Cerebral cortex, areas of the cerebral cortex. The structure and functions of the cerebral cortex

CRUST - chemogenic sheet-like formations of more or less significant sizes, growing on the surface of some substrate of a different composition (the bottom of a basin, a flat land area, etc.) until they are covered by some other sediment. They are formed by diffusion, infiltration, capillary rise of the substance that forms the crust through the substrate and its subsequent sedimentation, as well as by accretion or cementation of nodules genetically associated with the surface of the substrate. Power core ranges from mm to several m; the length can reach tens and even hundreds of km 2 . K. often have a zonal structure, reflecting changes in the conditions of their growth. The composition of K.'s substance is diverse; most often these are iron, or calcium sulfates, less often aluminum, etc. In modern landscapes, calcareous, ferruginous, gypsum, siliceous, mixed ferruginous-aluminous minerals are widespread; their composition, etc. naturally change depending on the landscape-climatic zonation and facies. Some powerful and long lengths create specific (for example, the so-called glandular shells). Many sieges are concentrated in many cities. ores.

Geological dictionary: in 2 volumes. - M.: Nedra. Edited by K. N. Paffengolts et al.. 1978 .

See what "KORA" is in other dictionaries:

bark- with. 1. Yueshlәnmәgan, chilanmagan, sulanmagan. Dymly tugel, composition of su parlary az bulgan (һava tur.). Yuesh, pychrak tugel (җir, tufrak) 2. Yavymsyz, yangyrsyz; ayaz, koyashly (hava toryshi tur.). Kyshyn bula torgan achy, zyky salkyn tour. k. suyk 3. Usudan,… … Tatar telenen anlatmaly suzlege

KORA- - chemogenic sheet-like outgrowths on the surface of another material before its overlap with sediment. They are formed by diffusion, infiltration, capillary rise of the substance through the source material underlying the crust, its subsequent precipitation, ... ... Paleomagnetology, petromagnetology and geology. Dictionary reference.

Ah, cf. A large oblong vessel for washing clothes and other household needs, previously made from a log split in half and hollowed out, later also from galvanized iron. In the yard, under the feet of people and near the people, at the trough ... Small Academic Dictionary

bark- Canvas shoes... Thieves' jargon

Selfish, ten, tna, tno, tna; comp. Art. her [sn] ... Russian word stress

Self-interest, and [not self-interest] ... Russian word stress

Korytse, a; R. pl. tsev and tsev ... Russian word stress

Koryatchy, at, ata, ato, ata ... Russian word stress

Dense near-surface soil and soil formations, consisting of loose material (pebbles, sandstones, loams, etc.), cemented with lime carbonate, gypsum, silica. Accordingly, calcareous, ... ... Great Soviet Encyclopedia

And, well. Property by value adj. selfish… Small Academic Dictionary

Books

Neurophysiology of the cerebral cortex: a modular principle of organization, Batuev A.S. The book contains basic information on the micro- and macrostructure of the higher part of the brain - the cerebral cortex. The characteristics of the cellular and subcellular level of levels, ...
Neurophysiology of the cerebral cortex: a modular principle of organization. A course of lectures, Batuev A.S. This book will be produced in accordance with your order using Print-on-Demand technology. The book contains basic information on the micro- and macrostructure of the higher part of the brain - the cortex ...

Cortex - outer layer nervous tissue brain of humans and other mammals. The cerebral cortex is divided by a longitudinal fissure (lat. Fissura longitudinalis) into two large parts, which are called the cerebral hemispheres or hemispheres - right and left. Both hemispheres are connected from below by the corpus callosum (lat. Corpus callosum). The cerebral cortex plays a key role in the performance of brain functions such as memory, attention, perception, thinking, speech, and consciousness.

In large mammals, the cerebral cortex is collected in the mesentery, giving a large area of its surface in the same volume of the skull. The ripples are called convolutions, and between them lie furrows and deeper ones - cracks.

Two-thirds of the human brain is hidden in furrows and crevices.

The cerebral cortex is 2 to 4 mm thick.

The cortex is formed by gray matter, which consists mainly of cell bodies, mainly astrocytes, and capillaries. Therefore, even visually, the tissue of the cortex differs from the white matter, which lies deeper and consists mainly of white myelin fibers - axons of neurons.

The outer part of the cortex, the so-called neocortex (lat. Neocortex), the most evolutionarily young part of the cortex in mammals, has up to six cell layers. Neurons from different layers are interconnected in cortical minicolumns. Different areas of the cortex, known as Brodmann's fields, differ in cytoarchitectonics (histological structure) and functional role in sensitivity, thinking, consciousness and cognition.

Development

The cerebral cortex develops from the embryonic ectoderm, namely from the anterior part of the neural plate. The neural plate folds and forms the neural tube. From the cavity inside the neural tube, the ventricular system arises, and from the epithelial cells of its walls - neurons and glia. From the frontal part of the neural plate, the forebrain, the cerebral hemispheres, and then the cortex are formed.

The zone of growth of cortical neurons, the so-called "S" zone, is located next to the ventricular system of the brain. This zone contains progenitor cells, which later in the process of differentiation become glial cells and neurons. Glial fibers formed in the first divisions of progenitor cells, radially oriented, cover the thickness of the cortex from the ventricular zone to the pia mater (lat. Pia mater) and form "rails" for the migration of neurons outward from the ventricular zone. These daughter nerve cells become the pyramidal cells of the cortex. The process of development is clearly regulated in time and guided by hundreds of genes and mechanisms of energy regulation. In the process of development, a layered structure of the cortex is also formed.

