The cerebral cortex has in its structure. The structure of the cerebral cortex. Motor cortex areas

Brain located in the brain part of the skull. Its average weight is 1360 g. There are three large sections of the brain: the brainstem, the subcortical section and the cerebral hemisphere. 12 pairs of cranial nerves emerge from the base of the brain.

1 - upper section of the spinal cord; 2 - medulla oblongata, 3 - pons, 4 - cerebellum; 5 - midbrain; 6 - quadrigeminal; 7 - diencephalon; 8 - cerebral cortex; 9 - corpus callosum, connecting the right hemisphere to the new one; 10 - optic chiasm; 11 - olfactory bulbs.

Sections of the brain and their functions

Brain parts		Department structures	Functions
BRAINSTEM	hindbrain	Medulla Here are the nuclei with departing pairs of cranial nerves: XII - sublingual; XI - additional; X - wandering; IX - glossopharyngeal nerves	Conductor - connection between the spinal and overlying parts of the brain. Reflex: 1) regulation of the activity of the respiratory, cardiovascular and digestive systems; 2) food reflexes of salivation, chewing, swallowing; 3) protective reflexes: sneezing, blinking, coughing, vomiting;
		Pons contains nuclei: VIII - auditory; VII - facial; VI - outlet; V - trigeminal nerves.	Conductor - contains ascending and descending nerve pathways and nerve fibers connecting the cerebellar hemispheres to each other and to the cortex big brain. Reflex - responsible for vestibular and cervical reflexes that regulate muscle tone, incl. facial muscles.
		Cerebellum The cerebellar hemispheres are connected to each other and are formed by gray and white matter.	Coordination of voluntary movements and maintaining body position in space. Regulation of muscle tone and balance.
	Reticular formation- a network of nerve fibers intertwining the brain stem and diencephalon. Provides interaction between the ascending and descending pathways of the brain, coordination of various body functions and regulation of the excitability of all parts of the central nervous system.
	Midbrain	Four Hills With the nuclei of the primary visual and auditory centers. Brain stems With nuclei IV - oculomotor III - trochlear nerves.	Conductor. Reflexive: 1) indicative reflexes to visual and sound stimuli, which manifest themselves in turning the head and body; 2) regulation of muscle tone and body posture.
SUBCORTEX	Forebrain	Diencephalon: a) thalamus (optic thalamus) with nuclei ll th pair of optic nerves;	Collection and evaluation of all incoming information from the senses. Isolation and transmission of the most important information to the cerebral cortex. Regulation of emotional behavior.
		b) hypothalamus.	The highest subcortical center of the autonomic nervous system and all vital functions of the body. Ensuring consistency internal environment and metabolic processes of the body. Regulation of motivated behavior and provision of defensive reactions (thirst, hunger, satiety, fear, rage, pleasure and displeasure). Participation in the transition between sleep and wakefulness.
		Basal ganglia (subcortical nuclei)	Role in regulation and coordination motor activity(together with the thalamus and cerebellum). Participation in the creation and memorization of programs for purposeful movements, learning and memory.
CORTEX OF THE LARGE HEMISPHERES		Ancient and old bark (olfactory and visceral brain)Contains the nuclei of the 1st pair of olfactory nerves.	The ancient and old cortex, together with some subcortical structures, formslimbic system, which: 1) is responsible for innate behavioral acts and the formation of emotions; 2) provides homeostasis and control of reactions aimed at self-preservation and preservation of the species: 3 affects the regulation of autonomic functions.
		New crust	1) Carries out the highest nervous activity, is responsible for complex conscious behavior and thinking. The development of morality, will, and intelligence are associated with the activity of the cortex. 2) Performs perception, evaluation and processing of all incoming information from the senses. 3) Coordinates the activities of all body systems. 4) Provides interaction of the body with the external environment.

The brain is designed in such a way that an amazing number of nerve cells and connections between them are concentrated in a small volume. The secret lies in the fact that there are grooves and convolutions. They allow you to increase the surface area without increasing the volume of the hemispheres themselves.

We will tell you what zones of the cerebral cortex are distinguished, what functions they perform, and what cells they consist of.

What is the bark

The cortex is a superficial, fairly thin layer of the brain that covers its hemispheres. It consists mainly of vertical nerve cells (or neurons), their processes, efferent (centrifugal), afferent (centripetal) bundles, and nerve fibers. In addition to nerve cells, the cortex also includes glia.

It is the sensory centers of the cerebral cortex that ensure the body’s relationship with the outside world and help adapt to its conditions.

Scientists have found that the cortex is the youngest of all formations of the central nervous system. Her work is based on the principles of creating a conditioned reflex. It is she who maintains a person’s connection with the external environment, helps the body adapt to the changing conditions of the surrounding world.

Structural features

There are zones (divisions) of the brain, regions, subregions, and fields. Zones are primary, secondary, tertiary. Each lobe contains special cells that are capable of receiving a signal from a specific receptor. In the secondary sections there are sections of the analyzer cores. Tertiary ones receive already processed information about the shares of primary and secondary ones. They regulate conditioned reflexes. Removal or disruption of any zone makes it impossible for the entire central nervous system to function normally. Each of them has its own share of the enormous work of controlling the body and its connection with the outside world.

Brain areas and their functions are the most important achievement of evolution, which was formed over millions of years. An important feature of the structure of the cortex is the horizontal layering of neurons and fibers. They are placed very densely and form peculiar layers. This streamlines the location of neurons, their processes, and allows the distribution of functions between zones and sides of the brain. It is customary to distinguish 6 layers, which differ significantly in location, width, size, shape of neurons, and density of their placement.

The sensory area of ​​the cerebral cortex allows you to transmit and read impulses from the senses. Thus, information from sensitive receptors (visual, auditory, olfactory, tactile, etc.) enters the brain.

Neurons are also responsible for unconscious breathing activity, work of cardio-vascular system, genitourinary, digestive, etc. They are responsible for thinking, memory, speech, hearing and even a sense of pleasure. These are the main control cells of the central nervous system.

