Age-related characteristics of the nervous system presentation. Features of the nervous system
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Anatomical and physiological features of the nervous system in children. Neuropsychic development
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NERVO-MENTAL DEVELOPMENT OF A CHILD By the time a child is born, his nervous system, compared to other organs and systems, is the least developed and differentiated. At the same time, the greatest demands are placed on this system. The nervous system ensures the body’s adaptation to environmental conditions; it regulates the vital functions of internal organs and ensures their coordinated activity.
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ANATOMICAL AND PHYSIOLOGICAL FEATURES The formation of the nervous system occurs very early - in the first week of intrauterine development. At 5-6 weeks, the brain and spinal cord begin to form. The most intense division of nerve cells occurs from 10 to 18 weeks, which is a critical period for the formation of the central nervous system. In the absence of a damaging factor during pregnancy and normal childbirth, the child is born with a healthy nervous system.
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If pathological factors affected the fetus during pregnancy, then the damaged brain tolerates even normal childbirth worse (antenatal damage). In addition, injury to brain tissue is possible during complicated childbirth (intrapartum damage). Severe inflammatory diseases (sepsis, meningitis, encephalitis, etc.), skull trauma, and malnutrition can lead to postnatal damage.
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The main antenatal risk factors: various chronic maternal diseases (anemia, hypertension, chronic glomerulonephritis, heart defects, diabetes mellitus, toxoplasmosis, rheumatic fever, etc.); acute infectious diseases of the mother during pregnancy. intrauterine infection of the fetus. genetic defects (mentally retarded parents are 2 times more likely to have similarly handicapped children than the healthy population); alcohol, parental smoking. occupational hazards (hard physical labor, vibration); exogenous teratogenic factors (increased background radiation, chemicals, etc.); signs of a burdened obstetric history (birth of the first child before 16-18 or after 30 years, interval between births less than 2 years, threat of miscarriage, stressful conditions); incompatibility with the Rh-shactor and the ABO system. post-term pregnancy, multiple pregnancy, malnutrition of the newborn.
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At birth, the brain is the most developed organ in size. However, although all the structures and convolutions are present, its functionality is reduced. In a newborn, the brain mass is 1/8-1/9 of body weight, by the end of the first year it doubles and is equal to 1/11-1/12 of body weight, at 5 years - 1/13-1/14, at 18 -20 years - 1/40 body weight. Thus, the smaller the child, the greater the brain mass relative to body weight.
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The child's brain tissue is characterized by significant vascularization, especially of the gray matter. At the same time, the outflow of blood from the brain tissue is weak. Therefore, toxic substances accumulate in it more often. A nerve cell requires 22 times more oxygen than any somatic cell. Therefore, in many diseases, it easily falls into oxygen starvation, which is manifested by hypoxic encephalopathy. Brain tissue is richer in proteins. And since 1 g of protein retains 17 g of water, this contributes to the frequent development of cerebral edema. With age, the amount of protein decreases from 46% to 27%. By the age of one and a half years, the amount of water in the brain tissue decreases and is equal to the indicators in older individuals.
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The amount of cerebrospinal fluid in a baby is less compared to an adult and gradually increases from 30-40 ml in a newborn to 40-60 ml at 12 months, and subsequently to 150 ml (as in adults). The anatomical structure of the child's brain, consisting of five parts, is similar to the structure of an adult. The cerebral cortex is the most immature in the newborn. It ensures the formation of higher nervous activity and matures later than all departments - by 5-6 years.
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The cerebellum is poorly developed, located higher, has a more elongated shape, shallow grooves; The medulla oblongata is located more horizontally;
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The main cell of the nervous system is the neurocyte. An adult has 16 billion such cells. However, by birth, the number of mature neurocytes, which will then become part of the cerebral cortex, is only 25% of the total available number of diffusely scattered cells. By 6 months there are already 66% of them, by the age of one year - 90-95%, by one and a half years, all 100% of neurocytes are similar to the neurocytes of an adult. Hence the conclusion: if some pathological factor damages brain cells, then compensation is possible only up to 18 months, i.e. the disease must be recognized before one and a half years, since later treatment will be ineffective.
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The process of normal formation of nerve cells is influenced by: nutrition (it must be rational in volume and composition); imprinting - the first impression that a child has immediately after birth shapes the nature of his response to environmental factors. This affects the entire future life and activity of the body. As you know, nowadays, in the delivery room, the baby is placed on the mother’s stomach and applied to her chest. He has been breastfed for a long time. All this is an impulse for the good development of the nervous system, a normal relationship between the child and the mother; raising a child, family ties, the usefulness of the family and the moral climate in it.
