The Histogenesis of Nuclei and Cortices

Abstract

In Chapters 7 through 9, we examined the differential expansions and foldings that produce the gross shape of the adult CNS. While this morphogenesis proceeds, the interior of the CNS is busy establishing its various cell groups and fiber tracts. Since all neurons are postsynaptic targets, they must arrive in the right place at the right time in order to receive the axons growing to meet them. Once in their proper positions, neurons elaborate their characteristic shapes and express the proper complement of neurotransmitters and receptors. In this chapter, we will consider some examples of how neurons migrate and assemble themselves into cortices and nuclei. We’ll examine the molecular determinants of neuronal and glial shape and other phenotypic traits. Finally, we’ll examine the factors that regulate the ultimate number of neurons that survive to CNS maturity. We’ll learn that the histogenesis of the cortices and nuclei of the CNS depends on interactions between its cells, interactions that are mediated by specific cell surface molecules. Any failure to express such molecules in the proper time and place will lead to malformed and dysfunctional central structures. The question of how axons bundle into tracts, find their way to their appropriate targets, and form synapses on the newly generated cortices and nuclei will be discussed in Chapter 31.