4-Joints: Movement & Support

Types of Joints by Structure:
- Fibrous Joints: No joint cavity, held by dense connective tissue, very limited movement.
- Examples: Sutures (skull), Syndesmosis (radius-ulna), Gomphosis (tooth).
- Cartilaginous Joints: No joint cavity, bones joined by cartilage.
- Examples: Synchondrosis (hyaline cartilage), Symphysis (fibrocartilage).
- Synovial Joints: Have a joint cavity, allowing free movement.
Types of Joints by Function:
- Synarthrosis: Immovable (e.g., sutures).
- Amphiarthrosis: Slightly movable (e.g., pubic symphysis).
- Diarthrosis: Freely movable (e.g., elbow, knee).

Structure:
- Articular capsule: Outer fibrous layer, inner synovial membrane.
- Synovial fluid: Lubrication, nutrient/O₂ supply, waste removal.
- Articular cartilage: Smooth surface, prevents bone-on-bone contact.
- Ligaments: Bone-to-bone support.
- Joint cavity: Space allowing movement.
- Menisci: Fibrocartilage pads for shock absorption.
- Bursae: Fluid-filled sacs reducing friction.

Types of Movements:
- Flexion: Decrease angle (e.g., elbow during bicep curl).
- Extension: Increase angle (e.g., releasing bicep curl).
- Abduction: Move away from midline (e.g., lifting arm).
- Adduction: Move towards midline (e.g., returning arm).
- Circumduction: Circular movement at a joint (e.g., wrist movement).
- Rotation: Bone revolves around its axis (e.g., shaking head "no").