Cortex. Function localization
The value of various parts of the cerebral cortex
brain.
2. Motor functions.
3. Functions of the skin and proprioceptive
sensitivity.
4. Auditory functions.
5. Visual functions.
6. Morphological bases of localization of functions in
cerebral cortex.
Motor Analyzer Core
Auditory Analyzer Core
The core of the visual analyzer
Taste Analyzer Core
Skin Analyzer Core
7. Bioelectric activity of the brain.
8. Literature.
THE SIGNIFICANCE OF DIFFERENT PARTS OF THE LARGE
HEMISPHERES OF THE BRAIN
Since ancient times, there has been a dispute between scientists about the location (localization) of areas of the cerebral cortex associated with various body functions. The most diverse and mutually opposing points of view were expressed. Some believed that a strictly defined point in the cerebral cortex corresponds to each function of our body, others denied the existence of any centers; they attributed any reaction to the entire cortex, considering it entirely unambiguous in functional terms. The method of conditioned reflexes made it possible for IP Pavlov to clarify a number of unclear questions and develop a modern point of view.
There is no strictly fractional localization of functions in the cerebral cortex. This follows from experiments on animals, when, after the destruction of certain areas of the cortex, for example, the motor analyzer, after a few days, neighboring areas take over the function of the destroyed area and the movements of the animal are restored.
This ability of cortical cells to replace the function of the prolapsed areas is associated with the great plasticity of the cerebral cortex.
IP Pavlov believed that individual areas of the cortex have different functional significance. However, there are no strictly defined boundaries between these areas. Cells in one region move to neighboring regions.
Figure 1. Scheme of communication between cortical regions and receptors.
1 - spinal or medulla oblongata; 2 - diencephalon; 3 - cerebral cortex
In the center of these areas are clusters of the most specialized cells - the so-called analyzer nuclei, and on the periphery - less specialized cells.
In the regulation of body functions, not strictly defined points take part, but many nerve elements of the cortex.
Analysis and synthesis of incoming impulses and the formation of a response to them are carried out by much larger areas of the cortex.
Consider some areas that are predominantly one or another value. The schematic location of these areas is shown in Figure 1.
motor functions. The cortical section of the motor analyzer is located mainly in the anterior central gyrus, anterior to the central (Roland) sulcus. In this area there are nerve cells, with the activity of which all movements of the body are connected.
The processes of large nerve cells located in the deep layers of the cortex descend into the medulla oblongata, where a significant part of them crosses, i.e., passes to the opposite side. After the transition, they descend along the spinal cord, where the rest is crossed. In the anterior horns of the spinal cord, they come into contact with the motor nerve cells located here. Thus, the excitation that has arisen in the cortex reaches the motor neurons of the anterior horns of the spinal cord and then, through their fibers, enters the muscles. Due to the fact that in the medulla oblongata, and partially in the spinal cord, there is a transition (crossing) of the motor pathways to the opposite side, the excitation that has arisen in the left hemisphere of the brain enters the right half of the body, and impulses from the right hemisphere arrive in the left half of the body. That is why a hemorrhage, injury or any other damage to one of the sides of the cerebral hemispheres entails a violation of the motor activity of the muscles of the opposite half of the body.
Figure 2. Scheme of individual areas of the cerebral cortex.
1 - motor area;
2 - skin area
and proprioceptive sensitivity;
3 - visual area;
4 - auditory area;
5 - taste area;
6 - olfactory area
In the anterior central gyrus, the centers that innervate different muscle groups are located in such a way that in the upper part of the motor area there are centers of movements of the lower extremities, then below the center of the muscles of the body, even lower - the center of the forelimbs and, finally, below all - the centers of the muscles of the head.
The centers of different muscle groups are represented differently and occupy uneven areas.
Functions of skin and proprioceptive sensitivity. The area of skin and proprioceptive sensitivity in humans is located mainly behind the central (Roland) sulcus in the posterior central gyrus.
The localization of this area in humans can be established by electrical stimulation of the cerebral cortex during operations. Irritation of various sections of the cortex and simultaneous questioning of the patient about the sensations that he experiences at the same time make it possible to form a fairly clear idea of \u200b\u200bthe indicated area. The so-called muscular feeling is connected with the same area. Impulses that arise in proprioreceptor receptors located in the joints, tendons and muscles arrive mainly in this section of the cortex.
The right hemisphere perceives impulses coming along centripetal fibers mainly from the left, and the left hemisphere, mainly from the right half of the body. This explains the fact that the defeat, say, of the right hemisphere will cause a violation of the sensitivity of the predominantly left side.
auditory functions. The auditory region is located in the temporal lobe of the cortex. When the temporal lobes are removed, complex sound perceptions are violated, since the possibility of analyzing and synthesizing sound perceptions is impaired.
visual functions. The visual area is located in the occipital lobe of the cerebral cortex. When the occipital lobes of the brain are removed, the dog loses sight. The animal does not see, stumbles upon objects. Only pupillary reflexes are preserved. In humans, a violation of the visual area of one of the hemispheres causes the loss of half of the vision of each eye. If the lesion touched the visual area of the left hemisphere, then the functions of the nasal part of the retina of one eye and the temporal part of the retina of the other eye fall out.
This feature of visual impairment is due to the fact that the optic nerves partially cross on the way to the cortex.
Morphological bases of dynamic localization of functions in the cortex of the cerebral hemispheres (centers of the cerebral cortex).
Knowledge of the localization of functions in the cerebral cortex is of great theoretical importance, since it gives an idea of the nervous regulation of all body processes and its adaptation to the environment. It is also of great practical importance for diagnosing lesions in the cerebral hemispheres.
The idea of the localization of functions in the cerebral cortex is associated primarily with the concept of the cortical center. Back in 1874, the Kievan anatomist V. A. Betz made the statement that each part of the cortex differs in structure from other parts of the brain. This was the beginning of the doctrine of the heterogeneity of the cerebral cortex - cytoarchitectonics (cytos - cell, architectones - system). At present, it has been possible to identify more than 50 different areas of the cortex - cortical cytoarchitectonic fields, each of which differs from the others in the structure and location of the nerve elements. From these fields, denoted by numbers, a special map of the human cerebral cortex was compiled.
P 
about IP Pavlov, the center is the brain end of the so-called analyzer. The analyzer is a nervous mechanism whose function is to decompose the known complexity of the external and internal world into separate elements, i.e., to perform analysis. At the same time, thanks to extensive connections with other analyzers, there is also a synthesis of analyzers with each other and with various activities of the organism.
Figure 3. Map of the cytoarchitectonic fields of the human brain (according to the data of the MoEG Institute of the USSR Academy of Medical Sciences) Above - the upper lateral surface, below - the medial surface. Explanation in the text.
At present, the entire cerebral cortex is regarded as a continuous perceiving surface. The cortex is a collection of cortical ends of the analyzers. From this point of view, we will consider the topography of the cortical sections of the analyzers, i.e., the main perceiving areas of the cortex of the cerebral hemispheres.
First of all, let us consider the cortical ends of the analyzers that perceive irritations from the internal environment of the organism.
1. The core of the motor analyzer, i.e., the analyzer of proprioceptive (kinesthetic) stimuli emanating from bones, joints, skeletal muscles and their tendons, is located in the precentral gyrus (fields 4 and 6) and lobulus paracentralis. Here motor conditioned reflexes are closed. I. P. Pavlov explains motor paralysis that occurs when the motor zone is damaged not by damage to motor efferent neurons, but by a violation of the core of the motor analyzer, as a result of which the cortex does not perceive kinesthetic stimuli and movements become impossible. The cells of the nucleus of the motor analyzer are laid down in the middle layers of the cortex of the motor zone. In its deep layers (V, partly VI) there are giant pyramidal cells, which are efferent neurons, which I. P. Pavlov considers as intercalary neurons connecting the cerebral cortex with the subcortical nuclei, the nuclei of the cranial nerves and the anterior horns of the spinal cord, i.e. with motor neurons. In the precentral gyrus, the human body, as well as in the posterior one, is projected upside down. At the same time, the right motor area is connected with the left half of the body and vice versa, because the pyramidal paths starting from it intersect partly in the medulla oblongata, and partly in the spinal cord. The muscles of the trunk, larynx, pharynx are under the influence of both hemispheres. In addition to the precentral gyrus, proprioceptive impulses (muscle-articular sensitivity) also come to the cortex of the postcentral gyrus.
2. The core of the motor analyzer, which is related to the combined rotation of the head and eyes in the opposite direction, is placed in the middle frontal gyrus, in the premotor region (field 8). Such a turn also occurs when field 17 is stimulated, located in the occipital lobe in the vicinity of the nucleus of the visual analyzer. Since when the muscles of the eye contract, the cerebral cortex (motor analyzer, field 8) always receives not only impulses from the receptors of these muscles, but also impulses from the esophagus (visual analyzer, field 77), various visual stimuli are always combined with a different position eyes, established by contraction of the muscles of the eyeball.
3. The core of the motor analyzer, through which the synthesis of purposeful complex professional, labor and sports movements takes place, is located in the left (in right-handers) lower parietal lobule, in the gyrus supramarginalis (deep layers of field 40). These coordinated movements, formed on the principle of temporary connections and developed by the practice of individual life, are carried out through the connection of the gyrus supramarginalis with the precentral gyrus. When field 40 is affected, the ability to move in general is preserved, but there is an inability to make purposeful movements, to act - apraxia (praxia - action, practice).
4. The core of the analyzer of the position and movement of the head - the static analyzer (vestibular apparatus) in the cerebral cortex has not yet been exactly localized. There is reason to believe that the vestibular apparatus is projected in the same area of the cortex as the cochlea, i.e., in the temporal lobe. So, with the defeat of fields 21 and 20, which lie in the region of the middle and lower temporal gyri, ataxia is observed, that is, an imbalance, swaying of the body when standing. This analyzer, which plays a decisive role in man's upright posture, is of particular importance for the work of pilots in jet aviation, since the sensitivity of the vestibular apparatus is significantly reduced on an airplane.