Development of the cortex between 26 and 39 weeks (human embryo)

Cell layers

Each of the cell layers has a characteristic density nerve cells and links with other areas. There are direct connections between different parts of the cortex and indirect connections, for example, through the thalamus. One typical pattern of cortical dissection is Gennari's streak in the primary visual cortex. This strand is visually whiter than tissue, visible to the naked eye at the base of the spur groove (lat. Sulcus calcarinus) in the occipital lobe (lat. Lobus occipitalis). The streak of Gennari is made up of axons that carry visual information from the thalamus to the fourth layer of the visual cortex.

Staining of cell columns and their axons allowed neuroanatomists at the beginning of the 20th century. make a detailed description of the layered structure of the cortex in different types. After the work of Korbinian Brodmann (1909), the neurons in the cortex were grouped into six main layers - from the outer, adjacent to the pia mater; to internal bordering white matter:

Layer I, the molecular layer, contains several scattered neurons and consists predominantly of vertically (apically) oriented pyramidal neurons and horizontally oriented axons, and glial cells. During development, this layer contains Cajal-Retzius cells and subpial cells (cells located just below the (pia mater) granular layer. Spiny astrocytes are also sometimes found here. Apical dendritic bundles are considered to be of great importance for reciprocal connections ("feedback") in the cerebral cortex, and are involved in the performance of the functions of associative learning and attention.
Layer II, the outer granular layer contains small pyramidal neurons and numerous stellate neurons (whose dendrites emerge from different sides cell body, forming a star shape).
Layer III, the outer pyramidal layer, contains predominantly small to medium pyramidal and non-pyramidal neurons with vertically oriented intracortical (those within the cortex). Cellular layers from I to III are the main targets of intraspinal afferents, and layer III is the main source of cortico-cortical connections.
Layer IV, the inner granular layer, contains Various types pyramidal and stellate neurons and serves as the main target of thalamocortical (from the thalamus to the cortex) afferent fibers.
Layer V, the inner pyramidal layer, contains large pyramidal neurons whose axons leave the measles and travel to subcortical structures (such as the basal ganglia. In the primary motor cortex, this layer contains Betz cells whose axons travel through the internal capsule, brainstem, and spinal cord and form a corticospinal pathway that controls voluntary movements.
Layer VI, the polymorphic or multiform layer, contains few pyramidal neurons and many polymorphic neurons; efferent fibers from this layer go to the thalamus, establishing a reverse (reciprocal) connection between the thalamus and the cortex.

The outer surface of the brain, on which the areas are marked, is supplied with blood by the cerebral arteries. The site marked in blue corresponds to the anterior cerebral artery. The section of the posterior cerebral artery is marked in yellow

The cortical layers are not just stacked one on one. There are characteristic connections between different layers and cell types in them, which permeate the entire thickness of the cortex. The basic functional unit of the cortex is considered to be a cortical minicolumn (a vertical column of neurons in the cerebral cortex that passes through its layers. Minicolumns include from 80 to 120 neurons in all areas of the brain, except for the primary visual cortex of primates).

Areas of the cortex without a fourth (inner granular) layer are called agranular, with a rudimentary granular layer - dysgranular. The speed of information processing within each layer is different. So in II and III - slow, with a frequency (2 Hz), while in the frequency of oscillations in layer V is much faster - 10-15 Hz.

Cortical zones

Anatomically, the cortex can be divided into four parts, which have names corresponding to the names of the bones of the skull that cover:

Frontal lobe (brain), (lat. Lobus frontalis)
Temporal lobe, (lat. Lobus temporalis)
Parietal lobe, (lat. Lobus parietalis)
Occipital lobe, (lat. Lobus occipitalis)

Given the features of the laminar (layered) structure, the cortex is divided into neocortex and alocortex:

Neocortex (lat. Neocortex, other names - isocortex, lat. Isocortex and neopallium, lat. Neopallium) - part of the mature cerebral cortex with six cell layers. An example of a neocortical region is Brodmann's area 4, also known as the primary motor cortex, primary visual cortex, or Brodmann's area 17. The neocortex is divided into two types: the isocortex (the actual neocortex, samples of which, Brodmann's areas 24,25 and 32 have only been considered) and prosocortex, which is represented, in particular, by Brodmann's field 24, Brodmann's field 25 and Brodmann's field 32
Alocortex (lat. Allocortex) - a part of the cortex with less than six cell layers, also divided into two parts: paleocortex (lat. Paleocortex) with a three-layer, archicortex (lat. Archicortex) of four to five, and the perialocortex adjacent to them (lat. piallocortex). Examples of areas with such a layered structure are the olfactory cortex: vaulted gyrus (lat. Gyrus fornicatus) with a hook (lat. Uncus), hippocampus (lat. Hippocampus) and structures close to it.

There is also a “transitional” (between the alocortex and neocortex) cortex, which is called paralimbic, where cell layers 2,3 and 4 merge. This zone contains the prosocortex (from the neocortex) and the perialocortex (from the alocortex).

Cortex. (according to Poirier fr. Poirier.). Livooruch - groups of cells, on the right - fibers.

Brodmann fields

Different parts of the cortex are involved in different functions. You can see and fix this difference in various ways - solitary lesions of certain areas, comparing patterns of electrical activity, using neuroimaging techniques, studying cell structure. Based on these differences, researchers classify areas of the cortex.

The most famous and cited for a century is the classification, which was created in 1905-1909 by the German researcher Korbinian Brodmann. He divided the cerebral cortex into 51 regions based on the cytoarchitectonics of neurons, which he studied in the cerebral cortex using Nissl cell staining. Brodman published his maps of cortical areas in humans, monkeys, and other species in 1909.

