- [Voiceover] We've been talking about all these bones,
but we need to talk about joints.
How do the bones come together?
Now there's gonna be a total of
three different classifications of joints.
Now these joints, or articulations,
are classified based on degree of movement,
based on what they're made of.
So first off, we have fibrous joints.
Like the name implies, they're made of fiber.
They're immovable, they're not meant
to move around or do anything.
Fontanels, those are those baby soft spots,
that's how the bones are being held together.
Those are an example of fibrous joints.
Cartilaginous joints.
Now these have a little bit of movement,
but they're not really meant to move much.
I mean, a little bit of a shimmer here,
a little shade there,
but all this movement can add up to quite a large amount.
Where the cartilage is joining the vertebrae
of the vertebral column, each one can move a little bit
because of a cartilaginous joint,
but add all of those together,
creates quite a bit of movement.
Synovial joint.
Well, synovial joints are by far
the most common in the body.
They're freely movable.
They can move on any plane, any direction.
The only limiting factor is going to be
the flexibility in the joint, and how the bones are aligned.
So for example, a synovial joint
could be your shoulder joint, could be your hip joint,
your elbow, the joints in your fingers.
So lots of things could be synovial joints.
On the left, we have a little deeper view.
On the right, we have a little more superficial view,
more towards the top.
You see on the left how they have the patella
actually pulled off.
The ligament is intact, going from bone, patella,
to bone, tibia.
What is being cut and reflected back is the tendon,
from bone to muscle.
So now in this case you can see how all those ligaments
are helping to anchor and keep the knee in place.
There's ligaments on both the right and left side.
We have ligaments inside, for a total of four,
helping to anchor it down.
So we have the left hand side, all ligaments,
right hand side, you can see the muscle.
You can see where the tendon is,
you can still some of the ligaments,
but if you notice that kind of purplish haze,
that purplish haze is the joint capsule.
It's what keeps all the fluid in the joint,
what keeps it healthy, keeps it functional.
So here's that joint capsule, what it's made of.
Joint capsule is made of the synovial membrane
and the hyaline cartilage found at the end of long bones.
The purpose of the synovial membrane
is to secrete the synovial fluid.
Synovial fluid can act as a lubricant.
It can also help to nourish a little bit.
We know that hyaline cartilage is meant for insulation,
and cushioning, for those nice shock absorbers.
The bones come together, it helps to cushion the blow
of both bones smacking into each other.
Now, we have a couple different types of synovial joints.
First to point out is the hinge joint.
Second, ball and socket joint.
Well, the names are kind of helping
to hopefully imply a little bit.
Ball and socket.
Well, that's your shoulder joint, for instance.
Your hip joint.
You have a round end on the bone. That's the ball.
The socket is where it goes into.
So in the case of the hip, there's that indent on the coxal.
Case of the shoulder,
there's a very shallow indent on the shoulder.
So that's the ball and socket.
Hinge, just think of a door.
That's the equivalent of a hinge joint.
Tendons, well we know ligaments are bone to bone,
tendons are muscle to bone.
So put all these joints and bones to work,
we have to see how they interact.
Now what do you muscle to cause the interaction?
Muscle pull against the bone.
We have the term abduction, a-b-duction.
And adduction, a-d-duction.
So look at the figure on the left, you see that,
sorry, the left arm, I should say.
The abduction is moving the arm away from midline,
while adduction, a-d-duction, is bringing it back
towards the midline.
So we're showing that abduction,
doesn't matter if it's the arm, the leg, the wrist,
abduction, a-b-duction is always carrying things
away from the midline,
while adduction, a-d-d,
seems to always be adding things to the midline.
So you're a-d-d, you're adding it.
Adding, or adduction, is bringing the arm back to midline,
bringing the leg back to midline,
even bringing the wrist back towards the midline.
So the terms abduction and adduction.
Now we have the difference between
circumduction and rotation.
The entire arm can go through rotation.
Now it's not the twisting at the elbow,
but the entire arm at the shoulder can twist in place.
It's not gonna do a full 180,
but should totally be 20-30 degrees.
Depends on the person.
But still, it's rotating around a central axis.
Now, the term circumduction, the actual limb isn't rotating,
what's happening is, the limb is working in a circle,
it's creating this kind of cone shape.
You can do it with your arm and your leg.
Imagine your arm is facing forward,
you have your palm facing forward.
Then just keep the palm forward,
and you can actually bring the arm into small circles.
That's circumduction,
moving the actual arm in small circles,
allowing for movement of arm and the leg together,
or make it separate.
Flexion and extension.
Those are the two common ones,
but you gotta also remember that there's something
that's called a hyperextension.
So let's start off with the first term, flexion, top left.
Flexion is meant to decrease the angle of a joint.
So look at your elbow.
If you start to bring your arm in, like bend at the elbow,
so bring it close to your body,
what's happening to the angle within that joint?
It's getting smaller and smaller.
Well, extension is the opposite.
In extension, you're increasing the joint angle
back to normality.
But one slight difference now is hyperextension.
In the case of hyperextension, hyper means too far.
So in a hyperextension,
sometimes it can become very problematic, very dangerous,
because you might not even realize it's injured.
But more often than not, majority of hyperextensions,
you're gonna know there's a problem.
The bones just won't align, muscles won't work properly,
it's been pulled or pushed too far.
So hyperextension, beyond normal point of extension.
Supination, pronation.
Tried to describe this a little bit earlier
how the forearms don't actually twist in place
'cause there's two bones.
So instead you have what's called supination and pronation.
Supination is the movement that causes the hand
to be facing the front, or facing anterior.
Supination is the opposite of pronation.
Pronation is going to have the palm facing back,
the palm facing posterior.
So we have supination and pronation,
the two bones of the arm, the radius and the ulna,
actually will overlap, or cross over each other.
That crossing over is what creates
the movement in your forearm.