The main areas of the cerebral cortex. Cerebral cortex: functions and structural features

The cerebral cortex is the outer layer of nervous tissue in the brain of humans and other mammalian species. 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 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, consciousness.

In large mammals, the cerebral cortex is collected in the mesenteries, giving a larger surface area 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 grooves and fissures.

The cerebral cortex has a thickness of 2 to 4 mm.

The cortex is formed by gray matter, which consists mainly of cell bodies, mainly astrocytes, and capillaries. Therefore, even visually, the cortical tissue differs from the white matter, which lies deeper and consists mainly of white myelin fibers - the 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 of different layers are interconnected in cortical mini-columns. Various areas of the cortex, known as Brodmann's areas, differ from each other 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. The ventricular system arises from the cavity inside the neural tube, and neurons and glia arise from the epithelial cells of its walls. From the frontal part of the neural plate, the forebrain, the cerebral hemispheres and then the cortex are formed

The growth zone of cortical neurons, the so-called “S” zone, is located next to the ventricular system of the brain. This zone contains progenitor cells that later in the process of differentiation become glial cells and neurons. Glial fibers, formed in the first divisions of precursor cells, are radially oriented, span 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 pyramidal cells of the cortex. The development process is clearly regulated in time and is guided by hundreds of genes and energy regulation mechanisms. During development, the layer-by-layer structure of the cortex is also formed.

Cortical development between 26 and 39 weeks (human embryo)

Cell layers

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

Staining columns of cells and their axons allowed neuroanatomists at the beginning of the twentieth century. make a detailed description of the layer-by-layer structure of the cortex in different species. After the work of Corbinian Brodmann (1909), neurons in the cortex were grouped into six main layers - from the outer ones, adjacent to the pia mater; to the internal ones, bordering the white matter:

Layer I, the molecular layer, contains a few scattered neurons and consists primarily of vertically (apically) oriented dendrites of pyramidal neurons and horizontally oriented axons and glial cells. During development, this layer contains Cajal-Retzius cells and subpial cells (cells located immediately under the granular layer. Spinous astrocytes are also sometimes found here. The apical tufts of dendrites are considered to be of great importance for reciprocal connections (“feedback”) in the cerebral cortex, and are involved in the functions of associative learning and attention.
Layer II, the outer granular layer, contains small pyramidal neurons and numerous stellate neurons (whose dendrites extend from different sides of the cell body, forming a star shape).
Layer III, the outer pyramidal layer, contains predominantly small and medium pyramidal and nonpyramidal neurons with vertically oriented intracortical ones (those within the cortex). Cell layers I to III are the main targets of intrapulmonary afferents, and layer III is the main source of cortico-cortical connections.
Layer IV, the internal granular layer, contains various types of pyramidal and stellate neurons and serves as the main target of thalamocortical (thalamus to cortex) afferents.
Layer V, the inner pyramidal layer, contains large pyramidal neurons, the axons of which leave the cortex and project to subcortical structures (such as the basal ganglia. In the primary motor cortex, this layer contains Betz cells, the axons of which extend through the internal capsule, brainstem and spinal cord and form the corticospinal pathway, which controls voluntary movements.
Layer VI, the polymorphic or multiforme 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 designated, is supplied with blood by cerebral arteries. The area indicated in blue corresponds to the anterior cerebral artery. The portion of the posterior cerebral artery is indicated in yellow

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

Areas of the cortex without the fourth (internal granular) layer are called agranular; those with a rudimentary granular layer are called disgranular. The speed of information processing within each layer is different. So in II and III it is slow, with a frequency (2 Hz), while in layer V the oscillation frequency 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 skull bones that cover:

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

Taking into account the features of the laminar (layer-by-layer) structure, the cortex is divided into neocortex and alocortex:

Neocortex (lat. Neocortex, other names - isocortex, lat. Isocortex and neopallium, lat. Neopallium) is part of the mature cerebral cortex with six cellular layers. The exemplar neocortical areas are Brodmann Area 4, also known as primary motor cortex, primary visual cortex, or Brodmann Area 17. The neocortex is divided into two types: isocortex (the true neocortex, examples of which Brodmann Areas 24, 25, and 32 are only discussed) and prosocortex, which is represented, in particular, by Brodmann area 24, Brodmann area 25 and Brodmann area 32
Alocortex (lat. Allocortex) - part of the cortex with the number of cell layers less than six, is also divided into two parts: paleocortex (lat. Paleocortex) with three layers, archicortex (lat. Archicortex) of four to five, and the adjacent perialocortex (lat. periallocortex). Examples of areas with such a layered structure are the olfactory cortex: the vaulted gyrus (lat. Gyrus fornicatus) with the hook (lat. Uncus), the 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 proisocortex (from the neocortex) and the perialocortex (from the alocortex).

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

Paul Brodmann

Different areas of the cortex are involved in performing different functions. This difference can be seen and recorded in various ways - by comparing lesions in certain areas, comparing patterns of electrical activity, using neuroimaging techniques, studying cellular structure. Based on these differences, researchers classify cortical areas.

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

Brodmann's fields have been actively and in detail discussed, debated, clarified, and renamed for almost a century and remain the most widely known and frequently cited structures of the cytoarchitectonic organization of the human cerebral cortex.

