ORGANIZATION OF THE SKELETAL SYSTEM Divisions of the Skeletal System ! The axial skeleton contains 80 bones, including the cranial bones, the facial bones, the bones of the middle ear, the hyoid bone, the vertebral column, and the thorax. ! The appendicular skeleton contains 126 bones, comprising the pectoral girdle and its attached upper limbs, and the pelvic girdle and its attached lower limbs. Joints ! An articulation or arthrosis or joint is a point of contact between two bones, or between a bone and cartilage, or between a bone and teeth. ! Joints can be classified according to the degree of movement that is allowed. < a synarthrosis is an immovable joint < an amphiarthrosis is a slightly movable joint < a diarthrosis is a freely movable joint ! Joints can be classified according to the presence or absence of a fluid-filled synovial cavity around the bones and on the type of connective tissue that binds the bones together. < fibrous joints have no synovial cavity and the bones are held together by collagen fibers < cartilaginous joints have no synovial cavity and the bones are held together by cartilage < synovial joints have a fluid-filled synovial cavity Structure of a Synovial Joint ! The ends of the articulating bones are covered with articular cartilage and held together by an articular capsule. < an outer fibrous capsule consists of dense, irregular connective tissue < an inner synovial membrane consists of areolar connective tissue ! Synovial fluid is a viscous, pale yellow fluid consisting of hyaluronic acid and interstitial fluid. < it lubricates the joint and nourishes the articular cartilage < it contains phagocytes that remove microbes and clean up debris ! Many synovial joints contain accessory ligaments. ! Some synovial joints contain fibrocartilage menisci. ! A bursa is a fluid-filled sac located between muscles or where a tendon passes over a bone. Types of Synovial Joints ! A gliding joint occurs between small bones which have flat articular surfaces. ! A hinge joint is designed so a convex surface of one bone fits into a concave surface of second bone. ! A pivot joint occurs when a rounded or pointed portion of one bone fits into a ring-like ligament that is associated with a second bone. ! A condyloid joint occurs when an oval condyle of one bone fits into an elliptical cavity of another bone. ! A saddle joint occurs between two bones whose articulating surfaces have both concave and convex regions. ! A ball-and-socket joint occurs when a ball-shaped head of one bone fits into a cup-like depression of another bone. Special Movements at Freely Movable Joints ! Flexion decreases the angle between bones; Extension increases the angle between bones. ! Abduction moves a bone away from the midline of the body; Adduction moves a bone toward the midline of the body. ! Circumduction moves the distal end of a bone in a circle. ! Supination rotates the forearm to place the palm in anatomical position; Pronation rotates the forearm to turn the palm away from anatomical position. ! Inversion rotates the sole of the foot inward; Eversion rotates the sole of the foot outward. ! Dorsiflexion bends the entire foot upward toward the shin; Plantarflexion bends the entire foot downward away from the shin. ! Protraction thrusts a body part forward; Retraction withdraws a body part to its original position. ! Elevation raises a bone vertically; Depression lowers a bone. Arthritis ! Arthritis describes pain, inflammation, and/or degeneration associated with a joint. ! Osteoarthritis is a progressive joint disease involving the degeneration of articular cartilages so the articular surfaces become rough. ! Gouty arthritis results from excessive uric acid accumulation. ! Rheumatoid arthritis refers to inflammation and thickening of the synovial membrane in a joint, followed by damage to the articular cartilage, and invasion of the joint by fibrous tissue. < rheumatoid arthritis is a systemic autoimmune disease < there is no cure for this crippling form of arthritis, so treatment is aimed at reducing inflammation and slowing the rate of degeneration freymima E:\Biology 214\OrganizationofSkeleton.notes.wpd
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