The Brodmann fields have been actively and extensively discussed, discussed, refined, and renamed for almost a century and remain the most widely known and often cited structures of the cytoarchitectonic organization of the human cerebral cortex.

Many of the Brodmann fields, originally defined solely by their neuronal organization, were later associated according to correlation with various cortical functions. For example, Fields 3, 1 & 2 are the primary somatosensory cortex; field 4 is the primary motor cortex; field 17 is primary to the visual cortex, and fields 41 and 42 are more correlated with the primary auditory cortex. Determination of the correspondence of the processes of Higher nervous activity to areas of the cerebral cortex and binding to specific Brodmann fields is carried out using neurophysiological studies, functional magnetic resonance imaging and other methods (as it was, for example, done with the binding of Broca's zones of speech and language in Brodmann fields 44 and 45). However, with the help of functional imaging, it is only possible to approximately determine the localization of the activation of brain processes in the Brodmann fields. And to accurately determine their boundaries in each individual brain, a histological study is needed.

Some of the important Brodmann fields. Where: Primary somatosensory cortex - primary somatosensory cortex Primary motor cortex - primary motor (motor) cortex; Wernicke's area - Wernicke's area; Primary visual area - primary visual area; Primary auditory cortex - primary auditory cortex; Broca's area - Broca's area.

bark thickness

In mammalian species with large brain sizes (in absolute terms, not just relative to body size), the cortex tends to be thicker in measles. The range, however, is not very large. Small mammals such as shrews have a neocortex about 0.5 mm thick; and the views with the most big brain, such as humans and cetaceans are 2.3–2.8 mm thick. There is an approximately logarithmic relationship between brain weight and cortical thickness.

Magnetic resonance imaging (MRI) of the brain makes possible intravital measurements of the thickness of the cortex and the alignment with respect to body size. The thickness of different areas is variable, but in general, sensory (sensitive) areas of the cortex are thinner than motor (motor). One of the studies shows the dependence of the thickness of the cortex on the level of intelligence. Another study showed greater cortical thickness in migraine sufferers. However, other studies show no such relationship.

Convolutions, furrows and fissures

Together, these three elements - convolutions, furrows and fissures - create a large surface area of the brain of humans and other mammals. When looking at the human brain, it is noticeable that two-thirds of the surface is hidden in the grooves. Both furrows and fissures are depressions in the cortex, but they vary in size. The sulcus is a shallow groove that surrounds the gyri. The fissure is a large groove that divides the brain into parts, as well as into two hemispheres, such as the medial longitudinal fissure. However, this distinction is not always clear-cut. For example, the lateral sulcus is also known as the lateral fissure and as the "Sylvian sulcus" and the "central sulcus", also known as the Central fissure and as the "Roland's sulcus".

This is very important in conditions where the size of the brain is limited by the internal size of the skull. An increase in the surface of the cerebral cortex with the help of a system of convolutions and furrows increases the number of cells that are involved in the performance of brain functions such as memory, attention, perception, thinking, speech, and consciousness.

blood supply

The supply of arterial blood to the brain and cortex, in particular, occurs through two arterial pools - the internal carotid and vertebral arteries. The terminal section of the internal carotid artery branches into branches - the anterior cerebral and middle cerebral arteries. In the lower (basal) parts of the brain, the arteries form the circle of Willis, due to which the arterial blood is redistributed between the arterial basins.

Middle cerebral artery

The middle cerebral artery (lat. A. Cerebri media) is the largest branch of the internal carotid artery. Violation of blood circulation in it can lead to the development of ischemic stroke and middle cerebral artery syndrome with the following symptoms:

Paralysis, plegia, or paresis of opposing muscles of the face and arm
Loss of sensory sensation opposing muscles of the face and arm
Defeat dominant hemisphere(often left) brain and development of Broca's aphasia or Wernicke's aphasia
Damage to the non-dominant hemisphere (often the right) of the brain leads to unilateral spatial agnosia from the remote side of the lesion
Heart attacks in the zone of the middle cerebral artery lead to déviation conjuguée, when the pupils of the eyes move towards the side of the brain lesion.

Anterior cerebral artery

The anterior cerebral artery is a smaller branch of the internal carotid artery. Having reached the medial surface of the cerebral hemispheres, the anterior cerebral artery goes to the occipital lobe. It supplies the medial parts of the hemispheres to the level of the parietal-occipital sulcus, the area of the superior frontal gyrus, the area of the parietal lobe, and also the areas of the lower medial parts of the orbital gyri. Symptoms of her defeat:

Paresis of the leg or hemiparesis with a primary lesion of the leg on the opposite side.
Blockage of the paracentral branches leads to monoparesis of the foot, resembling peripheral paresis. Urinary retention or incontinence may occur. There are reflexes of oral automatism and grasping phenomena, pathological foot bending reflexes: Rossolimo, Bekhterev, Zhukovsky. There are changes mental state caused by damage to the frontal lobe: reduced criticism, memory, unmotivated behavior.

Posterior cerebral artery

A steam vessel that supplies blood to the posterior parts of the brain (occipital lobe). Has an anastomosis with the middle cerebral artery. Its lesions lead to:

Homonymous (or upper quadrant) hemianopia (loss of part of the visual field)
Metamorphopsia (violation visual perception size or shape of objects and space) and visual agnosia,
Alexia,
sensory aphasia,
Transient (transient) amnesia;
tubular vision,
Cortical blindness (while maintaining a reaction to light),
prosopagnosia,
Disorientation in space
Loss of topographic memory
Acquired achromatopsia - color vision deficiency
Korsakov's syndrome (violation of working memory)
Emotionally - affective disorders

In the cortex, the conducting functions are performed by sieve tubes, the mechanical elements are bast fibers and stony cells, the storage ones are parenchymal cells, and the integumentary ones are cork cells. The sieve cells located in the bast are formed by long living cells located one above the other with thin cellulose membranes. The partitions separating the cells in the tube, with numerous small holes, look like a sieve (Fig. 26).