Many of the Brodmann fields, initially defined solely by their neuronal organization, were later associated by correlation with various cortical functions. For example, Fields 3, 1 & 2 are the primary somatosensory cortex; area 4 is the primary motor cortex; field 17 is primary visual cortex, and fields 41 and 42 are more correlated with primary auditory cortex. Determining the correspondence of processes of Higher nervous activity to areas of the cerebral cortex and linking them to specific Brodmann fields is carried out using neurophysiological studies, functional magnetic resonance imaging and other techniques (as this was, for example, done with linking Broca's areas of speech and language to Brodmann fields 44 and 45). However, functional imaging can only approximately determine the localization of brain activation in Brodmann's fields. And to accurately determine their boundaries in each individual brain, a histological examination 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. The range, however, is not very large. Small mammals such as shrews have a neocortex thickness of approximately 0.5 mm; and species with the largest brains, such as humans and cetaceans, are 2.3-2.8 mm thick. There is a roughly logarithmic relationship between brain weight and cortical thickness.

Magnetic resonance imaging (MRI) of the brain makes it possible to measure intravital cortical thickness and correlate it with body size. The thickness of different areas varies, but in general, the sensory (sensitive) areas of the cortex are thinner than the motor (motor) areas. One study showed the dependence of cortical thickness on intelligence level. Another study showed greater cortical thickness in migraine sufferers. However, other studies show the absence of such a connection.

Convolutions, grooves and fissures

Together, these three elements - Convolutions, sulci 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 grooves. Both grooves 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 fissure is also known as the lateral fissure and as the "Sylvian fissure" and the "central fissure", also known as the Central fissure and as the "Rolandic fissure".

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 using a system of convolutions and sulci increases the number of cells that are involved in the performance of brain functions such as memory, attention, perception, thinking, speech, consciousness.

Blood supply

The supply of arterial blood to the brain and cortex, in particular, occurs through two arterial basins - 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, arteries form a circle of Willis, due to which 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. Poor 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 the opposite muscles of the face and arms
Loss of sensory sensitivity in the opposite muscles of the face and arm
Damage to the dominant hemisphere (often left) of the brain and the 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 on the remote affected side
Infarctions in the area 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 areas of the hemispheres to the level of the parieto-occipital sulcus, the area of the superior frontal gyrus, the area of the parietal lobe, as well as areas of the lower medial sections of the orbital gyri. Symptoms of her defeat:

Paresis of the leg or hemiparesis with a predominant lesion of the leg on the opposite side.
Blockage of the paracentral branches leads to monoparesis of the foot, reminiscent of peripheral paresis. Urinary retention or incontinence may occur. Reflexes of oral automatism and grasping phenomena, pathological foot bending reflexes appear: Rossolimo, Bekhterev, Zhukovsky. Changes in mental state occur due to damage to the frontal lobe: decreased criticism, memory, unmotivated behavior.

Posterior cerebral artery

A paired 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) hemianopsia (loss of part of the visual field)
Metamorphopsia (impaired visual perception of the size or shape of objects and space) and visual agnosia,
Alexia,
Sensory aphasia,
Transient (transient) amnesia;
Tubular vision
Cortical blindness (while maintaining reaction to light),
Prosopagnosia,
Disorientation in space
Loss of topographic memory
Acquired achromatopsia - deficiency of color vision
Korsakoff's syndrome (impaired working memory)
Emotional and affective disorders

Shoshina Vera Nikolaevna

Therapist, education: Northern Medical University. Work experience 10 years.

Articles written

The brain of modern man and its complex structure is the greatest achievement of this species and its advantage, unlike other representatives of the living world.

The cerebral cortex is a very thin layer of gray matter that does not exceed 4.5 mm. It is located on the surface and sides of the cerebral hemispheres, covering them on top and along the periphery.

The anatomy of the cortex, or cortex, is complex. Each area performs its own function and plays a huge role in the implementation of nervous activity. This site can be considered the highest achievement of the physiological development of mankind.

Structure and blood supply

The cerebral cortex is a layer of gray matter cells that makes up approximately 44% of the total volume of the hemisphere. The area of the average person's cortex is about 2200 square centimeters. The structural features in the form of alternating grooves and convolutions are designed to maximize the size of the cortex and at the same time fit compactly within the cranium.

It is interesting that the pattern of convolutions and furrows is as individual as the prints of papillary lines on a person’s fingers. Each individual is individual in pattern and pattern.

The cerebral cortex consists of the following surfaces:

Superolateral. It is adjacent to the inside of the skull bones (vault).
Bottom. Its anterior and middle sections are located on the inner surface of the base of the skull, and the posterior sections rest on the tentorium of the cerebellum.
Medial. It is directed to the longitudinal fissure of the brain.

The most prominent places are called poles - frontal, occipital and temporal.

The cerebral cortex is symmetrically divided into lobes:

frontal;
temporal;
parietal;
occipital;
insular.

The structure includes the following layers of the human cerebral cortex:

molecular;
external granular;
layer of pyramidal neurons;
internal granular;
ganglion, internal pyramidal or Betz cell layer;
layer of multiformat, polymorphic or spindle-shaped cells.

Each layer is not a separate independent formation, but represents a single coherently functioning system.

Functional areas

Neurostimulation has revealed that the cortex is divided into the following sections of the cerebral cortex:

Sensory (sensitive, projection). They receive incoming signals from receptors located in various organs and tissues.
Motors send outgoing signals to effectors.
Associative, processing and storing information. They evaluate previously obtained data (experience) and issue an answer taking them into account.

