Lecture on the Axial Skeleton

Learning Objectives

• Define the axial skeleton.
• Identify the components and functions of the vertebral column.
• Understand the structure of vertebrae and their variations.
• Describe the thoracic cage.

Axial vs. Appendicular Skeleton

• Axial Skeleton: Central bones (skull, hyoid bone, rib cage, vertebral column).
• Appendicular Skeleton: Limbs and appendages (arms, shoulders, legs, hips).

Vertebral Column

• Functions:

  • Supports skull and trunk.
  • Protects spinal cord.
  • Muscle and limb attachment.

• Sections of Vertebrae:

  • Cervical (C1-C7)
  • Thoracic (T1-T12)
  • Lumbar (L1-L5)
  • Sacrum (fused)
  • Coccyx (fused)

• Mnemonic for Vertebrae Count: Start work at 7 a.m., lunch at 12, go home at 5 (7 cervical, 12 thoracic, 5 lumbar).

• Curves of the Vertebral Column:

  • Cervical, thoracic, lumbar, pelvic/sacral.
  • Born with thoracic and pelvic curves; develop others as secondary curves.

Abnormal Curvatures

• Scoliosis: Lateral deviation.
• Kyphosis: Hunchback, excessive thoracic curve.
• Lordosis: Excessive lumbar curve, common in pregnancy.

Vertebra Structure

• Typical Vertebra:

  • Vertebral foramen for spinal cord.
  • Lamina and pedicle form vertebral arch.
  • Spinous and transverse processes for muscle attachment.
  • Articular processes and facets for vertebrae connection.

• Cervical Vertebrae:

  • C1 (Atlas): Supports skull, allows nodding.
  • C2 (Axis): Dens allows head rotation.
  • C3-C7: Smaller, triangular foramen, bifid spinous processes.

• Thoracic Vertebrae:

  • Larger, heart-shaped body.
  • Circular vertebral foramen.
  • No transverse foramen.
  • Attach ribs via costal facets.

• Lumbar Vertebrae:

  • Largest and thickest.
  • Blunt, short spinous processes.
  • Medial/lateral oriented articular facets for weight support.

Sacrum and Coccyx

• Sacrum:

  • Fused vertebrae (S1-S5).
  • Articulates with hips and L5.
  • Holes for nerves, sacral canal, and hiatus.

• Coccyx:

  • Tailbone, fused vertebrae (Co1-Co4/5).

Intervertebral Discs

• Function:

  • Bind vertebrae, absorb shock, support weight.

• Structure:

  • Nucleus pulposus (inner, water/collagen).
  • Annulus fibrosus (outer, fibrocartilage).

Ligaments of the Vertebral Column

• Anterior/Posterior Longitudinal Ligament: Bind vertebrae and discs.
• Ligamentum Flavum: Connects laminae.
• Interspinous/Supraspinous Ligaments: Connect spinous processes.

Thoracic Cage

• Components:

  • Sternum: Manubrium, body, xiphoid process.
  • Ribs: 12 pairs, classified as true, false, floating.

• Ribs:

  • True Ribs (1-7): Directly connect to sternum.
  • False Ribs (8-12): Indirectly or not connected to sternum.
  • Floating Ribs (11-12): No anterior connection.

• Rib Structure:

  • Head, neck, tubercle, angle, shaft, costal groove.

This concludes the lecture on the axial skeleton.