Neural plate

In human embryology, formation of neural plate is the first step of neurulation. It is created by a flat thickening opposite to the primitive streak of the ectoderm.

Development
During the stage of neural plate formation the embryo consists of three cell layers: the previously mentioned ectoderm that eventually forms the skin and neural tissues, the mesoderm that forms muscle and bone, and the endoderm that will form the cells lining the digestive and respiratory tract. BMP-4 is a transforming growth factor that causes the cells of the ectoderm to differentiate into skin cells.

Without BMP-4 the ectoderm cells would automatically develop into neural cells. Axial mesoderm cells under the ectoderm secrete inhibitory signals called chordin, noggin and follistatin. These inhibitory signals inhibit BMP-4 and as a result cause the overlying cells of the ectoderm to develop into neural cells. The cells in the ectoderm that circumvent these neural cells do not receive the BMP-4 inhibitor signals and as a result BMP-4 induces these cells to develop into skin cells.

As the neural plate develops, it becomes surrounded by neural folds, which eventually create the cylindrical neural tube. This process is termed primary neurulation.