Human physiology is arranged as thoughtfully as possible. Its formation lasted millions of years, and this process does not end. It is very convenient that the neurons are located vertically. At the same time, they can be located on a small surface area, occupy very little space, and their processes can reach various parts of the cerebral hemispheres. Thanks to this dense arrangement, called columnar, a huge number of neurons can be accommodated, ensuring their maximum productivity.

pyramidal cells

Most of the nerve cells in the brain are pyramidal cells. This name is due to the fact that in their shape they are very similar to the shape of a cone. From their height, a dendrite emerges - a thick and long process, and from the base - an axon and shorter basal dendrites. They are directed deep into the white matter, which is located directly under the cortex, or branch into the cortex area.

On the dendrites there are many outgrowths, spines, which actively form so-called synaptic contacts where there are endings of nerve fibers that are sent from the subcortical zones to the cortex. The size of the pyramidal cell is 5-150 microns.

Along with pyramidal cells, spindle-shaped and stellate neurons can be found. They are responsible for receiving afferent signals and forming connections between nerve cells. Fusiform neurons create horizontal and vertical connections between different layers.

The crust is divided into ancient, old and new regions. During evolution, there is a gradual increase in the new, main surface and a slight decrease in the old, ancient area.

The ancient cortex, in addition to some other functions, is responsible for the sense of smell and helps all brain systems interact with each other. It was the smell that was for ancient man decisive in obtaining food. Now vision, hearing, speech activity. The old zone includes the hippocampus and cingulate gyrus. The occipital region of the brain is considered more ancient than, for example, the frontal region.

The new zone has the most functional differentiation. Its thickness is only 3-4 mm, but this area contains about 14 billion neurons that are directly involved in human brain activity.

If all these neurons are placed next to each other, then the length of such a row will be 1000 km. In old age, this number decreases significantly, since neurons are depleted throughout life and cannot be restored. In older people, their number decreases to 10 billion (about 700 km).

In the cortex there are a lot of glial cells that perform secretory, metabolic, trophic, and support functions.

Division into zones

Thanks to large grooves, the hemispheres are divided into lobes (frontal, parietal, occipital, temporal, insula).

Another peculiarity of the cortex is that its zones perform different functions. Each sensory system (vision, hearing, smell, touch) directs the received information to a precisely defined area. Such areas are also responsible for motor skills and the functioning of muscle fibers. The remaining departments that did not receive the task of controlling motor skills or sensory organs are called associative. Their area of ​​responsibility is speech, memory, thinking. It is the third group that occupies the largest volume.

So, according to functionality, the cortex is divided into the following zones:

• sensory;
• motor;
• associative.

Both sensory and motor divisions can be found on both hemispheres. There are also those that are represented only on one specific hemisphere, most often the left. These are two zones:

• Broca's and Wernicke's areas. They participate in creating speech and understanding it.
• Angular gyrus. It correlates two forms of words - auditory and visual.

In left-handers, these sections are located in the right hemisphere.

Paul Brodmann

There is another principle for dividing the functions of the cortex. It was called the Brodmann field map. Its creator is the German psychiatrist, psychologist, physiologist, anatomist K. Brodmann. In 1903, he described 52 cytoarchitectonic fields. These are areas of the cortex that have differences in cellular structure.

The mentioned fields differ in shape and size, nerve cells and fibers are located differently in them, and they ensure the performance of various functions.

Functions

In addition to the fact that the cortex has motor, sensory and associative zones, it is all responsible for the functioning of parts of the brain. Each zone consists of its own special neurons (pyramidal, basket-shaped, stellate, fusiform, etc.).

Based on their functions, neurons are divided into the following types:

• Insert. Participate in the processes of excitation and inhibition.
• Afferent. These are the famous stellate neurons. They receive impulses that come from the periphery (visual, auditory, tactile, etc.). They also participate in the formation of sensations. These cells transmit incoming impulses to efferent and intercalary neurons. It is curious that there are polysensory neurons that are capable of picking up different impulses from the visual thalamus.
• Efferent. These are large pyramidal cells that are responsible for transmitting impulses to the periphery, where they provide certain activities. Damage to this zone cuts off communication with certain sensory organs.

Layers of neurons

Neurons and processes on the cortex are arranged in layers. It is this layered arrangement that helps them interact as efficiently as possible. If the functioning of a certain section of the layer is disrupted, its functions can be taken over by neighboring columns of neurons. Scientists counted six such layers. Those neurons that are responsible for the same functions are located strictly above each other. It turns out that the basic unit of cortical structure is the columns that are responsible for recognizing and executing certain signals. All layers are interconnected. Most of all, the relationship is observed between the 3rd, 4th and 5th layers.

Columns

The diameter of the middle column reaches 50 µm. The cortex is designed in such a way that neighboring columns are closely interconnected and perform the same functions. Some of them inhibit the impulse, while others excite it.

When neurons are exposed to any stimulus, many columns are activated in response, and the resulting stimuli are synthesized and analyzed. This principle is called shielding. Each zone is strictly responsible for its own area of ​​work.

Vertical columns are considered to be the main functional component of the cortex. Its diameter is 500 microns. In each column there is a branching of the ascending fiber. Each contains about 1000 neural connections. When a column is excited, those adjacent to it are inhibited. The ascending path of the columns passes through all layers.

Between the basal ganglia and the cortex is the white medulla. It consists of a huge number of fibers that are directed in all directions. They are called telencephalon tracts. There are three types of such paths:

1. Projection. It provides communication with the diencephalon and parts of the central nervous system.
2. Commissural. These fibers create cerebral commissures that connect the left and right hemispheres. Commissures can also be found in the corpus callosum.
3. Associative. Connects areas of one hemisphere.

The entire surface of the cortex is correlated with signaling systems, which is why it contains a huge number of neurons (scientists put the figure at about 15 billion). The processes perform a closing function and help in transmitting impulses.

