[Neurosurgical embryology. Part 6: The principal models that can be used in developmental biology].

To study the mechanisms controlling embryonic development, experimental analyses must be performed on animal models. There are different species that are currently used as models in developmental biology. In invertebrates, drosophila remains a very useful model thanks to its rapid development and to the extensive study of genes involved in the control of its development.

[Neurosurgical embryology. Part 5: Temporal landmarks of the development of the central nervous system in humans].

The establishment of temporal landmarks of the development of the central nervous system was the primary goal of early human embryologists. The description of these landmarks has lost much of its interest since it is now largely accepted that the temporal profile of development is at best a poor indicator of the origin of malformative syndromes. However, we propose here a rapid review describing the principal data available.

[Neurosurgical Embryology. Part 3: Molecular control of corpus callosum development].

The corpus callosum is the most important cerebral commissure allowing axonal fibres to cross the midline. Corpus callosum agenesis is an important condition in man that can reveal numerous genetic syndromes. The corpus callosum develops from the commissural plate, a dorsal region of the telencephalon.

[Neurosurgical Embryology. Part 2: Recent data on normal and pathological development of the cortex].

Understanding how the cortex develops has gained very important new data thanks to both experimental and clinical studies. Experimental studies have shown that: --neurons are generated in the ventricular zone by asymmetric mitoses; --the first cortical region to differentiate is the so-called pre-plate that plays a major role in the control of neuroblasts migration; --neuroblasts arise according to an inside-outside gradient; they migrate either along the processes of radial cells or according to a new type of non radial migration; --all the cortical neurons are not generated by the dorsal telencephalon; some of these neurons derive from the basal telencephalon; --neuroblasts acquire their specificity during their way to the cortical plate. There are several genetic syndromes leading to a malformation of the cortex.

[Neurosurgical embryology. Part 1: Cell differentiation].

In pluricellular organisms, cell differentiation helps to decrease the total amount of energy needed for life. These differentiations can be evidenced at the tissular, the cellular or the molecular levels. Cell differentiation is a progressive process achieved during embryogenesis; different steps in the program can be described.