Clinical meaning
The musculoskeletal system provides structural support, protects vital organs, enables movement, stores minerals (calcium and phosphorus in bone), and houses bone marrow for hematopoiesis. The skeletal system consists of 206 bones in adults classified by shape: long bones (femur, humerus -- lever arms for movement), short bones (carpals, tarsals -- stability and some movement), flat bones (sternum, skull, pelvis -- protection and broad muscle attachment), irregular bones (vertebrae, facial bones), and sesamoid bones (patella -- embedded in tendons). Bone is a dynamic tissue undergoing constant remodeling through the balanced activity of osteoblasts (bone formation), osteoclasts (bone resorption), and osteocytes (mature bone cells maintaining bone matrix). Joints (articulations) are classified by degree of movement: synarthrosis (immovable -- skull sutures), amphiarthrosis (slightly movable -- intervertebral discs, pubic symphysis), and diarthrosis (freely movable synovial joints -- hip, knee, shoulder). Synovial joints contain a joint capsule, synovial membrane producing synovial fluid for lubrication, and articular cartilage covering bone ends to reduce friction. Skeletal muscle is composed of bundles of contractile fibers controlled by motor neurons; contraction occurs through the sliding filament mechanism where actin...