The structural and functional organization of the cerebral cortex includes the following elements:

visual, located in the occipital lobe;
auditory, occupying the temporal lobe and part of the parietal lobe;
the vestibular one has been studied to a lesser extent and still poses a problem for researchers;
the olfactory one is on the bottom;
gustatory is located in the temporal regions of the brain;
the somatosensory cortex appears in the form of two areas - I and II, located in the parietal lobe.

Such a complex structure of the cortex suggests that the slightest violation will lead to consequences that affect many functions of the body and cause pathologies of varying intensity, depending on the depth of the lesion and the location of the area.

How is the cortex connected to other parts of the brain?

All zones of the human cerebral cortex do not exist separately; they are interconnected and form inextricable bilateral chains with deeper brain structures.

The most important and significant connection is the cortex and thalamus. In case of a skull injury, the damage is much more significant if the thalamus is also injured along with the cortex. Injuries to the cortex alone are detected much less frequently and have less significant consequences for the body.

Almost all connections from different parts of the cortex pass through the thalamus, which gives grounds to unite these parts of the brain into the thalamocortical system. Interruption of connections between the thalamus and cortex leads to loss of functions of the corresponding part of the cortex.

Pathways from sensory organs and receptors to the cortex also pass through the thalamus, with the exception of some olfactory pathways.

Interesting facts about the cerebral cortex

The human brain is a unique creation of nature, which the owners themselves, that is, people, have not yet learned to fully understand. It is not entirely fair to compare it with a computer, because now even the most modern and powerful computers cannot cope with the volume of tasks performed by the brain within a second.

We are accustomed to not paying attention to the usual functions of the brain associated with maintaining our daily life, but if even the slightest disruption occurred in this process, we would immediately feel it “in our own skin.”

“Little gray cells,” as the unforgettable Hercule Poirot said, or from the point of view of science, the cerebral cortex is an organ that still remains a mystery to scientists. We have found out a lot, for example, we know that the size of the brain does not in any way affect the level of intelligence, because the recognized genius - Albert Einstein - had a brain mass below average, about 1230 grams. At the same time, there are creatures that have a brain of a similar structure and even larger size, but have never reached the level of human development.

A striking example is the charismatic and intelligent dolphins. Some people believe that once in ancient times the tree of life split into two branches. Our ancestors passed along one path, and dolphins along the other, that is, we may have had common ancestors with them.

A feature of the cerebral cortex is its irreplaceability. Although the brain is able to adapt to injury and even partially or completely restore its functionality, when part of the cortex is lost, the lost functions are not restored. Moreover, scientists were able to conclude that this part largely determines a person’s personality.

If there is an injury to the frontal lobe or the presence of a tumor here, after surgery and removal of the destroyed area of the cortex, the patient changes radically. That is, the changes concern not only his behavior, but also the personality as a whole. There have been cases when a good, kind person turned into a real monster.

Based on this, some psychologists and criminologists have concluded that prenatal damage to the cerebral cortex, especially the frontal lobe, leads to the birth of children with antisocial behavior and sociopathic tendencies. Such kids have a high chance of becoming a criminal and even a maniac.

CGM pathologies and their diagnosis

All disorders of the structure and functioning of the brain and its cortex can be divided into congenital and acquired. Some of these lesions are incompatible with life, for example, anencephaly - complete absence of the brain and acrania - absence of cranial bones.

Other diseases leave a chance for survival, but are accompanied by mental development disorders, for example, encephalocele, in which part of the brain tissue and its membranes protrudes out through an opening in the skull. An underdeveloped small brain, accompanied by various forms of mental retardation (mental retardation, idiocy) and physical development, also falls into this group.

A rarer variant of the pathology is macrocephaly, that is, enlargement of the brain. The pathology is manifested by mental retardation and seizures. With it, the enlargement of the brain can be partial, that is, the hypertrophy is asymmetrical.

Pathologies that affect the cerebral cortex are represented by the following diseases:

Holoprosencephaly is a condition in which the hemispheres are not separated and there is no complete division into lobes. Children with this disease are stillborn or die within the first day after birth.
Agyria is underdevelopment of the gyri, in which the functions of the cortex are disrupted. Atrophy is accompanied by multiple disorders and leads to the death of the infant during the first 12 months of life.
Pachygyria is a condition in which the primary gyri are enlarged to the detriment of the others. The furrows are short and straightened, the structure of the cortex and subcortical structures is disrupted.
Micropolygyria, in which the brain is covered with small convolutions, and the cortex has not 6 normal layers, but only 4. The condition can be diffuse and local. Immaturity leads to the development of plegia and muscle paresis, epilepsy, which develops in the first year, and mental retardation.
Focal cortical dysplasia is accompanied by the presence of pathological areas in the temporal and frontal lobes with huge neurons and abnormal ones. Improper cell structure leads to increased excitability and seizures accompanied by specific movements.
Heterotopia is an accumulation of nerve cells that during development did not reach their place in the cortex. A single condition can appear after the age of ten; large clusters cause attacks such as epileptic seizures and mental retardation.

Acquired diseases are mainly consequences of serious inflammation, trauma, and also appear after the development or removal of a tumor - benign or malignant. In such conditions, as a rule, the impulse emanating from the cortex to the corresponding organs is interrupted.

