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2 Atlas nervous system human structure and disorders 4th edition, revised and expanded Edited by V.M. Astapova Yu.V. Mikaze Approved by the Ministry of Education Russian Federation as a teaching aid for higher education students educational institutions, studying in the direction and specialties of psychology Moscow Psychological and Social Institute Moscow 2004
3 BBK ya6 N54 N54 Atlas “Human Nervous System. Structure and violations." Edited by V.M. Astapov and Yu.V. Mikaze. 4th edition, revised. and additional M.: PER SE, p. Reviewers: Dr. psychol. sciences, prof. Khomskaya E.D. doc. biol. Sciences Fishman M.N. The atlas presents the most successful illustrations from the works of a number of foreign and domestic authors, demonstrating the structure of the human nervous system (Section I), as well as models of higher human mental functions and individual examples of their impairment in local brain lesions (Section II). The atlas can be used as a visual aid tutorial in courses on psychology, defectology, biology, which examine issues of the structure of the nervous system and higher mental functions of humans. ID license from PER SE LLC, Moscow, st. Yaroslavskaya, 13, k Tel./fax: (095) Tax benefit All-Russian classification of products OK, volume 2; books, brochures. Signed for printing Format 60x90/8. Offset paper. Offset printing. Conditional oven l. 10.0 Printed by OJSC “Printing House “Novosti”” Circulation 5000 copies. Order L(03) ISBN Astapov V.M., 2004 Mikadze Yu.V., 2004 Tertyshnaya V.V., drawings, 2004 “PER SE”, original layout, design, 2004
4 HUMAN NERVOUS SYSTEM 3 Section I General views about the structure of the nervous system From a cytological point of view, the nervous system includes the bodies of all nerve cells, their processes (fibers, bundles formed by them, etc.), supporting cells and membranes. Neurophysiology considers the nervous system as part of a living system that specializes in the transmission, analysis and synthesis of information, and neuropsychology as the material substrate of complex forms of mental activity, formed on the basis of the unification of various parts of the brain into functional systems. The nervous system consists of central and peripheral parts. The central nervous system (CNS) includes those sections that are enclosed in the cranial cavity and the spinal canal, and the peripheral nodes and bundles of fibers that connect the central nervous system with the sensory organs and various effectors (muscles, glands, etc.). The central nervous system, in turn, is divided into the brain, located in the skull, and the spinal cord, located in the spine. The peripheral nervous system consists of cranial and spinal nerves. In addition, a distinction is made between the autonomic (autonomic) nervous system, which also has central and peripheral sections. The autonomic nervous system is a collection of nerves and nerve ganglia through which the heart, blood vessels, internal organs, glands, etc. are innervated. Internal organs receive double innervation from the sympathetic and parasympathetic divisions of the autonomic nervous system. These two departments have excitatory and inhibitory influences, determining the level of activity of the organs.
5 4 Midsagittal section of the human head
6 5 Autonomic part of the nervous system (diagram) The sympathetic part is shown in brown and the parasympathetic part in black. Prenodal fibers are shown as solid lines, postnodal fibers as broken lines. (According to Kurepina et al.)
7 6 Most Accepted Anatomical Notations A. A drawing showing man in the position corresponding to the body of a quadruped, so that the brain and roots of the spinal cord are arranged in such a way that the anterior and posterior rostral and caudal portions of these structures can be compared with their arrangement in animals. (According to Schade et al.) B, C. Common planes of section of the brain in anatomical and pathomorphological studies. a median (sagittal) plane; b parasagittal and c frontal (coronal) plane; g plane lying at an angle to the horizontal plane (According to Schade et al.)
8 7 Most accepted anatomical designations
9 8 Nervous network Anatomical and functional structure of a neuron A large neuron with many dendrites receives information through synaptic contact with another neuron (in the left top corner). The myelinated axon forms a synaptic contact with the third neuron (bottom). The surfaces of neurons are shown without the glial cells that surround the process towards the capillary (top right). (By Bloom)
10 9 Scheme of distribution of cellular elements of the cerebral cortex Associative connections in the cerebral cortex of the 1st pyramid of layer II; 2-3 pyramids of layer III; 4, 5, 17 stellate neurons; 6 pyramids of layer IV; 7, 8, 9 pyramids of layer V; pyramids of layer VI. (I-VI layers of the cortex) (According to Lorente de No) (According to Lorente de No)
11 10 The Undivided Brain Shows the main structures involved in sensory processes and internal regulation, as well as the structures of the limbic system and brain stem. (According to Bloom et al.)
12 11 The most important areas and details of the structure of the brain The left and right cerebral hemispheres, as well as a number of structures lying in the median plane, are divided in half. The internal parts of the left hemisphere are depicted as if they had been completely dissected. The eye and optic nerve connect to the hypothalamus, from the lower part of which the pituitary gland arises. The pons, medulla oblongata and spinal cord are continuations of the posterior side of the thalamus. The left side of the cerebellum is located under the left cerebral hemisphere, but does not cover the olfactory bulb. The upper half of the left hemisphere is cut so that some of the basal ganglia (putamen) and part of the left lateral ventricle can be seen. (According to Bloom et al.)
13 12 Large hemispheres The names of the convolutions are given in the pictures, and the furrows are near the pictures (According to Sinelnikov)
14 13 Large hemispheres Light brown indicates the frontal, light green the parietal, red the occipital, dark green the temporal, dark brown the marginal lobes, blue the old and ancient cortex, purple the cerebellum and gray the brain stem. The names of the convolutions are given in the pictures, and the names of the furrows are given next to the pictures. (According to Sinelnikov)
15 14 Topography of cranial nerves at the base of the skull Cranial nerves 12 paired nerves that arise from the brain. I olfactory nerve (n.olfactorius); II optic nerve (n.opticus); III oculomotor nerve (n.oculomotorius); IV trochlear nerve (n.trochlearis); V trigeminal nerve (n.trigeminus); VI abducens nerve (n.abducens); VII facial nerve (n.facialis) and VIIa intermediate nerve (n.intermedius Wrisbergi); VIII vestibular-cochlear nerve (n.vestibulocochlearis); IX glossopharyngeal nerve (n.glossopharyngeus); X vagus nerve (n.vagus); XI accessory nerve (n.accessorius); XII hypoglossal nerve (n.hypoglossus). Three cranial nerves are sensory (I, II, VIII); six motor (III, IV, VI, VII, XI, XII) and three mixed (V, IX, X). (According to Badalyan)
16 15 Cytoarchitectonic fields and representation of functions in the cerebral cortex 1, 2, 3, 5, 7, 43 (partially) representation of cutaneous and proprioceptive sensitivity; 4 motor zone; 6, 8, 9, 10 premotor and supplementary motor areas; 11 representation of olfactory reception; 17, 18, 19 representation of visual reception; 20, 21, 22, 37, 41, 42, 44 representation of auditory reception; 37, 42 auditory speech center; 41 projections of the organ of Corti; 44 motor center of speech. (According to Brodman)
17 16 Brain development A is the brain of a five-week embryo; B the brain of a thirty-two-thirty-four-week fetus; In the brain of a newborn. 1 telencephalon; 2 diencephalon; 3 midbrain; 4 hindbrain; 5 medulla oblongata; 6 pons brain; 7 cerebellum; 8 spinal cord. (According to Badalyan)
18 17 Proportions of the skull of a newborn and an adult Diagram of the timing of myelination of the main functional systems in the brain The ratio of the proportions of the skull in a five-month-old embryo (1), a newborn (2), a one-year-old child (3), an adult (4). (According to Badalyan)
19 18 Areas of vascularization of the brain Arterial blood supply to the upper lateral surface of the cerebral hemispheres. Color codes: red middle cerebral artery, blue anterior cerebral artery, green posterior cerebral artery. Arterial blood supply to the medial surface of the cerebral hemisphere. (According to Badalyan)
20 19 Areas of vascularization of the brain Arteries at the base of the brain (A). Circle of Willis and its branches (B). 1 anterior cerebral artery; 2 internal carotid artery; 3 middle cerebral artery; 4 posterior communicating artery; 5 posterior cerebral artery; 6 superior cerebellar artery; 7 basilar artery; 8 anterior inferior cerebellar artery; 9 labyrinthine artery; 10 posterior inferior cerebellar artery; 11 vertebral artery; 12 anterior spinal artery; 13 anterior communicating artery; 14 olfactory pathway; 15 visual chiasm; 16 mamillary body; 17 posterior communicating artery; 18 oculomotor nerve. (According to Duus)
21 20 Main commissures connecting the two hemispheres of the brain The large size of the corpus callosum compared to other connections is striking. The figure shows a cross-section of the brain along the median plane. (According to Bloom et al.)
22 21 Anatomical asymmetry of the cerebral hemispheres Top: the Sylvian fissure in the right hemisphere deviates upward at a large angle. Bottom: The posterior part of the planum temporale is usually much larger in the left hemisphere associated with speech functions. (According to Geschwind)
23 22 HUMAN NERVOUS SYSTEM Frequency (in percentage) of anatomical differences between the hemispheres Type of asymmetry Right-handed Left-handed and ambidextrous Sylvian fissure is higher on the right (Galaburda, LeMay, Kemper, Geschwind, 1978) The posterior horn of the lateral ventricle is longer on the left (McRae, Branch, Milner, 1968) yes no inverse relationship yes no inverse relationship Frontal lobe is wider on the right (LeMay, 1977) Occipital lobe is wider on the left (LeMay, 1977) Frontal lobe projects on the right (LeMay, 1977) Occipital lobe projects on the left (LeMay, 1977) 77 10.5 12, Frequency (in percentage) of anatomical differences between the hemispheres among right- and left-handed individuals, as well as people with equal use of both hands (ambidextrous). (By Corballis)
24 23 Brain structures Cerebellum. And the view from above; B bottom view. 1 leaves of the cerebellum; 2 cerebellar fissures; 3 cerebellar vermis; 4 cerebellar hemispheres; 5 anterior lobe of the cerebellum; 6 tongue (According to Fenish et al.) Diagram of the ventricles of the brain and their relationship to the surface structures of the cerebral hemispheres. a cerebellum; b occipital pole; to the parietal pole; d frontal pole; d temporal pole; e medulla oblongata. 1 lateral foramen of the fourth ventricle (foramen of Luschka); 2 lower horn of the lateral ventricle; 3 water supply; 4 interventricular foramen; 5 anterior horn of the lateral ventricle; 6 central part of the lateral ventricle; 7 fusion of the visual tuberosities (massa intermedia); 8 third ventricle; 9 entrance to the lateral ventricle; 10 posterior horn of the lateral ventricle; 11 fourth ventricle (According to Sade et al.)
25 24 Brain structures Topographic relationships of the basal ganglia (A). Relationship of the basal ganglia to the ventricular system (B). 1 pale ball; 2 thalamus; 3 shell; 4 caudate nucleus; 5 amygdala; 6 head of the caudate nucleus; 7 subthalamic nucleus; 8 tail of the caudate nucleus; 9 lateral ventricle. (According to Duus) Lateral ventricles, left caudate and lenticular nuclei (B). 1 lateral ventricle; 2 frontal horn of the lateral ventricle; 3 occipital (posterior) horn; 4 temporal (lower) horn; 5 head of the caudate nucleus; 6 body of the caudate nucleus; 7 tail; 8 lenticular nucleus. (According to Fenish et al.)