Cortex - the highest department of the central nervous system, ensuring the functioning of the body as a whole during its interaction with the environment.

brain (cerebral cortex, neocortex) is a layer of gray matter, consisting of 10-20 billion and covering the cerebral hemispheres (Fig. 1). The gray matter of the cortex makes up more than half of the total gray matter of the central nervous system. The total area of ​​the gray matter of the cortex is about 0.2 m2, which is achieved by the tortuous folding of its surface and the presence of grooves of different depths. The thickness of the cortex in its different parts ranges from 1.3 to 4.5 mm (in the anterior central gyrus). The neurons of the cortex are located in six layers oriented parallel to its surface.

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

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

Structure of the cerebral cortex

The cerebral cortex has a six-layer structure

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

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

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

Outer pyramidal layer consists of medium-sized pyramidal neurons, the processes of which are also involved in the formation of corticocortical connections between neighboring areas of the cortex.

Inner granular layer similar to the second layer in appearance of cells and arrangement of fibers. Bundles of fibers pass through the layer, connecting different areas of the cortex.

The neurons of this layer carry signals from specific nuclei of the thalamus. The layer is very well represented in the sensory areas of the cortex.

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

Layer of polymorphic cells represented predominantly by cells whose axons form corticothalamic tracts.

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

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

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

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

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

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

The listed types of fibers are involved in the creation of neural circuits and networks, the neurons of which are located at considerable distances from each other. The cortex also has a special type of local neural circuits formed by nearby neurons. These neural structures are called functional cortical columns. Neuronal columns are formed by groups of neurons located one above the other perpendicular to the surface of the cortex. The belonging of neurons to the same column can be determined by the increase in their electrical activity upon stimulation of the same receptive field. Such activity is recorded by slowly moving the recording electrode in the cortex in a perpendicular direction. If we record the electrical activity of neurons located in the horizontal plane of the cortex, we note an increase in their activity upon stimulation of various receptive fields.

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

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

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

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

Functional areas of the cerebral cortex

Based on their functional characteristics, the cortex is divided into sensory, associative and motor areas.

Sensory (sensitive, projection) areas of the cortex

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

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

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

Visual cortex

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

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

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

Auditory cortex

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

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

Vestibular cortex

Located in the superior and middle temporal gyri (areas 21-22). Its neurons receive signals from neurons of the vestibular nuclei of the brain stem, connected by afferent connections to the receptors of the semicircular canals of the vestibular apparatus. The vestibular cortex forms a feeling about the position of the body in space and the acceleration of movements. The vestibular cortex interacts with the cerebellum (via the temporopontine tract) and is involved in regulating body balance and adapting posture to carry out purposeful movements. Based on the interaction of this area with the somatosensory and association areas of the cortex, awareness of the body diagram occurs.

Olfactory cortex

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

Gustatory bark

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

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

Somatosensory cortex

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

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

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

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

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

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

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

Damage to neurons in the primary somatosensory cortex leads to decreased various types sensation on the opposite side of the body, and local damage leads to loss of sensation in a specific part of the body. Particularly vulnerable to damage to neurons of the primary somatosensory cortex is the discriminatory sensitivity of the skin, and the least sensitive is pain. Damage to neurons in the secondary somatosensory cortex may be accompanied by impairments in the ability to recognize objects by touch (tactile agnosia) and the ability to use objects (apraxia).

Motor cortex areas

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

Primary motor cortex

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

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

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

Since many Ml neurons increase electrical activity immediately before the onset of voluntary contractions, the primary motor cortex plays a leading role in controlling the activity of the motor nuclei of the brainstem and spinal cord motoneurons and initiating voluntary, goal-directed movements. Damage to the Ml field leads to muscle paresis and the inability to perform fine voluntary movements.

Secondary motor cortex

Includes areas of the premotor and supplementary motor cortex (MII, field 6). Premotor cortex located in area 6, on the lateral surface of the brain, anterior to the primary motor cortex. Its neurons receive afferent signals through the thalamus from the occipital, somatosensory, parietal associative, prefrontal areas of the cortex and cerebellum. Cortical neurons processed in it send signals along efferent fibers to the motor cortex MI, a small number to the spinal cord and a larger number to the red nuclei, nuclei of the reticular formation, basal ganglia and cerebellum. The premotor cortex plays a major role in programming and organizing movements under visual control. The cortex is involved in organizing posture and supporting movements for actions performed by the distal muscles of the limbs. Damage to the visual cortex often causes a tendency to repeat a started movement (perseveration), even if the movement achieved the goal.

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

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

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

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

With simultaneous damage to the motor areas MI and MII of the cortex, the ability to perform fine coordinated movements is lost. Point irritations in these areas of the motor zone are accompanied by activation not of individual muscles, but of an entire group of muscles that cause directed movement in the joints. These observations led to the conclusion that the motor cortex represents not so much muscles as movements.

Prefrontal cortex

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

The mechanisms that realize the transformation of a movement plan into a specific motor program, into volleys of impulses sent to certain muscle groups, remain insufficiently understood. It is believed that the intention of movement is formed due to the functions of the associative and other areas of the cortex, interacting with many structures of the brain.

Information about movement intention is transmitted to the motor areas of the frontal cortex. The motor cortex, through descending pathways, activates systems that ensure the development and use of new motor programs or the use of old ones, already practiced and stored in memory. An integral part of these systems are the basal ganglia and the cerebellum (see their functions above). Movement programs developed with the participation of the cerebellum and basal ganglia are transmitted through the thalamus to the motor areas and, above all, to the primary motor area of ​​the cortex. This area directly initiates the execution of movements, connecting certain muscles to it and ensuring the sequence of their contraction and relaxation. Commands from the cortex are transmitted to the motor centers of the brain stem, spinal motor neurons and motor neurons of the cranial nerve nuclei. In the implementation of movements, motor neurons act as the final pathway through which motor commands are transmitted directly to the muscles. Features of signal transmission from the cortex to the motor centers of the brain stem and spinal cord are described in the chapter on the central nervous system (brain stem, spinal cord).

Association cortical areas

In humans, association areas of the cortex occupy about 50% of the area of ​​the entire cerebral cortex. They are located in areas between the sensory and motor areas of the cortex. Association areas do not have clear boundaries with secondary sensory areas, both morphologically and functionally. There are parietal, temporal and frontal association areas of the cerebral cortex.

