9.4 Synovial Joints

fibrous membrane

usually consists of dense irregular connective tissue (mostly collagen fibers) that attaches to the periosteum of the articulating bones. In fact, the fibrous membrane is literally a thickened continuation of the periosteum between the bones.

synovial fluid

The synovial membrane secretes synovial fluid (ov- = egg), a viscous, clear or pale yellow fluid named for its similarity in appearance and consistency to uncooked egg white. Synovial fluid consists of hyaluronic acid secreted by synovial cells in the synovial membrane and interstitial fluid filtered from blood plasma. It forms a thin film over the surfaces within the articular capsule.

Many synovial joints also contain ______________________ called extracapsular ligaments and intracapsular ligaments

accessory ligaments

Inside some synovial joints, such as the knee, crescent-shaped pads of fibrocartilage lie between the articular surfaces of the bones and are attached to the fibrous capsule. These pads are called_____________

articular discs or menisci

Synovial joints

have certain characteristics that distinguish them from other joints.

The strength of these fiber bundles, called______________________ is one of the principal mechanical factors that hold bones close together in a synovial joint. Ligaments are often designated by individual names.

ligaments

The articular capsule is composed of two layers

outer fibrous capsule inner synovial membrane

labrum

prominent in the ball-and-socket joints of the shoulder and hipis the fibrocartilaginous lip that extends from the edge of the joint socket. The labrum helps deepen the joint socket and increases the area of contact between the socket and the ball-like surface of the head of the humerus or femur. ROLE: attached to the rim of the shoulder socket that helps keep the ball of the joint in place.

The functions of the menisci are not completely understood but are known to include the following:

(1) shock absorption; (2) a better fit between articulating bony surfaces; (3) providing adaptable surfaces for combined movements; (4) weight distribution over a greater contact surface; (5) distribution of synovial lubricant across the articular surfaces of the joint.

articular capsule

A sleevelike articular capsule or joint capsule surrounds a synovial joint, encloses the synovial cavity, and unites the articulating bones.

bursae and tendon sheaths

Bursae: Saclike structures called bursae are strategically situated to alleviate friction in some joints, such as the shoulder and knee joints . Bursae are not strictly part of synovial joints, but they do resemble joint capsules because their walls consist of an outer fibrous membrane of thin, dense connective tissue lined by a synovial membrane. They are filled with a small amount of fluid that is similar to synovial fluid. Bursae can be located between the skin and bones, tendons and bones, muscles and bones, or ligaments and bones. Tendon sheaths or synovial sheaths are tubelike bursae; they wrap around certain tendons that experience considerable friction as they pass through tunnels formed by connective tissue and bone. The inner layer of a tendon sheath, the visceral layer, is attached to the surface of the tendon. The outer layer, known as the parietal layer, is attached to bone . Between the layers is a cavity that contains a film of synovial fluid. A tendon sheath protects all sides of a tendon from friction as the tendon slides back and forth. Tendon sheaths are found where tendons pass through synovial cavities, such as the tendon of the biceps brachii muscle at the shoulder joint

______________________ lie outside the articular capsule. Examples are the fibular and tibial collateral ligaments of the knee joint._________________________occur within the articular capsule but are excluded from the synovial cavity by folds of the synovial membrane.

Extracapsular ligaments Intracapsular ligaments

Nerve and Blood Supply

Nerves: The nerves that supply a joint are the same as those that supply the skeletal muscles that move the joint. Synovial joints contain many nerve endings that are distributed to the articular capsule and associated ligaments. Some of the nerve endings convey information about pain from the joint to the spinal cord and brain for processing. Veins: Veins remove carbon dioxide and wastes from the joints. The arterial branches from several different arteries typically merge around a joint before penetrating the articular capsule. The chondrocytes in the articular cartilage of a synovial joint receive oxygen and nutrients from synovial fluid derived from blood; all other joint tissues are supplied directly by capillaries.

Menisci

Pads of cartilage that lie between the articular surfaces of the bones

Bursae

Saclike structures called bursae are strategically situated to alleviate friction in some joints, such as the shoulder and knee joints . Bursae are not strictly part of synovial joints, but they do resemble joint capsules because their walls consist of an outer fibrous membrane of thin, dense connective tissue lined by a synovial membrane. They are filled with a small amount of fluid that is similar to synovial fluid. Bursae can be located between the skin and bones, tendons and bones, muscles and bones, or ligaments and bones.

At many synovial joints the synovial membrane includes accumulations of adipose tissue, called _______________________ An example is the infrapatellar fat pad in the knee

articular fat pads.

Tendon sheaths

or synovial sheaths are tubelike bursae; they wrap around certain tendons that experience considerable friction as they pass through tunnels formed by connective tissue and bone. The inner layer of a tendon sheath, the visceral layer, is attached to the surface of the tendon. The outer layer, known as the parietal layer, is attached to bone . Between the layers is a cavity that contains a film of synovial fluid. A tendon sheath protects all sides of a tendon from friction as the tendon slides back and forth. Tendon sheaths are found where tendons pass through synovial cavities, such as the tendon of the biceps brachii muscle at the shoulder joint

. The unique characteristic of a synovial joint is the presence of a space called a ______________________or joint cavity between the articulating bones. Because the synovial cavity allows considerable movement at a joint, all synovial joints are classified functionally as freely movable (diarthroses). The bones at a synovial joint are covered by a layer of hyaline cartilage called ______________________.

synovial cavity articular cartilage.

also contains phagocytic cells that remove microbes and the debris that results from normal wear and tear in the joint.

synovial fluid

The inner layer of the articular capsule, the _____________________ is composed of areolar connective tissue with elastic fibers

synovial membrane,