• Cartilage: A flexible connective tissue; acts as a forerunner of bone in embryonic development and covers many joint surfaces.

Functions of the Skeletal System

Major Functions

• Support: Bones of limbs and vertebral column support the body; mandible and maxilla support teeth.

• Protection: Protects vital organs such as the brain, spinal cord, lungs, heart, and pelvic viscera.

• Movement: Provides attachment and leverage for muscles.

• Blood Formation: Bones are the major producer of blood cells (hematopoiesis).

• Storage: Main reservoir of calcium and phosphorus; bone marrow stores fuel.

Joints (Articulations)

Classification of Joints

• Fibrous Joints (Synarthrosis): Bones bound by collagen fibers; little mobility (e.g., skull sutures).

• Cartilaginous Joints (Amphiarthrosis): Bones linked by cartilage; limited movement (e.g., pubic symphysis, intervertebral discs).

• Synovial Joints (Diarthrosis): Most familiar and structurally complex joints (e.g., shoulder, elbow, hip, knee).

Anatomy of Synovial Joints

• Articular Capsule: Connective tissue enclosing the joint cavity.

• Synovial Membrane: Inner layer of joint capsule; secretes synovial fluid.

• Articular Disc: Fibrocartilage pad between bones.

• Meniscus: Crescent-shaped cartilage in the knee; absorbs shock and stabilizes joint.

• Bursa: Fluid-filled sacs that reduce friction between tissues.

Movements at Joints

Types of Movements

• Abduction/Adduction: Movement away from/toward the midline.

• Elevation/Depression: Raising/lowering a body part.

• Protraction/Retraction: Moving a body part forward/backward on a horizontal plane.

• Circumduction: Circular movement of a limb.

• Rotation: Turning a bone around its axis (lateral/medial rotation).

• Supination/Pronation: Rotating the forearm so the palm faces upward/downward.

• Dorsiflexion/Plantar Flexion: Moving the foot upward/downward at the ankle.

• Inversion/Eversion: Turning the sole of the foot inward/outward.

• Opposition: Movement of the thumb to touch the fingertips.

Summary Table: Skeletal System Components

Key Equations and Terms

• Bone Matrix Composition:

• Ossification: The process of bone formation from other tissues.

• Hematopoiesis: The formation of blood cells in bone marrow.

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