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Objectives
After studying this chapter, you should be able to:
Explain how the neural tube and neural crest cells are established during neurulation.
Trace the development of the central nervous system (CNS) from the neural tube, including the contributions of the layers of the neural tube to gray and white matter structures, and following the development of the primary and secondary brain vesicles.
Describe the formation of the supportive structures of the CNS, including the ventricles and meninges.
Trace the contributions of the neural crest cells to the peripheral nervous system (PNS), including the sensory ganglia of the spinal and cranial nerves and the autonomic ganglia.
Relate the motor and sensory components of the PNS and their targets to their embryonic origins.
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ORIGINS OF THE NERVOUS SYSTEM
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Nervous system development begins during week 3 with neurulation, or formation of the neural tube (Figure 10-1).
The notochord induces the cells of the ectoderm overlying it to thicken and form the neural plate (see Chapter 1).
The plate then folds into the neural groove with raised neural folds on each side. The cells at the peaks of these folds are the neural crest cells.
The neural folds bend medially toward each other and fuse in the midline, closing the neural tube and separating it from the rest of the ectoderm (Clinical Box 10-1). Simultaneously, the neural crest cells detach from the neural tube and ectoderm and assume a position dorsolateral to the neural tube.
Neural tube closure begins in the cervical region and proceeds from there in the cranial and caudal directions.
The cranial and caudal open ends of the neural tube are named the cranial neuropore and caudal neuropore, respectively. The cranial neuropore closes on day 25, and the caudal neuropore closes on day 28.
The neural tube gives rise to the brain and spinal cord, which comprise the CNS.
The neural crest cells give rise to the neurons and glia of the PNS and contribute to the meninges.
Neural crest cells also form craniofacial cartilage and bone (see Chapter 2 and 9), the conotruncal septum of the heart (see Chapter 4), and the chromaffin cells of the adrenal medulla (see Chapter 7), among other derivatives.
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