The book of one of the largest English scientists, well known to the Soviet reader from the book "Introduction to Cybernetics" translated into Russian, is devoted to one of the main problems of cybernetics - the analysis of the mechanisms of the nervous system, which ensure the adaptive behavior of the body. The translation is from the second edition, completely revised and partially re-written. Designed for a very wide range of readers - biologists, doctors, physicists, mathematicians, engineers.