The musculoskeletal system is a vital, integrated network that provides structural support, protects internal organs, and enables physical movement. It is composed of two main frameworks: the passive skeletal system, consisting of bones, joints, cartilage, ligaments, and tendons, and the active muscular system, consisting of skeletal muscles. Beyond locomotion, bones serve as a primary storage site for essential minerals like calcium and phosphorus, while also housing bone marrow responsible for hematopoiesis. Understanding this foundation is essential for nurses assessing mobility impairments and planning patient care in clinical practice.
Bone tissue is a specialized form of dense connective tissue organized into two distinct structural types: compact (cortical) bone and spongy (cancellous) bone. Compact bone forms the hard, dense outer layer that provides protection and strength. Spongy bone forms an internal network of trabeculae that reduces skeletal weight and houses red bone marrow. Microscopically, mature compact bone is built of cylindrical units called osteons. Each osteon contains a central canal surrounded by concentric rings of hard matrix known as lamellae, with tiny spaces called lacunae housing living bone cells.
Bones are dynamic living organs that constantly undergo remodeling throughout life. This process involves the coordinated action of osteoclasts, which break down bone matrix, and osteoblasts, which build new bone tissue. Remodeling allows the skeleton to repair micro-fractures and adapt to mechanical stress. Additionally, bone acts as a vast reservoir for calcium and phosphate. When blood calcium levels drop, parathyroid hormone stimulates osteoclastic activity to release stored calcium into the bloodstream.
Joints, or articulations, are the meeting points between bones. They are classified structurally based on the binding tissue and functionally based on their range of movement.
Skeletal muscle contraction is governed by the sliding filament theory, which explains how muscle fibers shorten to generate force. The process begins when an electrical impulse from a motor neuron reaches the neuromuscular junction, releasing acetylcholine. This triggers an action potential along the muscle cell membrane, causing calcium ions to be released from the sarcoplasmic reticulum. Calcium binds to regulatory proteins, exposing binding sites on actin filaments. Myosin heads then attach to actin, pull the filaments inward using ATP energy, and cause the muscle to contract.
Movement and stability require specialized connective tissues that assist the bones and muscles. Cartilage is a resilient, smooth connective tissue that covers bone ends in joints, reducing friction and absorbing shock. Ligaments are tough bands of fibrous connective tissue that connect bone to bone, providing joint stability. Tendons are strong fibrous cords that attach skeletal muscle to bone, transmitting the force generated by muscle contraction to produce movement. Unlike muscles, tendons and cartilage have a poor blood supply, which makes their healing process notoriously slow following an injury.
Skeletal muscles cannot contract independently; they require stimulation from the nervous system. The motor cortex of the brain initiates voluntary movement, sending signals down the spinal cord via motor neurons. Proprioceptors, specialized sensory receptors located in muscles and joints, continuously provide feedback to the central nervous system regarding body position and muscle tension. This feedback loop allows smooth coordination and maintenance of posture without constant conscious thought.
As individuals age, natural physiological changes affect the musculoskeletal system. Bone resorption gradually outpaces bone formation, leading to a decrease in bone mineral density and increased fracture risk, a condition known as osteoporosis. Joints experience wearing of articular cartilage and decreased synovial fluid production, causing stiffness and osteoarthritis. Muscle mass and strength also decline progressively, a process called sarcopenia. Nurses must recognize these changes to differentiate normal aging from pathological conditions and promote safe mobility interventions.