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

The cerebral hemispheres occupy about 80% of the volume of the cranium, and are composed of white matter, the basis of which consists of long myelinated axons of neurons. Outside, the hemisphere is covered with gray matter or the cerebral cortex, consisting of neurons, non-myelinated fibers and glial cells, which are also contained in the thickness of the departments of this organ.

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

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

Functions

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

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

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

At the same time, data is received, processed, stored due to a significant number of impulses that pass through and are formed in neurons connected by long processes or axons. The level of cell activity can be determined by the physiological and mental state of the body and described using amplitude and frequency indicators, since the nature of these signals is similar to electrical impulses, and their density depends on the area in which the psychological process occurs.

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

• lack of concentration on household items;
• manifestation of creative dysfunction;
• violations of the psycho-emotional state of a person.

The surface of the cerebral cortex is divided into 4 zones, outlined by the most clear and significant convolutions. Each of the parts at the same time controls the main functions of the cerebral cortex:

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

Features of the structure of the cerebral cortex

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

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

The large hemispheres of the brain consist mainly of long axons, and also contains clusters of neurons in its thickness, forming the largest nuclei of the base, which are part of the extrapyramidal system.

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

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

The neurons of this part of the brain are programmed to repair the damaged area through synoptic contacts, thus each of the cells actively tries to repair the damaged connections, which ensures the plasticity of neural cortical networks. For example, when the cerebellum is removed or dysfunction, the neurons that connect it with the final section begin to grow into the cerebral cortex. In addition, cortical plasticity also manifests itself under normal conditions, when a new skill is being learned or as a result of pathology, when the functions performed by the damaged area are transferred to neighboring parts of the brain or even the hemisphere.

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

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

Areas and zones of the cortex

The cortex is a relatively young part of the CNS, developed from the terminal part of the brain. The evolutionary formation of this organ occurred in stages, so it is usually divided into 4 types:

1. The archicortex or ancient cortex, due to atrophy of the sense of smell, has turned into a hippocampal formation and consists of the hippocampus and its associated structures. It regulates behavior, feelings and memory.
2. The paleocortex, or old cortex, makes up the bulk of the olfactory zone.
3. The neocortex or neocortex is about 3-4 mm thick. It is a functional part and performs higher nervous activity: it processes sensory information, gives motor commands, and it also forms conscious thinking and speech of a person.
4. The mesocortex is an intermediate variant of the first 3 types of cortex.

Physiology of the cerebral cortex

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

The system of micromodules is based on stellate cells and their axons, while all neurons respond in the same way to an incoming afferent impulse and also send an efferent signal synchronously in response.

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

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

• associative;
• sensory (sensitive);
• motor.

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

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

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

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

Impulses from the limbs and tactile organs on the left side of the body are sent along afferent pathways to the opposite lobe of the cerebral hemispheres for further processing.

The neurons of the motor zone are excited by impulses received from muscle cells and are located in the central gyrus of the frontal lobe. The input mechanism is similar to that of the sensory area, as the motor pathways form an overlap in the medulla oblongata and follow to the opposite motor area.

Crinkles furrows and fissures

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

Cortical architectonic fields determine the functional structure of sections of the cerebral cortex. All of them are different in morphological features and regulate different functions. Thus, 52 different fields are allocated, located in certain areas. According to Brodman, this division looks like this:

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

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

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

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

Cell layers

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

1. The surface molecular layer is formed mainly from dendrites, with a small interspersed with neurons, the processes of which do not leave the layer boundary.
2. The outer granular consists of pyramidal and stellate neurons, the processes of which connect it with the next layer.
3. The pyramidal neuron is formed by pyramidal neurons, the axons of which are directed downward, where they break off or form associative fibers, and their dendrites connect this layer with the previous one.
4. The inner granular layer is formed by stellate and small pyramidal neurons, the dendrites of which go into the pyramidal layer, and its long fibers go into the upper layers or go down into the white matter of the brain.
5. Ganglionic consists of large pyramidal neurocytes, their axons extend beyond the cortex and connect various structures and departments of the central nervous system with each other.

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

Video: Cerebral cortex

New bark(neocortex) is a layer of gray matter with a total area of ​​​​1500-2200 square centimeters, covering the large hemispheres. The neocortex makes up about 72% of the total area of ​​the cortex and about 40% of the mass of the brain. The new bark contains 14 mln. Neurons, and the number of glial cells is approximately 10 times greater.

The cerebral cortex in phylogenetic terms is the youngest nervous structure. In humans, it carries out the highest regulation of body functions and psychophysiological processes that provide various forms of behavior.

In the direction from the surface of the new cortex in depth, six horizontal layers are distinguished.

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

Outer granular layer. Composed mainly of stellate and partially 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 pyramidal cells of medium size. The axons of these cells, like the granular cells of the 2nd layer, form corticocortical associative connections.