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

Neurons of the parietal associative cortex are connected by efferent connections with neurons of the prefrontal, premotor, motor areas of the frontal lobe and cingulate gyrus. Based on experimental and clinical observations, it is generally accepted that one of the functions of the area 5 cortex is the use of somatosensory information to carry out purposeful voluntary movements and manipulate objects. The function of the area 7 cortex is to integrate visual and somatosensory signals to coordinate eye movements and visually driven hand movements.

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

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

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

Temporal association cortex. Located in fields 20, 21, 22. Cortical neurons receive sensory signals from neurons of the auditory, extrastriate visual and prefrontal cortex, hippocampus and amygdala.

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

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

The reticular formation of the brainstem occupies a central position in the medulla oblongata, pons, midbrain and diencephalon.

Neurons of the reticular formation do not have direct contacts with the body's receptors. When the receptors are excited, nerve impulses enter the reticular formation along the collaterals of fibers of the autonomic and somatic nervous systems.

Physiological role. The reticular formation of the brain stem has an ascending effect on the cells of the cerebral cortex and a descending effect on the motor neurons of the spinal cord. Both of these influences of the reticular formation can be activating or inhibitory.

Afferent impulses to the cerebral cortex arrive through two pathways: specific and nonspecific. Specific neural pathway necessarily passes through the visual thalamus and carries nerve impulses to certain areas of the cerebral cortex, as a result of which some specific activity is carried out. For example, when the photoreceptors of the eyes are irritated, impulses through the visual hillocks enter the occipital region of the cerebral cortex and a person experiences visual sensations.

Nonspecific nerve pathway necessarily passes through the neurons of the reticular formation of the brain stem. Impulses to the reticular formation arrive along the collaterals of a specific nerve pathway. Thanks to numerous synapses on the same neuron of the reticular formation, impulses of different values ​​(light, sound, etc.) can converge (converge), while they lose their specificity. From the neurons of the reticular formation, these impulses do not arrive to any specific area of ​​the cerebral cortex, but spread fan-shaped throughout its cells, increasing their excitability and thereby facilitating the performance of a specific function.

In experiments on cats with electrodes implanted into the area of ​​the reticular formation of the brain stem, it was shown that irritation of its neurons causes the awakening of a sleeping animal. When the reticular formation is destroyed, the animal falls into a prolonged sleepy state. These data indicate important role reticular formation in the regulation of sleep and wakefulness. The reticular formation not only influences the cerebral cortex, but also sends inhibitory and excitatory impulses to the spinal cord to its motor neurons. Thanks to this, it participates in the regulation of skeletal muscle tone.

The spinal cord, as already indicated, also contains neurons of the reticular formation. They are believed to maintain high levels of neuronal activity in the spinal cord. The functional state of the reticular formation itself is regulated by the cerebral cortex.

Cerebellum

Features of the structure of the cerebellum. Connections of the cerebellum with other parts of the central nervous system. The cerebellum is an unpaired formation; it is located behind the medulla oblongata and the pons, borders the quadrigeminals, and is covered from above by the occipital lobes of the cerebral hemispheres. The middle part is distinguished in the cerebellum - worm and located on either side of it are two hemispheres. The surface of the cerebellum consists of gray matter called the cortex, which includes the bodies of nerve cells. Located inside the cerebellum white matter, which are the processes of these neurons.

The cerebellum has extensive connections with various parts of the central nervous system through three pairs of legs. Lower legs connect the cerebellum to the spinal cord and medulla oblongata, average- with the pons and through it with the motor area of ​​the cerebral cortex, upper-with the midbrain and hypothalamus.

The functions of the cerebellum were studied in animals in which the cerebellum was partially or completely removed, and also by recording its bioelectrical activity at rest and during stimulation.

When half of the cerebellum is removed, there is an increase in the tone of the extensor muscles, so the animal’s limbs are stretched, bending of the body and deviation of the head to the operated side, and sometimes rocking movements of the head are observed. Often movements are made in a circle in the operated direction (“manege movements”). Gradually, the noted disturbances are smoothed out, but some awkwardness of movements remains.

When the entire cerebellum is removed, more severe movement disorders occur. In the first days after surgery, the animal lies motionless with its head thrown back and limbs extended. Gradually, the tone of the extensor muscles weakens, and muscle tremors appear, especially in the neck. Subsequently, motor functions are partially restored. However, until the end of its life, the animal remains motor disabled: when walking, such animals spread their limbs wide, raise their paws high, i.e. their coordination of movements is impaired.

Motor disorders after removal of the cerebellum were described by the famous Italian physiologist Luciani. The main ones are: atonia - disappearance or weakening of muscle tone; as well as a decrease in the strength of muscle contractions. Such an animal is characterized by rapid onset muscle fatigue; and stasis - loss of the ability for continuous tetanic contractions. Animals exhibit trembling movements of the limbs and head. After removal of the cerebellum, a dog cannot immediately raise its paws; the animal makes a series of oscillatory movements with its paw before lifting it. If you stand such a dog, then its body and head constantly sway from side to side.

As a result of atony, asthenia and astasia, the animal’s coordination of movements is impaired: a shaky gait, sweeping, awkward, imprecise movements are noted. The entire complex of movement disorders caused by damage to the cerebellum is called cerebellar ataxia.

Similar disturbances are observed in humans with damage to the cerebellum.

Some time after removal of the cerebellum, as already indicated, all movement disorders gradually smooth out. If the motor area of ​​the cerebral cortex is removed from such animals, then motor disorders intensify again. Consequently, compensation (restoration) of movement disorders in case of damage to the cerebellum is carried out with the participation of the cerebral cortex, its motor area.

Research by L.A. Orbeli has shown that when the cerebellum is removed, not only a drop in muscle tone (atony) is observed, but also its incorrect distribution (dystonia). L.L. Orbeli established that the cerebellum influences the state of the receptor apparatus, as well as vegetative processes. The cerebellum has an adaptive-trophic effect on all parts of the brain through the sympathetic nervous system, it regulates metabolism in the brain and thereby contributes to the adaptation of the nervous system to changing living conditions.

