Human brain

The mass of the human brain ranges from 1000 to more than 2000 grams, which on average is about 2% of body weight. The brain of men has an average weight of 100-150 grams more than the brain of women, however, a statistical difference between the ratio of body size and brain in adult men and women was not found ^[5] . It is widely believed that the mental abilities of a person depend on the mass of the brain: the greater the mass of the brain, the more gifted a person. However, it is obvious that this is far from always the case ^[6] . For example, the brain of I. S. Turgenev weighed 2012 ^{[7] [8]} , and the brain of Anatole France - 1017 g ^[9] . The heaviest brain - 2850 g - was found in an individual who suffered from epilepsy and idiocy ^{[10] [11]} . His brain was functionally inferior. Therefore, there is no direct relationship between brain mass and mental abilities of an individual.

However, in large samples, in numerous studies, a positive correlation is found between the mass of the brain and mental abilities, as well as between the mass of certain parts of the brain and various indicators of cognitive abilities ^{[12] [13]} . A number of scientists ^{[ who? ]} , however, warns against using these studies to substantiate the conclusion about the low mental abilities of certain ethnic groups (such as Australian aborigines ), whose average brain size is smaller ^[14] . A number of studies indicate that brain size, which is almost entirely dependent on genetic factors, cannot explain most of the differences in IQ ^{[15] [16] [17]} . As an argument, researchers from the University of Amsterdam point to a significant cultural difference between the civilizations of Mesopotamia and Ancient Egypt and their current descendants in Iraq and modern Egypt ^[18] .

The degree of brain development can be estimated, in particular, by the ratio of the mass of the spinal cord to the brain. So, in cats it is 1: 1, in dogs - 1: 3, in lower monkeys - 1:16, in humans - 1:50. In humans of the Upper Paleolithic, the brain was noticeably (10-12%) larger than the brain of modern man ^[19] - 1: 55-1: 56.

The brain volume of most people is in the range of 1250-1600 cubic centimeters and makes up 91-95% of the skull capacity. Five divisions are distinguished in the brain: the medulla oblongata , the posterior , including the bridge and cerebellum , the pineal gland , the middle , intermediate and forebrain , represented by the cerebral hemispheres . Along with the above division into departments, the whole brain is divided into three large parts:

• cerebral hemisphere;
• cerebellum;
• brain stem.

The cerebral cortex covers two hemispheres of the brain: the right and left.

The brain, like the spinal cord, is covered with three membranes: soft, arachnoid and hard.

The soft, or vascular, membrane of the brain ( lat. Pia mater encephali ) directly adjoins the substance of the brain, goes into all the grooves, covers all the convolutions. It consists of loose connective tissue, in which numerous vessels that feed the brain branch. Thin processes of connective tissue depart from the choroid, which deepen into the mass of the brain.

The arachnoid membrane of the brain ( lat. Arachnoidea encephali ) is thin, translucent, has no vessels. It is tightly attached to the convolutions of the brain, but does not go into the grooves, as a result of which subarachnoid tanks are formed between the vascular and arachnoid membranes, filled with cerebrospinal fluid, due to which the arachnoid is fed. The largest, cerebellar-oblong cistern, located behind the fourth ventricle, the median opening of the fourth ventricle opens into it; the cistern of the lateral fossa lies in the lateral groove of the cerebrum; interstitial - between the legs of the brain; tank intersection - at the site of visual chiasm (intersection).

The dura mater of the brain ( lat. Dura mater encephali ) is the periosteum for the inner cerebral surface of the bones of the skull. The highest concentration of pain receptors in the human body is observed in this shell, while pain receptors are absent in the brain itself (see Headache ).

The dura mater is built of dense connective tissue, lined with flat, moist cells from the inside, and fuses tightly with the bones of the skull in the region of its inner base. Between the solid and arachnoid membranes is a subdural space filled with serous fluid.

Medulla oblongata

The medulla oblongata ( lat. Medulla oblongata ) develops from the fifth cerebral vesicle (optional). The medulla oblongata is an extension of the spinal cord with impaired segmentality. The gray matter of the medulla oblongata consists of individual nuclei of the cranial nerves. White matter is the pathways of the spinal cord and brain that extend upward into the brain stem, and from there into the spinal cord.

