Bark cerebral hemispheres
Cerebral cortex or cerebral cortex(lat. cortex cerebri) - brain structure, layer gray matter 1.3-4.5 mm thick, located along the periphery of the hemispheres big brain, and covering them. The greatest thickness is observed in the upper parts of the precentral, postcentral gyri and paracentral lobule.
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 surface area of the cortex of one hemisphere in an adult is on average 220,000 mm². The superficial parts account for 1/3, and those lying deep between the gyri account for 2/3 of the total area of the cortex.
The size and shape of the grooves are subject to significant individual fluctuations - not only the brains of different people, but even the hemispheres of the same individual are not quite similar in the pattern of the grooves.
The entire cerebral cortex is usually divided into 4 types: ancient (paleocortex), old (archicortex), new (neocortex) and interstitial cortex. The surface of the human neocortex occupies 95.6%, old 2.2%, ancient 0.6%, intermediate 1.6%.
Anatomy
The cerebral cortex covers the surface of the hemispheres and forms a large number of grooves of varying depth and length (lat. sulci cerebri). Between the grooves are located the gyri of the cerebrum of varying sizes (lat. gyri cerebri) .
In each hemisphere the following surfaces are distinguished:
These three surfaces of each hemisphere, passing one into another, form three edges. Upper edge (lat. margo superior) separates the superolateral and medial surfaces. Inferolateral edge (lat. margo inferolateralis) separates the superolateral surface from the inferior one. Inferomedial edge (lat. margo inferomedialis) is located between the inferior and medial surfaces.
In each hemisphere, the most prominent places are distinguished: in front - the frontal pole (lat. polus frontalis), behind - occipital (lat. polus occipitalis), and from the side - temporal (lat. polus temporalis) .
The hemisphere is divided into five lobes. Four of them are adjacent to the corresponding bones of the cranial vault:
- frontal lobe (lat. lobus frontalis)
- parietal lobe (lat. lobus parietalis)
- occipital lobe (lat. lobus occipitalis)
- temporal lobe (lat. lobus temporalis)
Grooves and convolutions of the superolateral surface
Frontal lobe - indicated in blue. Parietal lobe - indicated in yellow. Temporal lobe - indicated in green. Occipital lobe - indicated in pink.
Frontal lobe
The frontal lobe is separated from the parietal lobe by a deep central sulcus (lat. sulcus centralis). It begins on the medial surface of the hemisphere, passes to its superolateral surface, runs along it slightly obliquely, from back to front, and usually does not reach the lateral sulcus of the brain.
Approximately parallel to the central sulcus is the precentral sulcus (lat. sulcus precentralis), which does not reach the upper edge of the hemisphere. The precentral sulcus borders the front of the precentral gyrus (lat. gyrus precentralis) .
Superior and inferior frontal sulcus (lat. sulci frontales superior et inferior ) are directed forward from the precentral sulcus. They divide the frontal lobe into:
From the lateral sulcus, small grooves called rami extend superiorly. The most constant of them are ascending (lat. ramus ascendens) and front (lat. ramus anterior) branches. The superior posterior section of the groove is called the posterior branch (lat. ramus posterior) .
The inferior frontal gyrus, within which the ascending and anterior branches pass, is divided into three parts:
Parietal lobe
It lies posterior to the central sulcus, which separates it from the frontal. It is delimited from the temporal by the lateral sulcus of the brain, from the occipital - by part of the parieto-occipital sulcus (lat. sulcus parietooccipitalis) .
Between the ascending and posterior branches of the lateral sulcus of the brain there is a section of the cortex designated as the frontoparietal operculum (lat. operculum frontoparietalis). It includes the posterior part of the inferior frontal gyrus, the lower parts of the precentral and postcentral gyri, as well as the lower part of the anterior part of the parietal lobe.
Occipital lobe
On the superolateral surface it has no boundaries separating it from the parietal and temporal lobes, with the exception of the upper part of the parieto-occipital sulcus, which is located on the medial surface of the hemisphere and separates the occipital lobe from the parietal lobe.
The largest of the grooves is the transverse occipital groove (lat. sulcus occipitalis transversus ). Sometimes it is a posterior continuation of the intraparietal sulcus and in the posterior section passes into the unstable semilunar sulcus (lat. sulcus lunatus) .
Temporal lobe
Has the most pronounced boundaries. It has a convex lateral surface and a concave bottom surface. The obtuse pole of the temporal lobe faces forward and slightly downward. The lateral cerebral sulcus sharply demarcates the temporal lobe from the frontal lobe.
Two grooves located on the superolateral surface: superior (lat. sulcus temporalis superior) and lower (lat. sulcus temporalis inferior) temporal sulci, following almost parallel to the lateral sulcus of the brain, divide the lobe into three temporal gyri: superior, middle and inferior (lat. gyri temporales superior, medius et inferior ) .
Those parts of the temporal lobe that are directed towards the lateral sulcus of the brain are cut by short transverse temporal sulci (lat. sulci temporales transversi). Between these grooves lie 2-3 short transverse temporal gyri, associated with the gyri of the temporal lobe (lat. gyri temporales transversi) and an island.
Insula (islet)
Lies at the bottom of the lateral fossa of the cerebrum (lat. fossa lateralis cerebri).
It is a three-sided pyramid, facing its apex - the pole of the insula - anteriorly and outwardly, towards the lateral sulcus. From the periphery, the insula is surrounded by the frontal, parietal and temporal lobes, which participate in the formation of the walls of the lateral sulcus of the brain.
The base of the island with three sides surrounded by a circular groove of the islet (lat. sulcus circularis insulae).
Its surface is cut by a deep central groove of the insula (lat. sulcus centralis insulae). This groove divides the insula into anterior and posterior parts.
On the surface there are a large number of small convolutions of the islet (lat. gyri insulae). The large anterior part consists of several short convolutions of the insula (lat. gyri breves insulae), posterior - one long gyrus (lat. gyrus longus insulae) .
Furrows and convolutions of the medial surface
The frontal, parietal and occipital lobes extend onto the medial surface of the hemisphere.
The cingulate gyrus is bounded superiorly by the cingulate groove (lat. sulcus cinguli). In the latter, there is a front part convex towards the frontal pole and a back part, which, following along the cingulate gyrus and not reaching its posterior section, rises to the upper edge of the cerebral hemisphere. The posterior end of the sulcus lies behind the upper end of the central sulcus. Between the precentral sulcus, the end of which is sometimes clearly visible at the upper edge of the medial surface of the hemisphere, and the end of the cingulate sulcus, there is a paracentral lobule (lat. lobulus paracentralis) .
Above the cingulate gyrus, in front of the subcallosal area, begins the medial frontal gyrus (lat. gyrus frontalis medialis). It extends to the paracentral lobule and is the lower part of the superior frontal gyrus.
