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As for alcoholism, experts from Cambridge University (UK) proved that alcohol abuse causes irreversible changes in the DNA structure of blood stem cells (double-strand break, poor DNA repair – the function of damage repair, rearrangement inside chromosome parts), which leads to malignant tumors[35 - Garaycoechea J., Crossan G., Langevin F., et al. Alcohol and endogenous aldehydes damage chromosomes and mutate stem cells. Nature. 2018;553, 171–177. doi:10.1038/nature25154.]. For example, alcohol dependence increases the risk of developing at least seven types of cancer, including the most common, breast, and colon cancer.
Numerous studies have shown that drugs, both light and heavy, are not only harmful to those who use them but also contribute to birth defects and genetic diseases in their children.
American researchers at Duke University have found a potential link between cannabis use by fathers and the development of mental illness in their children[36 - Schrott R., Acharya K., Itchon-Ramos N., et al. Cannabis use is associated with potentially heritable widespread changes in autism candidate gene DLGAP2 DNA methylation in sperm. Epigenetics. 2020;15(1–2):161–173. doi:10.1080/15592294.2019.1656158.]. In men who used marijuana, they found several adverse changes in gene activity associated with autism, schizophrenia, and post-traumatic stress disorder. Experiments on rats showed that the born offspring had similar epigenetic changes. This confirms the likelihood of the "marijuana" tag transmission for generations. Another study by the university showed that the father's use of marijuana affects the child's cognitive functions: abnormalities were found in certain brain areas related to learning, memory, reward, and mood[37 - Slotkin T. A., Skavicus S., Levin E. D., Seidler F. J. Paternal. 9-Tetrahydrocannabinol Exposure Prior to Mating Elicits Deficits in Cholinergic Synaptic Function in the Offspring. Toxicological Sciences. 2020 Apr;174(2), 210–217. doi:10.1093/toxsci/kfaa004.].
ENVIRONMENT. One of the factors that certainly affects gene expression, and thus our well-being, is air quality. Experts from Monash University in Australia proved that even short-term exposure to polluted air adversely affects the activity of six genes responsible for the severity of oxidative stress and inflammatory reactions in the body[38 - Madaniyazi L., Li S., Li S., Guo Y. Candidate gene expression in response to low-level air pollution. Environ Int. 2020 Jul;140: 105610. doi:10.1016/j.envint.2020.105610. Epub 2020 Apr 2. PMID:32248990.]. The "abnormal" methylation profile that was found in these DNA regions was associated with the development of dangerous cardiovascular, respiratory, and cancer diseases, as well as an increased risk of premature death.
CONTACT WITH PESTICIDES. Many recent studies have examined the effects of chemicals on gene expression, and several toxins have been identified that leave epigenetic tags in DNA. These are bisphenols in plastics and epoxy resins, phthalates in vinyl floors, plastic, perfluorochemicals used to create non-stick coatings on cookware, pesticides, herbicides, salts of heavy metals, etc. Russian scientists from the Institute of Experimental Medicine of the RAS conducted an experiment, the results of which showed that the introduction of a single dose of bisphenol into a pregnant female mouse disrupts the methylation profile of several DNA regions, which causes problems in fetal development[39 - Noniashvili E. M., Grudinina N. A., Kustova V. E., etc. DNA methylation in early mouse embryogenesis influenced by bisphenol A. Ecological genetics. 2017. 15 (3). P. 42–53.].
Significant epigenetic modifications can be caused by vinclozolin. This was proved by American scientists from the University of Nebraska-Lincoln and Rutgers University (USA) and showed another good example of epigenetic imprinting[40 - Anway M. D., Cupp A. S., Uzumcu M., Skinner M. K. Epigenetic transgenerational actions of endocrine disruptors and male fertility. Science. 2005 Jun 3;308(5727):1466-9. doi:10.1126/science.1108190. Erratum in: Science. 2010 May 7;328(5979):690. PMID: 15933200.]. In the experiment, pregnant rats were given vinclozolin in their food and observed how it would affect their babies. It turned out that male children had problems with sperm quality and quantity as they got older. And this effect persisted for four generations of laboratory animals and then disappeared.