5. The core of the analyzer of impulses coming from the viscera and blood vessels is located in the lower sections of the anterior and posterior central gyri. Centripetal impulses from the viscera, blood vessels, involuntary muscles and glands of the skin enter this section of the cortex, from where centrifugal paths depart to the subcortical vegetative centers.
In the premotor region (fields 6 and 8), the association of vegetative functions takes place.
Nerve impulses from the external environment of the organism enter the cortical ends of the analyzers of the external world.
1. The nucleus of the auditory analyzer lies in the middle part of the superior temporal gyrus, on the surface facing the insula - fields 41, 42, 52, where the cochlea is projected. Damage leads to deafness.
2. The core of the visual analyzer is located in the occipital lobe - fields 18, 19. On the inner surface of the occipital lobe, along the edges of the sulcus Icarmus, in field 77, the visual path ends. The retina is projected here. When the nucleus of the visual analyzer is damaged, blindness occurs. Above field 17 is field 18, in case of damage to which vision is preserved and only visual memory is lost. Even higher is the field, in the defeat of which orientation is lost in an unusual environment.
3. The core of the taste analyzer, according to some data, is located in the lower postcentral gyrus, close to the centers of the muscles of the mouth and tongue, according to others, in the immediate vicinity of the cortical end of the olfactory analyzer, which explains the close relationship between olfactory and taste sensations. It has been established that taste disorder occurs when field 43 is affected.
The analyzers of smell, taste and hearing of each hemisphere are connected with the receptors of the corresponding organs of both sides of the body.
4. The core of the skin analyzer (tactile, pain and temperature sensitivity) is located in the postcentral gyrus (fields 7, 2, 3) and in the upper parietal region (fields 5 and 7).
A particular type of skin sensitivity - recognition of objects by touch - stereognosia (stereos - spatial, gnosis - knowledge) is connected with the cortex of the upper parietal lobule (field 7) crosswise: the left hemisphere corresponds to the right hand, the right - to the left hand. When the surface layers of field 7 are damaged, the ability to recognize objects by touch, with eyes closed, is lost.
Bioelectric activity of the brain.
The assignment of biopotentials of the brain - electroencephalography - gives an idea of the level of physiological activity of the brain. In addition to the method of electroencephalography-recording of bioelectric potentials, the method of encephaloscopy-registration of fluctuations in the brightness of the glow of many points of the brain (from 50 to 200) is used.
An electroencephalogram is an integrative spatiotemporal indicator of spontaneous electrical activity of the brain. It distinguishes between the amplitude (range) of oscillations in microvolts and the frequency of oscillations in hertz. In accordance with this, four types of waves are distinguished in the electroencephalogram: -, -, - and -rhythms. The -rhythm is characterized by frequencies in the range of 8-15 Hz, with an oscillation amplitude of 50-100 μV. It is recorded only in humans and higher apes in the waking state, with closed eyes and in the absence of external stimuli. Visual stimuli inhibit the -rhythm.
In some people who have a vivid visual imagination, the -rhythm may be completely absent.
The active brain is characterized by (-rhythm. These are electrical waves with an amplitude of 5 to 30 μV and a frequency of 15 to 100 Hz. It is well recorded in the frontal and central regions of the brain. During sleep, the -rhythm appears. It is also observed with negative emotions, painful conditions.The frequency of potentials of the -rhythm is from 4 to 8 Hz, the amplitude is from 100 to 150 microvolts. ) fluctuations in the electrical activity of the brain.
In addition to the considered types of electrical activity, an E-wave (a wave of expectation of a stimulus) and spindle-shaped rhythms are recorded in a person. A wave of expectation is registered when performing conscious, expected actions. It precedes the appearance of the expected stimulus in all cases, even with its repeated repetition. Apparently, it can be considered as the electroencephalographic correlate of the action acceptor, which ensures the prediction of the results of the action before its completion. Subjective readiness to respond to the action of a stimulus in a strictly defined way is achieved by a psychological attitude (D. N. Uznadze). Spindle-shaped rhythms of non-constant amplitude, with a frequency of 14 to 22 Hz, appear during sleep. Various forms of life activity lead to a significant change in the rhythms of the bioelectrical activity of the brain.
During mental work, the -rhythm intensifies, while the -rhythm disappears. During muscular work of a static nature, desynchronization of the electrical activity of the brain is observed. Rapid oscillations with low amplitude appear. During dynamic operation, pe-. Periods of desynchronized and synchronized activity are observed, respectively, at the moments of work and rest.
The formation of a conditioned reflex is accompanied by desynchronization of the wave activity of the brain.
Wave desynchronization occurs during the transition from sleep to wakefulness. At the same time, the spindle-shaped rhythms of sleep are replaced
-rhythm, the electrical activity of the reticular formation increases. Synchronization (same in phase and direction of the wave)
characteristic of the inhibitory process. It is most clearly expressed when the reticular formation of the brain stem is turned off. Electroencephalogram waves, according to most researchers, are the result of the summation of inhibitory and excitatory postsynaptic potentials. The electrical activity of the brain is not a simple reflection of metabolic processes in the nervous tissue. It has been established, in particular, that signs of acoustic and semantic codes are found in the impulse activity of individual clusters of nerve cells.
In addition to the specific nuclei of the thalamus, associative nuclei arise and develop, which have connections with the neocortex and determine the development of the telencephalon. The third source of afferent influences on the cerebral cortex is the hypothalamus, which plays the role of the highest regulatory center of autonomic functions. In mammals, phylogenetically older sections of the anterior hypothalamus are associated with ...
The formation of conditioned reflexes is difficult, memory processes are disturbed, the selectivity of reactions is lost, and their immoderate amplification is noted. The large brain consists of almost identical halves - the right and left hemispheres, which are connected by the corpus callosum. Commissural fibers connect symmetrical areas of the cortex. However, the cortex of the right and left hemispheres is not symmetrical not only externally, but also ...
The approach to assessing the mechanisms of work of the higher parts of the brain using conditioned reflexes was so successful that it allowed Pavlov to create a new section of physiology - "Physiology of higher nervous activity", the science of the mechanisms of work of the cerebral hemispheres. UNCONDITIONAL AND CONDITIONAL REFLEXES The behavior of animals and humans is a complex system of interrelated ...
At present, it is customary to divide the bark into sensory, motor, or motor, and association areas. Such a division was obtained through animal experiments with the removal of various parts of the cortex, observations of patients with a pathological focus in the brain, as well as with the help of direct electrical stimulation of the cortex and peripheral structures by recording electrical activity in the cortex.
The cortical ends of all analyzers are represented in the sensory zones. For visual it is located in the occipital lobe of the brain (fields 17, 18, 19). In field 17, the central visual pathway ends, informing about the presence and intensity of the visual signal. Fields 18 and 19 analyze the color, shape, size and quality of the item. If field 18 is affected, the patient sees, but does not recognize the object and does not distinguish its color (visual agnosia).
Cortical end auditory analyzer localized in the temporal lobe of the cortex (Geshl's gyrus), fields 41, 42, 22. They are involved in the perception and analysis of auditory stimuli, the organization of auditory control of speech. A patient with damage to field 22 loses the ability to understand the meaning of spoken words.
The cortical end is also located in the temporal lobe leadbular analyzer.
Skin analyzer, as well as pain and temperatureChuvvalidity are projected onto the posterior central gyrus, in the upper part of which the lower limbs are represented, in the middle part - the torso, in the lower part - the arms and head.
Paths end in the parietal cortex somatic feelingrelated to speech functions, associated with the assessment of the impact on the skin receptors, the weight and properties of the surface, the shape and size of the object.
The cortical end of the olfactory and gustatory analyzers is located in the hippocampal gyrus. When this area is irritated, olfactory hallucinations occur, and damage to it leads to anosmia(loss of the ability to smell).
motor zones located in the frontal lobes in the region of the anterior central gyrus of the brain, the irritation of which causes a motor reaction. The cortex of the precentral gyrus (field 4) represents the primary motor zone. In the fifth layer of this field are very large pyramidal cells (giant Betz cells). The face is projected onto the lower third of the precentral gyrus, the hand occupies its middle third, the trunk and pelvis - the upper third of the gyrus. The motor cortex for the lower extremities is located on the medial surface of the hemisphere in the region of the anterior part of the paracentral lobule.
The premotor area of the cortex (field 6) is located anterior to the primary motor area. Field 6 is called secondary mothorny area. Her irritation causes rotation of the trunk and eyes with the raising of the contralateral arm. Similar movements are observed in patients during an epileptic attack, if the epileptic focus is localized in this area. Recently, the leading role of field 6 in the implementation of motor functions has been proven. The defeat of field 6 in a person causes a sharp restriction of motor activity, complex sets of movements are difficult to perform, and spontaneous speech suffers.
Field 6 is adjacent to field 8 (frontal oculomotor), the irritation of which is accompanied by a turn of the head and eyes in the opposite direction to the irritated one. Stimulation of different parts of the motor cortex causes contraction of the corresponding muscles on the opposite side.
Anterior frontal cortex associated with creative thinking. From a clinical and functional point of view, the region of interest is the inferior frontal gyrus (field 44). In the left hemisphere, it is associated with the organization of the motor mechanisms of speech. Irritation of this area can cause vocalization, but not articulate speech, as well as cessation of speech if the person has spoken. The defeat of this area leads to motor aphasia - the patient understands speech, but he cannot speak.
