Cortex - the higher part of the central nervous system, which ensures the functioning of the body as a whole in its interaction with the environment.

brain (cortex large brain, new bark) is a layer of gray matter, consisting of 10-20 billion and covering the large hemispheres (Fig. 1). The gray matter of the bark makes up more than half of the total gray matter of the central nervous system. The total area of ​​the gray matter of the bark is about 0.2 m 2, which is achieved by the tortuous folding of its surface and the presence of grooves of different depths. The thickness of the cortex in its different parts ranges from 1.3 to 4.5 mm (in the anterior central gyrus). The neurons of the cortex are located in six layers, oriented parallel to its surface.

In the areas of the cortex related to, there are zones with a three-layer and five-layer arrangement of neurons in the structure of the gray matter. These areas of the phylogenetically ancient cortex occupy about 10% of the surface of the cerebral hemispheres, the remaining 90% are new cortex.

Rice. 1. Mole of the lateral surface of the cerebral cortex (according to Brodman)

The structure of the cerebral cortex

The cerebral cortex has a six-layer structure

Neurons of different layers differ in cytological characteristics and functional properties.

Molecular layer- the most superficial. It is represented by a small number of neurons and numerous branching dendrites of pyramidal neurons lying in deeper layers.

Outer granular layer formed by densely spaced numerous small neurons of various shapes. The processes of the cells of this layer form corticocortical connections.

Outer pyramidal layer consists of pyramidal neurons average size, whose processes are also involved in the formation of corticocortical connections between adjacent areas of the cortex.

Inner granular layer similar to the second layer in terms of the type of cells and the arrangement of fibers. In the layer there are bundles of fibers connecting different parts of the cortex.

Signals from specific nuclei of the thalamus are transmitted to the neurons of this layer. The layer is very well represented in the sensory areas of the cortex.

Inner pyramids formed by medium and large pyramidal neurons. In the motor area of ​​the cortex, these neurons are especially large (50-100 microns) and are called giant, Betz pyramidal cells. The axons of these cells form fast-conducting (up to 120 m / s) fibers of the pyramidal tract.

Layer of polymorphic cells represented mainly by cells, the axons of which form corticothalamic pathways.

The neurons of the 2nd and 4th layers of the cortex are involved in the perception, processing of signals coming to them from the neurons of the associative areas of the cortex. Sensory signals from the switching nuclei of the thalamus come mainly to the neurons of the 4th layer, the severity of which is greatest in the primary sensory areas of the cortex. The neurons of the 1st and other layers of the cortex receive signals from other nuclei of the thalamus, basal ganglia, and the brain stem. The neurons of the 3rd, 5th and 6th layers form efferent signals that are sent to other areas of the cortex and along descending pathways to the lower parts of the central nervous system. In particular, layer 6 neurons form fibers that follow to the thalamus.

There are significant differences in the neuronal composition and cytological features of different parts of the cortex. Based on these differences, Brodmann divided the cortex into 53 cytoarchitectonic fields (see Fig. 1).

The location of many of these zeros, identified on the basis of histological data, coincides in topography with the location of the cortical centers, identified on the basis of their functions. Other approaches to dividing the cortex into regions are also used, for example, based on the content of certain markers in neurons, the nature of neural activity, and other criteria.

The white matter of the cerebral hemispheres is formed by nerve fibers. Allocate associative fibers, subdivided into arcuate fibers, but which signals are transmitted between neurons of adjacent convolutions and long longitudinal bundles of fibers that deliver signals to neurons in more distant sections of the hemisphere of the same name.

Commissural fibers - transverse fibers that transmit signals between neurons of the left and right hemispheres.

Projection fibers - conduct signals between neurons of the cortex and other parts of the brain.

The listed types of fibers are involved in the creation of neural circuits and networks, the neurons of which are located at considerable distances from each other. The cortex also contains a special kind of local neural circuits formed by adjacent neurons. These neural structures are called functional cortical columns. Neural columns are formed by groups of neurons located one above the other perpendicular to the surface of the cortex. The belonging of neurons to the same column can be determined by the increase in their electrical activity in response to stimulation of the same receptive field. Such activity is recorded with a slow movement of the recording electrode in the cortex in the perpendicular direction. If the electrical activity of neurons located in the horizontal plane of the cortex is recorded, then an increase in their activity is noted when various receptive fields are stimulated.

The diameter of the functional column is up to 1 mm. The neurons of one functional column receive signals from the same afferent thalamocortical fiber. Neurons of adjacent columns are connected to each other by processes, with the help of which they exchange information. The presence of such interconnected functional columns in the cortex increases the reliability of perception and analysis of information coming to the cortex.

Efficiency of perception, processing and use of information by the cortex for regulation physiological processes provided also somatotopic principle of organization sensory and motor fields of the cortex. The essence of such an organization is that in a certain (projection) area of ​​the cortex, not any, but topographically delineated areas of the receptive field of the body surface, muscles, joints or internal organs are represented. So, for example, in the somatosensory cortex, the surface of the human body is projected in the form of a diagram, when at a certain point of the cortex the receptive fields of a specific area of ​​the body surface are presented. In a strict topographic manner, efferent neurons are represented in the primary motor cortex, the activation of which causes the contraction of certain muscles of the body.

Bark fields are also inherent on-screen principle of operation. In this case, the receptor neuron sends a signal not to a single neuron or to a single point of the cortical center, but to a network or zero of neurons connected by processes. The functional cells of this field (screen) are the columns of neurons.

The cerebral cortex, forming at the later stages of the evolutionary development of higher organisms, to a certain extent subordinated to itself all the lower parts of the central nervous system and is able to correct their functions. At the same time, the functional activity of the cerebral cortex is determined by the influx of signals to it from neurons of the reticular formation of the brain stem and signals from the receptive fields of the body's sensory systems.

Functional areas of the cerebral cortex

On a functional basis, sensory, associative and motor areas are distinguished in the cortex.

Sensory (sensitive, projection) areas of the cortex

They consist of zones containing neurons, the activation of which by afferent impulses from sensory receptors or by direct action of stimuli causes the appearance of specific sensations. These zones are found in the occipital (fields 17-19), parietal (zero 1-3) and temporal (fields 21-22, 41-42) areas of the cortex.

In the sensory zones of the cortex, central projection fields are distinguished, providing a slushy, clear perception of sensations of certain modalities (light, sound, touch, heat, cold) and secondary projection zeros. The function of the latter is to provide an understanding of the connection of the primary sensation with other objects and phenomena of the surrounding world.

The zones of representation of receptive fields in the sensory zones of the cortex overlap to a large extent. The peculiarity of the nerve centers in the area of ​​the secondary projection fields of the cortex is their plasticity, which is manifested by the possibility of restructuring specialization and restoring functions after damage to any of the centers. These compensatory capabilities of the nerve centers are especially pronounced in childhood. At the same time, damage to the central projection fields after suffering a disease is accompanied by a gross violation of the functions of sensitivity and often the impossibility of its recovery.

Visual cortex

The primary visual cortex (VI, field 17) is located on both sides of the spur sulcus on the medial surface of the occipital lobe of the brain. In accordance with the identification of alternating white and dark stripes on unstained sections of the visual cortex, it is also called the striate (striped) cortex. The neurons of the lateral geniculate body send visual signals to the neurons of the primary visual cortex, which receive signals from the ganglion cells of the retina. The visual cortex of each hemisphere receives visual signals from the ipsilateral and contralateral halves of the retina of both eyes, and their delivery to the neurons of the cortex is organized according to the somatotopic principle. Neurons that receive visual signals from photoreceptors are topographically located in the visual cortex, similar to receptors in the retina. In this case, the area of ​​the macular retina has a relatively larger area of ​​representation in the cortex than other areas of the retina.

