Neural development

Developmental neurobiology or developmental neurobiology (English Developmental Neuroscience or Developmental Neurobiology ) deals with the development and maturation of the nervous systems of various animals. Model organisms are frequently used are, inter alia, the chicken (Gallus gallus), zebrafish (Danio rerio), a small fruit fly ( Drosophila melanogaster ), the nematode worm ( Caenorhabditis elegans ) and the African clawed frog (Xenopus laevis). It is of interest, inter alia, the development of progenitor cells and stem cells into neurons and the development of complex parts of the nervous system ( pattern formation ). The regeneration of nerve cells is the subject of research and therefore it is partially directly medically relevant.

Brief summary of the development of the nervous system of vertebrates

The development of the nervous system begins with gastrulation ( from Lat Gastrum " clay pot bellied " ) (see embryogenesis ), the transition from the two-bladed embryoblasts to a three-leaf form. The ectoderm forms an epithelial layer of cylindrical cells. The outermost, located at the back of the embryo layer develops into the ectoderm, which thickens and forms the neural plate from which the nervous system develops. Just after the formation of this layer of cells, the process of neurulation begins. Here, cells divide at the edge of the neural plate so strong that it eventually comes to an invagination ( intussusception ) and a pinch. Between the developed thereby neural tube and the overlying ectoderm arise neural crest cells, the dorsal root ganglia to perform. The part of the ectoderm, which is outside of the neural tube later forming the skin layer. From the neural tube adjacent tissue, the olfactory ( sense of smell ) and the auditory ( hearing ) epithelium, as well as some peripheral ganglia develop. At the edges of the neural plate caused the neural folds, which then form the neural crest from which the peripheral nervous system develops ......

From the neural tube portion formed in the front ( anterior or rostral ) three vesicles ( forebrain, midbrain and hindbrain ). From the rear ( posterior or caudal ), the spinal cord is formed. The brain develops through progressive subdivision of the vesicles: From the forebrain go telencephalon (later inter alia cerebral cortex, hippocampus ) and diencephalon ( thalamus, among other things, hypothalamus, retina) produced and the hindbrain divides into metencephalon and Myelencephalon. The mesencephalon does not change to the same extent and remains a single vesicle.

During the early development is mainly influenced by chemical signals, the refinement of synaptic connections coming through electrical activity with increasing age of the embryo an increasingly important role. This form of development is not yet complete, especially in mammals after birth. In humans, it does not end until puberty.

Even the adult brain is capable of in the context of learning processes still astonishing plasticity.

Key steps and mechanisms of brain development

Cell formation, migration, and cell death

The cells of the nervous system go from precursor cells produced ( progenitor cells ), which originate from the neural tube or the neural crest. First created by symmetric division ( = two identical offspring) in the early stage of development, a large number of progenitor cells in the late embryo then by asymmetric divisions ( = two different offspring) generate neurons and glial cells. A number of signaling pathways represents the correct sequence of histogenesis safe.

Brain regions with different layers, each containing different cell types, are usually the fact that the precursor cells produce in a fixed order for a certain period of time always of a type cells, which migrate into the corresponding layers. So gradually creates levels of cells, which then connect with each other and with other parts of the brain.

Not all cells are born and migrate in specific brain regions, survive. It is a fundamental principle that an excess of cells is formed and only a part of it in the adult animal is still present (apoptosis). Whether a neuron survives or not often depends on the availability of neurotrophins, while surviving the cells that contribute to the better functioning of the system.

Axonal growth and axonal pathfinding

For a functioning network neurons have to be interconnected. Since specific relationships among certain partially widely spaced, areas are needed, there are a variety of mechanisms that guide the outgrowing processes of newborn neurons to the intended target for them. Is the growth cone, which is capable of perceiving the present in its environment and respond to chemical stimuli On top of these extensions. These stimuli may be soluble substances that attract or repel the axon (similar chemotaxis) and so direct it over long distances or prevent ingrowth in certain areas. But also bound to the cell surface molecules may have such effects as the growth cone comes into direct contact with them. This is of particular importance when axons along the so-called Pionieraxonen (who have at least come a part of the path ) grow. A prominent example of the axononale Navigation is the origin of the connection between the retina and the downstream visual areas.

Swell

• Scott F. Gilbert: " Developmental Biology", 7th Edition.
• Eric Kandel: James H. Schwartz, Thomas M. Jessel. Principles of Neural Science. 4th edition. McGraw -Hill Companies, New York 2000
• Michael J. Zigmond, Floyd E.Bloom, Story C. Landis, James L. Roberts, Larry R. Squire. (Editor) "Fundamental Neuroscience", Academic Press, San Diego 1999

• Developmental Biology
• Neuroscience