Brain. Forebrain: diencephalon and cerebral hemispheres

Brain located in the cranial cavity. In its structure, five main sections are distinguished: the medulla oblongata, midbrain, cerebellum, diencephalon and brain (Fig. 61). Sometimes another section is distinguished in the midbrain - bridge. Medulla , midbrain(with the bridge) 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 trunk, 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, interconnected by special brain structures.

Parts of the brain and their functions

Medulla is the main part of the brain stem. It performs conductive and reflex functions. All the paths 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. So, in the medulla oblongata is respiratory centerwhose neurons respond to an increase in the level of carbon dioxide in the blood between breaths. Artificial stimulation of the neurons of the anterior part of this center leads to narrowing of arterial vessels, an increase in pressure, and an increase in heart rate. Stimulation of neurons in the back of this center leads to the opposite effects.

In the medulla oblongata are the bodies of neurons, the processes of which form nervus vagus. In the medulla oblongata there are also 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 stimulation of the neurons of which leads to the indomitable absorption of food or water. Lesions of the hypothalamus are accompanied by severe endocrine and vegetative disorders: a decrease or increase in pressure, a decrease or increase in heart rate, breathing difficulties, intestinal motility disorders, thermoregulation disorders, and changes in blood composition.

Large hemispheres of the brain human are divided by a deep longitudinal slit into the left and right halves. A special bridge formed by nerve fibers corpus callosum- connects these two halves, ensuring the 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 (neuronal bodies), only a few millimeters thick, covering the entire forebrain. The cortex is formed by several layers of neurons, and it includes most of all neurons of 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 furrows are the folds of the cortex of the hemispheres - convolutions. This structure allows you to significantly increase the surface of the cortex of the hemispheres. In the convolutions are the higher nerve centers. So, in the region of the anterior central gyrus of the frontal lobe, the higher centers of voluntary movements are located, and in the region of the posterior central gyrus, the centers of musculoskeletal sensitivity. To date, the cortex has been mapped in detail and the representation of each muscle, each area of ​​the 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 various types of neurons: some of them respond 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 in the depths of the temporal lobes.

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

In the depths of the cerebral hemispheres 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. The destruction of the nuclei of the limbic system leads to a decrease in emotionality, the absence of anxiety and fear, 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. Intermediate brain. Large hemispheres. The cerebral cortex

Answer the questions

1. What departments form the brain stem? 2. Which 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 what part of the brain are the highest centers of pain sensitivity located? 5. What disorders of the body occur in a person when the hypothalamus is disturbed? 6. What is the significance of the furrows and convolutions in the structure of the cerebral hemispheres?

THINK!

How can you check for deviations in the work of the cerebellum?

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

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

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

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

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

outer pyramidal layer. Consists mainly of pyramidal cells of medium size. The axons of these cells, like the granular cells of the 2nd layer, form corticocortical associative connections.

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

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

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

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

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

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

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

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

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

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

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

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

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

(section of the brain in the frontal plane)

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

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

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

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

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

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

thalamothemenal;

talomotemporal.

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

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

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

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

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

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

self-control of actions by constantly comparing the result of the 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, the acceptor of the result of the action).

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

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

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

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

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

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

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

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

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

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

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

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

functional asymmetry of the cerebral hemispheres:

joint activity of the cerebral hemispheres.

Functional asymmetry of the hemispheres is the most important psychophysiological property of the human brain. The study of functional asymmetry of the hemispheres began in the middle of the 19th century, when the French physicians M. Dax and P. Broca showed that a person’s speech 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-hemispheric dominance, which was formed evolutionarily as a result of labor activity and is a specific property of his brain. In the twentieth century, as a result of the use of various clinical techniques (especially in the study of patients with a split brain - transection was carried out), it was shown that in a number of psychophysiological functions, not the left, but the right hemisphere dominates in a person. Thus, the concept of partial dominance of the hemispheres arose (its author is R. Sperry).

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

In the sensory realm, the role of the right and left hemispheres is best manifested in visual perception. The right hemisphere perceives the visual image holistically, immediately in all details, it is easier to solve the problem of distinguishing objects and identifying visual images of objects that are difficult to describe in words, creates the prerequisites for concrete-sensory thinking. The left hemisphere evaluates the visual image dissected. Familiar objects are more easily recognized and problems of similarity of objects are solved, visual images are devoid of specific details and have a high degree of abstraction, the prerequisites for logical thinking are created.

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

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

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

Questions for self-control:

General characteristics of the new cortex.

