What is the human brain? Brain: structure and functions, general description. Functions of the diencephalon

The content of the article

an organ that coordinates and regulates all vital functions of the body and controls behavior. All our thoughts, feelings, sensations, desires and movements are associated with the work of the brain, and if it does not function, the person goes into a vegetative state: the ability to perform any actions, sensations or reactions to external influences is lost. This article is devoted to the human brain, which is more complex and highly organized than the animal brain. However, there are significant similarities in the structure of the brain of humans and other mammals, as well as most vertebrate species.

The brain is a symmetrical structure, like most other parts of the body. At birth, its weight is approximately 0.3 kg, while in an adult it is approx. 1.5 kg. When examining the brain externally, attention is primarily drawn to the two cerebral hemispheres, which hide deeper formations. The surface of the hemispheres is covered with grooves and convolutions, increasing the surface of the cortex (the outer layer of the brain). At the back is the cerebellum, the surface of which is more finely indented. Below the cerebral hemispheres is the brain stem, which passes into the spinal cord. Nerves extend from the trunk and spinal cord, along which information from internal and external receptors flows to the brain, and in the opposite direction signals go to the muscles and glands. 12 pairs of cranial nerves arise from the brain.

Inside the brain, there is gray matter, consisting mainly of nerve cell bodies and forming the cortex, and white matter - nerve fibers that form pathways (tracts) connecting various parts of the brain, and also form nerves that extend beyond the central nervous system and go to to various organs.

The brain and spinal cord are protected by bone cases - the skull and spine. Between the substance of the brain and the bone walls there are three membranes: the outer one is the dura mater, the inner one is the soft one, and between them is the thin arachnoid membrane. The space between the membranes is filled with cerebrospinal fluid, which is similar in composition to blood plasma, is produced in the intracerebral cavities (ventricles of the brain) and circulates in the brain and spinal cord, supplying it with nutrients and other factors necessary for life.

Blood supply to the brain is provided primarily by the carotid arteries; at the base of the brain they are divided into large branches going to its various parts. Although the brain weighs only 2.5% of the body's weight, it constantly receives, day and night, 20% of the blood circulating in the body and, accordingly, oxygen. The energy reserves of the brain itself are extremely small, so it is extremely dependent on the supply of oxygen. There are protective mechanisms that can maintain cerebral blood flow in the event of bleeding or injury. A feature of cerebral circulation is also the presence of the so-called. blood-brain barrier. It consists of several membranes that limit the permeability of the vascular walls and the flow of many compounds from the blood into the brain matter; thus, this barrier performs protective functions. For example, many medicinal substances do not penetrate through it.

BRAIN CELLS

The cells of the central nervous system are called neurons; their function is information processing. There are from 5 to 20 billion neurons in the human brain. The brain also includes glial cells; there are about 10 times more of them than neurons. Glia fill the space between neurons, forming the supporting framework of nervous tissue, and also perform metabolic and other functions.

The neuron, like all other cells, is surrounded by a semipermeable (plasma) membrane. Two types of processes extend from the cell body - dendrites and axons. Most neurons have many branching dendrites but only one axon. Dendrites are usually very short, while the length of the axon varies from a few centimeters to several meters. The neuron body contains a nucleus and other organelles, the same as in other cells of the body ( see also CELL).

Nerve impulses.

The transmission of information in the brain, as well as in the nervous system as a whole, is carried out through nerve impulses. They spread in the direction from the cell body to the terminal section of the axon, which can branch, forming many endings that contact other neurons through a narrow gap - the synapse; the transmission of impulses through the synapse is mediated by chemicals - neurotransmitters.

A nerve impulse usually originates in dendrites - thin branching processes of a neuron that specialize in receiving information from other neurons and transmitting it to the neuron's body. There are thousands of synapses on dendrites and, to a lesser extent, on the cell body; It is through synapses that the axon, carrying information from the neuron body, transmits it to the dendrites of other neurons.

The axon terminal, which forms the presynaptic part of the synapse, contains small vesicles containing the neurotransmitter. When the impulse reaches the presynaptic membrane, the neurotransmitter from the vesicle is released into the synaptic cleft. The axon terminal contains only one type of neurotransmitter, often in combination with one or more types of neuromodulators ( see below Neurochemistry of the brain).

The neurotransmitter released from the presynaptic membrane of the axon binds to receptors on the dendrites of the postsynaptic neuron. The brain uses a variety of neurotransmitters, each of which binds to its own specific receptor.

Connected to receptors on dendrites are channels in the semipermeable postsynaptic membrane, which control the movement of ions across the membrane. At rest, a neuron has an electrical potential of 70 millivolts (resting potential), with the inner side of the membrane being negatively charged relative to the outer. Although there are various transmitters, they all have either an excitatory or inhibitory effect on the postsynaptic neuron. The exciting influence is realized through increasing the flow of certain ions, mainly sodium and potassium, through the membrane. As a result, the negative charge of the inner surface decreases - depolarization occurs. The inhibitory effect is carried out mainly through a change in the flow of potassium and chlorides, as a result of which the negative charge of the inner surface becomes greater than at rest, and hyperpolarization occurs.

