Brain. Forebrain: diencephalon and cerebral hemispheres

Brain located in the cranial cavity. In its structure, there are five main sections: the medulla oblongata, midbrain, cerebellum, diencephalon and medulla (Fig. 61). Sometimes another section is distinguished in the midbrain - bridge. Medulla , midbrain(with the pons) and the cerebellum make up hindbrain, and the diencephalon and cerebral hemispheres - forebrain.

Up to the level of the midbrain, the brain is a single stem, but starting from the midbrain, it is divided into two symmetrical halves. At the level of the forebrain, the brain consists of two separate hemispheres connected to each other by special brain structures.

Sections of the brain and their functions

Medulla is the main part of the brain stem. It performs conductive and reflex functions. All pathways connecting the neurons of the spinal cord with the higher parts of the brain pass through it. By its origin, the medulla oblongata is the oldest thickening of the anterior end of the neural tube, and it contains the centers of many of the most important reflexes for human life. Thus, in the medulla oblongata there is a respiratory center, the neurons of which respond to an increase in the level of carbon dioxide in the blood between breaths. Artificial irritation of the neurons in the anterior part of this center leads to a narrowing of arterial vessels, an increase in pressure, and an increase in heart rate. Irritation of the neurons in the posterior part of this center leads to the opposite effects.

The medulla oblongata contains the bodies of neurons, the processes of which form nervus vagus. The medulla oblongata also contains the centers of a number of protective reflexes (sneezing, coughing, vomiting), as well as reflexes associated with digestion (swallowing, salivation, etc.).

In the hypothalamus there are centers of hunger and thirst, the irritation of the neurons of which leads to the indomitable absorption of food or water. Lesions of the hypothalamus are accompanied by severe endocrine and autonomic disorders: decreased or increased pressure, decreased or increased heart rate, difficulty breathing, impaired intestinal motility, thermoregulation disorders, changes in blood composition.

Greater hemispheres of the brain The human beings are divided by a deep longitudinal fissure into left and right halves. A special bridge formed by nerve fibers corpus callosum- connects these two halves, ensuring coordinated work of the cerebral hemispheres.

The youngest formation of the human brain in evolutionary terms is cerebral cortex. This is a thin layer of gray matter (neuron bodies), only a few millimeters thick, covering the entire forebrain. The cortex is composed of several layers of neurons and contains most of the neurons in the human central nervous system.

Deep furrows the cortex of each hemisphere is divided into lobes: frontal, parietal, occipital and temporal (Fig. 62). Different functions of the cortex are associated with different lobes. Between the grooves there are folds of the cerebral cortex - convolutions. This structure makes it possible to significantly increase the surface of the cerebral cortex. The higher nerve centers are located in the convolutions. Thus, in the area of ​​the anterior central gyrus of the frontal lobe there are higher centers of voluntary movements, and in the area of ​​the posterior central gyrus there are centers of musculoskeletal sensitivity. To date, the cortex has been mapped in detail and the representations of each muscle, each area of ​​skin in the cerebral cortex, as well as those areas of the cortex in which certain sensations are formed, are precisely known.

IN occipital lobe the highest centers of visual sensations are located. This is where the visual image is formed. Information to the neurons of the occipital lobe comes from the visual nuclei of the thalamus.

IN temporal lobes There are higher auditory centers containing different types of neurons: some of them react to the beginning of a sound, others to a certain frequency band, and others to a certain rhythm. Information in this area comes from the auditory nuclei of the thalamus. The centers of taste and smell are located deep in the temporal lobes.

IN information comes about all sensations. Here its summary analysis takes place and a holistic idea of ​​the image is created. Therefore, this zone of the cortex is called associative, and the ability to learn is associated with it. If the frontal cortex is destroyed, then there are no associations between the type of object and its name, between the image of a letter and the sound that it stands for. Learning becomes impossible.

In the depths of the cerebral hemispheres there are clusters of neurons that form nuclei limbic system, which is the main emotional center of the brain. The nuclei of the limbic system play an important role in memorizing new concepts and learning. At the very base of the brain are the limbic nuclei, in which the centers of fear, rage, and pleasure are found. Destruction of the nuclei of the limbic system leads to decreased emotionality, lack of anxiety and fear, and dementia.

All human activity is under the control of the cerebral cortex. This part of the brain ensures the interaction of the body with the environment and is the material basis for human mental activity.

New concepts

Brain stem. Brain. Medulla. Midbrain. Cerebellum. Diencephalon. Large hemispheres. Cerebral cortex

Answer the questions

1. What parts of the brainstem are formed? 2. What reflex centers are located in the medulla oblongata? 3. What is the importance of the cerebellum in the human body? What parts of the brain help it perform its functions? 4. In which part of the brain are the highest centers of pain sensitivity located? 5. What disorders of the body occur in a person when the functioning of the hypothalamus is disrupted? 6. What is the significance of grooves and convolutions in the structure of the cerebral hemispheres?

