Differentiation and Growth of Nerve Cells

Abstract

The diversification of the neuronal stem cells into thousands of anatomically and functionally different types of neurons is termed differentiation. Neural differentiation is initiated by the process of determination or specification which programmes the cells for their future course of development. Because the key to understanding the morphological differentiation of nerve cells is to be found in the early events occurring during neural development, the latter deserve to receive a considerable amount of our attention in this chapter. By contrast, I shall give less attention to the overt structural changes in differentiating young neurons which many authors have vested with great developmental significance. These fine structural changes in the developing nerve cells are interesting, but they are merely expressions of earlier steps in cell differentiation and cannot be understood without first considering the developmental programmes which precede visible changes in cellular pheno-types. The large number of different neurophenotypes are the terminal branches of a developmental tree which stems from the genotype and is shaped by epigenetic factors such as hormones and cellular interactions which modify the development of embryonic nerve cells. We should also try to see how these neurophenotypes represent evolutionary solutions to environmental challenges.