In hardwoods, sieve tubes are accompanied by narrow living cells tightly adjacent to them, which are called companions; their purpose is not exactly clear. The diameter of the sieve tubes is usually 20-30μ, the length of individual cells (segments) is a few tenths of a millimeter. Sieve tubes remain active usually only for 1 year; only in some breeds they can function for several years (for linden 3-4 years).

Rice. 26. Sieve tube: a - transverse; b - longitudinal section; 1 - protoplasm; 2 - sieve; 3-cell companion.

Bast fibers are similar to libriform fibers; their walls are lignified and so thickened that the cavity of the cell on the transverse section is noticeable only as a point; the pores on the walls are simple. The length of the bast fibers in the linden bark, where they are most typical, is from 0.875 to 1.225 mm, the thickness is from 0.03 to 0.25 mm. In addition to linden, a large amount of bast fibers contains the bast of poplars and willows. Stony cells have the usual form of parenchymal cells, but are equipped with strongly thickened, lignified layered membranes pierced by pore canals.

These cells got their name for the hardness of the shells. They are more common in the outer layer of the cortex. Bast rays are a continuation in the cortex of the core rays of wood and consist of the same parenchymal cells, but their walls do not always become woody. The core rays, passing into the bast, sometimes gradually expand, as is observed in the linden bark. Bast parenchyma consists of strands of parenchyma; cell membranes of the bast parenchyma usually remain cellulose; various substances are found in their cavities: starch, oil, tannins, crystals of mineral salts, etc.

Rice. 27. Cork tissue of cork oak under a microscope: a - transverse; b - radial; c - tangential section.

Between the crust and the bast there is a transitional layer consisting of parenchymal cells; the outer row of these cells forms the cork cambium. When the cells of this cambium divide, cells of the bast parenchyma are deposited towards the bast, and cork cells are deposited towards the crust, which are located in radial rows in the transverse section and have a quadrangular shape, and in the tangential section - polygonal (Fig. 27). They are tightly connected to each other; their shells do not have pores and are impregnated with suberin, which makes them impervious to water and air; under such conditions, the nutrition of the cell becomes impossible, and it inevitably dies. However, in the cork fabric that dresses the tree from the outside, small areas of loose tissue remain - lentils, which act as ventilation ducts that connect the inner parts of the tree with the atmosphere. In some species, the smooth surface of the bark, formed by cork tissue, persists for many years (in beech, hornbeam, birch).

However, in most species, the tree trunk sooner or later becomes covered with a crust. In these cases, the cork cambium periodically arises in the deep layers of the cortex, gradually separating more and more of its sections with layers of cork tissue; these areas are doomed to die off and in their totality form a crust (Fig. 28), sometimes covered from the surface with deep cracks (in pine, oak). In apple and pear, the formation of a crust in most cases begins in the 6th-8th year, in linden - in the 10th-12th year of life; in oak, the crust appears at the age of 25-35 years, and in fir and hornbeam - at 50 and even later. In some species (hornbeam, warty birch, etc.), the crust is formed only in the lower part of the trunk. By appearance spruce bark, i.e., by the shape and size of the cracks, you can determine the age of the tree.

The bark of many breeds has a large technical significance. So, the cork tissue reaches its greatest development in the cork oak. The outer part of the bark is represented by a thick layer of cork, which can be periodically removed from the trunk of a growing tree, after which it grows again. The technical cork obtained in this way is used for the manufacture of corks, heat-insulating plates, etc. The homeland of the cork oak is the coast mediterranean sea. In our country, it grows on Black Sea coast. In domestic breeds, cork tissue in the form of thick rollers is formed on the bark of a velvet tree growing in the forests of the Far East.

Rice. 28. Cross section of oak bark: 1 - cork; 2 - cork cambium; 3 - stony cells; 4 - cells with druses; 5 - bast parenchyma; 6 - a group of bast fibers; 7 - a group of sieve tubes (dead).

Velvet cork is used for the same purposes as oak cork and after removal it can grow again. The cork part of the birch bark (birch bark) is used for the manufacture of household containers and tar smoking. Instead of birch bark removed without damaging the bast part of the bark, new birch bark can form on the trunks of well-developed, healthy trees growing in close stands protected from the direct action of sunlight and wind.

Over time, a thick crust forms on the trunks of black poplar, growing in the form of rather large rollers, up to 10-12 cm wide at the base and up to 8-10 cm thick. Floats for fishing nets are made from this crust, which is called balbera. Bast is obtained from the bast of the linden bark in the form of disconnected ribbons of bast fibers; Bast is used to make matting, sacks, ropes, etc.

Bark

Olfactory brain

It develops from the ventral part of the telencephalon and consists of two sections: central and peripheral.

Peripheral department(olfactory lobe), located at the base of the brain consists of: olfactory bulb, olfactory tract, olfactory triangle, anterior perforated substance.

Central department represented by the vaulted gyrus, the hippocampus. , dentate gyrus.

