Human brain

     Human brain

    Understanding the organization of brain tissue and its logic is one of the central questions of modern neurobiology. But the human brain is the most complex structure we know alive. This body is not homogeneous and its complexity is expressed by the juxtaposition of different areas whose functions are more or less well specified.

On the basis of anatomical and functional data, we identified two brain regions. The outermost part of the brain, cerebral cortex, which envelops the whole cerebral mass, consists of networks relatively insensitive to genetic regulation. However, it is constantly remodeled by the subject's experience. Neural networks of the cerebral cortex are unstable, malleable, partly innate but largely influenced by epigenetic factors. In contrast, the deeper regions of the brain, internal and basal position relative to the cortex, ie the basal brain react structurally very little to change whether environmental or experimental, these structures are stable, genetically specified and ancient evolutionary origin (see nervous system - Neurogenesis). We called it wrongly brain, here referred to as "basal" reptilian. We will see how its sub-cortical areas, managing all vital functions, ensure the perfect match of a subject in its environment.We now know, thanks to the reverse genetics, that the same genotype can give rise to a large number of phenotypes in the brain, or a single phenotype can adapt continuously by epigenetic modifications. This reciprocity between epigenetic gene and shows how it is essential to take into account the developmental mechanisms that contribute to the construction of neural networks in the adult brain to better understand the overall behavior of adaptive type. Note here that the concept of adaptation of the organism to its environment (individuation) interested, above all, the central nervous system (CNS), which is the only one to integrate and manage information from the outside world. In other words, understanding the individuation seen as the result of cognitive processes (perception, language, memory, consciousness ...) returns to try to understand how the history of a subject is part of the CNS. But this story is recorded in the deep structures of the basal brain involved in the management of personal relationships, and extra-corporeal time of the organism with its environment.To account for the anatomical and functional characteristics of the nervous system, it is necessary to distinguish the two components, one central and one peripheral. The peripheral component includes, on the one hand, sensory neurons, connecting the CNS to sensory receptors and, on the other hand, neurons that innervate the muscles and viscera. Describes easily sensory pathways and motor pathways through a simple division of the nerves, or localized transects performed on the nervous centers that distinguish (as shown Magendie) centripetal sensory pathways and motor pathways (or inhibitory ) centrifugal. The second component to which these pathways are connected is called central because it is formed by the nerve centers: the spinal cord and the brain.

Because of the importance of the cerebral cortex are referred to as basal all structures located in the middle part of the brain that frame and hide the two cerebral hemispheres. They include back and forth and up and down the brain stem (Fig. 1), the encephalopathy, limbic system and basal ganglia which we successively analyze the role. These sub-cortical regions are defined by either stratified as in the cerebral cortex, but grouped into nuclei neurons.Like any classification, this division of the mammalian brain cortex in one hand, and basal regions, on the other hand, has its limits. If well aware of anatomical observations, it does not always correspond to a functional reality. The limbic system, for example, includes both cortical areas and sub-cortical areas. However, we consider separately here the properties of sub-cortical structures with emphasis on the rules governing the organization and major functions they perform in relation to the cortex. In this second part will be devoted to this article. We then consider as imaging can see the brain function before determining the study of brain plasticity.

 The basal brain

The brain-stem

The brain, with its two hemispheres, based on a region called the brainstem, consisting, from front to back, the midbrain, the bridge and the medulla. The latter joined through the foramen magnum, the spinal canal and extends through the spinal cord. It is traversed by descending pathways, which carry the electrical signals from the brain to the motor neurons, and ascending pathways that carry sensory information from the body and the outside world to the brain. Although the volume is relatively low compared to the brain, the brain stem is an essential structure for the survival of an individual. Accidental injury of this structure reflected nervous.

In the brain-stem, several nuclei occupy the space vacated by the fiber bundles. They participate in large vegetative functions and enable the integration of body signals. They consist of sensory and motor nuclei that support many signal processing related to eye function, vestibular functions (those in the inner ear) and hearing, but also the sensitivity and motor control of the face, the mouth, throat, respiratory system and heart. Alongside these nuclei, which are connected to the cranial nerves (see brain-stem), groups of neurons broad spectrum of action are also present. The latter, who receive information from what goes to the brain or down, plan (that is to say communicate their ramifications) diffusely in the brain on the one hand and the spinal cord on the other hand . Their free ends of mineralogical neurotransmitters (catecholamines, serotonin, oxyacetylene) that transmits instructions "modulator" type and broad-spectrum spatio-temporal distribution