development of the nervous system

• The first week of development of the fertilized egg to the button embryonic.

The human body is the result of a merger between a male sex cell (sperm) and a female sex cell (ovum). Upon fertilization, the divisions cell (or mitosis) successive lead to the formation of an egg is 2, then 4, 8, 16, 32, 64 cells. These will then push to the periphery to form a button
embryo, which derive the embryo. 

• The second week of development: the embryonic disc at first slip.

At this stage, the cells of the embryonic bud keep dividing and begin to differentiate by having two superposed layers, the most superficial give entire future embryo.

•  The third week of development of the neural plate to neural groove.

This first sheet differs in turn three layers, the most superficial epidermal ectoderm give the skin and the entire nervous system. Ectodermal region located on the center line is differentiated into neural plate, while the rest operates to give the epidermis, the outermost layer of the skin. Then, the neural plate thickens unevenly: the thin part will become the spinal cord and the brain give swollen portion. The lateral edges of the neural plate and forming a raised neural groove.

• The fourth week of development of the neural groove to neural tube and neural crest.   

The embryo is the overall shape of the newborn and the future. Both edges of the neural groove meet on line
middle to form the neural tube, which becomes the system CNS. When the neural tube closes, longitudinal strip detaches from each of its two sides, forming the neural crest, which will give the peripheral nervous system.

• Over the coming weeks and months.  

 The neural tube forms the entire Central Nervous System:
The posterior part of the neural tube remains hydrochloric cylindrical, straight, small arms and gives the spinal cord. Its anterior portion swollen, further increases considerably in volume and undergoes many curves and changes which result from the different parts of the brain: the brainstem, cerebellum and brain. Together, the cavity of the neural tube wife changes its shape and ventricular wall cavities filled with cerebrospinal fluid (CSF).
The neural crest forms Peripheral Nervous System:
The neural crest cells give rise to neurons of dorsal root ganglia, which are the primary sensory neurons, as well as Schwann cells (cells myelinating PNS).

• Manufacturing cells Central Nervous System.

The neural tube wall is made of neural stem cells. After proliferation, and these precursors derived differ: to neurons or to cells glia. As for microglial cells, which are mainly derived from blood cells (monocytes), which come from another germ layer.