26 25 Corticoreticular connections A diagram of the pathways of ascending activating influences; B diagram of descending influences of the cortex; Sp specific afferent pathways to the cortex with collaterals to the reticular formation. (According to Magun)
27 26 Conducting pathways and connections of the brain And the radiance of the corpus callosum and belt. B bundles of associative nerve fibers. In arcuate nerve fibers. D, E commissural fiber bundles. 1 corpus callosum; 2 arcuate fibers of the cerebrum, connect adjacent gyri; 3 bundles of fibers as part of the cingulate gyrus; 4 superior longitudinal bundle of associative fibers, starts from the frontal lobe, passes through the occipital lobe to the temporal lobe; 5 inferior longitudinal fasciculus, connects the temporal and occipital lobes of the hemispheres; 6 uncinate bundle of associative fibers, connects the lower surface of the frontal and anterior part of the temporal lobes; 7 radiance of the corpus callosum, formed by fibers connecting the cortex of the left and right hemispheres; 8 anterior commissure. (A, B, C according to Fenish and others. D, D according to Duus)
28 27 Conducting tracts of the spinal cord and brain (According to Kurepina et al.)
29 28 Systems of connections of primary, secondary and tertiary fields of the cortex I primary (central) fields; II secondary (peripheral) fields; III tertiary fields (areas of overlap of analyzers). The systems of projection (cortical-subcortical) projection-associative and association connections of the cortex are highlighted by a solid line; other connections are dotted; 1 receptor; 2 effector; 3 sensory node neuron; 4 motor neuron; 5.6 switching neurons of the spinal cord and brainstem; 7 10 switching neurons of subcortical formations; 11, 14 afferent fibers from the subcortex; 13 pyramid of layer V; 16 pyramid of sublayer III 3; 18 pyramids of sublayers III 2 and III 1; 12, 15, 17 stellate cells of the cortex. (According to Polyakov)
30 29 History of the development of ideas about the localization of mental functions A. Phrenological map of the localization of mental abilities. Given according to modern F.A. Hallu to the statue. B, C. Kleist localization map. (According to Luria)
31 30 Cortical projection of sensitivity and motor system The relative sizes of the organs reflect the area of the cerebral cortex from which the corresponding sensations and movements can be evoked. (According to Penfield)
32 31 Somatic organization of the motor and sensory areas of the human cortex
33 32 Structural and functional model of the integrative work of the brain, proposed by A.R. Luria A the first block of regulation of general and selective nonspecific activation of the brain, including the reticular structures of the brainstem, midbrain and diencephalic regions, as well as the limbic system and mediobasal regions of the cortex of the frontal and temporal lobes brain: 1 corpus callosum, 2 midbrain, 3 mediobasal sections of the right frontal lobe of the brain, 4 cerebellum, 5 reticular formation of the brainstem, 6 medial sections of the right temporal lobe of the brain, 7 thalamus; B the second block for receiving, processing and storing exteroceptive information, including the main analyzer systems (visual, skin-kinesthetic, auditory), the cortical zones of which are located in the posterior parts of the cerebral hemispheres: 1 parietal region (general sensitive cortex), 2 occipital region (visual cortex) , 3 temporal region (auditory cortex), 4 central sulcus; In the third block of programming, regulation and control over the course of mental activity, including the motor, premotor and prefrontal parts of the brain with their bilateral connections: 1 prefrontal area, 2 premotor area, 3 motor area (precentral gyrus), 4 central sulcus, (According to Chomsky)
34 33 The most important parts of the brain that form the limbic system Brain structures that play a role in emotions Are located along the edges of the cerebral hemispheres, as if “edging” them. (According to Bloom et al.) Dopamine fibers coming from the substantia nigra and norepinephrine fibers coming from the locus coeruleus innervate the entire forebrain. Both of these groups of neurons, as well as some others, are parts of the reticular activating system. (According to Bloom et al.)
35 34 Scheme of the limbic system A side view; B, C dorsal view: 1 supra-callosal strip; 2 hippocampal peduncle; 3 medial forebrain bundle; 4 anterior nucleus of the visual thalamus; 5 olfactory bulb; 6 transparent partition; 7 interpeduncular nucleus; 8 mamillary bodies; 9 leash; 10 vault; 11 marginal bundle; 12 dentate gyrus; 13 amygdala nucleus; 14 pineal gland (According to Badalyan)
36 35 Visual system Auditory system Connections are shown going from the primary receptors of the retina through the transmitting nuclei of the thalamus and hypothalamus to the primary visual cortex. (According to Bloom et al.) Connections are shown going from the primary receptors of the cochlea through the thalamus to the primary auditory cortex. (According to Bloom et al.)
37 36 Sensations from the surface of the body Olfactory system Taste system Connections are presented that go from skin receptors through interneurons of the spinal cord and thalamus to the primary sensory zone of the cortex. The connections are shown going from the receptors of the nasal mucosa through the olfactory bulbs and basal ganglia of the forebrain to the final points in the olfactory cortex. The connections are depicted going from the receptors of the tongue through the initial targets of the pons to the targets of the next order in the cerebral cortex. (According to Bloom et al.) (According to Bloom et al.) (According to Bloom et al.)
38 HUMAN NERVOUS SYSTEM 37 Pathways for specific types of sensory signals Modality Switching level primary (level 1) secondary (level 2) tertiary (level 3) Vision Retina Lateral geniculate body Primary visual cortex Superior colliculus quadrigeminal Secondary visual cortex Hearing Cochlear nuclei Nuclei of the lemniscus, quadrigeminal nucleus and Primary auditory cortex. medial geniculate body Touch Spinal cord or brain stem Thalamus Somatosensory cortex Olfaction Olfactory bulb Piriform cortex Limbic system, hypothalamus Taste Medulla Oblongata Thalamus Somatosensory cortex (According to Bloom et al.) Basic categories in the field of sensory processes modality and quality Modality Sensory organ Quality Receptors Vision Retina Brightness, Contrast, Rods and Cones Motion, Size, Color Hearing Cochlea Height, Timbre Hair Cells Equilibrium Vestibular Organ Gravity Macular Cells Rotation Vestibular Cells Touch Skin Pressure Ends Ruffini Merkel Discs Vibration Pacinian Corpuscles Taste Tongue Sweet and sour taste Taste buds on the tip of the tongue Bitter and salty taste Taste buds at the base of the tongue Smell Olfactory nerves Floral smell Olfactory receptors Fruity Musky Savory (According to Bloom et al.)
39 38 HUMAN NERVOUS SYSTEM Comparative characteristics of some types of analyzers Analyzer Visual (constant point signal) Absolute threshold Units of measurement Approximate value Units of measurement lux 4, lux arc. min Differential threshold Approximate value 1% of the initial intensity 0.6-1.5 Degree of performance in technical systems, % 90 Auditory Dyna/cm 2 0.0002 dB 0.3-0.7 9 Tactile mg/mm mg/mm 2 7% of the initial intensity 1 Taste mg/l mg/l 20% of the initial concentration extremely insignificant Olfactory mg/l 0.001-1 mg/l 16 50%, the same 2.5 9% of the original value Kinesthetic kg kg Temperature C 0 0.2-0.4 C 0 Vestibular (acceleration during rotation and linear motion) m/s 2 0.1-0.12 (According to Gomeso et al.)
40 40 HUMAN NERVOUS SYSTEM Sequence of processes in response to a visual stimulus Sequence of processes in response to a visual stimulus, traced through the entire brain from the retina and optic tract to the visual cortex and frontal association cortex. In a motor response, if it occurs, the excitation spreads from the frontal cortex to the motor cortex, is transmitted through the synapse to the motor neuron (shown enlarged on the right), then goes down the brain stem and along the corresponding nerve reaches the muscle, which causes the movement of the eyes. The neuron is surrounded by capillaries and glial cells. Many axons form synapses on the body and dendrites of the neuron. The axon is covered with a myelin sheath. (According to Bloom et al.)
41 41 Diagram of the visual system pathways Diagram of the visual system pathways: 1 visual field; 2 course of rays in the eyeball; 3 optic nerves; 4 visual chiasm; 5 optic tracts; 6 external geniculate body; 7 superior colliculi; 8 radiant radiance (Graziole beam); 9 cortical center. (According to Badalyan)
42 42 Diagram of the organ of Corti
43 43 Auditory system Auditory nerve pathways connect the cochlea of each ear with the auditory areas of the cerebral cortex. At the lowest level of the auditory system (auditory nerves and cochlear nuclei), the pathways from both ears are completely separated. (In this highly simplified diagram, the paths from the left ear are shown in bold lines, and from the right in bold lines.) At the next level (the olivary nucleus in the medulla oblongata), some nerve fibers from the right and left cochlear nuclei converge on the same neurons. These neurons, which transmit signals from both ears, are highlighted with a dotted line. At higher levels of the system, convergence consistently increases and, accordingly, the interaction between signals from both ears increases, which is reflected in the diagram by an increase in the proportion of neurons depicted in circles. Most of the nerve pathways coming from the cochlear nucleus pass to the opposite side of the brain. 1 auditory cortex, 2 inferior colliculus, 3 auditory nerve, 4 olive nucleus, 5 cochlear nucleus, 6 left cochlea, 7 right cochlea. (According to Rosenzweig)
44 44 Types of skin receptors A Pacinian corpuscle; B Meissner's body; In the nerve plexus at the base of the hair follicle; G Krause flask; D nerve plexus of the cornea. Nerve endings in the skin are receptors for touch, heat, cold and pain. 1 free nerve endings; 2 nerve endings around hair follicles; 3 sympathetic nerves innervating muscle fibers; 4 Ruffini endings; 5 Krause terminal bulbs; 6 Merkel discs; 7 Meissner's corpuscles; 8 sympathetic fibers innervating the sweat gland; 9 nerve trunks; 10 sweat gland; 11 sebaceous gland. The function of each individual ending type is still unknown. (According to Held et al.)
45 45 Scheme of the structure of the cutaneous-kinesthetic system Efferent neurons with a long axon are presented: 1 endings of sensory and nerve fibers in the skin and muscles, 2 sensory peripheral neurons of the intervertebral nodes, 3 switching nuclei in the medulla oblongata, 4 switching (relay) nuclei in the visual thalamus , 5 cutaneous-kinesthetic zone of the cortex, 6 motor zone of the cortex, 7 path from the motor cortex to the motor “centers” of the brain and spinal cord (pyramidal tract), 8 effector neuron of the spinal cord, 9 motor nerve endings in skeletal muscles. (According to Polyakov)
46 46 Map of cortical areas into which tactile signals from the surface of the body are projected PB mental vibrissae MB mandibular vibrissae P finger PB chin Areas of the body with high density sensory receptors, such as the face or fingers, have more extensive cortical projections than areas with low receptor density. The boundaries of these projections vary somewhat among different individuals. (According to Bloom et al.)
