Embryonic neurodevelopment is an important starting point for gaining an understanding of neurogenesis. It provides a foundational model for how neurons are produced and what happens to them after their birth.
Our discussion on embryonic neurodevelopment will begin with an embryo, which is composed of three distinct layers (endoderm, mesoderm, and ectoderm). Each layer gives rise to different structures of the developing body:
Endoderm- lining of many internal organs
Mesoderm- bones and muscles
Ectoderm- nervous system and skin
The neural plate of the ectoderm forms the neural tube (i.e. neurulation) and the entire central nervous system develops from the walls of the neural tube. Table 1 and Figure 1A outline the major divisions of the neural tube and the major structures that arise from those divisions.
These neuronal structures develop in three stages: (1.) cell proliferation, (2.) cell migration, and (3.) cell differentiation. This page will focus on the development of the cerebral cortex.
1. Cell Proliferation
2. Cell Migration
Cell migration is the movement of newly generated cells to their final destination. Many daughter cells (called neuroblasts) migrate by slithering along thin fibers (radial glial cells) that radiate from the ventricular zone toward the pia (Figure 2).
The cortex is said to be assembled inside-out (new neuroblasts migrate right past those in the existing cortical plate) (Figure 3).
3. Cell Differentiation
This is the stage when a newly generated cell begins to take on the appearance and characteristics of a neuron. Neuronal differentiation occurs first, followed by astrocyte differentiation and then oligodendrocyte differentiation. Figure 4 illustrates the differentiation of a neuroblast into a pyramidal neuron, which is one of the types of neurons found in the cerebral cortex.
While neurons differentiate, they also begin to form connections. Gradually, they form functional circuits.
Click here to learn about the differences between embryonic neurodevelopment/neurogenesis and adult neurogenesis.
Figures 1, 2, 3, and 4 were adapted from illustrations within the following two textbooks:
Bear, M., Connors, B., & Paradiso, M. (2007). Neuroscience: Exploring the Brain (Third Edition). Baltimore: Lippincott Williams & Wilkins.
Purves, D., Augustine, G., & Fitzpatrick, D. (2004). Neuroscience (Third Edition). Sunderland, MA: Sinauer Associates.
Page by Steve Conway