Inner granular layer. By the nature of the cells (stellate cells) and the location of their fibers, it is similar to the outer granular layer. In this layer, afferent fibers have synaptic endings coming from neurons of specific nuclei of the thalamus and, consequently, from receptors of sensory systems.

Inner pyramidal layer. Formed by medium and large pyramidal cells. Moreover, Betz's giant pyramidal cells are located in the motor cortex. The axons of these cells form the afferent corticospinal and corticobulbar motor pathways.

Layer of polymorphic cells. It is formed mainly by spindle-shaped cells, the axons of which form the corticothalamic pathways.

Assessing the afferent and efferent connections of the neocortex as a whole, it should be noted that in layers 1 and 4, perception and processing of signals entering the cortex occur. Neurons of the 2nd and 3rd layers carry out corticocortical associative connections. The efferent pathways leaving the cortex are formed mainly in the 5th and 6th layers.

Histological data show that the elementary neural circuits involved in information processing are located perpendicular to the surface of the cortex. At the same time, they are located in such a way that they capture all layers of the cortex. Such associations of neurons were called by scientists. neural columns. Neighboring neural columns can partially overlap and also interact with each other.

The increase in the phylogenesis of the role of the cerebral cortex, the analysis and regulation of body functions and the subordination of the underlying parts of the central nervous system by scientists are defined as function corticalization(Union).

Along with the corticalization of the functions of the neocortex, it is customary to single out the localization of its functions. The most commonly used approach to the functional division of the cerebral cortex is the allocation of sensory, associative and motor areas in it.

Sensory areas of the cortex - zones in which sensory stimuli are projected. They are located mainly in the parietal, temporal and occipital lobes. Afferent pathways enter the sensory cortex predominantly from specific sensory nuclei of the thalamus (central, posterior lateral, and medial). The sensory cortex has well-defined layers 2 and 4 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(nuclear parts of analyzers, as I.P. Pavlov believed). They consist mainly of monomodal neurons and form sensations of the same quality. Primary sensory areas usually have a clear spatial (topographic) representation of body parts, their receptor fields.

Around the primary sensory areas are less localized secondary sensory areas, whose polymodal neurons 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 postcentral lobule on the medial surface of the hemispheres (fields 1–3), which is designated as somatosensory area. Here there is a projection of 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, 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 body is located in the inferolateral areas of the postcentral gyrus, the projection of the lower half of the trunk and legs is in the upper medial zones of the gyrus, and the projection of the lower part of the lower leg and feet is in the cortex of the postcentral lobule on the medial surface hemispheres (Fig. 12).

At the same time, the projection of the most sensitive areas (tongue, larynx, fingers, etc.) has relatively large zones compared to other parts of the body.

Rice. 12. Projection of parts of the human body on the area of ​​the cortical end of the analyzer of general sensitivity

(section of the brain in the frontal plane)

In the depth of the lateral groove is located auditory cortex(cortex of the transverse temporal gyri of Heschl). In this zone, in response to irritation of the auditory receptors of the organ of Corti, sound sensations are formed that change in volume, tone, and other qualities. There is a clear topical projection here: in different parts of the cortex, different parts of the organ of Corti are represented. The projection cortex of the temporal lobe also includes, as scientists suggest, the center of the vestibular analyzer in the superior and middle temporal gyri. The processed sensory information is used to form the "body map" and regulate the functions of the cerebellum (temporal-bridge-cerebellar pathway).

Another area of ​​the neocortex is located in the occipital cortex. This is primary visual area. There is a topical representation of retinal receptors here. In this case, each point of the retina corresponds to its own area of ​​the visual cortex. In connection with the incomplete decussation of the visual pathways, the same halves of the retina are projected into the visual region 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 cerebral cortex in this area leads to the appearance of light sensations. Near the primary visual area secondary visual area. The neurons of this region are polymodal and respond not only to light, but also to tactile and auditory stimuli. It is no coincidence that it is in this visual area that the synthesis of various types of sensitivity occurs and more complex visual images and their identification arise. Irritation of this area of ​​the cortex causes visual hallucinations, obsessive sensations, eye movements.

The main part of the information about the surrounding world and the internal environment of the body, received in the sensory cortex, is transmitted for further processing to the associative cortex.

Association areas of the cortex (intersensory, interanalyzer), includes areas of the new cerebral cortex, which are located next to the sensory and motor areas, but do not directly perform sensory or motor functions. The boundaries of these areas are not clearly marked, which is associated with the secondary projection zones, the functional properties of which are transitional between the properties of the primary projection and associative zones. The associative cortex is phylogenetically the youngest area of ​​the neocortex, which has received the greatest development in primates and humans. In humans, it makes up about 50% of the entire cortex, or 70% of the neocortex.