STRESS, RELATIONSHIPS, THOUGHTS. Not only "clear" signals, such as food or toxin exposure, can change gene expression. Even the way a person thinks and feels affects gene activity. Genes very quickly respond to prolonged stress, constant anxiety, fear, arguments, and anger. They start a chain of adverse biochemical processes in the body, leading to disease development. But it is important that our genes also respond with a positive "reaction" to showing gratitude, love, and optimism.
A team of experts from Ohio State University (USA) conducted a study to find out how an ordinary family argument can affect the rate of wound healing, an important indicator of genetic activity[41 - Kiecolt-Glaser J. K., Loving T. J., Stowell J. R., et al. Hostile marital interactions, proinflammatory cytokine production, and wound healing. Arch Gen Psychiatry. 2005;62(12):1377–1384. doi:10.1001/ archpsyc.62.12.1377.]. Scientists gave slight injuries on the skin of all participants and monitored the rate of healing by the levels of three proteins responsible for tissue regeneration. During the first visit, the couples had to talk about any pleasant topic, and during the second visit, they had to remember their last unresolved argument. It turned out that after a family quarrel, spouses' wounds healed more slowly and the levels of produced proteins responsible for healing were lower than after a pleasant conversation. And in the most hostile couples – those who argued with mutual recriminations, humiliations, and accusations – the injuries took even longer to heal than in partners who were less hostile to each other. With thoughts and emotions alone, the spouses were able to induce appropriate epigenetic changes.
CONCLUSION
Discoveries in the field of epigenetics, which increase every year, convince us that genes are not a sentence: it does not matter whether we inherit "good" or "bad" genes, it is important how we use them. Most people probably have the potential for active long life in their genes. And in the future, no doubt, we will find a way to unlock it.
CHAPTER 4
BODY
IF YOU WANT TO PROPERLY USE SUCH A COMPLEX MECHANISM AS THE HUMAN BODY, IT IS NECESSARY TO UNDERSTAND HOW IT IS BUILT. A HUMAN IS VULNERABLE TO DISEASE WITHOUT KNOWING THEIR PHYSIOLOGY. THE MAIN TASK OF THOSE WHO WANT TO BE HEALTHY AND LIVE LONGER IS TO SUPPORT THE WORK OF THE BODY.
WHAT OUR BODY IS
CELLS
The human body is made up of cells, the basic structural units, which work together and perform the various functions necessary to sustain life.
The human body weighing 70 kilograms consists of an average of 30 trillion cells. And most of them are erythrocytes – they account for 84 %. Then there are thrombocytes – 4.9 %, bone marrow cells – 2.5 %, vascular endothelial cells – 2.1 %, lymphocytes – 1.6 %, and hepatocytes – 0.8 %. Muscle and fat cells account for 0.1 % of the total cell number[42 - Sender R., Fuchs S., Milo R. Revised Estimates for the Number of Human and Bacteria Cells in the Body. Published: August 19, 2016. doi:10.1371/journal.pbio.1002533.].
For the body to function properly, there is a continuous process of replacing old cells with new ones. About 3.8 million cells are renewed every second, and almost 330 billion cells per day. Even when a human dies, it will be a while before all the cells in the body die.
Researchers at the Karolinska Institute (Sweden), led by biologist Jonas Friesen, calculated the lifespan of individual cells, finding that they change differently – depending on the type[43 - Spalding K. L., Bhardwaj R. D., Buchholz B. A., Druid H., Frisén J. Retrospective Birth Dating of Cells in Humans. doi:10.1016/j. cell.2005.04.028PlumX Metrics.]. For example, the epidermal cells that make up human skin are renewed every two weeks. Erythrocytes, which carry oxygen from the lungs to the tissues of the body, live for four months, while neutrophils, a type of white blood cell, live only for two days.
The life of liver cells is between 300 and 500 days. The epithelial cells lining the intestine last only five days and then are replaced by new cells – they are among the shortest-lived in the body. Without them, the average age of all intestinal cells is 15.9 years. Skeletal tissue cells live about 10 years, while cells of rib muscles live 15.1 years[44 - Kong S., Zhang Y. H., Zhang W. Regulation of Intestinal Epithelial Cells Properties and Functions by Amino Acids. doi:10.1155/2018/ 2819154.].
