Central Nervous System Development Notes

Development of the Central Nervous System

A. Overview
  • Three Main Stages of Development:
    • Prenatal Development
    • Postnatal Development:
    • Childhood
    • Adolescence
    • Adulthood
    • Disorders of Neurodevelopment:
    • Autism Spectrum Disorder (ASD)
    • Williams Syndrome
B. Historical vs. Current Perspectives

  • Old View:

    • CNS development was seen as linear with a focus on fixed structure in adulthood.
    • Brain considered stable and unchangeable.

  • Modern Understanding:

    • Plasticity of the Brain: The brain continues to develop and change throughout life due to interactions between genes and environment (e.g., experiences).
C. Prenatal Development of the CNS

  • Process of Gametogenesis:

    • Involves formation of sperm and egg cells through meiosis, followed by fertilization
    • Results in a zygote (46 chromosomes).

  • Early Cellular Development:

    1. Cell Differentiation: Includes neuron, muscle, and glial cell formation.
    2. Cell Migration: Important for cells to reach specific locations.
    3. Functional Connections: Establishing synapses with other cells necessary for communication.
D. Embryonic Development Stages

  1. Induction of the Neural Plate:

    • Formation of the neural plate from the ectoderm driven by signals from the mesoderm.

  2. Neural Proliferation:

    • Neural tube formation takes place with key vesicle development around 40-50 days post-fertilization.

  3. Migration and Aggregation:

    • Neurons migrate following chemical signals; two methods:
      • Somal Translocation
      • Glial-Mediated Locomotion

  4. Axon Growth and Synapse Formation:

    • Axon guidance through (1) Chemoaffinity Hypothesis and (2) Topographic Gradient Hypothesis.

  5. Neuron Death and Synapse Rearrangement:

    • Approximately 50% of neurons produced die to refine synaptic connections.
    • Cell death types:
      • Apoptosis: Clean, programmed cell death.
      • Necrosis: Damage-induced, messy cell death.
E. Neurotrophins
  • Essential for neuronal health and communication, they include:
    1. Nerve Growth Factor (NGF)
    2. Brain-Derived Neurotrophic Factor (BDNF)
    3. Other neurotrophins that handle various functions such as neuronal survival, growth, and synaptogenesis.
F. Disorders Related to CNS Development
  • Neurodevelopmental Disorders:
    • Disorders such as Kallmann Syndrome and Lissencephaly are associated with migration errors.
    • Disorders like schizophrenia, ASD, and dyslexia are linked to improper neuron migration and synapse formation.
G. Understanding Plasticity and Gene-Environment Interaction
  • Case Study: The case of "Genie" highlights the role of experience in developmental outcomes, though specific cases largely emphasize just one branch of the complex gene-environment interaction.
H. Conclusion
  • The understanding of CNS development has evolved to recognize the dynamic interaction between genetic predisposition and environmental influences, shaping the development throughout life.