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In addition to the quantitative characteristics of mature cells, the histological immaturity of nerve cells before the birth of a child plays an equally important role: they are oval in shape, with one axon, there is granularity in the nuclei, and there are no dendrites. Subsequent differentiation consists of elongating them, elongating axons, and branching dendrites. Next comes myelination and the formation of synapses (connections between the processes of nerve cells). Differentiation begins in utero and ends by the age of 6-7 years.
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Morphological features of the spinal cord: Its structure is more complete than the brain; Relatively longer than in adults; In fetuses it reaches the sacral canal, in newborns - to the lower edge of the second lumbar vertebra, in older ones - to the first lumbar vertebra; The weight of the spinal cord at birth is 2-6 g, up to 5 years it doubles, and up to 20 years it increases 8-9 times.
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Autonomic nervous system: Sympathicotonia predominates; At 3-4 years of life - vagotonia; From 5 to 12 years the alignment of the two systems is established; From the age of 12-13 years, vegetative-vascular dystonia may occur due to hormonal changes.
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Indicators of cerebrospinal fluid in children of different ages: Indicators Newborns Children aged 1-3 months. Children aged 4-6 months. Children over 6 months of age. Color and transparency Xanthochrome, transparent colorless, transparent colorless, transparent colorless, transparent Pressure, mm H2O 50-60 50-100 50-100 80-150 Cytosis in 1 µl Up to 15-20 Up to 8-10 Up to 8-10 Up 3-5 Cell type Lymphocytes, single neutrophils Lymphocytes Lymphocytes Lymphocytes Protein, g/l 0.35-0.5 0.2-0.45 0.18-0.35 0.16-0.25 Pandi reaction + or + + + - or + - Sugar, mmol/l 1.7-3.9 2.2-3.9 2.2-4.4 2.2-4.4 Chlorides g/l 7-7.5 7- 7.5 7-7.5 7-7.5
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ASSESSMENT OF NEUROPSYCHIC DEVELOPMENT When characterizing the nervous system in pediatrics, two synonymous definitions are used: neuropsychic development (NPD) and psychomotor development (PMD). The criteria for assessing NP R are: - motor skills; - statics; - conditioned reflex activity (1 signal system); - speech (2 signal system); - higher nervous activity.
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Motor skills Motor skills (movement) are the purposeful, manipulative activities of a child. For a healthy newborn in a calm state, the so-called physiological muscle HYPERTONUS and, against this background, a flexion posture are characteristic. Muscle hypertonicity is symmetrically expressed in all positions: on the stomach, back, in positions of lateral and vertical suspension. The arms are bent at all joints, adducted and pressed to the chest. The hands are bent into a fist, the thumbs are brought towards the palm. The legs are also bent at all joints and slightly abducted at the hips; dorsiflexion predominates in the feet. Even during sleep, the muscles do not relax.
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The movements of the newborn are limited, chaotic, disorderly, athetosis-like = trembling. Tremor and physiological muscle hypertonicity gradually fade away after the first month of life.
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Subsequently, motor skills in a healthy child develop in the following order: 1) first, the movement of the eye muscles becomes coordinated (at 2-3 weeks), when the child fixes his gaze on a bright object; 2) turning the head after the toy indicates the development of the neck muscles: 3) manual activity of the hands develops at the 4th month of life: the child brings the upper limbs closer to the eyes and examines them, rubs the diaper, pillow. Movements become purposeful: the baby takes the toy with his hands (in the second half of the year he can take a bottle of milk himself and drink it, etc.); 4) at 4-5 months, coordination of the movement of the back muscles develops, which is manifested first by turning over from the back to the stomach, and at 5-6 months - from the stomach to the back; 5) when, by the end of the first year of life, the child himself goes for an interesting object to another corner of the room, then a sign of motor skills is not just the process of walking, but the coordinated, purposeful movement of all muscles in the required direction.
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Statics Statics is the fixation and holding of certain parts of the body in the required position. The first sign of statics - holding the head - appears in the second or third month of life; at 3 months the child should be able to hold his head well in an upright position. The second sign - the baby is sitting - is developed at 6-7 months. In addition, at the 6th month the baby begins to creep, and at the 7th month he crawls well. The third sign - the child is standing - at 9-10 months. The fourth sign - the baby is walking - towards the end of the first year of life.