The main physiological feature of the neurons of the associative cortex, which distinguishes them from the neurons of the primary zones, is polysensory (polymodality). They respond with almost the same threshold not to one, but to several stimuli - visual, auditory, skin, etc. The polysensory nature of the neurons of the associative cortex is created both by its corticocortical connections with different projection zones, and by its main afferent input from the associative nuclei of the thalamus, in which complex processing of information from various sensory pathways has already taken place. As a result, the associative cortex is a powerful apparatus for the convergence of various sensory excitations, which makes it possible to perform complex processing of information about the external and internal environment of the body and use it to implement higher mental functions.

According to thalamocortical projections, two associative systems of the brain are distinguished:

thalamothemenal;

talomotemporal.

thalamotenal system it is represented by associative zones of the parietal cortex, which receive the main afferent inputs from the posterior group of associative nuclei of the thalamus (lateral posterior nucleus and pillow). The parietal association cortex has afferent outputs to the nuclei of the thalamus and hypothalamus, the motor cortex, and the nuclei of the extrapyramidal system. The main functions of the thalamo-temporal system are gnosis, the formation of a "body schema" and praxis.

Gnosis- these are various types of recognition: shapes, sizes, meanings of objects, understanding of speech, etc. Gnostic functions include the assessment of spatial relationships, for example, the relative position of objects. In the parietal cortex, the center of stereognosis is isolated (located behind the middle sections of the postcentral gyrus). It provides the ability to recognize objects by touch. A variant of the gnostic function is also the formation in the mind of a three-dimensional model of the body (“body schema”).

Under praxis understand purposeful action. The praxis center is located in the supramarginal gyrus and ensures the storage and implementation of the program of motorized automated acts (for example, combing, shaking hands, etc.).

Thalamolobic system. It is represented by associative zones of the frontal cortex, which have the main afferent input from the mediodorsal nucleus of the thalamus. The main function of the frontal associative cortex is the formation of goal-directed behavior programs, especially in a new environment for a person. The implementation of this function is based on other functions of the thalomolobic system, such as:

the formation of the dominant motivation that provides the direction of human behavior. This function is based on the close bilateral connections of the frontal cortex and the limbic system and the role of the latter in the regulation of higher human emotions associated with his social activity and creativity;

providing probabilistic forecasting, which is expressed in a change in behavior in response to changes in the environment and the dominant motivation;

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 (according to the theory of the functional system of P.K. Anokhin, an acceptor of the result of an action).

As a result of the medically indicated prefrontal lobotomy, in which the connections between the frontal lobe and the thalamus intersect, there is the development of "emotional dullness", a lack of motivation, firm intentions and plans based on prediction. Such people become rude, tactless, they have a tendency to repeat any motor acts, although the changed situation requires the performance of completely different actions.

Along with the thalamo-temporal and thalamo-temporal systems, some scientists propose to distinguish the thalamo-temporal system. However, the concept of the thalamotemporal system has not yet received confirmation and sufficient scientific study. Scientists note a certain role of the temporal cortex. Thus, some associative centers (for example, stereognosis and praxis) also include sections of the temporal cortex. In the temporal cortex is the auditory center of Wernicke's speech, located in the posterior sections of the superior temporal gyrus. It is this center that provides speech gnosis - the recognition and storage of oral speech, both one's own and someone else's. In the middle part of the superior temporal gyrus, there is a center for recognizing musical sounds and their combinations. On the border of the temporal, parietal and occipital lobes there is a center for reading written speech, which provides recognition and storage of images of written speech.

It should also be noted that the psychophysiological functions performed by the associative cortex initiate behavior, an obligatory component of which is voluntary and purposeful movements, carried out with the obligatory participation of the motor cortex.

Motor areas of the cortex . The concept of the motor cortex of the cerebral hemispheres began to form in the 1980s, when it was shown that electrical stimulation of certain cortical zones in animals causes movement of the limbs of the opposite side. Based on modern research in the motor cortex, it is customary to distinguish two motor areas: primary and secondary.

AT primary motor cortex(precentral gyrus) are neurons that innervate the motor neurons of the muscles of the face, trunk and limbs. It has a clear topography of the projections 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 parts 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 parts of the gyrus and occupy a large area. The main pattern of topographic representation is that the regulation of the activity of muscles that provide the most accurate and diverse movements (speech, writing, facial expressions) requires the participation of large areas of the motor cortex. Motor reactions to stimulation of the primary motor cortex are carried out with a minimum threshold, which indicates its high excitability. They (these motor reactions) are represented by elementary contractions of the opposite side of the body. With the defeat of this cortical region, the ability to fine coordinated movements of the limbs, especially the fingers, is lost.

secondary motor cortex. It is located on the lateral surface of the hemispheres, in front of the precentral gyrus (premotor cortex). It performs higher motor functions associated with the planning and coordination of voluntary movements. The premotor cortex receives the bulk of the efferent impulses from the basal ganglia and the cerebellum and is involved in recoding information about the plan of complex movements. Irritation of this area of ​​the cortex causes complex coordinated movements (for example, turning the head, eyes and torso in opposite directions). In the premotor cortex there are motor centers associated with the social functions of a person: in the posterior part of the middle frontal gyrus is the center of written speech, in the posterior part of the inferior frontal gyrus is the center of motor speech (Broca's center), as well as the musical motor center, which determines the tonality of speech and the ability to sing.

