Spinal Cord Anatomy: The Vertebral Canal, Not Vertebral Bodies

The spinal cord does not pass through the vertebral bodies (centra). It runs within the vertebral canal (spinal canal), formed by the vertebral arches (pedicles, laminae, spinous processes) stacked atop the vertebral bodies.

Anatomical Relationship

• Vertebral body: Anterior weight-bearing cylinder; separated by intervertebral discs.
• Vertebral arch: Posterior ring (pedicles + laminae) forming the lateral and posterior walls of the canal.
• Vertebral foramen: The central opening in each vertebra; aligned, they form the vertebral canal.
• Spinal cord: Occupies upper 2/3 of canal (ends at L1–L2 in adults as conus medullaris); below, cauda equina nerve roots fill the canal.

Protective Layers (Meninges)

1. Dura mater: Tough outer layer; forms dural sac ending at S2.
2. Arachnoid mater: Web-like middle layer; subarachnoid space contains CSF.
3. Pia mater: Delicate inner layer adherent to cord surface.

Clinical Relevance

• Lumbar puncture: Performed at L3–L4 or L4–L5 (below conus) to access CSF safely.
• Epidural anesthesia: Outside dura, in epidural space (fat, vessels).
• Spinal stenosis: Narrowing of canal compresses cord/roots → myelopathy/radiculopathy.
• Vertebral body fracture: Retropulsed fragments can compress cord from anterior – cord is posterior to bodies.

Understanding this spatial relationship is fundamental to neuraxial procedures, trauma assessment, and spinal pathology.