On the front surface of the medulla oblongata contains the anterior median fissure, on the sides of which lie thickened white fibers called pyramids. The pyramids taper down due to the fact that part of their fibers goes to the opposite side, forming the intersection of the pyramids that form the side pyramidal path. Some white fibers that do not cross form a straight pyramidal path.

Bridge

The bridge ( lat. Pons ) lies above the medulla oblongata. This is a thickened roller with transverse fibers. In the center of it passes the main furrow, in which the main artery of the brain lies. On both sides of the furrow there are noticeable elevations formed by the pyramidal paths. The bridge consists of a large number of transverse fibers that form its white matter - nerve fibers. Between the fibers there are many accumulations of gray matter, which forms the core of the bridge. Continuing to the cerebellum, nerve fibers form its middle legs.

Cerebellum

The cerebellum ( lat. Cerebellum ) lies on the posterior surface of the bridge and medulla oblongata in the posterior cranial fossa. It consists of two hemispheres and a worm that connects the hemispheres to each other. The mass of the cerebellum is 120-150 g.

The cerebellum is separated from the cerebrum by a horizontal slit in which the dura mater forms the tent of the cerebellum, stretched over the posterior fossa of the skull. Each cerebellar hemisphere is composed of gray and white matter.

The gray matter of the cerebellum is contained over white in the form of a cortex. Nerve nuclei lie inside the cerebellar hemispheres, the mass of which is mainly represented by white matter. The cerebral cortex forms parallel grooves between which there are convolutions of the same shape. Fissures divide each cerebral hemisphere into several parts. One of the particles - a scrap adjacent to the middle legs of the cerebellum, stands out more than others. It is phylogenetically ancient. The flap and nodule of the worm appear already in the lower vertebrates and are associated with the functioning of the vestibular apparatus.

The cerebral cortex consists of two layers of nerve cells: the external molecular and granular. The thickness of the bark is 1-2.5 mm.

The gray matter of the cerebellum branches out into white (in the middle section of the cerebellum, it’s like an evergreen thuja branch), therefore it is called the cerebellum's life tree.

The cerebellum connects to the brain stem with three pairs of legs. The legs are represented by bundles of fibers. The lower (tail) legs of the cerebellum go to the medulla oblongata and are also called rope-like bodies. They include the posterior spinal cord.

The middle (bridge) legs of the cerebellum are connected to the bridge, in which transverse fibers pass to the neurons of the cortex of the hemispheres. The cortical-bridge pathway passes through the middle legs, due to which the cerebral cortex acts on the cerebellum.

The upper legs of the cerebellum in the form of white fibers go in the direction of the midbrain, where they are located along the legs of the midbrain and are adjacent to them. The upper (cranial) legs of the cerebellum consist mainly of the fibers of its nuclei and serve as the main pathways conducting impulses to the optic tubercles , the sub-tubercle area and the red nuclei.

The legs are located in front and the tire is in the back. Between the tire and legs runs the water supply of the midbrain (Silviev water supply). It connects the fourth ventricle to the third.

The main function of the cerebellum is the reflex coordination of movements and the distribution of muscle tone.

Midbrain

The cover of the midbrain ( lat. Mesencephalon ) lies above its lid and covers the top of the midbrain water supply. The cover contains a tire plate (quadruple). The two upper mounds are associated with the function of the visual analyzer, act as centers of orientational reflexes to visual stimuli, and therefore are called visual. The two lower tubercles are auditory, associated with indicative reflexes to sound stimuli. The upper knolls are connected with the lateral cranked bodies of the diencephalon using the upper arms, the lower knolls are connected with the lower arms with the medial cranked bodies.

From the plate of the tire begins the spinal path, which connects the brain with the spinal cord. Efferent impulses pass through it in response to visual and auditory irritations.

Hemisphere

The brain is divided by a furrow into two large hemispheres (Hemisphaerium cerebri): left and right. The large hemispheres include: cerebral cortex (cloak) , basal ganglia , olfactory brain and lateral ventricles . The hemispheres of the brain are separated by a longitudinal gap, in the recess of which contains the corpus callosum , which connects them. The following surfaces are distinguished on each hemisphere:

1. upper lateral, convex, facing the inner surface of the cranial vault;
2. the lower surface located on the inner surface of the base of the skull;
3. the medial surface with which the hemispheres are interconnected.

