Brain. Human brain
Animals, usually located in the head (anterior) part of the body and representing a compact accumulation of nerve cells and their dendritic processes. In many animals it also contains glial cells and may be surrounded by a sheath of connective tissue. In vertebrates (including humans), a distinction is made between the brain, located in the cranial cavity, and the spinal cord, located in the spinal canal.
Invertebrate brain
The brain is well developed in the overwhelming majority of Bilateria groups - bilaterally symmetrical animals. Even the most histologically primitive intestinal turbellarians (now classified as a separate phylum Acoelomorpha) have a fairly complex brain with a cortex, neuropil and commissures.
Mammalian brain regions
Mind and brain
In addition, there are statements that the mind is computer-like and algorithmic. The points of view “the mind is generated by the brain” and the “computer-like mind” do not necessarily go together.
Brain size in mammals
Brain mass (kg) as a function of body mass (Mt, kg) for various groups mammals:
Brain in culture
Because of the key importance of the brain in the body, the brain is a popular topic. In ancient times, eating the brain of a defeated person or animal along with other parts of the body symbolized gaining the enemy's strength. In the Middle Ages, the brain was understood as the center of life, along with the heart. Currently, the topic of the brain is widespread in fiction, video games and films, particularly zombie films.
History of brain research
The beginning of modern brain science was laid at the beginning of the 20th century by two discoveries: the analysis of reflex acts and the discovery of the localization of functions in the cerebral cortex. Based on these discoveries, it was suggested that simple adaptive involuntary movements are carried out thanks to the reflex arc of the segmental level passing through the lower parts of the brain, and conscious perception and voluntary movements are provided by reflexes higher order, whose sensorimotor arc passes through the higher parts of the brain.
The brain is part of the central nervous system, the main regulator of all vital functions of the body. As a result of its defeat, serious illnesses. The brain contains 25 billion neurons that make up the cerebral gray matter. The brain is covered by three membranes - hard, soft and arachnoid, located between them, through the channels of which cerebrospinal fluid (CSF) circulates. Liquor is a kind of hydraulic shock absorber. The brain of an adult man weighs on average 1375 g, a woman - 1245 g. However, this does not mean that it is better developed in men. Sometimes the weight of the brain can reach 1800 g.
Structure
The brain consists of 5 main sections: the telencephalon, diencephalon, midbrain, hindbrain and medulla oblongata. The telencephalon makes up 80% of the total mass of the brain. He reached out from frontal bone to the occipital. The telencephalon consists of two hemispheres, in which there are many grooves and convolutions. It is divided into several lobes (frontal, parietal, temporal and occipital). There is a distinction between the subcortex and the cerebral cortex. The subcortex consists of subcortical nuclei regulating various functions of the body. The brain is located in three cranial fossae. The cerebral hemispheres occupy the anterior and middle fossa, and posterior fossa- the cerebellum, under which the medulla oblongata is located.
Functions
The functions of different parts of the brain are different.
Finite brain
There are about 10 billion neurons in the gray cortex. They make up only a 3-mm layer, but their nerve fibers are branched like a network. Each neuron can have up to 10,000 contacts with other neurons. Part nerve fibers through the corpus callosum of the cerebrum connects the right and left hemispheres. Neurons make up gray matter, and fibers make up white matter. Inside the cerebral hemispheres, between frontal lobes and diencephalon, clusters are located gray matter. This basal ganglia. Ganglia are collections of neurons that transmit information.
Diencephalon
The diencephalon is divided into ventral (hypothalamus) and dorsal (thalamus, metathalamus, epithalamus) parts. The thalamus is a mediator in which all irritations received from the outside world converge and are sent to the cerebral hemispheres so that the body can adequately adapt to the constantly changing environment. The hypothalamus is the main subcortical center for regulating the autonomic functions of the body.
Midbrain
Extends from the anterior edge of the pons to the optic tracts and papillary bodies. Consists of the cerebrum and quadrigeminal peduncles. Through midbrain everyone passes ascending paths to the cerebral cortex and cerebellum and descending, carrying impulses to the medulla oblongata and spinal cord. It is important for processing nerve impulses coming from visual and auditory receptors.
Cerebellum and pons
The cerebellum is located in the occipital region behind the medulla oblongata and the pons. It consists of two hemispheres and a worm between them. The surface of the cerebellum is dotted with grooves. The cerebellum is involved in the coordination of complex motor acts.
Ventricles of the brain
The lateral ventricles are located in the forebrain hemispheres. The third ventricle is located between the optic thalamus and is connected to the fourth ventricle, which communicates with the subarachnoid space. The cerebrospinal fluid located in the ventricles also circulates in the arachnoid mater.
Functions of the cerebrum
Thanks to the work of the brain, a person can think, feel, hear, see, touch, and move. The big (final) brain controls all vital important processes, occurring in the human body, and is also the “receptacle” of all our intellectual abilities. From the animal world, humans are primarily distinguished by developed speech and ability to abstract thinking, i.e. the ability to think in moral or logical categories. Only in human consciousness can various ideas arise, for example, political, philosophical, theological, artistic, technical, creative.