The most dangerous is the so-called prefrontal syndrome. This area is actually the projection of all human organs, therefore damage to the frontal lobe leads to memory, speech, movements, thinking, as well as partial or complete deformation and changes in the patient’s personality.

A number of pathologies accompanied by external changes or deviations in behavior are quite easy to diagnose, others require more careful study, and removed tumors are subjected to histological examination to exclude a malignant nature.

Alarming indications for the procedure are the presence of congenital pathologies or diseases in the family, fetal hypoxia during pregnancy, asphyxia during childbirth, or birth trauma.

Methods for diagnosing congenital abnormalities

Modern medicine helps prevent the birth of children with severe malformations of the cerebral cortex. To do this, screening is performed in the first trimester of pregnancy, which makes it possible to identify pathologies in the structure and development of the brain at the earliest stages.

In a newborn baby with suspected pathology, neurosonography is performed through the “fontanel,” and older children and adults are examined by conducting. This method allows not only to detect a defect, but also to visualize its size, shape and location.

If there are hereditary problems in the family related to the structure and functioning of the cortex and the entire brain, consultation with a geneticist and specific examinations and tests are required.

The famous “gray cells” are the greatest achievement of evolution and the greatest benefit for humans. Damage can be caused not only by hereditary diseases and injuries, but also by acquired pathologies provoked by the person himself. Doctors urge you to take care of your health, give up bad habits, allow your body and brain to rest and not let your mind get lazy. Loads are useful not only for muscles and joints - they do not allow nerve cells to age and fail. Those who study, work and exercise their brain suffer less from wear and tear and later come to a loss of mental abilities.

Cerebral cortex - layer gray matter on the surface of the cerebral hemispheres, 2-5 mm thick, forming numerous grooves and convolutions significantly increasing its area. The cortex is formed by the bodies of neurons and glial cells arranged in layers (“screen” type of organization). Underneath lies white matter represented by nerve fibers.

The cortex is the youngest phylogenetically and the most complex in morphofunctional organization of the brain. This is the place of higher analysis and synthesis of all information entering the brain. This is where the integration of all complex forms of behavior occurs. The cerebral cortex is responsible for consciousness, thinking, memory, “heuristic activity” (the ability to make generalizations and discoveries). The cortex contains more than 10 billion neurons and 100 billion glial cells.

Cortical neurons in terms of the number of processes, they are only multipolar, but in terms of their place in the reflex arcs and the functions they perform, they are all intercalary and associative. Based on function and structure, more than 60 types of neurons are distinguished in the cortex. Based on their shape, there are two main groups: pyramidal and non-pyramidal. Pyramid neurons are the main type of neurons in the cortex. The sizes of their perikaryons range from 10 to 140 microns; in cross-section they have a pyramidal shape. A long (apical) dendrite extends upward from their upper corner, which is divided in a T-shape in the molecular layer. Lateral dendrites extend from the lateral surfaces of the neuron body. The dendrites and cell body of the neuron have numerous synapses with other neurons. An axon extends from the base of the cell, which either goes to other parts of the cortex, or to other parts of the brain and spinal cord. Among the neurons of the cerebral cortex there are associative– connecting areas of the cortex within one hemisphere, commissural– their axons go to the other hemisphere, and projection– their axons go to the underlying parts of the brain.

Among non-pyramidal The most common types of neurons are stellate and spindle cells. Star-shaped neurons are small cells with short, highly branching dendrites and axons that form intracortical connections. Some of them have an inhibitory effect, while others have an excitatory effect on pyramidal neurons. Fusiform neurons have a long axon that can go in a vertical or horizontal direction. The cortex is built according to screen type, that is, neurons similar in structure and function are arranged in layers (Fig. 9-7). There are six such layers in the cortex:

1.Molecular layer - the most external. It contains a plexus of nerve fibers located parallel to the surface of the cortex. The bulk of these fibers are branches of the apical dendrites of pyramidal neurons of the underlying layers of the cortex. Afferent fibers from the visual thalamus also come here, regulating the excitability of cortical neurons. Neurons in the molecular layer are mostly small and fusiform.

2. Outer granular layer. Consists of a large number of stellate cells. Their dendrites extend into the molecular layer and form synapses with thalamo-cortical afferent nerve fibers. Lateral dendrites communicate with neighboring neurons of the same layer. Axons form association fibers that travel through the white matter to neighboring areas of the cortex and form synapses there.

3. Outer layer of pyramidal neurons(pyramidal layer). It is formed by medium-sized pyramidal neurons. Just like the neurons of the second layer, their dendrites go to the molecular layer, and their axons go to the white matter.

4. Inner granular layer. It contains many stellate neurons. These are associative, afferent neurons. They form numerous connections with other cortical neurons. Here is another layer of horizontal fibers.

5. Inner layer of pyramidal neurons(ganglionic layer). It is formed by large pyramidal neurons. The latter are especially large in the motor cortex (precentral gyrus), where they measure up to 140 microns and are called Betz cells. Their apical dendrites rise into the molecular layer, lateral dendrites form connections with neighboring Betz cells, and axons are projection efferent fibers going to the medulla oblongata and spinal cord.

