Human Skeleton Anatomy

The Skeleton of the Human Body

• The skeleton forms a rigid supporting system in the human body, providing support for the body and its vital cavities, protection for vital structures, and serving as the mechanical basis for movement.

Axial Skeleton

• The axial skeleton consists of the central supporting axis of the body, including the skull, vertebral column, ribs, and sternum.
• The vertebral column consists of 33 vertebrae, divided into five groups: cervical (7), thoracic (12), lumbar (5), sacral (5), and coccygeal (4).
• The vertebral column includes intervertebral discs of fibrocartilage between most of the vertebrae.

Appendicular Skeleton

• The appendicular skeleton includes the bones of the upper limb and pectoral girdle, and bones of the lower limb and pelvic girdle.
• The shoulder girdle consists of the clavicle and scapula, while the pelvic girdle consists of the hip bones.
• The shoulder girdle and the pelvic girdle provide connection points between the appendicular and the axial skeletons, facilitating mechanical load transfer.
• Each of the upper and lower limbs consists of three segments: proximal, intermediate, and distal.

Bone Structure

• Bones are found in two forms: compact bone and cancellous bone.
• Compact bone is a dense mass of bone, forming the superficial layer of bone and the tubular shafts of long bones, providing strength.
• Cancellous bone (spongy or trabecular) is a less dense branching network of bone trabecula, occurring in the ends of long bones and filling the flat and irregular bones.

Bone Classification

• Bones are classified according to their shape into:
  • Long bones (e.g., the humerus in the arm)
  • Short bones (cuboidal, found in the tarsus and carpus)
  • Flat bones (e.g., the sternum, scapula, and vault of the skull)
  • Irregular bones (e.g., the vertebrae, hip bones, and bones of the face)
  • Sesamoid bones (e.g., the patella or knee cap, developing in certain tendons)
  • Pneumatic bones

Bone Development

• Bones develop in one of two ways:
  • Intramembranous ossification (membranous bone formation): flat bones develop in this way by direct calcium deposition into a mesenchymal model.
  • Endochondral ossification (cartilaginous bone formation): long and irregularly shaped bones develop by calcium deposition into a cartilaginous model of the bone.

Joints

• Joints (articulations) are unions or junctions between two or more bones or rigid parts of the skeleton.
• Joints exhibit a variety of forms and functions.

Types of Joints

• Fibrous joints (synarthrosis): bones joined by fibrous connective tissue, including:
  • Suture
  • Syndesmosis
  • Gomphosis
• Cartilaginous joints: bones joined by cartilage, or by cartilage and fibrous tissue, including:
  • Primary cartilaginous joints (e.g., the epiphysial plate of the growing long bones)
  • Secondary cartilaginous (symphysis) joints (e.g., the intervertebral joints between the vertebral bodies)
• Synovial joints (diarthroses): the most common type of joint, characterized by:
  • Articular surfaces covered by a thin layer of hyaline cartilage
  • A joint cavity filled with a small amount of synovial fluid
  • Subtypes include:
    • Plane (gliding) joints
    • Hinge joints
    • Pivot joints
    • Saddle joints
    • Condyloid joints
    • Ball and socket joints
    • Ellipsoid joints