Origin of neurons

     Neurons are post-mitotic cells, that's mean, who lost the ability to divide. Once through cell division (mitosis), which marks the beginning of their existence, these cells survive and extend their neuritics frequently until the death of the whole organism. 
   The formation of the nervous system of a vertebrate is done in several phases. The first is the differentiation of stem cells into neurons, followed by migration and differentiated cells to their final location, and finally the extension of their neuritics and establishing connections.These steps extend across the embryonic life in mammals. They take place in accordance with the general principles governing the development of the whole body: stem cells and neurons derived, have the property to "read" the molecular landscape. the fabric
life is full of chemical signals in the form of embedded in the living tissue or freely diffusing molecules in the extracellular medium. The contact of the cells with these molecules triggers and supports their multiple stages of differentiation and development.

    In vertebrates, neurons derived from cells initially contained in two specific regions of the embryo, the neural tube and neural crest. The molecular landscape in these two regions is heterogeneous and therefore the fate of stem cells depends on their precise location. For example, neurons in the sympathetic nervous system from the neural crest chest and those of the parasympathetic nervous system, cervical neural crest. Stem cells from the thoracic region may nevertheless become parasympathetic neurons, provided they are transplanted in the cervical region. Conversely, sympathetic neurons can be formed from transplanted into the thoracic region cervical cells. Stem cells have therefore, at least in some cases, may adopt the fate of cells counterparts in the region in which they are transplanted.