The function of a neuron is to integrate all the influences perceived through the synapses on its body and dendrites. Because these influences can be excitatory or inhibitory and not coincident in time, the neuron must calculate the overall effect of synaptic activity as a function of time. If the excitatory effect prevails over the inhibitory effect and the depolarization of the membrane exceeds the threshold value, activation of a certain part of the neuron membrane occurs - in the area of ​​​​the base of its axon (axon tubercle). Here, as a result of the opening of channels for sodium and potassium ions, an action potential (nerve impulse) occurs.

This potential propagates further along the axon to its end at a speed of 0.1 m/s to 100 m/s (the thicker the axon, the higher the conduction speed). When an action potential reaches the axon terminal, another type of ion channel that depends on the potential difference is activated: calcium channels. Through them, calcium enters the axon, which leads to the mobilization of vesicles with the neurotransmitter, which approach the presynaptic membrane, merge with it and release the neurotransmitter into the synapse.

Myelin and glial cells.

Many axons are covered with a myelin sheath, which is formed by the repeatedly twisted membrane of glial cells. Myelin is composed primarily of lipids, which gives the white matter of the brain and spinal cord its characteristic appearance. Thanks to the myelin sheath, the speed of the action potential along the axon increases, since ions can move through the axon membrane only in places not covered with myelin - the so-called. Ranvier interceptions. Between interceptions, impulses are conducted along the myelin sheath as if through an electrical cable. Since the opening of a channel and the passage of ions through it takes some time, eliminating the constant opening of the channels and limiting their scope to small areas of the membrane that are not covered with myelin speeds up the conduction of impulses along the axon by about 10 times.

Only a portion of glial cells participate in the formation of the myelin sheath of nerves (Schwann cells) or nerve tracts (oligodendrocytes). Much more numerous glial cells (astrocytes, microgliocytes) perform other functions: they form the supporting framework of nervous tissue, provide its metabolic needs and recovery after injuries and infections.

HOW THE BRAIN WORKS

Let's look at a simple example. What happens when we pick up a pencil lying on the table? The light reflected from the pencil is focused in the eye by the lens and directed to the retina, where the image of the pencil appears; it is perceived by the corresponding cells, from which the signal goes to the main sensitive transmitting nuclei of the brain, located in the thalamus (visual thalamus), mainly in that part of it called the lateral geniculate body. There, numerous neurons are activated that respond to the distribution of light and darkness. The axons of the neurons of the lateral geniculate body go to the primary visual cortex, located in the occipital lobe of the cerebral hemispheres. Impulses coming from the thalamus to this part of the cortex are converted into a complex sequence of discharges of cortical neurons, some of which react to the boundary between the pencil and the table, others to the corners in the pencil’s image, etc. From the primary visual cortex, information travels along axons to the associative visual cortex, where image recognition occurs, in this case a pencil. Recognition in this part of the cortex is based on previously accumulated knowledge about the external outlines of objects.

Planning a movement (i.e., picking up a pencil) probably occurs in the frontal cortex of the cerebral hemispheres. In the same area of ​​the cortex there are motor neurons that give commands to the muscles of the hand and fingers. The approach of the hand to the pencil is controlled by the visual system and interoceptors that perceive the position of muscles and joints, information from which is sent to the central nervous system. When we take a pencil in our hand, the pressure receptors in our fingertips tell us whether our fingers have a good grip on the pencil and how much force must be exerted to hold it. If we want to write our name in pencil, other information stored in the brain will need to be activated to enable this more complex movement, and visual control will help improve its accuracy.

The example above shows that performing a fairly simple action involves large areas of the brain, extending from the cortex to the subcortical regions. In more complex behaviors involving speech or thinking, other neural circuits are activated, covering even larger areas of the brain.

MAIN PARTS OF THE BRAIN

The brain can be roughly divided into three main parts: the forebrain, the brainstem, and the cerebellum. The forebrain contains the cerebral hemispheres, thalamus, hypothalamus and pituitary gland (one of the most important neuroendocrine glands). The brain stem consists of the medulla oblongata, pons (pons) and midbrain.

Large hemispheres

- the largest part of the brain, accounting for approximately 70% of its weight in adults. Normally, the hemispheres are symmetrical. They are connected to each other by a massive bundle of axons (corpus callosum), which ensures the exchange of information.

Each hemisphere consists of four lobes: frontal, parietal, temporal and occipital. The frontal cortex contains centers that regulate motor activity, as well as, probably, centers for planning and foresight. In the cortex of the parietal lobes, located behind the frontal lobes, there are zones of bodily sensations, including touch and joint-muscular sensation. Adjacent to the parietal lobe is the temporal lobe, in which the primary auditory cortex, as well as the centers of speech and other higher functions, are located. The posterior parts of the brain are occupied by the occipital lobe, located above the cerebellum; its cortex contains areas of visual sensation.

Areas of the cortex not directly associated with the regulation of movements or the analysis of sensory information are called the associative cortex. In these specialized zones, associative connections are formed between different areas and parts of the brain and the information coming from them is integrated. The association cortex supports complex functions such as learning, memory, language, and thinking.

Subcortical structures.

Below the cortex lies a number of important brain structures, or nuclei, which are collections of neurons. These include the thalamus, basal ganglia and hypothalamus. The thalamus is the main sensory transmitting nucleus; it receives information from the senses and, in turn, forwards it to the appropriate parts of the sensory cortex. It also contains nonspecific zones that are connected to almost the entire cortex and probably provide the processes of its activation and maintenance of wakefulness and attention. The basal ganglia are a collection of nuclei (the so-called putamen, globus pallidus and caudate nucleus) that are involved in the regulation of coordinated movements (starting and stopping them).