THINK!

How can you check for abnormalities in the cerebellum?

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

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

In the direction from the surface of the new crust inwards, six horizontal layers are distinguished.

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

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

Outer pyramidal layer. Consists mainly of medium-sized pyramidal cells. The axons of these cells, like granule cells of the 2nd layer, form corticocortical associative connections.

Inguinal granular layer. The nature of the cells (stellate cells) and the arrangement of their fibers is similar to the outer granular layer. In this layer, afferent fibers have synaptic endings coming from neurons of specific nuclei of the thalamus and, therefore, from receptors of sensory systems.

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

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

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

Histological evidence shows that the elementary neural circuits involved in information processing are located perpendicular to the surface of the cortex. Moreover, they are located in such a way that they cover all layers of the cortex. Such associations of neurons were called by scientists neural columns. Adjacent neural columns can partially overlap and also interact with each other.

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

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

Sensory cortical areas – zones into which sensory stimuli are projected. They are located mainly in the parietal, temporal and occipital lobes. Afferent pathways to the sensory cortex come predominantly from specific sensory nuclei of the thalamus (central, posterior lateral and medial). The sensory cortex has well-defined layers 2 and 4 and is called granular.

Areas of the sensory cortex, irritation or destruction of which causes clear and permanent changes in the sensitivity of the body, are called primary sensory areas(nuclear parts of analyzers, as I.P. Pavlov believed). They consist predominantly of unimodal neurons and form sensations of the same quality. In the primary sensory zones there is usually a clear spatial (topographic) representation of body parts and their receptor fields.

Around the primary sensory areas are less localized secondary sensory areas, whose multimodal neurons respond to the action of several stimuli.

The most important sensory area is the parietal cortex of the postcentral gyrus and the corresponding part of the postcentral lobule on the medial surface of the hemispheres (fields 1–3), which is designated as somatosensory area. Here there is a projection of skin sensitivity on the opposite side of the body from tactile, pain, temperature receptors, interoceptive sensitivity and sensitivity of the musculoskeletal system from muscle, joint, and tendon receptors. The projection of parts of the body in this area is characterized by the fact that the projection of the head and upper parts of the body is located in the inferolateral areas of the postcentral gyrus, the projection of the lower half of the body and legs is in the superomedial zones of the gyrus, and the projection of the lower part of the lower leg and feet is in the cortex of the postcentral lobule on the medial surface hemispheres (Fig. 12).

In this case, the projection of the most sensitive areas (tongue, larynx, fingers, etc.) is relatively relative to other parts of the body.

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

(section of the brain in the frontal plane)

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

Another area of ​​the neocortex is located in the occipital cortex. This primary visual area. Here there is a topical representation of retinal receptors. In this case, each point of the retina corresponds to its own section of the visual cortex. Due to the incomplete decussation of the visual pathways, the same halves of the retina are projected into the visual area of ​​each hemisphere. The presence of a retinal projection in both eyes in each hemisphere is the basis of binocular vision. Irritation of the cerebral cortex in this area leads to the appearance of light sensations. Located near the primary visual area secondary visual area. Neurons in this area are multimodal and respond not only to light, but also to tactile and auditory stimuli. It is no coincidence that it is in this visual area that the synthesis of various types of sensitivity occurs and more complex visual images and their recognition arise. Irritation of this area of ​​the cortex causes visual hallucinations, obsessive sensations, and eye movements.

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

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

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

Based on thalamocortical projections, two associative systems of the brain are distinguished:

thalamoparietal;

Thalomotemporal.

Thalamotparietal system is represented by associative zones of the parietal cortex, receiving the main afferent inputs from the posterior group of associative nuclei of the thalamus (lateral posterior nucleus and pillow). The parietal associative cortex has afferent outputs to the nuclei of the thalamus and hypothalamus, the motor cortex and the nuclei of the extrapyramidal system. The main functions of the thalamoparietal system are gnosis, the formation of a “body schema” and praxis.

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

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

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

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

ensuring probabilistic forecasting, which is expressed in changes in behavior in response to changes in environmental conditions and dominant motivation;

self-control of actions by constantly comparing the result of an action with the original intentions, which is associated with the creation of a foresight apparatus (according to the theory of the functional system of P.K. Anokhin, an acceptor of the result of an action).

As a result of a prefrontal lobotomy performed for medical reasons, in which the connections between the frontal lobe and the thalamus intersect, the development of “emotional dullness”, a lack of motivation, strong intentions and plans based on prediction, is observed. Such people become rude, tactless, they have a tendency to repeat certain motor acts, although the changed situation requires the performance of completely different actions.

