Lecture Notes: Understanding Spinal Cord Pathways

Introduction

• Lecture addresses common confusion in neurology regarding spinal cord pathways.
• Focus on high-yield facts for boards, not minute details.
• Objective: Understand pathways and their clinical manifestations.

Key Spinal Cord Pathways

1. Posterior Column Pathway

   • Controls discriminative touch (fine touch) and proprioception.
   • Pathway Synapses:
     • Sensory neurons send signals to dorsal column nuclei.
     • Decussates at medial lemniscus to thalamus.
     • Final synapse to primary sensory cortex.
   • Mnemonic: PC (Politically Correct) - Posterior Columns, "Some Doctors Think Politically" (S: Sensory, D: Dorsal, T: Thalamus, P: Primary cortex).

2. Corticospinal Tract

   • Upper motor neurons from the motor cortex control movement.
   • Pathway:
     • Descends from primary motor cortex through internal capsule and medullary pyramids.
     • Splits into anterior and lateral corticospinal tracts.
     • Lateral corticospinal is the focus (90% of neurons).
     • Synapses at anterior horn (lower motor neuron).
   • Mnemonic: PPLM (Primary motor, Pyramids, Lateral corticospinal, Movement).
   • Analogy: Cactus (prickly plants lack moisture) - spines remind of corticospinal tract.

3. Lateral Spinothalamic Tract

   • Responsible for pain and temperature sensation.
   • Manifests 2-3 segments below the level of injury on the contralateral side.
   • Key Fact: Unlike other pathways, symptoms appear on the opposite side.
   • Mnemonic: LST (Lower Segment Three) - 2-3 segments below.

Brown-Séquard Syndrome

• Definition: Hemisection of the spinal cord affecting all three pathways.
• Symptoms:
  • Corticospinal Tract: Upper motor neuron signs below the level of injury (ipsilateral).
  • Posterior Columns: Loss of discriminative touch (ipsilateral, same level).
  • Lateral Spinothalamic Tract: Pain and temperature loss 2-3 segments below, contralateral.
• Example:
  • Injury at T8 on the right:
    • Corticospinal and posterior column issues on the right at T8 and below.
    • Spinothalamic issues on the left, starting 2-3 segments below T8.

Summary

• These pathways are high-yield for board exams.
• Understand the synapses and mnemonic strategies for easy recall.
• Use Brown-Séquard syndrome to integrate understanding of pathways.
• Practice questions to solidify understanding.