The hypothalamus is a small region at the base of the brain that lies beneath the thalamus. Richly supplied with blood, the hypothalamus is an important center that controls the homeostatic functions of the body. It produces substances that regulate the synthesis and release of pituitary hormones. The hypothalamus contains many nuclei that perform specific functions, such as regulation of water metabolism, distribution of stored fat, body temperature, sexual behavior, sleep and wakefulness.

Brain stem

located at the base of the skull. It connects the spinal cord to the forebrain and consists of the medulla oblongata, pons, midbrain and diencephalon.

Through the midbrain and diencephalon, as well as through the entire trunk, there are motor pathways going to the spinal cord, as well as some sensory pathways from the spinal cord to the overlying parts of the brain. Below the midbrain there is a bridge connected by nerve fibers to the cerebellum. The lowest part of the trunk - the medulla oblongata - directly passes into the spinal cord. The medulla oblongata contains centers that regulate the activity of the heart and breathing depending on external circumstances, as well as controlling blood pressure, peristalsis of the stomach and intestines.

At the level of the brainstem, the pathways connecting each of the cerebral hemispheres with the cerebellum intersect. Therefore, each hemisphere controls the opposite side of the body and is connected to the opposite hemisphere of the cerebellum.

Cerebellum

located under the occipital lobes of the cerebral hemispheres. Through the pathways of the bridge, it is connected to the overlying parts of the brain. The cerebellum regulates subtle automatic movements, coordinating the activity of various muscle groups when performing stereotypical behavioral acts; he also constantly controls the position of the head, torso and limbs, i.e. participates in maintaining balance. According to recent data, the cerebellum plays a very significant role in the formation of motor skills, helping to remember sequences of movements.

Other systems.

The limbic system is a broad network of interconnected areas of the brain that regulate emotional states and support learning and memory. The nuclei that form the limbic system include the amygdala and hippocampus (part of the temporal lobe), as well as the hypothalamus and the so-called nuclei. transparent septum (located in the subcortical regions of the brain).

The reticular formation is a network of neurons that extends through the entire brainstem to the thalamus and is further connected to large areas of the cortex. It is involved in the regulation of sleep and wakefulness, maintains the active state of the cortex and promotes focusing attention on certain objects.

ELECTRICAL ACTIVITY OF THE BRAIN

Using electrodes placed on the surface of the head or inserted into the brain, it is possible to record the electrical activity of the brain caused by the discharges of its cells. Recording the electrical activity of the brain using electrodes on the surface of the head is called an electroencephalogram (EEG). It does not allow recording the discharge of an individual neuron. Only as a result of the synchronized activity of thousands or millions of neurons do noticeable oscillations (waves) appear in the recorded curve.

With continuous recording of the EEG, cyclic changes are revealed that reflect the general level of activity of the individual. In a state of active wakefulness, the EEG records low-amplitude, non-rhythmic beta waves. In a state of relaxed wakefulness with eyes closed, alpha waves predominate at a frequency of 7–12 cycles per second. The onset of sleep is indicated by the appearance of high-amplitude slow waves (delta waves). During periods of dreaming sleep, beta waves reappear on the EEG, and the EEG may give the false impression that the person is awake (hence the term “paradoxical sleep”). Dreams are often accompanied by rapid eye movements (with the eyelids closed). Therefore, dreaming sleep is also called rapid eye movement sleep ( see also DREAM). EEG allows you to diagnose some brain diseases, in particular epilepsy ( cm. EPILEPSY).

If you record the electrical activity of the brain during the action of a certain stimulus (visual, auditory or tactile), then you can identify the so-called. evoked potentials are synchronous discharges of a certain group of neurons that occur in response to a specific external stimulus. The study of evoked potentials made it possible to clarify the localization of brain functions, in particular, to associate speech function with certain areas of the temporal and frontal lobes. This study also helps to assess the state of sensory systems in patients with sensory impairment.

BRAIN NEUROCHEMISTRY

Some of the most important neurotransmitters in the brain include acetylcholine, norepinephrine, serotonin, dopamine, glutamate, gamma-aminobutyric acid (GABA), endorphins and enkephalins. In addition to these well-known substances, there are probably a large number of others functioning in the brain that have not yet been studied. Some neurotransmitters only act in certain areas of the brain. Thus, endorphins and enkephalins are found only in the pathways that conduct pain impulses. Other neurotransmitters, such as glutamate or GABA, are more widely distributed.

Action of neurotransmitters.

As already noted, neurotransmitters, acting on the postsynaptic membrane, change its conductivity for ions. This often occurs through activation of a second messenger system in the postsynaptic neuron, such as cyclic adenosine monophosphate (cAMP). The action of neurotransmitters can be modified by another class of neurochemicals - peptide neuromodulators. Released by the presynaptic membrane simultaneously with the transmitter, they have the ability to enhance or otherwise alter the effect of transmitters on the postsynaptic membrane.

The recently discovered endorphin-enkephalin system is important. Enkephalins and endorphins are small peptides that inhibit the conduction of pain impulses by binding to receptors in the central nervous system, including in the higher zones of the cortex. This family of neurotransmitters suppresses the subjective perception of pain.

