Sections of the cerebral cortex. The cerebral cortex and the variety of its functions. Middle cerebral artery
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The cerebral cortex (cloak) is the most highly differentiated part of the nervous system; it is heterogeneous and consists of a huge number of nerve cells. The total area of the bark is about 1200 square centimeters, 2/3 of which lies deep in the furrows. In accordance with phylogeny, ancient, old, middle and new bark are distinguished (Fig. 26).
ANCIENT CORTEX (paleocortecx) includes the unstructured cortex around the anterior perforated substance: periterminal gyrus, subcallosal area (located on the inner side of the hemispheres under the knee and beak of the corpus callosum).
OLD CORTEX (archicortex), two-three-layer, located in the hippocampus and dentate gyrus.
THE MIDDLE CORTEX (mesocortex) occupies the lower part of the insula, the parahippocampal gyrus and the inferior limbic region; its cortex is not completely differentiated.
NEW CORTEX (neocortex) makes up 96% of the entire surface of the hemispheres. According to its morphological features, there are 6 main layers, but in different areas of the cortex the number of layers varies.
Layers of bark(Fig. 26):
1 - MOLECULAR. There are few cells, it consists mainly of horizontal fibers of ascending axons, including nonspecific afferents from the thalamus, and also in this layer the branches of the apical (apical) dendrites of the 4th layer of the cortex end.
2 - EXTERNAL GRAINY. It consists of stellate and small pyramidal cells, the axons of which end in layers 3, 5 and 6, i.e. participates in connecting different layers of the cortex.
3 - EXTERNAL PYRAMIDS. This layer has two sublayers. External - consists of smaller cells that communicate with neighboring areas of the cortex, especially well developed in the visual cortex. The inner sublayer contains larger cells that participate in the formation of commissural connections (connections between the two hemispheres).
4 - INNER GRAINED. Includes granular, stellate and small pyramidal cells. Their apical dendrites rise into the 1st layer of the cortex, and the basal ones (from the base of the cell) into the 6th layer of the cortex, i.e. participate in the implementation of intercortical communication.
5 - GANGLIOUS. Its basis is made up of giant pyramids (Betz cells). Their apical dendrite extends to layer 1, basal dendrites run parallel to the surface of the cortex, and axons form projection tracts to the basal ganglia, brainstem, and spinal cord.
6 - POLYMORPHIC. It contains cells of various shapes, but predominantly spindle-shaped. Their axons go up, but mostly down, and form associative and projection pathways that pass into the white matter of the brain.
Cells of different layers of the cortex are combined into “modules” - structural and functional units. These are groups of neurons of 10-1000 cells that perform certain functions and “process” one or another type of information. The cells of this group are predominantly located perpendicular to the surface of the cortex and are often called “columnar modules”.
Rice. 26. Structure of the cerebral cortex
I. molecular
II. external granular
III. external pyramidal
IV. internal granular
V. ganglionic (giant pyramids)
VI. polymorphic
Rice. 27 Left hippocampus
7. corpus callosum
8. roller
9. bird spur
10. hippocampus
11. fringe
12. Leg
In humans, this is the superficial layer that covers the cerebral hemisphere and is predominantly formed by vertically oriented nerve cells (the so-called neurons), as well as their processes and efferent (centrifugal), afferent bundles (centripetal) and nerve fibers.
In addition, the composition of the cortex also includes cells, as well as neuroglia.
A very significant feature of the structure is the horizontal dense layering, which is primarily due to the entire ordered arrangement of each body of nerve cells and fibers. There are 6 main layers, which mainly differ in their own width, the overall density of its location, the size and shape of all the constituent external neurons.
Mainly, precisely because of their vertical orientation of the processes, these bundles of all the different nerve fibers, as well as the bodies of neurons, which have vertical striations. And for the full functional organization of the human cerebral cortex, the columnar, vertical location of absolutely all internal nerve cells on the surface of the cerebral cortex zone is of great importance here.
The main type of all the main nerve cells that make up the cerebral cortex are special pyramidal cells. The body of these cells resembles an ordinary cone, from the height of which one long and thick apical dendrite begins to extend. From the base of the body of this pyramidal cell, an axon and shorter basal dendrites also extend, heading into the full-fledged white matter, which is located directly under the cerebral cortex, or branching in the cortex.