Thus, the main functions of the cerebellum are coordination of movements, normal distribution of muscle tone and regulation of autonomic functions. The cerebellum exerts its influence through the nuclear formations of the midbrain and medulla oblongata, through the motor neurons of the spinal cord. Big role This influence belongs to the bilateral connection of the cerebellum with the motor zone of the cerebral cortex and the reticular formation of the brain stem.

Features of the structure of the cerebral cortex.

In phylogenetic terms, the cerebral cortex is the highest and youngest section of the central nervous system.

The cerebral cortex consists of nerve cells, their processes and neuroglia. In an adult, the thickness of the cortex in most areas is about 3 mm. The area of ​​the cerebral cortex, due to numerous folds and grooves, is 2500 cm 2. Most areas of the cerebral cortex are characterized by a six-layer arrangement of neurons. The cerebral cortex consists of 14-17 billion cells. The cellular structures of the cerebral cortex are presented pyramidal,fusiform and stellate neurons.

Stellate cells perform mainly an afferent function. Pyramid and fusiformcells- These are predominantly efferent neurons.

The cerebral cortex contains highly specialized nerve cells that receive afferent impulses from certain receptors (for example, visual, auditory, tactile, etc.). There are also neurons that are excited by nerve impulses coming from different receptors in the body. These are the so-called polysensory neurons.

The processes of nerve cells in the cerebral cortex connect its various parts with each other or establish contacts between the cerebral cortex and the underlying parts of the central nervous system. The processes of nerve cells connecting different parts of the same hemisphere are called associative, most often connecting identical areas of the two hemispheres - commissural and providing contacts of the cerebral cortex with other parts of the central nervous system and through them with all organs and tissues of the body - conductive(centrifugal). A diagram of these paths is shown in the figure.

Diagram of the course of nerve fibers in the cerebral hemispheres.

1 - short associative fibers; 2 - long associative fibers; 3 - commissural fibers; 4 - centrifugal fibers.

Neuroglial cells perform a number of important functions: they are supporting tissue, participate in brain metabolism, regulate blood flow inside the brain, secrete neurosecretion, which regulates the excitability of neurons in the cerebral cortex.

Functions of the cerebral cortex.

1) The cerebral cortex interacts between the body and the environment through unconditioned and conditioned reflexes;

2) it is the basis of higher nervous activity (behavior) of the body;

3) due to the activity of the cerebral cortex, higher mental functions are carried out: thinking and consciousness;

4) the cerebral cortex regulates and integrates the work of all internal organs and regulates such intimate processes as metabolism.

Thus, with the appearance of the cerebral cortex, it begins to control all processes occurring in the body, as well as all human activities, i.e., corticolization of functions occurs. I.P. Pavlov, characterizing the significance of the cerebral cortex, pointed out that it is the manager and distributor of all the activities of the animal and human body.

Functional meaning various areas bark brain . Localization of functions in the cerebral cortex brain . The role of individual areas of the cerebral cortex was first studied in 1870 by German researchers Fritsch and Hitzig. They showed that irritation of various parts of the anterior central gyrus and the frontal lobes themselves causes contraction of certain muscle groups on the side opposite to the irritation. Subsequently, the functional ambiguity of various areas of the cortex was revealed. It was found that the temporal lobes of the cerebral cortex are associated with auditory functions, the occipital lobes with visual functions, etc. These studies led to the conclusion that different parts of the cerebral cortex are responsible for certain functions. A doctrine was created about the localization of functions in the cerebral cortex.

According to modern concepts, there are three types of zones of the cerebral cortex: primary projection zones, secondary and tertiary (associative).

Primary projection zones- these are the central sections of the analyzer cores. They contain highly differentiated and specialized nerve cells, which receive impulses from certain receptors (visual, auditory, olfactory, etc.). In these zones, a subtle analysis of afferent impulses of various significance occurs. Damage to these areas leads to disorders of sensory or motor functions.

Secondary zones- peripheral parts of the analyzer nuclei. Here, further processing of information occurs, connections are established between stimuli of different nature. When secondary zones are damaged, complex perceptual disorders occur.

Tertiary zones (associative) . The neurons of these zones can be excited under the influence of impulses coming from receptors of various significance (from hearing receptors, photoreceptors, skin receptors, etc.). These are the so-called polysensory neurons, through which connections are established between different analyzers. Association zones receive processed information from the primary and secondary zones of the cerebral cortex. Tertiary zones play a big role in the formation of conditioned reflexes; they provide complex shapes knowledge of the surrounding reality.

The importance of different areas of the cerebral cortex . The cerebral cortex contains sensory and motor areas

Sensory cortical areas . (projective cortex, cortical sections of the analyzers). These are the areas 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 the relay sensory nuclei of the thalamus - ventral posterior, lateral and medial. The sensory areas of the cortex are formed by the projection and association zones of the main analyzers.

Skin reception area(the brain end of the skin analyzer) is represented mainly by the posterior central gyrus. Cells in this area receive impulses from tactile, pain and temperature receptors in the skin. The projection of cutaneous sensitivity within the posterior central gyrus is similar to that for the motor zone. The upper sections of the posterior central gyrus are connected with the receptors of the skin of the lower extremities, the middle ones - with receptors of the torso and arms, the lower ones - with receptors of the scalp and face. Irritation of this area in humans during neurosurgical operations causes sensations of touch, tingling, numbness, while no significant pain is ever observed.

Visual reception area(the cerebral end of the visual analyzer) is located in the occipital lobes of the cerebral cortex of both hemispheres. This area should be considered as a projection of the retina of the eye.

Auditory reception area(the brain end of the auditory analyzer) is localized in the temporal lobes of the cerebral cortex. Nerve impulses from the receptors of the cochlea of ​​the inner ear arrive here. If this zone is damaged, musical and verbal deafness may occur, when a person hears but does not understand the meaning of words; Bilateral damage to the auditory area leads to complete deafness.

Area of ​​taste perception(the brain end of the taste analyzer) is located in the lower lobes of the central gyrus. This area receives nerve impulses from taste buds oral mucosa.