Behind the cingulate groove lies a small quadrangular lobe - the precuneus (lat. precuneus). Its posterior border is the deep parieto-occipital sulcus (lat. sulcus parietooccipitalis), lower - subparietal groove (lat. sulcus subparietalis), separating the precuneus from the posterior cingulate gyrus.
Behind and below the precuneus lies a triangular lobe - wedge (lat. cuneus). The convex outer surface of the wedge participates in the formation of the occipital pole. The apex of the wedge, directed downward and forward, almost reaches the posterior part of the cingulate gyrus. The posteroinferior border of the wedge is a very deep calcarine groove (lat. sulcus calcarinus), anterior - parieto-occipital sulcus.
Grooves and convolutions of the lower surface
On the lower surface of the frontal lobe is the olfactory groove (lat. sulcus olfactorius). Inwardly from it, between it and the inferomedial edge of the hemisphere, lies the straight gyrus (lat. gyrus rectus). Its posterior section reaches the anterior perforated substance (lat. substantia perforata anterior). Outside the groove is the rest of the lower surface of the frontal lobe, indented by short orbital grooves (lat. sulci orbitales), into a number of small orbital gyri (lat. gyri orbitales) .
The lower surface of the temporal lobe is a deep groove of the hippocampus (lat. sulcus hippocampi) is separated from the cerebral peduncles. In the depths of the furrow lies a narrow dentate gyrus (lat. gyrus dentatus). Its anterior end passes into the hook, and its posterior end into the ribbon gyrus (lat. gyrus fasciolaris) lying under the splenium of the corpus callosum. Lateral to the sulcus is the parahippocampal gyrus (lat. gyrus parahippocampalis). In front of this gyrus there is a thickening in the form of a hook (lat. uncus), and continues posteriorly into the lingual gyrus (lat. gyrus lingualis). The parahippocampal and lingual gyri are limited on the lateral side by the collateral sulcus (lat. sulcus collateralis), passing anteriorly into the nasal groove (lat. sulcus rhinalis). The rest of the lower surface of the temporal lobe is occupied by the medial and lateral occipitotemporal gyri (lat. gyri occipitotemporales medialis et lateralis ), separated by the occipitotemporal groove (lat. sulcus occipitotemporalis). The lateral occipitotemporal gyrus is separated by the inferolateral edge of the hemisphere from the inferior temporal gyrus.
Histology
Structure
Cytoarchitecture (cell arrangement)
- molecular layer
- outer granular layer
- layer of pyramidal neurons
- inner granular layer
- ganglion layer (inner pyramidal layer; Betz cells)
- layer of polymorphic cells
Myeloarchitecture (arrangement of fibers)
The cerebral cortex is represented by a layer of gray matter with an average thickness of about 3 mm (1.3 - 4.5 mm). It is most strongly developed in the anterior central gyrus. The abundance of furrows and convolutions significantly increases the area of gray matter in the brain. The cortex contains about 10-14 billion nerve cells. Its various sections, which differ from each other in certain features of the location and structure of cells (cytoarchitectonics), the arrangement of fibers (myeloarchitectonics) and functional significance, are called fields. They represent places of higher analysis and synthesis of nerve impulses. There are no sharply defined boundaries between them. The cortex is characterized by an arrangement of cells and fibers in layers.
Cytoarchitecture
Pyramidal cells of different layers of the cortex differ in size and have different functional significance. Small cells are interneurons, the axons of which connect individual areas of the cortex of one hemisphere (associative neurons) or two hemispheres (commissural neurons). These cells are found in varying numbers in all layers of the cortex. The human cerebral cortex is especially rich in them. Axons of large pyramidal neurons take part in the formation of pyramidal tracts that project impulses to the corresponding centers of the brain stem and spinal cord.
The neurons of the cortex are located in vaguely delimited layers. Each layer is characterized by the predominance of one type of cell. There are 6 main layers in the motor cortex:
The cerebral cortex also contains a powerful neuroglial apparatus that performs trophic, protective, supporting and delimiting functions.
On the medial and lower surface of the hemispheres, sections of the old, ancient cortex have been preserved, which have a two-layer and three-layer structure.
Molecular layer
The molecular layer of the cortex contains a small number of small spindle-shaped association cells. Their axons run parallel to the surface of the brain as part of the tangential plexus of nerve fibers of the molecular layer. The bulk of the fibers of this plexus are represented by the branching of the dendrites of neurons in the underlying layers.
Outer granular layer
The outer granular layer is formed by small neurons with a diameter of about 10 microns, having a round, angular and pyramidal shape, and stellate neurons. The dendrites of these cells rise into the molecular layer. Axons either go into the white matter, or, forming arcs, also enter the tangential plexus of fibers of the molecular layer.
Layer of pyramidal neurons
It is the widest compared to other layers of the cerebral cortex. It is especially well developed in the precentral gyrus. The size of pyramidal cells consistently increases within 10-40 µm from the outer zone of this layer to the inner one. The main dendrite extends from the top of the pyramidal cell and is located in the molecular layer. The dendrites, originating from the lateral surfaces of the pyramid and its base, are of insignificant length and form synapses with adjacent cells of this layer. The axon of a pyramidal cell always extends from its base. In small cells it remains within the cortex; an axon belonging to a large pyramid usually forms a myelin association or commissural fiber that goes into the white matter.
Inner granular layer
In some fields of the cortex it is very developed (for example, in the visual cortex). However, in other areas it may be absent (in the precentral gyrus). This layer is formed by small stellate neurons. It contains a large number of horizontal fibers.
Ganglion layer (Inner pyramidal layer; Betz cells)
It is formed by large pyramidal cells, and the area of the precentral gyrus contains giant cells, first described by the Kyiv anatomist V. A. Betz in 1874 (Betz cells). They reach a height of 120 and a width of 80 microns. Unlike other pyramidal cells of the cortex, giant Betz cells are characterized by the presence of large clumps of chromatophilic substance. Their axons form the main part of the corticospinal and corticonuclear tracts and terminate on motor neurons of the brain stem and spinal cord.
Multimorph cell layer
Formed by neurons of various, predominantly spindle-shaped shapes. The outer zone of this layer contains larger cells. The neurons of the inner zone are smaller and lie at a greater distance from each other. The axons of the polymorphic layer cells extend into the white matter as part of the efferent pathways of the brain. The dendrites reach the molecular layer of the cortex.
Myeloarchitecture
Among the nerve fibers of the cerebral cortex we can distinguish:
In addition to the tangential plexus of the molecular layer, at the level of the internal granular and ganglion layers there are two tangential layers of myelin nerve fibers and axonal collaterals of cortical cells. By entering into synaptic connections with cortical neurons, horizontal fibers ensure widespread distribution of nerve impulses in it.
