CHAPTER 7

Overview of the Axial Skeleton

• The axial skeleton is one of the two major divisions of the skeletal system.

  • Other Division: Appendicular skeleton, which includes limbs (arms and legs).

• The axial skeleton comprises 80 bones.

• The appendicular skeleton contains 126 bones.

• Total number of bones in the human body: 206 bones (80 axial + 126 appendicular).

Components of the Axial Skeleton

• Includes the following key structures:

  • Skull: 22 bones

    • Cranial Bones: 8 total

    • Facial Bones: 14 total

  • Vertebral Column: Initially counted as 24 vertebrae

    • Cervical Vertebrae: 7 bones

    • Thoracic Vertebrae: 12 bones

    • Lumbar Vertebrae: 5 bones

  • Sacrum: 1 bone

  • Coccyx: 1 bone

  • Total for vertebral column when including sacrum and coccyx: 26 bones.

  • Ribs: 12 pairs (total 24 ribs)

  • Sternum: 1 bone (despite consisting of 3 pieces)

Skull Anatomy

• Skull Bones:

  • 8 Cranial Bones:

    • Mnemonic: "A Pest of 8"

      • P: Parietal (2)

      • E: Ethmoid (1)

      • S: Sphenoid (1)

      • T: Temporal (2)

      • O: Occipital (1)

      • F: Frontal (1)

    • Total: 22 bones in the skull

  • 14 Facial Bones

Vertebral Column Structure

• Breakdown of vertebrae:

  • Cervical: 7 vertebrae

  • Thoracic: 12 vertebrae

  • Lumbar: 5 vertebrae

• Costal Cartilages: Not counted as bones.

Additional Structures in the Axial Skeleton

• Auditory Ossicles: 3 bones in each ear (total of 6)

  • Important for hearing; often overlooked in discussions of axial skeleton.

• Sutures: Tiny bones that interlock cranial bones together, 4 main sutures.

Important Notes on Bones and Counting

• Pay attention to terminology when asked about bone counts:

  • Vertebrae count refers to 24 (not including sacrum and coccyx).

  • Vertebral column count includes sacrum and coccyx, totaling 26 bones.

Conclusion

• Understanding the composition and structure of the axial skeleton is crucial for a comprehensive grasp of human anatomy.