The brain is the largest organ of the newborn. Its mass is on the average 1 /8-1 /9 of the body weight, and by the end of the first year of life - 1 /11-1 /12 whereas in the adult - only 1/40 of the body weight. In childhood, the brain grows relatively little: its mass increases by 376 times, and the mass of the entire body - by 21 times. In appearance, the brain of the child in general terms resembles the brain of an adult, although the furrows are less pronounced, some do not. However, the microscopic structure of the brain is an immature organ. The brain tissue of newborns is very rich in water. Almost no myelin sheaths of nerve fibers, on the cut, gray matter differs little from white. This feature of the brain is microscopically determined in 4-5 years, when it is still developing morphologically. But the signs of immaturity in different departments are expressed unequally. Mature are old sites in evolutionary relation, containing vital centers (brain stem and hypothalamus). The most mature (morphologically and functionally) is cortex of the large brain . Although it functions already in the newborn, its significance at this age is small. In newborns, the influence of the thalamoplasid system predominates, it causes a reflex-stereotyped and atetozopodibny character of the movements. Subsequently, the function of the striatum and the cerebral cortex becomes more important, the movements become coordinated and purposeful, conditioned reflexes play an increasingly important role in the behavior of the child, which begin to form in the first months of life.
The spinal cord at the time of birth is a mature entity. Relatively to the spine, it is larger than that of an adult, reaching the newborn to the lower edge of the second lumbar vertebra.
The cerebrospinal fluid of a newborn child differs somewhat from the cerebrospinal fluid of older children. In 1 ml of cerebrospinal fluid of a newborn child there are an average of 15 cells. The protein content can reach 600-1000 mg /l, and in preterm infants - 1500-1800 mg /l. The content of cells gradually decreases with age, and amounts to C in a month independent of age, 4 cells per ml. The protein content also decreases, reaching a minimum at the age of 3-9 months (200 mg /l). In children under 10 years, the upper limit of the normal protein is 300 mg /l, and in adults - 400 mg /l. Since the GEB of newborn infants is penetrated, the ratio between the level of glucose of the cerebrospinal fluid and blood is higher than that of children outside the neonatal period. It is at least 2/3 whereas later the level of glucose in the cerebrospinal fluid can be equal to half its level in the blood.
Peripheral nerves. The main feature is a relatively later myelination of the cranial nerves, which ends at 15 months of age, and spinal nerves at 3-5 years. Due to the absence of the myelin sheath or incomplete myelination, the speed of excitation along the nerve in the first months of life is reduced.
The vegetative nervous system functions in the child from the moment of birth, when separate nodes merge and powerful plexuses of the sympathetic part - the autonomic nervous system are formed.