The motor cortex is often referred to as the agranular cortex because the granular layers are poorly expressed in it, but the layer containing Betz's giant pyramidal cells is more pronounced. Motor cortex neurons receive afferent inputs through the thalamus from muscle, joint, and skin receptors, as well as from the basal ganglia and cerebellum. The main efferent output of the motor cortex to the stem and spinal motor centers is formed by pyramidal cells. Pyramidal and associated intercalary neurons are located vertically with respect to the surface of the cortex. Such adjacent neuronal complexes that perform similar functions are called functional motor columns. Pyramidal neurons of the motor column can excite or inhibit the motor neurons of the stem and spinal centers. Neighboring columns functionally overlap, and pyramidal neurons that regulate the activity of one muscle are usually located in several columns.

The main efferent connections of the motor cortex are carried out through the pyramidal and extrapyramidal pathways, starting from the giant pyramidal cells of Betz and the smaller pyramidal cells of the cortex of the precentral gyrus, premotor cortex and postcentral gyrus.

pyramid path consists of 1 million fibers of the corticospinal tract, starting from the cortex of the upper and middle third of the precentral gyrus, and 20 million fibers of the corticobulbar tract, starting from the cortex of the lower third of the precentral gyrus. Arbitrary simple and complex purposeful motor programs are carried out through the motor cortex and pyramidal pathways (for example, professional skills, the formation of which begins in the basal ganglia and ends in the secondary motor cortex). Most of the fibers of the pyramidal pathways are crossed. But a small part of them remain uncrossed, which helps to compensate for impaired movement functions in unilateral lesions. Through the pyramidal pathways, the premotor cortex also performs its functions (motor skills of writing, turning the head and eyes in the opposite direction, etc.).

To cortical extrapyramidal pathways include corticobulbar and corticoreticular pathways, starting approximately in the same area as the pyramidal pathways. The fibers of the corticobulbar pathway terminate on the neurons of the red nuclei of the midbrain, from which the rubrospinal pathways continue. The fibers of the corticoreticular pathways terminate on the neurons of the medial nuclei of the reticular formation of the pons (the medial reticulospinal pathways originate from them) and on the neurons of the reticular giant cell nuclei of the medulla oblongata, from which the lateral reticulospinal pathways originate. Through these pathways, the regulation of tone and posture is carried out, providing accurate targeted movements. Cortical extrapyramidal pathways are a component of the extrapyramidal system of the brain, which includes the cerebellum, basal ganglia, and motor centers of the brainstem. This system regulates tone, posture, coordination and correction of movements.

Assessing in general 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 frontal system, the idea of ​​movement is created in the associative cortex of the cerebral hemispheres, the program of movements is created in the basal ganglia, cerebellum and premotor cortex, and the execution of complex movements occurs through the motor cortex, motor centers of the trunk and spinal cord.

Interhemispheric relationships Interhemispheric relationships are manifested in humans in two main forms:

functional asymmetry of the cerebral hemispheres:

joint activity of the cerebral hemispheres.

Functional asymmetry of the hemispheres is the most important psychophysiological property of the human brain. The study of functional asymmetry of the hemispheres began in the middle of the 19th century, when the French physicians M. Dax and P. Broca showed that a person’s speech disorder occurs when the cortex of the inferior frontal gyrus, usually the left hemisphere, is damaged. Some time later, the German psychiatrist K. Wernicke discovered an auditory speech center in the posterior cortex of the upper temporal gyrus of the left hemisphere, the defeat of which leads to impaired understanding of oral speech. These data and the presence of motor asymmetry (right-handedness) contributed to the formation of the concept according to which a person is characterized by left-hemispheric dominance, which was formed evolutionarily as a result of labor activity and is a specific property of his brain. In the 20th century, as a result of the use of various clinical methods (especially in the study of patients with a split brain, the corpus callosum was cut), it was shown that, in a number of psychophysiological functions, the right hemisphere dominates in a person, not the left one. Thus, the concept of partial dominance of the hemispheres arose (its author is R. Sperry).