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Conditioned reflex activity Conditioned reflex activity is the child’s adequate response to irritating environmental factors and his own needs. The main reflex in a newborn is the food dominant. It's time for feeding, the baby is hungry and he's crying - this is good. He sucked his mother's breast, ate, calmed down, and fell asleep. Towards the end of the first month, a few minutes after the start of feeding, there is a short pause - the baby carefully examines the mother’s face and feels the breast. In the second month, a smile forms, in the third, a joyful movement of the limbs at the sight of the mother. All this indicates the formation of conditioned reflexes to external stimuli.
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Signs of conditioned reflex activity include auditory and visual concentration. In the second month of life, these signs are checked by a neurologist: to assess hearing, the doctor claps his hands at a distance of 30-40 cm to the side of the ears of the child lying on the changing table, you can slam the table itself - in this case, a healthy child should BLINK his eyelids. to determine vision, the doctor holds a bright object at a height of 30 cm above the eyes of the lying baby from one side to the other - with developed vision, the child’s eyes should follow the movement of the object.
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Speech Until the end of the first year, sensory speech appears: the baby’s understanding of individual words that sound from the outside. This is detected by turning the head, pulling the arms, etc. Speech appears in a child at 4-6 weeks, when he begins to howl. The pronunciation of the first sounds is called humming (a, gu-u, uh-uh, etc. - the hum of voices in English hum, buzz). At 6 months, the child pronounces individual syllables (ba-ba-ba, ma-ma-ma, etc.), without understanding their meaning, which is called baby-talk, babble, prattle. By the end of the first year of life, the baby’s vocabulary already contains 8-12 words, the meaning of which he understands (give, na, dad, mom, etc.). Among them there are onomatopoeias (am-am - eat, aw-aw - dog, tick-tock - clock, etc.). At 2 years the vocabulary reaches 300, short sentences appear.
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Higher nervous activity Higher nervous activity - this criterion develops on the basis of the formation of the nervous system, the formation of all previous criteria, the upbringing and development of the child. It is a sign of the maturation of a person’s mental capacity and intelligence. The final conclusion about the state of higher nervous activity can be made at 5-6 years.
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Unconditioned reflexes: Persistent reflexes exist throughout life. Transient reflexes exist after birth, but gradually disappear at a certain age. Setting reflexes are reflexes that do not exist immediately after birth, but are formed at a certain age.
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PERSISTENT REFLEXES: swallowing; tendon reflexes of the limbs (one example is a blow to the tendon of the quadriceps femoris muscle below the kneecap causing extension of the leg at the knee joint); corneal (a light touch of soft paper or cotton wool to the cornea of the eye causes the eyelids to close; also called the corneal reflex); conjunctival (similar to corneal; called by the same method, but from the conjunctiva); brow (tapping on the inner edge of the brow causes the eyelids to close; also called the orbiculopalpebral reflex).
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TRANSITION REFLEXES: - oral = brainstem reflexes (the arc closes in the medulla oblongata); - spinal reflexes (the arc closes at the level of the spinal cord); - myeloencephalic postural reflexes (regulated by the centers of the medulla oblongata and midbrain).
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The development of a child’s body after birth is divided into several periods: Newborn period (up to 1 month) Infancy period (from 1 month to 1 year) Nursery period (from 1 year to 3 years) Preschool period (from 3 to 7 years) Primary school period (from 7 to 13 years for boys and from 7 to 11 years for girls) Adolescence (from 13 to 17 years for boys and from 11 to 15 years for girls)
At school age, both quantitative and qualitative changes occur in the child’s body: skeletal growth, growth of internal organs, increase in the overall dimensions of the body and the number of body cells, and in these cells the number of biomolecules increases. qualitative changes are the functional maturation of growing organs, for example, myelination of nerve fibers accelerates the conduction of nerve impulses, this leads to improved controllability of the body by the nervous system.
Functional maturation of brain structures manifests itself as an increase in the volume of memorized information, an increase in the degree of consciousness in controlling one’s emotions, one’s behavior, and the development of volitional qualities. At the level of the cardiovascular system, functional maturation manifests itself in the form of a restructuring of the vegetative status - in school-age children, the influence of the sympathetic nervous system gradually increases, reaching the level of the adult organism.
The period of organ growth and the period of its maturation do not always coincide. For example, muscles first grow in length following the growing bones, and then the required amount of enzymatic molecules, reserves of polysaccharides, fatty acids, myoglobin, etc. begins to accumulate in long but thin muscle fibers. The development of different organs occurs at different times - for example, the bones of the skeleton grow first, and then the internal organs begin to grow and mature. A complicating point in the interaction of qualitative and quantitative development processes is their separation in time, or heterochrony.
