The child's nervous system develops very quickly, the brain weight of a newborn weighs about 400g, by 1 year old it weighs 900-1000g, by 8 years old the brain weighs 1200-1300g, when grown up it is 1400g. The increase in brain weight is the result of the myelination process. The most important process in the development and completion of the nervous system is the myelination of nerve tissue and changes in the cerebral cortex.