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

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

Motor cortex areas . The concept of the motor cortex of the cerebral hemispheres began to form in the 80s of the 19th century, when it was shown that electrical stimulation of certain cortical zones in animals causes movement of the limbs of the opposite side. Based on modern research, it is customary to distinguish two motor areas in the motor cortex: primary and secondary.

IN primary motor cortex(precentral gyrus) there are neurons innervating the motor neurons of the muscles of the face, trunk and limbs. It has a clear topography of the projections of the body muscles. In this case, the projections of the muscles of the lower extremities and trunk are located in the upper parts of the precentral gyrus and occupy a relatively small area, and the projections of the muscles of the upper extremities, face and tongue are located in the lower parts of the gyrus and occupy a large area. The main pattern of topographic representation is that the regulation of the activity of muscles that provide the most accurate and varied movements (speech, writing, facial expressions) requires the participation of large areas of the motor cortex. Motor reactions to stimulation of the primary motor cortex are carried out with a minimum threshold, which indicates its high excitability. They (these motor reactions) are represented by elementary contractions of the opposite side of the body. When this cortical area is damaged, the ability to make fine coordinated movements of the limbs, especially the fingers, is lost.

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

The motor cortex is often called the agranular cortex because its granular layers are poorly defined, but the layer containing Betz's giant pyramidal cells is more pronounced. Neurons of the motor cortex receive afferent inputs through the thalamus from muscle, joint and skin receptors, as well as from the basal ganglia and cerebellum. The main efferent output of the motor cortex to the stem and spinal motor centers is formed by pyramidal cells. Pyramidal neurons and their associated interneurons are located vertically relative to the surface of the cortex. Such nearby neural complexes that perform similar functions are called functional motor speakers. Pyramidal neurons of the motor column can excite or inhibit motor neurons of the brainstem and spinal centers. Adjacent columns functionally overlap, and pyramidal neurons that regulate the activity of one muscle are located, as a rule, in several columns.

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

Pyramid Path consists of 1 million fibers of the corticospinal tract, starting from the cortex of the upper and middle third of the percentral gyrus, and 20 million fibers of the corticobulbar tract, starting from the cortex of the lower third of the precentral gyrus. Through the motor cortex and pyramidal tracts, voluntary simple and complex goal-directed motor programs are carried out (for example, professional skills, the formation of which begins in the basal ganglia and ends in the secondary motor cortex). Most of the fibers of the pyramidal tracts cross. But a small part of them remains uncrossed, which helps compensate for impaired movement functions in unilateral lesions. The premotor cortex also carries out its functions through the pyramidal tracts (motor writing skills, turning the head and eyes in the opposite direction, etc.).

To cortical extrapyramidal pathways These include the corticobulbar and corticoreticular tracts, which begin in approximately the same area as the pyramidal tracts. The fibers of the corticobulbar tract end on the neurons of the red nuclei of the midbrain, from which the rubrospinal tracts proceed. The fibers of the corticoreticular tracts end on the neurons of the medial nuclei of the reticular formation of the pons (the medial reticulospinal tracts extend from them) and on the neurons of the reticular giant cell nuclei of the medulla oblongata, from which the lateral reticulospinal tracts begin. Through these pathways, tone and posture are regulated, providing precise, targeted movements. Cortical extrapyramidal tracts are a component of the extrapyramidal system of the brain, which includes the cerebellum, basal ganglia, and motor centers of the brainstem. This system regulates tone, posture, coordination and correction of movements.

Assessing in general the role of various structures of the brain and spinal cord in the regulation of complex directed movements, it can be noted that the urge (motivation) to move is created in the frontal system, the intention of movement - in the associative cortex of the cerebral hemispheres, the program of movements - in the basal ganglia, cerebellum and premotor cortex, and the execution of complex movements occurs through the motor cortex, motor centers of the brainstem and spinal cord.

Interhemispheric relationships Interhemispheric relationships manifest themselves in humans in two main forms:

functional asymmetry of the cerebral hemispheres:

joint activity of the cerebral hemispheres.

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

It is customary to highlight mental, sensory And motor interhemispheric asymmetry of the brain. Again, when studying speech, it was shown that the verbal information channel is controlled by the left hemisphere, and the non-verbal channel (voice, intonation) by the right. Abstract thinking and consciousness are associated primarily with the left hemisphere. When developing a conditioned reflex, the right hemisphere dominates in the initial phase, and during exercise, that is, strengthening the reflex, the left hemisphere dominates. carries out information processing simultaneously statically, according to the principle of deduction, spatial and relative characteristics of objects are better perceived. processes information sequentially, analytically, according to the principle of induction, and better perceives the absolute characteristics of objects and temporal relationships. In the emotional sphere, the right hemisphere primarily determines older, negative emotions and controls the manifestation of strong emotions. In general, the right hemisphere is “emotional.” The left hemisphere determines mainly positive emotions and controls the manifestation of weaker emotions.

