Chapter 18: Central Nervous System

Central Nervous System details the embryological development of the central nervous system (CNS), beginning with the formation of the neural plate from the ectoderm and its subsequent folding into the neural tube, a process known as neurulation. It explains the molecular regulation of the spinal cord, where Sonic Hedgehog (SHH) and BMP signaling establish the dorsoventral axis, differentiating the neural tube into the basal plates for motor neurons and alar plates for sensory neurons. The summary traces the expansion of the neural tube into three primary brain vesicles—the prosencephalon, mesencephalon, and rhombencephalon—and their further subdivision into five secondary vesicles that give rise to adult structures including the medulla oblongata, pons, cerebellum, and cerebral hemispheres. Key developmental milestones are highlighted, such as the formation of the diencephalon (giving rise to the thalamus, hypothalamus, and the posterior pituitary) and the telencephalon, which expands to cover the lower brain centers and forms the corpus striatum and commissures like the corpus callosum. The text further explores the distinct dual origin of the pituitary gland from both the stomodeum (Rathke pouch) and the infundibulum. Additionally, the chapter covers the peripheral nervous system, detailing the organization of the twelve cranial nerves associated with hindbrain rhombomeres and the specific contributions of neural crest cells and ectodermal placodes to sensory ganglia. It outlines the autonomic nervous system (ANS), distinguishing between the thoracolumbar sympathetic and craniosacral parasympathetic divisions, and describes the formation of the adrenal gland with its cortex derived from mesoderm and its medulla from neural crest cells. Finally, significant clinical correlates are integrated throughout, explaining the embryological basis of neural tube defects (NTDs) like spina bifida and anencephaly, the importance of folic acid in prevention, and other congenital anomalies such as hydrocephalus, holoprosencephaly, and Hirschsprung disease.