In addition, the brain regulates and coordinates the work of all human muscles (both those that a person can control through willpower and those that do not depend on a person’s will, for example, the heart muscle). The muscles receive a series of impulses from the central nervous system, to which the muscles respond by contracting with a certain strength and duration. Impulses enter the brain from various organs feelings, causing the necessary reactions, for example, turning the head in the direction from which the noise is heard.
The left cerebral hemisphere controls the right half of the body, and the right hemisphere controls the left. The two hemispheres complement each other.
The brain resembles Walnut, there are three large sections in it - the trunk, the subcortical section and the cerebral cortex. The total surface of the cortex increases due to numerous grooves that divide the entire surface of the hemisphere into convex convolutions and lobes. Three main sulci - central, lateral and parieto-occipital - divide each hemisphere into four lobes: frontal, parietal, occipital and temporal. Individual areas of the cerebral cortex have different functional value. The cerebral cortex receives impulses from receptor formations. Each peripheral receptor apparatus in the cortex corresponds to an area called the cortical nucleus of the analyzer. An analyzer is an anatomical and physiological formation that provides perception and analysis of information about phenomena occurring in the environment and (or) inside the human body, and generates sensations specific to a particular analyzer (for example, pain, visual, auditory analyzer). The areas of the cortex where the cortical nuclei of the analyzers are located are called the sensory areas of the cerebral cortex. The motor zone of the cerebral cortex interacts with sensory zones, and when it is irritated, movement occurs. This can be shown with a simple example: when a candle flame approaches, the pain and heat receptors of the fingers begin to send signals, then the neurons of the corresponding analyzer identify these signals as pain caused by a burn, and the muscles are “given the order” to withdraw the hand.
Association zones
Association zones are functional areas of the cerebral cortex. They connect incoming sensory information with previously received and stored in memory, and also compare information received from different receptors. Sensory signals are comprehended, interpreted and, if necessary, transmitted to the associated motor area. Thus, associative zones are involved in the processes of thinking, remembering and learning.
Telencephalon lobes
The telencephalon is divided into the frontal, occipital, temporal and parietal lobes. The frontal lobe contains areas of intelligence, concentration, and motor areas; in the temporal - auditory zones, in the parietal - zones of taste, touch, spatial orientation, and in the occipital - visual zones.
Speech zone
Extensive damage to the left temporal lobe, for example, as a result of serious head injuries and various diseases, as well as after a stroke, are usually accompanied by sensory and motor speech disorders.
The telencephalon is the youngest and most developed part of the brain, which determines a person’s ability to think, feel, speak, analyze, and also controls all processes occurring in the body. The functions of other parts of the brain primarily include control and transmission of impulses, many vital functions - they regulate the exchange of hormones, metabolism, reflexes, etc.
For normal functioning the brain needs oxygen. For example, if during cardiac arrest or carotid artery injury the cerebral circulation, then after a few seconds the person loses consciousness, and after 2 minutes the brain cells begin to die.
Functions of the diencephalon
The thalamus and hypothalamus are parts of the diencephalon. Impulses from all receptors in the body enter the nuclei of the thalamus. The received information is processed in the thalamus and sent to the cerebral hemispheres. The thalamus connects to the cerebellum and the so-called limbic system. The hypothalamus regulates the autonomic functions of the body. The influence of the hypothalamus is carried out through the nervous system and endocrine glands. The hypothalamus is also involved in the regulation of the functions of many endocrine glands and metabolism, as well as in the regulation of body temperature and the activity of the cardiovascular and digestive systems.
Limbic system
The limbic system plays an important role in shaping human emotional behavior. The limbic system includes nerve formations located on the medial side of the telencephalon. This area has not yet been fully explored. It is assumed that the limbic system and the subthalamus controlled by it are responsible for many of our feelings and desires, for example, under their influence thirst and hunger, fear, aggressiveness, and sexual desire arise.
Brain stem functions
The brainstem is a phylogenetically ancient part of the brain, consisting of the midbrain, hindbrain and medulla oblongata. The midbrain contains primary visual and auditory centers. With their participation, orienting reflexes to light and sound are carried out. The medulla oblongata contains centers for the regulation of respiration, cardiovascular activity, and functions. digestive organs, as well as metabolism. Medulla takes part in the implementation of such reflex acts as chewing, sucking, sneezing, swallowing, vomiting.
Functions of the cerebellum
The cerebellum controls body movements. The cerebellum receives impulses from all receptors that are stimulated during body movements. Cerebellar function may be impaired by drinking alcohol or other substances that cause dizziness. Therefore, under the influence of intoxication, people are not able to normally coordinate their movements. IN last years There is growing evidence that the cerebellum is important in cognitive activity person.
Cranial nerves
Besides spinal cord Twelve cranial nerves are also very important: pairs I and II - the olfactory and optic nerves; III, IV VI pairs - oculomotor nerves; V pair -trigeminal nerve- innervates masticatory muscles; VII - facial nerve - innervates facial muscles, also contains secretory fibers to the lacrimal and salivary glands; VIII pair - vestibulocochlear nerve - connects the organs of hearing, balance and gravity; IX pair - glossopharyngeal nerve- innervates the pharynx and its muscles, parotid gland, taste buds of the tongue; X pair - nervus vagus-divided into a number of branches that innervate the lungs, heart, intestines, and regulate their functions; Pair XI - accessory nerve - innervates the muscles of the shoulder girdle. As a result of the fusion of spinal nerves, a XII pair - hypoglossal nerve- innervates the muscles of the tongue and the sublingual apparatus.