Module
I, II, III, IV, V, VI - layers of the cortex
Afferent fibers
1. corticocortical fiber
2. thalamo-cortical fiber
2a. area of distribution of specific thalamo-cortical fibers
3. pyramidal neurons
3a. inhibited pyramidal neurons
4. inhibitory neurons and their synapses
4a. cells with an axonal brush
4b. small basket cells
4c. large basket cages
4g. axoaxonal neurons
4d. cells with a double bouquet of dendrites (inhibitory inhibitory neurons)
5. spiny stellate cells, exciting pyramidal neurons directly and by stimulating cells with a double bouquet of dendrites
Studying the cerebral cortex of the brain, Sentagotai and representatives of his school established that its structural and functional unit is module- vertical column with a diameter of about 300 microns. The module is organized around a cortico-cortical fiber, which is an axon of the pyramidal cell of layer III (layer of pyramidal cells) of the same hemisphere (associative fiber), or from the pyramidal cells of the opposite (commissural). The module includes two thalamo-cortical fibers - specific afferent fibers ending in the fourth layer of the cortex on spiny stellate neurons and extending from the base (basal) dendrites of pyramidal neurons. Each module, according to Szentagothai, is divided into two micromodules with a diameter of less than 100 microns. In total, the human neocortex has approximately 3 million modules. The axons of the pyramidal neurons of the module project to three modules of the same side and through the corpus callosum through commissural fibers to two modules of the opposite hemisphere. Unlike specific afferent fibers ending in layer IV of the cortex, cortico-cortical fibers form endings in all layers of the cortex, and, reaching layer I, give rise to horizontal branches extending far beyond the module.
In addition to specific (thalamo-cortical) afferent fibers, spiny stellate neurons have an excitatory effect on the output pyramidal neurons. There are two types of spiny cells:
The module’s braking system is represented by the following types of neurons:
Inhibitory neuron inhibition system:
The powerful excitatory effect of focal spiny stellate cells is explained by the fact that they simultaneously excite pyramidal neurons and a cell with a double bouquet of dendrites. Thus, the first three inhibitory neurons inhibit pyramidal cells, and cells with a double bouquet of dendrites excite them, inhibiting inhibitory neurons.
However, there are also critical and alternative concepts , casting doubt on the modular organization of the cerebral cortex and cerebellum. Of course, these views were influenced by the prediction in 1985 and the subsequent discovery in 1992 of diffuse volumetric neurotransmission.
Resume
The interneuronal relationships of neurons in the cerebral cortex can be represented as follows: incoming (afferent) information comes from the thalamus along thalamo-cortical fibers, which end on the cells of the IV (internal granular) layer. Its stellate neurons have an excitatory effect on pyramidal cells of layers III (pyramidal neurons) and V (ganglionic) layers, as well as on cells with a double bouquet of dendrites that block inhibitory neurons. Cells of layer III form fibers (associative and commissural) that connect different parts of the cortex. Cells of layers V and VI (multimorphic cells) form projection fibers that go into the white matter and carry information to other parts of the central nervous system. In all layers of the cortex there are inhibitory neurons that play the role of a filter by blocking pyramidal neurons.
The cortex of various sections is characterized by the predominant development of certain layers. Thus, in the motor centers of the cortex, for example, in the anterior central gyrus, layers III, V and VI are highly developed and layers II and IV are poorly expressed. This is the so-called agranular type of bark. The descending pathways of the central nervous system originate from these areas. In the sensitive cortical centers, where the afferent conductors coming from the organs of smell, hearing and vision end, the layers containing large and medium-sized pyramidal cells are poorly developed, while the granular layers (II and IV) reach their maximum development. This granular type of cortex
The cerebral cortex covers the surface of the hemispheres and forms a large number of grooves of varying depth and length (lat. sulci cerebri). Between the grooves are located the gyri of the cerebrum of varying sizes (lat. gyri cerebri) .
In each hemisphere the following surfaces are distinguished:
These three surfaces of each hemisphere, passing one into another, form three edges. Upper edge (lat. margo superior) separates the superolateral and medial surfaces. Inferolateral edge (lat. margo inferolateralis) separates the superolateral surface from the inferior one. Inferomedial edge (lat. margo inferomedialis) is located between the inferior and medial surfaces.
In each hemisphere, the most prominent places are distinguished: in front - the frontal pole (lat. polus frontalis), behind - occipital (lat. polus occipitalis), and from the side - temporal (lat. polus temporalis) .
The hemisphere is divided into five lobes. Four of them are adjacent to the corresponding bones of the cranial vault:
Grooves and convolutions of the superolateral surface
Frontal lobe - indicated in blue. Parietal lobe - indicated in yellow. Temporal lobe - indicated in green. Occipital lobe - indicated in pink.
Frontal lobe
The frontal lobe is separated from the parietal lobe by a deep central sulcus (lat. sulcus centralis). It begins on the medial surface of the hemisphere, passes to its superolateral surface, runs along it slightly obliquely, from back to front, and usually does not reach the lateral sulcus of the brain.
Approximately parallel to the central sulcus is the precentral sulcus (lat. sulcus precentralis), which does not reach the upper edge of the hemisphere. The precentral sulcus borders the front of the precentral gyrus (lat. gyrus precentralis) .
Superior and inferior frontal sulcus (lat. sulci frontales superior et inferior ) are directed forward from the precentral sulcus. They divide the frontal lobe into:
From the lateral sulcus, small grooves called rami extend superiorly. The most constant of them are ascending (lat. ramus ascendens) and front (lat. ramus anterior) branches. The superior posterior section of the groove is called the posterior branch (lat. ramus posterior) .
The inferior frontal gyrus, within which the ascending and anterior branches pass, is divided into three parts:
Parietal lobe
It lies posterior to the central sulcus, which separates it from the frontal. It is delimited from the temporal by the lateral sulcus of the brain, from the occipital - by part of the parieto-occipital sulcus (lat. sulcus parietooccipitalis) .
Between the ascending and posterior branches of the lateral sulcus of the brain there is a section of the cortex designated as the frontoparietal operculum (lat. operculum frontoparietalis). It includes the posterior part of the inferior frontal gyrus, the lower parts of the precentral and postcentral gyri, as well as the lower part of the anterior part of the parietal lobe.
Temporal lobe
Has the most pronounced boundaries. It has a convex lateral surface and a concave bottom surface. The obtuse pole of the temporal lobe faces forward and slightly downward. The lateral cerebral sulcus sharply demarcates the temporal lobe from the frontal lobe.
Two grooves located on the superolateral surface: superior (lat. sulcus temporalis superior) and lower (lat. sulcus temporalis inferior) temporal sulci, following almost parallel to the lateral sulcus of the brain, divide the lobe into three temporal gyri: superior, middle and inferior (lat. gyri temporales superior, medius et inferior ) .
Those parts of the temporal lobe that are directed towards the lateral sulcus of the brain are cut by short transverse temporal sulci (lat. sulci temporales transversi). Between these grooves lie 2-3 short transverse temporal gyri, associated with the gyri of the temporal lobe (lat. gyri temporales transversi) and an island.