In the sensory sphere, the role of the right and left hemispheres is best demonstrated in visual perception. The right hemisphere perceives the visual image holistically, in all details at once, it more easily solves the problem of distinguishing objects and recognizing visual images of objects that are difficult to describe in words, creating the prerequisites for concrete sensory thinking. The left hemisphere evaluates the visual image as dissected. Familiar objects are easier to recognize and problems of object similarity are solved, visual images are devoid of specific details and have a high degree of abstraction, and the prerequisites for logical thinking are created.

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

Joint activity of the cerebral hemispheres is ensured by the presence of the commissural system (corpus callosum, anterior and posterior, hippocampal and habenular commissures, interthalamic fusion), which anatomically connect the two hemispheres of the brain.

Clinical studies have shown that in addition to transverse commissural fibers, which provide interconnection between the hemispheres of the brain, also longitudinal and vertical commissural fibers.

Questions for self-control:

General characteristics of the new cortex.

Functions of the neocortex.

The structure of the new cortex.

What are neural columns?

What areas of the cortex are identified by scientists?

Characteristics of the sensory cortex.

What are primary sensory areas? Their characteristics.

What are secondary sensory areas? Their functional purpose.

What is the somatosensory cortex and where is it located?

Characteristics of the auditory cortex.

Primary and secondary visual areas. Their general characteristics.

Characteristics of the associative area of ​​the cortex.

Characteristics of associative systems of the brain.

What is the thalamoparietal system? Its functions.

What is the thalamic system? Its functions.

General characteristics of the motor cortex.

Primary motor cortex; its characteristics.

Secondary motor cortex; its characteristics.

What are functional motor speakers?

Characteristics of cortical pyramidal and extrapyramidal tracts.

This is the part of the forebrain located between the brain stem and the cerebral hemispheres. The main structures of the diencephalon are the thalamus, pineal gland and hypothalamus, to which the pituitary gland is attached.

Thalamus can be called a collector of information about all types of sensitivity. Almost all signals from the centers of the spinal cord, brain stem, cerebellum and RF are received and processed there. From it, information is delivered to the hypothalamus and cerebral cortex.

In the thalamus there are nuclei where O stimuli are synthesized, acting simultaneously. So, when you pick up a lump of ice in your hand, various neurons are excited: neurons that are sensitive to mechanical influences, and those that perceive temperature changes, as well as sensitive neurons in the eye. However, all these signals simultaneously enter the same neurons in the nuclei of the thalamus. Here they are generalized, recoded, and complete information about the stimulus is transmitted to the cortex.

The forebrain is the most developed structure in the process of evolution.

It predetermines a person’s inclinations, his orientation, behavior, and personality development.

Location: cerebral part of the skull.

The article is intended for a general understanding of the structure and purpose.

General information

Formed from the anterior end of the primary neural tube. In embryogenesis, it is divided into 2 parts, one of which gives rise to the telencephalon, the second - the intermediate brain.

According to Alexander Luria’s model, it consists of 3 blocks:

1. Block regulating brain activity levels. Ensures the implementation of certain types of activities. Responsible for emotional reinforcement of activity based on predicting its results (success - failure).
2. Block for receiving, processing and storing incoming information. Participates in the formation of ideas about ways to implement activities.
3. Block of programming, regulation and control over the organization of mental activity. Compares the resulting result with the original intent.

The forebrain takes part in the work of all blocks. Based on information processing, it controls behavior. Administrator of higher psychological functions: perception, memory, imagination, thinking, speech.

Anatomy

The structure of a living individual is not easy to describe. Especially such a component as the brain. This universe that exists in everyone continues to hide its secrets. But this does not mean that they are not worth understanding.

Development

The forebrain is formed at 3-4 weeks of prenatal development. By the end of the 4th week of embryogenesis, the telencephalon, diencephalon, and the cavity of the third ventricle are formed from the forebrain.

It consists of the thalamic and hypothalamic regions, which are located on the sides of the third ventricle between the hemispheres and the midbrain.