Musculoskeletal system The skeletal system of primary schoolchildren is not yet strong enough, bone ossification is not complete, the joints are very mobile, the ligamentous apparatus is elastic, the skeleton contains a large amount of cartilaginous tissue. It is believed that early school age is optimal for the development of mobility in all major joints. On the other hand, during this age period the possibility of poor posture is also maximum. Children often experience curvature of the spine, flat feet, growth retardation, etc. The final formation of the skeletal system is completed mainly by adolescence
Musculoskeletal system The muscles of children of primary school age have thin fibers containing a minimal amount of proteins and energy resources (glycogen, fatty acids). Large muscles are developed and develop faster than small ones, so children find it difficult to perform small and precise movements; their coordination is not sufficiently developed. At an older age, there is a gradual strengthening of the ligamentous apparatus and an increase in muscle mass. At this age, insufficient physical activity leads to functional disorders of posture (asymmetry of the shoulders and shoulder blades, stooping)
Nervous system Morphological development of the nervous system is mainly completed by the age of 6-7 years. Myelination of the main nerve fibers is complete at this age. Children have a fairly developed sense of balance, coordination of movements, dexterity, and a fairly high speed of reaction to any stimuli.
Nervous system Functional maturation of the nervous system at 6-7 years is not yet complete. The main feature of primary school age is the predominance of excitation processes in the nervous system with a lack of inhibitory influences, hence the lack of stability of attention and rapid fatigue of primary school students. During puberty, all types of internal inhibition are also disrupted, and the formation of new conditioned reflexes and the consolidation and modification of existing dynamic stereotypes become difficult. With the end of puberty (13 years for girls and 15 years for boys), the processes of higher nervous activity improve.
A distinctive feature of children of primary school age is the need for movement as a need at the biological level. The needs (or motivations) of a person are divided into 3 large groups: Biological (energy, plastic substances, water, rest, procreation) - inherent in animals, plants, microorganisms. Social (definition and increase of social status) - inherent in fairly highly organized animals living in large groups Ideal (intellectual development, aesthetic development, spiritual development, mental development) - inherent only in humans
The need for movement becomes a need at the biological level only in mammals, representatives of the most evolutionarily advanced class of the animal world, since they have a stage of raising their young, when adults not only feed them, but also pass on their life experience. To master parental experience, cubs must do something, move somehow, communicate with peers and adults. That is why, in the evolution of young mammals, the need for movement becomes a need at the biological level, like food and sleep.
The need for movement of children of primary school age According to the pedometer, thousands of movements per day. In terms of time - 1.5-2 hours of active physical activity per day, of which at least 30 minutes are at a sufficiently high level of load, with heart rate up to beats/min. In energy consumption kcal per day. As part of the school program - 1 hour of physical education per day (5 per week) + classes in the sports section.
It is known that limiting children’s biological needs leads to disruptions in their development. Restriction in the amount of food causes retardation of growth and development, restriction in quality composition, for example, vegetarianism, causes a delay in functional maturation or even the inability to form some functions. It is known that children lacking protein nutrition suffer from intellectual abilities. Restricting children from water is often the cause of pathology of the excretory system. Limitation in communication leads to severe neuroses and psychopathological conditions. Sleep restriction is a severe torture even for adults.
In our real life, the restriction in children’s movement reaches % of the norm. The fact that restriction in movement is the cause of neuroses, psychopathology, and psychosomatic disorders is known to a lesser extent, although hypokinesia occupies one of the first places in terms of the level of impact on the child’s body.
Respiratory system The number of alveoli in the lungs reaches the final adult level by 8 years. Subsequently, there is only an increase in lung volumes. These volumes are directly proportional to body size, therefore an increase in lung volumes and an increase in maximum ventilation rates are also directly proportional to an increase in body size
Condition of the heart muscle The size of the heart is directly related to the size of the body; children have smaller hearts than adults. Indicators of cardiac performance (stroke volume, minute volume of blood circulation) in children are lower than in adults. The heart rate in children is higher than in adults (up to 100 beats/min). The maximum oxygen consumption in children is significantly lower than in adults. In general, children have lower functional capabilities of the cardiorespiratory system, which imposes quite strict restrictions on engaging in sports related to endurance.
Blood pressure Blood pressure directly depends on body size. At the age of 7-10 years, indicators of 90/60 – 100/70 mm Hg are considered normal. During puberty, as the influence of the sympathetic nervous system increases, it gradually reaches the level of an adult (115/70 mm Hg).