The structures of the telencephalon lying above the striatum (roof, lateral and medial walls of the lateral ventricles) are called raincoat(pallium). It is the cloak, which, growing significantly, forming folds on its surface, covers almost all parts of the brain. The surface layer of the cloak, consisting of gray matter, is called the cerebral cortex. The surface area of both hemispheres is about 1650 cm2. Each hemisphere has three surfaces: upper lateral (the most accessible for observation), medial (the hemispheres are directed towards each other) and lower. large furrows each hemisphere is divided into lobes. Central, or Roland's furrow, located in the upper part of the lateral surface of the hemisphere and separates the frontal lobe (lobus frontalis) from the parietal lobe (lobus parietalis). Lateral, or Silvieva furrow, also goes along the lateral surface of the hemisphere and separates the temporal lobe (lobus temporalis) from the frontal and parietal. Parieto-occipital sulcus separates the parietal and occipital (lobus occipitalis) lobes along the medial surface of the hemispheres. In the depths of the Sylvian furrow lies insular (insula) share, closed on all sides by sections of the bark that “creeped” onto it. In addition, another lobe is often distinguished, which is located deep in the medial surface of the hemisphere and arcuately covers the diencephalon. This is the limbic lobe.

Smaller furrows divide the lobes into convolutions(gyrus). Some of these furrows are constant (observed in all individuals), others are individual (observed not in all and not always), 2/3 of the surface of the cortex form the lateral walls of the furrows, and only 1/3 is located on the surface of the convolutions.

The origin and structure of the cerebral cortex is heterogeneous. Most of the human cortex is new cortex - neocortex(neocortex), phylogenetically the youngest crustal formation. Phylogenetically earlier cortical structures - ancient bark(paleocortex) and old bark(archicortex) - occupy a small part of the surface of the hemispheres. Bookmark new cortex formed in the lateral parts of the cloak. The new cortex develops intensively and pushes the ancient cortex to the base of the hemispheres, where it remains in the form of a narrow strip of the olfactory cortex and occupies 0.6% of the cortical surface on the ventral surface of the hemispheres, while the old cortex moves to the medial surfaces of the hemispheres, occupies 2.2% of the cortical surface and is represented by the hippocampus and dentate gyrus. In origin and cellular structure, the new bark differs from the ancient and old bark. However, there are no sharp cytoarchitectonic boundaries between them. The transition from one cortical formation to another in the cellular structure occurs gradually. The transitional type of bark is called the interstitial bark, it occupies 1.3% of the total area of the cortex. Thus, most of the surface of the cortex (95.6%) is occupied by the new cortex.

Ancient and old bark.

For ancient bark characterized by the absence of a layered structure. It is dominated by large neurons grouped into cell islands. old bark has three cell layers. The key structure of the old cortex is the hippocampus. Hippocampus (hippocampus), or ammon horn, Hippocampus (hippocampus), or ammon horn, is located mediobasally in the depth of the temporal lobes. It has a peculiar curved shape (the hippocampus in translation is a seahorse) and almost along its entire length forms an invagination into the cavity of the lower horn of the lateral ventricle. The hippocampus is actually a fold (gyrus) of the old cortex. The dentate gyrus is fused with it and wraps over it. As part of the old cortex, the hippocampus has a layered structure. A layer of terminal branches of the apical dendrites of the pyramidal cells of the hippocampus adjoins the dentate gyrus. Here they form a molecular layer. Various afferent fibers terminate on the terminal branches of the apical dendrites and their bases. The apical dendrites themselves form the next - the radial layer. Further, towards the lower horn of the lateral ventricle, there is a layer of pyramidal cell bodies and their basal dendrites, then there is a layer of polymorphic cells. A layer of white matter of the hippocampus (alveus) borders the wall of the lateral ventricle. It consists of both axons of the pyramidal neurons of the hippocampus (efferent fibers of the hippocampus, leaving as part of the fimbria in the arch), and of afferent fibers coming through the arch from the septum. The hippocampus has extensive connections with many other brain structures. It is the central structure of the limbic system of the brain.

All areas of the neocortex are built according to a single principle.

The initial type is a six-layer bark. Layers are presented as follows:

♦ Layer I - the most superficial, about 0.2 mm thick, is called molecular (lamina molecularis). It consists of fibers of apical dendrites and axons rising from the cells of the lower layers, which are in contact with each other. There are few neurons in the molecular layer. These are small horizontal cells and grain cells. All processes of the cells of the molecular layer are located within the same layer.

♦ II layer - outer granular (lamina granulans externa). ♦ II layer - outer granular (lamina granulans externa). The thickness of the outer granular layer is 0.10 mm. It consists of. small pyramidal and stellate neurons. The axons of these neurons terminate in the neurons of layers III, V, and VI.

♦ III layer - pyramidal (lamina pyramidalis), ♦ III layer - pyramidal (lamina pyramidalis), about 1 mm thick, consists of small and medium pyramidal cells. A typical pyramidal neuron has the shape of a triangle, the apex of which is directed upwards. An apical dendrite extends from the apex, branching in the overlying layers. The axon of the pyramidal cell departs from the base of the cell and heads down. The dendrites of the cells of the III layer are sent to the second layer. The axons of the cells of the III layer terminate on the cells of the underlying layers or form associative fibers.

♦ IV layer - internal granular (lamina granulans internus). ♦ IV layer - internal granular (lamina granulans internus). It consists of stellate cells with short processes and small pyramids. The dendrites of the cells of layer IV go into the molecular layer of the cortex, and their collaterals branch in their layer. The axons of the cells of layer IV can rise to the overlying layers or go into the white matter as associative fibers. The thickness of the IV layer is from 0.12 to 0.3 mm.