The association cortex includes the parietal-temporal-occipital, prefrontal, and limbic regions. It occupies about 80% of the entire surface of the cerebral cortex. Its neurons have multisensory functions. In the associative cortex, various sensory information is integrated and a program of purposeful behavior is formed, the associative cortex surrounds each projection zone, providing a relationship, for example, between sensory and motor areas of the cortex. The neurons located in these areas have polysensory, those. the ability to respond to both sensory and motor input.
Parietal association area the cerebral cortex is involved in the formation of a subjective idea of the surrounding space, of our body.
Temporal cortex participates in speech function through auditory control of speech. With the defeat of the auditory center of speech, the patient can speak, correctly express his thoughts, but does not understand someone else's speech (sensory auditory aphasia). This area of the cortex plays a role in the evaluation of space. The defeat of the visual center of speech leads to the loss of the ability to read and write. The function of memory and dreams is associated with the temporal cortex.
Frontal association fields are directly related to the limbic parts of the brain, they take part in the formation of a program of complex behavioral acts in response to the influence of the external environment based on sensory signals of all modalities.
A feature of the associative cortex is the plasticity of neurons capable of restructuring depending on the incoming information. After an operation to remove any area of the cortex in early childhood, the lost functions of this area are completely restored.
The cerebral cortex is capable, in contrast to the underlying structures of the brain, for a long time, throughout life, to preserve traces of incoming information, i.e. participate in the mechanisms of long-term memory.
The cerebral cortex is a regulator of the autonomic functions of the body (“corticolization of functions”). It presents all unconditioned reflexes, as well as internal organs. Without the cortex, it is impossible to develop conditioned reflexes to internal organs. When stimulating interoreceptors by the method of evoked potentials, electrical stimulation and destruction of certain areas of the cortex, its effect on the activity of various organs has been proven. Thus, the destruction of the cingulate gyrus changes the act of breathing, the functions of the cardiovascular system, and the gastrointestinal tract. The bark inhibits emotions - "know how to rule yourself."
Localization of functions in the cerebral cortex
General characteristics. In certain areas of the cerebral cortex, predominantly neurons are concentrated that perceive one type of stimulus: the occipital region - light, the temporal lobe - sound, etc. However, after the removal of the classical projection zones (auditory, visual), conditioned reflexes to the corresponding stimuli are partially preserved. According to the theory of I.P. Pavlov, in the cerebral cortex there is a “core” of the analyzer (cortical end) and “scattered” neurons throughout the cortex. The modern concept of function localization is based on the principle of multifunctionality (but not equivalence) of cortical fields. The property of multifunctionality allows one or another cortical structure to be included in the provision of various forms of activity, while realizing the main, genetically inherent function (O.S. Adrianov). The degree of multifunctionality of different cortical structures varies. In the fields of the associative cortex, it is higher. The multifunctionality is based on the multichannel input of afferent excitation into the cerebral cortex, the overlap of afferent excitations, especially at the thalamic and cortical levels, the modulating influence of various structures, for example, nonspecific nuclei of the thalamus, basal ganglia, on cortical functions, the interaction of cortical-subcortical and intercortical pathways for conducting excitation. With the help of microelectrode technology, it was possible to register in various areas of the cerebral cortex the activity of specific neurons that respond to stimuli of only one type of stimulus (only to light, only to sound, etc.), i.e. there is a multiple representation of functions in the cerebral cortex .
At present, the division of the cortex into sensory, motor and associative (non-specific) zones (areas) is accepted.
Sensory areas of the cortex. Sensory information enters the projection cortex, the cortical sections of the analyzers (I.P. Pavlov). These zones are located mainly in the parietal, temporal and occipital lobes. The ascending pathways to the sensory cortex come mainly from the relay sensory nuclei of the thalamus.
Primary sensory areas - these are zones of the sensory cortex, irritation or destruction of which causes clear and permanent changes in the sensitivity of the body (the core of the analyzers according to I.P. Pavlov). They consist 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.
Primary projection zones of the cortex consist mainly of neurons of the 4th afferent layer, which are characterized by a clear topical organization. A significant part of these neurons has the highest specificity. For example, the neurons of the visual areas selectively respond to certain signs of visual stimuli: some - to shades of color, others - to the direction of movement, others - to the nature of the lines (edge, stripe, slope of the line), etc. However, it should be noted that the primary zones of certain areas of the cortex also include multimodal neurons that respond to several types of stimuli. In addition, there are neurons there, the reaction of which reflects the impact of non-specific (limbic-reticular, or modulating) systems.
Secondary sensory areas located around the primary sensory areas, less localized, their neurons respond to the action of several stimuli, i.e. they are polymodal.
Localization of sensory zones. The most important sensory area is parietal lobe postcentral gyrus and its corresponding part of the paracentral lobule on the medial surface of the hemispheres. This zone is referred to as somatosensory areaI. 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 (Fig. 2).
Rice. 2. Scheme of sensitive and motor homunculi
(according to W. Penfield, T. Rasmussen). Section of the hemispheres in the frontal plane:
a- projection of general sensitivity in the cortex of the postcentral gyrus; b- projection of the motor system in the cortex of the precentral gyrus
In addition to somatosensory area I, there are somatosensory area II smaller, located on the border of the intersection of the central sulcus with the upper edge temporal lobe, deep in the lateral groove. The accuracy of localization of body parts is expressed to a lesser extent here. A well-studied primary projection zone is auditory cortex(fields 41, 42), which is located in the depth of the lateral sulcus (the cortex of the transverse temporal gyri of Heschl). The projection cortex of the temporal lobe also includes the center of the vestibular analyzer in the superior and middle temporal gyri.
AT occipital lobe located primary visual area(cortex of part of the sphenoid gyrus and lingular lobule, field 17). There is a topical representation of retinal receptors here. Each point of the retina corresponds to its own area of the visual cortex, while the zone of the macula has a relatively large zone of representation. 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. Bark is located near field 17 secondary visual area(fields 18 and 19). The neurons of these zones are polymodal and respond not only to light, but also to tactile and auditory stimuli. In this visual area, a synthesis of various types of sensitivity occurs, more complex visual images and their identification arise.
In the secondary zones, the leading ones are the 2nd and 3rd layers of neurons, for which the main part of the information about the environment and the internal environment of the body, received by the sensory cortex, is transmitted for further processing to the associative cortex, after which it is initiated (if necessary) behavioral response with the obligatory participation of the motor cortex.
motor areas of the cortex. Distinguish between primary and secondary motor areas.
AT primary motor area (precentral gyrus, field 4) there are neurons that innervate the motor neurons of the muscles of the face, trunk and limbs. It has a clear topographic projection of the muscles of the body (see Fig. 2). 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. Irritation of the primary motor cortex causes contraction of the muscles of the opposite side of the body (for the muscles of the head, the contraction can be bilateral). With the defeat of this cortical zone, the ability to fine coordinated movements of the limbs, especially the fingers, is lost.
secondary motor area (field 6) is located both on the lateral surface of the hemispheres, in front of the precentral gyrus (premotor cortex), and on the medial surface corresponding to the cortex of the superior frontal gyrus (additional motor area). In functional terms, the secondary motor cortex is of paramount importance in relation to the primary motor cortex, carrying out higher motor functions associated with planning and coordinating voluntary movements. Here, the slowly increasing negative readiness potential, occurring approximately 1 s before the start of movement. The cortex of field 6 receives the bulk of the impulses from the basal ganglia and the cerebellum, and is involved in recoding information about the plan of complex movements.
Irritation of the cortex of field 6 causes complex coordinated movements, such as turning the head, eyes and torso in the opposite direction, friendly contractions of the flexors or extensors on the opposite side. The premotor cortex contains motor centers associated with human social functions: the center of written speech in the posterior part of the middle frontal gyrus (field 6), the center of Broca's motor speech in the posterior part of the inferior frontal gyrus (field 44), which provide speech praxis, as well as musical motor center (field 45), providing the tone of speech, the ability to sing. Motor cortex neurons receive afferent inputs through the thalamus from muscle, joint, and skin receptors, from the basal ganglia, and the cerebellum. The main efferent output of the motor cortex to the stem and spinal motor centers are the pyramidal cells of layer V. The main lobes of the cerebral cortex are shown in Fig. 3.
Rice. 3. Four main lobes of the cerebral cortex (frontal, temporal, parietal and occipital); side view. They contain the primary motor and sensory areas, higher-order motor and sensory areas (second, third, etc.) and the associative (non-specific) cortex
Association areas of the cortex(nonspecific, intersensory, interanalyzer cortex) include areas of the new cerebral cortex, which are located around the projection zones and next to the motor zones, but do not directly perform sensory or motor functions, so they cannot be attributed primarily to sensory or motor functions, the neurons of these zones have large learning abilities. The boundaries of these areas are not clearly marked. The associative cortex is phylogenetically the youngest part of the neocortex, which has received the greatest development in primates and in humans. In humans, it makes up about 50% of the entire cortex, or 70% of the neocortex. The term "associative cortex" arose in connection with the existing idea that these zones, due to the cortico-cortical connections passing through them, connect the motor zones and at the same time serve as a substrate for higher mental functions. Main association areas of the cortex are: parietal-temporal-occipital, prefrontal cortex of the frontal lobes and limbic association zone.
The neurons of the associative cortex are polysensory (polymodal): they respond, as a rule, not to one (like the neurons of the primary sensory zones), but to several stimuli, i.e., the same neuron can be excited when stimulated by auditory, visual, skin and other receptors. Polysensory neurons of the associative cortex are created by cortico-cortical connections with different projection zones, connections with the associative nuclei of the thalamus. As a result, the associative cortex is a kind of collector of various sensory excitations and is involved in the integration of sensory information and in ensuring the interaction of sensory and motor areas of the cortex.
