would just grind away at each other.

And then we've got ligaments.

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

For example, again at the knee joint, as I'm twisting around, those ligaments are helping stop that twisting movement disconnect in my lower leg from my upper leg and then synovial fluid.

Well that provides a really important job of lubricating the joint to reduce friction and that enables me to run around more freely.

So it's that synovial fluid, that is why we call them synovial joints or freely movable joints.

And in the bursae, they help prevent bones, tendons and muscles, but also ligaments from rubbing against each other as we move, which would obviously cause irritation.

Well done with that one.

Okay, so it leaves just enough time to summarise today's lesson.

So we've learnt that movement occurs at all synovial joints in the body and that those synovial joints have got common features.

They've got a joint capsule which encloses the joint to provide stability and protection.

They've got a synovial membrane which secretes that synovial fluid.

The synovial fluid lubricates the joint to allow that free movement.

They've got a bursae which reduces the friction and allows smooth movement.

They've got cartilage, which acts as a shock absorber and prevents friction on the ends of those bones.

And they've got ligaments which connect bone to bone to help stabilise the joint.

And then we've got some examples of bones, haven't we? Sorry, of joints.

So we've got the elbow, knee and ankle, and we know collectively we've referred to those as hinge joints, whereas the hip and shoulder that allow more movements are called ball and socket joints.

I hope you've enjoyed that lesson today.

Thanks so much for joining me and I'll see you next time.