Age features of the brain
Last reviewed: 23.04.2024
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The brain of the newborn is relatively large, its mass is on the average 390 g (340-430 g) in boys and 355 g (330-370 g) in girls, which is 12-13% of body weight (in adults, about 2.5% ). The mass of the brain in relation to the mass of the body in a newborn is 5 times greater than that of an adult, and is determined by a ratio of 1: 8 (in an adult this ratio is 1:40). By the end of the first year of life, the mass of the brain doubles, and triples by 3-4 years. Later (after 7 years) the brain mass increases slowly and reaches its maximum value by the age of 20-29 (1355 g in men and 1220 g in women). In subsequent periods, up to 60 years in men and 55 years in women, the mass of the brain does not change significantly, and after 55-60 years there is a slight decrease in it.
The newborn has better developed phylogenetically older parts of the brain. The mass of the brainstem is 10.0-10.5 g, which is about 2.7% of the body weight (in the adult it is about 2%), and the cerebellum is 20 g (5.4% of the body weight). By the age of 5 months, the mass of the cerebellum increases 3 times, by 9 months - 4 times (the child can stand, starts walking). The hemispheres of the cerebellum develop most intensively. The final brain in the newborn is also developed relatively well. The frontal lobe of the large brain is strongly convex and relatively small. The temporal lobe is high. Island fraction (islet) is located deep. Up to 4 years of life the child's brain grows evenly in height, length and width. Further, the growth of the brain in height prevails. The frontal and parietal lobes grow most rapidly.
The newborn on the surface of the cerebral hemispheres already has furrows and convolutions. The main furrows (central, lateral, etc.) are well expressed, and the branches of the main furrows and small convolutions are weak. In the future, as the child's age increases, the furrows become deeper, the gyrations between them are more bold. The myelination of nerve fibers in the phylogenetically older parts of the brain begins and ends earlier than in the more recent departments. In the cerebral cortex, nerve fibers that carry out various types of sensitivity (general), and also those that make connections with the subcortical nuclei, are previously mielinized. Myelination of afferent fibers begins about 2 months and ends up to 4-5 years, and efferent fibers somewhat later, in the period from 4-5 months to 7-8 years.
The relationship of furrows and gyri with the bones and seams of the roof of the skull in a newborn is slightly different than that of an adult. The central furrow is located at the level of the parietal bone. The lower part of this furrow is 1.0-1.5 cm more cranial than the scaly suture. The dark-occipital furrow lies 12 mm anterior to the lambdoid suture. Ratios of furrows, brain gyrations and sutures, characteristic of an adult, are established in children 6-8 years old.
The corpus callosum in the newborn is thin, short, since, simultaneously with the development and enlargement of the cerebral hemispheres, the corpus callosum grows mainly in the cranial and caudal directions, located above the cavity of the intermediate brain (over the third ventricle). As the hemispheres develop, the thickness of the corpus callosum increases (up to 1 cm in an adult) and the corpus callosum (up to 2 cm), which is due to an increase in the number of commissural nerve fibers.
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