5.4 Skeleton: Movement & Locomotion

1. Functions of the Human Skeleton

• Support: Forms rigid framework, maintains shape and posture.
• Protection: Encases delicate internal organs (e.g., skull protects brain).
• Movement: Bones act as levers, joints as fulcrums; muscles pull on bones.
• Mineral Storage: Reservoir for calcium and phosphorus.
• Blood Cell Production (Hematopoiesis): In red bone marrow.
• Fat Storage: In yellow bone marrow.

2. Axial and Appendicular Skeleton

2.1 Axial Skeleton (80 bones)

• Definition: Forms the central axis of the body.
• Components: Skull, Auditory Ossicles, Hyoid Bone, Vertebral Column, Thoracic Cage (Sternum, Ribs).
• Functions: Protects vital organs, supports posture.

2.2 Appendicular Skeleton (126 bones)

• Definition: Bones of the limbs and girdles.
• Components:
  • Pectoral (Shoulder) Girdle: Clavicle, Scapula.
  • Upper Limbs: Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges.
  • Pelvic (Hip) Girdle: Coxal bones.
  • Lower Limbs: Femur, Patella, Tibia, Fibula, Tarsals, Metatarsals, Phalanges.
• Functions: Movement, locomotion, manipulation of objects.

3. Types of Joints

• Definition: Points where two or more bones meet.

3.1 Classification by Movement (Functional)

• Immovable Joints (Synarthroses): No movement (e.g., skull sutures).
• Slightly Movable Joints (Amphiarthroses): Limited movement (e.g., vertebral joints, pubic symphysis).
• Freely Movable Joints (Diarthroses / Synovial Joints): Wide range of motion (most common).

Types of Synovial Joints

• Hinge Joint: Movement in one plane (e.g., elbow, knee).
• Ball and Socket Joint: Greatest range of motion (e.g., shoulder, hip).
• Pivot Joint: Rotational movement (e.g., atlantoaxial joint in neck).
• Gliding (Plane) Joint: Flat, sliding movements (e.g., carpals).
• Condyloid (Ellipsoid) Joint: Movement in two planes, no rotation (e.g., wrist, knuckles).
• Saddle Joint: Wide range of motion, limited rotation (e.g., thumb carpometacarpal joint).

3.2 Classification by Structure (Brief)

• Fibrous Joints: Bones joined by dense fibrous connective tissue (e.g., skull sutures).
• Cartilaginous Joints: Bones united by cartilage (e.g., intervertebral discs).
• Synovial Joints: Bones separated by fluid-filled joint cavity (all freely movable joints).