Lecture Notes on Spinal Cord Pathways and Clinical Syndromes

Overview

• Common issue: Lecturers often focus too much on technical details rather than clinical implications.
• Focus of the lecture: Understanding key spinal cord pathways and their relevance for medical exams.
• Emphasis on clinically manifested pathways: Posterior column, corticospinal tract, lateral spinothalamic tract.
• Introduction of Brown-Sequard syndrome, a high-yield topic.

Key Spinal Cord Pathways

1. Posterior Column Pathway

• Function: Controls discriminative touch (fine touch) and proprioception.
• Pathway Details:
  • 3 synapses involved.
  • Sensory neuron → Dorsal column nuclei (first synapse).
  • Decussation at the medial lemniscus → Thalamus (second synapse).
  • Thalamus → Primary sensory cortex (third synapse).
• Mnemonic: "Some Doctors Think Politically" (SDTP).
  • PC = Politically Correct for Posterior Columns.
  • Mnemonic helps associate with non-discrimination, as issues here lead to discrimination problems.

2. Corticospinal Tract

• Function: Controls movement via upper motor neurons.
• Pathway Details:
  • Starts at primary motor cortex → Internal capsule → Medullary pyramids (splits into anterior and lateral corticospinal tracts).
  • Lateral corticospinal tract is most significant (75-90% neurons).
  • Synapse at anterior horn connecting to lower motor neurons.
• Mnemonic: "Prickly Plants Lack Moisture" (PPLM).
  • Cacti have spines (corticospinal), are prickly plants, live in deserts, and lack moisture.
  • PPLM = Primary Motor → Pyramids → Lateral CST → Movement.

3. Lateral Spinothalamic Tract

• Function: Responsible for pain and temperature sensation.
• Characteristics:
  • Manifests symptoms 2-3 segments below the injury on the contralateral side.
  • Associated with Lissauer's tract.
• Mnemonic: "Lower Segment Three" (LST).
  • LST = 2-3 segments below, opposite side.

Brown-Sequard Syndrome

• Results from hemisection of the spinal cord, affecting all three pathways.
• Clinical Presentation:
  • Corticospinal and posterior column injuries manifest ipsilaterally at the level of injury.
  • Lateral spinothalamic tract issues appear contralaterally, 2-3 segments below.
• Example:
  • Injury at T8 on the right:
    • Upper motor neuron signs below T8 ipsilaterally.
    • Discriminative touch issues from T8 down ipsilaterally.
    • Pain and temperature sensation loss at approximately T10 on the contralateral side.

Summary

• Key spinal cord pathways relevant for USMLE/COMLEX include corticospinal, posterior columns, and lateral spinothalamic tract.
• Understanding of pathway function and clinical implications is crucial for diagnosing and solving exam problems related to Brown-Sequard syndrome and similar spinal cord injuries.