Functions of the new cortex.

The structure of the new cortex.

What are neural columns?

What areas of the cortex are distinguished by scientists?

Characteristics of the sensory cortex.

What are primary sensory areas? Their characteristic.

What are secondary sensory areas? Their functional purpose.

What is the somatosensory cortex and where is it located?

Characteristics of the auditory cortex.

Primary and secondary visual areas. Their general characteristics.

Characteristics of the association area of ​​the cortex.

Characteristics of the associative systems of the brain.

What is the thalamotenoid system. Her functions.

What is the thalamolobal system. Her functions.

General characteristics of the motor cortex.

Primary motor cortex; her characteristic.

secondary motor cortex; her characteristic.

What are functional motor columns.

Characteristics of the cortical pyramidal and extrapyramidal pathways.

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, the pineal gland and the hypothalamus, to which the pituitary gland is attached.

thalamus can be called a collector of information about all kinds of sensitivity. It receives and processes almost all signals from the centers of the spinal cord, brain stem, cerebellum and RF. From it, information is delivered to the hypothalamus and the cerebral cortex.

In the thalamus are the nuclei, where O stimuli are synthesized, acting simultaneously. So, when you take 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 eye neurons. However, all these signals simultaneously arrive in 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 the inclinations of a person, his orientation, behavior, the formation of a personality.

Location - the brain 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 generates the telencephalon, the second - the intermediate.

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

1. Block regulation of brain activity levels. Provides for the implementation of certain activities. Responsible for the 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 the ways of implementing activities.
3. Block of programming, regulation and control over the organization of mental activity. Compares the 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 that doesn't mean they shouldn't be dealt with.

Development

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

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 structure 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 the epiphysis is located in it. Previously, it was believed that the soul lives here. Yogis associate the pineal gland with the seventh chakra. By awakening the organ, you can open the "third eye", becoming a clairvoyant. The gland is tiny, only 0.2 g. But the benefits to the body are enormous, although it was previously considered a rudiment;
• subthalamus - a formation located below the thalamus;
• metathalamus - bodies located in the back 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. It weighs 3-5 g. It consists of specialized groups of neurons. Connected with all departments. Governs the pituitary gland;
• the posterior lobe of the pituitary gland - the central organ of the endocrine system weighing 0.5 g. It is located at the base of the skull. The posterior lobe, together with the hypothalamus, form the hypothalamic-pituitary complex that controls the activity of the endocrine glands.

Combines:

• hemispheres covered with bark. The bark appeared at the later stages of the development of the animal world. It occupies half the volume of the hemispheres. Its surface may exceed 2000 cm 2 ;
• corpus callosum - the nerve tract connecting the hemispheres;
• striped body. Located on the side of the thalamus. On the cut, it looks like repeating bands of white and gray matter. Promotes the regulation of movements, motivation of behavior;
• olfactory brain. It unites structures that are different in purpose, appearance. Among them are the central section of the olfactory analyzer;

Anatomical features

Intermediate

The thalamus looks like a gray-brown egg. Structural unit - nuclei, which are classified according to functional and compositional features.

The epithalamus consists of several units, the best known of which is the greyish-reddish pineal gland.

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

The hypothalamus is made up of nuclei. There are about 30 of them. Most are paired. Classified by location.

Posterior pituitary. - formation of a rounded shape, location - pituitary fossa of the Turkish saddle.

Finite

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

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. The convolutions and sulci greatly increase the area of ​​the cortex, which contains billions of neurons and nerve fibers arranged in a certain order. Under the gray matter lies white - the processes of nerve cells. About 90% of the cortex has a typical six-layer structure, where neurons are connected via synapses to 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 broad band. Consists of 200-250 million nerve fibers. The largest structure connecting the hemispheres.

Functions

Mission - the organization of mental activity.

Intermediate

Participates in the coordination of the work of organs, regulation of body movement, maintaining temperature, metabolism, emotional background.

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

Epithalamus. Interaction with other structures occurs through melatonin, a hormone produced by the pineal gland at night (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 hypnotic, it affects memory and cognitive processes. It affects the localization of skin pigments (not to be confused with melanin), puberty, inhibits the growth of a number of cells, including cancer cells. Through connections with the basal ganglia, the epithalamus is involved in the optimization of motor activity, 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, directs its work. The complex controls the endocrine system. Its hormones help to cope with distress, maintain homeostasis.