The thalamic region unites:

• The thalamus is an ovoid formation located deep under the cerebral cortex. The oldest, largest (3-4 cm) formation of the diencephalon;
• The epithalamus is located above the thalamus. It is famous for the fact that it contains the pineal gland. Previously, it was believed that the soul lived here. Yogis associate the pineal gland with the seventh chakra. By awakening the organ, you can open the “third eye”, becoming clairvoyant. The gland is tiny, only 0.2 g. But the benefits for the body are enormous, although previously it was considered a rudiment;
• subthalamus - a formation located below the thalamus;
• metathalamus - bodies located in the posterior part of the thalamus (previously considered a separate structure). Together with the midbrain, they determine the work of the visual and auditory analyzers;

The hypothalamic region includes:

• hypothalamus. Located under the thalamus. Weighs 3-5 g. Consists of specialized groups of neurons. Connected with all departments. Controls the pituitary gland;
• the posterior lobe of the pituitary gland is the central organ of the endocrine system, weighing 0.5 g. Located at the base of the skull. The posterior lobe, together with the hypothalamus, forms the hypothalamic-pituitary complex, which controls the activity of the endocrine glands.

Unites:

• cortical hemispheres. The bark appeared late in the development of the animal world. Occupies half the volume of the hemispheres. Its surface can exceed 2000 cm 2;
• corpus callosum - a nerve tract connecting the hemispheres;
• striped body. Located on the side of the thalamus. On a section it looks like repeating stripes of white and gray matter. Promotes regulation of movements, motivation of behavior;
• olfactory brain. Unites structures that differ in purpose and origin. Among them is the central section of the olfactory analyzer;

Anatomical features

Intermediate

The thalamus is egg-shaped and gray-brown in color. Structural unit - nuclei, which are classified according to functional and compositional characteristics.

The epithalamus consists of several units, the most famous of which is the grayish-reddish pineal gland.

The subthalamus is a small region of gray matter nuclei connected to white matter.

The hypothalamus consists of nuclei. There are about 30 of them. Most are paired. Classified by location.

Posterior lobe of the pituitary gland. - a rounded formation, location - the pituitary fossa of the sella turcica.

Finite

Unites the hemispheres, corpus callosum and striatum. The largest department by volume.

The hemispheres are covered with gray matter 1-5 mm thick. The mass of the hemispheres is about 4/5 of the mass of the brain. Convolutions and grooves significantly increase the area of ​​the cortex, containing billions of neurons and nerve fibers arranged in a certain order. Underneath the gray matter lies white matter—the processes of nerve cells. About 90% of the cortex has a typical six-layer structure, where neurons are connected through synapses with each other.

From the point of view of phylogenesis, the cerebral cortex is divided into 4 types: ancient, old, intermediate, new. The main part of the human cortex is the neocortex.

The corpus callosum is shaped like a wide strip. Consists of 200-250 million nerve fibers. The largest structure connecting the hemispheres.

Functions

Mission – organization of mental activity.

Intermediate

Participates in coordinating the work of organs, regulating body movement, maintaining temperature, metabolism, and emotional background.

Thalamus. The main task is to sort information. It works like a relay - it processes and sends data coming from receptors and pathways to the brain. The thalamus affects the level of consciousness, attention, sleep, wakefulness. Supports speech functioning.

Epithalamus. Interaction with other structures occurs through melatonin, a hormone produced by the pineal gland in the dark (therefore, it is not recommended to sleep in the light). A derivative of serotonin - the “happiness hormone”. Melatonin is a participant in the regulation of circadian rhythms, being a natural sleep aid, it affects memory and cognitive processes. It affects the localization of skin pigments (not to be confused with melanin), puberty, and suppresses the growth of a number of cells, including cancer cells. Through connections with the basal ganglia, the epithalamus participates in the optimization of motor activity, and through connections with the limbic system, in the regulation of emotions.

Subthalamus. Controls the body's muscle responses.

Hypothalamus. Forms a functional complex with the pituitary gland and directs its work. The complex controls the endocrine system. The hormones it produces help cope with distress and maintain homeostasis.

Thirst and hunger centers are located in the hypothalamus. The department coordinates emotions, human behavior, sleep, wakefulness, and thermoregulation. Here are found similar in action to opiates, which help to endure pain.

Hemispheres

They act together with subcortical structures and the brain stem. Main destination:

1. Organization of interaction of an organism with the environment through its behavior.
2. Consolidation of the body.

Corpus callosum

The corpus callosum received attention after operations to dissect it in the treatment of epilepsy. The operations relieved seizures while changing a person’s personality. It was found that the hemispheres are adapted to work independently. However, to coordinate activities, information exchange between them is necessary. The corpus callosum is the main transmitter of information.

Striatum

1. Reduces muscle tone.
2. Contributes to the coordination of internal organ function and behavior.
3. Participates in the formation of conditioned reflexes.

The olfactory brain contains centers that control the sense of smell.

Cerebral cortex

Head of mental processes. Controls sensory and motor functions. Consists of 4 layers.

The ancient layer is responsible for elementary responses (for example, aggression) characteristic of humans and animals.

