Support and Movement

Skeletal System and Cartilage

The human skeletal system is divided into the axial skeleton (skull, vertebral column, and thoracic cage) and the appendicular skeleton (pectoral girdle, pelvic girdle, and limbs). A thorough understanding of bone markings, joint types—specifically synovial joints like the hinge and ball-and-socket joints—and the structural differences between compact and spongy bone is essential for answering both objective and subjective board questions. Additionally, students must know the types of cartilage: hyaline cartilage, elastic cartilage, and fibrocartilage, noting their specific locations and functions in the human body.

Bone Structure and Growth

At the microscopic level, bones are composed of osteocytes housed in lacunae within concentric rings called lamellae, which surround the Haversian canals (forming structural units known as osteons or Haversian systems). Board exams frequently test the processes of ossification (bone formation) and remodeling, involving bone-forming cells (osteoblasts) and bone-resorbing cells (osteoclasts). Common skeletal disorders such as osteoporosis (loss of bone mass) and arthritis (inflammation of joints) are high-yield clinical topics frequently featured in short-answer questions.

Muscle Contraction and Sliding Filament Theory

Movement is primarily driven by skeletal muscles working in antagonistic pairs. The microscopic anatomy of a muscle fiber centers on the sarcomere, the functional unit of contraction defined between two Z-lines. Students must be able to describe the Sliding Filament Theory, detailing how actin and myosin filaments interact. Key mechanisms include the role of calcium ions ($Ca^{2+}$) released from the sarcoplasmic reticulum, the exposure of binding sites on actin via troponin and tropomyosin, and the cross-bridge cycle powered by ATP hydrolysis.

Locomotion in Animals and Joint Disorders

Exam questions often compare locomotion across different media (water, land, and air). For instance, students should understand how antagonistic muscle action (gastrocnemius and triceps) facilitates movement in terrestrial animals like humans, contrasting skeletal adaptations for bipedalism. Furthermore, be prepared to define and differentiate common musculoskeletal injuries and conditions, such as sprains (ligament damage), strains (muscle/tendon overstretching), and myasthenia gravis (an autoimmune neuromuscular disorder), as these frequently appear in board paper case-based or conceptual questions.