So that finally brings us to a ball and socket joint
known as the shoulder joint.
The shoulder joint has a lot of components to it though.
We'll start with the distal components which begin with the humerus.
The typical long bone of the upper portion of our upper limb
which is actually what we call the arm.
The arm isn't everything from shoulder to fingertip.
It's actually just the part between our shoulder and our elbow.
So our arm bone is really the humerus
and at the proximal end, we have the humeral head.
And this humeral head is covered in articular cartilage
because it's going to participate at a joint
and the cavity that this humeral head is going to fit
into is something called the glenoid cavity
and it's the shallow depression of a bone called the scapula.
The scapula has a bunch of other parts and one part
we can see way up top coming up
and pointing towards us is the acromion.
Acro means highest or uppermost
and that's how it gets this name.
It's the uppermost projection of the scapula
and then connecting to that is a bone
you probably heard called the collar bone.
It's an easily palpable bone but we tend to call it the clavicle.
We also have a lot of muscles here
that you probably have heard of before
that provide a lot of structural
stability to the joint
called rotator cuff muscles
and they're going to attach from the scapula
to bumps or tuberosities
that exist on the humerus.
And if you were to look at an x-ray of the shoulder joint,
you would see some of those structures
but it might look kind of empty to you and you might think
that the humerus looks like it's just sort of floating.
And it's not really connected
right up to these bones
and that's because not everything in the joint
is going to show up in an x-ray
because not everything
is going to be bone.
For example, we have cartilage
which is radiolucent or invisible on x-rays.
Same thing with those rotator cuff muscles
that are going to provide support.
They're going to be invisible but we know
they're there providing stability at this joint.
So what kind of movements
can we have at the shoulder joint?
Well, there's some of the ones
that we've already talked about in the introduction.
So from the anatomic position, moving the humerus
more medially is going to be adduction
bringing it closer to the body,
moving it away is going to be abduction.
And once we get past the horizontal point,
it rotates a little bit
so that we can keep going
and at that point we call it elevation.
So we can essentially get another 90 degrees
and raise that arm almost a full 180 degrees.
Now, let's take a lateral point of view
to see some other movements.
If we were to move our arm backwards at the shoulder joint or posteriorly,
that would be extension or retroversion,
and moving it anteriorly where we can move it quite a bit further,
we will call that anteversion or flexion.
We'll rotate to a superior point of view
to see rotation a little bit better
and we know that if we rotate towards the midline,
that would be internal or medial rotation.
If we rotate outward, that's going
to be lateral or external rotation.
There is generally less movement here,
about 45 degrees at least in each direction.
So what about some muscles in this area?
So the first is right over that shoulder joint
and it's called the deltoid muscles
and delta is sort of a triangular shape
and that's why it's called deltoid.
It refers to its shape and this is going to be
our major abductor at this shoulder joint.
We also have a muscle running from the scapula to the ribs
that's a fairly minor one called pectoralis minor.
It's not called minor
because it doesn't do much.
It's because it's smaller than the big boy
over here, the pec major.
Pectoralis major is our big-time adductor although
can also do extension and internal rotation as well.
We also have some really large back muscles
that we saw on the back lecture
that we mentioned didn't really act on the back per se
but really acted on the upper limb.
To revisit those, we had the trapezius
and that was the one
that helps us shrug our shoulders
because it attaches to the scapula.
The wide flat latissimus dorsi
which is another major adductor
and then we also have some muscles that are a little smaller
and do sort of unique function.
These are the serratus anterior on the ribs
but they attach from the ribs to the scapula
and they pull the scapula forward as if you were punching forward
and that's called protraction of your scapula.
Then we have some smaller back muscles.
Fortunately, this first one tells you what it does.
The levator scapulae is going to elevate
or raise the scapula.
We have the rhomboids which are going from the medial edge
of the scapula to the vertebral column.
They're going to have the opposite effect of the serratus anterior
and they're going to retract the scapula
and pull it closer to the vertebra.
And then we have one called the teres major.
Now, I'll stop here because teres is probably an unfamiliar word.
Teres just means round so it's more of a descriptive term.
And when you see a major, that usually means
there's going to be a minor somewhere
and it turns out that teres minor
is one of the rotator cuff muscles
but it's important to point out
that the teres major,
although it's a very helpful adductor
and can help with internal rotation,
isn't actually one of the rotator cuff muscles
because it's not in the same location as the other ones.
So here are the nice posterior view of the scapula
and its little bump that we call the spine
and that's going to help us understand
these first rotator cuff muscle names.
We have the supraspinatus above it
and we have the infraspinatus below it.
They're crossing over that shoulder joint
to reach those tuberosities on the humerus.
And as you can tell maybe by this orientation,
when they contract, it's going to pull the shoulder joint
in such a way that it's going to cause lateral rotation.
Along with that other muscle we mentioned, the teres minor.
Again, not to confuse the two, it's still a round muscle
and it's still going out towards the upper limb
but this is actually attaching to those tuberosities
so it is actually one of your rotator cuff muscles.
If we swing around to an anterior point of view,
we see that all this anterior surface of the scapula
is filled in by our last rotator cuff muscle, the subscapularis
and this is on the opposite side as those other muscles
so we can kind of deduce that they're going to cause medial rotation.