All dendrites of the pyramid cells bear a fairly large number of spines and outgrowths, which take the most active part in the full formation of synaptic contacts at the end of afferent fibers that come to the cerebral cortex from other subcortical formations and parts of the cortex. The axons of these cells are capable of forming efferent main pathways that go directly from the C.G.M. The sizes of all pyramidal cells can vary from 5 to 150 microns (150 are Betz giant cells). In addition to pyramidal neurons K.G.M. it contains some fusiform and stellate types of interneurons, which are involved in the reception of incoming afferent signals, as well as the formation of interneuron functional connections.
Features of the cerebral cortex
Based on various phylogenetic data, the cerebral cortex is divided into ancient (paleocortex), old (archicortex) and new (neocortex). In the phylogeny of K.G.M. There is a relative universal increase in the territory of the new crustal surface with a slight decrease in the area of the old and ancient one.
Functionally, the areas of the cerebral cortex are divided into 3 types: associative, motor and sensory. In addition, the cerebral cortex is also responsible for the corresponding areas.
What is the cerebral cortex responsible for?
In addition, it is important to note that the entire cerebral cortex, in addition to all of the above, is responsible for everything. The zones of the cerebral cortex contain neurons of various structures, including stellate, small and large pyramidal, basket-shaped, fusiform and others. In functional terms, all main neurons are divided into the following types:
- Intercalary neurons (fusiform, small pyramidal and others). Interneurons have subdivisions and can be either inhibitory or excitatory (small and large basket neurons, neurons with brush-shaped neurons and candelabra-shaped axons)
- Afferent (these are the so-called stellate cells) - to which impulses arrive from all specific pathways, and various specific sensations arise. It is these cells that transmit impulses directly to efferent and intercalary neurons. Groups of polysensory neurons respectively receive different impulses from the visual thalamus of the associative nuclei
- Efferent neurons (they are called large pyramidal cells) - impulses from these cells go to the so-called periphery, where they provide a certain type of activity
Neurons, as well as processes on the surface of the cerebral cortex, are also arranged in six layers. Neurons that perform the same reflex functions are located strictly one above the other. Thus, individual columns are considered the main structural unit of the surface of the cerebral cortex. And the most pronounced connection is between the third, fourth and fifth stages of the K.G.M. layers.
Cortical pads
The following factors can also be considered evidence of the presence of columns in the cerebral cortex:
When introducing various microelectrodes into the C.G.M. the impulse is recorded (registered) strictly perpendicularly under the full impact of a similar reflex reaction. And when the electrodes are inserted in a strictly horizontal direction, characteristic impulses for various reflex reactions are recorded. Basically, the diameter of one column is 500 µm. All neighboring columns are tightly connected in all functional terms, and are also often located with each other in close reciprocal relationships (some inhibit, others excite).
When stimuli act on a response, many columns are also involved and a perfect synthesis and analysis of stimuli occurs - this is the principle of screening.
Since the cerebral cortex grows in the periphery, then all the superficial layers of the cerebral cortex are fully related to all signaling systems. These superficial layers consist of a very large number of nerve cells (about 15 billion) and together with their processes, with the help of which the possibility of such unlimited closure functions and broad associations is created - this is the essence of the entire activity of the second signaling system. But with all this, the second s.s. works with other systems.
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45. Cerebral cortex, its structure and significance.
Cerebral cortex- structure of the brain, a layer of gray matter 1.3-4.5 mm thick, located along the periphery of the cerebral hemispheres and covering them.
The cerebral cortex plays a very important role in the implementation of higher nervous (mental) activity.
In humans, the cortex makes up on average 44% of the volume of the entire hemisphere as a whole.
The cerebral cortex covers the surface of the hemispheres and forms a large number of grooves of varying depth and length. Between the grooves there are gyri of the cerebrum of varying sizes.
In each hemisphere the following surfaces are distinguished:
convex superolateral surface adjacent to the inner surface of the bones of the cranial vault
bottom surface, the anterior and middle sections of which are located on the inner surface of the base of the skull, in the region of the anterior and middle cranial fossae, and the posterior sections - on the tentorium of the cerebellum
medial surface directed towards the longitudinal fissure of the brain.
In each hemisphere, the most prominent places are distinguished: in front - the frontal pole, in the back - occipital, and on the side - temporal.
The hemisphere is divided into five lobes. Four of them are adjacent to the corresponding bones of the cranial vault:
The frontal, parietal, occipital, temporal, and insular lobes separate the frontal lobe from the temporal lobe.
