Neurulation: the process of formation of the neural tube

Neurulation is the process by which the neural tube is formed. during intrauterine development. The neural tube is essential for the differentiation of cells of the central nervous system, while the neural crests, structures associated with the one in question, are for the formation of the nervous system peripheral.

In this article we will describe the two phases of neurulation or formation of the neural tube: the primary, in which the neural plate begins to fold back on itself, and the secondary, which culminates this process and allows the subsequent development of the nervous system.

• Related article: "The development of the nervous system during pregnancy"

What is the neural tube?

The neural tube is an embryonic structure that forms during the first month of gestation; Specifically, the tube has just closed around the 28th week after fertilization. It is the precursor of the central nervous system, composed of the brain and spinal cord.

As embryonic development progresses, the neural tube divides into four sections: the forebrain (forebrain), middle (midbrain), hindbrain (rhombencephalon), and medulla spinal. Each of these parts will progress to give rise to the different elements that make up the adult central nervous system.

While most of the nervous system develops from the walls of the neural tube, the gap between the walls is also relevant: the neurocele or neural canal. This structure will progressively transform into the ventricles and the rest of the cavities of the brain, through which the cerebrospinal fluid.

primary neurulation

After fertilization, the zygote is formed, the original cell composed of the fusion of an egg and a sperm. The zygote divides successively, becoming a group of cells called a morula. Subsequently, the blastocoel, a fluid-filled cavity, appears within this structure; when this happens we speak of a “blastula”.

Later The blastula is divided into three layers: the endoderm, the mesoderm, and the ectoderm.. Each of these sections will give rise to different parts of the organism. The ectoderm is the most important for the matter at hand, since the nervous system develops from it, both central and peripheral.

The notochord, a structure located in the mesoderm, sends signals to the cells around it. Those that do not receive these signals become the neural plate or neuroectoderm, a group of cells that have already specialized in nervous functions. The word "plaque" refers to the flattened appearance of the neuroectoderm.

Primary neurulation consists of the proliferation of nerve cells in the neural plate. These cause the plate to become the neural tube, a fundamental step in the development of the human organism.

• You may be interested in: "How to take care of yourself during the first month of pregnancy: 9 tips"

Formation and closure of the neural tube

During the process of neurulation, the neural plate flattens, elongates, and folds in on itself around the neural groove, which becomes U-shaped as the walls rise. forming the neural crests and neural tube. At this point in the process, the tube is open at both ends; we refer to the caudal and rostral neuropores.

Typically, these openings close after a few days; however, sometimes the tube does not close properly, which gives rise to disorders such as spina bifida (affecting the spine) and the anencephaly (associated with very serious malformations in the brain).

It is important to differentiate the neural tube from the neural crest because the former becomes the most structures of the central nervous system, while the peripheral is a progression of the crest neural.

• Related article: "Parts of the human brain (and functions)"

secondary neurulation

Secondary neurulation is the process that culminates in the formation of the neural tube. This is not due to the signals sent by certain cells, as is the case with primary neurulation, but rather occurs as a consequence of the development of the neural tube itself.

This process is associated with the division of neural tube cells between mesenchymal and epithelial. The former are located in the central part of the tube, and the latter in its peripheral region. As these cells differentiate cavities form between the two sets.

The mesenchymal cells that are located in this part of the embryo condense and form what we know as the medullary cord; This, in turn, hollows out inside to make way for the cavity of the neural tube. This phenomenon begins in the sacral region of the spine.

Thus, while primary neurulation consists of the neural plate folding in on itself, secondary neurulation is corresponds to the emptying of the neural tube cavity, closely associated with the differentiation of the cells of the nervous system of the embryo.