6. Layer of fusiform neurons(layer of polymorphic cells) consists mainly of spindle neurons. Their dendrites go to the molecular layer, and their axons go to the visual hillocks.

The six-layer type of structure of the cortex is characteristic of the entire cortex, however, in different parts of it, the severity of the layers, as well as the shape and location of neurons and nerve fibers, vary significantly. Based on these characteristics, K. Brodman identified 50 cytoarchitectonics in the cortex fields. These fields also differ in function and metabolism.

The specific organization of neurons is called cytoarchitectonics. Thus, in the sensory zones of the cortex, the pyramidal and ganglion layers are poorly expressed, and the granular layers are well expressed. This type of bark is called granular. In the motor zones, on the contrary, the granular layers are poorly developed, while the pyramidal layers are well developed. This agranular type bark.

In addition, there is a concept myeloarchitecture. This is a specific organization of nerve fibers. Thus, in the cerebral cortex there are vertical and three horizontal bundles of myelinated nerve fibers. Among the nerve fibers of the cerebral cortex there are associative– connecting areas of the cortex of one hemisphere, commissural– connecting the cortex of different hemispheres and projection fibers – connecting the cortex with the nuclei of the brain stem.

Rice. 9-7. Cortex of the large hemispheres of the human brain.

A, B. Cell location (cytoarchitecture).

B. Location of myelin fibers (myeloarchitecture).

The cerebral cortex is the center of higher nervous (mental) activity in humans and controls the performance of a huge number of vital functions and processes. It covers the entire surface of the cerebral hemispheres and occupies about half of their volume.

The cerebral hemispheres occupy about 80% of the volume of the cranium, and consist of white matter, the basis of which consists of long myelinated axons of neurons. The outside of the hemisphere is covered by gray matter or the cerebral cortex, consisting of neurons, unmyelinated fibers and glial cells, which are also contained in the thickness of the sections of this organ.

The surface of the hemispheres is conventionally divided into several zones, the functionality of which is to control the body at the level of reflexes and instincts. It also contains the centers of higher mental activity of a person, ensuring consciousness, assimilation of received information, allowing adaptation in the environment, and through it, at the subconscious level, through the hypothalamus, the autonomic nervous system (ANS) is controlled, which controls the organs of circulation, respiration, digestion, excretion , reproduction, and metabolism.

In order to understand what the cerebral cortex is and how its work is carried out, it is necessary to study the structure at the cellular level.

Functions

The cortex occupies most of the cerebral hemispheres, and its thickness is not uniform over the entire surface. This feature is due to the large number of connecting channels with the central nervous system (CNS), which ensure the functional organization of the cerebral cortex.

This part of the brain begins to form during fetal development and is improved throughout life, by receiving and processing signals coming from the environment. Thus, it is responsible for performing the following brain functions:

connects the organs and systems of the body with each other and the environment, and also ensures an adequate response to changes;
processes incoming information from motor centers using mental and cognitive processes;
consciousness and thinking are formed in it, and intellectual work is also realized;
controls speech centers and processes that characterize the psycho-emotional state of a person.

In this case, data is received, processed, and stored thanks to a significant number of impulses passing through and generated in neurons connected by long processes or axons. The level of cell activity can be determined by the physiological and mental state of the body and described using amplitude and frequency indicators, since the nature of these signals is similar to electrical impulses, and their density depends on the area in which the psychological process occurs.

It is still unclear how the frontal part of the cerebral cortex affects the functioning of the body, but it is known that it is little susceptible to processes occurring in the external environment, therefore all experiments with the influence of electrical impulses on this part of the brain do not find a clear response in the structures . However, it is noted that people whose frontal part is damaged experience problems communicating with other individuals, cannot realize themselves in any work activity, and they are also indifferent to their appearance and outside opinions. Sometimes there are other violations in the performance of the functions of this body:

lack of concentration on everyday objects;
manifestation of creative dysfunction;
disorders of a person’s psycho-emotional state.

The surface of the cerebral cortex is divided into 4 zones, outlined by the most distinct and significant convolutions. Each part controls the basic functions of the cerebral cortex:

parietal zone - responsible for active sensitivity and musical perception;
the primary visual area is located in the occipital part;
the temporal or temporal is responsible for speech centers and the perception of sounds coming from the external environment, in addition, it is involved in the formation of emotional manifestations, such as joy, anger, pleasure and fear;
The frontal zone controls motor and mental activity, and also controls speech motor skills.

Features of the structure of the cerebral cortex

The anatomical structure of the cerebral cortex determines its characteristics and allows it to perform the functions assigned to it. The cerebral cortex has the following number of distinctive features:

neurons in its thickness are arranged in layers;
nerve centers are located in a specific place and are responsible for the activity of a certain part of the body;
the level of activity of the cortex depends on the influence of its subcortical structures;
it has connections with all underlying structures of the central nervous system;
the presence of fields of different cellular structure, which is confirmed by histological examination, while each field is responsible for performing some higher nervous activity;
the presence of specialized associative areas makes it possible to establish a cause-and-effect relationship between external stimuli and the body’s response to them;
the ability to replace damaged areas with nearby structures;
This part of the brain is capable of storing traces of neuronal excitation.

The large hemispheres of the brain consist mainly of long axons, and also contain in their thickness clusters of neurons that form the largest nuclei of the base, which are part of the extrapyramidal system.

