Neuroembryology Lecture Notes

Introduction

• Topic: Neuroembryology
• Focus: Basic embryology of the nervous system (neuralation)
• No discussion of abnormalities
• Goal: Understand high-yield embryological concepts

Early Embryonic Development

• Trilaminar Disc: Initial structure before organ development
  • Layers:
    • Ectoderm: Forms skin and nervous system (neuroectoderm)
    • Mesoderm: Connective tissues (bones, muscles, cartilage)
    • Endoderm: Internal organs (liver, gut)

Neuralation Process

• Week 3: Neural system formation begins
  • Notocord: Mesodermal origin, crucial for development
  • Sonic Hedgehog Transcription Factor: Induces changes in neuroectoderm, helps separate cerebral hemispheres

Formation of Neural Structures

1. Neuroectoderm transforms:

   • Invagination forms Neural Groove.
   • Neural Folds develop on either side of the groove.

2. Neural Crest:

   • Forms from the tips of neural folds.
   • Important for peripheral nervous system development.

3. Neural Tube:

   • Formed from the closure of the neural groove.
   • Gives rise to CNS neurons, ependymal cells, astrocytes.
   • Provides nucleus pulposus for intervertebral discs.

Nucleus Pulposus and Disc Herniation

• Nucleus Pulposus:
  • Gelatinous center of intervertebral discs (90% water).
  • Provides flexibility and reduces friction between vertebrae.
• Disc Herniation: Occurs when nucleus herniates through the anulus fibrosus, potentially compressing the spinal cord.

Closure of the Neural Tube

• Neural Tube Closure Process:

  • Day 23: Closure of middle part
  • Day 25: Anterior neuropore closes
  • Day 27: Posterior neuropore closes
  • Week 4: Complete closure expected

• Openings:

  • Anterior Neuropore: Leads to brain development
  • Posterior Neuropore: Leads to spinal cord development

• Neural Tube Defects: Result from failures in closure

Conclusion

• Recap of key points on neuralation and its significance
• Next lecture: Discussion on neural tube defects