Neurulation: the process by which the neural plate (a dorsal midline ectodermal thickening over the notochord) folds and fuses to form the neural tube, the primordium of brain and spinal cord.
Formation of the Neural Plate and Neural Folds
At about the 16th day, ectoderm overlying the notochord thickens in the midline to form the neural plate; its margins elevate as neural folds, and the sinking centre forms the neural groove.
The neural plate is initially flat and slipper shaped, its narrow end directed toward the primitive node, with somatic mesoderm developing on either side of the notochord.