It is customary to allocate mental, sensory and motor interhemispheric asymmetry of the brain. Again, in the study of speech, it was shown that the verbal information channel is controlled by the left hemisphere, and the non-verbal channel (voice, intonation) is controlled by the right. Abstract thinking and consciousness are predominantly associated with the left hemisphere. When developing a conditioned reflex, the right hemisphere dominates in the initial phase, and during exercises, that is, the strengthening of the reflex, the left hemisphere dominates. The right hemisphere processes information simultaneously statically, according to the principle of deduction, the spatial and relative features of objects are better perceived. The left hemisphere processes information sequentially, analytically, according to the principle of induction, it better perceives the absolute features of objects and temporal relationships. In the emotional sphere, the right hemisphere mainly determines the older, negative emotions, controls the manifestation of strong emotions. In general, the right hemisphere is "emotional". The left hemisphere determines mainly 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 holistically, immediately in all details, it is easier to solve the problem of distinguishing objects and identifying visual images of objects that are difficult to describe in words, creates the prerequisites for concrete-sensory thinking. The left hemisphere evaluates the visual image dissected. Familiar objects are more easily recognized and problems of similarity of objects are solved, visual images are devoid of specific details and have a high degree of abstraction, the prerequisites for logical thinking are created.

Motor asymmetry is due to the fact that the muscles of the hemispheres, providing a new, higher level of regulation of complex brain functions, simultaneously increase the requirements for combining the activities of the two hemispheres.

Joint activity of the cerebral hemispheres is 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.

Clinical studies have shown that in addition to the transverse commissural fibers that provide the interconnection of the cerebral hemispheres, there are also longitudinal, as well as vertical commissural fibers.

Questions for self-control:

General characteristics of the new cortex.

Functions of the new cortex.

The structure of the new cortex.

What are neural columns?

What areas of the cortex are distinguished by scientists?

Characteristics of the sensory cortex.

What are primary sensory areas? Their characteristic.

What are secondary sensory areas? Their functional purpose.

What is the somatosensory cortex and where is it located?

Characteristics of the auditory cortex.

Primary and secondary visual areas. Their general characteristics.

Characteristics of the association area of ​​the cortex.

Characteristics of the associative systems of the brain.

What is the thalamotenoid system. Her functions.

What is the thalamolobal system. Her functions.

General characteristics of the motor cortex.

Primary motor cortex; her characteristic.

secondary motor cortex; her characteristic.

What are functional motor columns.

Characteristics of the cortical pyramidal and extrapyramidal pathways.

Neocortex - evolutionarily 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 neocortex is very diverse, but approximately three-quarters of the neurons of the cortex are pyramidal neurons (pyramids), and therefore one of the main classifications of cortical neurons divides them into pyramidal and non-iramide (fusiform, stellate, granular, candelabra cells, Martinotti cells, etc. .). Another classification is related to the length of the axon (see section 2.4). The long-axon Golgi I cells are mainly pyramids and spindles, their axons can exit the cortex, the rest of the cells are short-axon Golgi II.

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 the 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 extends from this apex and ascends 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 upwards. Stellate cells do not have an apical dendrite; spinules on dendrites are absent in most cases. In fusiform cells, two large dendrites depart 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, slightly branched.

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

Let's list layers of neocortex(Fig. 9.8).

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

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

III layer - external pyramidal - the widest and thickest layer, contains mainly small and medium-sized pyramidal and stellate neurons. In the depths of the layer are large and giant pyramids.

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

V layer - internal 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; subsection 9.3.4) - giant pyramidal neurons (Betz pyramids). The apical dendrites of the pyramids, as a rule, reach the first layer.

VI layer - polymorphic, or multiform, - 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 of a seven-layer bark.

Rice. 9.8.

a- Neurons are stained as a whole; b- only the bodies of neurons are painted; in- painted

only processes 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 on 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 fields, all six layers are equally well expressed. Such a bark is called homotypic. However, in some fields, the severity of the layers may change during development. 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. Such a cortex is characteristic of primary sensory areas (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 II layer and practically no IV, but very wide pyramidal layers, especially the inner one (V).

New cortex (synonyms: neocortex, isocortex) (Latin neocortex) - new areas of the cerebral cortex, which in lower mammals are only outlined, and in humans they make up the main part of the cortex. The new cortex is located in the upper layer of the cerebral hemispheres, has a thickness of 2-4 millimeters and is responsible for higher nervous functions - sensory perception, execution of motor commands, conscious thinking and, in humans, speech.

The neocortex contains two main types of neurons: pyramidal neurons (~80% of neocortical neurons) and interneurons (~20% of neocortical neurons).

The structure of the neocortex is relatively homogeneous (hence the alternative name: "isocortex"). In humans, it has six horizontal layers of neurons that differ in the type and nature of connections. Vertically, neurons are organized into so-called columns of the cortex. In dolphins, the neocortex has 3 horizontal layers of neurons.