Insula (islet)
Lies at the bottom of the lateral fossa of the cerebrum (lat. fossa lateralis cerebri).
It is a three-sided pyramid, facing its apex - the pole of the insula - anteriorly and outwardly, towards the lateral sulcus. From the periphery, the insula is surrounded by the frontal, parietal and temporal lobes, which participate in the formation of the walls of the lateral sulcus of the brain.
The base of the islet is surrounded on three sides by a circular islet groove (lat. sulcus circularis insulae).
Its surface is cut by a deep central groove of the insula (lat. sulcus centralis insulae). This groove divides the insula into anterior and posterior parts.
On the surface there are a large number of small convolutions of the islet (lat. gyri insulae). The large anterior part consists of several short convolutions of the insula (lat. gyri breves insulae), posterior - one long gyrus (lat. gyrus longus insulae) .
Furrows and convolutions of the medial surface
The frontal, parietal and occipital lobes extend onto the medial surface of the hemisphere.
The cingulate gyrus is bounded superiorly by the cingulate groove (lat. sulcus cinguli). In the latter, there is a front part convex towards the frontal pole and a back part, which, following along the cingulate gyrus and not reaching its posterior section, rises to the upper edge of the cerebral hemisphere. The posterior end of the sulcus lies behind the upper end of the central sulcus. Between the precentral sulcus, the end of which is sometimes clearly visible at the upper edge of the medial surface of the hemisphere, and the end of the cingulate sulcus, there is a paracentral lobule (lat. lobulus paracentralis) .
Above the cingulate gyrus, in front of the subcallosal area, begins the medial frontal gyrus (lat. gyrus frontalis medialis). It extends to the paracentral lobule and is the lower part of the superior frontal gyrus.
Behind the cingulate groove lies a small quadrangular lobe - the precuneus (lat. precuneus). Its posterior border is the deep parieto-occipital sulcus (lat. sulcus parietooccipitalis), lower - subparietal groove (lat. sulcus subparietalis), separating the precuneus from the posterior cingulate gyrus.
Behind and below the precuneus lies a triangular lobe - wedge (lat. cuneus). The convex outer surface of the wedge participates in the formation of the occipital pole. The apex of the wedge, directed downward and forward, almost reaches the posterior part of the cingulate gyrus. The posteroinferior border of the wedge is a very deep calcarine groove (lat. sulcus calcarinus), anterior - parieto-occipital sulcus.
Grooves and convolutions of the lower surface
On the lower surface of the frontal lobe is the olfactory groove (lat. sulcus olfactorius). Inwardly from it, between it and the inferomedial edge of the hemisphere, lies the straight gyrus (lat. gyrus rectus). Its posterior section reaches the anterior perforated substance (lat. substantia perforata anterior). Outside the groove is the rest of the lower surface of the frontal lobe, indented by short orbital grooves (lat. sulci orbitales), into a number of small orbital gyri (lat. gyri orbitales) .
The lower surface of the temporal lobe is a deep groove of the hippocampus (lat. sulcus hippocampi) is separated from the cerebral peduncles. In the depths of the furrow lies a narrow dentate gyrus (lat. gyrus dentatus). Its anterior end passes into the hook, and its posterior end into the ribbon gyrus (lat. gyrus fasciolaris) lying under the splenium of the corpus callosum. Lateral to the sulcus is the parahippocampal gyrus (lat. gyrus parahippocampalis). In front of this gyrus there is a thickening in the form of a hook (lat. uncus), and continues posteriorly into the lingual gyrus (lat. gyrus lingualis). The parahippocampal and lingual gyri are limited on the lateral side by the collateral sulcus (lat. sulcus collateralis), passing in front into the nasal groove (lat. sulcus rhinalis). The rest of the lower surface of the temporal lobe is occupied by the medial and lateral occipitotemporal gyri (lat. gyri occipitotemporales medialis et lateralis ), separated by the occipitotemporal groove (lat. sulcus occipitotemporalis). The lateral occipitotemporal gyrus is separated by the inferolateral edge of the hemisphere from the inferior temporal gyrus.
Histology
Structure
Cytoarchitecture (cell arrangement)
- molecular layer
- outer granular layer
- layer of pyramidal neurons
- inner granular layer
- ganglion layer (inner pyramidal layer; Betz cells)
- layer of polymorphic cells
Myeloarchitecture (arrangement of fibers)
The cerebral cortex is represented by a layer of gray matter with an average thickness of about 3 mm (1.3 - 4.5 mm). It is most strongly developed in the anterior central gyrus. The abundance of furrows and convolutions significantly increases the area of gray matter in the brain. The cortex contains about 10-14 billion nerve cells. Its various sections, which differ from each other in certain features of the location and structure of cells (cytoarchitectonics), the arrangement of fibers (myeloarchitectonics) and functional significance, are called fields. They represent places of higher analysis and synthesis of nerve impulses. There are no sharply defined boundaries between them. The cortex is characterized by an arrangement of cells and fibers in layers.
Cytoarchitecture
Pyramidal cells of different layers of the cortex differ in size and have different functional significance. Small cells are interneurons, the axons of which connect individual areas of the cortex of one hemisphere (associative neurons) or two hemispheres (commissural neurons). These cells are found in varying numbers in all layers of the cortex. The human cerebral cortex is especially rich in them. Axons of large pyramidal neurons take part in the formation of pyramidal tracts that project impulses to the corresponding centers of the brain stem and spinal cord.
The neurons of the cortex are located in vaguely delimited layers. Each layer is characterized by the predominance of one type of cell. There are 6 main layers in the motor cortex:
The cerebral cortex also contains a powerful neuroglial apparatus that performs trophic, protective, supporting and delimiting functions.
On the medial and lower surface of the hemispheres, sections of the old, ancient cortex have been preserved, which have a two-layer and three-layer structure.
Molecular layer
The molecular layer of the cortex contains a small number of small spindle-shaped association cells. Their axons run parallel to the surface of the brain as part of the tangential plexus of nerve fibers of the molecular layer. The bulk of the fibers of this plexus are represented by the branching of the dendrites of neurons in the underlying layers.
Outer granular layer
The outer granular layer is formed by small neurons with a diameter of about 10 microns, having a round, angular and pyramidal shape, and stellate neurons. The dendrites of these cells rise into the molecular layer. Axons either go into the white matter, or, forming arcs, also enter the tangential plexus of fibers of the molecular layer.