The structure of the cerebral cortex and the interaction between its individual parts is called the architectonics of the cerebral cortex. The place where the cerebral cortex performs certain functions: analysis of information received from the senses, their storage, etc., are largely determined by the internal structure and construction of connections (morphology) within specific areas of the brain (such areas are called cortical fields). Another important function of the cerebral cortex is communication with certain external receivers of information(receptors), which are all sense organs, as well as with organs and tissues that carry out commands coming from the cerebral cortex (effectors).
Everything that a person sees is recognized and analyzed in occipital region cerebral cortex, the eye is just an image receiver that transmits it along nerve fibers for analysis to the occipital visual zone.
If the image is moving, then the analysis of the movement of this image occurs in parietal region, and as a result of this analysis we determine in what direction and at what speed the object we see is moving.
Parietal areas of the cortex, together with the temporal areas the cortex takes part in the formation of the act of articulate speech and in the perception of the shape of the human body and its location in space.
Frontal lobes The cerebral cortex in humans are those areas of the cortex that mainly carry out higher mental functions, manifested in the formation of personal qualities, temperament, character, abilities, will, reasonableness of behavior, creative inclinations and talent, drives and addictions, in general, everything that makes a person an individual, unlike all other people, and in building purposeful behavior based on foresight. All these abilities are sharply impaired when the frontal parts of the cerebral cortex are damaged.
The most extensive damage to the cerebral cortex is accompanied by a complete disappearance of mental activity.
1. What is the structure of the cerebral cortex?
The cerebral cortex is a layer of gray matter 2-4 mm thick. It is formed by nerve cells (about 14 billion) located on the surface of the forebrain. Furrows (depressions), convolutions (folds) increase the surface area of the cortex (up to 2000-2500 cm2).
2. What lobes are distinguished in the cerebral cortex?
The cortex of the cerebral hemispheres is divided into lobes by deep grooves. In each hemisphere there is a frontal lobe, parietal, temporal and occipital. The frontal lobe is separated from the parietal lobe by a central sulcus. The temporal lobe is separated from the frontal and parietal by a lateral sulcus. The occipital lobe is separated from the parietal by a less deep parieto-occipital sulcus.
3. What functions does the cerebral cortex perform?
The cerebral cortex is responsible for the perception of all information entering the brain (visual, auditory, tactile, gustatory, etc.), for the control of all complex muscle movements. Mental functions (memory, speech, thinking, etc.) are associated with the work of the large hemispheres.
4. What is the location of the areas responsible for the functions of the cortex?
In the cerebral cortex, sensory, motor and associative zones are distinguished.
The sensory zones contain the central sections of the analyzers, i.e. information received from the senses is processed. The somatosensory zone (skin sensitivity) is located in the posterior central gyrus, posterior to the central sulcus. This zone receives impulses from skeletal muscles, tendons and joints, as well as impulses from tactile, temperature and other skin receptors. The right hemisphere receives impulses from the left half of the body, and the left hemisphere receives impulses from the right. The visual zone is located in the occipital region of the cortex. Impulses from the retina come to this zone. The auditory zone is located in the temporal region. Stimulation of this area causes the sensation of low or high, loud or quiet sounds. The taste zone is located in the parietal region, in the lower part of the posterior central gyrus. When it is irritated, various taste sensations arise. Material from the site
Motor zones are the parts of the cerebral cortex, the stimulation of which causes movement. The motor zone is located in the anterior central villus (in front of the central sulcus). The upper part of the hemispheres is associated with the regulation of movements of the lower extremities, then the torso, even lower than the arms, and then the muscles of the face and head. The largest space is occupied by the motor zone of the hand and fingers and facial muscles, the smallest - by the muscles of the torso. The paths along which impulses travel from the cerebral hemispheres to the muscles form a cross, therefore, when the motor zone of the right side of the cortex is irritated, a contraction of the muscles on the left side of the body occurs.
Association zones (in particular, the parietal lobe) connect different areas of the cortex. The activity of these zones underlies the higher mental functions of a person. In this case, the right hemisphere is responsible for figurative (recognition of people, perception of music, artistic creativity) thinking, the left hemisphere for abstract (written and oral speech, mathematical operations) thinking.
The activity of each human organ is under the control of the cerebral cortex.
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The human brain has a small top layer, approximately 0.4 cm thick. This is the cerebral cortex. It serves to perform a large number of functions used in various aspects of life. This direct influence of the cortex most often affects human behavior and consciousness.