But not all cells are renewed: for example, the cells of the retina and lens do not change throughout life. This explains the natural deterioration of vision with age. For a long time, it was believed that nerve cells also live as long as humans, die with aging, and do not renew. However, recent data have shown that new neurons are formed from stem cells, but it is not yet known how functionally full-fledged they can be. Scientists estimate that the adult male brain contains 86.1 ± 8.1 billion neurons[45 - Azevedo F. A. C., Carvalho L. R. B., Grinberg L. T., et al. Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain. Published: 18 February 2009 doi:10.1002/cne.21974.].
According to Friesen, the average lifespan of a human cell is 7–10 years. This statement has caused the popular misconception that "the human body renews every seven years." This is not true, because cell replacement is a continuous process: the body renews in different parts at different rates depending on the needs and functions.
ATOMS
At a more fundamental level, cells consist of molecules, which, in turn, consist of atoms (from Greek ἄτομος "uncuttable"). An adult human body weighing 70 kg contains about 6.7 octillion (6.7 × 10
) atoms, 96.5 % of which are chemical elements[46 - Chemical element is a type of atom that has certain chemical properties. The adult body consists of more than 60 chemical elements – Ed. note.] such as hydrogen, oxygen, carbon, and nitrogen. About 4 % are other ones: calcium, phosphorus, sodium, potassium, sulfur, etc.[47 - Alberts B., Johnson A., Lewis J., et al. Molecular Biology of the Cell. 4th edition. The Chemical Components of a Cell. https://www.ncbi.nlm.nih.gov/books/NBK26883/#A166 (https://www.ncbi.nlm.nih.gov/books/NBK26883/#A166).].
Most of the chemical elements come from the environment. When we eat, drink, or breathe, atoms enter the body. They not only compose cellular structure but also ensure the flow of chemical processes, supporting vital activity.
When we exhale, sweat, or lose body tissues, i.e., excrete anything into the environment, the atoms return to the Earth's biosphere. From there they enter the bodies of other people, animals, and plants. Thus, most of the atoms in the body are constantly replaced. And they do it differently – some in a few hours, others in a few years.
All these atoms are not regenerated every day. They have been around for billions of years and existed long before the Earth was formed. The first atoms formed in the early days of the universe, 13.7 billion years ago, about 380,000 years after the Big Bang. By that time, the universe had already cooled enough for electrons and protons to combine and form hydrogen and helium. The first stars were born from these atoms, and because of nuclear reactions in them, other heavier elements were formed.
Every particle of our body was once inside such stars or was formed because of its death. "Every atom in your body came from a star that exploded. It is the most poetic thing I know about physics. And, the atoms in your left hand probably came from a different star than your right hand. You are all stardust," writes physicist Lawrence Krauss in his book "A Universe from Nothing."
BODY SYSTEMS
Cells composed of atoms form tissues: epithelial, connective, muscular, and nervous. And tissues form organs. The latter, in turn, are combined into systems.
All systems interact closely with each other. For example, the digestive system provides the intake of nutrients in the blood for energy. However, the cells can produce energy only with oxygen, which is supplied by the respiratory system.
HOMEOSTASIS
Each cell can only function under certain conditions: temperature, acidity level (pH), a certain concentration of fluids, electrolytes, and oxygen – there are a lot of factors. Maintaining the balance of the body's systems necessary to sustain life is called homeostasis.
Under the influence of harmful factors which can damage the body, there is a redistribution of innate resources: with hypothermia, the body provides a flow of extra blood and, consequently, heat to the vital organs by narrowing the blood vessels of the skin. When overheated, on the contrary, skin vessels expand, which increases heat loss and remains constant internal temperature.
A well-established system of self-regulation is the most crucial component for a long and healthy life. The functioning of the body allows it to respond adequately to dangers and adapt to changing environmental conditions. Dysfunction in one organ inevitably affects the functioning of other organs and systems. For this reason, in old age people often face several diseases at once, each of which provokes and accelerates the progression of other disorders. A complication of diabetes mellitus, which is often associated with obesity, is a vascular disruption in the whole body, which in turn increases the risk of cardiovascular disease. Joint problems limit a person's mobility, which contributes to weight gain, which, in turn, puts stress on the joints. It is a developmental factor of a wide range of diseases.
It is very important to bear in mind that even a small health issue may result in a cascade of abnormal changes that lead to serious diseases. Even a small nidus of persistent infection, such as a decayed tooth or chronic tonsillitis, provokes the development of inflammation in the digestive tract and creates determinants for intestinal issues. Any violation in the supply of macro and micronutrients will affect every body's cell function with time.
