Study Notes on the Skeletal System and Bone Classification

BONES IN THE BODY

OBJECTIVES

  • Understand the classification of bones based on shape.
  • Learn about the two subdivisions of the skeleton.
  • Study bone growth and fractures.

THE SKELETAL SYSTEM

  • Composed of bones and connective tissues.
  • Living tissue that is vascularized, containing collagen and minerals.
  • The human adult skeleton typically has 206 bones, while infants have around 300 bones due to the presence of more cartilaginous structures that fuse during growth.

TYPES OF BONE STRUCTURE

  • Compact Bone: Dense and forms the outer layer of bones.
  • Spongy Bone: Lighter, contains many small spaces, and is found chiefly at the ends of long bones and in the interior of flat bones.

CONNECTIVE TISSUES IN THE SKELETAL SYSTEM

  • Ligaments: Connective tissue that connects bone to bone, providing stability to the joints.
  • Tendons: Connective tissue that connects muscles to bones, facilitating movement.
  • Cartilage: A flexible connective tissue that cushions joints and provides structure in areas like the nose and ears.

CLASSIFICATION OF BONES BY SHAPE

  • Long Bones:
    • Generally longer than they are wide with a shaft and heads at both ends.
    • Contains mostly compact bone and bears the load during activities (e.g., femur, tibia).
  • Short Bones:
    • Cube-shaped or roughly equal in length and width (e.g., carpal bones).
    • Composed mostly of spongy bone. They provide support and stability with minimal movement.
    • Sesamoid Bones: A specific type of short bone, shaped like a sesame seed, that forms within tendons (e.g., patella).
  • Flat Bones:
    • Thin, flattened, usually curved bones that protect internal organs or provide a surface for muscle attachment (e.g., sternum).
    • Consist of two layers of compact bone enclosing spongy bone.
  • Irregular Bones:
    • Bones with complex shapes that do not fit into other categories (e.g., vertebrae, hyoid bone).
    • Include structures such as the maxilla, mandible, zygomatic bones, and the vertebral column.

SKELETAL DIVISIONS

  • The human skeleton is divided into two major subdivisions:
    • Axial Skeleton:
    • Includes the skull, vertebral column, and thoracic cage (ribcage).
    • Forms the longitudinal axis of the body and consists of 80 bones.
    • Appendicular Skeleton:
    • Composed of the bones of the limbs and the pelvic and pectoral girdles, totaling 126 bones.
DETAILS OF THE AXIAL SKELETON
  • Skull:
    • Made up of 22 bones, divided into:
    • Cranial Bones (8 total):
      • Frontal (1)
      • Parietal (2)
      • Sphenoid (1)
      • Temporal (2)
      • Ethmoid (1)
      • Occipital (1)
    • Facial Bones (14 total):
      • Nasal (2)
      • Lacrimal (2)
      • Inferior nasal concha (2)
      • Maxilla (2)
      • Mandible (1)
      • Palatine (2)
      • Zygomatic (2)
      • Vomer (1)
  • Vertebral Column:
    • Composed of 26 irregular bones:
    • Cervical (7 vertebrae, C₁-C₇)
    • Thoracic (12 vertebrae, T₁-T₁₂)
    • Lumbar (5 vertebrae, L₁-L₅)
    • Sacrum (5 fused vertebrae)
    • Coccyx (4 fused vertebrae)
  • Thoracic Cage: Houses the ribs (12 pairs) and the sternum.
DETAILS OF THE APPENDICULAR SKELETON
  • Pectoral Girdle: Consists of clavicles and scapulae, supporting the arms.
  • Upper Limb Bones:
    • Humerus, Ulna, Radius, Carpals, Metacarpals, Phalanges.
  • Pelvic Girdle: Supports the legs and includes hip bones.
  • Lower Limb Bones:
    • Femur, Patella, Tibia, Fibula, Tarsals, Metatarsals, Phalanges.

BONE STRUCTURE AND DEVELOPMENT

  • Bones are relatively lightweight yet capable of resisting various forces due to their structure.
    • Organic component: Composed of collagen fibers providing flexibility and tensile strength.
    • Inorganic component: Calcium salts give bones their hardness, enabling them to resist compression.
  • As an infant, the skeleton is primarily cartilage, which is gradually replaced by bone through ossification, leading to completed bone formation as growth halts. Not all cartilage is replaced in adults (e.g., the ends of bones, ears).
BONE FORMATION
  • Ossification: The process of replacing cartilage with bone.
    • Osteoblasts: Cells that create new bone.
    • Osteocytes: Mature bone cells responsible for maintaining bone structure.
BONE REMODELING
  • Ongoing process throughout life, influenced by:
    • Calcium ion levels: Determines whether bone matrix gets broken down or formed, essential for maintaining bone health.

BONE FRACTURES

  • Classified and treated through:
    • Reduction and immobilization: To ensure proper healing.
    • Closed reduction: Bones are realigned manually.
    • Open reduction: Surgical procedure where bones are secured with pins or wires.
  • Healing time for fractures typically spans 6–8 weeks.
  • Fracture healing stages:
    1. Hematoma formation: Initial grouping of blood and tissue at the fracture site.
    2. Fibrocartilage callus formation: Internal callus of fibrous tissue and cartilage begins to develop.
    3. Bony callus formation: Eventually, a bony callus replaces the fibrocartilage as healing progresses.
    4. Bone remodeling: Final step where the bone is reshaped to its original form.
BROKEN ARM FIRST AID
  • Steps to take:
    1. Call emergency services.
    2. Avoid moving the injured area.
    3. Apply a simple splint to immobilize.
    4. Apply an ice pack to reduce swelling.
    5. Seek medical care for further treatment.