Blood pressure Blood pressure depends not only on the state of the vascular system itself, but also on the psycho-emotional status of the child. The “white coat syndrome” is known, when blood pressure rises or falls significantly when entering a doctor’s office or simply when a person appears in a white coat. Any emotional impact causes a vascular reaction. Any adaptive changes in the body, for example, a change of place of study, the arrival of a new teacher, or joining a new team, cause changes in blood pressure.
In adults, a state of psycho-emotional stress or physical fatigue is usually accompanied by an increase in blood pressure. In children, with their still immature type of sympathetic regulation of vascular tone, on the contrary, a drop in blood pressure is much more often observed. In addition, when measuring blood pressure with automatic devices, especially with 2-3 measurements in a row, vascular spasm occurs very quickly in children, and measuring blood pressure becomes technically impossible. Blood pressure
Aerobic capacity of the body of primary school children The functional immaturity of the respiratory and cardiovascular systems of the body of children in primary school underlies their lower aerobic capacity, and, consequently, lower performance in sports related to endurance (running, skiing, cycling, rowing) . The Institute of Developmental Physiology has developed recommendations for the start time of the following sports: - Rowing - years, - Athletics - years, - Skiing - 9-12 years, - Swimming - 7-10 years.
Anaerobic capabilities of the body of younger schoolchildren The anaerobic capabilities of the child’s body are also less than those of an adult. This is due to the lower content of glycolysis enzymes in muscle fibers, as well as glycolysis substrates - polysaccharides and fatty acids. In this regard, children have lower performance in sports related to speed and strength (short distance running, jumping). According to the recommendations of the Institute of Developmental Physiology, children can engage in: -Basketball and volleyball - from the age, -Boxing - from the age, -Water polo - from the age, -Football, hockey - from the age.
Presentation on the topic: The nervous system is a system for controlling (regulating) functions in the body
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Presentation on the topic: The nervous system is a system for controlling (regulating) functions in the body
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Reflex principle of regulation of functions (reflex theory) The key point in the development of reflex theory is the classic work of I.M. Sechenov (1863) “Reflexes of the Brain.” Main thesis: All types of conscious and unconscious human life are reflex reactions.
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Reflex, reflex arc, receptive field Reflex is a universal form of interaction between the body and the environment, the body’s reaction that occurs to irritation of receptors and is carried out with the participation of the nervous system. Under natural conditions, a reflex reaction occurs with threshold, suprathreshold stimulation of the input of the reflex arc - the receptive field of this reflex. A receptive field is a certain area of the perceptive sensitive surface of the body with receptor cells located here, the irritation of which initiates and triggers a reflex reaction. The receptive fields of different reflexes have different localizations. Receptors are specialized for optimal perception of adequate stimuli. The structural basis of the reflex is the reflex arc. Reflex (<лат. reflexus отраженный). Термин ввел И. Прохаска. Идея отраженного функционирования принадлежит Р. Декарту.
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Reflex arc A reflex arc is a series-connected chain of neurons that ensures the implementation of a reaction (response) to stimulation. The reflex arc consists of: Afferent (A); Central (C,V); Efferent (E) links. The links are connected by synapses (c). Depending on the complexity of the structure of the reflex arc, reflexes are distinguished: Monosynaptic (A→c ¦E); Polysynaptic (A→c ¦B→c ¦E).
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Reflex ring Feedback (reverse afferentation) is the structural basis of the reflex ring: the impact of a working organ on the state of its center. Feedback loop – information about the implemented result of a reflex reaction to the nerve center that issues executive commands. Meaning: Makes constant amendments to a reflex act.
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Classification of reflexes Unconditioned and conditioned (according to the method of formation of the reflex arc: genetically programmed or formed in ontogenesis); Spinal, bulbar, mesencephalic, cortical (according to the location of the main neurons, without which the reflex is not realized); Interoreceptive, exteroceptive (according to receptor localization); Protective, nutritional, sexual (according to the biological significance of reflexes); Somatic, vegetative (based on the participation of the nervous system). If the effectors are internal organs, we talk about vegetative reflexes, if skeletal muscles - about somatic reflexes); Cardiac, vascular, salivary (according to the final result).
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Nerve center: definition The reflex activity of the body is largely determined by the general properties of the nerve centers. The nerve center is an “ensemble” of neurons that are coordinately involved in the regulation of a certain function or in the implementation of a reflex act. Neurons of the central nervous system (nerve centers): Mainly interneurons (interneurons); Multipolar (dendritic tree! spines); Diverse in chemistry: different neurons secrete different mediators (ACh, GABA, glycine, endorphins, dopamine, serotonin, neuropeptides, etc.)
