Axial Skeleton Overview

Introduction

The axial skeleton forms the central axis of the human body and consists of the vertebral column, the bony thorax, and the skull. This section focuses on the vertebral column and thoracic cage, highlighting their anatomical features, functions, and clinical relevance.

Vertebral Column / Spine of Axial Skeleton

Vertebrae

The vertebral column is composed of a series of bones called vertebrae, which protect the spinal cord and provide structural support.

• Cervical Vertebrae (C1–C7):

  • Transverse foramen: Openings in the transverse processes for vertebral arteries.

  • Atlas (C1): Supports the skull; allows nodding motion.

  • Axis (C2): Contains the odontoid process (dens), which acts as a pivot for rotation of the atlas and skull.

• Thoracic Vertebrae (T1–T12): Articulate with ribs; have long spinous processes.

• Lumbar Vertebrae (L1–L5): Largest vertebrae; support most body weight.

• Sacrum: Five fused vertebrae forming the posterior wall of the pelvis.

• Coccyx: Four fused vertebrae forming the tailbone.

Parts of a Generic Vertebra

Each vertebra shares common structural features that contribute to its function.

• Vertebral Body: Main weight-bearing portion.

• Vertebral Foramen: Central opening for the spinal cord.

• Vertebral Arch: Formed by laminae and pedicles; encloses the vertebral foramen.

  • Laminae: Posterior part of the arch.

  • Pedicles: Lateral sides of the arch.

• Spinous Process: Projects posteriorly; attachment for muscles and ligaments.

• Transverse Processes: Project laterally; attachment for muscles and ligaments.

• Articular Processes: Superior and inferior facets for articulation with adjacent vertebrae.

Intervertebral Foramen

The intervertebral foramen is the opening between adjacent vertebrae through which spinal nerves exit the spinal column.

Intervertebral Disc

Intervertebral discs are fibrocartilaginous pads between vertebral bodies that provide cushioning and flexibility.

• Annulus fibrosus: Tough outer layer of the disc.

• Nucleus pulposus: Gel-like inner core that absorbs shock.

Ligaments of the Vertebral Column

Ligaments stabilize the vertebral column and limit excessive movement.

• Anterior longitudinal ligament: Runs along the anterior surface of vertebral bodies; prevents hyperextension.

• Posterior longitudinal ligament: Runs along the posterior surface of vertebral bodies; prevents hyperflexion.

• Ligamentum flavum: Connects adjacent laminae; maintains upright posture.

• Ligamentum nuchae: Supports the head; found in the cervical region.

Normal & Abnormal Spinal Curvatures

Spinal Curvatures

The vertebral column has normal curves that help absorb shock and maintain balance. Abnormal curvatures can lead to clinical conditions.

• Lordosis: Exaggerated inward curve of the lumbar spine.

• Kyphosis: Excessive outward curve of the thoracic spine.

• Scoliosis: Lateral curvature of the spine.

The Thoracic Cage

Sternum

The sternum is a flat bone located in the center of the chest, forming the anterior portion of the thoracic cage.

• Manubrium: Superior portion; articulates with clavicles and first ribs.

• Body (Gladiolus): Middle and largest part; articulates with costal cartilages of ribs 2–7.

• Xiphoid process: Inferior, small cartilaginous extension; ossifies in adulthood.

Costals (Ribs)

The ribs are curved bones that form the lateral walls of the thoracic cage and protect vital organs.

• True ribs (1–7): Attach directly to the sternum via costal cartilages (vertebro-sternal).

• False ribs (8–12): Do not attach directly to the sternum.

  • Ribs 8–10: Attach to the sternum indirectly via the cartilage of rib 7 (vertebro-chondral).

  • Ribs 11–12: Floating ribs; do not attach to the sternum.

Summary Table: Vertebral Column Regions and Features

Clinical Application

• Imaging: X-rays, CT, and MRI are used to visualize bones and soft tissues of the axial skeleton.

• Physical Assessment: Palpation of bony landmarks aids in diagnosis of spinal and thoracic abnormalities.

Key Terms and Definitions

• Vertebra: Individual bone of the spine.

• Intervertebral disc: Cushioning pad between vertebrae.

• Ligament: Connective tissue that stabilizes joints.

• Sternum: Central bone of the thoracic cage.

• Costal: Refers to ribs.

Example: Identifying Vertebral Landmarks

When examining a vertebra, locate the vertebral body, vertebral foramen, spinous process, and transverse processes. In the cervical region, identify the transverse foramen and the unique features of the atlas and axis.

Additional info: Some context and terminology have been expanded for clarity and completeness, including definitions and clinical applications.