The old layer is involved in the formation of attachment and laying the foundations of altruism. Thanks to the layer we are happy or angry.

The intermediate layer is a formation of a transitional type, since the modification of old formations into new ones is carried out gradually. Ensures the activity of the new and old cortex.

The neocortex concentrates information from subcortical structures and the brainstem. Thanks to it, living beings think, talk, remember, and create.

5 cerebral lobes

The occipital lobe is the central section of the visual analyzer. Provides visual pattern recognition.

Parietal lobe:

• controls movements;
• orients in time and space;
• provides perception of information from skin receptors.

Thanks to the temporal lobe, living things perceive a variety of sounds.

The frontal lobe regulates voluntary processes, movements, motor speech, abstract thinking, writing, self-criticism, and coordinates the work of other areas of the cortex.

The insula is responsible for the formation of consciousness, the formation of an emotional response and the maintenance of homeostasis.

Interaction with other structures

The brain matures unevenly during ontogenesis. At birth, unconditioned reflexes are formed. As the individual matures, conditioned reflexes develop.

The parts of the brain are anatomically and functionally interconnected. The trunk, together with the cortex, is involved in the preparation and implementation of various forms of behavior.

The interaction of the thalamus, limbic system, hippocampus helps to reproduce the image of events: sounds, smells, place, time, spatial location, emotional coloring. The connections of the thalamus with areas of the temporal lobe of the cortex contribute to the recognition of familiar places and objects.

The thalamus, hypothalamus, and cortex have mutual connections with the medulla oblongata. Thus, the medulla oblongata contributes to the assessment of receptor activity and the normalization of the activity of the musculoskeletal system.

Cooperation of the reticular formation of the trunk and cortex causes excitation or inhibition of the latter. The cooperation of the reticular formation of the medulla oblongata and the hypothalamus ensures the functioning of the vasomotor center.

Having examined the structure and purpose, we are one step closer to understanding a living entity.

"Biology. Human. 8th grade." D.V. Kolesova et al.

Functions of the diencephalon and cerebral hemispheres (forebrain) of the brain

Question 1. What divisions are distinguished in the forebrain?
The forebrain consists of sections: the diencephalon and the cerebral hemispheres.

Question 2. What are the functions of the thalamus and hypothalamus?
Thalamus is the center for the analysis of all types of sensations, except olfactory. Despite the small volume (about 19 cm 3) in thalamus there are more than 40 pairs of nuclei (clusters of neurons) with diverse functions. Specific nuclei analyze various types of sensations and transmit information about them to the corresponding zones of the cerebral cortex.
The nonspecific nuclei of the thalamus are a continuation of the reticular formation of the brainstem and are necessary for the activation of forebrain structures. Lower part of the diencephalon - hypothalamus- also performs the most important functions, being the highest center of autonomic regulation. Anterior nuclei hypothalamus- the center of parasympathetic influences, and the posterior ones - sympathetic. The medial part of the hypothalamus is the main neuroendocrine organ, the neurons of which release into the blood a number of regulators that affect the activity of the anterior pituitary gland. In addition, the most important hormones oxytocin and vasopressin (antidiuretic hormone) are synthesized in this area. The hypothalamus also contains centers of hunger and thirst, the irritation of the neurons of which leads to the indomitable absorption of food or water.
Thus, we can say that the hypothalamus is necessary to provide vegetative support for voluntary and involuntary somatic activity of a person.

Question 3. Why is the surface of the hemispheres folded?
The cerebral cortex has a folded structure due to grooves in which 2/3 of its surface is hidden. The folding of the bark increases its area to 2000-2500 cm 2. Each hemisphere of the cortex (left and right) is divided into four lobes by deep grooves (depressions): frontal, parietal, temporal and occipital. The frontal lobe is separated from the parietal lobe by a deep central sulcus. The lateral sulcus limits the temporal lobe.

Question 4. How is gray and white matter distributed in the cerebral hemispheres? What functions do they perform?
Phylogenetically, the youngest brain formation is the cerebral cortex. This is a layer of gray matter (i.e. neuron bodies) covering the entire forebrain. Bark thickness - 1.5-4.5 mm, total weight - 600g. The cortex includes about 109 neurons, that is, the majority of all neurons in the human nervous system. The cortex consists of six layers, which differ in cell composition, functions, etc. Neurons of layers 1 to 4 mainly perceive and process information from other parts of the nervous system; The 5th layer is the main efferent one and, due to the peculiar shape of its constituent neurons, is called internal pyramidal.
Under the cortex is a white substance. In the depths of the hemispheres, among the white matter, there are accumulations of gray matter - the subcortical nuclei. Neurons of the cerebral hemispheres are responsible for the perception of information entering the brain from the senses, control of complex forms of behavior, and participate in the processes of memory, mental and speech activity of a person. Under the cortex is a white substance. In the depths of the hemispheres, among the white matter, there are accumulations of gray matter - the subcortical nuclei. Neurons of the cerebral hemispheres are responsible for the perception of information entering the brain from the senses, control of complex forms of behavior, and participate in the processes of memory, mental and speech activity of a person. White matter consists of a mass of nerve fibers that connect cortical neurons to each other and to underlying parts of the brain.