Both physical and mental aspects are important for keeping a healthy body. It is known that chronic stress is an equally important contributor to disease than, for example, nutritional disorder, physical inactivity, or bad habits. On the background of distress, the level of cortisol – a hormone of chronic stress – increases, which negatively affects the immune system, provokes obesity and increases the risk of depression.
Thus, to maintain the stability of the internal environment, and to ensure its functional integrity, it is necessary to take care of all aspects of health. This is achieved by daily measures to prevent both physical and mental disorders, primarily by following a healthy lifestyle, as well as by responding quickly and appropriately to any abnormalities in health.
BRAIN – BODY, BODY – BRAIN
The brain controls the body like a powerful computer. It stores and constantly updates information. Since the brain contains a unique "body map," it can monitor the condition of internal organs and regulate important life processes – heart rate, respiration, blood pressure, sleep quality, digestion, and others.
However, this connection is not one-way. The brain receives information about the work of any organ due to receptors – nerve endings that transform stimuli of
the external and internal environment into electrochemical impulses. These impulses are sent through the spinal tracts to the brain, which, based on the information received, regulates the work of peripheral organs.
Due to the connection between the body and the brain, the organs are sensitive to changing body needs. A water deficit signal in the body turns into thirst because of vasopressin. This hormone, responsible for fluid maintenance, affects both the brain and the kidneys, causing them to inhibit fluid excretion.
EXERCISE TO BE HEALTHY
In the modern world, it is important to monitor the condition of your body. It is easy to yield to laziness, stress, and bad habits and not think about what affects the quality of function of organs and the body as a whole. Lifestyle determines human health: junk food leads to weight gain and the development of chronic diseases – obesity, osteoporosis, type 2 diabetes, and others, and with low physical activity the human also deprives themselves of several advantages. In addition, psychic tension, low or high sleep hours, bad habits, etc. affect the overall health. Many aspects and everyday decisions determine how well the body will work not only now, but also in the future. What is the first thing you need to pay attention to maintain, strengthen and improve the health of your own body?
Experts urge monitoring the diet. It should be balanced, diverse and contain as few harmful substances as possible. You need to introduce into the diet as much as possible vegetables and fruits, which contain vitamins and minerals. Eating a healthful diet will help reduce the number of pathogenic microorganisms in the intestine and increase the number of beneficial bacteria that help digest food. Besides, it is important not to forget to drink enough water to avoid dehydration, which in turn leads to fatigue, lapse of concentration, mood swings, and even urinary tract infections.
FUN FACT
THE ABILITY TO HEAR YOUR BODY CREATES A POSITIVE BODY IMAGE
Scientists from Anglia Ruskin University (UK) believe that awareness of how the body functions and attention to feelings allow you to better perceive your own body. Therefore, a human who perceives their body positively better reads and correctly interprets its signals, such as hunger or a sense of fullness. The study involved about 200 people, residents of Great Britain and Malaysia. After a preliminary fast, volunteers were asked to drink water and talk about their feelings. Participants also answered questions regarding their body perception and understanding of how it works.
It was found that people with a positive body image, aware of the principles of its work, experienced more intense feelings from drinking water on an empty stomach, compared to participants with a negative image of themselves and a worse understanding of physiology.
Experts explain that body image refers to thoughts and feelings related to appearance, and positive body image refers to actions based on love for the body, attention, respect, and correct interpretation of its signals. According to scientists, the better human treats and takes care of the body, the better they understand its "language." In turn, increased attention to the signals coming from, for example, the stomach and intestines, allows us to better imagine the processes, to assess the body function higher, and to form a positive body image.
"Our study shows that there is a direct connection between bodily awareness – in this case, the feeling of fullness – and body image," explains lead author Jennifer Todd. "In other words, people who are more aware of body functions, give their bodies a higher rating."
Experts emphasize that the inability to correctly decode internal signals, such as feelings of fullness or hunger, contributes to a negative body image because of an over-reliance on external characteristics related to appearance (e.g., shape and size).
An active lifestyle improves not only the cardiovascular and musculoskeletal system, but also provides protection against many diseases, rejuvenates the body, and prolongs life. Well-chosen workouts improve mood, sleep quality, and blood circulation, and reduce high blood pressure and the risk of heart disease. And even here, variety is great: you can walk, jog, dance, do aerobics, and ride a bike. You must realize that life only happens in motion, so you must move as much as possible.