However, this term is used somewhat loosely to designate similar structures of highly organized invertebrates - for example, in insects, the “brain” is sometimes called a cluster of ganglia of the peripharyngeal nerve ring. When describing more primitive organisms, they speak of the cephalic ganglia rather than the brain.
The weight of the brain as a percentage of body weight is 0.06-0.44% in modern cartilaginous fish, 0.02-0.94% in bony fish, 0.29-0.36% in tailed amphibians, 0.0 in tailless amphibians. 50-0.73%. In mammals, the relative sizes of the brain are much larger: in large cetaceans 0.3%; in small cetaceans - 1.7%; in primates 0.6-1.9%. In humans, the ratio of brain mass to body mass is on average 2%.
The brains of mammals of the orders cetaceans, proboscideans, and primates are the largest in size. The most difficult and functional brain considered to be the brain of Homo sapiens.
The average brain mass of various living creatures is shown in the table.
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Brain tissue
The brain is enclosed in a durable shell of the skull (with the exception of simple organisms). In addition, it is covered with membranes (lat. meninges) made of connective tissue - hard (lat. dura mater) and soft (lat. pia mater), between which there is a vascular, or arachnoid (lat. arachnoidea) membrane. Between the membranes and the surface of the brain and spinal cord there is cerebrospinal fluid (often called cerebrospinal fluid) - cerebrospinal fluid (lat. liquor). Cerebrospinal fluid is also contained in the ventricles of the brain. Excess of this fluid is called hydrocephalus. Hydrocephalus can be congenital (more often) or acquired.
Brain cells
As a result of joint research conducted in 2006, scientists from the universities of Auckland (New Zealand) and Gothenburg (Sweden) found that thanks to the activity of stem cells, the human brain is able to reproduce new neurons. Researchers have discovered that in the part of the human brain that is responsible for the sense of smell, mature neurons are formed from precursor cells. Stem cells located in the brain stop dividing, some sections of chromosomes are reactivated, and neuron-specific structures and connections begin to form. From this moment on, the cell can be considered a full-fledged neuron. Two areas of active neuronal growth are known. One of them is the memory zone. The other includes the area of the brain responsible for movement. This explains the partial and complete restoration over time of the corresponding functions after damage to this area of the brain.
Blood supply
The functioning of brain neurons requires a significant expenditure of energy, which the brain receives through the blood supply network. The brain is supplied with blood from the basin of three large arteries - two internal carotid arteries(lat. a. carotis interna) and the main artery (lat. a. basilaris). In the cranial cavity, the internal carotid artery has a continuation in the form of the anterior and middle cerebral arteries (lat. aa. cerebri anterior et media). The basilar artery is located on the ventral surface of the brainstem and is formed by the fusion of the right and left vertebral arteries. Its branches are the posterior cerebral arteries. The listed three pairs of arteries (anterior, middle, posterior), anastomosing with each other, form the arterial (Willisian) circle. To do this, the anterior cerebral arteries are connected to each other by the anterior communicating artery (lat. a. communicans anterior), and between the internal carotid (or sometimes middle cerebral) and posterior cerebral arteries, on each side, there is a posterior communicating artery (lat. aa.communicans posterior). The absence of anastomoses between the arteries becomes noticeable with the development vascular pathology(stroke), when due to lack of vicious circle blood supply to the affected area increases. In addition, numerous structural options are possible (open circle, atypical division of vessels with the formation of trifurcation, and others). If the activity of neurons in one of the departments increases, the blood supply to that area also increases. Register changes in functional activity individual areas The brain is supported by non-invasive neuroimaging methods such as functional magnetic resonance imaging and positron emission tomography.
Between the blood and brain tissue there is a blood-brain barrier, which ensures selective permeability of substances found in vascular bed, into cerebral tissue. In some areas of the brain, this barrier is absent (hypothalamic region) or differs from other parts, which is due to the presence of specific receptors and neuroendocrine formations. This barrier protects the brain from many types of infection. At the same time, many drugs that are effective in other organs cannot penetrate the brain barrier.
With a mass of about 2% of total mass body, the adult brain consumes 15% of the circulating blood volume, using 50% of the glucose produced by the liver and entering the blood.
Functions
Brain parts
Main parts of the human brain
- Rhomboid (hind) brain
- rear (actually rear)
- pons (contains mainly projection nerve fibers and groups of neurons, is an intermediate link in the control of the cerebellum)
- cerebellum (consists of the vermis and hemispheres, on the surface of the cerebellum nerve cells form a crust)
- rear (actually rear)
The cavity of the rhomboid brain is the IV ventricle (at the bottom there are openings that connect it with the other three ventricles of the brain, as well as with the subarachnoid space).
- midbrain
- midbrain cavity - cerebral aqueduct (Aqueduct of Sylvius)
- cerebral peduncles
- the forebrain consists of the diencephalon and telencephalon.
- intermediate (through this section, all information that comes from the lower parts of the brain to the cerebral hemispheres is switched). The cavity of the diencephalon is the third ventricle.