The neurons of the primary visual cortex are responsible for visual perception, which, based on the analysis of input signals, is manifested by their ability to detect a visual stimulus, to determine its specific shape and orientation in space. In a simplified way, one can represent the sensory function of the visual cortex in solving a problem and answering the question of what a visual object is.

In the analysis of other qualities of visual signals (for example, location in space, movement, connection with other events, etc.), neurons of fields 18 and 19 of the extrastriatal cortex, located but adjacent to zero 17, take part. areas of the cortex, will be transferred for further analysis and use of vision to perform other brain functions in the associative areas of the cortex and other parts of the brain.

Auditory cortex

Located in the lateral groove of the temporal lobe in the area of ​​the Heschl gyrus (AI, fields 41-42). The neurons of the primary auditory cortex receive signals from the neurons of the medial geniculate bodies. The fibers of the auditory tract, which conduct sound signals to the auditory cortex, are organized tonotopically, and this allows the neurons of the cortex to receive signals from certain auditory receptor cells in the organ of Corti. The auditory cortex regulates the sensitivity of the auditory cells.

In the primary auditory cortex, sound sensations are formed and an analysis of individual qualities of sounds is carried out, which makes it possible to answer the question of what the perceived sound is. The primary auditory cortex plays an important role in the analysis of short sounds, intervals between sound signals, rhythm, sound sequence. A more complex analysis of sounds is carried out in the associative areas of the cortex adjacent to the primary auditory. Based on the interaction of neurons in these areas of the cortex, binaural hearing is carried out, the characteristics of pitch, timbre, sound volume, the belonging of the sound are determined, and the idea of ​​a three-dimensional sound space is formed.

Vestibular cortex

Located in the superior and middle temporal gyri (fields 21-22). Her neurons receive signals from neurons vestibular nuclei the brain stem, connected by afferent connections with the receptors of the semicircular canals of the vestibular apparatus. In the vestibular cortex, a sensation is formed about the position of the body in space and the acceleration of movements. The vestibular cortex interacts with the cerebellum (through the temporocerebellar pathway), participates in the regulation of body balance, the adaptation of posture to the implementation of targeted movements. Based on the interaction of this area with the somatosensory and associative areas of the cortex, awareness of the body scheme occurs.

Olfactory cortex

Located in the region of the upper part of the temporal lobe (hook, zero 34, 28). The cortex includes a number of nuclei and belongs to the structures of the limbic system. Its neurons are located in three layers and receive afferent signals from the mitral cells of the olfactory bulb, connected by afferent connections with the olfactory receptor neurons. In the olfactory cortex, a primary qualitative analysis of odors is carried out and a subjective sense of smell, its intensity, and belonging is formed. Damage to the cortex leads to a decrease in the sense of smell or to the development of anosmia - loss of smell. When this area is artificially irritated, sensations of various odors appear, such as hallucinations.

Taste bark

Located in the lower part of the somatosensory gyrus, immediately anterior to the projection area of ​​the face (field 43). Its neurons receive afferent signals from relay neurons in the thalamus, which are associated with neurons in the nucleus of the solitary tract of the medulla oblongata. The neurons of this nucleus receive signals directly from sensory neurons forming synapses on the cells of the taste buds. In the gustatory cortex, a primary analysis of the taste qualities of bitter, salty, sour, sweet is carried out, and on the basis of their summation, a subjective sensation of taste, its intensity, and belonging is formed.

The signals of smell and taste reach the neurons in the anterior part of the insular cortex, where, on the basis of their integration, a new, more complex quality of sensations is formed, which determines our attitude to the sources of smell or taste (for example, to food).

Somatosensory cortex

Occupies the area of ​​the postcentral gyrus (SI, fields 1-3), including the paracentral lobule on the medial side of the hemispheres (Fig. 9.14). The somatosensory region receives sensory signals from thalamic neurons connected by spinothalamic pathways with skin receptors (tactile, temperature, pain sensitivity), proprioceptors (muscle spindles, bursae, tendons) and interoreceptors (internal organs).

Rice. 9.14. The most important centers and areas of the cerebral cortex

Due to the crossing of afferent pathways, signaling from the right side of the body arrives in the somatosensory zone of the left hemisphere, respectively, to the right hemisphere - from the left side of the body. In this sensory area of ​​the cortex, all parts of the body are somatotopically represented, but the most important receptive zones of the fingers, lips, skin of the face, tongue, and larynx occupy relatively larger areas than the projections of such body surfaces as the back, front of the body, and legs.

The location of the representation of the sensitivity of body parts along the postcentral gyrus is often called the "inverted homunculus", since the projection of the head and neck is in the lower part of the postcentral gyrus, and the projection of the caudal trunk and legs is in the upper part. In this case, the sensitivity of the legs and feet is projected onto the cortex of the paracentral lobule of the medial surface of the hemispheres. Within the primary somatosensory cortex, there is a certain specialization of neurons. For example, neurons of field 3 receive mainly signals from muscle spindles and mechanoreceptors of the skin, field 2 - from receptors of joints.

The cortex of the postcentral gyrus is referred to as the primary somatosensory region (SI). Its neurons send processed signals to neurons in the secondary somatosensory cortex (SII). It is located posterior to the postcentral gyrus in the parietal cortex (fields 5 and 7) and belongs to the associative cortex. SII neurons do not receive direct afferent signals from thalamic neurons. They are associated with SI neurons and neurons in other areas of the cerebral cortex. This makes it possible to carry out here an integral assessment of signals entering the cortex along the spinothalamic pathway with signals coming from other (visual, auditory, vestibular, etc.) sensory systems. The most important function of these fields of the parietal cortex is the perception of space and the transformation of sensory signals into motor coordinates. In the parietal cortex, a desire (intention, urge) to carry out a motor action is formed, which is the basis for starting planning for the upcoming motor activity in it.

The integration of different sensory signals is associated with the formation of different sensations addressed to different parts body. These sensations are used both for the formation of mental and other responses, examples of which can be movements with the simultaneous participation of the muscles of both sides of the body (for example, moving, feeling with both hands, grabbing, unidirectional movement with both hands). The functioning of this area is necessary for recognizing objects by touch and determining spatial location these items.

The normal function of the somatosensory areas of the cortex is important condition the formation of such sensations as heat, cold, pain and their addressing to a specific part of the body.

Damage to neurons in the area of ​​the primary somatosensory cortex leads to a decrease in various types of sensitivity on the opposite side of the body, and local damage to a loss of sensitivity in a certain part of the body. The discriminatory sensitivity of the skin is especially vulnerable when the neurons of the primary somatosensory cortex are damaged, and the least painful one. Damage to neurons in the secondary somatosensory area of ​​the cortex may be accompanied by impaired ability to recognize objects by touch (tactile agnosia) and skills in using objects (apraxia).

Motor areas of the cortex

About 130 years ago, researchers, applying point stimuli to the cerebral cortex with an electric current, found that exposure to the surface of the anterior central gyrus causes muscle contraction on the opposite side of the body. So the presence of one of the motor areas of the cerebral cortex was discovered. Subsequently, it turned out that several areas of the cerebral cortex and its other structures are related to the organization of movements, and in the areas of the motor cortex there are not only motor neurons, but also neurons that perform other functions.

