Chapter 1.1 - Cellular Elements, Tissue Organization, Organogenesis

Abstract

This chapter addresses the development, structure and functions of neurons and microglia and discusses the intricate associations that these cells maintain to ensure proper neural function. Anatomically, the vertebrate nervous system consists of two divisions: the central nervous system (CNS) and the peripheral nervous system (PNS). At the cellular level, the CNS is composed of cell types the can be categorized as either neurons, macroglia, microglia or ependymal cells and the development of each of these major cell types have been discussed independently. The cell type responsible for capturing, transforming and conveying neural information within the organism is the nerve cell or neuron. In general, neurons are comprised of three cellular domains known as the cell body, the axon and dendrites. Each subcellular region can be distinguished both by its structural and functional specializations that are essential for maintaining the function of the nerve cell. Microglia are ubiquitously, but not uniformly, distributed throughout the CNS and are often found clustered near blood vessels. Although the morphology of microglia is highly variable, these cells have been categorized into three groups. Regardless of their morphological categorization, the inactivated form of these cells is known as ramified microglia. With the onset of CNS injury or infection, the ramified microglia undergoes a rounding and enlarging of their cell bodies and an up-regulation of complement receptors.