Olfactory reception area(the cerebral end of the olfactory analyzer) is located in the anterior part of the piriform lobe of the cerebral cortex. Nerve impulses from the olfactory receptors of the nasal mucosa come here.

Several were found in the cerebral cortex zones responsible for speech function(brain end of the speech motor analyzer). The motor speech center (Broca's center) is located in the frontal region of the left hemisphere (in right-handed people). When it is affected, speech is difficult or even impossible. The sensory center for speech (Wernicke's center) is located in the temporal region. Damage to this area leads to speech perception disorders: the patient does not understand the meaning of words, although the ability to pronounce words is preserved. In the occipital lobe of the cerebral cortex there are zones that provide the perception of written (visual) speech. If these areas are affected, the patient does not understand what is written.

IN parietal cortex The cerebral ends of the analyzers are not found in the cerebral hemispheres; it is classified as associative zones. Among the nerve cells of the parietal region, a large number of polysensory neurons were found, which contribute to the establishment of connections between various analyzers and play a large role in the formation of reflex arcs of conditioned reflexes

Motor cortex areas The idea of ​​the role of the motor cortex is twofold. On the one hand, it was shown that electrical stimulation of certain cortical zones in animals causes movement of the limbs of the opposite side of the body, which indicated that the cortex is directly involved in the implementation of motor functions. At the same time, it is recognized that the motor area is analytical, i.e. represents the cortical section of the motor analyzer.

The brain section of the motor analyzer is represented by the anterior central gyrus and the areas of the frontal region located near it. When it is irritated, various contractions of the skeletal muscles on the opposite side occur. A correspondence has been established between certain areas of the anterior central gyrus and skeletal muscles. In the upper parts of this zone the muscles of the legs are projected, in the middle parts - the torso, in the lower parts - the head.

Of particular interest is the frontal region itself, which reaches the greatest development in humans. When the frontal areas are damaged, a person’s complex motor functions that support work and speech, as well as the body’s adaptive and behavioral reactions, are disrupted.

Any functional zone of the cerebral cortex is in both anatomical and functional contact with other zones of the cerebral cortex, with the subcortical nuclei, with the formations of the diencephalon and the reticular formation, which ensures the perfection of the functions they perform.

1. Structural and functional features of the central nervous system in the antenatal period.

In the fetus, the number of DNS neurons reaches a maximum by the 20-24th week and remains in the postnatal period without a sharp decrease until old age. Neurons are small in size and have a small total area of ​​the synaptic membrane.

Axons develop before dendrites, and neuron processes grow and branch intensively. There is an increase in the length, diameter and myelination of axons towards the end of the antenatal period.

Phylogenetically old pathways myelinate earlier than phylogenetically new ones; for example, vestibulospinal tracts from the 4th month of intrauterine development, rubrospinal tracts from the 5th-8th month, pyramidal tracts after birth.

Na- and K-channels are evenly distributed in the membrane of myelinated and unmyelinated fibers.

Excitability, conductivity, and lability of nerve fibers are significantly lower than in adults.

The synthesis of most mediators begins during intrauterine development. In the antenatal period, gamma-aminobutyric acid is an excitatory mediator and, through the Ca2 mechanism, has morphogenic effects - it accelerates the growth of axons and dendrites, synaptogenesis, and the expression of pitoreceptors.

By the time of birth, the process of differentiation of neurons in the nuclei of the medulla oblongata, midbrain, and pons is completed.

There is structural and functional immaturity of glial cells.

2. Features of the central nervous system in the neonatal period.

> The degree of myelination of nerve fibers increases, their number is 1/3 the level of an adult organism (for example, the rubrospinal tract is completely myelinated).

> The permeability of cell membranes to ions decreases. Neurons have a lower MP amplitude - about 50 mV (in adults about 70 mV).

> There are fewer synapses on neurons than in adults; the neuron membrane has receptors for synthesized mediators (acetylcholine, GAM K, serotonin, norepinephrine and dopamine). The content of neurotransmitters in the neurons of the brain of newborns is low and amounts to 10-50% of mediators in adults.

> The development of the spiny apparatus of neurons and axospinous synapses is noted; EPSPs and IPSPs have a longer duration and smaller amplitude than in adults. The number of inhibitory synapses on neurons is less than in adults.

> The excitability of cortical neurons increases.

> Mitotic activity and the possibility of neuronal regeneration disappear (or rather, sharply decrease). Proliferation and functional maturation of gliocytes continues.

H. Features of the central nervous system in infancy.

CNS maturation progresses rapidly. The most intense myelination of CNS neurons occurs at the end of the first year after birth (for example, by 6 months the myelination of nerve fibers of the cerebellar hemispheres is completed).

The speed of excitation along the axons increases.

A decrease in the duration of AP of neurons is observed, the absolute and relative refractory phases are shortened (the duration of the absolute refractory phase is 5-8 ms, the relative duration is 40-60 ms in early postnatal ontogenesis, in adults it is 0.5-2.0 and 2-10 ms, respectively).

The blood supply to the brain is relatively greater in children than in adults.

4. Features of the development of the central nervous system in other age periods.

1) Structural and functional changes in nerve fibers:

Increasing the diameters of the axial cylinders (by 4-9 years). Myelination in all peripheral nerve fibers is close to completion by 9 years, and pyramidal tracts are completed by 4 years;

Ion channels are concentrated in the region of nodes of Ranvier, and the distance between nodes increases. Continuous conduction of excitation is replaced by saltatory conduction, the speed of its conduction after 5-9 years is almost no different from the speed in adults (50-70 m/s);

Low lability of nerve fibers is noted in children of the first years of life; with age it increases (in children 5-9 years old it approaches the adult norm - 300-1,000 impulses).

2) Structural and functional changes in synapses:

Significant maturation of nerve endings (neuromuscular synapses) occurs by 7-8 years;

The terminal branches of the axon and the total area of ​​its endings increase.

Profile material for students of the Faculty of Pediatrics

1. Development of the brain in the postnatal period.

In the postnatal period, the leading role in the development of the brain is played by flows of afferent impulses through various sensory systems (the role of an information-enriched external environment). The absence of these external signals, especially during critical periods, can lead to slower development, underdevelopment of function, or even its absence

The critical period in postnatal development is characterized by intense morphofunctional maturation of the brain and a peak in the formation of NEW connections between neurons.

