Embryonic development of the spinal cord
The spinal cord develops from the lower portion of the embryonic neural tube. By the sixth week of development, the cord has two clusters of neuroblasts that have moved outward from the original neural tube. they are recognizable as the dorsal alar plate and a ventral basal plate. Neuroblasts from the alar plate develop into interneurons and the neuroblasts from the basal plate develop into motor neurons that have axons that grow out to the effector organs. Axons that come from the alar plate cells form the white matter of the spinal cord and it grows down along the cord. As the embryo continues to develop the two plates expand and produce the central mass of gray mater in the adult spinal cord. Cells from the neural crest that lie next to the cord develop into dorsal root ganglia. These contain sensory neuron cell bodies that send their axons to the dorsal part of the spinal cord.