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

hemispheres

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

1. Organization of the interaction of the organism with the environment through its behavior.
2. Body consolidation.

corpus callosum

The corpus callosum was noticed after operations to dissect it in the treatment of epilepsy. Operations relieved seizures, while changing the personality of a person. It was found that the hemispheres are adapted to work independently. However, for coordination of 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 the functioning of internal organs and behavior.
3. Participates in the formation of conditioned reflexes.

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

The cerebral cortex

Head of mental processes. Manages 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, 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 bark.

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

5 cerebral lobes

The occipital lobe is the central part of the visual analyzer. Provides visual image recognition.

Parietal lobe:

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

Thanks to the temporal lobe, living beings 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 insular lobe is responsible for the formation of consciousness, the formation of an emotional response and the support of homeostasis.

Interaction with other structures

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

The parts of the brain are anatomically and functionally interconnected. The trunk together with the cortex are 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 interconnections of the thalamus with areas of the temporal lobe of the cortex contribute to the recognition of familiar places and objects.

The thalamus, hypothalamus, 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.

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

Having considered the structure and purpose, we have come one step closer to understanding the living essence.

"Biology. Human. Grade 8 ". D.V. Kolesova and others.

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

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

Question 2. What are the functions of the thalamus and hypothalamus?
thalamus is the center of analysis of all kinds of sensations, except for olfactory ones. Despite the small volume (about 19 cm 3) in thalamus there are more than 40 pairs of nuclei (clusters of neurons) with a variety of functions. Specific nuclei analyze various types of sensations and transmit information about them to the corresponding zones of the cerebral cortex.
Nonspecific nuclei of the thalamus are a continuation of the reticular formation of the brainstem and are necessary for the activation of the structures of the forebrain. The lower part of the diencephalon - hypothalamus- also performs the most important functions, being the highest center of vegetative regulation. Anterior nuclei hypothalamus- the center of parasympathetic influences, and the rear - 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. In the hypothalamus there are also centers of hunger and thirst, the stimulation 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 human activity.

Question 3. Why is the surface of the hemispheres folded?
The cerebral cortex has a folded structure due to furrows, in which 2/3 of its surface is hidden. Folding of the bark increases its area to 2000-2500 cm 2 . Each hemisphere of the cortex (left and right) is divided by deep grooves (recesses) into four lobes: 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 formation of the brain is the cerebral cortex. This is a layer of gray matter (that is, the bodies of neurons) that covers the entire forebrain. Bark thickness - 1.5-4.5 mm, total weight - 600g. The cortex contains about 109 neurons, that is, most of all neurons in the human nervous system. The cortex is made up of six layers, which differ in cell composition, function, and so on. 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 layer and, due to the peculiar shape of its constituent neurons, is called the internal pyramidal layer.
Under the bark is white matter. In the depths of the hemispheres, among the white matter, there are accumulations of gray matter - the subcortical nuclei. The neurons of the cerebral hemispheres are responsible for the perception of information entering the brain from the sense organs, the control of complex forms of behavior, and participate in the processes of memory, mental and speech activity of a person. Under the bark is white matter. In the depths of the hemispheres, among the white matter, there are accumulations of gray matter - the subcortical nuclei. The neurons of the cerebral hemispheres are responsible for the perception of information entering the brain from the sense organs, the 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 the neurons of the cortex with each other and with the underlying parts of the brain.

Question 5. What is the function of the old bark?
The centers associated with complex instincts, emotions, and memory are concentrated in the old cerebral cortex. The old cortex enables the body to respond correctly to favorable and unfavorable events. This is where information about past events is stored.

Question 6. How are functions distributed between the left and right hemispheres of the large brain?
The left hemisphere is responsible for regulating the work of the organs on the right side of the body, and also perceives information from the 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 and the formation of oral and written speech.
The right hemisphere controls the organs of the left side of the body and receives information from the space on the left. Also, the right hemisphere is involved in the processes of figurative 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. What connections in the body are called direct, which are reverse?
A direct connection in the body is the path along which the signal goes from the brain to the organs; feedback is the pathway by which information about the results achieved comes back to the brain.

The forebrain is the most rostral branch of the nervous system. It consists of (bark) and basal ganglia. The latter, being in the cortex, are located between the frontal parts of the brain and the diencephalon. These nuclear structures include the shell, which together make up the striatum. It got its name due to the alternation of gray matter, consisting of nerve cells, and white. These elements of the brain, together with the pale ball, which is called the pallidum, form the striopallidar 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 composition of the basal ganglia includes having a very diverse cellular composition. In the pale ball are large and small neurons. The striatum has a similar cellular organization. The neurons of the striopallidar system receive impulses from the cerebral cortex, thalamus, and stem nuclei.