- epithalamus
- leash
- gray stripe
- hypothalamus (center of the autonomic nervous system)
- pituitary infundibulum
- epithalamus
- finite
- basal ganglia (striatum)
- fence
- "olfactory brain"
- olfactory bulb (passes through the olfactory nerve)
- olfactory tract
- cavity of the telencephalon - lateral (I and II ventricles)
- basal ganglia (striatum)
- intermediate (through this section, all information that comes from the lower parts of the brain to the cerebral hemispheres is switched). The cavity of the diencephalon is the third ventricle.
The flow of signals to and from the brain is through the spinal cord, which controls the body, and through the cranial nerves. Sensory (or afferent) signals arrive from the sense organs to the subcortical (that is, preceding the cerebral cortex) nuclei, then to the thalamus, and from there to the higher department - the cerebral cortex.
The cortex consists of two hemispheres connected by a bundle of nerve fibers - the corpus callosum. The left hemisphere is responsible for right half body, right - behind left. In humans, the right and left hemispheres have different functions.
Visual signals enter the visual cortex (in the occipital lobe), tactile signals enter the somatosensory cortex (in parietal lobe), olfactory - into the olfactory cortex, etc. In the associative areas of the cortex, sensory signals are integrated different types(modalities).
On the one hand, there is a localization of functions in parts of the brain, on the other hand, they are all connected into a single network.
Plastic
The brain has the property of plasticity. If one of its departments is affected, other departments after some time can compensate for its function. Brain plasticity also plays a role in learning new skills.
Embryonic development
Embryonic development of the brain is one of the keys to understanding its structure and functions.
The brain develops from the rostral part of the neural tube. Most of the brain (95%) is a derivative of the pterygoid plate.
Embryogenesis of the brain goes through several stages.
- Stage of three brain vesicles - in humans, at the beginning of the fourth week of intrauterine development, the rostral end of the neural tube forms three vesicles: Prosencephalon (forebrain), Mesencephalon (midbrain), Rhombencephalon (diamond-shaped brain, or primary hindbrain).
- Stage of five brain vesicles - in humans, at the beginning of the ninth week of intrauterine development, the Prosencephalon is finally divided into Telencephalon (telecephalon) and Diencephalon (diencephalon), Mesencephalon is preserved, and Rhombencephalon is divided into Metencephalon (hindbrain) and Myelencephalon (medulla oblongata).
During the formation of the second stage (from the third to the seventh weeks of development), the human brain acquires three bends: midbrain, cervical and pavement. First, the midcerebral and pontine flexures are formed simultaneously and in one direction, then the cervical flexure is formed in the opposite direction. As a result, the linear brain “folds” in a zigzag manner.
During the development of the human brain, a certain similarity between phylogeny and ontogenesis can be noted. In the process of evolution of the animal world, the telencephalon was formed first, and then the midbrain. The forebrain is an evolutionarily newer brain formation. Also in intrauterine development In a child, the hindbrain is first formed as the most evolutionarily ancient part of the brain, and then the midbrain and then the forebrain. After birth with infancy Before adulthood, the organizational complication of neural connections in the brain occurs.
Research methods
Ablations
One of oldest methods Brain research is a technique called ablations, which consists of removing one part of the brain and scientists observing the changes that such an operation leads to.
Not every area of the brain can be removed without killing the organism. Thus, many parts of the brain stem are responsible for vital important functions, such as breathing, and their defeat can cause immediate death. However, damage to many parts, although it affects the viability of the body, is non-fatal. This, for example, applies to areas of the cerebral cortex. A major stroke causes paralysis or loss of speech, but the body continues to live. A vegetative state, in which most of the brain is dead, can be maintained through artificial nutrition.
Research using ablations has a long history and is currently ongoing. If scientists of the past removed areas of the brain surgically, then modern researchers use toxic substances, selectively affecting brain tissue (for example, cells in a certain area, but not nerve fibers passing through it).
After a section of the brain is removed, some functions are lost, while others are retained. For example, a cat whose brain is dissected above the thalamus retains many postural reactions and spinal reflexes. An animal whose brain is dissected at the level of the brain stem (decerebrated) maintains extensor muscle tone, but loses postural reflexes.
Observations are also being made of people with lesions of brain structures. Thus, cases of gunshot wounds to the head during the Second World War provided rich information for researchers. Research is also being conducted on patients with stroke and brain damage due to trauma.
Transcranial magnetic stimulation
Transcranial magnetic stimulation is a method that allows non-invasive stimulation of the cerebral cortex using short magnetic pulses. TMS is not associated with painful sensations and therefore can be used as a diagnostic procedure in outpatient setting. The magnetic pulse generated by TMS is a rapidly varying time-varying magnetic field that is produced around an electromagnetic coil when current flows through it. high voltage after the discharge of a powerful capacitor (magnetic stimulator). Magnetic stimulators used today in medicine are capable of generating a magnetic field with an intensity of up to 2 Tesla, which makes it possible to stimulate elements of the cerebral cortex at a depth of up to 2 cm. Depending on the configuration of the electromagnetic coil, TMS can activate areas of the cortex of different sizes, that is, be either 1) focal, which makes it possible to selectively stimulate small areas of the cortex, or 2) diffuse, which allows simultaneous stimulation different departments bark.