It is important to know that even the way a human breathes affects their health. Improper breathing is dangerous, because less oxygen enters the lungs, which means that the functions of other organs can be impaired due to oxygen imbalance. The skin condition depends on the lungs: there is a high risk of wrinkles with a violation of gas exchange.
You need to quit bad habits: any addiction leads to physiological and psychological problems. Smoking increases the risk of premature death by 40 %, and smoking one pack a day by as much as 400 %. You should limit your alcohol intake, as excessive consumption of alcohol increases the risk of cancer, heart disease, cirrhosis, and others.
Body health depends firstly on lifestyle. Therefore, it is the human who is fully responsible for the condition of their body. Keeping the body in shape helps to prevent the development of many diseases, improve overall health, maintain it, and high activity for years to come.
CHAPTER 5
BRAIN AND NERVOUS SYSTEM
"THE WORLD IS SMALL, BUT THE HUMAN BRAIN IS IMMENSE," WROTE THE GREAT GERMAN ROMANTICIST FRIEDRICH SCHILLER IN HIS DRAMA "WALLENSTEIN'S DEATH." "ENGIST DIE WELT, UND DAS GEHIRNISTWEIT" TRANSLATES FROM GERMAN AS "THE WORLD IS NARROW, THE BRAIN IS WIDE." IN TERMS OF LOGIC, IT MAY SEEM ABSURD, SINCE IT IS THE WORLD THAT CAN BE CHARACTERIZED AS "WIDE" AND "IMMENSE," WHILE THE PHYSICAL PARAMETERS OF THE HUMAN BRAIN ARE EASILY MEASURABLE.
Yet we realize that we are talking not just about the organ enclosed in the braincase, but about what it generates: mind, consciousness, something truly immeasurable and spanless, which makes us human.
Brain damage – trauma, tumors, age-related changes – often has severe and sometimes irreversible consequences. And it is not just because the brain has vital centers, controlling something like breathing and heartbeat. Adverse changes in the structures responsible for higher nervous activity often lead to personal degradation and anomie. Loss of memory, cognitive powers, and full communication "turn off" the person from society, leaving them to a helpless existence. That is why maintaining brain health, preventing age-related disorders, and slowing their progression is a priorities for people who intend to live happily ever after.
HOW DOES HUMAN NERVOUS SYSTEM WORK?
The human nervous system consists of central (CNS) and peripheral (PNS) systems. The CNS consists of the brain and spinal cord, and the PNS consists of nerves "supervising" the work of each cell in the body. The main task of the nervous system is to combine the work of all body organs, tissues, and cells into a harmonious "mechanism," as well as to provide a rapid and adequate reaction to changes in the internal and external environment. The nervous system works in close tandem with the endocrine (hormonal) system, forming a neuroendocrine system that regulates the entire body with nerve impulses and special chemical matters – hormones.
BRAIN
The brain is the supreme commander of the nervous system, controlling the entire body. In addition, its unique structure of it is the basis for the higher mental functions that underlie consciousness. The brain weighs only 1.2–1.4 kg, representing an average of about 2 % of the human body weight. The male brain generally is 10–12 % heavier and 10 % bulkier than the female brain[48 - Zaidi Z. F. Gender Differences in Human Brain: A Review. The Open Anatomy Journal. 2010;2:37–55. https://benthamopen.com/AB-STRACT/TOANATJ2-37.].
The brain consists of several divisions.
● The largest part of the human brain is the forebrain. The cerebral cortex is a part of it. Both hemispheres (right and left) are divided into four lobes: frontal, occipital, temporal, and parietal. The cerebral cortex is responsible for the perception of all information coming from the external and internal environment: visual, auditory, olfactory, gustatory, and somesthetic cortices are located here. The cortex is also responsible for the human higher nervous activity, including thinking and speech.
● The midbrain contains the visual and auditory centers, which are responsible for processing impulses from the corresponding analyzers. In addition, the midbrain has a tremendous impact on the cerebral cortex. If the cortex is the "consciousness realm," then the midbrain is the "kingdom of the subconscious." The processes occurring in the midbrain can stimulate or inhibit the processes occurring in the cortex. There is also dopamine, a neurotransmitter that plays a key role in the formation of motivation, healthy habits, and addiction, is synthesized.
