Axial Skeleton and Vertebrae Structure

Axial Skeleton

• Definition
  • The axial skeleton includes the bones of the skull, vertebral column, and rib cage.

Structure of Vertebrae

• General Features

  • Composed of 33 vertebrae in total (7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused), and 4 coccygeal (fused)).
  • Each vertebra consists of:
    • Body: weight-bearing anterior part.
    • Vertebral Arch: posterior part that forms a protective canal for the spinal cord.
    • Processes: projections for muscle and ligament attachment (spinous, transverse).
    • Intervertebral Discs: fibrocartilage pads between vertebrae, providing cushioning and flexibility.

• Types of Vertebrae

  • Cervical Vertebrae (C1-C7): Smallest; support the neck and allow head movement.
    • C1 (Atlas): Supports the skull; allows nodding.
    • C2 (Axis): Allows rotational movement; has odontoid process (dens).
  • Thoracic Vertebrae (T1-T12): Larger; articulate with ribs.
  • Lumbar Vertebrae (L1-L5): Largest; support lower back and bear significant weight.
  • Sacral Vertebrae (S1-S5): Fused into the sacrum; connects spine to pelvis.
  • Coccygeal Vertebrae (Co1-Co4): Fused to form the coccyx; serves as an attachment point for ligaments and muscles.

Spinal Column Segments

• Regions of the Spinal Column

  1. Cervical Region: 7 vertebrae (C1-C7)
  2. Thoracic Region: 12 vertebrae (T1-T12)
  3. Lumbar Region: 5 vertebrae (L1-L5)
  4. Sacral Region: 5 fused vertebrae (S1-S5) forming the sacrum.
  5. Coccygeal Region: 4 fused vertebrae forming the coccyx.

• Curvatures of the Spine

  • Cervical Curve: Lordosis (concave); develops as infants start to hold their heads up.
  • Thoracic Curve: Kyphosis (convex); primary curve present at birth.
  • Lumbar Curve: Lordosis (concave); develops as children begin to walk.

Rib Cage Function

• Structure

  • Composed of 12 pairs of ribs, sternum, and thoracic vertebrae.
  • Ribs categorized as:
    • True Ribs (1-7): Directly attach to the sternum.
    • False Ribs (8-10): Indirectly attach to the sternum via costal cartilage.
    • Floating Ribs (11-12): Do not attach to the sternum.

• Functions

  • Protects vital organs in the thoracic cavity (heart, lungs).
  • Supports the upper body and provides structure.
  • Aids in respiration by expanding and contracting during breathing.

Joint Movements in Axial Skeleton

• Types of Movements

  • Flexion and Extension: Bending and straightening movements mainly in cervical and lumbar regions.
  • Lateral Flexion: Side bending of the spine; primarily occurs in cervical and lumbar regions.
  • Rotation: Twisting motion, primarily occurs in the cervical region (e.g., turning the head) and limited in the thoracic region.

• Joints Involved

  • Intervertebral Joints: Between vertebrae, allow limited movement.
  • Zygapophyseal Joints: Facet joints between vertebral arches; allow gliding movements.
  • Costovertebral Joints: Between ribs and thoracic vertebrae; allow movement during respiration.

Axial Skeleton Overview

• Comprises the skull, vertebral column, and rib cage.

Structure of Vertebrae

• Total of 33 vertebrae:
  • 7 cervical,
  • 12 thoracic,
  • 5 lumbar,
  • 5 sacral (fused),
  • 4 coccygeal (fused).
• Vertebral components:
  • Body: Anterior part that bears weight.
  • Vertebral Arch: Encases and protects the spinal cord.
  • Processes: Projections for muscle/ligament attachment (spinous and transverse).
  • Intervertebral Discs: Fibrocartilage pads that cushion and provide flexibility.

Types of Vertebrae

• Cervical Vertebrae (C1-C7): Smallest, supporting neck mobility.
  • C1 (Atlas): Holds the skull, facilitates nodding.
  • C2 (Axis): Enables rotation, features the odontoid process (dens).
• Thoracic Vertebrae (T1-T12): Larger, connect to ribs.
• Lumbar Vertebrae (L1-L5): Largest, support lower back, bear significant weight.
• Sacral Vertebrae (S1-S5): Form sacrum, connects the spine to the pelvis (fused).
• Coccygeal Vertebrae (Co1-Co4): Form the coccyx, providing attachment for ligaments and muscles (fused).

Spinal Column Segments

• Regions:
  • Cervical Region: 7 vertebrae (C1-C7).
  • Thoracic Region: 12 vertebrae (T1-T12).
  • Lumbar Region: 5 vertebrae (L1-L5).
  • Sacral Region: 5 fused vertebrae forming the sacrum (S1-S5).
  • Coccygeal Region: 4 fused vertebrae forming the coccyx.

Curvatures of the Spine

• Cervical Curve: Lordosis (concave), develops as infants lift their heads.
• Thoracic Curve: Kyphosis (convex), primary curve from birth.
• Lumbar Curve: Lordosis (concave), develops when children begin walking.

Rib Cage Structure and Function

• Composed of 12 pairs of ribs, the sternum, and thoracic vertebrae.
• Rib Types:
  • True Ribs (1-7): Directly attach to the sternum.
  • False Ribs (8-10): Indirect connection to sternum via costal cartilage.
  • Floating Ribs (11-12): Do not attach to the sternum.
• Functions:
  • Protects thoracic cavity organs (heart, lungs).
  • Supports upper body structure.
  • Assists respiration through expansion and contraction.

Joint Movements in Axial Skeleton

• Types of Movements:
  • Flexion and Extension: Bending and straightening, mainly in cervical and lumbar regions.
  • Lateral Flexion: Side bending, occurring in cervical and lumbar regions.
  • Rotation: Twisting, primarily in the cervical region with limited thoracic involvement.
• Joints:
  • Intervertebral Joints: Allow limited movement between vertebrae.
  • Zygapophyseal Joints: Facet joints permitting gliding movements.
  • Costovertebral Joints: Connect ribs to thoracic vertebrae, allowing respiratory movement.

Explore the intricacies of the axial skeleton, focusing on the structure and function of vertebrae. This quiz covers the various types of vertebrae and their roles within the human body, including cervical, thoracic, and lumbar regions. Test your knowledge of their anatomical features and relationships.