Joints

In this lesson, we’re going to talk about joints, and their structure and function.

As with any good A&P lesson, you should start with the function and the structure of the joint. But we also need to figure out what the purpose of a joint is.

The main purpose for joints is that they allow for movement between two different bones.

As we get going through these joints, we need to think about what the important parts of a join are. We need to look at the amount of movement in between the two bones, we need to look at any tissues in these joints, we also need to look for a presence of a joint cavity which gives us more information about how bones are supposed to move either separately or in unison.

What start with the different types of joints. You have amphiarthroses, synarthroses, and diarthroses.

In amphiarthrosis, there is some movement, and there is no cavity within the bone. Synarthroses, this is where you have a movable joints. So these are things like cranial bones, that join at suture lines.

Then you have diarthroses, which are movable joints and they have a joint cavity that’s filled with fluid. We’re going to look at is the complexities of a diarthrotic joints.

Now this is not a completely cumulative list, but these are the big types of joints that you’re going to see throughout the entire body. There are three different joint classes at we’re going to look at it, which are the hinge joint, on the ball and socket joint, and a planar joint. The hinge joint is one where it acts just like a hinge. This occurs at the ankle, elbow, and knee.

Then you have the ball and socket joint. This is where you have a ball that fits into a socket and you have more rotation throughout. These are joints like the hip and shoulder.

Then you have planar joints. These are the joints like wrists and ankles. They move along each other but they don’t necessarily articulate with each other at a particular point.

The structure of the diarthrotic joint is really important too. There’s typically a joint capsule, and there’s an outer layer and an inner layer. The outer layer is covered in something called white functional connective tissue and fibers and it creates this capsule, and this capsule is really important because it has things like the synovial membrane, and different types of connective tissue. Typically you’re going to see things like areolar and adipose connective tissue, and there’s also synovial fluid inside these joints. The synovial fluid is really important because it provides a cushion and lubrication for the joint to move fluidly.

A really important part of anatomical structure of joints, is that you have these things called bursa.

Bursa are essentially fluid filled capsules or cushions, if you will that go between bones and tendons. They reduce friction and they allow for free movement. The two though you can think of are the prepatellar bursa seen here, and a subacromial bursa in the shoulder. What they do is add extra padding to really help with movement and to reduce pain. Their structure is identical to a joint capsule.
Okay so let’s recap.

What defines a joint, well there a place of articulation and they allow for movement between two bones.

There are three different types of joints, which are amphiarthroses, diarthroses, and synarthroses.

There are three main types of diarthroses classes, which are hinge, ball and socket, and planer.

The synovial fluid is really important because it lubricates and cushions inside the joint capsule.

And then you have bursa which are responsible for cushioning reducing friction and improving movement in between bones and tendons.
That’s it for our lesson on joints.

Make sure you check out all the resources attached to this lesson. Now go out and be your best selves today, and as always happy nursing