Primary motor cortex

Primary motor cortex located in the anterior central gyrus (MI, field 4). Its neurons receive the main afferent signals from neurons of the somatosensory cortex - fields 1, 2, 5, premotor cortex and thalamus. In addition, cerebellar neurons send signals to the MI via the ventrolateral thalamus.

The efferent fibers of the pyramidal pathway begin from the pyramidal neurons Ml. Some of the fibers of this pathway follow to the motor neurons of the cranial nerve nuclei of the brain stem (corticobulbar tract), some - to the neurons of the stem motor nuclei (red nucleus, nuclei of the reticular formation, stem nuclei associated with the cerebellum) and some - to the inter- and motor neurons of the spinal cord. brain (corticospinal tract).

There is a somatotopic organization of the arrangement of neurons in MI, which control the contraction of various muscle groups of the body. The neurons that control the muscles of the legs and trunk are located in the upper portions of the gyrus and occupy a relatively small area, while the control muscles of the hands, especially the fingers, face, tongue, and pharynx, are located in the lower portions and occupy a large area. Thus, in the primary motor cortex, a relatively large area is occupied by those neural groups that control muscles that carry out various, precise, small, finely regulated movements.

Since many Ml neurons increase electrical activity immediately before the onset of voluntary contractions, the primary motor cortex is assigned a leading role in controlling the activity of the motor nuclei of the trunk and motor neurons of the spinal cord and initiating voluntary, purposeful movements. Damage to the Ml field leads to muscle paresis and the impossibility of performing fine voluntary movements.

Secondary motor cortex

Includes areas of the premotor and accessory motor cortex (MII, field 6). Premotor cortex located in field 6, on the lateral surface of the brain, anterior to the primary motor cortex. Its neurons receive afferent signals through the thalamus from the occipital, somatosensory, parietal associative, prefrontal regions of the cortex and cerebellum. Signals processed in it are sent by neurons of the cortex along efferent fibers to the motor cortex MI, a small number to the spinal cord and more to the red nuclei, nuclei of the reticular formation, basal ganglia and cerebellum. The premotor cortex plays a major role in programming and organizing vision-controlled movements. The bark is involved in the organization of posture and auxiliary movements for actions carried out by the distal muscles of the limbs. Damage to the proximal cortex often causes a tendency to re-execute the initiated movement (perseveration), even if the movement performed has reached the goal.

In the lower part of the premotor cortex of the left frontal lobe, immediately anterior to the area of ​​the primary motor cortex, which contains the neurons that control the muscles of the face, is located speech area, or the motor center of Broca's speech. Violation of its function is accompanied by impaired speech articulation, or motor aphasia.

Additional motor cortex is located in the upper part of field 6. Its neurons receive afferent signals from the somatosensory, parietal and prefrontal regions of the cerebral cortex. Signals processed in it are sent by neurons of the cortex through efferent fibers to the primary motor cortex MI, spinal cord, and stem motor nuclei. The activity of neurons in the additional motor cortex increases earlier than neurons in the MI cortex, mainly due to the implementation of complex movements. At the same time, the increase in neural activity in the additional motor cortex is not associated with movements as such; for this, it is enough to mentally imagine a model of the upcoming complex movements. The additional motor cortex takes part in the formation of the program of the forthcoming complex movements and in the organization of motor responses to the specificity of sensory stimuli.

Since neurons in the secondary motor cortex send many axons to the MI field, it is considered a higher structure in the hierarchy of motor centers of the organization of movements, standing above the motor centers of the MI motor cortex. The nerve centers of the secondary motor cortex can influence the activity of motor neurons in the spinal cord in two ways: directly through the corticospinal pathway and through the MI field. Therefore, they are sometimes called supra-motor fields, whose function is to instruct the centers of the MI field.

It is known from clinical observations that maintaining the normal function of the secondary motor cortex is important for the implementation of precise hand movements, and especially for the performance of rhythmic movements. So, for example, if they are damaged, the pianist ceases to feel the rhythm and to maintain the interval. The ability to carry out opposite hand movements is impaired (manipulation with both hands).

With simultaneous damage to the MI and MII motor zones of the cortex, the ability to fine coordinated movements is lost. Point irritations in these areas of the motor zone are accompanied by the activation not of individual muscles, but of a whole group of muscles that cause directional movement in the joints. These observations gave rise to the conclusion that the motor cortex contains not so much muscles as movements.

Prefrontal cortex

Located in the area of ​​field 8. Its neurons receive the main afferent signals from the occipital visual, parietal associative cortex, upper hillocks of the quadruple. The processed signals are transmitted along the efferent fibers to the premotor cortex, the superior hillocks of the quadruple, and the brainstem motor centers. The cortex plays a decisive role in organizing eye-controlled movements and is directly involved in the initiation and control of eye and head movements.

The mechanisms that implement the transformation of the concept of movement into a specific motor program, into bursts of impulses sent to specific muscle groups, remain insufficiently understood. It is believed that the concept of movement is formed due to the functions of the associative and other areas of the cortex that interact with many structures of the brain.

Information about the intention of movement is transmitted to the motor areas of the frontal cortex. The motor cortex through the descending pathways activates systems that ensure the development and use of new motor programs or the use of old ones, already worked out in practice and stored in memory. The basal ganglia and cerebellum are part of these systems (see their functions above). The movement programs developed with the participation of the cerebellum and basal ganglia are transmitted through the thalamus to the motor zones and, above all, to the primary motor cortex. This area directly initiates the execution of movements, connecting certain muscles to it and providing a sequence of alternating their contraction and relaxation. The commands of the cortex are transmitted to the motor centers of the brainstem, spinal motor neurons and motor neurons of the cranial nerve nuclei. In the implementation of movements, motor neurons play the role of the final path through which motor commands are transmitted directly to the muscles. The features of signal transmission from the cortex to the motor centers of the trunk and spinal cord are described in the chapter on the central nervous system (brain stem, spinal cord).

Associative areas of the cortex

In humans, the associative areas of the cortex occupy about 50% of the area of ​​the entire cerebral cortex. They are located in the areas between the sensory and motor areas of the cortex. Associative areas do not have clear boundaries with secondary sensory areas both in morphological and functional features... The parietal, temporal and frontal associative areas of the cerebral cortex are distinguished.

The parietal associative area of ​​the cortex. Located in fields 5 and 7 of the superior and inferior parietal lobes of the brain. The area is bordered by the somatosensory cortex in front, and the visual and auditory cortex behind. The neurons of the parietal associative region can receive and activate their visual, sound, tactile, proprioceptive, pain, signals from the memory apparatus and other signals. Some neurons are polysensory and can increase their activity when they receive somatosensory and visual signals. However, the degree of increase in the activity of neurons in the associative cortex to the receipt of afferent signals depends on the current motivation, the subject's attention, and information retrieved from memory. It remains insignificant if the signal coming from the sensory regions of the brain is indifferent for the subject, and it increases significantly if it coincided with the existing motivation and attracted his attention. For example, when a monkey is presented with a banana, the activity of neurons in the associative parietal cortex remains low if the animal is full, and vice versa, the activity increases sharply in hungry animals that like bananas.

