Читать книгу The Handy Psychology Answer Book - Lisa J. Cohen - Страница 310

All vertebrates start life the same way. In their earliest stages of embryonic development, a flat plate is formed composed of three layers, the ectoderm, mesoderm, and endoderm. Cells in certain sections divide more quickly than cells in adjacent areas, causing the layers of cells to buckle and fold. In this way, curves and bends are formed and the different parts of the body begin to take shape. The outer layer of the flat plate is called the ectoderm and it is this layer of cells that will curl into the neural tube, out of which the brain and spinal cord will develop.

After an initial period of furious cell division, some cells are created that are post-mitotic, that is, they stop dividing. These cells begin the fascinating process of migrating to their final destination. They do so by means of molecular and cellular signposts that guide their progress. After the cells arrive at their proper place, neuronal connections must be established. Axons are then sent out to travel across broad swaths of territory to create synaptic connections with other cells. Their journey throughout the brain is also directed by chemical signals that point them toward their destination. The establishment of specific synaptic connections between neurons is partially controlled by genetic factors during pregnancy. However, the refinement of these synaptic connections takes place largely after birth and is highly dependent on experience.

Diagram of the three bulges at the head of the neural tube that will develop into the hindbrain, midbrain, and forebrain.