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Classification of nerve centers Morphological criterion (localization in parts of the central nervous system): Spinal centers (in the spinal cord); Bulbar (in the medulla oblongata); Mesencephalic (in the midbrain); Diencephalic (in the diencephalon); Thalamic (in the visual thalamus); Cortical and subcortical.
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Nerve centers Nervous activity is based on processes that are active and opposite in their functional properties: Excitation; Braking. Functional meaning of inhibition: Coordinates functions, i.e. directs excitation along certain paths, to certain nerve centers, turning off those paths and neurons whose activity is not currently needed for a specific adaptive result. Performs a protective (protective) function, protecting neurons from overexcitation and exhaustion under the influence of extremely strong and prolonged stimuli.
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Features of the spread of excitation in the central nervous system: one-sidedness In the central nervous system, within the reflex arc and neural circuits, excitation goes, as a rule, in one direction: from the afferent neuron to the efferent one. This is due to the structural features of the chemical synapse: the transmitter is released only by the presynaptic part.
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Features of the spread of excitation in the central nervous system: slow conduction It is known that excitation along nerve fibers (periphery) is carried out quickly, and in the central nervous system it is relatively slow (synapses!). The time during which excitation is carried out in the central nervous system from the afferent to the efferent pathway is the central reflex time (3 ms). The more complex the reflex reaction, the longer its reflex time. In children, the central delay time is longer; it also increases with various influences on the human body. When the driver is tired, it can exceed 1000 ms, which in dangerous situations leads to slow reactions and road accidents.
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Features of the propagation of excitation in the central nervous system: summation This property was first described by I.M. Sechenov (1863): When a number of subthreshold stimuli act on a receptor or afferent pathway, a response occurs. Types of summation: Sequential (temporary); Spatial. One subthreshold afferent stimulus does not cause a response, but creates local excitation in the central nervous system (local response) - an amount of mediator insufficient for action).
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Features of the propagation of excitation in the central nervous system: temporal summation A. In response to a single stimulus, a synaptic current (shaded area) and a synaptic potential arise, B. If soon after one postsynaptic potential another occurs, then it is added to it. This phenomenon is called temporal summation. The shorter the interval between two successive synaptic potentials, the higher the amplitude of the total potential.
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Features of the spread of excitation in the central nervous system: spatial summation Spatial summation: two or more subthreshold impulses enter the central nervous system along different afferent pathways and cause a reflex response. For an impulse to occur in a neuron, it is necessary that the initial segment of the axon, which has a low excitation threshold, be depolarized to a critical level
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Features of the spread of excitation in the central nervous system: occlusion The phenomenon of occlusion (<лат occlusus запертый) – уменьшение (ослабление) ответной реакции при совместном раздражении двух рецептивных полей по сравнению с арифметической суммой реакций при изолированном (раздельном) раздражении каждого из рецептивных полей. Причина феномена – перекрытие путей на вставочных или эфферентных нейронах благодаря конвергенции.
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Features of the spread of excitation in the central nervous system: protobranie (post-activation facilitation) Protobranie (post-activation facilitation): After excitation caused by rhythmic stimulation, the subsequent stimulus causes a greater effect; To maintain the same level of response, less force of subsequent stimulation is required. Explanation: Structural and functional changes in synaptic contact: Accumulation of vesicles with transmitter at the presynaptic membrane;
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Properties of nerve centers: high fatigue Prolonged repeated stimulation of the receptive field of the reflex → weakening of the reflex reaction until complete disappearance - fatigue. Explanation: At synapses: the supply of transmitter is depleted, energy resources are reduced, postsynaptic receptors adapt to the transmitter; Low lability of the center → the nerve center functions with maximum load, as it receives stimuli from a highly labile nerve fiber that exceeds the lability of the nerve → fatigue.
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Properties of nerve centers: increased sensitivity to lack of oxygen. This is due to the high intensity of metabolic processes: 100 g of nervous tissue (dog’s brain) uses 22 times more O2 than 100 g of muscle tissue. The human brain absorbs 40 - 50 ml of O2 per minute: 1/6 - 1/8 of the total O2 consumed by the body at rest. Sensitivity of neurons in different parts of the brain: Death of neurons in the cerebral cortex - after 5 – 6 minutes. after complete cessation of blood supply; Restoration of the functions of brain stem neurons is possible after 15–20 minutes of complete cessation of blood supply; The functions of spinal cord neurons are preserved even after 30 minutes of lack of blood circulation.
