The spinal cord is a vital part of the central nervous system (CNS), comprising a tubular bundle of nervous tissue and supporting cells. It extends from the brainstem to the lumbar vertebrae and is integral to transmitting information between the brain and the rest of the body. This guide provides an overview of the macroscopic anatomy, membranous coverings, blood supply, and clinical considerations related to the spinal cord.

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Anatomical Position and Structure

Overview

• Shape and Appearance: Cylindrical, greyish-white structure.
• Course:
  • Originates as a continuation of the medulla oblongata.
  • Extends inferiorly through the vertebral canal.
  • Terminates at the L2 vertebral level, forming the conus medullaris.
  • Occupies approximately two-thirds of the vertebral canal.

Key Features

Feature	Description
Cervical Enlargement	Located at C4–T1; origin of the brachial plexus.
Lumbar Enlargement	Found between T11–L1; origin of lumbar and sacral plexi.
Cauda Equina	Bundle of spinal nerves arising from the conus medullaris.
Depressions	– Anterior median fissure: deep groove on anterior surface. – Posterior median sulcus: shallower groove on posterior surface.

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Spinal Meninges

The spinal cord is surrounded by three protective membranes called meninges, which also contain cerebrospinal fluid (CSF).

Meningeal Layers

Layer	Description
Dura Mater	Outer layer: extends from the foramen magnum to the filum terminale. Surrounded by the epidural space.
Arachnoid Mater	The middle layer separates from the pia mater via the subarachnoid space, which contains CSF.
Pia Mater	Inner layer: closely adheres to the spinal cord and nerve roots, forming denticulate ligaments for stability.

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Formation of Spinal Nerves

• Structure: Each spinal nerve originates from anterior (motor) and posterior (sensory) roots.
• Division:
  • Posterior rami: Supply synovial joints of the vertebral column, deep back muscles, and skin.
  • Anterior rami: Supply motor and sensory fibers to most of the body.

Feature	Description
Cauda Equina	Bundle of nerve roots (L2–S5) that extend beyond the conus medullaris.

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Vasculature

Arterial Supply

• Longitudinal Arteries:
  • Anterior Spinal Artery: Supplies the anterior 2/3 of the spinal cord.
  • Posterior Spinal Arteries: Paired arteries supply the posterior 1/3 of the spinal cord.
• Segmental Medullary Arteries: Reinforce longitudinal arteries, including the artery of Adamkiewicz.

Venous Drainage

• Spinal Veins: Three anterior and three posterior veins, draining into vertebral venous plexuses.

Blood Supply Feature	Description
Artery of Adamkiewicz	Supplies the inferior two-thirds of the spinal cord; it is vital for its vascular integrity.
Vertebral Plexuses	Drain into systemic segmental veins and dural venous sinuses.

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Clinical Relevance

Cauda Equina Syndrome

• Cause: Compression of the cauda equina due to herniated discs, tumors, or trauma.
• Signs:
  • Saddle anesthesia.
  • Incontinence (urinary or fecal).
  • Reduced anal tone.
  • Lower limb paralysis or sensory loss.
• Management: Requires urgent MRI and surgical decompression within 36 hours.

Spinal Cord Infarction

• Cause: Ischemia due to arterial supply interruption (e.g., trauma, vascular disease).
• Signs: Muscle weakness, paralysis, and loss of reflexes.
• Management: Reverse the underlying cause promptly.

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Points to Remember

1. The spinal cord ends at the L2 vertebral level, forming the conus medullaris.
2. The cauda equina is a bundle of nerve roots extending below the conus medullaris.
3. The spinal meninges (dura, arachnoid, and pia mater) provide protection and support.
4. Blood supply is critical to the spinal cord’s function, with the artery of Adamkiewicz being particularly significant.
5. Clinical conditions like cauda equina syndrome and spinal cord infarction require immediate intervention.