NERVOUS SYSTEM : definition of a neuron

        The neuron is the basic cell of the nervous system, the study of which is closely linked to that of another. The properties of the neuron have been, at least in part, selected throughout the history of the animal world by evolutionary constraints on whole organisms. Conversely, the functional capabilities of the nervous system has been constrained by those cells that up.
       Invertebrates to humans, the nervous system still performs two types of functions : the adaptation behavior of the environment and the regulation of a number of vegetative functions. It collects sensory information, determines the actions to be taken and communicated to the appropriate organs necessary for survival commands. These tasks are performed by the neurons through the spread and integration of electrical and chemical signals.
       Like most cells, neurons together in their cell body core and all the machinery necessary for protein synthesis and metabolism. But they are characterized morphologically by the presence of neuritics, that's mean, long processes more or less branched. These fall into two functional classes: the axon (one per neuron) and dendrites.
      The dendrites receive electrical and chemical signals from afferent neurons and axon carries electrical signals to other neurons, over distances that can reach tens of thousands of times the size of the cell body.
Axons contact neuritics of other neurons or cells of target organs (eg muscle fibers) at specialized structures, the synapses. A neuron may have several thousands of synapses on the dendrites and axons can form as.
     The human brain consists of about 10^11 neurons, hundreds or thousands of different types, connected by approximately 10^14 synaptic contacts. These neurons form a highly developed specific network connections. The analysis necessarily a complex password system by studying simpler models. The study of other animal species, including invertebrates, has made ​​valuable contributions to our knowledge of neurons.
The rudimentary nervous system can hardly be compared to that of the man, however, neurons from each other have both similarities in the mechanisms of their genesis, survival and establishment of their connections, in the details of their function. These are the fundamental characteristics that we will consider here.