Associative areas occupy the 2nd and 3rd cell layers of the associative cortex, where powerful unimodal, multimodal, and nonspecific afferent flows meet. The work of these parts of the cerebral cortex is necessary not only for the successful synthesis and differentiation (selective discrimination) of stimuli perceived by a person, but also for the transition to the level of their symbolization, that is, for operating with the meanings of words and using them for abstract thinking, for the synthetic nature of perception.
Since 1949, D. Hebb's hypothesis has become widely known, postulating the coincidence of presynaptic activity with the discharge of a postsynaptic neuron as a condition for synaptic modification, since not all synaptic activity leads to excitation of a postsynaptic neuron. On the basis of D. Hebb's hypothesis, it can be assumed that individual neurons of the associative zones of the cortex are connected in various ways and form cell ensembles that distinguish "subimages", i.e. corresponding to unitary forms of perception. These connections, as noted by D. Hebb, are so well developed that it is enough to activate one neuron, and the entire ensemble is excited.
The apparatus that acts as a regulator of the level of wakefulness, as well as selective modulation and actualization of the priority of a particular function, is the modulating system of the brain, which is often called the limbic-reticular complex, or the ascending activating system. The nervous formations of this apparatus include the limbic and nonspecific systems of the brain with activating and inactivating structures. Among the activating formations, first of all, the reticular formation of the midbrain, the posterior hypothalamus, and the blue spot in the lower parts of the brain stem are distinguished. The inactivating structures include the preoptic area of the hypothalamus, the raphe nucleus in the brainstem, and the frontal cortex.
Currently, according to thalamocortical projections, it is proposed to distinguish three main associative systems of the brain: thalamo-temporal, thalamolobic and thalamic temporal.
thalamotenal system It is represented by associative zones of the parietal cortex, which receive the main afferent inputs from the posterior group of the associative nuclei of the thalamus. The parietal associative cortex has efferent outputs to the nuclei of the thalamus and hypothalamus, to the motor cortex and nuclei of the extrapyramidal system. The main functions of the thalamo-temporal system are gnosis and praxis. Under gnosis understand the function of various types of recognition: shapes, sizes, meanings of objects, understanding of speech, knowledge of processes, patterns, etc. Gnostic functions include the assessment of spatial relationships, for example, the relative position of objects. In the parietal cortex, a center of stereognosis is distinguished, which provides 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 schema”). Under praxis understand purposeful action. The praxis center is located in the supracortical gyrus of the left hemisphere; it provides storage and implementation of the program of motorized automated acts.
Thalamolobic system It is represented by associative zones of the frontal cortex, which have the main afferent input from the associative mediodorsal nucleus of the thalamus and other subcortical nuclei. The main role of the frontal associative cortex is reduced to the initiation of basic systemic mechanisms for the formation of functional systems of purposeful behavioral acts (P.K. Anokhin). The prefrontal region plays a major role in the development of a behavioral strategy. The violation of this function is especially noticeable when it is necessary to quickly change the action and when some time elapses between the formulation of the problem and the beginning of its solution, i.e. stimuli that require proper inclusion in a holistic behavioral response have time to accumulate.
The thalamotemporal system. Some associative centers, for example, stereognosis, praxis, also include areas of the temporal cortex. The auditory center of Wernicke's speech is located in the temporal cortex, located in the posterior regions of the superior temporal gyrus of the left hemisphere. This center provides speech gnosis: 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 reading center that provides recognition and storage of images.
An essential role in the formation of behavioral acts is played by the biological quality of the unconditioned reaction, namely its importance for the preservation of life. In the process of evolution, this meaning was fixed in two opposite emotional states - positive and negative, which in a person form the basis of his subjective experiences - pleasure and displeasure, joy and sadness. In all cases, goal-directed behavior is built in accordance with the emotional state that arose under the action of a stimulus. During behavioral reactions of a negative nature, the tension of the vegetative components, especially the cardiovascular system, in some cases, especially in continuous so-called conflict situations, can reach great strength, which causes a violation of their regulatory mechanisms (vegetative neuroses).
In this part of the book, the main general questions of the analytical and synthetic activity of the brain are considered, which will make it possible to proceed in subsequent chapters to the presentation of particular questions of the physiology of sensory systems and higher nervous activity.
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In the cerebral cortex there is an analysis of all stimuli that come from the external and internal environment. The largest number of afferent impulses goes to the cells of the 3rd and 4th layers of the cerebral cortex. In the cerebral cortex there are centers that regulate the performance of certain functions. IP Pavlov considered the cerebral cortex as a set of cortical ends of analyzers. The term "analyzer" refers to a complex set of anatomical structures, which consists of a peripheral receptor (perceiving) apparatus, conductors of nerve impulses and a center. In the process of evolution, functions are localized in the cerebral cortex. The cortical end of the analyzers is not a strictly defined zone. In the cerebral cortex, the "core" of the sensory system and "scattered elements" are distinguished. The nucleus is the location of the largest number of cortical neurons, in which all the structures of the peripheral receptor are accurately projected. Scattered elements are located near the nucleus and at different distances from it. If the highest analysis and synthesis is carried out in the nucleus, then it is simpler in the scattered elements. In this case, the zones of "scattered elements" of various analyzers do not have clear boundaries and are layered on top of each other.
Functional characteristics of the cortical zones of the frontal lobe. In the region of the precentral gyrus of the frontal lobe is the cortical nucleus of the motor analyzer. This area is also called the sensorimotor cortex. Here comes part of the afferent fibers from the thalamus, carrying proprioceptive information from the muscles and joints of the body (Fig. 8.7). Descending pathways to the brainstem and spinal cord also begin here, providing the possibility of conscious regulation of movements (pyramidal pathways). The defeat of this area of the cortex leads to paralysis of the opposite half of the body.
Rice. 8.7. Somatotopic distribution in the precentral gyrus
The center of writing lies in the posterior third of the middle frontal gyrus. This zone of the cortex gives projections to the nuclei of the oculomotor cranial nerves, and also communicates with the center of vision in the occipital lobe and the control center of the muscles of the arms and neck in the precentral gyrus with the help of cortical-cortical connections. The defeat of this center leads to impaired writing skills under visual control (agraphia).
In the zone of the inferior frontal gyrus, there is a speech motor center (Broc's center). It has a pronounced functional asymmetry. When it is destroyed in the right hemisphere, the ability to regulate timbre and intonation is lost, speech becomes monotonous. With the destruction of the speech-motor center on the left, speech articulation is irreversibly disturbed, up to the loss of the ability to articulate speech (aphasia) and singing (amusia). With partial violations, agrammatism can be observed - the inability to correctly build phrases.
In the region of the anterior and middle thirds of the superior, middle, and partially inferior frontal gyri, there is an extensive anterior associative cortical zone that programs complex forms of behavior (planning various forms of activity, decision-making, analysis of the results obtained, volitional reinforcement of activity, correction of the motivational hierarchy).
The region of the frontal pole and the medial frontal gyrus is associated with the regulation of the activity of the emotive areas of the brain that are part of the limbic system and is related to the control of psycho-emotional states. Violations in this area of the brain can lead to changes in what is commonly called the “personality structure” and affect the character of a person, his value orientations, and intellectual activity.
The orbital region contains the centers of the olfactory analyzer and is closely connected in anatomical and functional terms with the limbic system of the brain.
Functional characteristics of the cortical zones of the parietal lobe. In the postcentral gyrus and the superior parietal lobule is the cortical center of the analyzer of general sensitivity (pain, temperature and tactile), or somatosensory cortex. The representation of various parts of the body in it, as well as in the precentral gyrus, is built according to the somatotopic principle. This principle assumes that body parts are projected onto the surface of the furrow in the same topographical relationship that they have in the human body. However, the representation of different parts of the body in the cerebral cortex varies significantly. Those areas (hand, head, especially tongue and lips) that are associated with complex movements such as writing, speech, etc. have the greatest representation. Cortical disorders in this area lead to partial or complete anesthesia (loss of sensitivity).
Damage to the cortex in the region of the superior parietal lobule leads to a decrease in pain sensitivity and a violation of stereognosis - recognition of objects by touch without the help of vision.
In the lower parietal lobe in the region of the supramarginal gyrus, there is a center of praxia, which regulates the ability to carry out complexly coordinated actions that form the basis of labor processes and require special training. This is also the origin of a significant number of descending fibers that follow as part of the paths that control conscious movements (pyramidal paths). This area of the parietal cortex interacts closely with the cortex of the frontal lobe and with all the sensory areas of the posterior half of the brain with the help of cortical-cortical connections.
The visual (optical) center of speech is located in the angular gyrus of the parietal lobe. Its damage leads to the inability to understand the readable text (alexia).
Functional characteristics of the cortical zones of the occipital lobe. In the region of the spur groove is the cortical center of the visual analyzer. Its damage leads to blindness. In case of disturbances in the areas of the cortex adjacent to the spur groove in the region of the occipital pole on the medial and lateral surfaces of the lobe, there may be a loss of visual memory, the ability to navigate in an unfamiliar environment, the functions associated with binocular vision are impaired (the ability to assess the shape of objects with the help of vision, the distance to them , to correctly measure movements in space under visual control, etc.).
Functional characteristics of the cortical zones of the temporal lobe. In the region of the superior temporal gyrus, in the depths of the lateral sulcus, is the cortical center of the auditory analyzer. Its damage leads to deafness.
In the posterior third of the superior temporal gyrus lies the auditory speech center (Wernicke's center). Injuries in this area lead to the inability to understand spoken language: it is perceived as noise (sensory aphasia).
In the region of the middle and inferior temporal gyri, there is a cortical representation of the vestibular analyzer. Damage to this area leads to imbalance when standing and a decrease in the sensitivity of the vestibular apparatus.
Functional characteristics of the cortical zones of the insular lobe.