When stimulating the motor area of the cerebral cortex, TMS causes contraction of certain peripheral muscles in accordance with their topographic representation in the cortex. The method makes it possible to assess the excitability of the motor system of the brain, including its excitatory and inhibitory components. TMS is used in the treatment of brain diseases such as Alzheimer's syndrome, the study of blindness, deafness, epilepsy, etc.
Electrophysiology
Electrophysiologists record the electrical activity of the brain - using thin electrodes that make it possible to record the discharges of individual neurons, or using electroencephalography (a technique for removing brain potentials from the surface of the head).
The thin electrode can be made of metal (coated with an insulating material exposing only the sharp tip) or glass. A glass microelectrode is a thin tube filled inside with a saline solution. The electrode can be so thin that it penetrates into the cell and allows intracellular potentials to be recorded. Another way to record neuronal activity, extracellular -
"Wikipedia of the Brain"
against dementia mental illness and brain "catastrophes"
Professor Vladimir Lazarevich Zelman, foreign member of the Russian Academy of Medical Sciences and the Russian Academy of Sciences, one of the pioneers of neuroanesthesiology, member of the International Academic Council of Novosibirsk state university, a graduate of the Novosibirsk Medical Institute, is today one of the three best American anesthesiologists. The University of Southern California (Los Angeles, USA), where V. L. Zelman heads the Department of Anesthesiology and Reanimatology, is one of the leaders in the field of neuroscience in the United States and takes part in a number of major brain research projects, such as ENIGMA. In his lecture at NSMU and in an interview with SCIENCE First Hand, Professor Zelman spoke about the most interesting results obtained by university staff in partnership with colleagues from other organizations in one of the hottest spots at the intersection of modern biology and medicine. Among them is a genetic database developing brain, which will allow you to assess the genetic risks of diseases; a map of the location of all neurons in the brain and the “wiring” connecting them; neurocomputer technologies that allow the “power of thought” to control bionic prostheses
First, some statistics: according to experts, by 2050, the number of people in the world suffering from dementia - acquired dementia - may increase almost three times and reach 132 million. The most common form of dementia is associated with Alzheimer's disease - a neurodegenerative disease that develops mainly in old age. And delaying the onset of the disease by only 5 years (from 76 to 81 years) will reduce the number of patients by half!
And this is just one eloquent example of the importance of neurosciences involved in the study of the brain - the physical basis of our consciousness, subconscious and mental activity, one of the most complex and most mysterious organs human body. The mechanisms of brain functioning have not been fully elucidated, although over the past quarter century, thanks to the emergence of new research technologies such as magnetic resonance imaging, electroencephalography and others, more has become known about the biology of healthy and diseased brains than in the entire previous history of its study. Over the past ten years, it has become clear that at least 80% of currently known genes are expressed to one degree or another in the central and peripheral nervous system.
Investments in neuroscience are currently estimated at billions of dollars. Thus, over the last decade of the 20th century, declared the “decade of the brain,” the US Congress allocated about $3 billion for research in this area. For comparison: about $3.7 billion was allocated for research into the human genome at the same time; it is symbolic that these two most important scientific project walked in parallel.
Founded in 1880, the University of Southern California is California's oldest private research university. In recent years, according to authoritative ratings, it has traditionally been included in the top hundred best universities peace. Currently there are over 40 thousand students studying at the university. In 1994, university professor D. E. Olah received the Nobel Prize in Chemistry
The University of Southern California has been a leader in brain research in recent years, not only in the United States but also around the world, using a unique multidisciplinary approach to collaboratively solve the mysteries of brain disease in ways not possible in isolated laboratories.
So, for several years now scientists from the Institute of Neurogenetics named after. Zilka University of Southern California is conducting joint research with a group of collaborators from Yale University and the Brain Institute. Allen. Their goal is to create a complete genetic database of the developing human brain, which will allow the assessment genetic risk emergence of various brain disorders. Today, more than 300 genetic loci associated with the pathology of the central nervous system have already been identified; in total, the unique Atlas of Gene Transcription of the Brain plans to present gene expression data for 15 brain regions in 13 age categories. Today this database is the largest in the world, and since 2011 it has been available to all interested users.
The University of Southern California has initiated a global brain research project ENIGMA, which is headed by university professor P. Thompson and funded by the US National Institutes of Health. Today, about 200 mathematicians, geneticists, neurobiologists and physicians from more than 35 countries of the world, including Russia (from Novosibirsk State University, a number of institutes of the SB RAS, the N.N. Burdenko Institute of Neurosurgery, the Institute of transmission of information named after A. A. Kharkevich, etc.). The project is conducting research into the structures and functions of the brain and predisposition to diseases such as schizophrenia, Alzheimer's disease, depression, drug addiction, etc. The main focus is on identifying factors that cause or, conversely, prevent a particular disease, such as lifestyle , eating habits and, of course, heredity. For example, a gene was recently discovered that is involved in the development of obesity through disturbances in the functioning of brain structures.
The human brain contains about 100 billion specialized nerve cells - neurons, each of which has about 10 thousand synapses that serve to transmit nerve impulse between cells. Various areas our brain, responsible for thinking, perception and sensations, are connected by nerve fibers total length 100 thousand miles (161 thousand km)
The most important part of the project ENIGMA is Connectome– a project to study the conduction system of the brain. The very concept of “connectome” was introduced by analogy with the concept of “genome” for full description structures of connections in the nervous system. During the project Connectome a four-dimensional (the fourth dimension is time) map of the location of all neurons in the brain and the “wirings” connecting them will be created, describing all 100 trillion possible interactions between cells. This project, where all the results of brain imaging will be combined in a single map, can rightfully be called the “Wikipedia of the brain.” As a result, it will be possible to establish the variability and genetic predetermination of neurons, monitor their interactions in real time, and also identify the presence of neuronal pathologies.
