Many years' studies in functional neurochemistry have provided a concept of the functionally induced biochemical heterogeneity of neurons and their subcellular components, which is formed during ontogenesis as the functions of the central nervous system are developed. It has been established that it manifests itself at the systemic, cellular, and subcellular levels: (1) between brain formations which constitute the single functional system; (2) between the neurons of various morphofunctional types (associative, efferent, afferent ones) between the neurons and the glia; (3) between individual components (the nucleus and the cytoplasm) of a neuron and its subcellular (synaptosomes, mitochondria, synaptosomal membranes) components. It is concluded that the functionally determined biochemical heterogeneity and morphofunctional features found in animals of various strains may be regarded as one of the ways of compensatory, rehabilitative, and adaptative processes in the central nervous system.