47 47 Normal touch error The normal touch error can be defined in two ways: first, as the average value of the minimum distance between the contacts at which the subject feels a pair of separate clicks when the contacts are simultaneously turned on (black bars); secondly, as the average distance between the point and the real contact (white bars). As can be seen from the figure, the accuracy of touch varies significantly in different parts of the body; The greatest accuracy is observed on the lips and fingertips. (According to Geldard et al.)
48 48 Scheme of the taste system A connections and insertion systems of the taste analyzer. (According to Smirnov) B receptors of four main taste qualities. The tip of the tongue senses all four qualities to some extent, but is most sensitive to sweet and salty. The edges of the tongue are more sensitive to sour, but also perceive salty taste. The base of the tongue is most sensitive to bitter. (According to Bloom et al.)
49 49 Odor Reception A. According to the stereochemical theory, different olfactory nerve cells are excited by different molecules depending on the size, shape or charge of the molecule; these properties determine which of the various pits or clefts at the endings of the olfactory nerve the molecule will approach; Here you can see that the l-menthol molecule corresponds to the deepening of the “mint” receptor site. B. Air, carrying molecules of an odorous substance, is drawn into the nasal cavity and passes past three oddly shaped bones to the islands of epithelium, in which the endings of numerous olfactory nerves are immersed. B. Histological section of the olfactory epithelium shows olfactory nerve cells and their processes, trigeminal nerve endings and supporting cells. (According to Eymour et al.)
50 50 Scheme of the olfactory system and its connections intercalary systems 1 cingulate gyrus; 2 anterior nucleus of the visual thalamus; 3 brain strip; 4 end strip; 5 vault; 6 leash core; 7 vault columns; 8 mamillary-optic tract; 9 mamillary body; 10 dentate gyrus; 11 temporal lobe; 12 amygdala; 13 lateral (side) gyrus; 14 olfactory tract; 15 olfactory bulb; 16 medial (middle) olfactory gyrus; 17 olfactory triangle; 18 anterior commissure; 19 about the olfactory circle; 20 near callosal gyrus; 21 transparent partitions. (According to Gutchin)
51 51 Course of the pyramidal tract 1 parietotemporal-pontine tract; 2 occipital-mesencephalic tract; 3 front bridge track; 4 corticospinal tract with extrapyramidal fibers; 5 lenticular nucleus; 6 thalamus; 7 caudate nucleus; 8 tire core; 9 red core; 10 substantia nigra; 11 bridge core; 12 from the cerebellum (tent nucleus); 13 reticular formation; 14 lateral nucleus of the vestibule nerve; 15 tire central track; 16 olive; 17 pyramid; 18 red nuclear spinal tract; 19 olivospinal tract; 20 vestibulospinal tract; 21 lateral corticospinal tract; 22 reticulospinal tract; 23 tegnospinal tract; 24 anterior corticospinal tract; 25 midbrain; 26 bridge leg; 27 bridge; 28 medulla oblongata; 29 pyramid intersection; 30 anterior central gyrus. (According to Duus)
52 52 HUMAN NERVOUS SYSTEM Section II Higher mental functions: models and examples of disturbances in local brain lesions Schematic diagram of the functional system as the basis of neurophysiological architecture M dominant motivation; P memory; OA situational afferentation; PA triggering afferentation; PR decision making; PD action program; ARD acceptor of action results; EV efferent excitations; D action; Res. result; Steam. Res. result parameters; O. Aff. reverse afferentation. (According to Anokhin)
53 HUMAN NERVOUS SYSTEM 53 Visual disorders If: I optic nerve is damaged (complete blindness on the affected side); II internal parts of the chiasm (heteronymous bitemporal hemianopsia); III external part of the chiasm (internal, nasal hemianopsia); IV optic tract (contralateral homonymous hemianopsia); V lower parts of the Graziole bundle or gurus lingualis (contralateral upper quadrant homonymous hemianopsia); VI upper parts of the Graziole or cuneus bundle (contralateral homonymous hemianopsia); VII diameter of the Graziole bundle (contralateral homonymous hemianopia with preservation of central vision). (According to Badalyan)
54 54 Drawings of patients with visual agnosia Drawings typical of the syndrome of opto-spatial agnosia of the subdominant type, right-handed patients with massive lesions of the posterior parts of the right hemisphere involving its parietal lobe. A: a, b, c, d independent drawing according to assignment (house, face or person, chair, table); e drawing (e sample) with options (I, I, III); B: a, b, c, d, e, f, g, h arrangement of hands on the clock (a circle with a center and “12 o’clock” is set) according to the proposed time (indicated by numbers after completing the task). (By Kok)
55 55 Drawings of patients with visual agnosia Drawings and errors in tests with a clock, typical for the syndrome of spatial agnosia and apraxia of the dominant type, right-handed patients with massive lesions of the posterior parts of the right hemisphere involving its parietal lobe (A, B, C, D, D, E). a, b, c, d independent drawing according to instructions (house, face or person, chair, table). G arrangement of hands on the clock (the circle, center and “12 o’clock” are set) according to the proposed time (indicated by numbers after completing the task). (By Kok)
56 56 Drawings of patients with visual agnosia I. Drawings of patients with damage to the right temporal lobe. Independent drawing according to the assignment: a, d, d house; b bicycle; c, e, f little man. (By Kok) II. Drawings of patients with lesions of the left temporal lobe. A: a, b independent drawing according to instructions; c, d copying from samples; B: a, b independent drawing according to instructions; c sample, d drawing with flipping from left to right and top to bottom. (By Kok) III. Disturbances in spatial concepts in patient A., 16 years old (epilepsy), left-handed with family left-handedness. (According to Simernitskaya et al.)
57 57 Drawings of patients with visual agnosia A. Changes in signs of simultaneous agnosia and optomotor ataxia after administration of caffeine to B. (bilateral wound of the parieto-occipital region). The patient is asked to trace the outline of the figure or place a dot in its center. B. Violation of optomotor coordination in patient R. (bilateral vascular lesion of the occipital region): a drawing and tracing of figures; b letter. B. Drawings from life and from memory in a patient with agnosia for faces (according to E.S. Bein). B-noy Chern. (bilateral vascular lesion of the occipital region): a copying from a sample; b drawing the same image from memory (According to Luria)
58 58 Ignoring the left side III. Ignores the left side when copying a design. (According to Badalyan) II. Crossing out dots for patients B during the rehabilitation process: 49 (a), 58 (b) and 81 days (c) after severe traumatic brain injury. (According to Dobrokhotova et al.)
59 59 Drawing of a patient with visual neglect Impaired perception of the left visual hemifield in an artist who suffered a hemorrhage in the posterior parietal region of the right hemisphere of the brain. Self-portraits A, B, C, and D were written respectively 2, 2.5, 6 and 9 months after the stroke. In the first portrait, only the right half of the image was taken. Over time, the perception of the left side is gradually restored. (According to Young)
60 60 Device for conducting experiments on patients with a dissected corpus callosum The principle of operation of the Z-lens Names or images of objects are briefly presented on the right or left sides of the screen, and the objects themselves are positioned so that they can only be recognized by touch. (according to Gazzaniga) The lens fits directly to the eye, and rays of light passing through it project an image onto only one half of the retina. The other eye is covered with an overlay, so that the possibility for the other hemisphere to “see” the same material is completely excluded. Therefore, subjects can look at the image for much longer than in experiments with a tachistoscope. (According to Bloom et al.)
61 61 Drawings of a patient with depression of the right or left hemisphere Sick. Sh-va. Drawings of the patient: 1 In normal condition; 2 In a state of depressed right hemisphere; 3 In a state of depressed left hemisphere. (According to Deglin et al.)
62 62 HUMAN NERVOUS SYSTEM The influence of commissurotomy on drawing and writing Differences between the hemispheres when visual perception Left hemisphere Right hemisphere And drawing a cube before and after commissurotomy: before the operation, the patient can draw a cube with each hand; after surgery drawing a cube right hand grossly violated; the patient is right-handed. (according to Gazzaniga and Ledoc); B “dysgraphia-discopia” syndrome and its dynamics after crossing the posterior sections of the corpus callosum. (According to Moskovichiute et al.) Stimuli are better recognized Verbal Non-verbal Easily distinguishable Difficult to distinguish Familiar Unfamiliar Tasks are better perceived Assessing temporal relationships Establishing similarities Establishing the identity of stimuli by names Transition to verbal coding Assessing spatial relationships Establishing differences Establishing the physical identity of stimuli Visual-spatial analysis Features of processes perception Analytical perception Holistic perception Sequential (Gestalt) perception Simultaneous perception Abstract, generalized, Concrete recognition invariant recognition Estimated morphophysiological differences Focused Diffuse representation representation elementary functions(According to Leushina et al.)
63 63 Different types of errors when writing with the left and right hand I. Writing from dictation with the right hand. II. Involuntary writing (habitual words). III. Free writing. (According to Simernitskaya)
64 64 Writing disorders Patient Kul. A. Writing letters under different conditions. B. Writing letters in alphabetical order Writing a letter included in a well-strengthened word or an automated series does not require the optical-spatial analysis necessary for writing an isolated letter and is carried out based on the well-established system of kinesthetic stereotypes in the patient (not affected by local brain damage) . (According to Luria et al.)
65 65 Types of sensitivity disorders a neuritic type; b segmental type; in violation of sensitivity when the visual thalamus is damaged; d polyneuritic type. When the trunk of a peripheral nerve or nerve plexus is damaged, all types of sensitivity in the zone of innervation of this nerve (a) are disrupted. Multiple nerve damage (polyneuritis) causes sensory disturbances in the hands and feet like gloves and stockings (d). Damage to the root or intervertebral node causes disruption of all types of sensitivity in the corresponding segmental zones (b). Damage to the thalamus opticus and the posterior central gyrus of the cerebral cortex causes loss of all types of sensitivity on the opposite side (c). (According to Badalyan)
66 66 HUMAN NERVOUS SYSTEM Functional model of objective action (According to Gordeeva, Zinchenko)
67 HUMAN NERVOUS SYSTEM 67 Construction of movement according to H.A. Bernstein Diagram of the main centers and pathways of the brain with their distribution into levels “A, B, C, D, E”, ensuring the construction and coordination of basic human movements and actions. (For clarity, the true spatial location of brain centers is significantly distorted.) (According to Naidin)
68 68 Scheme of regulation of speech activity
69 69 Lateral surface of the left hemisphere with the supposed boundaries of the “speech zones” Areas of the cortex of the left hemisphere of the brain associated with speech functions Internal region (shaded) part of the brain, lesions of which always lead to aphasia. The pathology of the surrounding part (point) also often leads to aphasia. Pathology of other zones is rarely accompanied by speech disorders. (According to Benson et al.) And the “speech zone” of the left hemisphere cortex; a Broca's area, c Wernicke's area, c the “center” of visual representations of words (According to Dejerine), B areas of the cortex of the left hemisphere, electrical stimulation of which causes various speech disorders in the form of speech stopping, stuttering, repetition of words, various motor speech defects, as well as inability to name an object. (According to Penfield and Roberts)
70 70 Location of lesions in the left hemisphere of the brain in various forms of aphasia a with sensory aphasia, b with acoustic-mnestic aphasia, c with afferent motor aphasia, d with “semantic” aphasia, e with dynamic aphasia, f with efferent motor aphasia. (according to Luria)
71 71 Localization of brain lesions in various forms of agraphia combined with aphasia I. Lesions affecting the anterior parts of the cerebral cortex. A. Agraphia combined with Broca's aphasia. B. Agraphia combined with transcortical motor aphasia. B. Agraphia combined with global aphasia. D. Agraphia combined with mixed transcortical aphasia. P. Lesions of the posterior parts of the cerebral cortex. D. Agraphia combined with Wernicke's aphasia. E. Agraphia combined with transcortical sensory aphasia. G. Agraphia combined with anomic aphasia. 3. Agraphia combined with conduction aphasia. (The note provides the classification of aphasias accepted in foreign psychology.) (According to Blackwell’s dictionary)
72 72 Magnetic resonance image of the brain of a patient with Gerstmann's syndrome Localization of lesions of the cerebral cortex in alexia Foci of pathology corresponding to the three main syndromes of alexia: A in the anterior regions; B in the central departments; In the posterior regions. Infarction in the left angular gyrus (the left hemisphere is on the right side of the photo. (According to Blackwell's Dictionary) (According to Blackwell's Dictionary)
Atlas of the human nervous system, structure and disorders, 4th edition, revised and expanded Edited by V.M. Astapova Yu.V. Mikadze Approved by the Ministry of Education of the Russian Federation as
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ABOUT THE PROJECT
Academician of the Russian Academy of Sciences, Professor Alexander Nikolaevich Konovalov
Dear friends!
