Neuroblasts: the precursors of nerve cells

Today, the term neuron is widely known by the majority of the population. We know that this is the main type of cell that is part of our nervous system, being the basic unit of this system, and which transmits bioelectric impulses throughout the system in order to transfer commands or information to different parts. of our body.

But do we know how or where they come from? At what point in our development do they appear? The answer to these questions lies in neuroblasts, Which we will know throughout this article.

    Neuroblasts: what are they?

    Neuroblasts are a type of embryonic cell of ectodermal origin that is characterized by being the precursor of nerve cells, Specifically neurons and neuroglia.

    It is a type of cell that appears during pregnancy, born in the neural plate of the ectoderm tissue to begin to mature and migrate made its final location and end up shaping our nervous system.

    Neuroblasts are particularly active and visible during pregnancy, decreasing dramatically after birth, although they can still be found to be active. It is the immediate precursor of the neuron, which transforms into it after a process of maturation.

      The development of the nervous system

      As we said, neuroblasts are embryonic cells, which arise during the pregnancy of a future individual. Before nerve tissue can form it was necessary for some development to occur in the fetus and neurulation is initiated.

      This happens approximately in the third week after fertilization. At this point, the ectoderm is stimulated to eventually generate the neuroextoderm, until it eventually generates the neural plate.

      This plaque, a layer of initially epithelial cells (called matrix cells), will continue to grow and cephalocaudally dilate and generate folds in which they will begin to differentiate from ectodermal cells. The plate will close on itself generating what is called a neural tube, which will eventually close its ends during the fourth week.

      The cells of the matrix are directed to the cavity or empty area of ​​the tube and, at this point, they continuously divide and replicate, which will cause the neural tube to increase in size. The first neuroblasts will begin to mature and form as such, losing the ability to replicate (with small exceptions) and may only end up maturing into a mature nerve cell.

      From that point on, the neuroblast will continue to migrate behind its final location, the point at which it will eventually turn into a neuron. Generally, the older the neuron, the greater the depth at which it will be found.

      An example can be seen in the spinal cord. Once formed, neuroblasts begin to migrate to the periphery of the neural tube, Arriving at the so-called intermediate zone which will end up being the gray matter of the spinal cord, where they will begin to mature and grow on the periphery until generating the marginal zone (future white matter). Other types of cells will also be generated by the matrix, such as glial cells and microglia.

      Neuron formation

      The neuroblast does not immediately turn into a neuron, but requires a maturation process to form it. Initially, the cell from which the neuroblast will form and the future nerve cell they have a nucleus and a protodendrite, Being inserted into the wall of the neural plate. However, as it migrates to the cavity to begin to replicate, it loses this dendrite, becoming an apolar spherical nucleus.

      At the end of the replication process and when the neuroblast begins to form as such, two opposing extensions gradually appear, forming something that looks like a bipolar neuron. One of these extensions elongates and eventually turns into an axon, while the others fragment to generate future dendrites. These elements matured over time until they finally formed an adult neuron.

        Do they exist in adults?

        Although it was previously believed that neuroblasts could only be found during pregnancy and the first years of life, with the discovery of adult neurogenesis in certain regions of the brain it has been observed how neuroblasts form in certain regions throughout our life, especially in the subventricular region of the third ventricle and in the rotation of the hippocampus.

        these neuroblasts they are mainly directed to the olfactory bulb or to the hippocampus itself, To generate inhibitory neurons of the gabaergic type or glutamatergic exciters, and allow the maintenance of a large number of functions.

        The neurogenesis that its existence presupposes is fundamental to allow mental plasticity, learning and discrimination of stimuli. In terms of pathology, it can allow the overcoming of strokes, strokes and trauma and recovery at the slightest of lost functions.

          Possible problems and associated diseases

          Since neuroblasts are the prelude to the existence of neurons, we are dealing with one of the most relevant embryonic cell types for our development. However, as with all types of cells, we can experience different issues throughout their generation and maturation.

          Neuroblasts may not mature to form complete neurons, That there is an uncontrolled, sudden and harmful growth in their numbers, that they are not migrating to the areas where their existence would be necessary or that, for some reason, there are not enough of them in the organization.

          The causes of these alterations can be learned, but since much of the formation and migration of neuroblasts occurs during pregnancy, it is much more likely that cases are due to genetic disorders, problems during pregnancy of the fetus or when mutations appear.

          Two examples of neuroblast related disorders are it can be found in the presence of anencephaly or in the presence of malignant tumors linked to these cells called neuroblastomas.

          Bibliographical references:

          • Snell, RS (2007). Clinical neuroanatomy. 6th edition. Editorial Médica Panamericana. Madrid, Spain.
          • López, N. (2012). Developmental biology. Workbook. McGraw Hill.

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