Abstract
With the objective to recognize IN and its precursors, as well as its structural morfofunctioning, was carried through a bibliographical revision by means of article research indexados in the scientific bases: Bireme, LILACS, SciELO, PubMed and MEDLINE. The sample constituted of 18 (eighteen) articles, amongst these, had been selected 7 (seven) articles for basic theoretical recital (excellent group 1) and 2 (two) articles complementary theoretical recital (excellent group 2). 9 (nine) articles had only been discarded of the study (not excellent group) for the criterion “thematic relevance”. On the basis of the findings, are concluded that IN It he is one of the most important systems of the organism, being essential for the development of vital, regulatory the actions, either as messenger, either as agonist. Being thus, not the functioning of this system can general diverse secondary problems and innumerable organic processes.