Principle of operation

A fundamentally new theory of the algorithms of the neocortex was developed in Menlo Park, California, USA (Silicon Valley), by Jeff Hawkins. The theory of hierarchical temporary memory has been implemented in software as a computer algorithm, which is available for use under a license from numenta.com.

The same algorithm processes all the senses.

The function of a neuron is based on memory over time, something like causal relationships that hierarchically develop into larger and larger objects from smaller ones.

Question 21

The roots of the cranial nerves depart from the medulla oblongata: XII - hypoglossal, XI - accessory nerve, X - vagus nerve, IX - glossopharyngeal nerve. Between the medulla oblongata and the bridge, the roots of the VII and VIII cranial nerves - facial and auditory - emerge. The roots of the VI and V nerves emerge from the bridge - the abducens and trigeminal.

In the hindbrain, the paths of many complexly coordinated motor reflexes are closed. Here are vital centers for the regulation of respiration, cardiovascular activity, the functions of the digestive organs, and metabolism. The nuclei of the medulla oblongata are involved in the implementation of such reflex acts as the separation of digestive juices, chewing, sucking, swallowing, vomiting, sneezing.

In a newborn, the medulla oblongata together with the bridge weighs about 8 g, which is 2% of the mass of the brain (in an adult - 1.6%). The nuclei of the medulla oblongata begin to form in the prenatal period of development and are already formed by the time of birth. The maturation of the nuclei of the medulla oblongata ends by 7 years.

The IX pair - the glossopharyngeal nerve, according to the composition of the fibers, includes both sensory and motor, as well as secretory fibers. The glossopharyngeal nerve originates from four nuclei located in the medulla oblongata. The ninth pair of nerves is closely connected with the tenth pair of the vagus nerve (some nuclei are shared with the vagus nerve). The glossopharyngeal nerve supplies sensory (gustatory) fibers to the posterior third of the tongue and palate, and also innervates the middle ear and pharynx along with the vagus nerve. The motor fibers of this nerve, together with the branches of the vagus nerve, supply the muscles of the pharynx.

Secretory fibers innervate the parotid salivary gland. When the glossopharyngeal nerve is affected, a number of disorders are observed, for example, taste disorders, decreased sensitivity in the pharynx, as well as mild spasms of the pharyngeal muscles. In some cases, salivation may be impaired.

X pair - vagus nerve. Departs from the nuclei located in the medulla oblongata. Some of the cores are shared with the ninth pair. The vagus nerve performs a number of complex functions of a sensitive, motor and secretory nature. So, it supplies motor and sensory fibers to the muscles of the pharynx (together with the IX nerve), soft palate, larynx, epiglottis, vocal cords (see Fig. 8). Unlike other cranial nerves, this nerve extends far beyond the skull and innervates the trachea, bronchi, lungs, heart, gastrointestinal tract and some other internal organs, as well as blood vessels. Thus, the further course of its fibers takes part in autonomic innervation, forming a kind of system - parasympathetic.

In case of violation of the function of the vagus nerve (with bilateral partial damage), swallowing disorder occurs, a change in the timbre of the voice (nasal, nasal tone), up to complete anarthria; there are a number of severe disorders of the cardiovascular and respiratory systems. With the complete shutdown of the function of the vagus nerve, death may occur due to paralysis of the heart and respiratory activity.

XI pair - accessory nerve. It is a motor nerve. Its nuclei are located in the spinal cord and medulla oblongata. The fibers of this nerve innervate the muscles of the neck and shoulder girdle, in connection with which movements such as turning the head, raising the shoulders, and bringing the shoulder blades to the spine are carried out. With damage to the accessory nerve, atrophic paralysis of these muscles develops, as a result of which it is difficult to turn the head, the shoulder is lowered. When the nerve is irritated, tonic convulsions of the cervical muscles can occur, as a result of which the head is forcibly tilted to the side (torticollis). Clonic spasm in these muscles (bilateral) causes violent nodding movements.

XII pair - hypoglossal nerve. The fibers start from the nucleus located at the bottom of the rhomboid fossa. They innervate the muscles of the tongue, which gives it maximum flexibility and mobility. When the hypoglossal nerve is damaged, its ability to move is weakened, which is necessary to perform the speech function and the function of eating. In such cases, speech becomes unclear, it becomes impossible to pronounce complex words.

With bilateral damage to the hypoglossal nerve, speech becomes impossible (anarthria). A typical picture of speech and phonation disorders is observed with a combined lesion of the IX, X and XII pairs of nerves, known as bulbar palsy.

In these cases, the nuclei of the medulla oblongata or the roots and nerves extending from them are affected. There is paralysis of the tongue, severe speech disorders, as well as swallowing disorders, choking, liquid food pours out through the nose, the voice becomes nasal.

