| Popis: |
During the past 25 years or so, the use of increasingly sophisticated genetically engineered mutant mice, combined with innovation in the use of molecular tracers for visual detection of cells and extending axons, has dramatically increased our understanding of the mechanisms underlying developmental anatomy of the spinal cord and the peripheral nervous system (PNS). These approaches have also made major contributions to understanding the causes of human neural developmental disorders. This applies to the whole spectrum of nervous system development, from neurulation and neural tube defects through the role of Hox genes in spinal cord regionalization, to the refinement of neural circuits as the early coarse patterns of connectivity of axons to their targets is altered through functional activity. This chapter follows the development of the spinal cord and the PNS from neurulation and neural crest cell (NCC) emigration onward. It includes the role of morphogens in the anteroposterior (AP) and dorsoventral (DV) patterning of the spinal cord; the establishment of central and peripheral segmentation; spinal cord regionalization; formation of the motor, sensory, parasympathetic, sympathetic, and enteric elements of the PNS; and the development of mixed spinal nerves and their division into dorsal and ventral branches within the limb buds. While particularly interesting new observations are mentioned, such as the recent discovery that postganglionic parasympathetic nerves originate from Schwann cell precursors, the major aim of the chapter is to provide a concise, accessible, and up-to-date summary of the essential elements of the system and to give references to sources that supply more detailed molecular information. |