● The diencephalon mediates the transfer of stimuli to the hemispheres and helps adapt adequately to environmental modifications. Regulates the work of metabolic processes and endocrine glands. Manages the cardiovascular and digestive systems. Regulates sleep and wake, water, and food intake.
● The cerebellum is a brain region that is primarily responsible for maintaining balance and load distribution between muscles, unconscious body skills, and bodily memory.
● The medulla oblongata is an extension of the spinal cord. Nerve pathways that carry information from the whole body and back pass through it, as well as breathing and blood flow control centers. Damage to the medulla oblongata leads to quick death. It is connected to the overlying parts of the brain by the pons, part of the brain stem.
NERVE CELLS
The main structural unit of the central nervous system is the nerve cell or neuron. Neurons consist of a body and several projections. Nerve cell bodies form the gray matter of the brain and spinal cord, and the long myelin-covered projections form the white matter. Gray matter forms the cerebral cortex and the underlying nuclei, and the white matter forms the nerve pathways – a kind of "wires" through which different parts of the brain and other structures "communicate."
At last count, the number of neurons in the cerebral cortex is 14–16 billion, while in the cerebellum is 55–70 billion[49 - Von Bartheld C. S., Bahney J., Herculano-Houzel S. The search for true numbers of neurons and glial cells in the human brain: A review of 150 years of cell counting. J Comp Neurol. 2016;524(18):3865–3895. doi:10.1002/cne.24040.].
The neuron body contains many fibers that form the cytoskeleton: it helps the nerve cell to keep its shape. It also forms some sort of "tracks" where vesicles with neurotransmitters are delivered to the ends of the projections. There are two types of projections – short (dendrites) and long (axons). Most often, neurons have many dendrites and only one axon.
Axons can transmit nerve impulses over long distances – to other brain structures, to the spinal cord and to target organs. As a rule, several neurons located above or below the "author" of the impulse are involved in impulse delivery from the brain to the "distant regions" and back.
Axon terminals approach the body of the next chain member, releasing a neurotransmitter into the gap between the terminal and the body (or projection) of the other neuron. These "meeting places" are called synapses[50 - Synapses are divided into chemical, electrical, and mixed. – Ed. note.]: this is where the electrical impulse is converted into a chemical. The next neuron "receives" the chemical signal and converts it again into an electrical one, sending an impulse to its destination.
Sometimes there are several such "stop-overs" on the way of "agents" to the destination – this system makes it possible to maintain a high intensity of the impulse, not allowing it to fade away. Axons are covered with myelin sheath, which is like an electrical insulator. Myelin consists of glial cells, as will be discussed later. Short projections of neurons – dendrites – help to set "local communication" between neurons. They are myelin-free. Each neuron is connected to thousands and tens of thousands of other neurons and target cells with short and long projections.
NEUROGLIA: THE BRAIN'S LIFE SUPPORT AND DEFENSE SYSTEM
Besides neurons, the "base" cells of the brain, the nervous system includes auxiliary structures – glial cells. There are several types of glial cells: for example, astrocytes, oligodendrocytes, microglia, and microglia. For many years the number of glial cells was believed to be exceeding the number of neurons by 8–10 times, but nowadays, it is proved that the ratio of neurons and glial cells is approximately the same[51 - Von Bartheld C. S., Bahney J., Herculano-Houzel S. The search for true numbers of neurons and glial cells in the human brain: A review of 150 years of cell counting. J Comp Neurol. 2016 Dec 15;524(18):3865–3895. doi:10.1002/cne.24040. Epub 2016 Jun 16. PMID: 27187682; PMCID: PMC5063692.].
Glial cells are involved in the formation of the blood-brain barrier, a filter protecting the brain from microbes, some cells, and toxins. Glial cells also form the microenvironment around neurons, transport nutrients to nerve cells, excrete waste, form myelin sheaths, etc.
FUN FACT
HOW THE "INTESTINAL BRAIN" AFFECTS THE ENTIRE BODY
The human intestine contains a unique cluster of nerve cells – the enteric nervous system (ENS). Sometimes it is also called the intestinal or "abdominal" brain. The ENS uniqueness, its difference from the nerve clusters in other organs, is associated with several characteristics. Firstly, it includes about half a billion neurons! Secondly, the ENS is very similar in structure to the brain. Several types of neurons can receive and send signals and provide the motor function of muscles. The enteric nervous system has its glial cells, which, as in the brain, nourish neurons and activate immune mechanisms. Thirdly, a huge number of neurotransmitters are synthesized in the intestine. The spectrum of the internal neurotransmitters in the ENS is as wide as in the central nervous system. Over 90 % of serotonin and 50 % of dopamine are synthesized in the body being produced in the intestine. Almost all ENS neurotransmitters are of bacterial origin.