With great professional pleasure, I am pleased to present the result of many years of work on creating a multimedia three-dimensional Atlas of the human brain. This fundamental work is based on many years of brain research conducted at the Research Institute of Neurosurgery named after. Academician N.N. Burdenko - data from magnetic resonance and computed tomography, digital angiography, results of anatomical studies, as well as data systematized in previous scientific publications and atlases. Advanced computer technologies have made it possible to create a convenient interactive three-dimensional version of the Atlas.
The human brain is the most complex and most perfect structure created by nature, and it is very difficult to comprehend the features of its structure. Therefore, knowledge of the anatomy of the central nervous system and, in particular, the brain, is the foundation for successful work not only us neurosurgeons, but also scientists of many specialties.
Knowledge of anatomy is also the basis for training young specialists in the field of neurology and neurosurgery. This three-dimensional anatomical Atlas of the human central nervous system is intended to help solve these problems.
I would like to especially note that volumetric reconstruction of the most important structures of the brain - the cerebral cortex, subcortical nuclei, brainstem, conduction tracts, ventricular system, veins and arteries, spinal cord and cranial nerves - allows us to create a complete spatial picture of the structure of the brain. This knowledge is important for all specialists studying diseases of the nervous system and, first of all, for neurosurgeons. The Atlas presented will be very useful not only for novice specialists, but also for their experienced and experienced senior colleagues.
Academician of the Russian Academy of Sciences Alexander Nikolaevich Konovalov
ABOUT THE PROJECT
One of the priority areas of scientific and practical activity of the TOLYKETI company is developments in the field of virtualization of human neuroanatomy.
Three-dimensional computer software technologies allow us to take a completely new look at the structure of the human central nervous system. The defining concept of three-dimensional reconstruction opens up endless possibilities in the study of the laws of construction of the organic world.
Publishing house "TOLYKETI" represented by Doctor of Medical Sciences, Head of the Department of Neuro-Oncology of the Research Institute of Neurosurgery named after. acad. N.N. Burdenko David Ilyich Pitskhelauri and the Scientific Design Studio “BRAIN.ERA” represented by Dmitry Yaroslavovich Samborsky, who performed work related to three-dimensional modeling and design of the project, with the financial support of the “International Foundation for the Development of Neurosurgery and Neurorehabilitation”, developed a project to create a 3D ATLAS HUMAN CENTRAL NERVOUS SYSTEM.
The software part of the project was developed by programming specialists Denis Islamov and Pavel Loginov.
The initial data used were native computer and magnetic resonance imaging scans of the average person, data from anatomical studies, as well as information on the anatomy of the human central nervous system systematized in scientific publications of previous years.
The creation of the Atlas is the main component of the project for use in scientific, practical and educational purposes in neurosurgery, neurology and other related disciplines. This development is based on unique material obtained during 10 years of collaboration between neurosurgeons and specialists in the field of three-dimensional software technologies.
The concept of a virtual neuroanatomical atlas
The virtual atlas of the human central nervous system represents a three-dimensional software concept that combines, firstly, various types of information about the brain and, secondly, a set of methods for working with this information. Atlases of the central nervous system naturally allow the integration of geometric, physical, and physiological information obtained from various sources, giving users the opportunity to work with the entire set of data at once. The amount of information stored in a neuroanatomical atlas can be colossal, and therefore the internal organization of work with information is an extremely important parameter of the atlas - no less important than the information about the brain itself.
The structure and functional connections of complex intracerebral structures have been developed in detail: the hypothalamus, thalamus, amygdala complex, hippocampal formation, basal ganglia, cerebellum, reticular formation, cranial nerves, central nervous system pathways, etc.
The software includes a large number of interactive neuroanatomical reconstructions and additional options that expand the functionality of the product.
The concept of dividing information into layers that can be turned on and off depending on the task at hand makes it possible to manage huge amounts of information that are characteristic of biological objects.
At all stages of the creation of the Atlas, much attention was paid to the accuracy of the anatomical information provided, achieved through an audit of expert studies.
The content is divided into 12 sections, which contain virtual neuroanatomical block preparations.
Selecting the optimal angle, determining a set of assembly elements, virtual dissection of structures that overlap the field of view and dividing the preparation into several nested scenes ensure maximum disclosure of the area of interest.
The original solutions for three-dimensional reconstruction of biological objects developed in the project made it possible to create a unique virtual product for neurosurgical purposes.
To construct the cerebral cortex, taking into account the internal course of the gyri, which is an extremely difficult task, a step-by-step extrusion method was used based on embedded MR slices. This was a unique advantage of the atlas-simulator.
Also, three-dimensional solutions were found for algorithms for the structure of vessels with a branching system that is complex from the point of view of three-dimensional modeling.
The construction of the tanks required enormous resources and in-depth analysis of the adjacent structures that determine their shape.
The construction of conductive systems required the search for a solution for three-dimensional modeling of such complex organic objects as the fibrous systems of the central nervous system.
The system of animation modules made it possible to simulate the movement of signal impulses in 12 cranial nerves and the main functional systems of the central nervous system.
One of the practical useful features of the atlas is the possibility of using it as a neurosurgical simulator. By simulating the rotation and scaling of the virtual surgical field in selected reconstructions, and identifying structures from different angles, the surgeon gains a unique navigation experience for subsequent use in real operating conditions.
Built-in stereo mode using special glasses and VR mode (virtual helmets and other devices) allow you to work with content in modern formats.
STAGES OF PROJECT DEVELOPMENT
INTERACTIVE OPERATIONAL NAVIGATOR
Based on the Atlas, it is planned to create an interactive surgical navigator operating on the basis of three-dimensional reconstructions of the main neurosurgical approaches. The user-selected access reconstruction is synchronized with the patient's position in a given angle, which allows the neurosurgeon to quickly determine anatomical landmarks in the modified surgical field.
The surgeon’s work in the intraoperative navigator mode provides the following functions: rotation, scaling, and content management with the ability to hide anatomical objects that overlap the surgical field.
The use of augmentative (augmented) reality elements - cut lines, contours of burr holes, markers critical for the patient’s life, anatomical loci, etc. allows you to optimally plan the operation and visualize instructions for assistants “opening” the surgical field.
In software mode, access reconstruction can be supplemented and refined with virtual content: features of the individual structure, reconstruction of the pathological focus (tumor, aneurysm, etc.) and dislocation of adjacent brain structures.
VARIABILITY BANK
The next important direction in the development of the project is the creation of a bank of variations in the anatomical structures of the central nervous system with an open filling architecture. Anatomical structures created on the basis of elements of individual three-dimensional reconstructions will allow us to evaluate the entire diversity of human neuroanatomy.
Individual virtual reconstructions, in addition to the intraoperative mode, can be used in preoperative planning and postoperative analysis.
The developed atlas-simulator aims to achieve a significantly higher level of realism with the ability to simulate neurosurgical operations in virtual reality mode.
An important component of the simulator is the development of “dynamic methods” that evaluate changes in brain structures under certain influences, in particular, when using a retractor and other neurosurgical instruments.
PERSONALIZATION
The final stage of the project is the development and implementation of a method for personalizing the atlas. The method will allow, based on diagnostic data from high-tech CT, MRI, digital angiography methods, converging on a virtual three-dimensional reconstruction of a specific patient, to plan real operations and develop surgical tactics.
The virtual neuroanatomical simulator software was developed for WINDOWS with subsequent versions being created for iPad, iPhone and Android. The development provides for the possibility of constant software upgrades via an Internet service.
Name: Human nervous system. Structure and disturbances. Atlas.
Astapov V.M., Mikadze Yu.V.
The year of publishing: 2004
Size: 13.36 MB
Format: pdf
Language: Russian
In this atlas, the first section presents beautifully executed illustrations from a number of works by domestic and foreign authors on the structure of the human nervous system. The second section demonstrates models of higher mental functions and examples of their disturbances in local brain lesions. The atlas is designed for use as a visual aid in the study of disciplines that consider the structure of the nervous system and higher mental activity of a person.
Name: Neurology. National leadership. 2nd edition
Gusev E.I., Konovalov A.N., Skvortsova V.I.
The year of publishing: 2018
Size: 24.08 MB
Format: pdf
Language: Russian
Description: The National Guide "Neurology" in its 2nd edition in 2018 has been supplemented with modern information. The book "Neurology. National Guide" contains three sections, which describe at the modern level... Download the book for free
Name: Backache.
Podchufarova E.V., Yakhno N.N.
The year of publishing: 2013
Size: 4.62 MB
Format: pdf
Language: Russian
Description: The book "Back Pain" examines such an important medical aspect of neurology as back pain. The guide discusses the epidemiology of back pain, risk factors, morphofunctional basis of pain in... Download the book for free
Name: Neurology. National leadership. Brief edition.
Gusev E.I., Konovalov A.N., Gekht A.B.
The year of publishing: 2018
Size: 4.29 MB
Format: pdf
Language: Russian
Description: The book "Neurology. National Guide. Brief edition" edited by E.I. Guseva and co-authors consider basic issues of neurology, where neurological syndromes are considered (pain, mening... Download the book for free
Name: Amyotrophic lateral sclerosis
Zavalishin I.A.
The year of publishing: 2009
Size: 19.9 MB
Format: pdf
Language: Russian
Description: The book "Amyotrophic lateral sclerosis" ed., Zavalishin I.A., examines current issues this pathology from the position of a neurologist. Issues of epidemiology, etiopathogenesis, clinical... Download the book for free
Name: Headache. Guide for doctors. 2nd edition.
Tabeeva G.R.
The year of publishing: 2018
Size: 6.14 MB
Format: pdf
Language: Russian
Description: The presented guide “Headache” examines current issues of the topic, highlighting such aspects of the cephalgic syndrome as the classification of headaches, tactics for managing patients with headaches... Download the book for free
Name: Manual therapy in vertebroneurology.