As already mentioned, the formation of the cerebral cortex occurs during intrauterine development, and at first the cortex consists of the lower layer of cells, and already at 6 months of the child all structures and fields are formed in it. The final formation of neurons occurs by the age of 7, and the growth of their bodies is completed at 18 years.

An interesting fact is that the thickness of the cortex is not uniform over its entire length and includes a different number of layers: for example, in the area of the central gyrus it reaches its maximum size and has all 6 layers, and sections of the old and ancient cortex have 2 and 3 layers. x layer structure, respectively.

The neurons of this part of the brain are programmed to restore the damaged area through synoptic contacts, so each of the cells actively tries to restore damaged connections, which ensures the plasticity of neural cortical networks. For example, when the cerebellum is removed or dysfunctional, the neurons connecting it with the terminal section begin to grow into the cerebral cortex. In addition, the plasticity of the cortex also manifests itself under normal conditions, when the process of learning a new skill occurs or as a result of pathology, when the functions performed by the damaged area are transferred to neighboring areas of the brain or even hemispheres.

The cerebral cortex has the ability to retain traces of neuronal excitation for a long time. This feature allows you to learn, remember and respond with a certain reaction of the body to external stimuli. This is how the formation of a conditioned reflex occurs, the neural pathway of which consists of 3 series-connected apparatuses: an analyzer, a closing apparatus of conditioned reflex connections and a working device. Weakness of the closure function of the cortex and trace manifestations can be observed in children with severe mental retardation, when the formed conditioned connections between neurons are fragile and unreliable, which entails learning difficulties.

The cerebral cortex includes 11 areas consisting of 53 fields, each of which is assigned its own number in neurophysiology.

Regions and zones of the cortex

The cortex is a relatively young part of the central nervous system, developing from the terminal part of the brain. The evolutionary development of this organ occurred in stages, so it is usually divided into 4 types:

The archicortex or ancient cortex, due to the atrophy of the sense of smell, has turned into the hippocampal formation and consists of the hippocampus and its associated structures. With its help, behavior, feelings and memory are regulated.
The paleocortex, or old cortex, makes up the bulk of the olfactory area.
The neocortex or new cortex has a layer thickness of about 3-4 mm. It is a functional part and performs higher nervous activity: it processes sensory information, gives motor commands, and also forms conscious thinking and human speech.
The mesocortex is an intermediate version of the first 3 types of cortex.

Physiology of the cerebral cortex

The cerebral cortex has a complex anatomical structure and includes sensory cells, motor neurons and internerons, which have the ability to stop the signal and be excited depending on the received data. The organization of this part of the brain is built according to the columnar principle, in which the columns are divided into micromodules that have a homogeneous structure.

The basis of the micromodule system is made up of stellate cells and their axons, while all neurons react equally to the incoming afferent impulse and also send an efferent signal synchronously in response.

The formation of conditioned reflexes that ensure the full functioning of the body occurs due to the connection of the brain with neurons located in various parts of the body, and the cortex ensures synchronization of mental activity with the motor skills of organs and the area responsible for analyzing incoming signals.

Signal transmission in the horizontal direction occurs through transverse fibers located in the thickness of the cortex, and transmit the impulse from one column to another. Based on the principle of horizontal orientation, the cerebral cortex can be divided into the following areas:

associative;
sensory (sensitive);
motor.

When studying these zones, various methods of influencing the neurons included in its composition were used: chemical and physical stimulation, partial removal of areas, as well as the development of conditioned reflexes and registration of biocurrents.

The associative zone connects incoming sensory information with previously acquired knowledge. After processing, it generates a signal and transmits it to the motor zone. In this way, it is involved in remembering, thinking, and learning new skills. Association areas of the cerebral cortex are located in proximity to the corresponding sensory area.

The sensitive or sensory area occupies 20% of the cerebral cortex. It also consists of several components:

somatosensory, located in the parietal zone, is responsible for tactile and autonomic sensitivity;
visual;
auditory;
taste;
olfactory.

Impulses from the limbs and organs of touch on the left side of the body enter along afferent pathways to the opposite lobe of the cerebral hemispheres for subsequent processing.

Neurons of the motor zone are excited by impulses received from muscle cells and are located in the central gyrus of the frontal lobe. The mechanism of data receipt is similar to the mechanism of the sensory zone, since the motor pathways form an overlap in the medulla oblongata and follow to the opposite motor zone.

Convolutions, grooves and fissures

The cerebral cortex is formed by several layers of neurons. A characteristic feature of this part of the brain is a large number of wrinkles or convolutions, due to which its area is many times greater than the surface area of the hemispheres.

Cortical architectonic fields determine the functional structure of areas of the cerebral cortex. All of them are different in morphological characteristics and regulate different functions. In this way, 52 different fields are identified, located in certain areas. According to Brodmann, this division looks like this:

The central sulcus separates the frontal lobe from the parietal region; the precentral gyrus lies in front of it, and the posterior central gyrus lies behind it.
The lateral groove separates the parietal zone from the occipital zone. If you separate its side edges, you can see a hole inside, in the center of which there is an island.
The parieto-occipital sulcus separates the parietal lobe from the occipital lobe.

The core of the motor analyzer is located in the precentral gyrus, while the upper parts of the anterior central gyrus belong to the muscles of the lower limb, and the lower parts belong to the muscles of the oral cavity, pharynx and larynx.

