Hi, and welcome again to anatomy basics. In Section two, lecture one, I will inform you in more detail about the form and function of joints. The joints that you need to know about when you want to understand the movement of your arms and legs are actually synovial joints. synovial joint is a specific connection between two bones. The articular surfaces of both bones are covered with cartilage, which is a smooth tissue to allow the movements to happen without a lot of friction. The joint is surrounded by a capsule that has two layers.
The outer layer is made out of fibrous tissue and is strengthened with ligaments. The ligaments are interweaved with a capsule and sometimes like right next to it the inner layer of the capsule called the synovial membrane, and its function is producing cinetopia, which is the oily joint fluid that has a main function in reducing friction while the joint is moving. When you have an injury, the synovial membrane becomes hyperactive to make things right again, and therefore the membrane will produce more synovial fluid. This is part of the inflammation process after the injury of a joint. The capsule has some slack to enable the joints to move. When the joint is in its resting position, the capsule is not stretched at all, and this is called the LPP the loose pack position.
At the end of the movement, the capsule has completely used up the slack, and no further movement is possible without tearing the capsule or dislocating the joint. This is called the closed back position the CPP As you will have experienced yourself, not all joints can move in all directions. This has to do with the form of the joints. We will look at the most common forms of joints in the body. Before explaining about the joints it's good to know these two words that will return in describing all joints convex and concave. You have a convex surface that is like a bulb.
And the opposite part of the joint on the other bone is concave that means hollow like a bowl. First we have the ball and socket joint. You see it here and by its form it has a lot of freedom in moving it can actually move in all directions. Examples of a ball and socket joint are the shoulder and the hip joint. Then there is a hinge joint. This joint has a Like a door and hinges, only one direction in which it can move up and down.
An example is the knee joint and the humeral owner joint in the elbow. Another specific model is the settled joint. The most important one we have is the subtle joint at the base of the thumb, couple metacarpal one. This joint has a different form when you look at it in different directions. For flexion and extension, the proximal surface is convex, and for an ad duction the proximal surface is concave However, this form gives the joint the necessary freedom to be able to grab things. And at the same time, the joint has more stability by its form than a ball and socket joint.
Next to these three basic models, you can discriminate some other basic forms, like the pivot and ellipses video joints. But I will not get into those because they are beyond the framework of this course. The example shown here are simplified models of course, and in real life there is often a kind of combination of forms that will allow some extra movement in certain directions. But for this course will do to know the basic forms of joints as illustrated in these models. Now that you have a better understanding of the joints I will continue in the next lesson to tell you about the muscles and how using them leads to movement. Thank you for watching this lecture about the joint and I hope to see you soon in the next lecture.