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Properties of nerve centers: plasticity and tone Plasticity is the functional mobility of the nerve center: the possibility of its inclusion in the regulation of various functions. Tone is the presence of a certain background activity. Explanation: a certain number of brain neurons at rest (in the absence of special external stimuli) are in a state of constant excitation - generating background impulse flows. The presence of “sentinel neurons” in the higher parts of the brain was discovered even in a state of physiological sleep
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Inhibition in the central nervous system Inhibition is an active process that weakens existing activity or prevents its occurrence. The process of inhibition in the central nervous system was first experimentally observed in 1862 by I.M. Sechenov in an experiment that was called the “Sechenov inhibition experiment.” "Copernicus of the Second Universe".
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Types of inhibition Primary and secondary (presence or absence of a special morphological formation - inhibitory synapse); Presynaptic and postsynaptic (place of origin – zone of interneuronal contact); And also Returnable; Reciprocal; Lateral.
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Secondary inhibition is carried out without the participation of special inhibitory structures and develops in excitatory synapses. It was studied by N.E. Vvedensky and called pessimal. NOT. Vvedensky showed that excitation can be replaced by inhibition in any area that has low lability. In the central nervous system, synapses have the least lability.
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Primary inhibition in the central nervous system Primary inhibition is associated with the presence in the central nervous system of a special morphological substrate - an inhibitory synapse (neuron). Inhibitory neurons are a type of interneurons whose axons form inhibitory synapses on the bodies and dendrites of excitatory neurons. Examples of inhibitory neurons: piriform cells (Purkinje cells) of the cerebellar cortex and Renshaw cells in the spinal cord.
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Inhibition in the central nervous system: presynaptic inhibition Mechanism: excitation T → depolarization of the afferent membrane → decrease in AP amplitude in afferents → decrease in the amount of transmitter released from the presynaptic region of the synapse → decrease in EPSP amplitude on the motor neuron membrane → decrease in motor neuron activity. The inhibitory synapse mediator is GABA. Meaning: coordinating. Provides fine regulation.
Slide no. 30
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Inhibition in the central nervous system: reciprocal inhibition An example of reciprocal (conjugate) inhibition is mutual inhibition of the centers of antagonist muscles. Mechanism: excitation of proprioceptors (stretch receptors) of flexor muscles → activation of motor neurons of these muscles and intercalary inhibitory neurons → postsynaptic inhibition of motor neurons of extensor muscles.
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Principles of coordination of nerve centers: “common final path” (convergence) Put forward by Ch.S. Sherrington in 1906. Convergence, the morphological basis of coordination, comes from the anatomical ratio between afferent and efferent neurons (5:1). Sherrington schematically presented this relationship in the form of a funnel:
Slide no. 33
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Principles of coordination of nerve centers: “common final path” According to this principle, many impulses from various reflexogenic zones come to one motor neuron, but only some of them acquire working significance. A wide variety of stimuli can cause the same reflex reaction, i.e. there is a struggle for a “common final path.” The functional characteristics of the nerve centers determine which of the impulses colliding on the way to the motor neuron will be the winner and take over the common final path.
Slide no. 34
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Principles of coordination of nerve centers: dominant The principle of dominance (lat. dominare to dominate) was established by A. A. Ukhtomsky (1923). According to Ukhtomsky: dominant is the dominant focus of excitation, predetermining the nature of the current reactions of the nerve centers at the moment. A dominant center (focus) can arise in various floors of the central nervous system with prolonged action of humoral or reflex stimuli. “...The external expression of the dominant is the stationary supported work or working posture of the body...”. (A.A. Ukhtomsky. T.1. P. 165. 1950)
Slide No. Description of slide:
Dominant A.A. Ukhtomsky about (+) and (–) dominants: “... The dominant, as a general formula, does not promise anything. As a general formula, the dominant only says that from the smartest things a fool will find a reason to continue stupidity, and from the most unfavorable conditions a smart person will extract smart things.”
Slide no. 37
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Principles of coordination of nerve centers: hierarchy and subordination In the central nervous system there are: Hierarchical relationships (Greek: hierarchia< hieros – священный + arche – власть) – высшие отделы мозга контролируют нижележащие; Субординация (соподчинение) –нижележащий отдел подчиняется вышележащим отделам.
Slide no. 38
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Principles of coordination of nerve centers: irradiation Irradiation (lat. irradio to illuminate, illuminate) is the spread of excitation (inhibition) processes. The wider the irradiation, the stronger and longer the afferent stimulation. Irradiation is based on numerous connections between the axons of afferent neurons and the dendrites and bodies of interneurons that unite nerve centers. Irradiation underlies the formation of a temporary (conditioned reflex) connection. Irradiation (both excitation and inhibition) has its limits: →concentration (formation of a dominant, exclusion of chaos).