Like any cell, each type of neuron uses a specific set of genes to create its molecular machinery; Successively interacting neurons form so-called neural circuits (the simplest example is a reflex arc). Understanding all the nuances of how neural circuits work should also help in understanding the pathogenesis of brain diseases, which will make their diagnosis more effective. After all, then it will be possible to recognize pathological processes not only based on symptoms, and search for diseases literally at the level of individual synapses.
Today, about one and a half dozen varieties of mental illnesses have been described. It is possible that in the next decade, when it becomes known at what stage and in what place genes that redirect synaptic activity in the “wrong” direction are turned on and off, the number of identified diseases will increase by one or two orders of magnitude. Treatment will become more personalized, and in case early diagnosis it will be possible to correct such “wrong” processes with complete rehabilitation patient.
In the project's boundaries ENIGMA A huge array of genetic data and brain imaging data has already been collected - about 50 thousand brain visualizations from 33 thousand people from more than three dozen countries around the world! Collecting such material today is not so difficult, but to decipher and interpret these huge information flows, supercomputers and specialists in working with “big” data—bioinformaticians—are required. Modern science is fundamentally capable of such tasks, so it is possible that in the near future each of us will become the owner of a “flash drive” on which the decoding of not only our genome, but also our very personality will be recorded.
Already today, research into the brain's conduction system offers hope of making life easier for patients with serious brain damage resulting from trauma. We are talking about neurocomputer technology (the so-called brain-computer interface), which allows a paralyzed person to control bionic prostheses, for example, a mechanical arm, “with the power of thought.”
Professor Zelman:“On April 17, 2012, for the first time, we performed surgery on a patient with a shot in the cervical spine, suffering from tetraplegia - impaired motor ability of all four limbs. Special electronic chips were implanted into the patient's brain, each of which has 96 sensors that read signals brain activity; Through antennas, this information is transmitted to a computer that controls the operation of a specially designed bionic arm. Currently, six patients have been operated on in this manner in the United States. This work is funded by the US Department of Defense."
One of the problems with such brain-computer technologies is the choice of brain signals that should be used to control bionic prostheses. According to a number of researchers, it is necessary to read the activity of nerve cells in the motor cortex of the brain, which is directly responsible for movements - in this case feedbacks are formed at the level of the action itself. But there is another approach, in which preference is given not to the action itself, but to the intention to do it! The idea of installing chips in the area of the medial cortex, involved in action planning, belongs to Zelman's colleague, Professor R. Anderson from the California Institute of Technology.
Richard Anderson has spent the last 25 years researching the brain in search of clusters of neurons whose activity can be used to control the movements of an artificial limb. He was sure that this did not require information about the movement itself, because each of them was provided in the connectome by hundreds of thousands of neural connections that were difficult to track. In this sense, the very intention to do this or that action is much more promising, and Anderson eventually discovered in the posterior cranial fossa, next to visual analyzers, the area where it is formed.
And indeed, in the other five patients in whom the chip was implanted in the area of the motor cortex, coordination turned out to be much worse; they missed more often when making a movement, for example, when picking up a can of juice. But also a big problem is that so far all such bionic limbs are used only as part of experiments that sooner or later end. Chips implanted in the brain are perceived by the latter as a foreign body and ultimately become encapsulated and lose connection with neurons. Nevertheless, the essence of these works is that they show the fundamental possibility of making life easier for completely paralyzed patients using a brain-computer interface.
...Returning to Alzheimer's disease, let us recall that the brain healthy people loses less than 1% of its weight per year, and this loss is compensated due to tissue regeneration under the influence mental activity. Alzheimer's disease symptoms begin to appear when 10% of brain tissue is lost, and normal conditions this is an irreversible process. However, to date, scientists have already discovered 9 genes that can accelerate and slow down the development of this disease, including Apoe4, which is the leading risk factor for this most common form senile dementia(substances capable of transforming the “aggressive” Apoe4 protein encoded by this gene into a safer isoform are already being tested on animals).
Moreover: today, scientists at the University of Southern California, together with their colleagues from Wake Forest University (North Carolina), are working on “recording” information stored in the brain, thanks to which the brain of a person suffering from Alzheimer’s disease can be “rebooted”, returning, at least temporarily, lost memories. This result, which seems fantastic even today, is only clear evidence of the successes that modern science achieved in the study of the brain - an organ that for centuries was considered suitable only for the function of cooling the blood!
Despite significant progress in the study of the brain in recent years, much of its working still remains a mystery. The functioning of individual cells is fairly well explained, but understanding how the brain functions as a whole through the interaction of thousands and millions of neurons is only available in a very simplified form and requires further in-depth research.
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✪ Brain. Structure and functions. Biology video lesson 8th grade
✪ How the brain works
✪ Brain
✪ Human anatomy. Brain.
✪ Biology lesson No. 45. The structure and functions of parts of the brain.