The neurons of the parietal associative cortex are connected by efferent connections with the neurons of the prefrontal, premotor, motor regions of the frontal lobe and cingulate gyrus. Based on experimental and clinical observations, it is generally accepted that one of the functions of the cortex of field 5 is the use of somatosensory information for the implementation of purposeful voluntary movements and manipulation of objects. The function of the cortex of field 7 is the integration of visual and somatosensory signals to coordinate eye movements and visually guided hand movements.

Violation of these functions of the parietal associative cortex when its connections with the frontal lobe cortex are damaged or a disease of the frontal lobe itself, explains the symptoms of the consequences of diseases localized in the parietal associative cortex. They can be manifested by difficulty in understanding the semantic content of signals (agnosia), an example of which is the loss of the ability to recognize the shape and spatial location of an object. The processes of transformation of sensory signals into adequate motor actions may be disrupted. In the latter case, the patient loses the skills of practical use of well-known instruments and objects (apraxia), and he may develop the inability to carry out visually guided movements (for example, the movement of the hand in the direction of the object).

Frontal associative area of ​​the cortex. It is located in the prefrontal cortex, which is part of the frontal lobe cortex, located anterior to fields 6 and 8. Neurons in the frontal associative cortex receive processed sensory signals via afferent connections from neurons in the cortex of the occipital, parietal, temporal lobes of the brain and from neurons in the cingulate gyrus. The frontal associative cortex receives signals about the current motivational and emotional states from the nuclei of the thalamus, limbic and other structures of the brain. In addition, the frontal cortex can operate with abstract, virtual signals. The associative frontal cortex sends efferent signals back to the brain structures from which they were received, to the motor regions of the frontal cortex, the caudate nucleus of the basal ganglia and the hypothalamus.

This area of ​​the cortex plays a primary role in the formation of the higher mental functions of a person. It provides the formation of target attitudes and programs of conscious behavioral reactions, recognition and semantic assessment of objects and phenomena, understanding of speech, logical thinking. After extensive damage to the frontal cortex, patients may develop apathy, a decrease in the emotional background, a critical attitude towards their own actions and the actions of others, complacency, a violation of the ability to use past experience to change behavior. Patient behavior can become unpredictable and inappropriate.

The temporal associative area of ​​the cortex. Located in fields 20, 21, 22. Cortex neurons receive sensory signals from neurons of the auditory, extrastriatal visual and prefrontal cortex, hippocampus and amygdala.

After a bilateral disease of the temporal associative areas with the involvement of the hippocampus in the pathological process or connections with it, patients may develop pronounced memory impairments, emotional behavior, inability to concentrate (absent-mindedness). In some people, if the lower temporal region is damaged, where the center of face recognition is presumably located, visual agnosia may develop - the inability to recognize the faces of familiar people, objects, while maintaining vision.

On the border of the temporal, visual and parietal areas of the cortex in the lower parietal and posterior parts of the temporal lobe, there is an associative section of the cortex, called the sensory center of speech, or Wernicke's center. After its damage, a violation of the function of understanding speech develops, while the speech-motor function is preserved.

So, the area of ​​the cerebral cortex of one hemisphere of a person is about 800 - 2200 square meters. see, thickness - 1.5 × 5 mm. Most of the bark (2/3) lies deep in the furrows and is not visible from the outside. Thanks to such an organization of the brain, in the process of evolution, it was possible to significantly increase the area of ​​the cortex with a limited volume of the skull. The total number of neurons in the cortex can reach 10-15 billion.

The cerebral cortex itself is heterogeneous, therefore, in accordance with phylogeny (by origin), the ancient cortex (paleocortex), the old cortex (archicortex), the intermediate (or middle) cortex (mesocortex) and the new cortex (neocortex) are distinguished.

Ancient bark

Ancient bark, (or paleocortex)- this is the simplest arrangement of the cerebral cortex, which contains 2 × 3 layers of neurons. According to a number of famous scientists such as H. Fenish, R.D.Sinelnikov and Ya.R. Sinelnikov, who indicate that the ancient cortex corresponds to the region of the brain that develops from the pear-shaped lobe, and the olfactory tubercle and the surrounding cortex, including area of ​​the anterior perforated substance. The structure of the ancient cortex includes the following structural formations such as the prepiriform, periamygdala region of the cortex, the diagonal cortex and the olfactory brain, which includes the olfactory bulbs, the olfactory tubercle, the transparent septum, the nuclei of the transparent septum and the fornix.

According to MG Prives and a number of some scientists, the olfactory brain is topographically divided into two sections, including a number of formations and convolutions.

1.the peripheral section (or the olfactory lobe), which includes the formations underlying the brain:

olfactory bulb;

olfactory tract;

the olfactory triangle (inside which the olfactory tubercle is located, that is, the apex of the olfactory triangle);

internal and lateral olfactory convolutions;

inner and lateral olfactory stripes (the fibers of the inner stripe end in the podmozolic field of the paraterminal gyrus, the transparent septum and in the anterior perforated substance, and the fibers of the lateral stripe end in the parahippocampal gyrus);

anterior perforation, or substance;

diagonal stripe, or Broca's stripe.

2.the central section includes three convolutions:

parahippocampal gyrus (hippocampal gyrus, or seahorse gyrus);

dentate gyrus;

the cingulate gyrus (including its anterior part - the hook).

Old and intermediate crust

Old bark (or archicortex)- this cortex appears later than the ancient cortex and contains only three layers of neurons. It consists of the hippocampus (seahorse or ammonium horn) with its base, dentate gyrus and cingulate gyrus. cortex brain neuron

Intermediate bark (or mesocortex)- representing the five-layer fate of the cortex, separating the new cortex (neocortex), from the ancient cortex (paleocortex) and old cortex (archicortex) and because of this, the middle cortex is divided into two zones:

• 1. peripaleocortical;
• 2.periarchiocortical.

According to V.M. Pokrovsky and G.A.Kuraev, the composition of the mesocortex includes the ostarvic, as well as in the entorial region, the parahippocampal gyrus bordering on the old cortex and the pre-base of the hippocampus.

According to R.D.Sinelnikov and Ya. R. Sinelnikov, the intermediate cortex includes such formations as the lower part of the ostravic lobe, the parahippocampal gyrus and the lower part of the limbic region of the cortex. But it should be understood that the limbic region is understood as a part of the neocortex of the cerebral hemispheres, which occupies the cingulate and parahippocampal gyrus. It is also believed that the intermediate cortex is an incompletely differentiated zone of the ostravka cortex (or visceral cortex).

Due to the ambiguity of such an interpretation of structures related to the ancient and old crust, it translated to the expediency of using the unified concept as an archiopaleocortex.

The structures of the archiopaleocortex have multiple connections, both among themselves and with other formations of the brain.

New bark

New bark (or neocortex)- phylogenetically, that is, by its origin, it is the latest formation of the brain. Due to the later evolutionary emergence and rapid development of the new cerebral cortex in its organization of complex forms of higher nervous activity and its highest hierarchical level, which is vertically consistent with the activity of the central nervous system making up the most of the features of this part of the brain. For many years, the features of the neocortex have attracted and continue to hold the attention of many researchers studying the physiology of the cerebral cortex. At present, the old ideas about the monopoly participation of the neocortex in the formation of complex forms of behavior, including conditioned reflexes, have been replaced by the idea of ​​it as the highest level of thalamocortical systems functioning in conjunction with the thalamus, limbic and other systems of the brain. The new cortex is involved in the mental experience of the external world - its perception and the creation of its images, which persist for a more or less long time.

