The principle of the minimal support of a functional system. The neuronal mechanisms]

Developing nervous cells are characterized by an important trait: a capability for functioning long before the full maturity. During this period, the excitable membrane of a neuron has specific characteristics, the dendritic apparatus is not fully developed, and the level of afferent input is low. All this complicates the initiation of synaptic and impulse potentials. It is suggested that the functioning of neurons at the early developmental stages is underlain by a system of adaptation including: 1) the phenomenon of redundancy (increased number of neurons, spines, and synapses, increased branching); 2) factors increasing the probability to receive the expected afferentation (orientation and growth of dendrites towards the afferent input, structure and localization of branching foci); 3) factors facilitating the initiation of neuronal discharge (juvenile channels generating ion currents, electric interaction between cells, additional triggering zones). The common goal of this whole group of factors is to facilitate the response of a cell to a single or weak signal. This is the principal condition ensuring the realization of neuronal interaction at early stages of brain development. Thus, the essence of the principle of the minimal provision of the early functional systems in Anokhin's theory of systemogenesis that the early functional system involves receptor cells and neurons of hierarchical brain structures that have been the first to mature heterochronously and are at the earliest maturation stage. Achieving the result analogous to that achieved by an adult organism is subserved by additional mechanisms characteristic exclusively for the early maturation stages of neurons and functional systems, which enable the nervous cells to function efficiently even at the early stages of maturity.