Subtitles
The brain as a vertebrate organ
The brain is the main part of the central nervous system. We can talk about the presence of a brain in the strict sense only in relation to vertebrates, starting with fish. However, this term is used somewhat loosely to designate similar structures of highly organized invertebrates - for example, in insects, the “brain” is sometimes called the accumulation of ganglia of the peripharyngeal nerve ring. When describing more primitive organisms, they speak of the cephalic ganglia rather than the brain.
The weight of the brain as a percentage of body weight is 0.06-0.44% in modern cartilaginous fish, 0.02-0.94% in bony fish, 0.29-0.36% in tailed amphibians, 0.0 in tailless amphibians. 50-0.73%. In mammals, the relative sizes of the brain are much larger: in large cetaceans 0.3%; in small cetaceans - 1.7%; in primates 0.6-1.9%. In humans, the ratio of brain mass to body mass is on average 2%.
The brains of mammals of the orders cetaceans, proboscideans, and primates are the largest in size. The most complex and functional brain is considered to be that of Homo sapiens.
Brain tissue
The brain is enclosed in a durable shell of the skull (with the exception of simple organisms). In addition, it is covered with membranes (lat. meninges) made of connective tissue - hard (lat. dura mater) and soft (lat. pia mater), between which there is a vascular, or arachnoid (lat. arachnoidea) membrane. Between the membranes and the surface of the brain and spinal cord there is cerebrospinal fluid (often called cerebrospinal fluid) - cerebrospinal fluid (lat. liquor). Cerebrospinal fluid is also contained in the ventricles of the brain. Excess of this fluid is called hydrocephalus. Hydrocephalus can be congenital (more often) or acquired.
Brain cells
Until now, it was known that nerve cells were restored only in animals. However, scientists have recently discovered that in the part of the human brain that is responsible for the sense of smell, mature neurons are formed from precursor cells. One day they may be able to help “fix” a damaged brain. Stem cells located in the brain stop dividing, some sections of chromosomes are reactivated, and neuron-specific structures and connections begin to form. From this moment on, the cell can be considered a full-fledged neuron. To date, only 2 areas of active neuronal growth are known. One of them is the memory zone. The other includes the area of the brain responsible for movement. This explains the partial and complete restoration over time of the corresponding functions after damage to this area of the brain.
Blood supply
The functioning of brain neurons requires a significant expenditure of energy, which the brain receives through the blood supply network. The brain is supplied with blood from the basin of three large arteries - two internal carotid arteries (lat. a. carotis interna) and the main artery (lat. a. basilaris). In the cranial cavity, the internal carotid artery has a continuation in the form of the anterior and middle cerebral arteries (lat. aa. cerebri anterior et media). The basilar artery is located on the ventral surface of the brainstem and is formed by the confluence of the right and left vertebral arteries. Its branches are the posterior cerebral arteries. The listed three pairs of arteries (anterior, middle, posterior), anastomosing with each other, form the arterial (Willisian) circle. To do this, the anterior cerebral arteries are connected to each other by the anterior communicating artery (lat. a. communicans anterior), and between the internal carotid (or sometimes middle cerebral) and posterior cerebral arteries, on each side, there is a posterior communicating artery (lat. aa. communicans posterior). The absence of anastomoses between arteries becomes noticeable with the development of vascular pathology (strokes), when, due to the lack of a closed circle of blood supply, the affected area increases. In addition, numerous structural options are possible (open circle, atypical division of vessels with the formation of trifurcation, etc.). If the activity of neurons in one of the departments increases, the blood supply to that area also increases. Non-invasive neuroimaging methods such as functional magnetic resonance imaging and positron emission tomography make it possible to record changes in the functional activity of individual areas of the brain.
There is a blood-brain barrier between the blood and brain tissue, which ensures selective permeability of substances in the vascular bed into the cerebral tissue. In some areas of the brain, this barrier is absent (hypothalamic region) or differs from other parts, which is due to the presence of specific receptors and neuroendocrine formations. This barrier protects the brain from many types of infection. At the same time, many drugs that are effective in other organs cannot penetrate the brain barrier.
Functions
Brain functions include processing sensory information from the senses, planning, decision-making, coordination, motor control, positive and negative emotions, attention, memory. The human brain performs higher function- thinking. One of the functions of the human brain is the perception and generation of speech.
Brain parts
The cortex consists of two hemispheres connected by a bundle of nerve fibers - the corpus callosum. The left hemisphere is responsible for the right half of the body, the right - for the left. In humans, the right and left hemispheres have different functions.
Visual signals enter the visual cortex (in the occipital lobe), tactile signals enter the somatosensory cortex (parietal lobe), olfactory signals enter the olfactory cortex, etc. In the associative areas of the cortex, sensory signals of different types (modalities) are integrated.
On the one hand, there is a localization of functions in parts of the brain, on the other hand, they are all connected into a single network.
Plastic
The brain has the property of plasticity. If one of its departments is affected, other departments after some time can compensate for its function. Brain plasticity also plays a role in learning new skills.
Embryonic development
Embryonic development of the brain is one of the keys to understanding its structure and functions.
The brain develops from the rostral part of the neural tube. Most of the brain (95%) is derived from the pterygoid plate.
Embryogenesis of the brain goes through several stages.