Layer of pyramidal neurons
It is the widest compared to other layers of the cerebral cortex. It is especially well developed in the precentral gyrus. The size of pyramidal cells consistently increases within 10-40 µm from the outer zone of this layer to the inner one. The main dendrite extends from the top of the pyramidal cell and is located in the molecular layer. The dendrites, originating from the lateral surfaces of the pyramid and its base, are of insignificant length and form synapses with adjacent cells of this layer. The axon of a pyramidal cell always extends from its base. In small cells it remains within the cortex; an axon belonging to a large pyramid usually forms a myelin association or commissural fiber that goes into the white matter.
Inner granular layer
In some fields of the cortex it is very developed (for example, in the visual cortex). However, in other areas it may be absent (in the precentral gyrus). This layer is formed by small stellate neurons. It contains a large number of horizontal fibers.
Ganglion layer (Inner pyramidal layer; Betz cells)
It is formed by large pyramidal cells, and the area of the precentral gyrus contains giant cells, first described by the Russian anatomist V. A. Betz in 1874 (Betz cells). They reach a height of 120 and a width of 80 microns. Unlike other pyramidal cells of the cortex, giant Betz cells are characterized by the presence of large clumps of chromatophilic substance. Their axons form the main part of the corticospinal and corticonuclear tracts and end on motor neurons of the brainstem and spinal cord.
Myeloarchitecture
Among the nerve fibers of the cerebral cortex we can distinguish:
In addition to the tangential plexus of the molecular layer, at the level of the internal granular and ganglion layers there are two tangential layers of myelin nerve fibers and axonal collaterals of cortical cells. By entering into synaptic connections with cortical neurons, horizontal fibers ensure widespread distribution of nerve impulses in it.
Module
I, II, III, IV, V, VI - layers of the cortex
Afferent fibers
1. corticocortical fiber
2. thalamo-cortical fiber
2a. area of distribution of specific thalamo-cortical fibers
3. pyramidal neurons
3a. inhibited pyramidal neurons
4. inhibitory neurons and their synapses
4a. cells with an axonal brush
4b. small basket cells
4c. large basket cages
4g. axoaxonal neurons
4d. cells with a double bouquet of dendrites (inhibitory inhibitory neurons)
5. spiny stellate cells, exciting pyramidal neurons directly and by stimulating cells with a double bouquet of dendrites
Studying the cerebral cortex, Ya. Szentagothai and representatives of his school established that its structural and functional unit is module- vertical column with a diameter of about 300 microns. The module is organized around a cortico-cortical fiber, which is an axon of the pyramidal cell of layer III (layer of pyramidal cells) of the same hemisphere (associative fiber), or from the pyramidal cells of the opposite (commissural). The module includes two thalamo-cortical fibers - specific afferent fibers ending in the fourth layer of the cortex on spiny stellate neurons and extending from the base (basal) dendrites of pyramidal neurons. Each module, according to Szentagothai, is divided into two micromodules with a diameter of less than 100 microns. In total, the human neocortex has approximately 3 million modules. The axons of the pyramidal neurons of the module project to three modules of the same side and through the corpus callosum via commissural fibers to two modules of the opposite hemisphere. Unlike specific afferent fibers ending in layer IV of the cortex, cortico-cortical fibers form endings in all layers of the cortex, and, reaching layer I, give rise to horizontal branches extending far beyond the module.
In addition to specific (thalamo-cortical) afferent fibers, spiny stellate neurons have an excitatory effect on the output pyramidal neurons. There are two types of spiny cells:
The module’s braking system is represented by the following types of neurons:
Inhibitory neuron inhibition system:
The powerful excitatory effect of focal spiny stellate cells is explained by the fact that they simultaneously excite pyramidal neurons and a cell with a double bouquet of dendrites. Thus, the first three inhibitory neurons inhibit pyramidal cells, and cells with a double bouquet of dendrites excite them, inhibiting inhibitory neurons.
However, there are also critical and alternative concepts , casting doubt on the modular organization of the cerebral cortex and cerebellum. Of course, these views were influenced by the prediction in 1985 and the subsequent discovery in 1992 of diffuse volumetric neurotransmission.
Resume
The interneuronal relationships of neurons in the cerebral cortex can be represented as follows: incoming (afferent) information comes from the thalamus along thalamo-cortical fibers, which end on the cells of the IV (internal granular) layer. Its stellate neurons have an excitatory effect on pyramidal cells of layers III (pyramidal neurons) and V (ganglionic) layers, as well as on cells with a double bouquet of dendrites that block inhibitory neurons. Cells of layer III form fibers (associative and commissural) that connect different parts of the cortex. Cells of layers V and VI (multimorphic cells) form projection fibers that extend into the white matter and carry information to other parts of the central nervous system. In all layers of the cortex there are inhibitory neurons that play the role of a filter by blocking pyramidal neurons.
The cortex of various sections is characterized by the predominant development of certain layers. Thus, in the motor centers of the cortex, for example, in the anterior central gyrus, layers III, V and VI are highly developed and layers II and IV are poorly expressed. This is the so-called agranular type of bark. The descending pathways of the central nervous system originate from these areas. In the sensitive cortical centers, where the afferent conductors coming from the organs of smell, hearing and vision end, the layers containing large and medium-sized pyramidal cells are poorly developed, while the granular layers (II and IV) reach their maximum development. This granular type of cortex .
Brodmann's cytoarchitectonic fields I. N. Filippov and S. A. Sarkisov created maps of the cerebral cortex, including 47 cytoarchitectonic fields.
The components of the cerebral hemispheres are the cerebral cloak and the subcortical ganglia. Surround them lateral ventricles.
There is a deep longitudinal groove between the right hemisphere and the left. In its depths is the corpus callosum. It is formed by nerve fibers.
The cerebral cortex is represented by the cerebral cloak. This gray matter is formed by nerve cells with processes extending from them, and it is believed that the latter perform a supporting function for neurons and participate in the metabolism of their substances.
The cerebral cortex is the highest, from a phylogenetic point of view, the youngest formation of the central nervous system. The thickness of its layer is from one and a half to three millimeters. The cerebral cortex has about twelve to eighteen billion neurons.
Its total surface increases due to the presence of numerous grooves. They divide the surfaces of the hemispheres into lobes and convex convolutions. There are four lobes in each hemisphere. They are formed by three grooves: lateral, parieto-occipital and central. As a result, the occipital, temporal, parietal and frontal lobes are formed.
The latter is located in front of the central groove. The parietal lobe is limited by the central sulcus in front, below - lateral, parieto-occipital - behind. The temporal lobe is limited by a deep lateral groove at the top. The occipital lobe is located posterior to the parieto-occipital lobe.
Above the corpus callosum is located. It includes projection, commissural and associative fibers. The cerebral cortex has a two-way connection with the underlying parts of the central nervous system through ascending and descending pathways. They include projection fibers that extend beyond the hemispheres.
Individual cortical areas have functional different meaning. At the same time, the cerebral cortex works as a single whole. However, there is no strict functional localization in it. Experiments on animals showed that after the destruction of individual areas in the cortex, after a certain period of time, neighboring areas began to perform the functions of the destroyed areas. This feature is associated with high cell plasticity.