A general pattern of human brain development is heterochronicity of maturation: phvlogenetically older parts develop earlier than younger ones.

The medulla oblongata of a newborn is functionally more developed than other sections: ALMOST all of its centers operate - breathing, regulation of the heart and blood vessels, sucking, swallowing, coughing, sneezing, a little later the chewing center begins to function. In the regulation of muscle tone, the activity of the vestibular nuclei is reduced (reduced extensor tone) By the age of 6, differentiation of neurons and myelination of fibers are completed in these Centers, and the coordination activity of the Centers is improved

The midbrain of newborns is functionally less mature. For example, the orientation reflex and the activity of the centers that control eye movement and IR are carried out in infancy. The function of the Substantia Nigra as part of the striopallidal system reaches perfection by the age of 7 years.

The cerebellum in a newborn is structurally and functionally underdeveloped; during infancy, it undergoes increased growth and differentiation of neurons, and connections between the cerebellum and other motor centers increase. Functional maturation of the cerebellum generally begins at age 7 and is completed by age 16.

Maturation of the diencephalon includes the development of the sensory nuclei of the thalamus and hypothalamic centers

The function of the sensory nuclei of the thalamus is already carried out in the Newborn, which allows the Child to distinguish between taste, temperature, tactile and pain sensations. The functions of the nonspecific nuclei of the thalamus and the ascending activating reticular formation of the brain stem are poorly developed in the first months of life, which determines the short time of his wakefulness during the day. The nuclei of the thalamus finally develop functionally by the age of 14.

The centers of the hypothalamus in a newborn are poorly developed, which leads to imperfections in the processes of thermoregulation, regulation of water-electrolyte and other types of metabolism, and the need-motivational sphere. Most hypothalamic centers mature functionally by 4 years of age. The sexual hypothalamic centers begin to function most late (by the age of 16).

By the time of birth, the basal ganglia have varying degrees of functional activity. The phylogenetically older structure, the globus pallidus, is functionally well formed, while the function of the striatum becomes apparent by the end of 1 year. In this regard, the movements of newborns and infants are generalized and poorly coordinated. As the striopalidal system develops, the child performs more and more precise and coordinated movements and creates motor programs for voluntary movements. Structural and functional maturation of the basal ganglia is completed by the age of 7 years.

In early ontogenesis, the cerebral cortex matures later in structural and functional terms. The motor and sensory cortex develops the earliest, the maturation of which ends in the third year of life (the auditory and visual cortex is somewhat later). The critical period in the development of the association cortex begins at the age of 7 years and continues until puberty. At the same time, cortical-subcortical relationships are intensively formed. The cerebral cortex provides corticalization of body functions, regulation of voluntary movements, creation and implementation of motor stereotypes, and higher psychophysiological processes. The maturation and implementation of the functions of the cerebral cortex are described in detail in specialized materials for students of the pediatric faculty in topic 11, volume 3, topics 1-8.

The blood-cerebrospinal fluid and blood-brain barriers in the postnatal period have a number of features.

In the early postnatal period, large veins form in the choroid plexuses of the ventricles of the brain, which can deposit a significant amount of blood, thereby participating in the regulation of intracranial pressure.

The brain is the main regulator of the functions of any living organism, one of the elements. Until now, medical scientists are studying the features of the brain and discovering its incredible new capabilities. This is a very complex organ that connects our body with the external environment. The parts of the brain and their functions regulate all life processes. External receptors catch signals and inform some part of the brain about incoming stimuli (light, sound, tactile and many others). The response comes instantly. Let’s take a closer look at how our main “processor” works.

General description of the brain

The parts of the brain and their functions completely control our life processes. Consists of human brain of 25 billion neurons. This incredible number of cells forms Gray matter. The brain is covered by several membranes:

• soft;
• hard;
• arachnoid (cerebrospinal fluid circulates here).

Liquor is cerebrospinal fluid, in the brain plays the role of a shock absorber, a protector from any impact force.

Both men and women have exactly the same brain development, although their weight is different. More recently, debate has subsided that brain weight plays some role in mental development and intellectual abilities. The conclusion is clear - this is not so. The weight of the brain is approximately 2% of the total weight of a person. In men, its weight is on average 1,370 g, and in women - 1,240 g. The functions of the parts of the human brain are developed as standard, and life activity depends on them. Mental abilities depend on the quantitative connections created in the brain. Each brain cell is a neuron that generates and transmits impulses.

The cavities inside the brain are called ventricles. Paired cranial nerves go to different sections.

Functions of brain regions (table)

Each part of the brain does its own job. The table below clearly demonstrates this. The brain, like a computer, clearly performs its tasks, receiving commands from the outside world.

The table reveals the functions of the brain sections schematically and succinctly.

Below we will look at the parts of the brain in more detail.

Structure

The picture shows how the brain works. Despite this, all parts of the brain and their functions play a huge role in the functioning of the body. There are five main departments:

• final (of the total mass is 80%);
• posterior (pons and cerebellum);
• intermediate;
• oblong;
• average.

At the same time, the brain is divided into three main parts: the brain stem, the cerebellum, and the two cerebral hemispheres.

Finite brain

It is impossible to briefly describe the structure of the brain. To understand the parts of the brain and their functions, it is necessary to closely study their structure.

The telencephalon extends from the frontal to the occipital bone. Here we consider two large hemispheres: left and right. This section differs from others in the largest number of grooves and convolutions. The development and structure of the brain are closely interconnected. Experts have identified three types of bark:

• ancient (with olfactory tubercle, anterior perforated substance, semilunar subcallosal and lateral subcallosal gyrus);
• old (with the dentate gyrus - fascia and hippocambus);
• new (represents the entire remaining part of the cortex).