What are the functions of the subcortical nuclei?

The nuclei of the striopallidar 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. In the course of the study, it was found that it is important in the processes of memorizing movements. The irritating effect on this structure disrupts learning. It has an inhibitory effect on motor activity and its emotional components, for example, on aggressive reactions.

cerebral cortex

The forebrain includes a formation 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 is made up of a huge number of nerve cells. Due to this, the number of synoptic connections is very large; this ensures the processes of storing and processing the information received. Based on the appearance and evolution, ancient, old and new bark are distinguished. During the period of mammalian evolution, the new cortex developed especially rapidly. The ancient bark in its composition has olfactory bulbs and tracts, olfactory tubercles. The composition of the old includes the cingulate gyrus, the amygdala and the gyrus of the hippocampus. The remaining areas belong to the new crust.

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

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

2nd - called external granular. It consists of small neurons of various 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 that reaches the caudal sections 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 closer study of it showed differences 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 experiments on animals, with an irritating effect on the old bark, effects associated with the digestive system appear: chewing, swallowing, peristalsis. Also, the 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, the limbic region and the 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, and nerve fibers that form the white matter.

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

In the five-bubble stage of development, the diencephalon (thalamus, epithalamus, subthalamus, hypothalamus, and metathalamus), as well as the telencephalon, are separated 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 slot located in the median sagittal plane, this is the third cerebral ventricle (ventriculus tertius). Behind it, it passes into the aqueduct of the midbrain, and in front it connects to the two lateral ventricles of the cerebral hemispheres through two interventricular holes of Monro (forâmena interventricularia). 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), lower to the anterior cerebral commissure (comissura anterior) and further to the final plate (lamina terminalis). The posterior wall consists of a posterior commissure (comissura posterior) above the entrance to the aqueduct of the brain. The roof of the third ventricle consists of an epithelial plate. Above it is the choroid plexus. Above the plexus is the arch, and even higher - the corpus callosum. Along the side walls of the third ventricle, from the interventricular openings to the entrance to the cerebral aqueduct, there are hypothalamic grooves that separate the thalamus from the hypothalamus. The thalamus are connected to each other in the middle part of the third ventricle by adhesion - interthalamic fusion (adhesio interthalamica). The diencephalon includes several structures: the visual tubercle itself - the thalamus, metathalamus, hypothalamus, subthalamus, epithalamus, pituitary gland.

thalamus(thalamus) - the main part of the diencephalon. It makes up the lateral walls of the third ventricle. Includes actually thalamusand metathalamus(lateral and medial geniculate bodies). The shape of the thalamus is ovoid, the narrow part is directed backwards. The protruding rear part of the thalamus is called the pillow (pulvinar), and in front of the thalamus has an anterior tubercle. Below and lateral to the pillow are oblong-oval tubercles: medial (corpus geniculatum mediale) and lateral (corpus geniculatum laterale) cranked bodies. The medial surface of the thalamus forms the lateral wall of the third ventricle, the upper and lateral surfaces are adjacent to the internal capsule of the cerebral hemispheres, and the lower borders on the hypothalamus. Metathalamus(metathalamus) is represented by cranked bodies located below and lateral to the pillow. The medial geniculate body is better expressed, lies under the pillow of the optic tubercle and, along with the lower tubercles of the quadrigemina, is the subcortical center of hearing. Lateral geniculate body - a small elevation lying on the inferolateral surface of the pillow. It, together with the superior tubercles of the quadrigemina, is the subcortical visual center. In the pillow and cranked bodies are the nuclei of the same name. The external geniculate bodies include the so-called optic tracts, which are visual pathways made up of already crossed axons of retinal ganglion cells. The internal structure of the thalamus is a nuclear accumulation of gray matter separated by white matter. There are about 150 nuclei in the thalamus. They are divided into six groups: anterior, midline, medial, lateral, posterior, and pretectal. In accordance with the 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 nuclei of the thalamus 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 areas 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. Associative nuclei are the lateral and medial nuclei of the pillow. Nonspecific nuclei are concentrated mainly in the lateral, medial and middle groups of the nuclei of the thalamus. The thalamus is connected to all parts of the CNS. The thalamus is involved in the processing of sensory stimuli going to the cerebral cortex, and also regulates the wake-sleep cycle.