We're going to start our discussion of the upper limb
by talking about the shoulder and the arm
but before we do that, I'm going to say a little bit about
the types of bones and bones in general.
A lot of the bones we talk about
are what's called long bones.
In fact, one that we're going to see
very soon called the humerus.
We also have short bones
such as ones we're going to find down in the foot.
We have some flat bones
such as the sternum or breastbone
and one we already saw that are just too crazy
so we call them irregular bones like the vertebra.
The structure of a bone though from bone to bone
regardless of its shape tends to be pretty similar
so let's look at the shape and structure
of a long bone such as this one.
The longest part of the bone, the shaft,
is also called the diaphysis and at the ends we have the epiphyses.
We have one proximally called the proximal epiphysis
and one distally called the distal epiphysis
and the way to keep this straight
is that in between these is a physis.
So the diaphysis and the epiphyses are on either side of the physis (fi-sis)
or physis (fahy-sis) which is the growth plate
or at least it was during development.
And epi means upon so the ends of the bone are called epiphyses
because they're upon the growth plates.
If we were to look at a cross-section of bone,
we're going to see there's really two types of bone
surrounded by connective tissue
called periosteum meaning around the bone.
The outer bone is very thick and tough
giving it the strength of the bone.
That's the compact bone but the inner portion is spongy and there's a lot of gaps
and that's where the bone marrow will be found.
It's also worth noting cartilage.
So cartilage is very closely related to bone in a lot of senses.
Developmentally, a lot of our bones come from a cartilage model but then
there are a lot of structures that remain cartilage throughout life
such as the ear, the nose, and joint cartilages, really important for us.
So articular cartilage, articulate to move.
Articular cartilage is the type of cartilage found lining
the end of a bone that's participating at a joint.
We also have some structural cartilage
such as costal cartilages up in the ribs.
We have cartilage in the intervertebral discs
that provide a degree of strength and stability.
And a similar type that exists between the two halves of the pelvic bones,
that's something called the pubic symphysis.
We also have something called the meniscus
in the knee you might have heard like
and it too is a supportive structure, sort of like a pad
between the two halves of the knee joint.
We have a lot of different types of joints.
In the skull, for example, we have joints
that you might not realize are joints called sutures
and they're the type of joint that isn't like other joints
in the sense that they don't allow movement.
Sutures are really connections more than they are joints
the way we typically think about them.
Then we have more mobile joints
such as ball and socket joints
like we'll see at the hip where you can have
a wide degree of movement.
Other joints are a little more limited
where two flat surfaces rub up
against each other
and you can have a gliding motion.
Similarly, at places like the elbow or the knee,
the way they're oriented
means you can only have a hinge-like movement
and we call those hinge joints.