Psychoactive drugs

– substances that can specifically bind to certain receptors in the brain and cause changes in behavior. Several mechanisms of their action have been identified. Some affect the synthesis of neurotransmitters, others affect their accumulation and release from synaptic vesicles (for example, amphetamine causes the rapid release of norepinephrine). The third mechanism is to bind to receptors and imitate the action of a natural neurotransmitter, for example, the effect of LSD (lysergic acid diethylamide) is attributed to its ability to bind to serotonin receptors. The fourth type of drug action is receptor blockade, i.e. antagonism with neurotransmitters. Commonly used antipsychotics such as phenothiazines (eg, chlorpromazine or aminazine) block dopamine receptors and thereby reduce the effect of dopamine on postsynaptic neurons. Finally, the last common mechanism of action is inhibition of neurotransmitter inactivation (many pesticides interfere with the inactivation of acetylcholine).

It has long been known that morphine (a purified product of the opium poppy) has not only a pronounced analgesic effect, but also the property of causing euphoria. That is why it is used as a drug. The effect of morphine is associated with its ability to bind to receptors of the human endorphin-enkephalin system ( see also DRUG). This is just one of many examples that a chemical substance of a different biological origin (in this case, plant) can influence the functioning of the brain of animals and humans by interacting with specific neurotransmitter systems. Another well-known example is curare, which is derived from a tropical plant and can block acetylcholine receptors. The Indians of South America lubricated arrowheads with curare, using its paralyzing effect associated with the blockade of neuromuscular transmission.

BRAIN RESEARCH

Brain research is difficult for two main reasons. Firstly, direct access to the brain, which is well protected by the skull, is not possible. Secondly, brain neurons do not regenerate, so any intervention can lead to irreversible damage.

Despite these difficulties, research on the brain and some forms of its treatment (primarily neurosurgery) have been known since ancient times. Archaeological finds show that already in ancient times man performed craniotomy to gain access to the brain. Particularly intensive brain research was carried out during periods of war, when a variety of traumatic brain injuries could be observed.

Brain damage as a result of a wound at the front or an injury received in peacetime is a kind of analogue of an experiment in which certain areas of the brain are destroyed. Since this is the only possible form of “experiment” on the human brain, experiments on laboratory animals became another important method of research. By observing the behavioral or physiological consequences of damage to a particular brain structure, one can judge its function.

The electrical activity of the brain in experimental animals is recorded using electrodes placed on the surface of the head or brain or inserted into the brain substance. In this way, it is possible to determine the activity of small groups of neurons or individual neurons, as well as to detect changes in ion flows across the membrane. Using a stereotactic device, which allows you to insert an electrode into a certain point of the brain, its inaccessible deep parts are examined.

Another approach is to remove small sections of living brain tissue, then maintain it in the form of a slice placed in a nutrient medium, or the cells are isolated and studied in cell cultures. In the first case, it is possible to study the interaction of neurons, in the second - the vital activity of individual cells.

When studying the electrical activity of individual neurons or their groups in different areas of the brain, the initial activity is usually recorded first, then the effect of a particular influence on cell function is determined. Another method uses an electrical impulse through an implanted electrode to artificially activate nearby neurons. This way you can study the effect of certain areas of the brain on other areas of the brain. This method of electrical stimulation has proven useful in the study of brainstem activating systems passing through the midbrain; it is also used when trying to understand how learning and memory processes occur at the synaptic level.

Already a hundred years ago it became clear that the functions of the left and right hemispheres are different. The French surgeon P. Broca, observing patients with cerebrovascular accident (stroke), discovered that only patients with damage to the left hemisphere suffered from speech disorders. Subsequently, studies of hemispheric specialization were continued using other methods, such as EEG recording and evoked potentials.

In recent years, sophisticated technologies have been used to obtain images (visualization) of the brain. Thus, computed tomography (CT) has revolutionized clinical neurology, making it possible to obtain intravital detailed (layer-by-layer) images of brain structures. Another imaging technique, positron emission tomography (PET), provides a picture of the metabolic activity of the brain. In this case, a person is injected with a short-lived radioisotope, which accumulates in various parts of the brain, and the more, the higher their metabolic activity. Using PET, it was also shown that speech functions in the majority of those examined were associated with the left hemisphere. Because the brain operates using a huge number of parallel structures, PET provides information about brain function that cannot be obtained using single electrodes.

As a rule, brain studies are carried out using a complex of methods. For example, the American neurobiologist R. Sperry and his colleagues, as a therapeutic procedure, performed transection of the corpus callosum (a bundle of axons connecting both hemispheres) in some patients with epilepsy. Subsequently, the specialization of the hemispheres was studied in these split-brain patients. It was found that the dominant (usually left) hemisphere is primarily responsible for speech and other logical and analytical functions, while the non-dominant hemisphere analyzes the spatiotemporal parameters of the external environment. So, it is activated when we listen to music. The mosaic pattern of brain activity suggests that numerous specialized areas exist within the cortex and subcortical structures; the simultaneous activity of these areas supports the concept of the brain as a parallel processing computing device.

