Icon module 22

Preliminary remarks

The morphogenesis of the nervous system begins extraordinarily early in embryogenesis. The generation of the nervous system has its beginning on the 19th day (stage 7) with the formation of the neural plate, the subdivision of its essential parts commences with the 12th week. The maturation of the CNS, though, extends far beyond the infant's birth.

The histogenesis of the CNS leads to the formation of 100 billion neurons! Despite being limited in time the mitotic potential of the neural epithelium is thus enormous, but the cell proliferation gradually diminishes between the 16th week and birth. Nevertheless, it is today generally recognized that in mammals neuronal stem cells are present lifelong, especially in the regions of the hippocampus and the bulbus olfactorius. In addition, a second wave of postnatal neurogenesis generates a considerable number of interneurons in the cerebellar cortex, the hippocampus and the bulbus olfactorius.

Numerous fundamental developmental processes are involved in the emergence of the CNS. To these belong namely induction, proliferation, intercellular communication, cell migration and differentiation as well as apoptosis (programmed cell death). These processes are also extensively treated within the framework of this module.

The anatomy of the brain is extremely complex. In order to understand it, a solid knowledge of embryonic development is indispensible.