♦ V layer - ganglionic (lamina ganglionaris) - a layer of large pyramids. The largest cells of the cortex are located precisely in this layer (the giant Betz pyramids of the anterior central gyrus) (see Fig. 49B). Their apical dendrites reach the molecular layer, while the basal dendrites are distributed in their own layer. The axons of the cells of the V layer leave the cortex and are associative, commissural or projection fibers. The thickness of the V layer reaches 0.5 mm. 93

♦ VI layer of the cortex - polymorphic (lamina multiformis). Contains cells of various shapes and sizes, has a thickness of 0.1 to 0.9 mm. Part of the dendrites of the cells of this layer reaches the molecular layer, while others remain within the IV and V layers. The axons of the cells of layer VI can rise to the upper layers or leave the cortex as short or long associative fibers. The cells of one layer of the cortex perform a similar function in information processing. Layers I and IV are the site of branching of associative and commissural fibers, i.e. receive information from other cortical structures. Layers III and IV are input, afferent for projection fields, since it is in these layers that the thalamic fibers end. Layer V of cells performs an efferent function, its axons carry information to the underlying structures of the brain. Layer VI is also an output layer, but its axons do not leave the cortex, but are associative. The basic principle of the functional organization of the cortex is the association of neurons into columns. The column is located perpendicular to the surface of the cortex and covers all its layers from the surface to the white matter. Connections between cells of one column are carried out vertically along the axis of the column. The lateral processes of the cells are short. The connection between the speakers of neighboring zones is carried out through fibers that go deep into, and then enter another zone, i.e. short association fibers. The functional organization of the cortex in the form of columns was found in the somatosensory, visual, motor and associative cortex.

Separate zones of the cortex have fundamentally the same cellular structure, however, there are also differences, especially in the structure of layers III, IV, and V, which can break up into several sublayers. In addition, essential cytoarchitectonic features are the density and size of cells, the presence of specific types of neurons, the location and direction of myelin fibers.

Cytoarchitectonic features made it possible to divide the entire surface of the cortex into 11 cytoarchitectonic regions, including 52 fields (according to Brodman). Each cytoarchitectonic field is indicated on brain maps by a number that was assigned to it in the order of description. It should be noted that there are no sharp boundaries between the cytoarchitectonic fields; the cell layers smoothly change their structure when moving from one field to another. Each field of the cortex performs a specific function. Part of the cortical fields are sensory. In the primary sensory fields, projection afferent fibers end. From the primary sensory fields, information is transmitted via short associative fibers to the secondary projection fields located next to them. So, fields 1 and 3, occupying the medial and lateral surface of the posterior central gyrus, are the primary projection fields of skin sensitivity of the opposite half of the body surface. The areas of skin located next to each other are also projected next to each other on the cortical surface. Such an organization of projections is called topical. In the medial part, the lower limbs are represented, and the projections of the receptor fields of the skin surface of the head are located the lowest on the lateral part of the gyrus. In this case, areas of the body surface richly supplied with receptors (fingers, lips, tongue) are projected onto a larger area of the cortex than areas with a smaller number of receptors (thigh, back, shoulder). Field 2, located in the lower lateral part of the same gyrus, is a secondary projection field of skin sensitivity. Fields 17-19, located in the occipital lobe, are the visual center of the cortex, the 17th field, which occupies the occipital pole itself, is primary. The 18th and 19th fields adjacent to it perform the function of secondary associative fields and receive inputs from the 17th field. The auditory projection fields are located in the temporal lobes. Next to them, on the border of the temporal, occipital, and parietal lobes, are the 37th, 39th, and 40th, which are characteristic only of the human cerebral cortex. In most people, in these fields of the left hemisphere, the speech center is located, which is responsible for the perception of oral and writing. Field 43, occupying lower part posterior central gyrus, receives taste afferents. The structures of olfactory sensitivity u send their signals to the cerebral cortex without switching in other parts of the CNS. The olfactory bulbs are located under the lower frontal lobes. The olfactory tract begins from them, which is the first pair of cranial nerves (p. Olfact o rius). Cortical projections of olfactory sensitivity are the structures of the ancient cortex.

The motor areas of the cortex are located in the precentral gyrus of the frontal lobe (in front of the projection zones of skin sensitivity). This part of the cortex is occupied by fields 4 and 5. From the V layer of these fields, the pyramidal path originates, ending at the motor neurons of the spinal cord. The location and ratio of the innervation zones is similar to the projection representation of the skin analyzer, i.e. has a somatotopic organization. In the medial parts of the gyrus there are columns that regulate the activity of the muscles of the legs, in the lower part, at the lateral groove - the muscles of the face and head of the opposite side of the body.

Afferent and efferent projection zones crusts occupy a relatively small area. Most of the surface of the cortex is occupied by tertiary or interanalyzer zones, called associative.

Association zones the cortex occupy a significant space between the frontal, occipital and temporal cortex (60-70% of the new cortex). They receive polymodal inputs from sensory areas.

Association zones provide integration touch inputs and play essential role in the processes of higher nervous and mental activity.

Modern scientists know for certain that thanks to the functioning of the brain, such abilities as awareness of signals that are received from external environment, mental activity, remembering thinking.

The ability of a person to be aware of his own relationships with other people is directly related to the process of excitation of neural networks. And we are talking about those neural networks that are located in the cortex. It is the structural basis of consciousness and intellect.

In this article, we will consider how the cerebral cortex is arranged, the zones of the cerebral cortex will be described in detail.

neocortex

The cortex includes about fourteen billion neurons. It is thanks to them that the functioning of the main zones is carried out. The vast majority of neurons, up to ninety percent, form the neocortex. It is part of the somatic NS and its highest integrative department. The most important functions of the cerebral cortex are the perception, processing, interpretation of information that a person receives with the help of various sense organs.