The cerebral cortex has an average thickness of approximately 0.3 cm and a rather impressive volume due to the presence of connecting channels with the central nervous system. Information is perceived, processed, and a decision is made due to a large number of impulses that pass through neurons, as if along an electrical circuit. Depending on various conditions, electrical signals are produced in the cerebral cortex. The level of their activity can be determined by a person’s well-being and described using amplitude and frequency indicators. There is a fact that many connections are localized in areas that are involved in complex processes. In addition to the above, the human cerebral cortex is not considered complete in its structure and develops throughout the entire period of life in the process of forming human intelligence. When receiving and processing information signals that enter the brain, a person is provided with reactions of a physiological, behavioral, and mental nature due to the functions of the cerebral cortex. These include:
- The interaction of organs and systems in the body with the environment and with each other, the proper course of metabolic processes.
- Proper reception and processing of information signals, their awareness through mental processes.
- Maintaining the interconnection of the different tissues and structures that make up the organs in the human body.
- Education and functioning of consciousness, intellectual and creative work of the individual.
- Control over speech activity and processes that are associated with psycho-emotional situations.
It is necessary to say about the incomplete study of the place and significance of the anterior sections of the cerebral cortex in ensuring the functioning of the human body. It is known about such zones that they are low susceptibility to external influences. For example, the impact of an electrical impulse on these areas does not manifest itself in bright reactions. According to some scientists, their functions are self-awareness, the presence and nature of specific features. People with lesions in the anterior cortex have problems with socialization, they lose interest in the world of work, and they lack attention to their appearance and the opinions of others. Other possible effects:
- loss of ability to concentrate;
- creative skills are partially or completely lost;
- deep psycho-emotional disorders of the individual.
Layers of bark
The functions performed by the cortex are often determined by the structure of the structure. The structure of the cerebral cortex is distinguished by its characteristics, which are expressed in a different number of layers, sizes, topography and structure of the nerve cells that form the cortex. Scientists distinguish several different types of layers, which, interacting with each other, contribute to the complete functioning of the system:
- molecular layer: it creates a large number of chaotically woven dendritic formations with a small content of spindle-shaped cells that are responsible for associative functioning;
- outer layer: expressed by a large number of neurons, which have a varied shape and high content. Behind them are the outer limits of the structures, shaped like a pyramid;
- the outer layer is pyramidal in appearance: it contains neurons of small and significant dimensions while the larger ones are located deeper. These cells resemble a cone in shape; a dendrite extends from the top point, which has maximum dimensions; neurons containing gray matter are connected through division into small formations. As they approach the cerebral cortex, the branches are thin and form a structure resembling a fan;
- the inner layer is granular in appearance: it contains nerve cells that are small in size, located at a certain distance, between them there are grouped structures of a fibrous appearance;
- inner layer of pyramidal type: includes neurons that have medium and large dimensions. The upper ends of the dendrites can reach the molecular layer;
- a covering that contains spindle-shaped neuron cells. It is characteristic of them that the part of them that is at the lowest point can reach the level of the white matter.
The various layers that the cerebral cortex includes differ from each other in shape, location and purpose of the elements of their structure. The combined action of neurons in the form of a star, pyramid, spindle and branched species between various layers forms more than 50 fields. Despite the fact that there are no clear limits for the fields, their interaction makes it possible to regulate a large number of processes that are associated with the reception of nerve impulses, information processing and the formation of a counter reaction to stimuli.
The structure of the cerebral cortex is quite complex and has its own characteristics, expressed in a different number of covers, dimensions, topography and structure of cells that form layers.
Cortical areas
The localization of functions in the cerebral cortex is viewed differently by many experts. But most researchers have come to the conclusion that the cerebral cortex can be divided into several main areas, which include cortical fields. Based on the functions performed, this structure of the cerebral cortex is divided into 3 areas:
Area associated with pulse processing
This area is associated with the processing of impulses that come through receptors from the visual system, smell, and touch. The main part of the reflexes that are associated with motor skills is provided by pyramidal-shaped cells. The area responsible for receiving muscle information has a smooth interaction between the various layers of the cerebral cortex, which plays a special role at the stage of proper processing of incoming impulses. When the cerebral cortex is damaged in this area, it provokes disorders in the well-functioning sensory functions and actions that are inextricable from motor skills. Externally, malfunctions in the motor department can manifest themselves with involuntary movements, convulsive twitching, and severe forms leading to paralysis.
