Some synovial joints also have a fat pad, which can serve as a cushion between the bones.Īdditional structures located outside of a synovial joint serve to prevent friction between the bones of the joint and the overlying muscle tendons or skin. Finally, an articular disc can serve to smooth the movements between the articulating bones, as seen at the temporomandibular joint.

At other synovial joints, the disc can provide shock absorption and cushioning between the bones, which is the function of each meniscus within the knee joint. Examples of this include the articular discs found at the sternoclavicular joint or between the distal ends of the radius and ulna bones. In some places, an articular disc may act to strongly unite the bones of the joint to each other. These structures can serve several functions, depending on the specific joint.

This is called an articular disc, which is generally small and oval-shaped, or a meniscus, which is larger and C-shaped. Additional Structures Associated with Synovial JointsĪ few synovial joints of the body have a fibrocartilage structure located between the articulating bones. This type of indirect support by muscles is very important at the shoulder joint, for example, where the ligaments are relatively weak. As forces acting on a joint increase, the body will automatically increase the overall strength of contraction of the muscles crossing that joint, thus allowing the muscle and its tendon to serve as a “dynamic ligament” to resist forces and support the joint.

A tendon is the dense connective tissue structure that attaches a muscle to bone. An extrinsic ligament is located outside of the articular capsule, an intrinsic ligament is fused to or incorporated into the wall of the articular capsule, and an intracapsular ligament is located inside of the articular capsule.Īt many synovial joints, additional support is provided by the muscles and their tendons that act across the joint. Ligaments are classified based on their relationship to the fibrous articular capsule. Ligaments allow for normal movements at a joint, but limit the range of these motions, thus preventing excessive or abnormal joint movements. These strengthen and support the joint by anchoring the bones together and preventing their separation. Outside of their articulating surfaces, the bones are connected together by ligaments, which are strong bands of fibrous connective tissue. The ability of the bones to move smoothly against each other within the joint cavity, and the freedom of joint movement this provides, means that each synovial joint is functionally classified as a diarthrosis. This fluid also provides nourishment to the articular cartilage, which does not contain blood vessels. The cells of this membrane secrete synovial fluid (synovia = “a thick fluid”), a thick, slimy fluid that provides lubrication to further reduce friction between the bones of the joint. Lining the inner surface of the articular capsule is a thin synovial membrane. Instead, the articular cartilage acts like a Teflon ® coating over the bone surface, allowing the articulating bones to move smoothly against each other without damaging the underlying bone tissue. However, unlike at a cartilaginous joint, the articular cartilages of each bone are not continuous with each other. The bones of the joint articulate with each other within the joint cavity.įriction between the bones at a synovial joint is prevented by the presence of the articular cartilage, a thin layer of hyaline cartilage that covers the entire articulating surface of each bone.

The walls of this space are formed by the articular capsule, a fibrous connective tissue structure that is attached to each bone just outside the area of the bone’s articulating surface. Synovial joints are characterized by the presence of a joint cavity. Ligaments support the joint by holding the bones together and resisting excess or abnormal joint motions. The articulating surfaces of the bones are covered by a thin layer of articular cartilage. The joint is surrounded by an articular capsule that defines a joint cavity filled with synovial fluid. Figure 9.8 Synovial Joints Synovial joints allow for smooth movements between the adjacent bones.

Functions of synovial fluid