The cerebral cortex receives centripetal impulses from receptor formations. For each receptor apparatus there corresponds a section called I.P. Pavlov “cortical nucleus of the analyzer”. The areas of the cortex in which they are located are called sensory areas.
The nuclear region of the motor analyzer is located in the posterior central and anterior central zones of the cortex. Excitation is transmitted to it from receptors in tendons, skeletal muscles and joints.
The area is located behind the central sulcus (in the posterior central zone). It is associated with tactile, pain and temperature sensitivity.
The largest area is occupied by the area of analyzers of the face, voice apparatus, and hands. The smallest area is allocated to the representation of the analyzers of the lower leg, thigh and torso.
In the occipital zone there is a nuclear region in the temporal - auditory region. The area is near the lateral sulcus.
Movement occurs as a result of stimulation generated from interaction with the sensory areas of the motor cortex. It is located anteriorly from the central sulcus.
The nuclear regions of the analyzers are represented in the cortex by areas in which most of their pathways end. Beyond them are scattered elements. They receive impulses from the same receptors that enter the analyzer core.
Cerebral cortex
Modern methods for studying brain functions.
“The brain is the last of nature’s secrets that will ever be revealed to man.”
English physiologist Charles Scott Sherrington.
"Asymmetry is a fundamental property of life."
Louis Pasteur.
The cerebral hemispheres are paired formations of the brain. In humans, they reach ≈ 80% of the total brain mass. The cerebral hemispheres regulate the higher nervous functions that underlie all human mental processes, while the brainstem provides the lower functions of the nervous system associated with the regulation of activity internal organs.
Higher functions are provided by the activity of a special part of the cerebral hemispheres - the cerebral cortex, which is primarily responsible for the formation of conditioned reflex reactions. In humans, compared to animals, the cortex is simultaneously responsible for coordinating the work of internal organs. This increase in the role of the cortex in the regulation of all functions in the body is called corticalization of functions.
The cortex performs the following functions:
1 – interaction of the body with the external environment due to unconditioned and conditioned reflexes.
2 – implementation of higher nervous activity (behavior) of the body.
3 – performance of higher mental functions (thinking and consciousness).
4 – regulation of the functioning of internal organs and metabolism in the body.
The cerebral cortex is represented by 12-18 billion cells, located in a thin layer of 3-4 mm over an area of 2400 cm2. 65-70% of this area is located deep in the grooves, and 30-35% is on the visible surface of the hemispheres. The cortex consists of nerve cells, their processes and neuroclays, which are characterized by an abundance of interneuron connections.
The functional unit of the cortex is a vertical column of interconnected neurons. All neurons of the vertical column respond to the same afferent stimulation with the same reaction and jointly form an efferent response. The spread of excitation in the horizontal direction (irradiation) is ensured by transverse fibers running from one vertical column to another, and is limited by inhibition processes. The occurrence of excitation in the vertical column of neurons leads to the activity of spinal motor neurons and to the contraction of the muscles associated with them.
The ordered position of cells in the cortex is called cytoarchitectonics, and their fibers are called myeloarchitectonics.
When examined microscopically, six layers of nerve cells are distinguished in the cortex:
1 – molecular (horizontally located cells and fibers + dendrites of pyramidal cells),
2 – external granular (stellate and small pyramidal cells + thin nerve fibers),
3 – external pyramidal (medium and small pyramidal cells + ascending fibers),
4 – internal granular (stellate cells + thalamo-cortical fibers and horizontal myelin fibers),
5 – internal pyramidal (large pyramidal Betz cells from which pyramidal pathways begin),
6 – multiform (small polymorphic cells).
In the first layer of the cortex, the fibers form a strip of molecular lamina. The second layer contains thin fibers of the outer granular plate. The fourth layer of bark contains a strip of internal granular plate (outer strip of Baillarger). The fifth layer contains fibers of the internal pyramidal plate (internal strip of Baillarger).
The main information in the cortex comes through specific afferent pathways ending in the cells of layers 3 and 4. Nonspecific pathways from the RF end in the upper layers of the cortex and regulate its functional state (excitation, inhibition).
Stellate neurons perform mainly a sensory (afferent) function. Pyramidal and spindle cells are predominantly motor (efferent) neurons.
Some cortical cells receive information from any receptors in the body - these are polysensory neurons that perceive impulses only from certain receptors (visual, auditory, tactile, etc.). Neuroglial cells perform auxiliary functions: trophic, neurosecretory, protective, insulating.
Specialized neurons and other cells that make up the vertical columns form separate areas of the cortex, which are called projection zones (cytoarchitectonic fields). These functional areas of the cortex are divided into 3 groups:
– afferent (sensory);
– efferent (motor or motor);
– associative (connect previous zones and determine difficult work brain, underlying the higher mental activity).
In humans, associative zones reach their greatest development. The localization of functions in the cerebral cortex is relative - no clear boundaries can be drawn here, therefore the brain has high plasticity and adaptability to damage. However, the morphological and functional heterogeneity of the cortex made it possible to identify 52 cytoarchitectonic fields in it (K. Brodman), and among them are the centers of vision, hearing, touch, etc. All of them are interconnected by fibers of the white matter pathways, which are divided into 3 type:
1 – associative (connect cortical zones within one hemisphere),
2 – commissural (connect the symmetrical zones of the cortex of the two hemispheres through the corpus callosum),
3 – projection (connect the cortex and subcortex with peripheral organs, there are sensory and motor).
The importance of the most important areas of the cerebral cortex.
1. The sensitive zone of the cortex (in the postcentral gyrus) receives impulses from tactile, temperature and pain receptors of the skin, as well as from proprioceptors of the opposite half of the body.
2. The motor zone of the cortex (in the precentral gyrus) contains Betz pyramidal cells in the 5th layer of the cortex, from which impulses of voluntary movements go to the skeletal muscles of the opposite half of the body.
3. The premotor zone (at the base of the middle frontal gyrus) provides a combined rotation of the head and eyes in the opposite direction.
4. The praxic zone (in the supramarginal gyrus) provides complex goal-directed movements practical activities and professional motor skills. The zone is asymmetrical (for right-handers - in the left hemisphere, and for left-handers - in the right hemisphere).
5. The center of proprioceptive gnosis (in the superior parietal lobule) ensures the perception of proprioceptor impulses, controls the sensations of the body and its parts as an integral formation.
6. The reading center (in the superior parietal lobule, near the occipital lobe) controls the perception of written text.
7. The auditory cortex (in the superior temporal gyrus) receives information from the receptors of the hearing organ.
8. Auditory speech center, Wernicke's center (at the base of the superior temporal gyrus). The zone is asymmetrical (for right-handers - in the left hemisphere, and for left-handers - in the right hemisphere).