Sensory zone
This area is responsible for processing signals that enter the brain. By its structure, it is a system of interaction between analyzers in order to establish feedback on the effect of the stimulant. Scientists have identified several areas that are responsible for sensitivity to impulses. These include the occipital, which provides visual processing; The temporal lobe is associated with hearing; hippocampal area - with the sense of smell. The area that is responsible for processing information from taste stimulants is located near the crown of the head. There, the centers responsible for receiving and processing tactile signals are localized. Sensory ability directly depends on the number of neural connections in a given area. Approximately these zones can occupy up to 1/5 of the total size of the cortex. Damage to such a zone will lead to incorrect perception, which will not make it possible to produce a counter signal adequate to the stimulus influencing it. For example, a malfunction in the auditory zone does not always provoke deafness, but can cause certain effects that distort the proper perception of information. This is expressed in the inability to grasp the length or frequency of a sound, its duration and timbre, failures in recording effects with a short duration of action.
Association zone
This zone makes possible contact between the signals that are received by neurons in the sensory part and motor activity, which is a counter reaction. This department forms meaningful reflexes of behavior, participates in ensuring their actual implementation, and is largely covered by the cerebral cortex. According to the areas of location, the anterior sections are distinguished, which are located near the frontal parts, and the posterior sections, occupying the space between the temples, crown and back of the head. Humans are characterized by a strong development of the posterior parts of the areas of associative perception. These centers are important in ensuring the implementation and processing of speech activity. Damage to the anterior associative area provokes disruptions in the ability to perform analytical functions, forecasting, based on facts or early experience. A malfunction in the posterior association zone complicates orientation in space, slows down abstract three-dimensional thinking, construction and proper interpretation of difficult visual models.
Features of neurological diagnostics
In the process of neurological diagnostics, much attention is paid to movement and sensitivity disorders. Therefore, it is much easier to detect malfunctions in the conductive ducts and initial zones than damage to the associative cortex. It must be said that neurological symptoms may be absent even with extensive damage to the frontal, parietal or temporal area. It is necessary that the assessment of cognitive functions be as logical and consistent as neurological diagnostics.
This type of diagnosis is aimed at fixed relationships between the function of the cerebral cortex and structure. For example, during the period of damage to the striate cortex or optic tract, in the vast majority of cases there is contralateral homonymous hemianopsia. In a situation where the sciatic nerve is damaged, the Achilles reflex is not observed.
Initially, it was believed that the functions of the associative cortex could operate in this way. There was an assumption that there are centers of memory, spatial perception, word processing, therefore, through special tests it is possible to determine the localization of damage. Later, opinions emerged regarding distributed neural systems and the functional orientation within their boundaries. These ideas suggest that distributed systems are responsible for the complex cognitive functions of the cortex - intricate neural circuits, within which cortical and subcortical formations are located.
Consequences of damage
Experts have proven that due to the interconnection of neural structures with each other, in the process of damage to one of the above areas, partial or complete functioning of other structures is observed. As a result of incomplete loss of the ability to perceive, process information or reproduce signals, the system is capable of remaining operational for a certain period of time, having limited functions. This can happen due to the restoration of relationships between undamaged areas of neurons using the distribution system method.
But there is a possibility of the opposite effect, during which damage to one of the parts of the cortex leads to impairment of a number of functions. Be that as it may, a failure in the normal functioning of such an important organ is considered a dangerous deviation, the formation of which should promptly seek help from doctors in order to avoid the subsequent development of disorders. The most dangerous malfunctions in the functioning of such a structure include atrophy, which is associated with the aging and death of some neurons.
The most commonly used examination methods by people are CT and MRI, encephalography, diagnostics using ultrasound, X-rays and angiography. It must be said that current research methods make it possible to detect pathology in the functioning of the brain at a preliminary stage, if you consult a doctor in time. Depending on the type of disorder, it is possible to restore damaged functions.
The cerebral cortex is responsible for brain activity. This leads to changes in the structure of the human brain itself, since its functioning has become much more complex. On top of the brain zones associated with the sensory organs and the motor system, zones were formed that were very densely endowed with associative fibers. Such areas are needed for complex processing of information received by the brain. As a result of the formation of the cerebral cortex, the next stage comes, at which the role of its work increases sharply. The human cerebral cortex is an organ that expresses individuality and conscious activity.