Such paralysis is accompanied by muscle atrophy and bears all the signs of peripheral paralysis. More often there are cases of lesions of the central path (cortical-bulbar). In childhood, for example, after suffering parainfectious encephalitis, with bilateral damage to the cortical-bulbar tract, phenomena develop that are outwardly similar to bulbar palsy, but differ in the nature of localization. Since this paralysis is central, there is no muscle atrophy. This type of disorder is known as pseudobulbar palsy.

Question 22. Cranial nerves of the bridge (V. VI. VII. VIII)

V pair - trigeminal nerve (mixed). It provides motor and sensory innervation, provides conduction of sensitivity from the skin of the face, anterior scalp, mucous membrane of the nasal and oral cavities, tongue, eyeball, meninges. The motor fibers of the trigeminal nerve innervate the masticatory muscles.

The sensory fibers of the trigeminal nerve, like the spinal nerves, begin in the sensory ganglion, which lies on the anterior surface of the pyramid of the temporal bone. The peripheral processes of the nerve cells of this node terminate in receptors in the face, scalp, and so on, and their central processes go to the sensory nuclei of the trigeminal nerve, where the second neurons of the sensory pathways from the face are located. The fibers coming from them form the so-called loop of the trigeminal nerve, then go to the opposite side and join the medial loop (a common sensory path from the spinal cord to the thalamus).

The third neuron lies in the thalamus. The propulsion core is on the bridge. At the base of the brain, the trigeminal nerve emerges from the thickness of the bridge in the region of the cerebellopontine angle. Three branches of the trigeminal nerve depart from the Hesser node. The nerves exit the skull to the facial surface and form three branches: a) ophthalmic, b) zygomatic, c) mandibular.

The first two branches are sensitive. They innervate the skin of the upper facial region, as well as the mucous membranes of the nose, eyelids, eyeball, upper jaw, gums and teeth. Part of the fibers supplies the meninges.

The third branch of the trigeminal nerve is mixed in terms of fiber composition. Its sensory fibers innervate the lower part of the skin surface of the face, the anterior two-thirds of the tongue, the mucous membrane of the mouth, teeth and gums of the lower jaw. The motor fibers of this branch innervate the masticatory muscles and take part in the implementation of the function of taste. The sympathetic nerve plays an important role in the innervation of the trigeminal nerve.

With the defeat of the peripheral branches of the trigeminal nerve, the skin sensitivity of the face is upset. There are excruciating attacks of pain (trigeminal neuralgia), due to the inflammatory process in the nerve. Disorders of the motor portion of the fibers cause paralysis of the masticatory muscles, as a result of which the movements of the lower jaw are sharply limited, which makes it difficult to chew food, and disrupts sound pronunciation (Fig. 8).

VI pair - abducens nerve (motor), innervates the external rectus muscle of the eye, which moves the eyeball outward. The nerve nucleus is located in the posterior part of the bridge at the bottom of the rhomboid fossa. Nerve fibers exit to the base of the brain at the border between the pons and the medulla oblongata. Through the superior orbital fissure, the nerve passes from the cranial cavity to the orbit.

VII pair - the facial nerve (motor), innervates the mimic muscles and muscles of the auricle. The nerve nucleus is located on the border between the bridge and the medulla oblongata. Nerve fibers leave the brain in the region of the cerebellopontine angle and, together with the vestibulocochlear nerve (VIII pair), enter the internal auditory opening of the temporal bone, then into the canal of the temporal bone.

In the canal of the temporal bone, this nerve goes along with the intermediate nerve, which carries sensory fibers of taste sensitivity from the anterior two-thirds of the tongue and autonomic salivary fibers to the sublingual and submandibular salivary glands. The facial nerve leaves the skull through the stylomastoid foramen, dividing into a number of terminal branches that innervate the facial muscles.

With a unilateral lesion of the facial nerve (often as a result of a cold), nerve paralysis develops, in which the following picture is observed: a low eyebrow position, the palpebral fissure is wider than on the healthy side, the eyelids do not close tightly, the nasolabial fold is smoothed, the corner of the mouth sags, arbitrary movements, it is not possible to frown and raise the eyebrows, puff out the cheeks evenly, whistle with the lips or make the sound “u”. At the same time, numbness is felt in the affected half of the face, pain. Due to the fact that the composition of the facial nerve includes secretory and taste fibers, salivation is disturbed, taste is upset.

VIII pair - auditory nerve. The auditory nerve begins in the inner ear with two branches. The first branch - the auditory nerve - leaves the spiral ganglion located in the cochlea of ​​the labyrinth. The cells of the spiral ganglion are bipolar, that is, they have two processes, with one group of processes (peripheral) going to the hair cells of the organ of Corti, the other forming the auditory nerve.

The second branch of the mixed auditory nerve is called the vestibular nerve. This branch departs from the vestibular apparatus, also located in the inner ear and consisting of three bony tubules and two sacs. Inside the channels, a fluid circulates - endolymph, in which calcareous stones - otoliths float.