In addition, the neocortex controls complex movements muscle systems of the human body. It contains centers that take part in the process of speech, memory storage, abstract thinking. Most of the processes that take place in it form the neurophysical basis of human consciousness.

What parts of the cerebral cortex are made up of? The areas of the cerebral cortex will be discussed below.

paleocortex

It is another large and important section of the cortex. Compared to the neocortex, the paleocortex has a simpler structure. The processes that take place here are rarely reflected in consciousness. In this section of the cortex, the higher vegetative centers are localized.

Communication of the cortical layer with other parts of the brain

It is important to consider the connection that exists between the underlying parts of the brain and the cerebral cortex, for example, with the thalamus, bridge, middle bridge, basal ganglia. This connection is carried out with the help of large bundles of fibers that form the inner capsule. The fiber bundles are represented by wide layers, which are composed of white matter. They are located great amount nerve fibers. Some of these fibers provide transmission of nerve signals to the cortex. The rest of the beams transmits nerve impulses to the underlying nerve centers.

How is the cerebral cortex structured? The areas of the cerebral cortex will be presented below.

The structure of the bark

The largest part of the brain is its cortex. Moreover, cortical zones are only one type of parts distinguished in the cortex. In addition, the cortex is divided into two hemispheres - right and left. Between themselves, the hemispheres are connected by bundles of white matter, forming the corpus callosum. Its function is to ensure the coordination of the activities of both hemispheres.

Classification of areas of the cerebral cortex according to their location

Despite the fact that the bark has a huge number of folds, in general, the location of its individual convolutions and furrows is constant. The main ones are a guideline in the selection of areas of the cortex. These zones (lobes) include - occipital, temporal, frontal, parietal. Although they are classified by location, each of them has its own specific functions.

auditory area of the cerebral cortex

For example, the temporal zone is the center in which the cortical section of the hearing analyzer is located. If there is damage to this section of the cortex, deafness may occur. In addition, Wernicke's speech center is located in the auditory zone. If it is damaged, then the person loses the ability to perceive oral speech. The person perceives it as simple noise. Also in the temporal lobe there are neuronal centers that belong to the vestibular apparatus. If they are damaged, the sense of balance is disturbed.

Speech areas of the cerebral cortex

The speech zones are concentrated in the frontal lobe of the cortex. The speech motor center is also located here. If it is damaged in the right hemisphere, then the person loses the ability to change the timbre and intonation of his own speech, which becomes monotonous. If the damage speech center happened in the left hemisphere, then articulation, the ability to articulate speech and singing disappear. What else is the cerebral cortex made of? The areas of the cerebral cortex have different functions.

visual zones

In the occipital lobe is the visual zone, in which there is a center that responds to our vision as such. The perception of the surrounding world occurs precisely with this part of the brain, and not with the eyes. It is the occipital cortex that is responsible for vision, and damage to it can lead to partial or complete loss of vision. The visual area of the cerebral cortex is considered. What's next?

The parietal lobe also has its own specific functions. It is this zone that is responsible for the ability to analyze information that relates to tactile, temperature and pain sensitivity. If there is damage to the parietal region, the reflexes of the brain are disturbed. A person cannot recognize objects by touch.

Motor zone

Let's talk about the motor zone separately. It should be noted that this area of the cortex does not correlate in any way with the lobes discussed above. It is part of the cortex containing direct connections to motor neurons in the spinal cord. This name is given to neurons that directly control the activity of the muscles of the body.

The main motor area of the cerebral cortex is located in the gyrus, which is called the precentral. This gyrus is a mirror image of the sensory area in many ways. Between them there is a contralateral innervation. In other words, the innervation is directed to the muscles that are located on the other side of the body. An exception is the facial area, which is characterized by bilateral muscle control located on the jaw, lower face.

Slightly below the main motor zone is an additional zone. Scientists believe that it has independent functions that are associated with the process of outputting motor impulses. The additional motor zone has also been studied by specialists. Experiments that were performed on animals show that stimulation of this zone provokes the occurrence of motor reactions. The peculiarity is that such reactions occur even if the main motor zone was isolated or completely destroyed. It is also involved in planning movements and motivating speech in the dominant hemisphere. Scientists believe that if the additional motor is damaged, dynamic aphasia can occur. The reflexes of the brain suffer.

Classification according to the structure and functions of the cerebral cortex

Physiological experiments and clinical trials, which were carried out at the end of the nineteenth century, made it possible to establish the boundaries between areas on which different receptor surfaces are projected. Among them, there are sense organs that are directed to the outside world (skin sensitivity, hearing, vision), receptors embedded directly in the organs of movement (motor or kinetic analyzers).

The areas of the cortex, in which various analyzers are located, can be classified according to their structure and functions. So, there are three of them. These include: primary, secondary, tertiary areas of the cerebral cortex. The development of the embryo involves the laying of only primary zones, characterized by simple cytoarchitectonics. Next comes the development of secondary ones, tertiary ones develop in the very last turn. Tertiary zones are characterized by the most complex structure. Let's consider each of them in a little more detail.

Center fields

Over the years of clinical research, scientists have managed to accumulate significant experience. Observations made it possible to establish, for example, that damage to various fields, as part of the cortical sections of different analyzers, can affect the general clinical picture. If we consider all these fields, then among them we can single out one that occupies central position in the nuclear zone. Such a field is called the central or primary. It is located simultaneously in the visual zone, in the kinesthetic zone, in the auditory zone. Damage to the primary field entails very serious consequences. A person cannot perceive and carry out the most subtle differentiation of stimuli that affect the corresponding analyzers. How else are areas of the cerebral cortex classified?

