Development of the Spinal Cord

The spinal cord, and with it the Central Nervous System (CNS), begin its development in the 3rd week of the embryonic period.

At approximal 21 days after fertilization, the ectodermal germ layer is pear shaped, and broder in the cephalic (head) than in the caudal region. Around this time, the Epiblast cells move towards the primitive streak and slip under it to migrate along the median line cranially to form the notochordal process and later Notochord. The appearance of the notochord generates the overlying ectoderm to elevate and therby forming the Neural Plate. The cells found in the neural plate represent the neuroectoderm. It´s occurence represent the beginning in the process of neurulation.

Neurulation
Is the process where the neural plate forms the neural tube. At the end of the 3rd week, the lateral edges of the neural plate rises due to elevation caused by the underlying migration ef epiblast cells, and forms the so called neural folds. Between these neural folds, a depressed region appear, namely the neural groove. The neural folds on each side of the neural groove fuse together. This fusion proceeds from cranial to caudal. The result of this fusion is the formation of the neural tube Until the fusion is completed at about day 28, the cephalic and caudal ends of the neural tube communicate with the surrounding amniotic cavity by the cranial and caudal neuropores. When these neuropores are closed, the CNS is represented by the closed neural tube with a broader cephalic portion, the brain vesicles and the caudal portion which represent the spinal cord

Spinal Cord
The wall of the neural tube consist of neuroepithelial cells. They are significant due to their pseudostratified epithelial formation. After cloure of the neural tube, these cells divide and therby increase rapidily in number, and give rise to the primitive nerve cells, Neuroblast. The neuroblast cells accumulate themself around the neuroepithelial layer and form the so called Mantle Layer which later will form the gray matter of the spinal cord. The lateral layer of the spinal cord is known as the marginal layer and contains nerve fibers which rises from the neuroblast cells in the mantle layer. These fibers become myelinated, which gives this layer the significant white colour and there for this part is called the white matter of the spinal cord.

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