A feature of the structure of the neocortex is the screen principle of its organization. The main thing in this principle - the organization of neural systems lies in the geometric distribution of the projections of the higher receptor fields on the large surface of the neuronal field of the cortex. Also for the screen organization, the characteristic organization of cells and fibers that run perpendicular to the surface or parallel to it. This orientation of the cortical neurons provides opportunities for grouping neurons.

As for the cellular composition in the neocortex, it is very diverse, the size of neurons is approximately from 8-9 microns to 150 microns. The overwhelming majority of cells are of two types - priramidny and stellate. There are also fusiform neurons in the neocortex.

In order to better consider the features of the microscopic structure of the cerebral cortex, it is necessary to turn to architectonics. Under the microscopic structure, cytoarchitectonics (cellular structure) and myeloarchitectonics (fibrous structure of the cortex) are distinguished. The beginning of the study of the architectonics of the cerebral cortex dates back to the end of the 18th century, when, in 1782, Gennari first discovered the heterogeneity of the structure of the cortex in the occipital lobes of the hemispheres. In 1868 Meinert divided the diameter of the hemispheric cortex into layers. In Russia, the first researcher of the bark was V. A. Betz (1874), who discovered large pyramidal neurons in the 5th layer of the cortex in the precentral gyrus, named after him. But, there is another division of the cerebral cortex - the so-called Brodmann field map. In 1903, the German anatomist, physiologist, psychologist and psychiatrist K. Brodmann published a description of fifty-two cytoarchitectonic fields, which are areas of the cerebral cortex, different in their cellular structure. Each such field is different in size, shape, location of nerve cells and nerve fibers, and, of course, different fields are associated with different functions of the brain. Based on the description of these fields, a map of 52 Brodman fields was compiled.

NEOCORTEX NEOCORTEX

(from neo ... and lat. cortex- bark, shell), new bark, neopallium, osn. part of the cerebral cortex. N. carries out highest level coordination of the brain and the formation of complex forms of behavior. In the course of evolution, N. first appears in reptiles, in which it is insignificant in size and is relatively simple in structure (the so-called lateral cortex). N. receives a typical multilayer structure only in mammals, in which it consists of 6-7 layers of cells (pyramidal, stellate, fusiform) and is subdivided into lobes: frontal, parietal, temporal, occipital, and mediobasal. In turn, the lobes are subdivided into regions, subregions and fields, differing in their cellular structure and connections with the deep parts of the brain. Along with projection (vertical) fibers, N.'s neurons form associative (horizontal) fibers, to-rye in mammals and especially in humans are collected in anatomically expressed bundles (for example, the occipital-frontal bundle), providing simultaneous coordinated activity of dec. N.'s zones. As part of N., a naib is distinguished, a complexly constructed associative cortex, which in the process of evolution experiences the greatest increase, while N.'s primary sensory fields are relatively reduced. (see CEREAL BRAIN).

.(Source: "Biological encyclopedic Dictionary. " Ch. ed. M. S. Gilyarov; Editorial board .: A. A. Babaev, G. G. Vinberg, G. A. Zavarzin and others - 2nd ed., Revised. - M .: Sov. Encyclopedia, 1986.)

See what "NEOCORTEX" is in other dictionaries:

The neocortex ...

New cortex (synonyms: neocortex, isocortex) (lat. Neocortex) new areas of the cerebral cortex, which are only outlined in lower mammals, and in humans they make up the bulk of the cortex. The new crust is located in the upper layer of the hemispheres ... ... Wikipedia

neocortex- 3.1.15 neocortex: A new cerebral cortex that provides the implementation of intellectual mental activity by human thinking. 3.1.16 Source ... Dictionary-reference book of terms of normative and technical documentation

- (neocortex; neo + lat. cortex bark) see new bark ... Comprehensive Medical Dictionary

neocortex- at, h. Evolutionarily ninety and the most complex of nerve tissues, from which the foreheads, tempo yang, skrone and strong parts of the brain are stored ... Ukrainian Tlumachny vocabulary

NEOCORTEX (NOVAYA KORA)- Evolutionarily the newest and most complex of nerve tissues. The frontal, parietal, temporal and occipital lobes of the brain are composed of the neocortex ... Explanatory dictionary in psychology

Archi, paleo, neocortex ... Spelling dictionary-reference

cortex- the brain: the cortex (cerebral cortex) is the upper layer of the cerebral hemispheres, consisting primarily of nerve cells with a vertical orientation (pyramidal cells), as well as of afferent (centripetal) and efferent bundles ... ... Great psychological encyclopedia

The term cortex refers to any outer layer of cells in the brain. The mammalian brain has three types of cortex: the pyriform cortex, which has olfactory functions; old bark (archicortex), constituting the main. part… … Psychological encyclopedia

Neocortex - Evolutionary is the youngest part of the cortex, occupying most of the surface of the hemispheres. Its thickness in humans is approximately 3 mm.

The cellular composition of the neocorhex is very diverse, but about three quarters of the neurons of the cortex are pyramidal neurons (pyramids), in connection with which one of the main classifications of neurons of the cortex divides them into pyramidal and non-iramidal (fusiform, stellate, granular, candelabra cells, Martinotti cells, etc. .). Another classification is related to the length of the axon (see paragraph 2.4). Longaxon Golgi I cells are mainly pyramids and spindles, their axons can exit from the cortex, the rest of the cells are shortaxon Golgi II cells.

Cortical neurons also differ in the size of the cell body: the size of ultra-small neurons is 6x5 microns, the size of giant ones is more than 40 x 18. The largest neurons are Betz pyramids, their size is 120 x 30-60 microns.

Pyramidal neurons (see Fig. 2.6, G) have the shape of a body in the form of a pyramid, the top of which is directed upwards. An apical dendrite departs from this apex and rises into the overlying cortical layers. Basal dendrites extend from the rest of the soma. All dendrites have spines. A long axon departs from the base of the cell, forming numerous collaterals, including recurrent ones, which bend and rise up. Stellate cells have no apical dendrite; spines on dendrites are absent in most cases. In fusiform cells, two large dendrites extend from opposite poles of the body, there are also small dendrites extending from the rest of the body. Dendrites have spines. The axon is long, with little branching.

During embryonic development, the new cortex necessarily goes through the stage of a six-layer structure; with maturation in some areas, the number of layers may decrease. The deeper layers are phylogenetically older, the outer layers are younger. Each layer of the cortex is characterized by its own neuronal composition and thickness, which in different areas of the cortex may differ from each other.

We list new crust layers(Figure 9.8).

I layer - molecular- the outermost, contains a small number of neurons and mainly consists of fibers running parallel to the surface. Also, dendrites of neurons located in the underlying layers rise here.

Layer II - outer granular, or outer granular, - consists mainly of small pyramidal neurons and a small number of medium-sized stellate cells.

III layer - outer pyramidal - the widest and thickest layer, contains mainly small and medium-sized pyramidal and stellate neurons. Large and giant pyramids are located in the depths of the layer.

IV layer - internal granular, or internal granular, - consists mainly of small neurons of all varieties, there are also a few large pyramids.

V layer - inner pyramidal, or ganglionic, a characteristic feature of which is the presence of large and in some areas (mainly in fields 4 and 6; Fig. 9.9; subparagraph 9.3.4) - giant pyramidal neurons (Betz pyramids). The apical dendrites of the pyramids, as a rule, reach layer I.