Gubenko V.P.
The year of publishing: 2003
Size: 18.16 MB
Format: pdf
Language: Russian
Description: The book "Manual Therapy in Vertebroneurology" examines general issues of manual therapy, describes the method of manual examination, clinical and diagnostic aspects of osteochondrosis and vertebrogenic... Download the book for free
Name: Neurology for General Practitioners
Ginsberg L.
The year of publishing: 2013
Size: 11.41 MB
Format: pdf
Language: Russian
Description: The practical guide “Neurology for general practitioners”, edited by L. Ginsberg, examines in detail neurological semiotics and neurological disorders in clinical practice. Introducing... Download the book for free
Name: Child Behavioral Neuroscience. Volume 2. 2nd edition.
Njokiktien Ch., Zavadenko N.N.
The year of publishing: 2012
Size: 1.7 MB
Format: pdf
Language: Russian
Description: Presented book "Children's Behavioral Neurology. Volume 2. 2nd Edition" by Charles Njokiktien, edited by Zavadenko N.N. is the final edition of a two-volume series examining the development and disorders...
SOCIAL-TECHNOLOGICAL INSTITUTE OF MOSCOW STATE SERVICE UNIVERSITY
ANATOMY OF THE CENTRAL NERVOUS SYSTEM
(Tutorial)
O.O. Yakimenko
Moscow - 2002
A manual on the anatomy of the nervous system is intended for students of the Socio-Technological Institute, Faculty of Psychology. The content includes basic issues related to the morphological organization of the nervous system. In addition to anatomical data on the structure of the nervous system, the work includes histological cytological characteristics of nervous tissue. As well as questions of information about the growth and development of the nervous system from embryonic to late postnatal ontogenesis.
For clarity of the presented material, illustrations are included in the text. For independent work of students, a list of educational and scientific literature, as well as anatomical atlases, is provided.
Classic scientific data on the anatomy of the nervous system are the foundation for the study of the neurophysiology of the brain. Knowledge of the morphological characteristics of the nervous system at each stage of ontogenesis is necessary to understand the age-related dynamics of human behavior and psyche.
SECTION I. CYTOLOGICAL AND HISTOLOGICAL CHARACTERISTICS OF THE NERVOUS SYSTEM
General plan of the structure of the nervous system
The main function of the nervous system is to quickly and accurately transmit information, ensuring the interaction of the body with the outside world. Receptors respond to any signals from the external and internal environment, converting them into streams of nerve impulses that enter the central nervous system. Based on the analysis of the flow of nerve impulses, the brain forms an adequate response.
Together with the endocrine glands, the nervous system regulates the functioning of all organs. This regulation is carried out due to the fact that the spinal cord and brain are connected by nerves to all organs, bilateral connections. Signals about their functional state are received from organs to the central nervous system, and the nervous system, in turn, sends signals to the organs, correcting their functions and ensuring all vital processes - movement, nutrition, excretion and others. In addition, the nervous system ensures coordination of the activities of cells, tissues, organs and organ systems, while the body functions as a single whole.
The nervous system is the material basis of mental processes: attention, memory, speech, thinking, etc., with the help of which a person not only cognizes the environment, but can also actively change it.
Thus, the nervous system is that part of a living system that specializes in transmitting information and integrating reactions in response to environmental influences.
Central and peripheral nervous system
The nervous system is divided topographically into the central nervous system, which includes the brain and spinal cord, and the peripheral nervous system, which consists of nerves and ganglia.
Nervous system
According to the functional classification, the nervous system is divided into somatic (divisions of the nervous system that regulate the work of skeletal muscles) and autonomic (vegetative), which regulates the work of internal organs. The autonomic nervous system has two divisions: sympathetic and parasympathetic.
Nervous system
somatic autonomic
sympathetic parasympathetic
Both the somatic and autonomic nervous systems include central and peripheral divisions.
Nervous tissue
The main tissue from which the nervous system is formed is nervous tissue. It differs from other types of tissue in that it lacks intercellular substance.
Nervous tissue consists of two types of cells: neurons and glial cells. Neurons play a major role in providing all functions of the central nervous system. Glial cells have an auxiliary role, performing supporting, protective, trophic functions, etc. On average, the number of glial cells exceeds the number of neurons in a ratio of 10:1, respectively.
The meninges are formed by connective tissue, and the brain cavities are formed by a special type of epithelial tissue (epindymal lining).
Neuron is a structural and functional unit of the nervous system
A neuron has characteristics common to all cells: it has a plasma membrane, a nucleus and cytoplasm. The membrane is a three-layer structure containing lipid and protein components. In addition, on the surface of the cell there is a thin layer called glycocalis. The plasma membrane regulates the exchange of substances between the cell and the environment. For a nerve cell, this is especially important, since the membrane regulates the movement of substances that are directly related to nerve signaling. The membrane also serves as the site of electrical activity that underlies rapid neural signaling and the site of action of peptides and hormones. Finally, its sections form synapses - the place of contact between cells.
Each nerve cell has a nucleus that contains genetic material in the form of chromosomes. The nucleus performs two important functions - it controls the differentiation of the cell into its final form, determining the types of connections and regulates protein synthesis throughout the cell, controlling the growth and development of the cell.
The cytoplasm of a neuron contains organelles (endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, ribosomes, etc.).
Ribosomes synthesize proteins, some of which remain in the cell, the other part is intended for removal from the cell. In addition, ribosomes produce elements of the molecular machinery for most cellular functions: enzymes, carrier proteins, receptors, membrane proteins, etc.
The endoplasmic reticulum is a system of channels and membrane-surrounded spaces (large, flat, called cisterns, and small, called vesicles or vesicles). There are smooth and rough endoplasmic reticulum. The latter contains ribosomes
The function of the Golgi apparatus is to store, concentrate and package secretory proteins.
In addition to systems that produce and transport various substances, the cell has an internal digestive system consisting of lysosomes that do not have a specific shape. They contain a variety of hydrolytic enzymes that break down and digest a variety of compounds occurring both inside and outside the cell.
Mitochondria are the most complex organ of the cell after the nucleus. Its function is the production and delivery of energy necessary for the life of cells.
Most of the body's cells are capable of metabolizing various sugars, and energy is either released or stored in the cell in the form of glycogen. However, nerve cells in the brain use glucose exclusively, since all other substances are retained by the blood-brain barrier. Most of them lack the ability to store glycogen, which increases their dependence on blood glucose and oxygen for energy. Therefore, nerve cells have the largest number of mitochondria.
Neuroplasm contains organelles special purpose: microtubules and neurofilaments, which vary in size and structure. Neurofilaments are found only in nerve cells and represent the internal skeleton of the neuroplasm. Microtubules stretch along the axon along the internal cavities from the soma to the end of the axon. These organelles distribute biologically active substances (Fig. 1 A and B). Intracellular transport between the cell body and the processes extending from it can be retrograde - from nerve endings to the cell body and orthograde - from the cell body to the endings.
Rice. 1 A. Internal structure of a neuron
A distinctive feature of neurons is the presence of mitochondria in the axon as an additional source of energy and neurofibrils. Adult neurons are not capable of division.
Each neuron has an extended central body - the soma and processes - dendrites and axon. The cell body is enclosed in a cell membrane and contains a nucleus and nucleolus, maintaining the integrity of the membranes of the cell body and its processes, ensuring the conduction of nerve impulses. In relation to the processes, the soma performs a trophic function, regulating the metabolism of the cell. Impulses travel along dendrites (afferent processes) to the body of the nerve cell, and through axons (efferent processes) from the body of the nerve cell to other neurons or organs.
Most dendrites (dendron - tree) are short, highly branched processes. Their surface increases significantly due to small outgrowths - spines. An axon (axis - process) is often a long, slightly branched process.
Each neuron has only one axon, the length of which can reach several tens of centimeters. Sometimes lateral processes - collaterals - extend from the axon. The endings of the axon usually branch and are called terminals. The place where the axon emerges from the cell soma is called the axonal hillock.
Rice. 1 B. External structure of a neuron
There are several classifications of neurons based on different characteristics: the shape of the soma, the number of processes, the functions and effects that the neuron has on other cells.
Depending on the shape of the soma, granular (ganglionic) neurons are distinguished, in which the soma has a rounded shape; pyramidal neurons of different sizes - large and small pyramids; stellate neurons; fusiform neurons (Fig. 2 A).
Based on the number of processes, unipolar neurons are distinguished, having one process extending from the cell soma; pseudounipolar neurons (such neurons have a T-shaped branching process); bipolar neurons, which have one dendrite and one axon; and multipolar neurons, which have several dendrites and one axon (Fig. 2 B).
Rice. 2. Classification of neurons according to the shape of the soma and the number of processes
Unipolar neurons are located in sensory nodes (for example, spinal, trigeminal) and are associated with such types of sensitivity as pain, temperature, tactile, a sense of pressure, vibration, etc.
These cells, although called unipolar, actually have two processes that fuse near the cell body.
Bipolar cells are characteristic of the visual, auditory and olfactory systems
Multipolar cells have a varied body shape - spindle-shaped, basket-shaped, stellate, pyramidal - small and large.
According to the functions they perform, neurons are divided into: afferent, efferent and intercalary (contact).
Afferent neurons are sensory (pseudo-unipolar), their somas are located outside the central nervous system in ganglia (spinal or cranial). The shape of the soma is granular. Afferent neurons have one dendrite that connects to receptors (skin, muscle, tendon, etc.). Through dendrites, information about the properties of stimuli is transmitted to the soma of the neuron and along the axon to the central nervous system.
Efferent (motor) neurons regulate the functioning of effectors (muscles, glands, tissues, etc.). These are multipolar neurons, their somas have a stellate or pyramidal shape, lying in the spinal cord or brain or in the ganglia of the autonomic nervous system. Short, abundantly branching dendrites receive impulses from other neurons, and long axons extend beyond the central nervous system and, as part of the nerve, go to effectors (working organs), for example, to skeletal muscle.
Interneurons (interneurons, contact neurons) make up the bulk of the brain. They communicate between afferent and efferent neurons and process information coming from receptors to the central nervous system. These are mainly multipolar stellate-shaped neurons.
Among the interneurons, neurons with long and short axons differ (Fig. 3 A, B).
The following are depicted as sensory neurons: a neuron whose process is part of the auditory fibers of the vestibulocochlear nerve (VIII pair), a neuron that responds to skin stimulation (SC). Interneurons are represented by amacrine (AmN) and bipolar (BN) cells of the retina, an olfactory bulb neuron (OLN), a locus coeruleus neuron (LPN), a pyramidal cell of the cerebral cortex (PN) and a stellate neuron (SN) of the cerebellum. A spinal cord motor neuron is depicted as a motor neuron.
Rice. 3 A. Classification of neurons according to their functions
Sensory neuron:
1 - bipolar, 2 - pseudobipolar, 3 - pseudounipolar, 4 - pyramidal cell, 5 - spinal cord neuron, 6 - neuron of the p. ambiguus, 7 - neuron of the nucleus of the hypoglossal nerve. Sympathetic neurons: 8 - from the stellate ganglion, 9 - from the superior cervical ganglion, 10 - from the intermediolateral column of the lateral horn of the spinal cord. Parasympathetic neurons: 11 - from the muscular plexus ganglion of the intestinal wall, 12 - from the dorsal nucleus of the vagus nerve, 13 - from the ciliary ganglion.
