Brain Development


The central nervous system (CNS) begins as germ cells. By around day eighteen of development in the womb, the inner layer of endoderm cells (cells that create vital organs) thicken to form the neural plate (basis for the nervous system).

At this point, cells are already differentiated to become the forebrain, midbrain and hindbrain.

Neurogenesis (birth of neurons), and neuronal migration (movement of neurons to specific predetermined locations), begins and continue until around six months gestation.

In the last trimester of pregnancy, the cerebral cortex develops its characteristic sulci and gyri (peaks and valleys). The frontal, parietal and occipital lobes are formed, and are studied via imaging techniques (ultrasound).

Stages of brain development:

  • Generation of billions of identical neurons
  • Migration of neurons to predetermined locations
  • Separation into specific neurons appropriate for the location
  • Collection of individual neurons to form specialized brain regions
  • Formation of neuronal connections (synaptogenesis)
  • Elimination of under-used connections (synaptic pruning)

If brain development occurs in this order, exposure teratogens (listed below) have potential to impact on the development of specific brain structures or functions.

  • Drugs (e.g. alcohol, heroin, and tobacco).
  • Disease (e.g. rubella).
  • Radiation
  • Parental factors (e.g. age and diet).

Key Terms

 Germ cells – a cell containing half the number of chromosomes of a normal cell, with the ability to form a new individual; a gamete.

Gamete – a mature germ cell, with 23 chromosomes, able to join with the opposite sex in sexual reproduction to form a zygote

 Zygote – a cell resulting from the fusion of two gametes, thus containing 46 chromosomes

Sulci – the characteristic grooves found on the surface of the brain

Gyri – the characteristic ridges found on the surface of the brain

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