Information concerning the functions of the insular lobe is contradictory and insufficient. There is evidence that the cortex of the anterior part of the insula is related to the analysis of olfactory and gustatory sensations, and the back part is related to the processing of somatosensory information and auditory perception of speech.
Functional characteristics of the limbic system. limbic system- a combination of a number of brain structures, including the cingulate gyrus, isthmus, dentate and parahippocampal gyrus, etc. Participates in the regulation of the functions of internal organs, smell, instinctive behavior, emotions, memory, sleep, wakefulness, etc.
The cingulate and parahippocampal gyrus are directly related to the limbic system of the brain (Fig. 8.8 and 8.9). It controls the complex of vegetative and behavioral psycho-emotional reactions to external environmental influences. In the parahippocampal gyrus and hook, there is a cortical representation of the gustatory and olfactory analyzers. At the same time, the hippocampus plays an important role in learning: the mechanisms of short-term and long-term memory are associated with it.
Rice. 8.8. Medial surface of the brain
Basal (subcortical central) nuclei - accumulations of gray matter, forming separately lying nuclei, which lie closer to the base of the brain. These include the striatum, which makes up the predominant mass of the hemispheres in lower vertebrates; fence and amygdala (Fig. 8.10).
Rice. 8.9. limbic system
Rice. 8.10. Basal ganglia
The striatum consists of the caudate and lenticular nuclei. The gray matter of the caudate and lenticular nuclei alternates with layers of white matter, which led to the common name for this group of subcortical nuclei - the striatum.
The caudate nucleus is located laterally and above the thalamus, being separated from it by a terminal strip. The caudate nucleus has a head, body and tail. The lentiform nucleus is located lateral to the caudate. A layer of white matter - the inner capsule, separates the lenticular nucleus from the caudate and from the thalamus. In the lenticular nucleus, a pale ball (medially) and a shell (laterally) are distinguished. The outer capsule (a narrow strip of white matter) separates the shell from the fence.
The caudate nucleus, putamen and globus pallidus control complexly coordinated automated movements of the body, control and maintain the tone of skeletal muscles, and are also the highest center of regulation of such vegetative functions as heat production and carbohydrate metabolism in the muscles of the body. With damage to the shell and pale ball, slow stereotyped movements (athetosis) can be observed.
The nuclei of the striatum belong to the extrapyramidal system involved in the control of movements, the regulation of muscle tone.
The fence is a vertical plate of gray matter, the lower part of which continues into the substance of the anterior perforated plate at the base of the brain. The fence is located in the white matter of the hemisphere lateral to the lenticular nucleus and has numerous connections with the cerebral cortex.
The amygdala lies in the white matter of the temporal lobe of the hemisphere, 1.5–2 cm posterior to its temporal pole, through the nuclei it has connections with the cerebral cortex, with the structures of the olfactory system, with the hypothalamus and the nuclei of the brain stem that control the autonomic functions of the body. Its destruction leads to aggressive behavior or an apathetic, lethargic state. Through its connections to the hypothalamus, the amygdala influences the endocrine system as well as reproductive behavior.
The white matter of the hemisphere includes the internal capsule and fibers passing through the commissures of the brain (corpus callosum, anterior commissure, commissure of the fornix) and heading to the cortex and basal ganglia, the fornix, as well as systems of fibers connecting areas of the cortex and subcortical centers within one half of the brain (hemispheres).
I and II lateral ventricles. The cavities of the cerebral hemispheres are the lateral ventricles (I and II), located in the thickness of the white matter under the corpus callosum. Each ventricle consists of four parts: the anterior horn lies in the frontal, the central part - in the parietal, the posterior horn - in the occipital and the lower horn - in the temporal lobe (Fig. 8.11).
The anterior horns of both ventricles are separated from each other by two plates of a transparent septum. The central part of the lateral ventricle curves from above around the thalamus, forms an arc and passes backwards - into the posterior horn, downwards into the lower horn. The choroid plexus protrudes into the central part and the lower horn of the lateral ventricle, which, through the interventricular foramen, connects to the choroid plexus of the third ventricle.
Rice. 8.11. Ventricles of the brain:
1 - left hemisphere of the brain, 2 - lateral ventricles, 3 - third ventricle, 4 - aqueduct of the midbrain, 5 - fourth ventricle, 6 - cerebellum, 7 - entrance to the central canal of the spinal cord, 8 - spinal cord
The ventricular system includes paired C-shaped cavities - the lateral ventricles with their anterior, inferior and posterior horns, extending respectively into the frontal lobes, into the temporal lobes and into the occipital lobes of the cerebral hemispheres. About 70% of all cerebrospinal fluid is secreted by the choroid plexus of the walls of the lateral ventricles.
From the lateral ventricles, fluid passes through the interventricular openings into the slit-like cavity of the third ventricle, located in the sagittal plane of the brain and dividing the thalamus and hypothalamus into two symmetrical halves. The cavity of the third ventricle is connected by a narrow canal - the aqueduct of the midbrain (Sylvian aqueduct) with the cavity of the fourth ventricle. The fourth ventricle communicates with the subarachnoid spaces of the brain and spinal cord through several channels (apertures).
diencephalon
The diencephalon is located under the corpus callosum and consists of the thalamus, epithalamus, metathalamus, and hypothalamus (Fig. 8.12, see Fig. 7.2).
thalamus(optic tubercle) - paired, ovoid, formed mainly by gray matter. The thalamus is the subcortical center of all kinds of sensitivity. The medial surface of the right and left thalamus, facing each other, form the side walls of the cavity of the diencephalon - the third ventricle, they are interconnected by interthalamic fusion. The thalamus contains gray matter, which is made up of clusters of neurons that form the nuclei of the thalamus. The nuclei are separated by thin layers of white matter. About 40 nuclei of the thalamus were studied. The main nuclei are anterior, medial, posterior.
Rice. 8.12. Departments of the brain
Epithalamus includes the pineal gland, the leashes, and the triangles of the leashes. The pineal body, or pineal gland, which is an endocrine gland, is, as it were, suspended on two leashes, interconnected by adhesions and connected to the thalamus by means of triangles of leashes. The triangles of the leashes contain nuclei related to the olfactory analyzer. In an adult, the average length of the epiphysis is ~ 0.64 cm, and the weight is ~ 0.1 g. Metathalamus formed by paired medial and lateral geniculate bodies, lying behind each thalamus. The medial geniculate body is located behind the pillow of the thalamus, it is, along with the lower hillocks of the plate of the roof of the midbrain (the quadrigemina), the subcortical center of the auditory analyzer. Lateral - located down from the pillow, it, together with the upper mounds of the roof plate, is the subcortical center of the visual analyzer. The nuclei of the geniculate bodies are connected with the cortical centers of the visual and auditory analyzers.
Hypothalamus, which is the ventral part of the diencephalon, is located anterior to the legs of the brain and includes a number of structures that have a different origin - the anterior visual part (optic chiasm, optic tract, gray tubercle, funnel, neurohypophysis) is formed from the telencephalon; from the intermediate - the olfactory part (mastoid bodies and the actual subthalamic region - the hypothalamus) (Fig. 8.13).
Figure 8.13. Basal ganglia and diencephalon
The hypothalamus is the center of regulation of endocrine functions, it combines the nervous and endocrine regulatory mechanisms into a common neuroendocrine system, coordinates the nervous and hormonal mechanisms of regulation of the functions of internal organs. In the hypothalamus there are neurons of the usual type and neurosecretory cells. The hypothalamus forms a single functional complex with the pituitary gland, in which the former plays a regulatory and the latter an effector role.
There are more than 30 pairs of nuclei in the hypothalamus. Large neurosecretory cells of the supraoptic and paraventricular nuclei of the anterior hypothalamic region produce neurosecretions of a peptide nature.
The medial hypothalamus contains neurons that perceive all changes that occur in the blood and cerebrospinal fluid (temperature, composition, hormone levels, etc.). The medial hypothalamus is also connected to the lateral hypothalamus. The latter does not have nuclei, but has bilateral connections with the overlying and underlying parts of the brain. The medial hypothalamus is the link between the nervous and endocrine systems. In recent years, enkephalins and endorphins (peptides) with a morphine-like effect have been isolated from the hypothalamus. It is believed that they are involved in the regulation of behavior and vegetative processes.
Anterior to the posterior perforated substance lie two small spherical mastoid bodies formed by a gray substance covered with a thin layer of white. The nuclei of the mastoid bodies are the subcortical centers of the olfactory analyzer. Anterior to the mastoid bodies is a gray tubercle, which is bounded in front by the optic chiasm and optic tract, it is a thin plate of gray matter at the bottom of the third ventricle, which is extended downward and anteriorly and forms a funnel. Its end goes to pituitary - an endocrine gland located in the pituitary fossa of the Turkish saddle. The nuclei of the autonomic nervous system lie in the gray hillock. They also influence a person's emotional reactions.
The part of the diencephalon, located below the thalamus and separated from it by the hypothalamic groove, constitutes the hypothalamus proper. Here the tires of the legs of the brain continue, here the red nuclei and the black substance of the midbrain end.
III ventricle. The cavity of the diencephalon III ventricle It is a narrow, slit-like space located in the sagittal plane, bounded laterally by the medial surfaces of the thalamus, below by the hypothalamus, in front by the columns of the fornix, the anterior commissure and the terminal plate, behind the epithalamic (posterior) commissure, and above by the vault, over which the corpus callosum is located. The upper wall itself is formed by the vascular base of the third ventricle, in which its choroid plexus lies.
The cavity of the third ventricle posteriorly passes into the aqueduct of the midbrain, and in front on the sides through the interventricular openings communicates with the lateral ventricles.
midbrain
midbrain - the smallest part of the brain, lying between the diencephalon and the bridge (Fig. 8.14 and 8.15). The area above the aqueduct is called the roof of the midbrain, and there are four bulges on it - the plate of the quadrigemina with the upper and lower hillocks. From here exit the paths of visual and auditory reflexes heading to the spinal cord.
