Types and structure of human bones

• Human bones are a type of connective tissue with a mineral matrix
• Bones support the body, protect organs, and enable movement

Types of Bones

• Long bones are longer than they are wide, with a shaft and two ends, such as the femur and humerus
  • They primarily function in leverage
• Short bones are cube-shaped, such as the carpals and tarsals
  • They provide stability and support with limited movement
• Flat bones are thin, flattened, and usually curved, such as skull bones, ribs, and the sternum
  • They have a large surface area for protection of organs and attachment of muscles
• Irregular bones have complex shapes, such as vertebrae and facial bones
  • They vary in shape and structure and therefore do not fit into any other category
• Sesamoid bones are embedded in tendons, such as the patella
  • They reinforce tendons, protecting them from stress and wear

Bone Structure

• Periosteum is the outer fibrous layer covering the bone
  • It contains blood vessels and nerves
  • It is involved in bone growth and repair
• Compact bone is the dense outer layer
  • It provides strength and protection
• Spongy bone (cancellous bone) is the inner layer with a honeycomb-like structure
  • It contains spaces filled with bone marrow
  • It is the site of hematopoiesis (blood cell formation)
• Bone marrow is soft tissue within bones
  • Red marrow is the site of hematopoiesis
  • Yellow marrow stores fat
• Osteon is the basic structural unit of compact bone
  • It consists of concentric layers (lamellae) around a central canal (Haversian canal)
• Haversian canal contains blood vessels and nerves
  • It provides nutrients and innervation to bone cells
• Volkmann's canals are channels that connect Haversian canals
  • They transmit blood vessels and nerves from the periosteum to the Haversian canals
• Osteocytes are mature bone cells
  • They are located in lacunae (small cavities) within the bone matrix
  • They maintain bone tissue
• Osteoblasts are bone-forming cells
  • They are responsible for synthesizing and mineralizing bone matrix
• Osteoclasts are bone-resorbing cells
  • They break down bone tissue to release minerals (calcium and phosphate) into the blood
  • They are important for bone remodeling
• Bone matrix is composed of organic and inorganic components
  • Organic components of collagen fibers provide flexibility and tensile strength
  • Inorganic components of hydroxyapatite (calcium phosphate crystals) provide hardness and rigidity

Bone Names

• Skull
  • Frontal bone forms the forehead
  • Parietal bones form the sides and roof of the cranium
  • Temporal bones form the lower sides of the cranium and surround the ears
  • Occipital bone forms the back of the skull
  • Sphenoid bone is located in the middle of the skull and articulates with all other cranial bones
  • Ethmoid bone is located between the eyes and contributes to the nasal cavity
  • Mandible is the lower jaw bone
  • Maxilla is the upper jaw bone
  • Zygomatic bones are the cheek bones
• Vertebral Column
  • Cervical vertebrae (7) are located in the neck
    • C1 (atlas) supports the skull
    • C2 (axis) allows for rotation of the head
  • Thoracic vertebrae (12) are located in the chest and articulate with the ribs
  • Lumbar vertebrae (5) are located in the lower back
  • Sacrum is formed by five fused vertebrae
  • Coccyx is the tailbone, formed by fused vertebrae
• Thoracic Cage
  • Ribs (12 pairs) protect the thoracic organs
    • True ribs (7 pairs) attach directly to the sternum
    • False ribs (5 pairs) attach indirectly to the sternum or not at all
    • Floating ribs (2 pairs) do not attach to the sternum
  • Sternum is the breastbone
    • Manubrium is the upper part of the sternum
    • Body is the middle part of the sternum
    • Xiphoid process is the lower part of the sternum
• Upper Limb
  • Clavicle is the collarbone
  • Scapula is the shoulder blade
  • Humerus is the upper arm bone
  • Radius is the forearm bone on the thumb side
  • Ulna is the forearm bone on the pinky side
  • Carpals (8) are the wrist bones
  • Metacarpals (5) are the bones of the hand
  • Phalanges (14) are the bones of the fingers
• Lower Limb
  • Hip bones (2) are formed by the fusion of the ilium, ischium, and pubis
  • Femur is the thigh bone
  • Patella is the kneecap
  • Tibia is the shin bone
  • Fibula is the lateral lower leg bone
  • Tarsals (7) are the ankle bones
    • Calcaneus is the heel bone
    • Talus is the bone that articulates with the tibia and fibula
  • Metatarsals (5) are the bones of the foot
  • Phalanges (14) are the bones of the toes