Question 5: What is the function of the old cortex?
The old cerebral cortex contains centers associated with complex instincts, emotions, and memory. The old cortex enables the body to respond correctly to favorable and unfavorable events. Information about experienced events is stored here.

Question 6. How are functions distributed between the left and right hemispheres of the cerebrum?
The left hemisphere is responsible for regulating the functioning of the organs of the right side of the body, and also perceives information from space on the right. In addition, the left hemisphere is responsible for the implementation of mathematical operations and the process of logical, abstract thinking; Here are the auditory and motor centers of speech, which provide the perception of oral speech and the formation of oral and written speech.
The right hemisphere controls the organs of the left side of the body and perceives information from space on the left. Also, the right hemisphere is involved in the processes of imaginative thinking, plays a leading role in recognizing human faces and is responsible for musical and artistic creativity; it is also responsible for recognizing people by voice and

Question 7. Which connections in the body are called direct and which are called reverse?
Direct communication in the body is the path along which the signal goes from the brain to the organs; Feedback is the path through which information about the results achieved comes back to the brain.

The forebrain is the most rostral part of the nervous system. It consists of (cortex) and basal ganglia. The latter, located in the cortex, are located between the frontal parts of the brain and the diencephalon. These nuclear structures include the putamen, which together make up the striatum. It got its name due to the alternation of gray matter, consisting of nerve cells, and white matter. These elements of the brain, together with the globus pallidus, which is called the pallidum, form the striopallidal system. This system in mammals, including humans, is the main nuclear apparatus and is involved in the processes of motor behavior and other important functions.

The basal ganglia have a very diverse cellular composition. The globus pallidus contains large and small neurons. The striatum has a similar cellular organization. The neurons of the striopallidal system receive impulses from the cerebral cortex, thalamus, and brainstem nuclei.

What functions do the subcortical nuclei perform?

The nuclei of the striopallidal system are also involved in motor activity. Irritation of the caudate nucleus causes stereotypical head turns and trembling movements of the arms or forelimbs in animals. During the study, it was found that it is important in the processes of memorizing movements. An irritating effect on this structure also disrupts learning. has an inhibitory effect on motor activity and its emotional components, for example on aggressive reactions.

Cerebral cortex

The forebrain includes a structure called the cortex. It is considered the youngest formation of the brain. Morphologically, the cortex consists of gray matter that covers the entire brain and has a large area due to numerous folds and convolutions. Gray matter consists of a huge number of nerve cells. Due to this, the number of synoptic connections is very large, which ensures the processes of storing and processing the received information. Based on the appearance and evolution, ancient, old and new bark are distinguished. During the evolution of mammals, the neocortex developed especially rapidly. The ancient cortex contains olfactory bulbs and tracts, olfactory tubercles. The old one includes the cingulate gyrus, amygdala and hippocampal gyrus. The remaining areas belong to the neocortex.

The nerve cells of the cerebral cortex are arranged in layers and in an orderly manner, forming six layers in their composition:

1st - called molecular, formed by a plexus of nerve fibers and contains a minimal number of nerve cells.

2nd - called external granular. It consists of small neurons of different shapes, similar to grains.

3rd - consists of pyramidal neurons.

4th - internal granular, like the outer layer, consists of small neurons.

5th - contains Betz cells (giant pyramidal cells). The processes of these cells (axons) form a pyramidal tract, which reaches the caudal areas and passes into the anterior roots

6th - multiform, consists of triangular and spindle-shaped neurons.

Although the neural organization of the cortex has much in common, a more detailed study of it showed differences that appear in the course of the fibers, the size and number of cells and the branching of their detritus. By studying, a map of the crust was compiled, which includes 11 regions and 52 fields.

What is the forebrain responsible for??

Very often, ancient and old bark are combined. They form the olfactory brain. The forebrain is also responsible for alertness and attention, and is involved in autonomic reactions. The system takes part in instinctive behavior and the formation of emotions. In animal experiments, when the old cortex is irritated, effects associated with the digestive system appear: chewing, swallowing, peristalsis. Also, an irritating effect on the tonsils causes a change in the function of internal organs (kidneys, uterus, bladder). Some areas of the cortex are involved in memory processes.