VI layer - polymorphic, or multiforme, - contains predominantly spindle-shaped neurons, as well as cells of all other forms. This layer is divided into two sublayers, which a number of researchers consider as independent layers, speaking in this case about a seven-layer crust.

Rice. 9.8.

a- neurons are colored entirely; b- only the bodies of neurons are painted; v- painted

only outgrowths of neurons

Main functions each layer is also different. Layers I and II carry out connections between neurons of different layers of the cortex. Callosal and associative fibers mainly come from the pyramids of layer III and come to layer II. The main afferent fibers entering the cortex from the thalamus terminate in layer IV neurons. Layer V is mainly associated with the system of descending projection fibers. The axons of the pyramids of this layer form the main efferent pathways of the cerebral cortex.

In most cortical areas, all six layers are equally well expressed. Such a crust is called homotypic. However, in some fields during development, the severity of the layers may change. This bark is called heterotypic. It is of two types:

granular (zeros 3, 17, 41; Fig. 9.9), in which the number of neurons in the outer (II) and especially in the inner (IV) granular layers is greatly increased, as a result of which the IV layer is divided into three sublayers. This cortex is characteristic of the primary sensory zones (see below);

Agranular (fields 4 and 6, or motor and premotor cortex; Fig. 9.9), in which, on the contrary, there is a very narrow layer II and practically no IV, but very wide pyramidal layers, especially the inner one (V).

Topic 14

Brain physiology

PartV

New cerebral cortex

The new cortex (neocortex) is a layer of gray matter with a total area of ​​1500-2200 cm 2, covering the cerebral hemispheres. It makes up about 40% of the mass of the brain. The cortex contains about 14 billion neurons and about 140 billion glial cells. The cerebral cortex is phylogenetically the youngest neural structure. In humans, it carries out the highest regulation of body functions and psychophysiological processes that provide various forms of behavior.

Structural and functional characteristics of the cortex... The cerebral cortex consists of six horizontal layers located in the direction from the surface to the interior.

Molecular layer has very few cells, but a large number of branching dendrites of pyramidal cells, forming a plexus parallel to the surface. On these dendrites, synapses form afferent fibers coming from the associative and nonspecific nuclei of the thalamus.

Outer granular layer composed mainly of stellate and partly small pyramidal cells. The fibers of the cells of this layer are located mainly along the surface of the cortex, forming corticocortical connections.

Outer pyramidal layer consists mainly of medium-sized pyramidal cells. The axons of these cells, like the granular cells of layer II, form corticocortical associative connections.

Inner granular layer by the nature of the cells and the location of their fibers, it is similar to the outer granular layer. On the neurons of this layer, synaptic endings form afferent fibers coming from neurons of specific nuclei of the thalamus and, therefore, from receptors of sensory systems.

Inner pyramid formed by medium and large pyramidal cells, and the giant Betz pyramidal cells are located in the motor cortex. The axons of these cells form the efferent corticospinal and corticobulbar motor pathways.

Layer of polymorphic cells formed mainly by fusiform cells, the axons of which form corticothalamic pathways.

▓ Afferent and efferent connections of the cortex... In layers I and IV, signals are perceived and processed into the cortex. The neurons of the II and III layers carry out corticocortical associative connections. The efferent pathways leaving the cortex are formed mainly in the V - VI layers. The division of the cortex into different fields was carried out in more detail on the basis of cytoarchitectonic features (shape and location of neurons) by K. Brodman, who identified 11 areas, including 52 fields, many of which are characterized by functional and neurochemical features. According to Brodman, the frontal area includes fields 8, 9, 10, 11, 12, 44, 45, 46, 47. The precentral area includes fields 4 and 6, and the postcentral area includes fields 1, 2, 3, 43. The parietal region includes fields 5, 7, 39, 40, and the occipital region 17 18 19. The temporal region consists of a very large number of cytoarchitectonic fields: 20, 21, 22, 36, 37, 38, 41, 42, 52.

Fig. 1. Cytoarchitectonic fields of the human cerebral cortex (according to K. Brodman): a - the outer surface of the hemisphere; b - the inner surface of the hemisphere.

Histological data show that the elementary neural circuits involved in information processing are located perpendicular to the surface of the cortex. In the motor and various zones of the sensory cortex, there are neural columns with a diameter of 0.5-1.0 mm, which represent a functional association of neurons. Adjacent neural columns can partially overlap, as well as interact with each other by the mechanism of lateral inhibition and self-regulation by the type of return inhibition.

In phylogeny, the role of the cerebral cortex in the analysis and regulation of body functions and the subordination of the lower parts of the central nervous system to itself increases. This process is called corticolization functions.

The function localization problem has three concepts:

The principle of narrow localizationism - all functions are placed in one, separately taken structure.

Equipotentialism concept - different cortical structures are functionally equivalent.

The principle of multifunctionality of cortical fields. The property of multifunctionality allows this structure to be included in the software different forms activity, while realizing the main, genetically inherent function of it. The degree of multifunctionality of various cortical structures is not the same: for example, in the fields of the associative cortex it is higher than in the primary sensory fields, and in the cortical structures it is higher than in the stem. Multifunctionality is based on the multichannel flow of afferent excitation into the cerebral cortex, the overlap of afferent excitations, especially at the thalamic and cortical levels, the modulating effect of various structures (nonspecific thalamus, basal ganglia) on cortical functions, the interaction of cortical-subcortical and intercortical pathways of excitation.

One of the largest options for the functional division of the neocortex is the selection of sensory, associative and motor areas in it.

Sensory areas of the cerebral cortex... Sensory areas of the cortex are areas into which sensory stimuli are projected. The sensory areas of the cortex are otherwise called: the projection cortex or cortical parts of the analyzers. They are located mainly in the parietal, temporal and occipital lobes. Afferent pathways in the sensory cortex come mainly from specific sensory nuclei of the thalamus (ventral, posterior lateral and medial). The sensory cortex has well-defined II and IV layers and is called granular .

Areas of the sensory cortex, irritation or destruction of which causes clear and permanent changes in the sensitivity of the body, are called primary sensory areas ... They consist mainly of monomodal neurons and form sensations of the same quality. In the primary sensory zones, there is usually a clear spatial (topographic) representation of body parts, their receptor fields. There are less localized areas around the primary sensory areas. secondary sensory zones , polymodal neurons of which respond to the action of several stimuli.

╠ The most important sensory area is the parietal cortex of the postcentral gyrus and the corresponding part of the paracentral lobule on the medial surface of the hemispheres (fields 1-3), which is designated as the primary somatosensory area (S I). There is a projection of the skin sensitivity of the opposite side of the body from tactile, pain, temperature receptors, interoceptive sensitivity and sensitivity of the musculoskeletal system from muscle, articular and tendon receptors. The projection of body parts in this area is characterized by the fact that the projection of the head and upper parts of the trunk is located in the lower lateral parts of the postcentral gyrus, the projection of the lower half of the body and legs is in the upper medial zones of the gyrus, the projection of the lower part of the leg and feet is in the cortex of the paracentral lobule on the medial surface of the hemispheres. ... In this case, the projection of the most sensitive areas (tongue, lips, larynx, fingers) has relatively large zones compared to other parts of the body (see Figure 2). It is assumed that the projection of taste sensitivity is also located in the zone of tactile sensitivity of the tongue.

