ABSTRACT
INTRODUCTION AND BACKGROUND General Features of the Mammalian Nervous System It is well established that the nervous system is not an especially vulnerable system relative to other organ systems; however, there are features of the developing nervous system that make it susceptible to developmental perturbations. With these vulnerabilities in mind, the objective of this chapter is to provide an overview of some of the critical aspects of mammalian nervous system development and function for the purpose of developing studies and interpreting data that are applicable to neurodevelopment. The subsequent sections will explore the structure and function of the mammalian nervous system and provide a comparison of developmental endpoints across species when those data are available. As there are entire books dedicated to this topic, the intent of this chapter is not to be all-inclusive; however, it serves to highlight some of the major developmental milestones that require consideration when testing compounds that could potentially disrupt the development of the nervous system. The primary division of the mammalian nervous system is between the central nervous system (CNS), which processes information, and the peripheral nervous system (PNS), which carries information to and from the CNS and the sensory, muscle, and gland cells. In the simplest terms, the CNS includes the brain and spinal cord, and the PNS consists of all the nervous tissue outside the CNS. There are two types of cells in the nervous system: neurons and neuroglial cells, or glia. The neuron is the structural and functional unit of the nervous system. Neurons are specialized for long-distance transmission of electrical stimuli throughout the body. Glial cells, which greatly outnumber neurons, have a variety of supportive functions within the nervous system. Peripheral nerves serve either somatic (skeletal, muscle, skin) or visceral (involuntary muscles and glands) tissues and carry sensory or motor information. Because of the extensive amount of literature on this topic, the focus of the subsequent sections will be development of the CNS, and more specifically, the developing brain.