COMPARATIVE ANATOMY

The brain structure of different vertebrate species is remarkably similar. When compared at the neuronal level, there are clear similarities in characteristics such as the neurotransmitters used, fluctuations in ion concentrations, cell types and physiological functions. Fundamental differences are revealed only when compared with invertebrates. Invertebrate neurons are much larger; often they are connected to each other not by chemical, but by electrical synapses, which are rarely found in the human brain. In the nervous system of invertebrates, some neurotransmitters are detected that are not characteristic of vertebrates.

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The brain is a walnut-shaped organ, protected by the bones of the skull and consisting of a huge number of nerve cells. The bodies of these nerve cells are called gray matter, and their fibers are called white matter. The deep grooves on the surface of the brain account for a huge surface area of ​​324 square inches (2,090 cm2). A man's brain is typically heavier than a woman's: an adult male brain weighs about 3 pounds (1.4 kg), an adult female brain weighs about 2.8 pounds (1.3 kg). However, there is no direct evidence of a relationship between brain size and intelligence.

Brain Facts

. The brain alone consumes a fifth of the total oxygen required by the body.

The human brain reaches its full size by age 6.

The brain is the source of emotions and mood, as well as the seat of the mind.

Brain

The brain is the main part of the central nervous system, which also includes the spinal cord. It controls all processes occurring in the body. Most signals from the brain are transmitted to the body through the spinal cord.

Brain structure

The brain is divided into three main areas:

1 The forebrain, where memory, reason and intelligence reside. It is also involved in body movement, sensation, speech, hearing and vision.

2 The midbrain, which functions as a relay station for messages to and from the brain. Here eye movements are controlled.

3 The rhomboid brain, which coordinates complex movements of the body, especially the arms and legs.

Forebrain

Rising above the brainstem (the thin rod at the top of the spinal cord), the brain fills the entire space at the front of the skull. The forebrain, or the brain itself, consists of two hemispheres (A). Inside the brain is the corpus callosum (b) connecting the two hemispheres, the thalamus (V) and hypothalamus (G). The thalamus (thalamus) and hypothalamus are also part of a region of the brain called the diencephalon.

Midbrain

Midbrain (d)- this is the shortest and highest part of the brain stem (which also includes the rhombencephalon). The midbrain is a relay station between the reticular system (lower on the brain stem) and the forebrain above it. The midbrain is also involved in controlling eye movements and pupil size.

Diamond brain

This includes all major structures under the midbrain, including the pons (e), medulla (and) and cerebellum (h). The pons and medulla oblongata are the main part of the brain stem that connects to the spinal cord. The medulla oblongata is responsible for controlling breathing, heart rate and other vital processes. The pons is the connection between the cerebellum and the rest of the brain. The cerebellum coordinates body movements.

The brain is the main regulator of all functions of a living organism. It is one of the elements of the central nervous system. The structure and functions of the brain are still the subject of study by doctors.

general description

The human brain consists of 25 billion neurons. These cells are the gray matter. The brain is covered with membranes:

• hard;
• soft;
• arachnoid (the so-called cerebrospinal fluid, which is cerebrospinal fluid, circulates through its channels). Liquor is a shock absorber that protects the brain from shock.

Despite the fact that the brains of women and men are equally developed, they have different masses. So, among representatives of the stronger sex, its weight is on average 1375 g, and among women - 1245 g. The weight of the brain is about 2% of the weight of a person of normal build. It has been established that the level of a person’s mental development is in no way related to his weight. It depends on the number of connections created by the brain.

Brain cells are neurons that generate and transmit impulses and glia that perform additional functions. Inside the brain there are cavities called ventricles. Paired cranial nerves (12 pairs) depart from it to different parts of the body. The functions of the parts of the brain are very different. The vital functions of the body completely depend on them.

Structure

The structure of the brain, pictures of which are presented below, can be considered in several aspects. So there are 5 main parts of the brain:

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

The brain is also divided into 3 parts:

• cerebral hemispheres;
• brain stem;
• cerebellum.

Structure of the brain: drawing with the names of the departments.

Finite brain

The structure of the brain cannot be briefly described, since without studying its structure it is impossible to understand its functions. The telencephalon extends from the occipital to the frontal bone. It distinguishes 2 large hemispheres: left and right. It differs from other parts of the brain by the presence of a large number of convolutions and grooves. The structure and development of the brain are closely interrelated. Experts distinguish 3 types of cerebral cortex:

• ancient, which includes the olfactory tubercle; perforated anterior substance; semilunar, subcallosal and lateral subcallosal gyri;
• old, which includes the hippocambus and dentate gyrus (fascia);
• new, represented by the rest of the cortex.

The structure of the cerebral hemispheres: they are separated by a longitudinal groove, in the depths of which the fornix and. They connect the hemispheres of the brain. The corpus callosum is a new cortex made up of nerve fibers. There is a vault underneath it.

The structure of the cerebral hemispheres is presented as a multi-level system. So they distinguish between lobes (parietal, frontal, occipital, temporal), cortex and subcortex. The cerebral hemispheres perform many functions. The right hemisphere controls the left half of the body, and the left hemisphere controls the right. They complement each other.