The right-sided gyrus forms a connection with the motor system of the left half of the body, the left-sided one - with the right side.

The posterior central gyrus of the 1st lobe of the hemisphere contains the core of the tactile sensation analyzer and is also connected with the opposite part of the body.

Cell layers

The cerebral cortex carries out its functions through neurons located in its thickness. Moreover, the number of layers of these cells may differ depending on the area, the dimensions of which also vary in size and topography. Experts distinguish the following layers of the cerebral cortex:

The surface molecular layer is formed mainly from dendrites, with a small inclusion of neurons, the processes of which do not leave the boundaries of the layer.
The external granular consists of pyramidal and stellate neurons, the processes of which connect it with the next layer.
The pyramidal layer is formed by pyramidal neurons, the axons of which are directed downward, where they break off or form associative fibers, and their dendrites connect this layer with the previous one.
The internal granular layer is formed by stellate and small pyramidal neurons, the dendrites of which extend into the pyramidal layer, and its long fibers extend into the upper layers or descend down into the white matter of the brain.
The ganglion consists of large pyramidal neurocytes, their axons extend beyond the cortex and connect various structures and sections of the central nervous system with each other.

The multiform layer is formed by all types of neurons, and their dendrites are oriented into the molecular layer, and axons penetrate the previous layers or extend beyond the cortex and form associative fibers that form a connection between gray matter cells and the rest of the functional centers of the brain.

Video: Cerebral cortex

glial cells; it is located in some parts of the deep brain structures; the cerebral cortex (as well as the cerebellum) is formed from this substance.

Each hemisphere is divided into five lobes, four of which (frontal, parietal, occipital and temporal) are adjacent to the corresponding bones of the cranial vault, and one (insular) is located in depth, in the fossa that separates the frontal and temporal lobes.

The cerebral cortex has a thickness of 1.5–4.5 mm, its area increases due to the presence of grooves; it is connected to other parts of the central nervous system, thanks to impulses carried out by neurons.

The hemispheres reach approximately 80% of the total mass of the brain. They regulate higher mental functions, while the brain stem regulates lower ones, which are associated with the activity of internal organs.

Three main areas are distinguished on the hemispheric surface:

convex superolateral, which is adjacent to the inner surface of the cranial vault;
lower, with the anterior and middle sections located on the inner surface of the cranial base and the posterior ones in the area of the tentorium of the cerebellum;
the medial one is located at the longitudinal fissure of the brain.

Features of the device and activity

The cerebral cortex is divided into 4 types:

ancient - occupies slightly more than 0.5% of the entire surface of the hemispheres;
old – 2.2%;
new – more than 95%;
the average is approximately 1.5%.

The phylogenetically ancient cerebral cortex, represented by groups of large neurons, is pushed aside by the new one to the base of the hemispheres, becoming a narrow strip. And the old one, consisting of three cellular layers, moves closer to the middle. The main area of the old cortex is the hippocampus, which is the central part of the limbic system. The middle (intermediate) cortex is a formation of a transitional type, since the transformation of old structures into new ones occurs gradually.

The cerebral cortex in humans, unlike that in mammals, is also responsible for the coordinated functioning of internal organs. This phenomenon, in which the role of the cortex in the implementation of all functional activities of the body increases, is called corticalization of functions.

One of the features of the cortex is its electrical activity, which occurs spontaneously. Nerve cells located in this section have a certain rhythmic activity, reflecting biochemical and biophysical processes. Activity has different amplitudes and frequencies (alpha, beta, delta, theta rhythms), which depends on the influence of numerous factors (meditation, sleep phases, stress, the presence of seizures, neoplasms).

Structure

The cerebral cortex is a multilayered formation: each layer has its own specific composition of neurocytes, a specific orientation, and location of processes.

The systematic position of neurons in the cortex is called “cytoarchitecture”; fibers located in a certain order are called “myeloarchitecture”.

The cerebral cortex consists of six cytoarchitectonic layers.

Surface molecular, in which there are not very many nerve cells. Their processes are located within itself, and they do not go beyond.
The outer granular is formed from pyramidal and stellate neurocytes. The processes emerge from this layer and go to subsequent ones.
Pyramidal consists of pyramidal cells. Their axons go down, where they end or form association fibers, and their dendrites go up into the second layer.
The internal granular cell is formed by stellate cells and small pyramidal cells. Dendrites go to the first layer, lateral processes branch within their layer. Axons extend into the upper layers or into the white matter.
The ganglion is formed by large pyramidal cells. The largest neurocytes of the cortex are located here. Dendrites are directed into the first layer or distributed in its own. Axons emerge from the cortex and begin to become fibers that connect various sections and structures of the central nervous system with each other.
Multiform - consists of different cells. Dendrites go to the molecular layer (some only to the fourth or fifth layers). Axons are directed to overlying layers or exit the cortex as association fibers.

The cerebral cortex is divided into areas - the so-called horizontal organization. There are 11 of them in total, and they include 52 fields, each of which has its own serial number.

Vertical organization

There is also a vertical division - into columns of neurons. In this case, small columns are combined into macrocolumns, which are called a functional module. At the heart of such systems are stellate cells - their axons, as well as their horizontal connections with the lateral axons of pyramidal neurocytes. All nerve cells of the vertical columns respond to the afferent impulse in the same way and together send an efferent signal. Excitation in the horizontal direction is due to the activity of transverse fibers that follow from one column to another.