The legs of the brain are white rounded strands emerging from the bridge and heading forward to the cerebral hemispheres. From the groove on the medial surface of each leg comes the oculomotor nerve (III pair of cranial nerves). Each leg consists of a tire and a base, the border between them is a black substance. The color depends on the abundance of melanin in its nerve cells. Substance nigra refers to the extrapyramidal system, which is involved in maintaining muscle tone and automatically regulates muscle function. The base of the stalk is formed by nerve fibers running from the cerebral cortex to the spinal cord and medulla oblongata and the pons. The covering of the legs of the brain contains mainly ascending fibers heading to the thalamus, among which the nuclei lie. The largest are the red nuclei, from which the motor red-nuclear-spinal path begins. In addition, the reticular formation and the nucleus of the dorsal longitudinal bundle (intermediate nucleus) are located in the tegmentum.
Hind brain
The pons located ventrally and the cerebellum lying behind the pons belong to the hindbrain.
Rice. 8.14. Schematic representation of a longitudinal section of the brain
Rice. 8.15. Cross section through the midbrain at the level of the superior colliculi (cut plane shown in Figure 8.14)
Bridge it looks like a transversely thickened roller, from the lateral side of which the middle cerebellar legs extend to the right and left. The posterior surface of the bridge, covered by the cerebellum, is involved in the formation of the rhomboid fossa, the anterior (adjacent to the base of the skull) borders on the medulla oblongata below and the legs of the brain above (see Fig. 8.15). It is transversely striated due to the transverse direction of the fibers that go from the own nuclei of the bridge to the middle cerebellar peduncles. On the front surface of the bridge along the midline, the basilar sulcus is located longitudinally, in which the artery of the same name passes.
The bridge consists of many nerve fibers that form pathways, among which are cell clusters - nuclei. The pathways of the anterior part connect the cerebral cortex with the spinal cord and with the cortex of the cerebellar hemispheres. In the back of the bridge (tire) there are ascending pathways and partially descending, there is a reticular formation, the nuclei of V, VI, VII, VIII pairs of cranial nerves. On the border between both parts of the bridge lies a trapezoid body formed by nuclei and transversely running fibers of the auditory analyzer pathway.
Cerebellum plays a major role in maintaining body balance and coordination of movements. The cerebellum reaches its greatest development in humans in connection with upright walking and the adaptation of the hand to work. In this regard, the hemispheres (new part) of the cerebellum are highly developed in humans.
In the cerebellum, two hemispheres and an unpaired median phylogenetically old part - the worm (Fig. 8.16) are distinguished.
Rice. 8.16. Cerebellum: top and bottom view
The surfaces of the hemispheres and the vermis are separated by transverse parallel grooves, between which are located narrow long leaves of the cerebellum. In the cerebellum, the anterior, posterior, and flocculent-nodular lobes are distinguished, separated by deeper fissures.
The cerebellum consists of gray and white matter. The white matter, penetrating between the gray, branches, as it were, forming on the median section the figure of a branching tree - the "tree of life" of the cerebellum.
The cerebellar cortex consists of gray matter 1–2.5 mm thick. In addition, in the thickness of the white matter there are accumulations of gray - paired nuclei: a jagged nucleus, a corky, a spherical and a tent nucleus. Afferent and efferent fibers connecting the cerebellum with other departments form three pairs of cerebellar peduncles: the lower ones go to the medulla oblongata, the middle ones go to the pons, and the upper ones go to the quadrigemina.
By the time of birth, the cerebellum is less developed than the telencephalon (especially the hemispheres), but in the first year of life it develops faster than other parts of the brain. A pronounced increase in the cerebellum is noted between the 5th and 11th months of life, when the child learns to sit and walk.
Medulla is a direct continuation of the spinal cord. Its lower boundary is considered to be the exit point of the roots of the 1st cervical spinal nerve or the intersection of the pyramids, the upper one is the posterior edge of the bridge, its length is about 25 mm, the shape approaches a truncated cone, turned base up.
The anterior surface is divided by the anterior median fissure, on the sides of which there are pyramids formed by pyramidal pathways, partially crossing (crossing the pyramids) in the depth of the described fissure on the border with the spinal cord. Fibers of the pyramidal pathways connect the cerebral cortex with the nuclei of the cranial nerves and the anterior horns of the spinal cord. On the side of the pyramid, on each side, there is an olive, separated from the pyramid by the anterior lateral groove.
The posterior surface of the medulla oblongata is divided by the posterior median sulcus, on the sides of it there are continuations of the posterior cords of the spinal cord, which diverge upward, passing into the lower cerebellar peduncles.
The medulla oblongata is built of white and gray matter, the latter is represented by the nuclei of the IX-XII pairs of cranial nerves, olives, centers of respiration and circulation, and the reticular formation. White matter is formed by long and short fibers that make up the corresponding pathways.
Reticular formation is a collection of cells, cell clusters and nerve fibers located in the brainstem (medulla oblongata, pons and midbrain) and forming a network. The reticular formation is connected with all sense organs, motor and sensitive areas of the cerebral cortex, the thalamus and hypothalamus, and the spinal cord. It regulates the level of excitability and tone of various parts of the central nervous system, including the cerebral cortex, is involved in the regulation of the level of consciousness, emotions, sleep and wakefulness, autonomic functions, purposeful movements.
IV ventricle- this is the cavity of the rhomboid brain, from top to bottom it continues into the central canal of the spinal cord. The bottom of the IV ventricle, due to its shape, is called the rhomboid fossa (Fig. 8.17). It is formed by the posterior surfaces of the medulla oblongata and the pons, the upper sides of the fossa are the upper ones, and the lower ones are the lower cerebellar peduncles.
Rice. 8.17. brain stem; back view. The cerebellum is removed, the rhomboid fossa is open
The median sulcus divides the bottom of the fossa into two symmetrical halves, on both sides of the sulcus, medial elevations are visible, expanding in the middle of the fossa into the right and left facial tubercles, where they lie: the nucleus of the VI pair of cranial nerves (abducens nerve), deeper and more lateral - the nucleus of the VII pair ( facial nerve), and downwards the medial eminence passes into the triangle of the hypoglossal nerve, lateral to which is the triangle of the vagus nerve. In triangles, in the thickness of the substance of the brain, the nuclei of the nerves of the same name lie. The upper corner of the rhomboid fossa communicates with the aqueduct of the midbrain. The lateral sections of the rhomboid fossa are called the vestibular fields, where the auditory and vestibular nuclei of the vestibulocochlear nerve (VIII pair of cranial nerves) lie. Transverse cerebral stripes extend from the auditory nuclei to the median sulcus, which are located on the border between the medulla oblongata and the pons and are fibers of the auditory analyzer pathway. In the thickness of the rhomboid fossa lie the nuclei of the V, VI, VII, VIII, IX, X, XI and XII pairs of cranial nerves.
Blood supply to the brain
Blood enters the brain through two paired arteries: the internal carotid and vertebral. In the cranial cavity, both vertebral arteries merge, together forming the main (basal) artery. At the base of the brain, the main artery merges with two carotid arteries, forming a single arterial ring (Fig. 8.18). This cascading mechanism of blood supply to the brain guarantees sufficient blood flow if any of the arteries fail.
Rice. 8.19. Arteries at the base of the brain and the circle of Willis (the right hemisphere of the cerebellum and the right temporal lobe are removed); The circle of Willis is shown as a dotted line.
Three vessels depart from the arterial ring: the anterior, posterior and middle cerebral arteries that feed the cerebral hemispheres. These arteries run along the surface of the brain, and from them, blood is delivered deep into the brain by smaller arteries.
The system of carotid arteries is called the carotid pool, which provides 2/3 of the needs of the brain in arterial blood and supplies blood to the anterior and middle parts of the brain.
The system of arteries "vertebral - main" is called the vertebrobasilar basin, which provides 1/3 of the needs of the brain and delivers blood to the posterior sections.
The outflow of venous blood occurs mainly through the superficial and deep cerebral veins and venous sinuses (Fig. 8.19). Ultimately, blood is sent to the internal jugular vein, which exits the skull through the jugular foramen, located at the base of the skull, lateral to the foramen magnum.
Shells of the brain
The membranes of the brain protect it from mechanical damage and from the penetration of infections and toxic substances (Fig. 8.20).
Rice. 8.19. Veins and venous sinuses of the brain
Fig.8.20. Coronal section through skull meninges and brain
The first layer that protects the brain is called the pia mater. It closely adjoins the brain, enters all the grooves and cavities (ventricles) that are present in the thickness of the brain itself. The ventricles of the brain are filled with a fluid called cerebrospinal fluid or cerebrospinal fluid. The dura mater is directly adjacent to the bones of the skull. Between the soft and hard shell is the arachnoid (arachnoid) shell. Between the arachnoid and soft shells there is a space (subarachnoid or subarachnoid space) filled with cerebrospinal fluid. Above the furrows of the brain, the arachnoid membrane is thrown over, forming a bridge, and the soft one merges with them. Due to this, cavities called cisterns are formed between the two shells. The cisterns contain cerebrospinal fluid. These tanks protect the brain from mechanical injury, acting as "airbags".
Nerve cells and blood vessels are surrounded by neuroglia - special cell formations that perform protective, supporting and metabolic functions, providing reactive properties of the nervous tissue and participating in the formation of scars, in inflammation reactions, etc.
When the brain is damaged, the mechanism of plasticity is activated, when the preserved structures of the brain take on the functions of the affected areas.