Bark

The hypothalamus is a subcortical center in which the regulation of autonomic functions occurs. Its influence occurs through the endocrine glands and the nervous system. It is involved in the regulation of the functioning of some endocrine glands and metabolism. Below it is the pituitary gland. Thanks to it, body temperature, digestive and cardiovascular systems are regulated. The hypothalamus regulates wakefulness and sleep, shapes drinking and eating behavior.

hindbrain

This section consists of the pons located in front and the cerebellum located behind it. The structure of the cerebral pons: its dorsal surface is covered by the cerebellum, and its ventral surface has a fibrous structure. These fibers are directed transversely. On each side of the bridge they pass into the cerebellar middle peduncle. The bridge itself looks like a white thick roller. It is located above the medulla oblongata. The nerve roots emerge from the bulbar-pontine groove. Hindbrain: structure and functions - on the frontal section of the bridge, it is noticeable that it consists of a large ventral (anterior) and a small dorsal (posterior) part. The border between them is the trapezoidal body. Its thick transverse fibers belong to the auditory tract. The hindbrain provides the conductive function.

Often called the small brain, it is located behind the pons. It covers the rhomboid fossa and occupies almost the entire posterior fossa of the skull. Its mass is 120-150 g. The cerebral hemispheres hang above the cerebellum, separated from it by a transverse fissure of the brain. The inferior surface of the cerebellum is adjacent to the medulla oblongata. It distinguishes 2 hemispheres, as well as the upper and lower surfaces and the worm. The boundary between them is called a deep horizontal gap. The surface of the cerebellum is cut by many slits, between which there are thin ridges (gyri) of the medulla. The groups of gyri located between the deep grooves are lobules, which, in turn, make up the lobes of the cerebellum (anterior, flocnonodular, posterior).

There are 2 types of substance in the cerebellum. Gray is on the periphery. It forms the cortex, which contains the molecular, pyriform neurons and granular layer. The white matter of the brain is always located under the cortex. Likewise, in the cerebellum it forms the brain body. It penetrates into all convolutions in the form of white stripes covered with gray matter. The white matter of the cerebellum itself contains interspersed gray matter (nuclei). In cross-section, their relationship resembles a tree. Our coordination of movement depends on the functioning of the cerebellum.

Midbrain

This section extends from the anterior edge of the pons to the papillary bodies and optic tracts. It contains a cluster of nuclei, which are called quadrigeminal tubercles. The midbrain is responsible for hidden vision. It also contains the center of the orienting reflex, which ensures the body turns in the direction of a sharp noise.

Located in the brain section of the skull, which protects it from mechanical damage. On the outside, it is covered with meninges with numerous blood vessels. The weight of an adult reaches 1100–1600 g. The brain can be divided into three sections: posterior, middle and anterior.

The rear ones include medulla, pons and cerebellum, and to the anterior - diencephalon and cerebral hemispheres. All sections, including the cerebral hemispheres, form the brain stem. Inside the cerebral hemispheres and in the brain stem there are cavities filled with fluid. The brain consists of white matter and the form of conductors that connect parts of the brain to each other, and gray matter located inside the brain in the form of nuclei and covering the surface of the hemispheres and cerebellum in the form of the cortex.

Functions of parts of the brain:

Oblongata - is a continuation of the spinal cord, contains nuclei that control the vegetative functions of the body (breathing, heart function, digestion). In its nuclei there are centers of digestive reflexes (salivation, swallowing, separation of gastric or pancreatic juice), protective reflexes (coughing, vomiting, sneezing), centers of breathing and cardiac activity, and the vasomotor center.
The pons is a continuation of the medulla oblongata; nerve bundles pass through it, connecting the forebrain and midbrain with the medulla oblongata and spinal cord. Its substance contains the nuclei of the cranial nerves (trigeminal, facial, auditory).
The cerebellum is located in the occipital part behind the medulla oblongata and the pons, and is responsible for coordinating movements, maintaining posture and body balance.
The midbrain connects the forebrain and hindbrain, contains the nuclei of orienting reflexes to visual and auditory stimuli, and controls muscle tone. It contains pathways between other parts of the brain. It contains the centers of visual and auditory reflexes (it turns the head and eyes when fixating vision on a particular object, as well as when determining the direction of sound). It contains centers that control simple monotonous movements (for example, tilting the head and torso).
The diencephalon is located in front of the middle brain, receives impulses from all receptors, and is involved in the generation of sensations. Its parts coordinate the work of internal organs and regulate autonomic functions: metabolism, body temperature, blood pressure, respiration, homeostasis. All sensory pathways to the cerebral hemispheres pass through it. The diencephalon consists of the thalamus and. The thalamus acts as a transducer of signals coming from sensory neurons. Here the signals are processed and transmitted to the corresponding parts of the cerebral cortex. The hypothalamus is the main coordinating center of the autonomic nervous system; it contains the centers of hunger, thirst, sleep, and aggression. The hypothalamus regulates blood pressure, heart rate and rhythm, breathing rhythm and the activity of other internal organs.
The cerebral hemispheres are the most developed and largest part of the brain. Covered with cortex, the central part consists of white matter and subcortical nuclei, consisting of gray matter - neurons. Folds of bark increase the surface area. Here are the centers of speech, memory, thinking, hearing, vision, musculoskeletal sensitivity, taste and smell, and movement. The activity of each organ is under the control of the cortex. The number of neurons in the cerebral cortex can reach 10 billion. The left and right hemispheres are connected to each other by the corpus callosum, which is a wide, dense area of ​​white matter. The cerebral cortex has a significant area due to the large number of convolutions (folds).
Each hemisphere is divided into four lobes: frontal, parietal, temporal and occipital.

