NEURAL PLATE Three Layers: Endoderm, Mesoderm, Ectoderm
Neurons are produced from a subset of ECTODERMAL cells.
The ectodermal cells that become neurons receive a signal from the cells in the medodermal layer called a “neuralizing signal” and that signal triggers a change in the cells in a small region of the ectodermal layer. That begins the developmental cascade of events that will eventually result in the formation of the Central Nervous System (CNS)
Thus, a message from one set of cells is required to trigger developmental change in another set of cells: The capacity to become a brain cell is inherent in the cell (lineage), but requires a signal from the environment -- the message to become a brain cell does not exist in the ectodermal cell itself (commitment).