Based on the effect that neurons have on other cells, excitatory neurons and inhibitory neurons are distinguished. Excitatory neurons have an activating effect, increasing the excitability of the cells with which they are connected. Inhibitory neurons, on the contrary, reduce the excitability of cells, causing an inhibitory effect.
The space between neurons is filled with cells called neuroglia (the term glia means glue, the cells “glue” the components of the central nervous system into a single whole). Unlike neurons, neuroglial cells divide throughout a person's life. There are a lot of neuroglial cells; in some parts of the nervous system there are 10 times more of them than nerve cells. Macroglia cells and microglia cells are distinguished (Fig. 4).
Four main types of glial cells.
Neuron surrounded by various glial elements
1 - macroglial astrocytes
2 - oligodendrocytes macroglia
3 – microglia macroglia
Rice. 4. Macroglia and microglia cells
Macroglia include astrocytes and oligodendrocytes. Astrocytes have many processes that extend from the cell body in all directions, giving the appearance of a star. In the central nervous system, some processes end in a terminal stalk on the surface of blood vessels. Astrocytes lying in the white matter of the brain are called fibrous astrocytes due to the presence of many fibrils in the cytoplasm of their bodies and branches. In gray matter, astrocytes contain fewer fibrils and are called protoplasmic astrocytes. They serve as a support for nerve cells, provide repair to nerves after damage, isolate and unite nerve fibers and endings, and participate in metabolic processes that model the ionic composition and mediators. The assumptions that they are involved in the transport of substances from blood vessels to nerve cells and form part of the blood-brain barrier have now been rejected.
1. Oligodendrocytes are smaller than astrocytes, contain small nuclei, are more common in white matter, and are responsible for the formation of myelin sheaths around long axons. They act as an insulator and increase the speed of nerve impulses along the processes. The myelin sheath is segmental, the space between the segments is called the node of Ranvier (Fig. 5). Each of its segments, as a rule, is formed by one oligodendrocyte (Schwann cell), which, as it becomes thinner, twists around the axon. The myelin sheath is white (white matter) because the membranes of oligodendrocytes contain a fat-like substance - myelin. Sometimes one glial cell, forming processes, takes part in the formation of segments of several processes. It is assumed that oligodendrocytes carry out complex metabolic exchanges with nerve cells.
1 - oligodendrocyte, 2 - connection between the glial cell body and the myelin sheath, 4 - cytoplasm, 5 - plasma membrane, 6 - node of Ranvier, 7 - plasma membrane loop, 8 - mesaxon, 9 - scallop
Rice. 5A. Participation of oligodendrocyte in the formation of the myelin sheath
Four stages of “envelopment” of the axon (2) by a Schwann cell (1) and its wrapping with several double layers of membrane, which after compression form a dense myelin sheath, are presented.
Rice. 5 B. Scheme of formation of the myelin sheath.
Neuron soma and dendrites covered thin shells, which do not form myelin and make up gray matter.
2. Microglia are represented by small cells capable of amoeboid movement. The function of microglia is to protect neurons from inflammation and infections (via the mechanism of phagocytosis - the capture and digestion of genetically foreign substances). Microglial cells deliver oxygen and glucose to neurons. In addition, they are part of the blood-brain barrier, which is formed by them and the endothelial cells that form the walls of blood capillaries. The blood-brain barrier traps macromolecules, limiting their access to neurons.
Nerve fibers and nerves
The long processes of nerve cells are called nerve fibers. Through them, nerve impulses can be transmitted over long distances up to 1 meter.
The classification of nerve fibers is based on morphological and functional characteristics.
Nerve fibers that have a myelin sheath are called myelinated (myelinated), and fibers that do not have a myelin sheath are called unmyelinated (non-myelinated).
Based on functional characteristics, afferent (sensory) and efferent (motor) nerve fibers are distinguished.
Nerve fibers extending beyond the nervous system form nerves. A nerve is a collection of nerve fibers. Each nerve has a sheath and a blood supply (Fig. 6).
1 - common nerve trunk, 2 - nerve fiber branches, 3 - nerve sheath, 4 - bundles of nerve fibers, 5 - myelin sheath, 6 - Schwann cell membrane, 7 - node of Ranvier, 8 - Schwann cell nucleus, 9 - axolemma.
Rice. 6 Structure of a nerve (A) and nerve fiber (B).
There are spinal nerves connected to the spinal cord (31 pairs) and cranial nerves (12 pairs) connected to the brain. Depending on the quantitative ratio of afferent and efferent fibers within one nerve, sensory, motor and mixed nerves are distinguished. In sensory nerves, afferent fibers predominate, in motor nerves, efferent fibers predominate, in mixed nerves, the quantitative ratio of afferent and efferent fibers is approximately equal. All spinal nerves are mixed nerves. Among the cranial nerves, there are three types of nerves listed above. I pair - olfactory nerves (sensitive), II pair - optic nerves (sensitive), III pair - oculomotor (motor), IV pair - trochlear nerves (motor), V pair - trigeminal nerves (mixed), VI pair - abducens nerves ( motor), VII pair - facial nerves (mixed), VIII pair - vestibulo-cochlear nerves (mixed), IX pair - glossopharyngeal nerves (mixed), X pair - vagus nerves (mixed), XI pair - accessory nerves (motor), XII pair - hypoglossal nerves (motor) (Fig. 7).
I - para-olfactory nerves,
II - para-optic nerves,
III - para-oculomotor nerves,
IV - paratrochlear nerves,
V - pair - trigeminal nerves,
VI - para-abducens nerves,
VII - parafacial nerves,
VIII - para-cochlear nerves,
IX - paraglossopharyngeal nerves,
X - pair - vagus nerves,
XI - para-accessory nerves,
XII - para-1,2,3,4 - roots of the upper spinal nerves.
Rice. 7, Diagram of the location of the cranial and spinal nerves
Gray and white matter of the nervous system
Fresh sections of the brain show that some structures are darker - this is the gray matter of the nervous system, and other structures are lighter - the white matter of the nervous system. The white matter of the nervous system is formed by myelinated nerve fibers, the gray matter by the unmyelinated parts of the neuron - somas and dendrites.
The white matter of the nervous system is represented by central tracts and peripheral nerves. The function of white matter is the transmission of information from receptors to the central nervous system and from one part of the nervous system to another.
The gray matter of the central nervous system is formed by the cerebellar cortex and the cerebral cortex, nuclei, ganglia and some nerves.
Nuclei are accumulations of gray matter in the thickness of white matter. They are located in different parts of the central nervous system: in the white matter of the cerebral hemispheres - subcortical nuclei, in the white matter of the cerebellum - cerebellar nuclei, some nuclei are located in the diencephalon, midbrain and medulla oblongata. Most nuclei are nerve centers that regulate one or another function of the body.
Ganglia are a collection of neurons located outside the central nervous system. There are spinal, cranial ganglia and ganglia of the autonomic nervous system. Ganglia are formed predominantly by afferent neurons, but they may include intercalary and efferent neurons.
Interaction of neurons
The place of functional interaction or contact of two cells (the place where one cell influences another cell) was called a synapse by the English physiologist C. Sherrington.
Synapses are peripheral and central. An example of a peripheral synapse is the neuromuscular synapse, where a neuron makes contact with a muscle fiber. Synapses in the nervous system are called central synapses when two neurons come into contact. There are five types of synapses, depending on what parts the neurons are in contact with: 1) axo-dendritic (the axon of one cell contacts the dendrite of another); 2) axo-somatic (the axon of one cell contacts the soma of another cell); 3) axo-axonal (the axon of one cell contacts the axon of another cell); 4) dendro-dendritic (the dendrite of one cell is in contact with the dendrite of another cell); 5) somo-somatic (the somas of two cells are in contact). The bulk of contacts are axo-dendritic and axo-somatic.
Synaptic contacts can be between two excitatory neurons, two inhibitory neurons, or between an excitatory and an inhibitory neuron. In this case, the neurons that have an effect are called presynaptic, and the neurons that are affected are called postsynaptic. The presynaptic excitatory neuron increases the excitability of the postsynaptic neuron. In this case, the synapse is called excitatory. The presynaptic inhibitory neuron has the opposite effect - it reduces the excitability of the postsynaptic neuron. Such a synapse is called inhibitory. Each of the five types of central synapses has its own morphological features, although the general scheme of their structure is the same.
Synapse structure
Let us consider the structure of a synapse using the example of an axo-somatic one. The synapse consists of three parts: the presynaptic terminal, the synaptic cleft and the postsynaptic membrane (Fig. 8 A, B).
A-Synaptic inputs of a neuron. Synaptic plaques at the endings of presynaptic axons form connections on the dendrites and body (soma) of the postsynaptic neuron.
Rice. 8 A. Structure of synapses
The presynaptic terminal is the extended part of the axon terminal. The synaptic cleft is the space between two neurons in contact. The diameter of the synaptic cleft is 10-20 nm. The membrane of the presynaptic terminal facing the synaptic cleft is called the presynaptic membrane. The third part of the synapse is the postsynaptic membrane, which is located opposite the presynaptic membrane.
The presynaptic terminal is filled with vesicles and mitochondria. The vesicles contain biologically active substances - mediators. Mediators are synthesized in the soma and transported via microtubules to the presynaptic terminal. The most common mediators are adrenaline, norepinephrine, acetylcholine, serotonin, gamma-aminobutyric acid (GABA), glycine and others. Typically, a synapse contains one of the transmitters in greater quantities compared to other transmitters. Synapses are usually designated by the type of mediator: adrenergic, cholinergic, serotonergic, etc.
The postsynaptic membrane contains special protein molecules - receptors that can attach molecules of mediators.
The synaptic cleft is filled with intercellular fluid, which contains enzymes that promote the destruction of neurotransmitters.
One postsynaptic neuron can have up to 20,000 synapses, some of which are excitatory, and some are inhibitory (Fig. 8 B).
B. Scheme of transmitter release and processes occurring in a hypothetical central synapse.
Rice. 8 B. Structure of synapses
In addition to chemical synapses, in which neurotransmitters are involved in the interaction of neurons, electrical synapses are found in the nervous system. In electrical synapses, the interaction of two neurons is carried out through biocurrents. The central nervous system is dominated by chemical stimuli.
In some interneuron synapses, electrical and chemical transmission occurs simultaneously - this is a mixed type of synapse.
The influence of excitatory and inhibitory synapses on the excitability of the postsynaptic neuron is summed up and the effect depends on the location of the synapse. The closer the synapses are located to the axonal hillock, the more effective they are. On the contrary, the further the synapses are located from the axonal hillock (for example, at the end of dendrites), the less effective they are. Thus, synapses located on the soma and axonal hillock influence the excitability of the neuron quickly and efficiently, while the influence of distant synapses is slow and smooth.