The cells of the cortex perform various functions and therefore three types of zones can be distinguished in the cortex:

Sensory zones (receive impulses from receptors).
Associative zones (process and store received information, and also develop a response taking into account past experience).
Motor zones (send signals to organs).
The interconnected work of all zones allows a person to carry out all types of activities; processes such as learning and memory depend on their work, and they determine personality traits.

Human brain

Brain, the anterior section of the central nervous system of vertebrates and humans, located in the cranial cavity. G.m.- the material substrate of higher nervous activity and the main regulator of all vital functions of the body.

In invertebrate animals that have a central nervous system, the function g.m. performs the cephalic ganglion, so developed in higher insects and mollusks that it is also called g.m.

G.m. consists of the telencephalon (cerebral hemispheres); interstitial brain, which includes the visual thalamus [Thalamus], subthalamus [Hypothalamus], subthalamus (metathalamus), suprathalamus (epithalamus); midbrain, including the cerebral peduncles and quadrigeminal region; hindbrain, consisting of the pons and cerebellum; medulla oblongata ( rice. 1).

Rice. 1.Adult brain(right half, left view):

1 – cerebral hemisphere;

2 – visual thalamus (thalamus);

3 – epithalamus (epithalamus);

4 – hypothalamus (hypothalamus);

5 – corpus callosum;

6 – pituitary gland;

7 – quadrigeminal;

8 – cerebral peduncles;

9 – bridge (Varoliev);

10 – cerebellum;

11 – medulla oblongata;

12 – fourth ventricle.

The medulla oblongata is a direct continuation of the spinal cord. All sections located between the spinal cord and the interstitial cord form the brainstem. Afferent (centripetal, sensitive) nerve fibers pass through it, heading from the spinal cord and cranial nerves to the overlying sections g.m., and efferent (centrifugal, motor) nerve fibers running in the opposite direction. The brainstem contains groups of specific afferent nerve cells (nuclei) that receive information from skin and muscle receptors located in the head, as well as from other senses (hearing, balance, taste). In the brain stem there is a cluster of nerve cells in the form of a structure called a reticular formation, or reticular formation, and a number of nerve centers in charge of vital functions (breathing, blood circulation, digestion, etc.).

Primitive g.m. already present in the predecessor of vertebrates - the lancelet. Among the vertebrates g.m. gradually becomes more complex and the listed departments are formed in it ( Rice.2 ).

Rice.2. Gradual complication of the brain brain in vertebrates animals (brain view from above):

A – shark brain; B – frogs; B – alligator;

mammal brain: G – tupai; D – horses; E – human (side view).

1 – olfactory lobe; 2 – olfactory bulb; 3 – pineal gland; 4 – third ventricle; 5 – optic lobe; 6 – cerebellum; 7 – medulla oblongata; 8 – interstitial brain; 9 – fourth ventricle; 10 – cerebral hemispheres; 11 – gyrus; 12 – furrow.

Gradual complication g.m. can be traced during embryonic development ( rice. 3).

Rice.3. Lateral surface of the human brain at various stages of embryonic development (the telencephalon is shaded): at the age of 2 weeks (1), 3 weeks (2), 4 weeks (3), 8 weeks (4), 6 months (5); adult brain (6).

The highest development g.m. achieved in humans, mainly due to the increase and complexity of the structure of the two cerebral hemispheres, morphologically and functionally connected by a powerful bundle of nerve fibers - the corpus callosum. Average g.m. an adult weighs 1470 g, its volume is 1456 cm3, and its surface is 1622 cm2. And in absolute numbers g.m. human brain is second only to the brain of a whale (6000–7000 g) and an elephant (5700 g). The relative mass g.m., according to the indicator Ya.Ya. Roginsky, in humans the highest (human - 32; dolphin - 16; elephant - 10.4; monkey - 2-4). Increase in the surface of the cerebral hemispheres g.m. In humans and higher animals, it proceeded through an increase in the number of grooves and convolutions that form the lobes of the hemispheres (frontal, parietal, temporal, insular, occipital and cingulate). Large hemispheres g.m. consist of:

1 ) the superficial layer of gray matter called the cerebral cortex; in humans, the thickness of this layer is 1–5 mm; the total number of neurons in the cortex is about 14 billion; they are connected with each other and other departments g.m. and spinal cord afferent, efferent and associative nerve fibers. In the cortex, as in other brain structures, there are glial cells (neuroglia, or glia), which participate in the metabolic processes of nervous tissue, perform a support function, etc. perhaps they play some specific role in brain activity;

2 ) white matter formed by nerve fibers heading into the brain from the periphery and coming from g.m. to the periphery, as well as fibers connecting different parts of the cortex and both hemispheres;

3 ) a number of subcortical nodes (basal ganglia), located deep in the hemispheres, that is, in the thickness of the white matter, but consisting of gray matter; The most important of these ganglia are the striatum and the globus pallidus.

G.m. covered with dura, arachnoid and pia mater, between which there is cerebrospinal fluid, which also fills the cavities of the cerebral ventricles. Circulatory system g.m. and cerebrospinal fluid serve as transport channels for nutrients, oxygen and other substances necessary for the functioning of neurons. Decay products are removed from the brain along these same channels. G.m. very sensitive to lack of oxygen.