9. Auditory center for singing (in the superior temporal gyrus). The zone is asymmetrical (for right-handers - in the left hemisphere, and for left-handers - in the right hemisphere).
10. Motor center oral speech, Broca's center (at the base of the inferior frontal gyrus) controls voluntary contractions of the muscles involved in speech production. The zone is asymmetrical (for right-handers - in the left hemisphere, and for left-handers - in the right hemisphere).
11. The motor center for written speech (at the base of the middle frontal gyrus) provides voluntary movements associated with writing letters and other characters. The zone is asymmetrical (for right-handers - in the left hemisphere, and for left-handers - in the right hemisphere).
12. The stereognostic zone (in the angular gyrus) controls the recognition of objects by touch (stereognosis).
13. The visual cortex (in the occipital lobe) receives information from the receptors of the organ of vision.
14. The visual speech center (in the angular gyrus) controls the movement of the lips and facial expressions of the speaking opponent, and is closely connected with other sensory and motor speech centers. Speech and consciousness are the youngest phylogenetic functions of the brain, therefore speech centers have a large number of scattered elements and are the least localized. Speech and thinking functions are performed with the participation of the entire cortex. Speech centers in humans were formed on the basis of work activity, therefore they are asymmetrical, unpaired and associated with the working hand.
If the sensitive zone of the cortex is damaged, partial loss of sensitivity (hypesthesia) may occur. Unilateral damage leads to impaired skin sensitivity on the opposite side of the body. With bilateral damage, complete loss of sensation (anesthesia) is observed. Depending on the extent of damage to the motor cortex, partial (paresis) or complete (paralysis) loss of movements occurs. When the praxic zone is damaged, (motor or constructive) apraxia develops. Apraxia of another kind (ideational apraxia - “apraxia of design”) occurs when the anterior parts of the frontal lobes are damaged. Here, there may be a violation of coordination of movements (cortical ataxia), complex motor functions (akinesia), ensuring work activity, writing (agraphia) and speech (motor aphasia). Damage to the center of proprioceptive gnosis causes agnosia of parts of one’s own body (autotopagnosia) - a violation of the body diagram. Damage to the stereognostic zone leads to loss of reading ability (Alexia). With bilateral damage to the auditory cortex, complete cortical deafness occurs. Damage to the auditory center of speech (Wernicke) results in verbal deafness (sensory aphasia), and damage to the auditory center of singing results in musical deafness (sensory amusia) and the inability to compose meaningful sentences from individual words (agrammatism). Damage to the visual cortex in equal parts of it causes loss of the ability to navigate in an unfamiliar environment and loss of visual memory. Bilateral lesions lead to complete cortical blindness.
Any functional zone of the cortex is in anatomical and functional connection with other zones of the cortex, with the subcortical nuclei, structures of the diencephalon and reticular formation, which ensures the perfection of the functions they perform.
The limbic system is the most ancient part of the cortex, which includes a number of formations at the cortical and subcortical levels ( frontal lobes brain, cingulate gyrus, corpus callosum, gray integument, fornix, hippocampus, amygdala and mammillary bodies, thalamus, striopallidal system, reticular formation). Its main functions:
1 – regulation of vegetative processes (especially digestion),
2 – regulation of behavioral reactions,
3 – formation and regulation of emotions, sleep,
4 – formation and manifestation of memory.
The limbic system creates positive and negative emotions with all accompanying and vegetative, endocrine and motor components. She creates motivation for behavior, calculates methods of action, ways to achieve a useful result. The ability to recreate past events before your eyes is one of the amazing abilities brain The hippocampus (seahorse) plays a key role in information processing. This is where its quality sorting takes place. Some of the information enters the associative zones of the cortex and is analyzed there, while the other part is immediately consolidated in long-term memory. Individual memories are systematized and transformed into stable ones during sleep, in the deep sleep phase, when a person does not dream.
When the limbic system is damaged, the formation of conditioned reflexes becomes difficult, memory processes are disrupted, selectivity of reactions is lost and their excessive strengthening is noted.
The cerebrum consists of almost identical halves - the right and left hemispheres, which are connected by the corpus callosum. Commissural fibers connect symmetrical zones of the cortex. However, the cortex of the right and left hemispheres are not symmetrical not only externally, but also functionally. It has been established that left hemisphere provides logical abstract thinking. It is responsible for writing, reading, and mathematical calculations. The right hemisphere provides specific imaginative thinking. It is responsible for emotional coloring speech, musicality, spatial orientation, perception geometric shapes, drawings, natural objects.
Both hemispheres work together, but one of them is usually dominant in each person. According to the way of thinking and the nature of memorizing information, all people are practically divided into left-hemisphere type and right-hemisphere type. The rates of maturation of the left and right hemispheres have gender characteristics. In girls, the left hemisphere develops faster, which is confirmed by faster speech development and psychomotor development. In abnormal children, the development of the left hemisphere is significantly delayed, functional asymmetry poorly expressed. In children with high mental performance, the difference between the right and left hemispheres is more pronounced (Human Physiol., No. 1, 1983).
Various methods are used to study the functions of the cerebral cortex:
1. Removal of individual sections of the cortex by surgery (extirpation).
2. Method of irritation with electrical, chemical and temperature stimuli.
3. Method of withdrawing biopotentials and recording the electrical activity of cortical zones or individual neurons, EEG.
4. Classical method of conditioned reflexes.
5. Clinical method for studying functions in people with lesions of the cerebral cortex.
6. Scanning techniques such as nuclear magnetic resonance and positron emission tomography. Using these methods, observing the flow of blood to certain areas of the brain during thought processes, the researchers determined which areas of the cortex help hear words, see words and pronounce words.
7. The thermal imaging method made it possible to clarify the hypothesis that, despite the complex structure of the cortex, an image can be seen on its surface. This hypothesis was put forward by scientists from the Institute of VND and Neurophysiology. Employees of the Institute of Radio Engineering and Electronics of the Russian Academy of Sciences confirmed the hypothesis. A thermal imager with a sensitivity of hundredths of a degree transmitted thermal maps of the cerebral cortex of a white rat to a computer at a speed of 25 frames per second. The rat was shown images of geometric shapes. On the display, these figures were clearly visible on the surface of the cerebral cortex. The primary image entering the retina is converted by receptors into impulses and restored again in the cortex as on a screen.
Electroencephalography (EEG) is a common method for studying the brain. The rhythm of electrical oscillations corresponds to one or another functional state of the brain.
Active wakefulness is accompanied by the (beta) rhythm with a frequency of 14-100 vibrations per second.
At rest with eyes closed, an (alpha) rhythm is observed with a frequency of 8–13 vibrations per second.
During deep sleep, (delta) rhythm is recorded with a frequency of 0.5-3 vibrations per second.
In a state of shallow sleep, (theta) is observed - a rhythm with a frequency of 4-7 vibrations per second.
