The neural tube is an embryonic anlage in early pregnancy that is found not only in humans but in all vertebrates. As development proceeds, it gives rise to the central nervous system, the spinal cord, and the brain. If there are disturbances in the formation and further development of the neural tube, severe malformations are the result.
What is the neural tube?
The formation of the neural tube is one of the first differentiations of embryonic cells. It forms on the surface of the outer cotyledon. In humans, this occurs between the 22nd and 28th day after fertilization of the egg. As the precursor of the central nervous system, spinal cord and brain, the undisturbed formation and remodeling of the neural tube is of enormous importance for the further development of the embryo.
Anatomy and structure
At the beginning of the formation of the neural tube, also called neurulation, part of the surface of the embryonic cotyledon thickens. The neural plate emerges from the bulging area between the primordial mouth and the primitive streak. The edges of this neural plate then begin to bulge out further. Between them lies the neural groove, an elongated depression. Finally, the neural ridges reform into neural folds and unite above the neural groove to form the neural tube. This development first begins in the middle of the area. Shortly thereafter, the anterior opening closes and finally the posterior opening of the neural tube closes. As the ectoderm overlays the neural tube, it migrates into the interior of the embryo where it forms a cavity. This also forms neural crests, which are found on both sides of the neural tube. These later become various organs and elements of the body. The neural tube itself forms the basis for the development of the brain, spinal cord and central nervous system. The anterior region of the neural tube gives rise to the various parts of the brain as the embryo continues to grow. The spinal cord and central nervous system emerge from the posterior end of the neural tube. The middle region of the neural tube, which has a distinct cavity, becomes the central canal of the spinal cord and gradually fills with fluid. Throughout the course of development, the growing and rounding neural tube determines the external appearance of the embryo. About the middle of the sixth week of embryonic development, nerulation is complete and the remodeling of the neural tube begins.
Function and tasks
Disturbances in the formation and further development of the neural tube are very common. Between one and five children born alive have a neural tube defect. However, the total number is much higher, because pregnancy is usually terminated prematurely in cases of severe malformations detected by screening. Natural abortions in early pregnancy are also not infrequently due to defects of the neural tube. Various clinical pictures are possible in children born alive with neural tube defects. Children with anencephaly completely lack large parts of the brain and the cranial vault. They are usually blind, deaf and without consciousness and usually die shortly after birth. In the case of encephalocele, the brain is present but malformed. It is sometimes located in conspicuous sac-like protrusions outside the bones of the skull, which may be filled with a great deal of fluid. After surgical removal of these protuberances, life is often possible without physical or mental limitations. Hydranencephaly is characterized by the complete or partial absence of various areas of the brain. Since the skull is externally inconspicuous, this defect is only noticed after some time due to severe developmental delays of the child. Children with hydranencephaly have a very short life expectancy. A very rare disorder associated with a malformation of the neural tube is iniencephaly. Affected children usually have a disproportionately large head and have a severe backward curvature of the spine. Of all the neural tube defects, the best known is spina bifida. Although this malformation is colloquially called an open back, it is not necessarily visible from the outside. A common feature of all forms of spina bifida is a cleft formation in the spinal column. Parts of the spinal cord skin or the spinal cord itself bulge into the respective gap.In severe cases, the nerve tissue is not covered by other tissue and is actually exposed. Depending on the severity of spina bifida, the physical impairments differ significantly. Very common are impairments in mobility and disturbances in bladder and bowel function. It is also not uncommon for other malformations to occur along with spina bifida that are due to a neural tube defect. However, spina bifida is the only malformation associated with a developmental disorder of the neural tube that can be operated on in utero today.
Diseases
The causes of disorders in the formation and further development of the neural tube have not yet been conclusively determined. However, an important factor is a deficiency of folic acid in the diet already before, but also during, pregnancy. Studies have shown that an adequate supply of folic acid significantly reduces the number of neural tube defects. It is therefore recommended that all women who wish to have children take folic acid as a dietary supplement. Drug, alcohol or medication abuse by pregnant women can also cause maldevelopments of the neural tube. External influences that can promote the development of neural tube defects include X-rays and other radiation, as well as various environmental toxins. Various infectious diseases may also interfere with the proper formation of the neural tube.