According to a number of anatomical and functional characteristics g.m. can be represented as a collection of sensory systems. Receptors [nerve endings] of any afferent system perceive irritations, which then, in the form of nerve impulses, spread along centripetal nerve pathways to g.m. Streams of nerve impulses carry g.m. information about the strength and quality of irritations perceived by the receptors of the sense organs (eyes, ears, skin, etc.), all internal organs, muscles and tendons. In the subcortical structures, then in the cortical sections of the analyzers, and ultimately in the entire cortex, this information is processed - its analysis and synthesis are carried out. Then g.m. sends commands to the executive organs (efferent systems) about the nature of responses to irritations. Responses can be of two types: unconditioned reflexes or conditioned reflexes [Reflexes]. Motor reflexes are carried out primarily with the participation of the extrapyramidal system, consisting of subcortical nodes: the striatum receives impulses from the thalamus and cortex and transmits them to the globus pallidus, from where they enter the nuclei of the brain stem and, finally, to the motor neurons of the anterior horns of the spinal cord. In lower vertebrates (fish, amphibians and reptiles), this system of movement coordination is the only one. In mammals, in addition to it, a pyramidal system appears, through which impulses are directly transmitted from the cortex to the motor neurons of the spinal cord. It reaches the highest level of development in monkeys and humans and provides the most complex conditioned reflex, voluntary movements. The pyramidal system, being interconnected with the extrapyramidal system, already plays a leading role. Unconditional autonomic reactions (vascular, secretory, metabolic, etc.) are carried out by the nerve centers of the thalamus, hypothalamus and other structures of the brain stem. The cerebral cortex is also connected to these structures, so various kinds of autonomic conditioned reactions can occur [Autonomic nervous system]. Normal operation g.m. is possible only at a certain level of excitability of its main parts. There are three ways to maintain this level. The first is through the reticular formation of the brain stem, where impulses arrive along branches (collaterals) from centripetal pathways going to the thalamus, and from there to the corresponding areas of the cortex. After processing in the reticular formation, nerve impulses lose the specific features of belonging to a particular analyzer and acquire a nonspecific character. This impulse is sent at the right moment along ascending pathways to all areas of the cortex g.m. and activates them - sets a certain level of excitability [Tone]. The second way to maintain cortical tone is through the sympathetic nervous system and the cerebellum. Finally, the third is through specific pathways coming from the senses. Conditioned reflex mechanisms can also take part in the process of maintaining tone. It is assumed that higher vertebrates have cortical self-regulation (including self-regulation of cortical tone), which is especially developed in humans. Self-regulation of tone is ensured by bilateral connections between the cortex and the reticular formation, as well as the sympathetic nervous system and the cerebellum. Self-regulatory mechanisms are being intensively studied g.m., providing those levels of higher nervous activity of a person, which are called thinking, consciousness and are determined by the ability of the brain to perceive, process, store information and produce the results of its processing.

Larger role in activities g.m. played by the limbic system, located on the inner surface of the hemispheres g.m. and deep in the lateral ventricles. It consists of the hippocampus, septum, amygdala, pyriform and cingulate gyri, mamillary bodies, and fringe. Sometimes it also includes the thalamus and hypothalamus (and a number of other structures). It is believed that the limbic system is related to instinctive, hereditary reactions that determine the innate basis of emotions, and to some types of memory. In humans, disorders of certain types of memory were observed with significant destruction of the hippocampus and amygdala nuclei. Patients in these cases remember the events preceding the operation, but if they are distracted by something, they cannot remember what they intended to do 5-10 minutes ago. The destruction of individual structures of the limbic system in animals is accompanied by a violation of the sequence of actions; the animal, without completing one movement, begins another. Electrical stimulation of the amygdaloid nuclei, septum, and hypothalamus in monkeys causes pugnacity, aggressiveness, and increased sexual activity. At the same time, the relationships between individuals in the herd may change: a “subordinate” monkey becomes a “dominant” one and vice versa.

Despite significant advances in studying the function g.m., in which science owes much to the classical works of I.M. Sechenova, I.P. Pavlova, V.M. Bekhterev, Ch. Sherrington, the internal mechanisms of his integrative, holistic activity still remain unclear. In this regard, the structure and functions g.m. are subjected to intensive study in laboratories and clinics in many countries of the world using physiological, psychological, clinical, biochemical, biophysical, morphological, cybernetic and other research methods.

Lit.: Shmalgauzen I.I., Fundamentals of comparative anatomy of vertebrates, 4th ed., M., 1947, p. 225–76; Orbeli L.A., Questions of higher nervous activity, M. - L., 1949, p. 397–419, 448–63; Pavlov I. P., Complete. collection op., vol. 3, book. 2, M. – L., 1951, p. 320–44; Bykov K.M., Cerebral cortex and internal organs, Izbr. proizv., vol. 2, M., 1954, p. 358–84; Sechenov I.M., Reflexes of the brain, M., 1961; Voronin L.G., Course of lectures on the physiology of higher nervous activity, M., 1965, p. 225–59; Human Physiology, M., 1966, ch. 15; Prosser L., Brown F., Comparative physiology of animals, trans. from English, M., 1967, ch. 21; Luria A.R., Higher cortical functions of humans..., M., 1969, p. 7–80.

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