The brain is the part of the CNS that is located in the head or skull of vertebrates. It is the central control organ of the body.
The development of the brain begins with the occlusion of the neural tube. At the cranial end of the neural tube three vesicles are formed. The wall of the neural tube is formed by undifferentiated neural epithelium. The neural epithelial cells divide and form two new cell types: the primitive neurons, the so-called neuroblasts and the glioblasts (primitive scaffold cells of the neural tube). The neuroblasts form the motor neurons of the ventral horn and the sensory neurons of the dorsal horn. Neuroblasts continuously migrate into the marginal layer and form a ventral and dorsal thickening: the motor basal plate and the sensory alar plate. Between the two is the Sulcus limitans. It provides neurons of the autonomous nervous system. Between the two alar plates is the roof plate, between the basal plates is the floor plate. Around the basal and alar plates is the marginal zone. As soon as the formation of neuroblasts is finished glioblasts are formed. These migrate into the marginal layer and differentiate into protoplasmatic and fibrillary astrocytes.
