Lecture on Nervous System Development

Overview

• Continuation of the discussion on gastrulation and the development of the notochord.
• Focus on the process of developing the nervous system from this stage.

Formation of Germ Layers

• Trilemma Nordisk: Formation of ectoderm, mesoderm, and endoderm.
• Notochord formation from mesoderm-derived cells during day 15-17.

Role of Notochord

• Notochord releases growth factors (e.g., fibroblast growth factors, transforming growth factor-beta, Wnt pathway) around day 17.
• These factors induce ectodermal cell proliferation, thickening to form the neural plate.

Development of the Neural Plate

• Begins involution process: central part of the plate is pulled down, edges move towards center.
• Formation of neural folds and neural groove.
• Emergence of neural crest cells around neural folds.

Timing of Events

• Neural plate forms around day 17.
• Neural folds, groove, and crest cells appear around day 18.
• Neural folds fuse, forming the neural tube by day 21.

Importance of Folate

• Necessary for closure of anterior and posterior neuropores.
• Lack of folate can lead to defects such as anencephaly, spina bifida.
• Recommended folate intake: 3-5 mg during pregnancy.

Neuropore Closure

• Anterior neuropore closes by day 24.
• Posterior neuropore closes by day 26.

Vesiculation

• Neural tube develops into central nervous system via vesiculation.
• Formation of primary vesicles:
  • Prosencephalon (forebrain)
  • Mesencephalon (midbrain)
  • Rhombencephalon (hindbrain)
• Further development into secondary vesicles:
  • Telencephalon, Diencephalon from Prosencephalon
  • Mesencephalon remains midbrain
  • Metencephalon, Myelencephalon from Rhombencephalon

Structures from Vesicles

• Telencephalon: Cerebrum
• Diencephalon: Thalamus, Hypothalamus
• Mesencephalon: Midbrain
• Metencephalon: Pons, Cerebellum
• Myelencephalon: Medulla
• Remaining structure: Spinal cord

Neural Crest Cell Differentiation

• Neural crest cells migrate and differentiate into:
  • Melanocytes
  • Adrenal medulla chromaffin cells
  • Enteric nervous system (submucosal and myenteric plexuses)
  • Dorsal root and sympathetic ganglia
  • Leptomeninges (pia mater, arachnoid mater)
  • Cranial nerves (V, VII, IX, X)
  • Bones and muscles of head and neck

Development of Spinal Cord from Neural Tube

• Neural tube's three layers: Marginal, Mantle, Neuroepithelial zones.
• Formation of alar and basal plates:
  • Alar plate: Posterior gray horn (sensory)
  • Basal plate: Anterior gray horn (motor)

Conclusion

• This lecture covered the neurulation process and early stages of CNS development.
• Next session to cover placental development.

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