He first discovered units that unite neurons of different layers vertically in 1943. Lorente de No - using histology. This was subsequently confirmed using electrophysiological methods in animals by V. Mountcastle.

The development of the cortex in intrauterine development begins early: already at 8 weeks the embryo has a cortical plate. First, the lower layers are differentiated, and at 6 months the unborn child has all the fields that are present in an adult. The cytoarchitectonic features of the cortex are fully formed by the age of 7, but the bodies of neurocytes increase even up to 18. For the formation of the cortex, the coordinated movement and division of precursor cells from which neurons appear is necessary. It has been established that this process is influenced by a special gene.

Horizontal organization

It is customary to divide the areas of the cerebral cortex into:

associative;
sensory (sensitive);
motor.

Scientists, when studying localized areas and their functional characteristics, used a variety of methods: chemical or physical irritation, partial removal of brain areas, development of conditioned reflexes, registration of brain biocurrents.

Sensitive

These areas occupy approximately 20% of the cortex. Damage to such areas leads to impaired sensitivity (decreased vision, hearing, smell, etc.). The area of the zone directly depends on the number of nerve cells that perceive impulses from certain receptors: the more there are, the higher the sensitivity. Zones are distinguished:

somatosensory (responsible for cutaneous, proprioceptive, vegetative sensitivity) - it is located in the parietal lobe (postcentral gyrus);
visual, bilateral damage that leads to complete blindness, is located in the occipital lobe;
auditory (located in the temporal lobe);
gustatory, located in the parietal lobe (localization - postcentral gyrus);
olfactory, bilateral impairment of which leads to loss of smell (located in the hippocampal gyrus).

Disruption of the auditory zone does not lead to deafness, but other symptoms appear. For example, the inability to distinguish short sounds, the meaning of everyday noises (footsteps, pouring water, etc.) while maintaining the differences in sounds in pitch, duration, and timbre. Amusia may also occur, which is the inability to recognize, reproduce melodies, and also distinguish between them. Music can also be accompanied by unpleasant sensations.

Impulses traveling along afferent fibers on the left side of the body are perceived by the right hemisphere, and on the right side - by the left (damage to the left hemisphere will cause a violation of sensitivity on the right side and vice versa). This is due to the fact that each postcentral gyrus is connected to the opposite part of the body.

Motor

Motor areas, the irritation of which causes muscle movement, are located in the anterior central gyrus of the frontal lobe. Motor areas communicate with sensory areas.

The motor tracts in the medulla oblongata (and partly in the spinal cord) form a decussation with a transition to the opposite side. This leads to the fact that irritation that occurs in the left hemisphere enters the right half of the body, and vice versa. Therefore, damage to the cortex of one of the hemispheres leads to disruption of the motor function of muscles on the opposite side of the body.

The motor and sensory areas, which are located in the area of the central sulcus, are combined into one formation - the sensorimotor zone.

Neurology and neuropsychology have accumulated a lot of information about how damage to these areas leads not only to elementary movement disorders (paralysis, paresis, tremors), but also to disorders of voluntary movements and actions with objects - apraxia. When they appear, movements during writing may be disrupted, spatial representations may be disrupted, and uncontrolled patterned movements may appear.

Associative

These zones are responsible for linking incoming sensory information with that which was previously received and stored in memory. In addition, they allow you to compare information that comes from different receptors. The response to the signal is formed in the associative zone and transmitted to the motor zone. Thus, each associative area is responsible for the processes of memory, learning and thinking. Large association zones are located next to the corresponding functional sensory zones. For example, any associative visual function is controlled by the visual associative area, which is located next to the sensory visual area.

Establishing patterns of brain function, analyzing its local disorders and checking its activity is carried out by the science of neuropsychology, which is at the intersection of neurobiology, psychology, psychiatry and computer science.

Features of localization by fields

The cerebral cortex is plastic, which affects the transition of the functions of one section, if it is disrupted, to another. This is due to the fact that analyzers in the cortex have a core, where higher activity occurs, and a periphery, which is responsible for the processes of analysis and synthesis in a primitive form. Between the analyzer cores there are elements that belong to different analyzers. If damage concerns the nucleus, peripheral components begin to be responsible for its activity.

Thus, the localization of the functions that the cerebral cortex possesses is a relative concept, since there are no definite boundaries. However, cytoarchitectonics suggests the presence of 52 fields that communicate with each other via conductive pathways:

associative (this type of nerve fibers is responsible for the activity of the cortex in one hemisphere);
commissural (connect symmetrical areas of both hemispheres);
projection (promote communication between the cortex and subcortical structures and other organs).

Table 1

		Relevant fields
Motor
Sensitive
Visual
Olfactory
Flavoring
Speech motor, which includes the centers:	Wernicke, which allows you to perceive spoken language
	Broca - responsible for the movement of the lingual muscles; defeat threatens complete loss of speech
	Perception of speech in writing

So, the structure of the cerebral cortex involves viewing it in horizontal and vertical orientation. Depending on this, vertical columns of neurons and zones located in the horizontal plane are distinguished. The main functions performed by the cortex are the implementation of behavior, regulation of thinking, and consciousness. In addition, it ensures the interaction of the body with the external environment and takes part in controlling the functioning of internal organs.