The hemispheres are separated by a longitudinal groove; in its depths there is the fornix and corpus callosum, which connect the hemispheres. The corpus callosum itself is lined and belongs to the neocortex. The structure of the hemispheres is quite complex and resembles a multi-level system. Here we distinguish between the frontal, temporal, parietal and occipital lobes, subcortex and cortex. The cerebral hemispheres perform a huge number of functions. It is worth noting that the left hemisphere controls the right side of the body, and the right hemisphere, on the contrary, controls the left.

Bark

The surface layer of the brain is the cortex, it is 3 mm thick and covers the hemispheres. The structure consists of vertical nerve cells with processes. The cortex also contains efferent and afferent nerve fibers, as well as neuroglia. The parts of the brain and their functions are discussed in the table, but what is the cortex? Its complex structure has horizontal layering. The structure has six layers:

• external pyramidal;
• external granular;
• internal granular;
• molecular;
• internal pyramidal;
• with spindle cells.

Each has a different width, density, and shape of neurons. Vertical bundles of nerve fibers give the cortex vertical striations. The area of ​​the cortex is approximately 2,200 square centimeters, the number of neurons here reaches ten billion.

Parts of the brain and their functions: cortex

The cortex controls several specific functions of the body. Each share is responsible for its own parameters. Let's take a closer look at the functions associated with calving:

• temporal - controls the sense of smell and hearing;
• parietal - responsible for taste and touch;
• occipital - vision;
• frontal - complex thinking, movement and speech.

Each neuron contacts other neurons, there are up to ten thousand contacts (gray matter). Nerve fibers are white matter. A certain part unites the hemispheres of the brain. White matter includes three types of fibers:

• association ones connect different cortical areas in one hemisphere;
• commissural connect the hemispheres to each other;
• projection ones communicate with lower formations and have analyzer paths.

Considering the structure and functions of parts of the brain, it is necessary to emphasize the role of gray and white matter. The hemispheres have (gray matter) inside, their main function is the transmission of information. White matter is located between the cerebral cortex and the basal ganglia. There are four parts here:

• between the grooves in the gyri;
• in the outer places of the hemispheres;
• included in the inner capsule;
• located in the corpus callosum.

The white matter located here is formed by nerve fibers and connects the gyral cortex with the underlying sections. form the subcortex of the brain.

The telencephalon controls all the vital functions of the body, as well as the intellectual abilities of a person.

Diencephalon

The parts of the brain and their functions (the table is presented above) include the diencephalon. If you look in more detail, it is worth saying that it consists of ventral and dorsal parts. The ventral region includes the hypothalamus, the dorsal region includes the thalamus, metathalamus, and epithalamus.

The thalamus is an intermediary that sends the received irritations to the hemispheres. It is often called the “visual thalamus.” It helps the body quickly adapt to changes in external environment. The thalamus is connected to the cerebellum via the limbic system.

The hypothalamus controls autonomic functions. The influence goes through the nervous system, and, of course, the endocrine glands. Regulates the functioning of the endocrine glands, controls metabolism. The pituitary gland is located directly below it. Body temperature, cardiovascular and digestive systems are regulated. The hypothalamus also controls our eating and drinking behavior, regulates wakefulness and sleep.

Rear

The hindbrain includes the pons, which is located in front, and the cerebellum, which is located behind. Studying the structure and functions of parts of the brain, let's take a closer look at the structure of the pons: the dorsal surface is covered by the cerebellum, the ventral surface is represented by a fibrous structure. The fibers are directed transversely in this section. On each side of the pons they extend to the middle cerebellar peduncle. In appearance, the bridge resembles a thickened white cushion located above the medulla oblongata. The nerve roots exit into the bulbar-pontine groove.

The structure of the posterior bridge: the frontal section shows that there is a section of the anterior (large ventral) and posterior (small dorsal) parts. The boundary between them is the trapezoidal body, the transverse thick fibers of which are considered to be the auditory tract. The conduction function is entirely dependent on the hindbrain.

Cerebellum (small brain)

The table “Brain Division, Structure, Functions” indicates that the cerebellum is responsible for coordination and movement of the body. This section is located behind the bridge. The cerebellum is often referred to as the “little brain.” It occupies the posterior cranial fossa and covers the rhomboid fossa. The mass of the cerebellum ranges from 130 to 160 g. The cerebral hemispheres are located above, which are separated by a transverse fissure. The lower part of the cerebellum is adjacent to the medulla oblongata.

Here there are two hemispheres, the lower, upper surface and the vermis. The boundary between them is called a horizontal deep gap. Many fissures cut the surface of the cerebellum, between them there are thin convolutions (ridges). Between the grooves there are groups of gyri, divided into lobules; they represent the lobes of the cerebellum (posterior, flocnonodular, anterior).

The cerebellum contains both the gray and the gray is located in the periphery, forms the cortex with molecular and piriform neurons, and the granular layer. Under the cortex there is a white substance that penetrates into the convolutions. The white matter contains inclusions of gray (its nuclei). In cross-section, this relationship looks like a tree. Those who know the structure of the human brain and the functions of its parts will easily answer that the cerebellum is a regulator of the coordination of movements of our body.

Midbrain

The midbrain is located in the anterior pons and extends to the papillary bodies, as well as to the optic tracts. Here, clusters of nuclei are identified, which are called quadrigeminal tubercles. The structure and functions of the brain sections (table) indicate that this section is responsible for latent vision, the orientation reflex, gives orientation to reflexes to visual and sound stimuli, and also maintains the tone of the muscles of the human body.

Medulla oblongata: stem part

The medulla oblongata is a natural extension of the spinal cord. That is why there are many similarities in the structure. This becomes especially clear if we examine the white matter in detail. Its short and long nerve fibers represent it. The gray matter is represented here in the form of nuclei. The parts of the brain and their functions (the table above) indicates that the medulla oblongata controls our balance, coordination, regulates metabolism, controls breathing and blood circulation. It is also responsible for such important reflexes of our body as sneezing and coughing, vomiting.

The brainstem is divided into the hindbrain and midbrain. The trunk is called the middle, medulla oblongata, pons and diencephalon. Its structure consists of descending and ascending pathways connecting the trunk with the spinal cord and brain. This part monitors heartbeat, breathing, and articulate speech.