EEG allows you to objectively assess the mobility, prevalence and relationships in the cortex of the processes of excitation and inhibition.
Similar abstracts:
Anatomy of brain parts.
The nervous system is a collection of anatomically and functionally interconnected nerve cells with their processes. Structure and functions of the central and peripheral nervous system. The concept of the myelin sheath, reflex, functions of the cerebral cortex.
The main reflex centers of the medulla oblongata and pons. Bulbar reflexes.
The structure of the brain regions.
The part of the nervous system that provides body functions. Centers of the sympathetic and parasympathetic parts of the autonomic nervous system. Centers of the frontal and temporal lobes of the cerebrum. Ascending and descending pathways of surface sensitivity.
Morphophysiology of the nervous system. Biochemistry of the nervous system. Neurophysiological processes that provide voluntary movements. Classification of neurons. Amines (norepinephrine, dopamine, serotonin, histamine). Synaptic effect.
White matter of the hemispheres. Gray matter of the hemisphere.
The cerebral cortex is the highest section of the central nervous system, which appears later in the process of phylogenetic development and is formed during individual (ontogenetic) development later than other parts of the brain. The cortex is a layer of gray matter 2-3 mm thick, containing on average about 14 billion (from 10 to 18 billion) nerve cells, nerve fibers and interstitial tissue (neuroglia). In its cross section, based on the location of neurons and their connections, 6 horizontal layers are distinguished. Thanks to numerous convolutions and grooves, the surface area of the cortex reaches 0.2 m2. Directly below the cortex is white matter, consisting of nerve fibers that transmit excitation to and from the cortex, as well as from one area of the cortex to another.
Cortical neurons and their connections. Despite the huge number of neurons in the cortex, very few of their varieties are known. Their main types are pyramidal and stellate neurons.
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In the afferent function of the cortex and in the processes of switching excitation to neighboring neurons, the main role belongs to stellate neurons. They make up more than half of all cortical cells in humans. These cells have short branching axons that do not extend beyond the gray matter of the cortex, and short branching dendrites. Stellate neurons are involved in the processes of perception of irritation and combining the activities of various pyramidal neurons.
Pyramidal neurons carry out the efferent function of the cortex and intracortical processes of interaction between neurons remote from each other. They are divided into large pyramids, from which projection, or efferent, paths to subcortical formations begin, and small pyramids, forming associative paths to other parts of the cortex. The largest pyramidal cells - the giant pyramids of Betz - are located in the anterior central gyrus, in the so-called motor zone of the cortex. Feature large pyramids - their vertical orientation in the thickness of the crust. From the cell body, the thickest (apical) dendrite is directed vertically upward to the surface of the cortex, through which various afferent influences from other neurons enter the cell, and an efferent process, the axon, extends vertically downwards.
The large number of contacts (for example, on the dendrites of a large pyramid alone there are from 2 to 5 thousand) provides the possibility of broad regulation of the activity of pyramidal cells by many other neurons. This makes it possible to coordinate the responses of the cortex (primarily its motor function) with various influences from the external environment and the internal environment of the body.
The cerebral cortex is characterized by an abundance of interneuron connections. As the human brain develops after birth, the number of intercentral connections increases, especially intensely until the age of 18.
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Primary, secondary and tertiary cortical fields. The structural features and functional significance of individual areas of the cortex make it possible to distinguish individual cortical fields.
There are three main groups of fields in the cortex: primary, secondary and tertiary fields.
Primary fields are associated with sensory organs and organs of movement on the periphery; they mature earlier than others in ontogenesis and have the largest cells. These are the so-called nuclear zones of the analyzers, according to I. P. Pavlov (for example, the field of pain, temperature, tactile and muscle-articular sensitivity in the posterior central gyrus of the cortex, the visual field in the occipital region, the auditory field in the temporal region and the motor field in the anterior central gyrus of the cortex) (Fig. 54). These fields analyze individual stimuli entering the cortex from the corresponding receptors. When primary fields are destroyed, so-called cortical blindness, cortical deafness, etc. occur. Nearby are secondary fields, or peripheral zones of analyzers, which are connected to individual organs only through primary fields. They serve to summarize and further process incoming information. Individual sensations are synthesized in them into complexes that determine the processes of perception. When secondary fields are damaged, the ability to see objects and hear sounds is retained, but the person does not recognize them and does not remember their meaning. Both humans and animals have primary and secondary fields.
The furthest from direct connections with the periphery are the tertiary fields, or the overlap zones of the analyzers. Only humans have these fields. They occupy almost half of the cortex and have extensive connections with other parts of the cortex and with nonspecific brain systems. These fields are dominated by the smallest and most diverse cells. The main cellular element here are stellate neurons. Tertiary fields are located in the posterior half of the cortex - at the boundaries of the parietal, temporal and occipital regions and in the anterior half - in the anterior parts of the frontal regions. In these zones it ends greatest number nerve fibers connecting the left and right hemisphere, therefore their role is especially great in organizing the coordinated work of both hemispheres. Tertiary fields mature in humans later than other cortical fields; they carry out the most complex functions of the cortex. Processes happen here higher analysis and synthesis. In tertiary fields, based on the synthesis of all afferent stimulation and taking into account traces of previous stimulation, goals and objectives of behavior are developed. According to them, motor activity is programmed. The development of tertiary fields in humans is associated with the function of speech. Thinking (inner speech) is possible only with the joint activity of analyzers, the integration of information from which occurs in tertiary fields.
With congenital underdevelopment of the tertiary fields, a person is not able to master speech (pronounces only meaningless sounds) and even the simplest motor skills (cannot dress, use tools, etc.).
Perceiving and evaluating all signals from the internal and external environment, the cerebral cortex carries out the highest regulation of all motor and emotional-vegetative reactions.
Functions of the cerebral cortex. The cerebral cortex performs the most complex functions of organizing the adaptive behavior of the body during external environment. This is primarily a function of higher analysis and synthesis of all afferent stimulation.
Afferent signals enter the cortex through different channels, into different nuclear zones of the analyzers (primary fields), and then are synthesized in the secondary and tertiary fields, thanks to the activity of which a holistic perception of the external world is created. This synthesis underlies the complex mental processes of perception, representation, and thinking. The cerebral cortex is an organ closely associated with the emergence of consciousness in humans and its regulation social behavior. An important aspect of the activity of the cerebral cortex is the closure function - the formation of new reflexes and their systems ( conditioned reflexes, dynamic stereotypes - see. Chapter XV).
Due to the unusually long duration of preservation of traces of previous irritations (memories) in the cortex, a huge amount of information accumulates in it. This goes a long way to maintaining a personalized experience that is used as needed.
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It has been experimentally shown that in higher representatives of the animal world, after complete surgical removal of the cortex, the highest nervous activity deteriorates sharply. They lose the ability to subtly adapt to the external environment and exist independently in it.