Morphological bases of dynamic localization of functions in the cortex of the cerebral hemispheres (centers of the cerebral cortex)
Knowledge of the localization of functions in the cerebral cortex is of great theoretical importance, since it gives an idea of the nervous regulation of all body processes and its adaptation to the environment. It is also of great practical importance for diagnosing lesions in the cerebral hemispheres.
The idea of the localization of a function in the cerebral cortex is associated primarily with the concept of the cortical center. Back in 1874, the Kievan anatomist V. A. Betz made the statement that each section of the cortex differs in structure from other sections of the brain. This was the beginning of the doctrine of the heterogeneity of the cerebral cortex - cytoarchitectonics (cytos - cell, architectones - system). The studies of Brodman, Economo and employees of the Moscow Institute of the Brain, led by S. A. Sarkisov, managed to identify more than 50 different sections of the cortex - cortical cyto-architectonic fields, each of which differs from the others in the structure and location of nerve elements; there is also a division of the cortex into more than 200 fields. From these fields, designated by numbers, a special “map” of the human cerebral cortex was compiled (Fig. 299).
According to IP Pavlov, the center is the brain end of the so-called analyzer. The analyzer is a nervous mechanism whose function is to decompose the known complexity of the external and internal world into separate elements, i.e., to perform analysis. At the same time, thanks to extensive connections with other analyzers, synthesis also takes place here, a combination of analyzers with each other and with various activities of the organism. "The analyzer is a complex nervous mechanism that begins with an external perceiving apparatus and ends in the brain." From the point of view of I. P. Pavlov, the brain center, or the cortical end of the analyzer, does not have strictly defined boundaries, but consists of a nuclear and diffuse part - the theory of the nucleus and scattered elements. The "nucleus" represents a detailed and accurate projection in the cortex of all elements of the peripheral receptor and is necessary for the implementation of higher analysis and synthesis. "Scattered elements" are located on the periphery of the nucleus and can be scattered far from it; they carry out a simpler and more elementary analysis and synthesis. When the nuclear part is damaged, scattered elements can to a certain extent compensate for the lost function of the nucleus, which is of great clinical importance for the restoration of this function.
Prior to I.P. Pavlov, in the cortex, the motor zone, or motor centers, the anterior central gyrus and the sensitive zone, or sensitive centers, located behind the sulcus centralis Rolandi, were distinguished. IP Pavlov showed that the so-called motor zone, corresponding to the anterior central gyrus, is, like other zones of the cerebral cortex, a perceiving area (the cortical end of the motor analyzer). "The motor area is the receptor area ... This establishes the unity of the entire cortex of the hemispheres."
At present, the entire cerebral cortex is regarded as a continuous perceiving surface. The cortex is a collection of cortical ends of the analyzers. From this point of view, we will consider the topography of the cortical sections of the analyzers, i.e., the main perceiving areas of the cortex of the cerebral hemispheres.
Let us first consider the cortical ends of internal analyzers.
1. The core of the motor analyzer, i.e., the analyzer of proprioceptive (kinesthetic) stimuli emanating from bones, joints, skeletal muscles and their tendons, is located in the anterior central gyrus (fields 4 and 6) and lobulus paracentralis. Here motor conditioned reflexes are closed. I. P. Pavlov explains motor paralysis that occurs when the motor zone is damaged not by damage to motor efferent neurons, but by a violation of the core of the motor analyzer, as a result of which the cortex does not perceive kinesthetic stimuli and movements become impossible. The cells of the nucleus of the motor analyzer are laid down in the middle layers of the cortex of the motor zone. In its deep layers (5th, partly also 6th) lie Betz's giant pyramidal cells, which are efferent neurons, which I.P. Pavlov considers as intercalary neurons connecting the cerebral cortex with subcortical nodes, nuclei of the head nerves and anterior horns spinal cord, i.e. with motor neurons. In the anterior central gyrus, the human body, as well as in the posterior one, is projected upside down. At the same time, the right motor area is connected with the left half of the body and vice versa, because the pyramidal paths starting from it intersect partly in the medulla oblongata, and partly in the spinal cord. .The muscles of the trunk, larynx, pharynx are under the influence of both hemispheres. In addition to the anterior central gyrus, proprioceptive impulses (muscle-articular sensitivity) also come to the cortex of the posterior central gyrus.
2. The core of the motor analyzer, which is related to the combined rotation of the head and eyes in the opposite direction, is placed in the middle frontal gyrus, in the premotor region (field 8). Such a turn also occurs when field 17 is stimulated, located in the occipital lobe in the vicinity of the nucleus of the visual analyzer. Since when the muscles of the eye contract, the cerebral cortex (motor analyzer, field 8) always receives not only impulses from the receptors of these muscles, but also impulses from the retina (visual analyzer, field 17), various visual stimuli are always combined with a different position of the eyes, established contraction of the muscles of the eyeball.
3. The core of the motor analyzer, through which the synthesis of purposeful combined movements takes place, is placed in the left (in right-handers) lower parietal lobule, in the gyrus supramarginalis (deep layers of field 40). These coordinated movements, formed on the principle of temporary connections and developed by the practice of individual life, are carried out through the connection of the gyrus supramarginalis with the anterior central gyrus. When field 40 is affected, the ability to move in general is preserved, but there is an inability to make purposeful movements, to act - apraxia (praxia - action, practice).
4. The core of the analyzer of the position and movement of the head - the static analyzer (vestibular apparatus) - has not yet been exactly localized in the cerebral cortex. There is reason to believe that the vestibular apparatus is projected in the same area of the cortex as the cochlea, i.e., in the temporal lobe. So, with the defeat of fields 21 and 20, which lie in the region of the middle and lower temporal gyri, ataxia is observed, that is, an imbalance, swaying of the body when standing. This analyzer, which plays a decisive role in man's upright posture, is of particular importance for the work of pilots in rocket aviation, since the sensitivity of the vestibular apparatus is significantly reduced on an airplane.
5. The core of the analyzer of impulses coming from the viscera and blood vessels (vegetative functions) is located in the lower sections of the anterior and posterior central gyri. Centripetal impulses from the viscera, blood vessels, smooth muscles and glands of the skin enter this section of the cortex, from where the centrifugal paths proceed to the subcortical vegetative centers.
In the premotor region (fields 6 and 8), the vegetative and animal functions are combined. However, it should not be considered that only this area of the cortex affects the activity of the viscera. They are influenced by the state of the entire cerebral cortex.
Nerve impulses from the external environment of the organism enter the cortical ends of the analyzers of the external world.
1. The nucleus of the auditory analyzer lies in the middle part of the superior temporal gyrus, on the surface facing the insula - fields 41, 42, 52, where the cochlea is projected. Damage leads to cortical deafness.
2. The core of the visual analyzer is located in the occipital lobe - fields 17, 18, 19. On the inner surface of the occipital lobe, along the edges of the sulcus calcarinus, the visual path ends in field 17. The retina of the eye is projected here, and the visual analyzer of each hemisphere is associated with the fields of view and the corresponding halves of the retina of both eyes (for example, the left hemisphere is associated with the lateral half of the left eye and the medial right). When the nucleus of the visual analyzer is damaged, blindness occurs. Above field 17 is field 18, in case of damage to which vision is preserved and only visual memory is lost. Even higher is field 19, with the defeat of which one loses orientation in an unusual environment.
3. The nucleus of the olfactory analyzer is located in the phylogenetically most ancient part of the cerebral cortex, within the base of the olfactory brain - uncus, partly Ammon's horn (field 11).
4. According to some data, the core of the taste analyzer is located in the lower part of the posterior central gyrus, close to the centers of the muscles of the mouth and tongue, according to others - in the uncus, in the immediate vicinity of the cortical end of the olfactory analyzer, which explains the close connection between olfactory and taste sensations. It has been established that taste disorder occurs when field 43 is affected.
The analyzers of smell, taste and hearing of each hemisphere are connected with the receptors of the corresponding organs of both sides of the body.
5. The core of the skin analyzer (tactile, pain and temperature sensitivity) is located in the posterior central gyrus (fields 1, 2, 3) and in the cortex of the upper parietal region (fields 5 and 7). In this case, the body is projected in the posterior central gyrus upside down, so that in its upper part there is a projection of the receptors of the lower extremities, and in the lower part there is a projection of the receptors of the head. Since in animals the receptors of general sensitivity are especially developed at the head end of the body, in the region of the mouth, which plays an enormous role in capturing food, a strong development of the mouth receptors has also been preserved in humans. In this regard, the region of the latter occupies an unreasonably large zone in the cortex of the posterior central gyrus. At the same time, in connection with the development of the hand as a labor organ, the tactile receptors in the skin of the hand increased sharply, which also became the organ of touch. Correspondingly, the areas of the cortex related to the receptors of the upper limb sharply outnumber the region of the lower limb. Therefore, if you draw a figure of a person head down (to the base of the skull) and feet up (to the upper edge of the hemisphere) into the posterior central gyrus, then you need to draw a huge face with an incongruously large mouth, a large hand, especially a hand with a thumb that is sharply superior to the rest, small body and small legs. Each posterior central gyrus is connected to the opposite part of the body due to the intersection of sensory conductors in the spinal cord and a part in the medulla oblongata.
A particular type of skin sensitivity - recognition of objects by touch, stereognosia (stereos - spatial, gnosis - knowledge) - is associated with a section of the cortex of the upper parietal lobule (field 7) crosswise: the left hemisphere corresponds to the right hand, the right - to the left hand. When the surface layers of field 7 are damaged, the ability to recognize objects by touch, with eyes closed, is lost.