Primary Zones

In the primary zones, there is a complex of neurons that is most predisposed to providing bilateral connections between the cortical and subcortical zones. It is this complex that connects the cerebral cortex with a variety of sensory organs in the most direct and shortest way. In this regard, these zones have the ability to very detailed identification of stimuli.

An important common feature of the functional and structural organization of the primary areas is that they all have a clear somatic projection. This means that individual peripheral points, for example, skin surfaces, retina, skeletal muscles, cochlea of the inner ear, have their own projection into strictly limited, corresponding points that are located in the primary zones of the cortex of the corresponding analyzers. In this regard, they were given the name of the projection zones of the cerebral cortex.

Secondary zones

In another way, these zones are called peripheral. This name was not given to them by chance. They are in peripheral departments sections of the cortex. Secondary zones differ from the central (primary) zones in their neuronal organization, physiological manifestations, and architectonic features.

Let's try to figure out what effects occur if the secondary zones are affected by an electrical stimulus or if they are damaged. The effects that arise mainly concern the most complex types of processes in the psyche. In the event that secondary zones are damaged, elementary sensations remain relatively intact. Basically, there are violations in the ability to correctly reflect the mutual relationships and entire complexes of elements that make up the various objects that we perceive. For example, if the secondary zones of the visual and auditory cortex were damaged, then one can observe the occurrence of auditory and visual hallucinations that unfold in a certain temporal and spatial sequence.

Secondary areas are of significant importance in the implementation of the mutual connections of stimuli that are distinguished using the primary areas of the cortex. In addition, they play a significant role in the integration of functions that are carried out by the nuclear fields of different analyzers as a result of combining into complex complexes of receptions.

Thus, secondary zones are of particular importance for the implementation of mental processes in more complex forms, which require coordination and which are associated with a detailed analysis of the relationships between subject stimuli. During this process, specific connections are established, which are called associative. Afferent impulses entering the cortex from the receptors of various external sense organs reach the secondary fields through many additional switches in the associative nucleus of the thalamus, which is also called the thalamic thalamus. Afferent impulses following in the primary zones, in contrast to impulses, follow in the secondary zones, reach them in a way that is shorter. It is implemented by means of a relay-core, in the thalamus.

We figured out what the cerebral cortex is responsible for.

What is the thalamus?

From the thalamic nuclei, fibers approach each lobe of the cerebral hemispheres. The thalamus is a visual mound located in the central part of the anterior part of the brain, consists of a large number of nuclei, each of which transmits an impulse to certain areas of the cortex.

All signals that enter the cortex (the only exception is olfactory ones) pass through the relay and integrative nuclei of the thalamus opticus. From the nuclei of the thalamus, the fibers are sent to the sensory zones. Taste and somatosensory zones are located in the parietal lobe, auditory sensory zone- in the temporal lobe, visual - in the occipital.

Impulses come to them, respectively, from the ventrobasal complexes, medial and lateral nuclei. Motor zones are associated with the ventral and ventrolateral nuclei of the thalamus.

EEG desynchronization

What happens if a very strong stimulus acts on a person who is in a state of complete rest? Naturally, a person will completely concentrate on this stimulus. The transition of mental activity, which is carried out from a state of rest to a state of activity, is reflected on the EEG by a beta rhythm, which replaces the alpha rhythm. The fluctuations become more frequent. This transition is called EEG desynchronization; it appears as a result of sensory excitation entering the cortex from nonspecific nuclei located in the thalamus.

activating reticular system

Diffuse nervous system is made up of non-specific nuclei. This system is located in the medial parts of the thalamus. It is the anterior part of the activating reticular system that regulates the excitability of the cortex. A variety of sensory signals can activate this system. Sensory signals can be both visual and olfactory, somatosensory, vestibular, auditory. activating reticular system is a channel that transmits signal data to the surface layer of the cortex through non-specific nuclei located in the thalamus. The arousal of ARS is necessary for a person to be able to maintain a state of wakefulness. If disturbances occur in this system, then coma-like sleep-like states can be observed.

Tertiary zones

There are functional relationships between the analyzers of the cerebral cortex, which have an even more complex structure than the one described above. In the process of growth, the fields of the analyzers overlap. Such overlap zones, which are formed at the ends of the analyzers, are called tertiary zones. They are the most complex types of combining the activities of the auditory, visual, skin-kinesthetic analyzers. The tertiary zones are located outside the boundaries of the analyzers' own zones. In this regard, damage to them does not have a pronounced effect.

Tertiary zones are special cortical areas in which scattered elements of different analyzers are collected. They occupy a very vast territory, which is divided into regions.

The upper parietal region integrates the movements of the whole body with the visual analyzer, and forms a scheme of bodies. The lower parietal region combines generalized forms of signaling, which are associated with differentiated subject and speech actions.

No less important is the temporo-parieto-occipital region. She is responsible for the complicated integration of auditory and visual analyzers with oral and written speech.

It should be noted that in comparison with the first two zones, the tertiary ones are characterized by the most complex chains interactions.

Based on all the above material, we can conclude that the primary, secondary, tertiary zones of the human cortex are highly specialized. Separately, it is worth emphasizing the fact that all three cortical zones that we considered, in a normally functioning brain, together with the connection systems and formations of the subcortical location, function as a single differentiated whole.

We examined in detail the zones and sections of the cerebral cortex.