When it degenerates, arthritis develops. Synovial fluid serves to protect the joint, lubricate the joint and provide nourishment to the articular cartilage. A bursa is a small sac that is not part of the joint but is near the joint. It contains a fluid that lubricates the movement of muscles as the muscle moves across muscle or as the muscle moves across bone. In some ways it is similar to the synovial sac.
Muscles are elastic tissues that have the ability to change length.
By becoming shorter and longer, muscles allow for motion at the joints. Tendons are fibrous cords that attach muscles to the bones. However, as the muscle moves, the tendon to which it is attached also moves. You can feel the tendons on the back of your hand or in the back of your knee. Typically, ligaments are located around the joints.