In each hemisphere there are parts that protrude most: in front - the frontal pole, in the back - the occipital pole, on the side - the temporal pole. In addition, each cerebral hemisphere is divided into four large lobes: frontal, parietal, occipital and temporal. In the deepening of the lateral fossa of the brain lies a small fraction - an islet. The hemisphere is divided into shares by furrows. The deepest of them is lateral, or lateral, it is also called a Sylvian furrow. The lateral groove separates the temporal lobe from the frontal and parietal. From the upper edge of the hemispheres, the central sulcus, or Roland sulcus, descends. It separates the frontal lobe of the brain from the parietal. The occipital lobe is separated from the parietal only from the medial surface of the hemispheres - the parietal-occipital groove.

The cerebral hemispheres are covered from the outside with gray matter, which forms the cerebral cortex, or cloak. There are 15 billion cells in the cortex, and if we take into account that each of them has from 7 to 10 thousand bonds with neighboring cells, then we can conclude about the flexibility, stability and reliability of the functions of the cortex. The surface of the cortex is significantly increased due to furrows and convolutions. The phylogenetic cortex is the largest structure of the brain; its area is approximately 220 thousand mm ² .

The brain of an adult male is on average 11-12% heavier and 10% larger in volume than the female ^{[20] [21]} . A statistical difference between the ratio of body and brain sizes in men and women was not found ^{[22] [23]} . Methods of tomographic scanning allowed us to experimentally fix the differences in the structure of the brain of women and men ^{[24] [25]} . It was established that the male brain has more connections between the zones within the hemispheres, and the female - between the hemispheres. These differences in brain structure were most pronounced when comparing groups aged 13.4 to 17 years. However, with age, in the brain of women, the number of bonds between zones within the hemispheres increased, which minimizes previously distinct structural differences between the sexes ^[25] .

At the same time, despite the existence of differences in the anatomical and morphological structure of the brain of women and men, there are no crucial signs or their combinations that allow us to speak of a specifically “male” or specifically “female” brain ^[26] . There are brain features that are more common among women, and there are more often observed in men, however, both of them can be manifested in the opposite sex, and there are practically no any stable ensembles of this kind.

Prenatal development

The development that occurs in the period before birth, intrauterine development of the fetus. In the prenatal period, intensive physiological development of the brain, its sensory and effector systems occurs.

Natal condition

Differentiation of the cerebral cortex systems occurs gradually, which leads to uneven maturation of individual brain structures.

At birth, the subcortical formations are almost formed in the child and the projection areas of the brain are close to the final stage of maturation, in which the nerve connections coming from the receptors of different senses (analyzer systems) end and the motor pathways begin ^[27] .

These areas act as a conglomerate of all three brain blocks . But among them, the structure of the block regulating brain activity (the first block of the brain) reaches the highest level of maturation. In the second (block of reception, processing and storage of information) and third (block of programming, regulation and control of activity) blocks, the most mature are only those sections of the cortex that relate to the primary lobes that receive incoming information (second block) and generate outgoing motor impulses (3rd block) ^[28] .

Other areas of the cerebral cortex do not reach a sufficient level of maturity at the time of birth. This is evidenced by the small size of the cells entering them, the small width of their upper layers that perform an associative function, the relatively small size of the area occupied by them and the insufficient myelination of their elements.

2 to 5 years

At the age of two to five years, secondary, associative brain fields mature, some of which (secondary gnostic zones of the analyzer systems) are in the second and third blocks (premotor region). These structures provide for the processes of perception and the execution of a sequence of actions ^[27] .

5-7 Years

The tertiary (associative) fields of the brain ripen next. First, the posterior associative field develops - the parietal-temporal-occipital region, then, the front associative field - the prefrontal region.

Tertiary fields occupy the highest position in the hierarchy of interaction of various brain zones, and here the most complex forms of information processing are carried out. The back associative area provides a synthesis of all incoming multimodal information into a supramodal holistic reflection of the surrounding subject of reality in the totality of its connections and relationships. The front associative area is responsible for the arbitrary regulation of complex forms of mental activity, including the selection of the necessary information that is essential for this activity, the formation of activity programs on its basis and the control of their correct course.