The described cortical ends of the analyzers are located in certain areas of the cerebral cortex, which is thus "a grandiose mosaic, a grandiose signaling board." Thanks to the analyzers, signals from the external and internal environment of the body fall onto this “board”. These signals, according to I. P. Pavlov, constitute the first signal system of reality, manifested in the form of concrete visual thinking (sensations and complexes of sensations - perceptions). The first signaling system is also found in animals. But “in the developing animal world, an extraordinary addition to the mechanisms of nervous activity took place in the human phase. For an animal, reality is signaled almost exclusively only by stimuli and their traces in the cerebral hemispheres, which directly arrive at special cells of the visual, auditory, and other receptors of the organism. This is what we also have in ourselves as impressions, sensations and ideas from the external environment, both general natural and from our social, excluding the word, audible and visible. This is the first signaling system we have in common with animals. But the word constituted the second, specially our signal system of reality, being the signal of the first signals... it was the word that made us human.”
Thus, I. P. Pavlov distinguishes between two cortical systems: the first and second signal systems of reality, from which the first signal system first arose (it is also found in animals), and then the second - it is only in humans and is a verbal system. The second signal system is human thinking, which is always verbal, because language is the material shell of thinking. Language is "... the immediate reality of thought."
Through a very long repetition, temporary connections were formed between certain signals (audible sounds and visible signs) and movements of the lips, tongue, muscles of the larynx, on the one hand, and with real stimuli or ideas about them, on the other. Thus, on the basis of the first signal system, the second one arose.
Reflecting this process of phylogenesis, in ontogeny, the first signal system is first laid down in a person, and then the second. In order for the second signaling system to begin to function, communication of the child with other people and the acquisition of oral and written language skills are required, which takes a number of years. If a child is born deaf or loses his hearing before he has begun to speak, then his inherent ability to speak is not used and the child remains mute, although he can pronounce sounds. In the same way, if a person is not taught to read and write, then he will forever remain illiterate. All this testifies to the decisive influence of the environment for the development of the second signaling system. The latter is associated with the activity of the entire cerebral cortex, but some areas of it play a special role in the implementation of speech. These areas of the cortex are the nuclei of speech analyzers.
Therefore, in order to understand the anatomical substrate of the second signaling system, in addition to knowing the structure of the cerebral cortex as a whole, it is also necessary to take into account the cortical ends of speech analyzers (Fig. 300).
1. Since speech was a means of communication between people in the course of their joint labor activity, motor analyzers of speech developed in the immediate vicinity of the core of the common motor analyzer.
The motor analyzer of speech articulation (speech-motor analyzer) is located in the posterior part of the inferior frontal gyrus (gyrus Vgoca, field 44), in close proximity to the lower motor zone. It analyzes the stimuli coming from the muscles involved in the creation of oral speech. This function is associated with the motor analyzer of the muscles of the lips, tongue and larynx, located in the lower part of the anterior central gyrus, which explains the proximity of the speech motor analyzer to the motor analyzer of these muscles. When field 44 is affected, the ability to produce the simplest movements of the speech muscles, to scream and even sing, remains, but the ability to pronounce words is lost - motor aphasia (phasis - speech). In front of field 44 is field 45 related to speech and singing. When it is defeated, vocal amusia arises - the inability to sing, compose musical phrases, as well as agrammatism - the inability to compose sentences from words.
2. Since the development of oral speech is associated with the organ of hearing, an auditory analyzer of oral speech has developed in close proximity to the sound analyzer. Its nucleus is located in the back of the superior temporal gyrus, deep in the lateral sulcus (field 42, or Wernicke's center). Thanks to the auditory analyzer, various combinations of sounds are perceived by a person as words that mean various objects and phenomena and become their signals (second signals). With the help of it, a person controls his speech and understands someone else's. When it is damaged, the ability to hear sounds is preserved, but the ability to understand words is lost - verbal deafness, or sensory aphasia. When field 22 (the middle third of the superior temporal gyrus) is affected, musical deafness occurs: the patient does not know the motives, and musical sounds are perceived by him as chaotic noise.
3. At a higher stage of development, mankind has learned not only to speak, but also to write. Written speech requires certain hand movements when writing letters or other signs, which is associated with a motor analyzer (general). Therefore, the motor analyzer of written speech is placed in the posterior part of the middle frontal gyrus, near the zone of the anterior central gyrus (motor zone). The activity of this analyzer is connected with the analyzer of the learned hand movements necessary for writing (field 40 in the lower parietal lobule). If field 40 is damaged, all types of movement are preserved, but the ability of subtle movements necessary to draw letters, words and other signs (agraphia) is lost.
4. Since the development of written speech is also connected with the organ of vision, a visual analyzer of written speech has developed in close proximity to the visual analyzer, which, naturally, is connected to the sulcus calcarinus, where the general visual analyzer is located. The visual analyzer of written speech is located in the lower parietal lobule, with gyrus angularis (field 39). If field 39 is damaged, vision is preserved, but the ability to read (alexia) is lost, that is, to analyze written letters and compose words and phrases from them.
All speech analyzers are laid down in both hemispheres, but develop only on one side (in right-handers - on the left, in left-handers - on the right) and functionally turn out to be asymmetric. This connection between the motor analyzer of the hand (organ of labor) and speech analyzers is explained by the close connection between labor and speech, which had a decisive influence on the development of the brain.
"... Labor, and then articulate speech along with it ..." led to the development of the brain. This connection is also used for medicinal purposes. With damage to the speech-motor analyzer, the elementary motor ability of the speech muscles is preserved, but the possibility of oral speech is lost (motor aphasia). In these cases, it is sometimes possible to restore speech by a long exercise of the left hand (in right-handed people), the work of which favors the development of the rudimentary right-hand nucleus of the speech-motor analyzer.
Analyzers of oral and written speech perceive verbal signals (as I. P. Pavlov says - signal signals, or second signals), which constitutes the second signal system of reality, manifested in the form of abstract abstract thinking (general ideas, concepts, conclusions, generalizations), which characteristic only of man. However, the morphological basis of the second signaling system is not only these analyzers. Since the function of speech is phylogenetically the youngest, it is also the least localized. It is inherent in the entire cortex. Since the cortex grows along the periphery, the most superficial layers of the cortex are related to the second signaling system. These layers consist of a large number of nerve cells (100 billion) with short processes, which create the possibility of an unlimited closing function, wide associations, which is the essence of the activity of the second signaling system. At the same time, the second signaling system does not function separately from the first, but in close connection with it, more precisely on the basis of it, since the second signals can arise only in the presence of the first. “The basic laws established in the operation of the first signaling system must also govern the second, because this is the work of the same nervous tissue.”
IP Pavlov's doctrine of two signal systems gives a materialistic explanation of human mental activity and constitutes the natural scientific basis of VI Lenin's theory of reflection. According to this theory, the objective real world, which exists independently of our consciousness, is reflected in our consciousness in the form of subjective images.
Feeling is a subjective image of the objective world.
In the receptor, an external stimulus, such as light energy, is converted into a nervous process, which becomes a sensation in the cerebral cortex.
The same quantity and quality of energy, in this case light, in healthy people will cause a sensation of green color in the cerebral cortex (subjective image), and in a patient with color blindness (due to a different structure of the retina) - a sensation of red color.
Consequently, light energy is an objective reality, and color is a subjective image, its reflection in our consciousness, depending on the structure of the sense organ (eye).
Hence, from the point of view of Lenin's theory of reflection, the brain can be characterized as an organ of reflection of reality.
After all that has been said about the structure of the central nervous system, one can note the human signs of the structure of the brain, that is, the specific features of its structure that distinguish man from animals (Fig. 301, 302).
1. The predominance of the brain over the spinal cord. So, in carnivores (for example, in a cat), the brain is 4 times heavier than the spinal cord, in primates (for example, in a macaque) - 8 times, and in humans - 45 times (the weight of the spinal cord is 30 g, the brain - 1500 g) . According to Ranke, the spinal cord by weight in mammals is 22-48% of the weight of the brain, in the gorilla - 5-6%, in humans - only 2%.
2. The weight of the brain. In terms of the absolute weight of the brain, a person does not take first place, since in large animals the brain is heavier than that of a person (1500 g): in a dolphin - 1800 g, in an elephant - 5200 g, in a whale - 7000 g. To reveal the true ratios of brain weight to body weight, recently they began to define the "square index of the brain", that is, the product of the absolute weight of the brain by the relative one. This pointer made it possible to distinguish a person from the entire animal world.
So, in rodents it is 0.19, in carnivores - 1.14, in cetaceans (dolphins) - 6.27, in anthropoids - 7.35, in elephants - 9.82, and, finally, in humans - 32, 0.
3. The predominance of the cloak over the brain stem, i.e., the new brain (neencephalon) over the old (paleencephalon).
4. The highest development of the frontal lobe of the brain. According to Brodman, 8-12% of the entire surface of the hemispheres falls on the frontal lobes in lower monkeys, 16% in anthropoid monkeys, and 30% in humans.
5. The predominance of the new cerebral cortex over the old (see Fig. 301).
6. The predominance of the cortex over the "subcortex", which in humans reaches its maximum figures: the cortex, according to Dalgert, makes up 53.7% of the total brain volume, and the basal ganglia - only 3.7%.
7. Furrows and convolutions. Furrows and convolutions increase the area of the gray matter cortex, therefore, the more developed the cortex of the cerebral hemispheres, the greater the folding of the brain. The increase in folding is achieved by the large development of small furrows of the third category, the depth of the furrows and their asymmetric arrangement. Not a single animal has at the same time such a large number of furrows and convolutions, while being as deep and asymmetrical as in humans.
8. The presence of a second signaling system, the anatomical substrate of which is the most superficial layers of the cerebral cortex.
Summing up the above, we can say that the specific features of the structure of the human brain, which distinguish it from the brain of the most highly developed animals, are the maximum predominance of the young parts of the central nervous system over the old ones: the brain - over the spinal cord, the cloak - over the trunk, the new cortex - over the old, superficial layers of the cerebral cortex - over the deep ones.