In addition to S I, a smaller secondary somatosensory region is distinguished (S II). It is located on the upper wall of the lateral groove, at the border of its intersection with the central groove. The functions of S II are poorly understood. It is known that the localization of the body surface in it is less clear, impulses come here both from the opposite side of the body and from “our” side, suggesting its participation in the sensory and motor coordination of the two sides of the body.

╠ Another primary sensory area is the auditory cortex (fields 41, 42), which is located deep in the lateral groove (cortex of Heschl's transverse temporal gyri). In this zone, in response to stimulation of the auditory receptors of Corti's organ, sound sensations are formed, varying in volume, tone, and other qualities. It has a clear topical projection: in different parts of the cortex, different parts of the organ of Corti are represented. The projection cortex of the temporal lobe also includes the center of the vestibular analyzer in the superior and middle temporal gyri (fields 20 and 21). The processed sensory information is used to form the "body map" and to regulate the functions of the cerebellum (temporocerebellar pathway).

Fig. 2. Diagram of the sensory and motor homunculi. Section of the hemispheres in the frontal plane: a - projection of the general sensitivity in the cortex of the postcentral gyrus; b - projection of the motor system in the cortex of the precentral gyrus.

╠ Another primary projection area of ​​the neocortex is located in the occipital cortex - the primary visual area (cortex of a part of the wedge-shaped gyrus and lingular lobule, field 17). Here it has a topical representation of retinal receptors, and each point of the retina corresponds to its own section of the visual cortex, while the macular area has a large area of ​​representation. Due to the incomplete intersection of the visual pathways, the retina halves of the same name are projected into the visual area of ​​each hemisphere. The presence in each hemisphere of the projection of the retina of both eyes is the basis of binocular vision. Irritation of the cortex of the 17th field leads to the appearance of light sensations. Near field 17 is the cortex of the secondary visual area (fields 18 and 19). The neurons of these zones are polymodal and respond not only to light, but also to tactile, auditory stimuli. In this visual area, a synthesis of various types of sensitivity occurs and more complex visual images and their recognition arise. Irritation of these fields causes visual hallucinations, obsessive sensations, and eye movements.

The bulk of information about the environment and the internal environment of the body, which entered the sensory cortex, is transmitted for further processing in the associative cortex.

Associative areas of the cortex... The associative areas of the cortex include areas of the neocortex located adjacent to the sensory and motor areas, but not directly performing sensory and motor functions. The boundaries of these areas are not clearly marked, the uncertainty is mainly associated with the secondary projection zones, the functional properties of which are transitional between the properties of the primary projection and associative zones. In humans, the associative cortex makes up 70% of the neocortex.

The main physiological feature of neurons in the associative cortex is polymodality: they respond to several stimuli with almost the same strength. Polymodality (polysensory) of neurons in the associative cortex is created due, firstly, to the presence of corticocortical connections with different projection zones, and secondly, due to the main afferent input from the associative nuclei of the thalamus, in which complex information processing from various sensory pathways has already occurred. As a result, the associative cortex is a powerful apparatus for the convergence of various sensory stimuli, which makes it possible to perform complex processing of information about the external and internal environment of the body and use it for the implementation of higher psychophysiological functions. In the associative cortex, there are three associative systems of the brain: thalamotemporal, thalamophobic, and thalamic temporal.

╠ Thalamo-parietal system represented by the associative zones of the parietal cortex (fields 5, 7, 40), receiving the main afferent inputs from the posterior group of associative nuclei of the thalamus (lateral posterior nucleus and cushion). The parietal associative cortex has efferent outputs to the nuclei of the thalamus and hypothalamus, the motor cortex and the nuclei of the extrapyramidal system. The main functions of the thalamotemic system are gnosis, the formation of a "body scheme" and praxis. Under gnosis understand the function of various types of recognition: forms, sizes, meanings of objects, understanding of speech, cognition of processes, patterns. Gnostic functions include the assessment of spatial relationships. In the parietal cortex, the center of stereognosis is distinguished, located behind the middle sections of the postcentral gyrus (fields 7, 40, partly 39) and providing the ability to recognize objects by touch. A variant of the gnostic function is the formation in the mind of a three-dimensional model of the body ("body scheme"), the center of which is located in field 7 of the parietal cortex. Under praxis understand purposeful action, its center is located in the supra-marginal gyrus (fields 39 and 40 of the dominant hemisphere). This center provides storage and implementation of the program of motor automated acts.

╠ Thalamophobic system It is represented by the associative zones of the frontal cortex (fields 9-14), which have the main afferent input from the associative mediodorsal nucleus of the thalamus. The main function of the frontal associative cortex is the formation of programs of purposeful behavior, especially in a new environment for a person. The implementation of this general function is based on other functions of the thalamophobic system: 1) the formation of a dominant motivation that provides direction for human behavior. This function is based on the close bilateral connections of the palatine cortex with the limbic system and the role of the latter in the regulation of human higher emotions associated with his social activity and creativity .; 2) providing probabilistic forecasting, which is expressed by a change in behavior in response to changes in the situation environment and dominant motivation; 3) self-control of actions by constantly comparing the result of an action with the original intentions, which is associated with the creation of a foresight apparatus (an acceptor of the result of an action).

When the prefrontal frontal cortex is damaged, where the connections between the frontal lobe and the thalamus intersect, a person becomes rude, tactless, unreliable, he has a tendency to repeat any motor acts, although the situation has already changed and other actions must be performed.

╠ Thalamotemporal system not studied enough. But if we talk about the temporal cortex, then it should be noted that some associative centers, for example, stereognosis and praxis, also include areas of the temporal cortex (field 39). In the temporal cortex, the auditory center of Wernicke's speech is located, located in the posterior sections of the superior temporal gyrus (fields 22, 37, 42 of the left dominant hemisphere). This center provides speech gnosis - recognition and storage oral speech, both your own and someone else's. In the middle part of the superior temporal gyrus (field 22) there is a recognition center for musical sounds and their combinations. On the border of the temporal, parietal and occipital lobes (field 39) there is a center for reading written speech, which provides recognition and storage of images of written speech.

Motor areas of the cortex... In the motor cortex, primary and secondary motor regions are distinguished.

╠ In the primary motor cortex(precentral gyrus, field 4) there are neurons that innervate the motor neurons of the muscles of the face, trunk and extremities. It has a clear topographic projection of the muscles of the body. In this case, the projections of the muscles of the lower extremities and the trunk are located in the upper sections of the precentral gyrus and occupy a relatively small area, and the projection of the muscles of the upper extremities, face and tongue are located in the lower sections of the gyrus and occupy a large area (see Figure 2). The main regularity of topographic representation is that the regulation of the activity of muscles that provide the most accurate and varied movements (speech, writing, facial expressions) requires the participation of large areas of the motor cortex. Motor reactions to irritation of the primary motor cortex are carried out with a minimum threshold (high excitability), and are represented by elementary contractions of the muscles of the opposite side of the body (for the muscles of the head, contraction can be bilateral). When this area of ​​the cortex is damaged, the ability to fine coordinated movements of the hands, especially fingers, is lost.

