The two principal cell types of the nervous system are, neurons and glial cells. The neural tube develops into brain and spinal cord. The nerve cells and other cells of the nervous system develop from the neural crest cells (formed from raised edges of neural plate).
The process of development of neurons is known as “neurogenesis.” The process of formation of glial cells is known as “gliogenesis.”
Thus, the blanks can be filled with neurogenesis; gliogenesis.