Spinal Cord and Meninges

Spinal Cord Overview - The Neural Highway

• Cylindrical CNS component in vertebral canal.
• Extends from foramen magnum (medulla) to L1 vertebra (adults).

  ⭐ Spinal cord terminates at L1/L2 in adults, but at L3 in neonates.

• Segments: 31 pairs of spinal nerves:
  • 8 Cervical (C1-C8)
  • 12 Thoracic (T1-T12)
  • 5 Lumbar (L1-L5)
  • 5 Sacral (S1-S5)
  • 1 Coccygeal (Co1)
• Enlargements:
  • Cervical (C5-T1): For upper limbs (brachial plexus).
  • Lumbosacral (L1-S3): For lower limbs (lumbosacral plexus).
• Conus Medullaris: Tapered inferior end.
• Cauda Equina: "Horse's tail"; lumbosacral nerve roots.
• Filum Terminale: Pial extension from conus; anchors to coccyx.

Meningeal Layers - Protective Wrappings

• Three protective membranes (meninges) cover the spinal cord.
• 📌 Mnemonic: PAD (Pia, Arachnoid, Dura - from innermost to outermost).
  • Pia Mater: Innermost, vascular, adheres to cord. Forms filum terminale internum, denticulate ligaments.
  • Arachnoid Mater: Middle, avascular, web-like. Lines dural sac.
  • Dura Mater: Outermost, tough. Forms dural sac (thecal sac), ends at S2 vertebra. Epidural space external.
• 

⭐ The subarachnoid space (between arachnoid and pia mater) contains Cerebrospinal Fluid (CSF) & major spinal vessels.

Internal Cord Structure - Cord's Inner Circuitry

• Grey Matter (Central H-shape): Neuron cell bodies, dendrites, unmyelinated axons, glial cells.
  • Posterior Horn: Sensory nuclei (e.g., substantia gelatinosa for pain/temp). Receives sensory input.
  • Anterior Horn: Motor nuclei (alpha for muscle contraction, gamma for muscle spindle tone). Sends motor output.
  • Lateral Horn (Thoracolumbar T1-L2): Sympathetic preganglionic neurons.
  • Intermediate Zone: Interneurons, Clarke's nucleus (proprioception to cerebellum).
• White Matter (Outer Region): Myelinated axons in funiculi (columns) containing tracts.
  • Dorsal Funiculus: Ascending sensory (Fasciculus Gracilis - lower body, Cuneatus - upper body).
  • Lateral Funiculus: Mixed (Lateral Corticospinal - motor; Lateral Spinothalamic - pain/temp).
  • Anterior Funiculus: Mixed (Anterior Corticospinal - motor; Anterior Spinothalamic - crude touch/pressure).

⭐ The lateral corticospinal tract, controlling voluntary skilled limb movements, decussates (crosses over) at the pyramids of the medulla oblongata.

Spinal Cord Vasculature - Lifeline Arteries & Veins

• Arterial Supply:
  • 1 Anterior Spinal Artery (ASA): From vertebral arteries; supplies anterior 2/3 of cord.
  • 2 Posterior Spinal Arteries (PSAs): From vertebral arteries or PICA; supply posterior 1/3.
  • Segmental/Radicular Arteries: Reinforce ASA & PSAs; includes Artery of Adamkiewicz.
• Venous Drainage:
  • Anterior and Posterior Spinal Veins.
  • Drain into Internal Vertebral Venous Plexus (Batson's plexus).

⭐ The Artery of Adamkiewicz (Great Anterior Radicular Artery of Luhska), typically arising from T9-T12 on the left, is crucial for thoracolumbar cord irrigation; its occlusion can lead to Anterior Spinal Artery Syndrome below the lesion level.

Clinical Correlations - Cord in Crisis

• Lumbar Puncture (LP):
  • Site: Adults L3-L4 / L4-L5 interspace; Children L4-L5 / L5-S1.

  ⭐ Structures pierced (superficial to deep): Skin → Subcutaneous tissue → Supraspinous lig. → Interspinous lig. → Ligamentum flavum → Epidural space → Dura mater → Arachnoid mater → Subarachnoid space.

• Disc Herniation: Common sites: L4-L5, L5-S1. Can cause radiculopathy or cord compression.
• Spinal Cord Compression: Urgent MRI & management. Causes: trauma, tumor, disc, abscess.
• Cauda Equina Syndrome: ⚠️ Surgical emergency! Presents with saddle anesthesia, bowel/bladder dysfunction, leg weakness. oka

High‑Yield Points - ⚡ Biggest Takeaways

• Spinal cord terminates at L1-L2 (adults), L3 (newborns).
• Dural sac and subarachnoid space (with CSF) end at S2 vertebra.
• Lumbar puncture safely performed at L3-L4 or L4-L5 interspace.
• Epidural space contains fat and the internal vertebral venous plexus.
• Pia mater forms denticulate ligaments (anchoring cord laterally) and filum terminale (anchoring inferiorly).
• Anterior Spinal Artery supplies anterior 2/3 of the spinal cord; two Posterior Spinal Arteries supply posterior 1/3.
• Artery of Adamkiewicz (major anterior segmental medullary artery) typically at T9-L2, crucial for lower cord perfusion.