The inner surface of the sacs and canals is equipped with sensory nerve endings coming from the Scarpov nerve ganglion, which lies at the bottom of the internal auditory canal. The long processes of the node form the vestibular nerve branch. When leaving the inner ear, the auditory and vestibular branches join and form the so-called auditory nerve - the eighth pair.

Having entered the cavity of the medulla oblongata, these nerves approach the nuclei lying here, after which they are again disconnected, each following its own direction. From the nuclei of the medulla oblongata, the auditory nerve goes already under the name of the auditory pathway. Moreover, part of the fibers crosses at the level of the bridge and passes to the other side. The other part goes along its side, including neurons from some nuclear formations (trapezoid body, etc.). This segment of the auditory pathway is called the lateral loop. It ends in the posterior tubercles of the quadrigemina and the internal geniculate bodies. The crossed auditory pathway also fits here.

From the internal geniculate bodies, the third segment of the auditory pathway begins, which passes through the internal bag and approaches the temporal lobe, where the central nucleus of the auditory analyzer is located. With unilateral damage to the auditory nerve and its nuclei, deafness develops in the ear of the same name. With unilateral damage to the auditory tract (lateral loop), as well as the cortical auditory zone, there are no pronounced auditory disorders, but there is some hearing loss in the opposite ear (due to double innervation). Complete cortical deafness is possible only with bilateral foci in the corresponding auditory zones. The vestibular apparatus, starting from the Scarp's node and having traveled some distance together with the auditory branch, enters the cavity of the medulla oblongata and approaches the angular nucleus.

The angular nucleus consists of the lateral nucleus of Deiters, the superior nucleus of Bekhterev and the inner nucleus. From the angular nucleus, the conductors go to the cerebellar vermis (dentate and roofing nuclei), to the spinal cord along the fibers of the vestibulo-spinal and posterior longitudinal bundle, through which communication with the thalamus is carried out. When the vestibular apparatus is damaged, the balance is upset, dizziness, nausea, and vomiting appear.

Question 23. Cranial nerves of the midbrain. (I. II. III. IV)

The cranial nerves originate in the brainstem, where their nuclei are located. The exceptions are the olfactory, auditory and optic nerves, the first neuron of which is located outside the brain stem.

By nature, most cranial nerves are mixed: they contain both sensory and motor fibers, with sensory predominating in some, and motor in others. There are twelve pairs of cranial nerves.

I couple- olfactory nerve. The olfactory pathway begins in the nasal mucosa in the form of thin nerve threads that pass through the ethmoid bone of the skull, exit at the base of the brain and gather in the olfactory pathway. Most of the olfactory fibers end in the uncinate gyrus on the inner surface of the cortex, in the central nucleus of the olfactory analyzer.

II pair- optic nerve. The visual pathway begins in the retina, which is made up of cells called rods and cones. These cells are receptors that perceive various light and color stimuli. In addition to these cells, there are ganglionic nerve cells in the eye, the dendrites of which end in cones and rods, and the axons form the optic nerve. The optic nerves enter the cranial cavity through the bony opening and pass along the bottom of the base of the brain. At the base of the brain, the optic nerves form a half decussation - chiasm.

Not all nerve fibers are crossed, but only fibers coming from the inner halves of the retina. The fibers coming from the outer halves do not cross, they remain on their side. The massive bundle of nerve pathways that forms after the intersection of the optic fibers is called the optic tract. In the optic tract of each side, nerve fibers pass not from one eye, but from the same halves of the retinas of both eyes. For example, in the left optic tract from both left halves of the retinas, and in the right tract from both right halves. Most of the nerve fibers of the optic tract go to the external geniculate bodies, a small part of the nerve fibers approach the nuclei of the anterior tubercles of the quadrigemina, to the pillow of the optic tubercle. From the cells of the lateral geniculate body, the visual path goes to the cerebral cortex . This segment of the path is called the Graziole beam. The visual path ends in the cortex of the occipital lobe, where the central nucleus of the visual analyzer is located. Visual acuity in children can be checked using a special table. Color perception is also checked by a set of color pictures. Damage to the visual pathway can occur at any segment. Depending on this, a different clinical picture of visual impairment will also be observed.

III couple- oculomotor nerve.

IV couple- trochlear nerve.

VI couple- abducens nerve. All three pairs of cranial nerves carry out the movements of the eyeball and are oculomotors. These nerves carry impulses to the muscles that move the eyeball.

There are paralysis of the corresponding muscles and restrictions on the movements of the eyeball - strabismus. In addition, with damage to the third pair of cranial nerves, ptosis (drooping of the upper eyelid) and inequality of the pupils are observed. The latter is also associated with damage to the branch of the sympathetic nerve that takes part in the innervation of the eye.