Skeletal System: Divisions and Bone Terminology

  • Skeletal System Overview
    • The average adult human body contains 206206 bones.

    • Individual differences can lead to variations (e.g., fused bones, incorrectly developed bones), but 206206 is the typical average.
  • Divisions of the Skeleton
    • The skeleton is broadly segregated into two major parts:
      • Axial Skeleton: (represented in red in the visual guide)
        • Includes the Cranial Skeleton as a subset.
        • Will be a focus in Week 6.
      • Appendicular Skeleton: (represented in green in the visual guide)
        • Comprises approximately 120120 of the 206206 bones.
        • Consists of the two girdles (pectoral and pelvic) and the associated limbs.
          • Pectoral Girdle and Upper Limbs (left and right arm).
          • Pelvic Girdle and Lower Limbs (left and right leg).
        • The primary focus for Week 5 will be the appendicular skeleton.
  • Bone Classification
    • Bones are classified based on their shape:
      • Long bones
      • Flat bones
      • Irregular bones (no true shape)
      • Short bones
        • Sesamoid bones (e.g., the patella or kneecap) are a specific class that falls under short bones.
  • Study Resources and Schedule
    • Table 7.1 in the textbook lists all bones and their regional counts.
    • Table 7.12 is a critical reference for anatomical terms, and students are advised to keep it accessible (e.g., by cropping it from an e-book).
      • Referring back to this table helps in learning structural names rather than pure memorization.
    • Weekly Focus:
      • Week 5: Appendicular skeleton.
      • Week 6: Cranial and axial skeleton.
      • Week 7: Joints, which are the regions where bones come together.
  • Anatomical Terms for Bone Features (Referenced from Table 7.12)
    • Body: The main, central part of a bone.
    • Head: Any enlarged area of a bone. Examples include the head of the femur, radius, ulna, humerus, and metacarpals.
    • Neck: A constriction located between the head and the body of a bone (e.g., a prominent neck on the femur).
    • Margins/Borders: The edges of bones, particularly evident on flat bones.
    • Ramus: A branch that extends off the body of a bone (e.g., multiple rami on the mandible).
    • Condyle: An articular surface of a bone, typically convex, that usually articulates with a facet on another bone.
    • Facet: A smooth, flat articular surface of a bone, typically concave, that usually articulates with a condyle on another bone.
    • Projections: Structures that noticeably extend or stick out from the main bone body.
      • Process: A very prominent projection.
      • Tubercle: A small, rounded projection.
      • Tuberosity: A knob-like projection on a bone.
      • Trochanters: Two specific large tuberosities located on the proximal femur (the textbook does not list any other trochanters).
      • Annulus: A hook-shaped projection.
      • Horns: Horn-shaped projections.
    • Ridges: Linear elevations on a bone's surface, which can be lines or very low ridges.
      • Linea Aspera: A prominent long linear ridge located on the femur.
      • Significance: Ridges are important because they provide points for orientation and serve as insertion sites for muscles onto the bone.