All these factors underlie the fourth key feature of the ENS: its autonomy. Unlike other parts of the nervous system, the intestinal brain can function without control by the central and peripheral nervous system, even with extensive brain injury. At the same time, the brain, and the intestine nervous system are closely linked, forming the "gut-brain" axis[52 - The gut-brain axis includes the entire pool of intestinal microorganisms (microbiota), the "intestinal brain" and the central nervous system. – Ed. note.]. Therefore, the ENS not only regulates the digestive tract but also affects the entire body.
Studies show that some diseases affecting the brain, such as Parkinson's disease, are associated with certain changes in the intestinal microbiota.
Scientists at Washington University reviewed 150 studies and found that age-related loss of glial cells (pericytes), which form the blood-brain barrier, significantly increases the risk of developing Alzheimer's disease[53 - Banks W. A., Reed M. J., Logsdon A. F., et al. Healthy aging and the blood-brain barrier. Nat Aging. 2021;1:243–254. doi:10.1038/s43587-02100043-5.].
Glial cells in the blood-brain barrier act as "pumps" that remove toxic beta-amyloid proteins from the brain. Clusters of these proteins are one of the causes of Alzheimer's disease. Disruption of the "pump," caused by age-related loss of glial cells, increases the risk of dementia. Scientists believe that due to a decrease of glial cells in the blood-brain barrier during aging, the brain starts, figuratively speaking, to "leak out," which contributes to cognitive impairment.
SPINAL CORD
The spinal cord is part of the human central nervous system and an extension of the brain. It is in the spinal canal and has the form of a long rod, which extends from the medulla oblongata. The rod center contains a spinal canal filled with cerebrospinal fluid. The central part of the spinal cord is represented by gray matter formed by the bodies of neurons, around which there is white matter formed by the long neuron processes.
White matter consists of nerve pathways through which impulses travel from the brain to the spinal cord (descending tract) and back (ascending tract). That is how different parts of the spinal cord come into contact. Gray matter contains sensory and motor neurons. Their projections connect and form sensory and motor roots, which also connect and form spinal nerves.
The spinal cord performs a conductive function – it is a link between the brain and the peripheral nervous system. At the same time, the spinal cord regulates some processes independently, without the direct involvement of the brain. For example, when we touch a heating object, we pull our hand back automatically. This reflex is formed at the spinal cord level – the movement occurs unconsciously.
NERVES (PERIPHERAL NERVOUS SYSTEM)
A total of 31 pairs of spinal nerves depart from the spinal cord – at the level of each vertebra. All spinal nerves contain sensory fibers, neuron projections that collect information from tactile, pain, temperature receptors of the skin, etc., and send it for "processing" to the central nervous system. They also contain motor fibers through which impulses from the brain and spinal cord travel to the muscles, making them contract.
As they move away from the spinal cord, the roots begin to branch, forming nerve trunks, large nerves, and then dividing into smaller ones. Each nerve ends with a nerve ending near a specific body part. All nerves divide into motor, sensory, and mixed (containing both types of projections) ones.
A separate group consists of 12 pairs of cranial nerves. The bodies of neurons, which projections form the cranial nerves, are part of the special clusters of gray matter, the nuclei of the brain stem. They go beyond the periphery from openings in the skull, and the areas they "work with" do not extend beyond the head and neck. The only exception is the vagus nerve, which plays a crucial role in regulating the work of internal organs.
The peripheral nervous system is divided into autonomic and somatic. The somatic nervous system regulates the functioning of the skeletal muscles, which are responsible for movements that we consciously control. The autonomic nervous system regulates the living environment, which is beyond our consciousness. These include breathing, heartbeat, sweating, etc.
For example, when we face any danger, the autonomic nervous system first activates: the pulse and breath quicken, cold sweat appears, and the muscles turn rigid. All these reactions are unconscious. And then the somatic nervous system comes into play: we decide "fight or flight" by giving the appropriate orders to our skeletal muscles.