╠ Secondary motor cortex(field 6) is located on the lateral surface of the hemispheres, in front of the precentral gyrus (premotor cortex). She carries out the higher motor functions associated with the planning and coordination of voluntary movements. The cortex of field 6 receives the main part of the efferent impulses of the basal nuclei and cerebellum and participates in the recoding of information about the program of complex movements. Irritation of the cortex of field 6 causes more complex coordinated movements, for example, turning the head, eyes and trunk in the opposite direction, concomitant contractions of the flexor or extensor muscles on the opposite side. In the premotor cortex, there are motor centers associated with human social functions: the center of written speech in the posterior part of the middle frontal gyrus (field 6), Broca's motor leak center in the posterior part of the inferior frontal gyrus (field 44), which provides speech praxis, as well as the musical motor center (field 45), which determines the tone of speech, the ability to sing.

▓ Afferent and efferent connections of the motor cortex... In the motor cortex, a layer containing giant Betz pyramidal cells is better expressed than in other areas of the cortex. The neurons of the motor cortex receive afferent inputs through the thalamus from muscle, articular and cutaneous receptors, as well as from the basal nuclei and cerebellum. The main efferent exit of the motor cortex to the stem and spinal motor centers is formed by the pyramidal cells of the V layer. Pyramidal and intercalated neurons are located vertically with respect to the surface of the cortex and form neuronal motor columns. Pyramidal neurons of the motor column can excite or inhibit motor neurons of the brainstem and spinal centers. The adjacent columns functionally overlap, and the pyramidal neurons that regulate the activity of one muscle are usually located not in one, but in several columns.

The main efferent connections of the motor cortex are carried out through the pyramidal and extrapyramidal pathways, which start from the giant pyramidal Betz cells and the smaller pyramidal cells of the V layer of the precentral gyrus cortex (60% of fibers), the premotor cortex (20% of the fibers) and the postcentral gyrus (20% of the fibers) ... Large pyramidal cells have fast-conducting axons and a background impulse activity of about 5 Hz, which increases to 20-30 Hz during movement. These cells innervate large (high-threshold) ά-motoneurons in the motor centers of the trunk and spinal cord, which regulate physical movement. Thin, slow-conducting myelin axons extend from the small pyramidal cells. These cells have a background activity of about 15 Hz, which increases or decreases during movement. They innervate small (low-threshold) ά-motoneurons in the brainstem and spinal motor centers, which regulate muscle tone.

Pyramid paths consist of 1 million fibers of the corticospinal tract, which start from the cortex of the upper and middle third of the precentral gyrus, and 20 million fibers of the corticobulbar tract, which starts from the cortex of the lower third of the precentral gyrus. The fibers of the pyramidal tract end on the ά-motor neurons of the motor nuclei III - VII and IX - XII of the cranial nerves (corticobulbar pathway) or on the spinal motor centers (corticospinal pathway). Through the motor cortex and pyramidal pathways, voluntary simple movements and complex purposeful motor programs are carried out, for example, professional skills, the formation of which begins in the basal ganglia and cerebellum and ends in the secondary motor cortex. Most of the fibers of the pyramidal pathways cross, but a small part of the fibers remains uncrossed, which helps to compensate for impaired movement functions in unilateral lesions. The premotor cortex also performs its functions through the pyramidal pathways: motor skills of writing, turning the head, eyes and body in the opposite direction, as well as speech (Broca's speech motor center, field 44). In the regulation of writing and especially oral speech, there is a pronounced asymmetry of the cerebral hemispheres: in 95% of right-handers and 70% of left-handers, oral speech is controlled by the left hemisphere.

To the cortical extrapyramidal pathways include corticorubular and corticoreticular pathways starting approximately from those zones that give rise to the pyramidal pathways. The fibers of the corticorubral pathway end on the neurons of the red nuclei of the midbrain, from which the rubrospinal pathways go further. The fibers of the corticoreticular pathways end on the neurons of the medial nuclei of the reticular formation of the pons (medial reticulospinal pathways go from them) and on the neurons of the reticular giant cell nuclei of the medulla oblongata, from which the lateral reticulospinal pathways begin. Through these pathways, the regulation of tone and posture is carried out, which provide precise, targeted movements. The cortical extrapyramidal pathways are a component of the extrapyramidal system of the brain, which includes the cerebellum, basal ganglia, and motor centers of the trunk. The extrapyramidal system regulates tone, postures of balance, and the fulfillment of memorized motor acts such as walking, running, speaking, writing. Since the corticopyramidal pathways give their numerous collaterals to the structures of the extrapyramidal system, both systems work in functional unity.

Assessing in general terms the role of various structures of the brain and spinal cord in the regulation of complex directed movements, it can be noted that the impulse (motivation) to move is created in the limbic system, the intention of movement - in the associative cortex of the cerebral hemispheres, the program of movements - in the basal ganglia, cerebellum, etc. the premotor cortex, and complex movements are performed through the motor cortex, motor centers of the trunk and spinal cord.

Interhemispheric relationships... Interhemispheric relationships in humans are manifested in two forms - functional asymmetry of the cerebral hemispheres and their joint activity.

╠ Functional asymmetry of the hemispheres is the most important psychophysiological property of the human brain. Allocate mental, sensory and motor interhemispheric functional asymmetries of the brain. In the study of psychophysiological functions, it was shown that in speech, the verbal information channel is controlled by the left hemisphere, and the non-verbal channel (voice, intonation) - by the right. Abstract thinking and consciousness are associated primarily with the left hemisphere. During the development of a conditioned reflex, the right hemisphere dominates in the initial phase, and during the strengthening of the reflex, the left one. The right hemisphere processes information simultaneously, synthetically, according to the principle of deduction, the spatial and relative features of the object are better perceived. The left hemisphere processes information sequentially, analytically, according to the principle of induction, better perceives the absolute features of the object and temporal relationships. In the emotional sphere, the right hemisphere predominantly determines negative emotions, controls the manifestations of strong emotions, in general it is more "emotional". The left hemisphere mainly determines positive emotions, controls the manifestation of weaker emotions.

In the sensory realm, the role of the right and left hemispheres is best manifested in visual perception. The right hemisphere perceives the visual image in a holistic manner, at once in all details, it is easier to solve the problem of distinguishing objects and recognizing visual images of objects, which is difficult to describe in words, creates the prerequisites for concrete-sensory thinking. The left hemisphere evaluates the visual image in a dismembered, analytical way, with each feature being analyzed separately. Familiar objects are recognized more easily and problems of similarity of objects are solved, visual images are devoid of specific details and have a high degree of abstraction; prerequisites for logical thinking are created.

Motor asymmetry is expressed primarily in right-left-handedness, which is controlled by the motor cortex of the opposite hemisphere. The asymmetry of other muscle groups is individual, not specific.

Fig. 3. Asymmetry of the cerebral hemispheres.

╠ Pairing in the activity of the cerebral hemispheres provided by the presence of the commissural system (corpus callosum, anterior and posterior, hippocampal and habenular commissures, interthalamic fusion), which anatomically connect the two hemispheres of the brain. In other words, both hemispheres are connected not only by horizontal connections, but also by vertical ones. The basic facts obtained using electrophysiological techniques showed that excitation from the site of irritation of one hemisphere is transmitted through the commissural system not only to the symmetrical area of ​​the other hemisphere, but also to asymmetrical areas of the cortex. The study of the method of conditioned reflexes showed that in the process of developing a reflex there is a "transfer" of a temporary connection to the other hemisphere. Elementary forms of interaction between the two hemispheres can be carried out through the quadruple and the reticular formation of the trunk.

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