Together, the hypothalamus, limbic region and forebrain (ancient and old cortex) form which maintains homeostasis and ensures the preservation of the species.

The forebrain (lat. prosencephalon) is the anterior part of the brain of vertebrates, consisting of two hemispheres. Includes the gray matter of the cortex, subcortical nuclei, as well as nerve fibers that form the white matter.

The forebrain, midbrain, and hindbrain are the three main components of the brain that developed in the central nervous system.

In the five-vesicle stage of development, the diencephalon (thalamus, epithalamus, subthalamus, hypothalamus and metathalamus), as well as the telencephalon, are distinguished from the forebrain. The telencephalon consists of the cerebral cortex, white matter and basal ganglia.

Diencephalon(diencéphalon) connects caudally with the midbrain, and rostrally passes into the cerebral hemispheres of the telencephalon. The cavity of the diencephalon is a vertical slit located in the midsagittal plane; this is the third cerebral ventricle (ventriculus tertius). At the back it passes into the midbrain aqueduct, and at the front it connects with the two lateral ventricles of the cerebral hemispheres through two interventricular foramina of Monroe (foramena interventricularià). The lateral walls of the third ventricle are formed by the medial surfaces of the right and left thalamus, the bottom - by the hypothalamus and subthalamus. The anterior border approaches the descending columns of the fornix (columnae fornicis), below to the anterior cerebral commissure (comissura anterior) and further to the terminal plate (lamina terminalis). The posterior wall consists of the posterior commissure (comissura posterior) above the entrance to the cerebral aqueduct. The roof of the third ventricle consists of an epithelial plate. Above it is the choroid plexus. Above the plexus is the fornix, and even higher is the corpus callosum. Along the lateral walls of the third ventricle, from the interventricular foramina to the entrance to the cerebral aqueduct, hypothalamic grooves run, separating the thalamus from the hypothalamus. The thalamus are connected to each other in the middle part of the third ventricle by a commissure - interthalamic fusion (adhesio interthalamica). The diencephalon includes several structures: the visual thalamus itself - the thalamus, metathalamus, hypothalamus, subthalamus, epithalamus, pituitary gland.

Thalamus(thalamus) - the main part of the diencephalon. It forms the lateral walls of the third ventricle. Includes itself thalamusand metathalamus(lateral and medial geniculate bodies). The shape of the thalamus is ovoid, the narrow part is directed backward. The protruding posterior part of the thalamus is called the pulvinar, and in the anterior part the thalamus has the anterior tubercle. Below and lateral to the pillow there are oblong-oval tubercles: the medial (corpus geniculatum mediale) and lateral (corpus geniculatum laterale) geniculate bodies. The medial surface of the thalamus forms the lateral wall of the third ventricle, the upper and lateral are adjacent to the internal capsule of the cerebral hemispheres, and the lower borders the hypothalamus. Metathalamus(metathalamus) is represented by geniculate bodies located below and lateral to the pillow. The medial geniculate body is better expressed, lies under the cushion of the visual thalamus and, along with the lower thalamus of the quadrigeminal, is the subcortical center of hearing. The lateral geniculate body is a small elevation lying on the inferolateral surface of the cushion. It, together with the superior colliculus of the quadrigeminal, is the subcortical visual center. The cushion and geniculate bodies contain nuclei of the same name. The external geniculate bodies include the so-called optic tracts, which are visual pathways composed of already crossed axons of retinal ganglion cells. The internal structure of the thalamus consists of nuclear accumulations of gray matter separated by white matter. The thalamus has about 150 nuclei. They are divided into six groups: anterior, midline, medial, lateral, posterior and pretectal. In accordance with their functions, specific and nonspecific nuclei of the thalamus are distinguished. Specific, in turn, are switching (sensory and non-sensory) and associative nuclei. The axons of the cells of the thalamic nuclei approach certain areas of the cortex. Switching nuclei receive afferents from different sensory systems or from other parts of the brain, and direct their afferents to certain projection zones of the cortex. In the associative nuclei, afferents from other thalamic nuclei end, and the axons of their cells go to the associative zones of the cortex. Nonspecific nuclei do not have specific afferent connections with individual sensory systems, and their afferents rush diffusely to many areas of the cortex. The switching nuclei of the visual and auditory sensory systems are the nuclei of the lateral and medial geniculate bodies, and the somatosensory system is the posterior ventral nucleus of the thalamus. The association nuclei are the lateral and medial nuclei of the cushion. Nonspecific nuclei are concentrated mainly in the lateral, medial and middle groups of thalamic nuclei. The thalamus is connected to all parts of the central nervous system. The thalamus is involved in the processing of sensory stimuli going to the cerebral cortex, and also regulates the wakefulness-sleep cycle.