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Age-related characteristics of the properties of nerve centers The child’s body is characterized by higher fatigue of the nerve centers compared to adults, associated with smaller reserves of mediators in the synapses and their rapid depletion as a result of rhythmic stimulation. The nerve centers of children are more sensitive to a lack of oxygen and glucose due to a high level of metabolism. In the early stages of development, nerve centers have greater compensatory capacity and plasticity.
Slide no. 41
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Age-related features of coordination of nervous processes A child is born with imperfect coordination of reflex reactions. The response in a newborn is always associated with an abundance of unnecessary movements and widespread uneconomical vegetative shifts. The phenomena under consideration are based on a higher degree of irradiation of nervous processes, which is largely associated with poor “insulation” of nerve fibers (the absence of a myelin sheath in many peripheral and central nerve fibers) → the process of excitation from one nerve easily transfers to the neighboring one. in the first stages of postnatal development, the leading role in the regulation of reflex activity is not the cortex, but the subcortical structures of the brain.
Slide no. 42
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Age-related features of coordination of nervous processes Children, in comparison with adults, have: less specialization of nerve centers, more widespread phenomena of convergence and more pronounced phenomena of induction of nervous processes. A dominant focus in a child arises faster and easier (instability of children's attention). New stimuli easily evoke a new dominant in the child’s brain. Coordination processes reach their perfection only by the age of 18–20.
Slide 2
Age changes
Age-related changes in the nervous system determine the most important manifestations of aging of the entire human body (shifts in mental and behavioral reactions), a decrease in mental and muscular performance, reproductive ability, adaptation to the environment, etc.
Slide 3
With aging, there is a decrease in brain weight, thinning of the gyri, widening and deepening of the sulci, and expansion of the ventricular-cisternal system. There is a decrease in the number of neurons and their replacement with glial elements; in certain areas of the cerebral cortex, the loss of neurons can reach 25-45% (relative to their number in newborns). In the spinal nodes of people 70-79 years old, the number of nerve cells is 30.4% less than in people 40-49 years old.
Slide 4
Absent-mindedness
In the process of aging, the integrative activity of the nervous system changes: conditioned reflexes are formed more slowly, the mobility and strength of the main nervous processes decrease, the processes of concentration and concentration, and memory deteriorate.
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Lability
Significant age-related changes occur in the autonomic ganglia. In particular, changes in the perception, processing and transmission of information in nerve cells are associated with a decrease in their lability.
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Rhythms
Older people are characterized by a slowdown in the alpha rhythm, but an increase in slow oscillations (theta and delta waves), and a decrease in the ability to assimilate imposed rhythms.
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Walking disorders
Gradually, the length of steps decreases, the gait becomes slower, and the person begins to stoop. All movements become less smooth. It is difficult for a person to take off his trousers while standing alternately on one leg and the other. Handwriting changes, all movements of the arms and hands lose dexterity. Undoubtedly, this complex of movement disorders is associated with loss of neurons in the spinal cord, cerebellum and brain, as well as loss of muscle mass.
Slide 8
Falls
Falls are a significant threat to life in older adults without obvious neurological symptoms. On average, 30% of these individuals living in their home fall one or more times per year. Falls have many causes, some of which were just mentioned when describing gait disorders. An important provoking factor is age-related decline in vision and vestibular function.
Slide 9
Analyzer status
Along with psychological changes, the functioning of the sense organs also changes with age. In older people, accommodative ability decreases over the years, senile farsightedness often develops, the field of vision narrows, and hearing acuity decreases, which can lead to the development of a mild form of hearing loss. Basically, these changes do not reach drastic manifestations.
Slide 10
Diseases
Separately, it is worth mentioning such a brain pathology as Parkinson's disease. It is based on a violation of subcortical structures, which consists of a lack of certain chemicals, which leads to a disruption of the connections between them. The main manifestation of this disease is frequently repeated movements of the body (or a separate area), which occur without the will of the patient. It all starts with small twitches of certain muscle groups, which makes it very difficult to perform certain actions. For example, writing is impaired, objects begin to fall out of hands, and a person has difficulty getting dressed.
Slide 11
Senile dementia is one of the most terrible pathologies of the human brain. One of the causes of dementia is the so-called Alzheimer's disease. After a person passes the 60-year mark, the risk of developing this disease increases with each subsequent year of his life. Primarily, senile dementia is caused by a decrease in the number of neurotransmitters. A decrease in the level of their content in the body disrupts the activity of many parts of the brain, including those responsible for memory, learning and other cognitive functions. This is how the external symptoms of Alzheimer's disease appear.
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