Chapter 8 Anatomy & Physiology Joints of the Body Chapter 8 Anatomy & Physiology

Introduction to Articulations Sites where 2 or more bones meet are called joints or articulations. Our joints give our skeleton mobility and hold it together.

Classification of Joints Structural classification focuses on the material binding the bones together and whether or not a joint cavity is present. Fibrous joints – bones are jointed together by fibrous tissue and lack a joint cavity. Cartilaginous joints – bones are joined together by cartilage and they lack a joint cavity. Synovial joints – articulating bones are separated by a fluid- containing joint cavity.

Functional classification is based on the amount of movement allowed at the joint. Synarthroses are immovable joints Amphiarthoses are slightly moveable joints. Diarthroses are freely movable joints.

Fibrous Joints Sutures occur between bones of the skull and use very short connective tissue fibers hold the bone together. In syndesmoses the bones are connected by a ligament (which is a cord or band of fibrous tissue) A gomphosis is a peg-in-socket fibrous joint

Cartilaginous Joints Synchondroses involve a bar or plate of hyaline cartilage connecting the bones (like an epiphyseal plate) Symphyses have the articular surfaces are covered with articular cartilage that is then fused to an intervening pad or plate of fibrocartilage. (like the pubic symphysis)

Synovial Joints The general structure of a synovial joint contains 5 distinguishing features: Ends of articulating bones are covered with articular cartilage. The joint cavity is a space filled with synovial fluid. A two-layered articular capsule encloses the joint cavity. Synovial fluid is a viscous and slippery fluid that fills all free space within the joint cavity. Reinforcing ligaments cross synovial joints to strengthen the joint.

Bursae and tendon sheaths are bags of lubricants that reduce friction at synovial joints.

Factors Influencing the Stability of Synovial Joints The shapes of the articular surfaces of bones found a the a synovial joint determine the movements that occur at the joint. They play a minimal role in stabilizing the joint. Ligaments at a synovial joint prevent excessive or unwanted movements and help to stabilize the joint; the greater the number of ligaments at the joint the greater the stability. Muscle tone keeps tendons crossing joints taut which is the most important factor stabilizing joints.

Movements Allowed by Synovial Joints In gliding movements one flat bone surface glides or slips over another. Angular movements increase of decrease the angle between 2 bones

Angular Movements of Synovial Joints Flexion decreased the angle of the joint and brings the articulating bones closer together. Extension increases the angle between the articulating bones. Dorsiflexion decreases the angle between the top of the foot and the anterior surface of the tibia.

Plantar flexion decreases the angle between the sole of the foot and the posterior side of the tibia. Abduction is the movement of a limb (or fingers) away from the body (or the hand) Adduction is the movement of a limb (or fingers) toward the midline of the body (or hand) Circumduction is moving a limb so that it makes a cone in the air.

Special Movements Rotation is the turning of a bone along its own axis. Supination is rotating the forearm laterally so that the palm faces anteriorly. Pronation is rotating the arm medially so that the palm faces posteriorly.

Inversion turns the sole of the foot so that it faces medially. Eversion turns the sole of the foot so that it faces laterally. Protraction moves the mandible anteriorly (juts the jaw forward) Retraction returns the mandible to its original position.

Elevation means lifting a body part superiorly. Depression means to move an elevated body part inferiorly Opposition occurs when you touch your thumb to the fingers on the same hand.

Types of Synovial Joints Plane joints have flat articular surfaces and allow gliding and transitional movements. Hinge joints consist of a cylindrical projection that nests in a trough-shaped structure and allows movement along a single plane.

Pivot joints consist of a rounded structure that protrudes into a sleeve or ring and allow uniaxial rotation of a bone around the long axis. Condyloid or ellipsoid joints consist of an oval articular surface that nests in a complementary depression and permit all angular movements.

Saddle joints consist of each articular surface bearing complementary concave and convex areas and allow more freedom of movement than condyloid joints. Ball-and-socket joints consist of a spherical or hemispherical structure that articulates with a cuplike structure. They are the most freely moving joints and allow multi-axial movements.

Selected Synovial Joints Knee joint – enclosed in one joint cavity. The knee joint is actually three joints in one – tibiofemoral joint (femoropatellar joint; the lateral and medial joints between the femoral condyles and the minisci of the tibia)

Many different types of ligaments stabilize and strengthen the capsule of the knee joint The knee capsule is reinforced by muscle tendons. Shoulder joint (Glenohumeral) – stability has been sacrificed to provide the most freely moving joint in the body. The tendons that cross the shoulder joint and provide the most stabilizing effect of the joint are the tendon of the long head of the biceps brachii and the 4 tendons that make up the rotator cuff.

Hip (Coxal) Joint – is a ball- and-socket joint that provides a good range of motion. Several strong ligaments reinforce the capsule of the hip joint. The muscle tendons that cross the joint contribute to the stability and strength of the joint; but the majority of the stability of the hip joint is due to the deep socket of the acetabulum and the ligaments.

Elbow Joint – provides a stable and smoothly operating hinge joint that allows flexion and extension only. Tendons and several arm muscles also provide additional stability by crossing the elbow joint.

Homeostatic Imbalances of Joints Common Joint Injuries – sprains and dislocations. Inflammation and degenerative conditions – Bursitis – an inflammation of the bursa is usually caused by a blow or friction. Tendonitis – inflammation of the tendons is usually caused by overuse

Arthritis describes many inflammations or diseases that damage the joints. They result in pain,stiffness and swelling of the joints Osteoarthritis – the most common chronic arthritis. It is the result of the breakdown of articular cartilage and a thickening of bone tissue which may restrict joint movement. Rheumatoid arthritis – a chronic inflammatory disorder that is an autoimmune disease.