The basis of the brain can already be seen in a two-week-old embryo. At that time the embryo consists of three layers: the ectoderm, mesoderm and endoderm. From the mesoderm the muscles and bones are formed, and from the endoderm the organs. For now, the ectoderm is especially important, because from it the brain and the skin are formed. At the age of two weeks, the ectoderm folds inward to form the neural groove. At the age of three weeks, the neural groove has grown closed. It now has a membrane over it so that a hollow tube has formed. This tube is called the neural tube, and is the base of the brain.
The neural tube is filled with a fluid called the cerebrospinal fluid. This fluid can be found later in the development of the brain in the four vesicles of the brain. The lower part of the neural tube develops into the spinal cord, the part above it into the brain. In this we distinguish three different structures. The hindbrain consists of the myelencephalon and the metencephalon (which includes the cerebellum). The midbrain consists of the mesencephalon. The forebrain consists of the diencephalon and the telencephalon (containing the cerebrum, also called the cerebral cortex).
With the above changes in the brain, however, nothing has been said about the development of the neurons in the brain. After all, how is it possible that the brain weighs only 350 grams at birth, and after it is fully grown it weighs as much as 1.4 kilograms?
Several processes are distinguished in the development of neurons in the brain:
- Migration, the moving of cells to their final location in the brain
- Myelination, the formation of myelin around the axons
During the different stages of development, the brain is most susceptible to damage. For example, you can think of mothers who drink alcohol during pregnancy, which can lead to Fetal Alcohol Syndrome. Characteristics of this are hyperactivity, impulsivity, attention problems, mental retardation, heart problems and abnormal appearance. These characteristics are caused by disruptions in the children's differentiation and synaptogenesis. Children with this syndrome often have few dendrites, and these dendrites have few connections to other neurons.
Author: Myrthe Princen (translated by Melanie Smekal)