Neural networks
Thanks to synaptic connections, neurons are united into functional units - neural networks. Neural networks can be formed by neurons located at a short distance. Such a neural network is called local. In addition, neurons remote from each other from different areas of the brain can be combined into a network. The highest level of organization of neuronal connections reflects the connection of several areas of the central nervous system. This neural network is called by or system. There are descending and ascending paths. Along ascending pathways, information is transmitted from underlying areas of the brain to higher ones (for example, from the spinal cord to the cerebral cortex). Descending tracts connect the cerebral cortex with the spinal cord.
The most complex networks are called distribution systems. They are formed by neurons in different parts of the brain that control behavior, in which the body participates as a whole.
Some nerve networks provide convergence (convergence) of impulses on a limited number of neurons. Nervous networks can also be built according to the type of divergence (divergence). Such networks enable the transmission of information over considerable distances. In addition, neural networks provide integration (summarization or generalization) of various types of information (Fig. 9).
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Rice. 9. Nervous tissue.
A large neuron with many dendrites receives information through a synaptic contact with another neuron (top left). The myelinated axon forms a synaptic contact with the third neuron (bottom). The surfaces of neurons are shown without the glial cells that surround the process towards the capillary (top right).
Reflex as the basic principle of the nervous system
One example of a nerve network would be a reflex arc, which is necessary for a reflex to occur. THEM. In 1863, Sechenov, in his work “Reflexes of the Brain,” developed the idea that the reflex is the basic principle of operation not only of the spinal cord, but also of the brain.
A reflex is the body's response to irritation with the participation of the central nervous system. Each reflex has its own reflex arc - the path along which excitation passes from the receptor to the effector (executive organ). Any reflex arc includes five components: 1) a receptor - a specialized cell designed to perceive a stimulus (sound, light, chemical, etc.), 2) an afferent pathway, which is represented by afferent neurons, 3) a section of the central nervous system , represented by the spinal cord or brain; 4) the efferent pathway consists of axons of efferent neurons extending beyond the central nervous system; 5) effector - working organ (muscle or gland, etc.).
The simplest reflex arc includes two neurons and is called monosynaptic (based on the number of synapses). A more complex reflex arc is represented by three neurons (afferent, intercalary and efferent) and is called three-neuron or disynaptic. However, most reflex arcs include a large number of interneurons and are called polysynaptic (Fig. 10 A, B).
Reflex arcs can pass through the spinal cord only (withdrawing the hand when touching a hot object) or through the brain only (closing the eyelids when a stream of air is directed at the face), or through both the spinal cord and the brain.
Rice. 10A. 1 - intercalary neuron; 2 - dendrite; 3 - neuron body; 4 - axon; 5 - synapse between sensory and interneurons; 6 - axon of a sensitive neuron; 7 - body of a sensitive neuron; 8 - axon of a sensitive neuron; 9 - axon of a motor neuron; 10 - body of the motor neuron; 11 - synapse between intercalary and motor neurons; 12 - receptor in the skin; 13 - muscle; 14 - sympathetic gaglia; 15 - intestine.
Rice. 10B. 1 - monosynaptic reflex arc, 2 - polysynaptic reflex arc, 3K - posterior root of the spinal cord, PC - anterior root of the spinal cord.
Rice. 10. Scheme of the structure of the reflex arc
Reflex arcs are closed into reflex rings using feedback connections. The concept of feedback and its functional role was indicated by Bell in 1826. Bell wrote that two-way connections are established between the muscle and the central nervous system. With the help of feedback, signals about the functional state of the effector are sent to the central nervous system.
The morphological basis of feedback is the receptors located in the effector and the afferent neurons associated with them. Thanks to feedback afferent connections, fine regulation of the effector’s work and an adequate response of the body to environmental changes are carried out.
Meninges
The central nervous system (spinal cord and brain) has three connective tissue membranes: hard, arachnoid and soft. The outermost of these is the dura mater (it fuses with the periosteum lining the surface of the skull). The arachnoid membrane lies under the dura mater. It is pressed tightly against the hard surface and there is no free space between them.
Directly adjacent to the surface of the brain is the pia mater, which contains many blood vessels that supply the brain. Between the arachnoid and soft membranes there is a space filled with liquid - cerebrospinal fluid. The composition of cerebrospinal fluid is close to blood plasma and intercellular fluid and plays an anti-shock role. In addition, the cerebrospinal fluid contains lymphocytes that provide protection against foreign substances. It is also involved in the metabolism between the cells of the spinal cord, brain and blood (Fig. 11 A).
1 - dentate ligament, the process of which passes through the arachnoid membrane located on the side, 1a - dentate ligament attached to the dura mater of the spinal cord, 2 - arachnoid membrane, 3 - posterior root passing in the canal formed by the soft and arachnoid membranes, For - posterior root passing through the hole in the dura mater of the spinal cord, 36 - dorsal branches of the spinal nerve passing through the arachnoid membrane, 4 - spinal nerve, 5 - spinal ganglion, 6 - dura mater of the spinal cord, 6a - dura mater turned to the side , 7 - pia mater of the spinal cord with the posterior spinal artery.
Rice. 11A. Spinal cord membranes
Brain cavities
Inside the spinal cord is the spinal canal, which, passing into the brain, expands in the medulla oblongata and forms the fourth ventricle. At the level of the midbrain, the ventricle passes into a narrow canal - the aqueduct of Sylvius. In the diencephalon, the Sylvian aqueduct expands, forming the cavity of the third ventricle, which smoothly passes at the level of the cerebral hemispheres into the lateral ventricles (I and II). All of the listed cavities are also filled with cerebrospinal fluid (Fig. 11 B)
Figure 11B. Diagram of the ventricles of the brain and their relationship to the surface structures of the cerebral hemispheres.
a - cerebellum, b - occipital pole, c - parietal pole, d - frontal pole, e - temporal pole, f - medulla oblongata.
1 - lateral opening of the fourth ventricle (Lushka's foramen), 2 - lower horn of the lateral ventricle, 3 - aqueduct, 4 - recessusinfundibularis, 5 - recrssusopticus, 6 - interventricular foramen, 7 - anterior horn of the lateral ventricle, 8 - central part of the lateral ventricle, 9 - fusion of the visual tuberosities (massainter-melia), 10 - third ventricle, 11 - recessus pinealis, 12 - entrance to the lateral ventricle, 13 - posterior pro of the lateral ventricle, 14 - fourth ventricle.
Rice. 11. Meninges (A) and cavities of the brain (B)
SECTION II. STRUCTURE OF THE CENTRAL NERVOUS SYSTEM
Spinal cord
External structure of the spinal cord
The spinal cord is a flattened cord located in the spinal canal. Depending on the parameters of the human body, its length is 41-45 cm, average diameter is 0.48-0.84 cm, weight is about 28-32 g. In the center of the spinal cord there is a spinal canal filled with cerebrospinal fluid, and by the anterior and posterior longitudinal grooves it is divided into the right and left half.
In front, the spinal cord passes into the brain, and in the back it ends with the conus medullaris at the level of the 2nd vertebra of the lumbar spine. A connective tissue filum terminale (a continuation of the terminal membranes) departs from the conus medullaris, which attaches the spinal cord to the coccyx. The filum terminale is surrounded by nerve fibers (cauda equina) (Fig. 12).
There are two thickenings on the spinal cord - cervical and lumbar, from which nerves arise that innervate, respectively, the skeletal muscles of the arms and legs.
The spinal cord is divided into cervical, thoracic, lumbar and sacral sections, each of which is divided into segments: cervical - 8 segments, thoracic - 12, lumbar - 5, sacral 5-6 and 1 - coccygeal. Thus, the total number of segments is 31 (Fig. 13). Each segment of the spinal cord has paired spinal roots - anterior and posterior. Through the dorsal roots, information from receptors in the skin, muscles, tendons, ligaments, and joints enters the spinal cord, which is why the dorsal roots are called sensory (sensitive). Transection of the dorsal roots turns off tactile sensitivity, but does not lead to loss of movement.
a - front view (its ventral surface);
b - rear view (its dorsal surface).
The dura and arachnoid membranes are cut. The choroid is removed. Roman numerals indicate the order of cervical (c), thoracic (th), lumbar (t)
and sacral(s) spinal nerves.
1 - cervical thickening
2 - spinal ganglion
3 - hard shell
4 - lumbar thickening
5 - conus medullaris
6 - terminal thread
Rice. 13. Spinal cord and spinal nerves (31 pairs).
Along the anterior roots of the spinal cord, nerve impulses travel to the skeletal muscles of the body (except for the muscles of the head), causing them to contract, which is why the anterior roots are called motor or motor. After cutting the anterior roots on one side, there is a complete shutdown of motor reactions, while sensitivity to touch or pressure remains.
The anterior and posterior roots of each side of the spinal cord unite to form the spinal nerves. Spinal nerves are called segmental; their number corresponds to the number of segments and is 31 pairs (Fig. 14)
The distribution of spinal nerve zones by segment was established by determining the size and boundaries of the skin areas (dermatomes) innervated by each nerve. Dermatomes are located on the surface of the body according to a segmental principle. Cervical dermatomes include the back surface of the head, neck, shoulders and anterior surface of the forearms. Thoracic sensory neurons innervate the remaining surface of the forearm, chest, and most of the abdomen. Sensory fibers from the lumbar, sacral, and coccygeal segments extend to the rest of the abdomen and legs.
Rice. 14. Scheme of dermatomes. Innervation of the body surface by 31 pairs of spinal nerves (C - cervical, T - thoracic, L - lumbar, S - sacral).
Internal structure of the spinal cord
The spinal cord is built according to the nuclear type. There is gray matter around the spinal canal, and white matter at the periphery. Gray matter is formed by neuron somas and branching dendrites that do not have myelin sheaths. White matter is a collection of nerve fibers covered with myelin sheaths.
In the gray matter, anterior and posterior horns are distinguished, between which lies the interstitial zone. There are lateral horns in the thoracic and lumbar regions of the spinal cord.
The gray matter of the spinal cord is formed by two groups of neurons: efferent and intercalary. The bulk of the gray matter consists of interneurons (up to 97%) and only 3% are efferent neurons or motor neurons. Motor neurons are located in the anterior horns of the spinal cord. Among them, a- and g-motoneurons are distinguished: a-motoneurons innervate skeletal muscle fibers and are large cells with relatively long dendrites; g-motoneurons are small cells and innervate muscle receptors, increasing their excitability.
Interneurons are involved in information processing, ensuring coordinated operation of sensory and motor neurons, and also connect the right and left halves of the spinal cord and its various segments (Fig. 15 A, B, C)
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Rice. 15A. 1 - white matter of the brain; 2 - spinal canal; 3 - posterior longitudinal groove; 4 - posterior root of the spinal nerve; 5 – spinal node; 6 - spinal nerve; 7 - gray matter of the brain; 8 - anterior root of the spinal nerve; 9 - anterior longitudinal groove
Rice. 15B. Gray matter nuclei in the thoracic region
1,2,3 - sensitive nuclei of the posterior horn; 4, 5 - intercalary nuclei of the lateral horn; 6,7, 8,9,10 - motor nuclei of the anterior horn; I, II, III - anterior, lateral and posterior cords of white matter.
The contacts between sensory, intercalary and motor neurons in the gray matter of the spinal cord are depicted.