- Stage of three brain vesicles - in humans, at the beginning of the fourth week of intrauterine development, the rostral end of the neural tube forms three vesicles: Prosencephalon (forebrain), Mesencephalon (midbrain), Rhombencephalon (diamond-shaped brain, or primary hindbrain).
- Stage of five brain vesicles - in humans, at the beginning of the ninth week of intrauterine development, the Prosencephalon is finally divided into Telencephalon (endbrain) and Diencephalon (midbrain), Mesencephalon is preserved, and Rhombencephalon is divided into Metencephalon (hindbrain) and Myelencephalon (medulla oblongata).
During the formation of the second stage (from the third to the seventh weeks of development), the human brain acquires three bends: midbrain, cervical and pavement. First, the midcerebral and pontine flexures are formed simultaneously and in one direction, then the cervical flexure is formed in the opposite direction. As a result, the linear brain “folds” in a zigzag manner.
During the development of the human brain, a certain similarity between phylogeny and ontogenesis can be noted. In the process of evolution of the animal world, the telencephalon was formed first, and then the midbrain. The forebrain is an evolutionarily newer brain formation. Also, during the intrauterine development of a child, the hindbrain is first formed as the most evolutionarily ancient part of the brain, and then the midbrain and then the forebrain. After birth, from infancy to adulthood, an organizational complication of neural connections in the brain occurs.
Research methods
Ablations
One of the oldest methods of brain research is the ablation technique, which consists of removing one of the parts of the brain, and scientists observe the changes that such an operation leads to.
Not every area of the brain can be removed without killing the organism. Thus, many parts of the brain stem are responsible for vital functions, such as breathing, and damage to them can cause immediate death. However, damage to many parts, although it affects the viability of the body, is non-fatal. This, for example, applies to areas of the cerebral cortex. A major stroke causes paralysis or loss of speech, but the body continues to live. A vegetative state, in which most of the brain is dead, can be maintained through artificial nutrition.
Research using ablations has a long history and is currently ongoing. If scientists of the past removed areas of the brain surgically, modern researchers use toxic substances that selectively damage brain tissue (for example, cells in a certain area, but not the nerve fibers passing through it).
After a section of the brain is removed, some functions are lost, while others are retained. For example, a cat whose brain is dissected above the thalamus retains many postural reactions and spinal reflexes. An animal whose brain is dissected at the level of the brain stem (decerebrated) maintains extensor muscle tone, but loses postural reflexes.
Observations are also being made of people with lesions of brain structures. Thus, cases of gunshot wounds to the head during the Second World War provided rich information for researchers. Research is also being conducted on patients with stroke and brain damage due to trauma.
Transcranial magnetic stimulation
In some cases, thin electrodes (from one to several hundred) are implanted into the brain, and researchers record activity over an extended period of time. In other cases, the electrode is inserted into the brain only for the duration of the experiment, and is removed at the end of the recording.
Using a thin electrode, you can record both the activity of individual neurons and local field potentials resulting from the activity of many hundreds of neurons. Using EEG electrodes, as well as surface electrodes placed directly on the brain, it is possible to record only the global activity of a large number of neurons. It is believed that the activity recorded in this way consists of both neural action potentials (that is, neural impulses) and subthreshold depolarizations and hyperpolarizations.
When analyzing brain potentials, their spectral analysis is often performed, and different components of the spectrum have different names: delta (0.5-4 Hz), theta 1 (4-6 Hz), theta 2 (6-8 Hz), alpha (8-13 Hz), beta 1 (13-20 Hz), beta 2 (20 -40 Hz), gamma waves (includes the frequency of beta 2 rhythms and higher).
Electrical stimulation
One method for studying brain function is electrical stimulation of specific areas. Using this method, for example, the “motor homunculus” was studied - it was shown that by stimulating certain points in the motor cortex, it is possible to cause arm movement, stimulating other points - leg movements, etc. The map thus obtained is called the homunculus. Different parts of the body are represented by areas of the cerebral cortex that differ in size. Therefore, the homunculus has a large face, thumbs and palms, but a small torso and legs.
If you stimulate the sensory areas of the brain, you can cause sensations. This has been shown both in humans (in the famous Penfield experiments) and in animals.
Electrical stimulation is also used in medicine - from electric shock, shown in many films about the horrors of psychiatric clinics, to stimulation of structures deep in the brain, which has become a popular method of treating Parkinson's disease.
Other techniques
X-ray CT and MRI are used to study the anatomical structures of the brain. Also used in anatomical and functional studies of the brain are PET, single-photon emission computed tomography (SPECT), and functional MRI. It is possible to visualize brain structures using the method ultrasound diagnostics(ultrasound) in the presence of an ultrasound “window” - a defect in the cranial bones, for example, a large fontanel in young children.
Lesions and diseases
The study and treatment of brain lesions and diseases falls within the scope of biology and medicine (neurophysiology, neurology, neurosurgery, psychiatry and psychology).
Inflammation meninges called meningitis (corresponding to three membranes - pachymeningitis, leptomeningitis and arachnoiditis).
The weight of the adult brain is on average one fiftieth of the total body weight. In this case, the human brain consumes one fifth of the circulating blood (that is, one fifth of oxygen), one fifth of the glucose entering the body.
The average brain weight of various living creatures is given in the table.
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