Spinal Cord Anatomy

Spinal Cord 101 - The Grand Design

• Location: CNS, vertebral canal. Extends from foramen magnum to Conus Medullaris (L1-L2 adult). Filum terminale to coccyx.
• Segments: 31 pairs: 8C, 12T, 5L, 5S, 1Co.
  • 📌 Mnemonic: Breakfast at 8, Lunch at 12, Dinner at 5 (twice for L, S).
• Enlargements: Supply limbs.
  • Cervical (C5-T1): Brachial plexus (upper limb).
  • Lumbosacral (L1-S3): Lumbosacral plexus (lower limb).
• Cross-section:
  • Inner Grey Matter (H-shape): Cell bodies. Horns: Dorsal (sensory), Ventral (motor), Lateral (T1-L2, autonomic).
  • Outer White Matter: Myelinated tracts. Funiculi/Columns: Dorsal, Lateral, Ventral.

⭐ Spinal cord ends at L1-L2 in adults, L3 in neonates. Critical for lumbar puncture site selection to avoid iatrogenic injury.

Ascending Tracts - Sensory Express Lane

• Dorsal Column-Medial Lemniscus (DCML): Fine touch, vibration, proprioception.
  • 1st Order: DRG → Fasciculus Gracilis (T6↓, legs) / Fasciculus Cuneatus (T6↑, arms).
  • 2nd Order: Nucleus Gracilis/Cuneatus (Medulla). Decussates → Medial Lemniscus.
  • 3rd Order: VPL (Thalamus) → Somatosensory Cortex.
  • 📌 Mnemonic: "Dorsal columns for Dolce & Gabbana (D&G) - Fine things."
• Spinothalamic Tract (Anterolateral System - ALS): Pain, temperature, crude touch.
  • 1st Order: DRG → Dorsal Horn (e.g., Substantia Gelatinosa).
  • 2nd Order: Dorsal Horn. Decussates (Anterior White Commissure) → Ascends.
  • 3rd Order: VPL (Thalamus) → Somatosensory Cortex.

  ⭐ Lesion causes contralateral loss of pain & temperature 1-2 segments below the lesion level.

• Spinocerebellar Tracts: Unconscious proprioception to cerebellum.
  • Dorsal (DSCT), Ventral (VSCT), Cuneocerebellar, Rostral. Mostly ipsilateral input to cerebellum.

Descending Tracts - Motorway Mania

• Pyramidal Tracts (Voluntary Movement)

  • Corticospinal (CST): Cerebral Cortex. Precise, skilled voluntary movements.
    • Lateral CST: ~80-90% fibers; decussates medulla (pyramidal decussation) → limbs.
    • Anterior CST: ~10-20% fibers; uncrossed/decussates spinal level → axial/proximal.

  ⭐ UMN lesion (e.g., CST): spastic paralysis, hyperreflexia, Babinski sign.

• Extrapyramidal Tracts (Involuntary/Postural Control)

  • Rubrospinal: Red Nucleus; decussates midbrain. Flexors ↑, extensors ↓ (upper limb).
  • Vestibulospinal: Vestibular Nuclei.
    • Lateral: Ipsilateral; balance, extensor tone.
    • Medial: Bilateral; head/neck position.
  • Reticulospinal: Reticular Formation.
    • Pontine (Medial): Ipsilateral; extensors ↑, posture.
    • Medullary (Lateral): Bilateral; extensors ↓, muscle tone ↓.
  • Tectospinal: Superior Colliculus; decussates midbrain. Reflex head/neck to visual stimuli. 📌 Mnemonic (Origins): "Red Vest Really Tough" (Red Nucleus, Vestibular Nuclei, Reticular Formation, Tectum)

Blood & Damage - Cord SOS

• Arterial Supply:
  • Anterior Spinal Artery (ASA): supplies anterior 2/3rds.
  • Posterior Spinal Arteries (PSAs): supply posterior 1/3rd.
  • Artery of Adamkiewicz: major supply to lumbosacral cord, typically T9-L2.
• Key Syndromes & Lesions:
  • Anterior Cord Syndrome: ASA occlusion. Loss of motor, pain, temperature. Proprioception/vibration spared.

    ⭐ Most common spinal cord infarction.

  • Central Cord Syndrome: Cervical hyperextension. Upper limb > lower limb weakness. Sacral sparing.
  • Brown-Séquard Syndrome: Hemisection. 📌 Ipsilateral: motor, vibration, proprioception loss. Contralateral: pain, temperature loss. oka

High‑Yield Points - ⚡ Biggest Takeaways

• Spinal cord typically terminates at L1-L2 in adults, and L3 in newborns.
• There are 31 pairs of spinal nerves: 8C, 12T, 5L, 5S, 1Co.
• Cervical (C5-T1) and Lumbar (L2-S3) enlargements correspond to limb innervation.
• Anterior Spinal Artery supplies the anterior 2/3; Posterior Spinal Arteries (paired) supply posterior 1/3.
• Key tracts: Dorsal columns (vibration, proprioception), Spinothalamic (pain, temperature), Corticospinal (voluntary motor).
• Lumbar puncture is safely done at L3-L4 or L4-L5, accessing CSF in the cauda equina.