Thus, each of the three functional blocks of the brain reaches full maturity at different times and maturation occurs in sequence from the first to the third block. This is the way from bottom to top - from underlying formations to overlying ones, from subcortical structures to primary fields, from primary fields to associative. Damage during the formation of any of these levels can lead to deviations in the maturation of the next due to the lack of stimulating effects from the underlying damaged level ^[27] .

С точки зрения кибернетики , мозг представляет собой гигантскую обучающуюся статистическую аналоговую машину из живых ионных элементов без жесткой структуры связей между элементами, с потребляемой мощностью около ${\displaystyle \mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">25</span></span>}}${\displaystyle 25}   Ватт. Оценки объема памяти мозга у различных авторов колеблются от ${\displaystyle {\mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">ten</span></span>}}^{\mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">6</span></span>}}}${\displaystyle 10^{6}}   before ${\displaystyle {\mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">ten</span></span>}}^{\mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">sixteen</span></span>}}}${\displaystyle 10^{16}}   бит ^{[29] [30]} . Высшая нервная деятельность заключается в работе с образами внешнего мира многоступенчатым иерархическим методом параллельной обработки информации ^{[31] [32]} . Память мозга устроена по особому принципу - запоминаемая информация одновременно является адресом запоминания в коре головного мозга, причем запоминается не только информация, но и частота её повторения. ^[thirty]

Американские учёные попытались сравнить человеческий мозг с жестким диском компьютера и подсчитали, что человеческая память способна содержать в себе около 1 миллиона гигабайт (или 1 петабайт) (например, поисковая система Google обрабатывает ежедневно около 24 петабайт данных). Если учесть, что для обработки такого большого массива информации мозг человека тратит только 20 ватт энергии, его можно назвать самым эффективным вычислительным устройством на Земле ^[33] .

Об этом мало кто догадывается, но одним из важнейших свойств мозга является его способность к построению моделей, как при попытках описания происходящих в природе процессов, так и для описания выдуманных абстрактных явлений, как осознанно, так и неосознанно. Поведение подавляющего большинства (если не всех) людей определяется именно созданными ими моделями (а в первую очередь предсказаниями, которые они дают) в процессе жизнедеятельности: как для социального взаимодействия, так и для профессиональной деятельности в какой-либо области. Интересно, что человек может поступать иррационально только по той причине, что он когда-то создал искажённую модель (которая даёт искажённые выводы) для какого-либо явления.

• Саган, Карл. Драконы Эдема. Рассуждения об эволюции человеческого разума = Sagan, Carl . The Dragons of Eden. Speculations on the evolution of human intelligence / пер. from English Н. С. Левитина (1986). - SPb. : ТИД Амфора, 2005. — С. 265.
• Блум Ф., Лейзерсон А., Хофстедтер Л. Мозг, разум и поведение. - M., 1988.
• Davidson's Principles and Practice of Medicine. — 21st. — Edinburgh : Churchill Livingstone/Elsevier, 2010. — ISBN 978-0-7020-3085-7 .
• Hall, John. Guyton and Hall Textbook of Medical Physiology. — 12th. — Philadelphia, PA : Saunders/Elsevier, 2011. — ISBN 978-1-4160-4574-8 .
• Larsen, William J. Human Embryology. - 3rd. — Philadelphia, PA : Churchill Livingstone, 2001. — ISBN 978-0-443-06583-5 .
• Bogart, Bruce Ian. Elsevier's Integrated Anatomy and Embryology / Bruce Ian Bogart, Victoria Ort. — Philadelphia, PA : Elsevier Saunders, 2007. — ISBN 978-1-4160-3165-9 .
• Pocock, G. Human Physiology: The Basis of Medicine / G. Pocock, C. Richards. - 3rd. - Oxford: Oxford University Press, 2006 .-- ISBN 978-0-19-856878-0 .
• Purves, Dale. Neuroscience. - 5th. - Sunderland, MA: Sinauer associates, 2012 .-- ISBN 978-0-87893-695-3 .
• Squire, Larry. Fundamental Neuroscience. - Waltham, MA: Elsevier, 2013 .-- ISBN 978-0-12-385-870-2 .
• Gray's Anatomy: The Anatomical Basis of Clinical Practice. - 40th. - London: Churchill Livingstone, 2008 .-- ISBN 978-0-8089-2371-8 .

• Brain basics by NIMH
• Atlas of the Human Brain
• Brain facts and figures
• Brain Maps: Brain Anatomy, Functions and Disorders