Rice. 15. Cross section of the spinal cord
Spinal cord pathways
The white matter of the spinal cord surrounds the gray matter and forms the columns of the spinal cord. There are front, rear and side pillars. The columns are tracts of the spinal cord formed by long axons of neurons running up towards the brain (ascending tracts) or downwards from the brain to lower segments of the spinal cord (descending tracts).
The ascending tracts of the spinal cord transmit information from receptors in muscles, tendons, ligaments, joints and skin to the brain. The ascending pathways are also conductors of temperature and pain sensitivity. All ascending pathways intersect at the level of the spinal cord (or brain). Thus, the left half of the brain (cerebral cortex and cerebellum) receives information from receptors right half bodies and vice versa.
Main ascending paths: from the mechanoreceptors of the skin and the receptors of the musculoskeletal system - these are muscles, tendons, ligaments, joints - the Gaulle and Burdach bundles or, respectively, the tender and wedge-shaped bundles are represented by the posterior columns of the spinal cord.
From these same receptors, information enters the cerebellum along two pathways represented by lateral columns, which are called the anterior and posterior spinocerebellar tracts. In addition, two more pathways pass through the lateral columns - these are the lateral and anterior spinothalamic tracts, which transmit information from temperature and pain sensitivity receptors.
The posterior columns provide faster transmission of information about the localization of stimuli than the lateral and anterior spinothalamic tracts (Fig. 16 A).
1 - Gaulle's bundle, 2 - Burdach's bundle, 3 - dorsal spinocerebellar tract, 4 - ventral spinocerebellar tract. Neurons of groups I-IV.
Rice. 16A. Ascending tracts of the spinal cord
Descending Paths, passing through the anterior and lateral columns of the spinal cord, are motor, as they affect the functional state of the skeletal muscles of the body. The pyramidal tract begins mainly in the motor cortex of the hemispheres and passes to the medulla oblongata, where most of the fibers cross and pass to the opposite side. After this, the pyramidal tract is divided into lateral and anterior bundles: the anterior and lateral pyramidal tracts, respectively. Most pyramidal tract fibers terminate on interneurons, and about 20% form synapses on motor neurons. The pyramidal influence is exciting. Reticulospinal path, rubrospinal way and vestibulospinal the pathway (extrapyramidal system) begins respectively from the nuclei of the reticular formation, the brain stem, the red nuclei of the midbrain and the vestibular nuclei of the medulla oblongata. These pathways run in the lateral columns of the spinal cord and are involved in coordinating movements and ensuring muscle tone. Extrapyramidal tracts, like the pyramidal ones, are crossed (Fig. 16 B).
The main descending spinal tracts of the pyramidal (lateral and anterior corticospinal tracts) and extra pyramidal (rubrospinal, reticulospinal and vestibulospinal tracts) systems.
Rice. 16 B. Diagram of pathways
Thus, the spinal cord performs two important functions: reflex and conduction. The reflex function is carried out due to the motor centers of the spinal cord: motor neurons of the anterior horns ensure the functioning of the skeletal muscles of the body. At the same time, the preservation of muscle tone, coordination of the work of the flexor-extensor muscles underlying the movements and the preservation of the constancy of the posture of the body and its parts are maintained (Fig. 17 A, B, C). Motor neurons located in the lateral horns of the thoracic segments of the spinal cord provide respiratory movements (inhalation-exhalation, regulating the work of the intercostal muscles). Motor neurons of the lateral horns of the lumbar and sacral segments represent the motor centers of smooth muscles that are part of the internal organs. These are the centers of urination, defecation, and the functioning of the genital organs.
Rice. 17A. The arc of the tendon reflex.
Rice. 17B. Arcs of the flexion and cross-extensor reflex.
Rice. 17V. Elementary diagram of an unconditioned reflex.
Nerve impulses arising from irritation of the receptor (p) along afferent fibers (afferent nerve, only one such fiber is shown) go to the spinal cord (1), where through the intercalary neuron they are transmitted to efferent fibers (efferent nerve), along which they reach effector. The dotted lines represent the spread of excitation from the lower parts of the central nervous system to its higher parts (2, 3,4) up to the cerebral cortex (5) inclusive. The resulting change in the state of the higher parts of the brain in turn affects (see arrows) the efferent neuron, influencing the final result of the reflex response.
Rice. 17. Reflex function of the spinal cord
The conduction function is performed by the spinal tracts (Fig. 18 A, B, C, D, E).
Rice. 18A. Rear pillars. This circuit, formed by three neurons, transmits information from pressure and touch receptors to the somatosensory cortex.
Rice. 18B. Lateral spinothalamic tract. Along this path, information from temperature and pain receptors reaches large areas of the coronary brain.
Rice. 18V. Anterior spinothalamic tract. Along this pathway, information from pressure and touch receptors, as well as pain and temperature receptors, enters the somatosensory cortex.
Rice. 18G. Extrapyramidal system. Rubrospinal and reticulospinal tracts, which are part of the multineural extrapyramidal tract running from the cerebral cortex to the spinal cord.
Rice. 18D. Pyramidal or corticospinal tract
Rice. 18. Conductive function of the spinal cord
SECTION III. BRAIN.
General diagram of the structure of the brain (Fig. 19)
Brain
Figure 19A. Brain
1. Frontal cortex (cognitive area)
2. Motor cortex
3. Visual cortex
4. Cerebellum 5. Auditory cortex
Figure 19B. Side view
Figure 19B. The main formations of the medal surface of the brain in a midsagittal section.
Fig 19G. Lower surface of the brain
Rice. 19. Structure of the brain
hindbrain
The hindbrain, including the medulla oblongata and the Varoliev pons, represent phylogenetically ancient region central nervous system, preserving the features of the segmental structure. The hindbrain contains nuclei and ascending and descending pathways. Afferent fibers from vestibular and auditory receptors, from receptors in the skin and muscles of the head, from receptors in internal organs, as well as from higher structures of the brain enter the hindbrain along the pathways. The hindbrain contains the nuclei of the V-XII pairs of cranial nerves, some of which innervate the facial and oculomotor muscles.
Medulla
The medulla oblongata is located between the spinal cord, the pons and the cerebellum (Fig. 20). On the ventral surface of the medulla oblongata, the anterior median groove runs along the midline; on its sides there are two cords - pyramids; olives lie on the side of the pyramids (Fig. 20 A-B).
Rice. 20A. 1 - cerebellum 2 - cerebellar peduncles 3 - pons 4 - medulla oblongata
Rice. 20V. 1 - bridge 2 - pyramid 3 - olive 4 - anterior medial fissure 5 - anterior lateral groove 6 - cross of the anterior cord 7 - anterior cord 8 - lateral cord
Rice. 20. Medulla oblongata
On the posterior side of the medulla oblongata there is a posterior medial groove. On its sides lie the posterior cords, which go to the cerebellum as part of the hind legs.
Gray matter of the medulla oblongata
The medulla oblongata contains the nuclei of four pairs of cranial nerves. These include the nuclei of the glossopharyngeal, vagus, accessory and hypoglossal nerves. In addition, the tender, wedge-shaped nuclei and cochlear nuclei of the auditory system, the nuclei of the inferior olives and the nuclei of the reticular formation (giant cell, parvocellular and lateral), as well as the respiratory nuclei are distinguished.
The nuclei of the hypoglossal (XII pair) and accessory (XI pair) nerves are motor, innervating the muscles of the tongue and the muscles that move the head. The nuclei of the vagus (X pair) and glossopharyngeal (IX pair) nerves are mixed; they innervate the muscles of the pharynx, larynx, and thyroid gland, and regulate swallowing and chewing. These nerves consist of afferent fibers coming from the receptors of the tongue, larynx, trachea and from the receptors of the internal organs of the chest and abdominal cavity. Efferent nerve fibers innervate the intestines, heart and blood vessels.
The nuclei of the reticular formation not only activate the cerebral cortex, maintaining consciousness, but also form the respiratory center, which ensures respiratory movements.
Thus, some of the nuclei of the medulla oblongata regulate vital functions (these are the nuclei of the reticular formation and the nuclei of the cranial nerves). The other part of the nuclei is part of the ascending and descending pathways (grass and cuneate nuclei, cochlear nuclei of the auditory system) (Fig. 21).
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2 - wedge-shaped nucleus;
3 - the end of the fibers of the posterior cords of the spinal cord;
4 - internal arcuate fibers - the second neuron of the propria pathway of the cortical direction;
5 - the intersection of loops is located in the inter-olive loop layer;
6 - medial loop - continuation of the internal arcuate voles
7 - seam, formed by the intersection of loops;
8 - olive core - intermediate core of balance;
9 - pyramidal paths;
10 - central channel.
Rice. 21. Internal structure of the medulla oblongata
White matter of the medulla oblongata
The white matter of the medulla oblongata is formed by long and short nerve fibers
Long nerve fibers are part of the descending and ascending pathways. Short nerve fibers ensure coordinated functioning of the right and left halves of the medulla oblongata.
Pyramids medulla oblongata - part descending pyramidal tract, going to the spinal cord and ending at interneurons and motor neurons. In addition, the rubrospinal tract passes through the medulla oblongata. The descending vestibulospinal and reticulospinal tracts originate in the medulla oblongata, respectively, from the vestibular and reticular nuclei.
The ascending spinocerebellar tracts pass through olives medulla oblongata and through the cerebral peduncles and transmit information from the receptors of the musculoskeletal system to the cerebellum.
Tender And wedge-shaped nuclei The medulla oblongata is part of the spinal cord tracts of the same name, running through the visual thalamus of the diencephalon to the somatosensory cortex.
Through cochlear auditory nuclei and through vestibular nuclei ascending sensory pathways from auditory and vestibular receptors. In the projection zone of the temporal cortex.
Thus, the medulla oblongata regulates the activity of many vital functions of the body. Therefore, the slightest damage to the medulla oblongata (trauma, swelling, hemorrhage, tumors) usually leads to death.
Pons
The pons is a thick ridge that borders the medulla oblongata and the cerebellar peduncles. The ascending and descending tracts of the medulla oblongata pass through the bridge without interruption. At the junction of the pons and the medulla oblongata, the vestibulocochlear nerve (VIII pair) emerges. The vestibulocochlear nerve is sensitive and transmits information from the auditory and vestibular receptors of the inner ear. In addition, the pons contains mixed nerves, the nuclei of the trigeminal nerve (V pair), abducens nerve (VI pair), and facial nerve (VII pair). These nerves innervate the facial muscles, scalp, tongue, and lateral rectus muscles of the eye.
On a cross section, the bridge consists of a ventral and dorsal part - between them the border is the trapezoidal body, the fibers of which are attributed to the auditory tract. In the region of the trapezius body there is a medial parabranchial nucleus, which is connected with the dentate nucleus of the cerebellum. The pontine nucleus proper communicates the cerebellum with the cerebral cortex. In the dorsal part of the bridge lie the nuclei of the reticular formation and the ascending and descending pathways of the medulla oblongata continue.
The bridge performs complex and varied functions aimed at maintaining posture and maintaining body balance in space when changing speed.
Vestibular reflexes are very important, the reflex arcs of which pass through the bridge. They provide tone to the neck muscles, stimulation of the autonomic centers, breathing, heart rate, and activity of the gastrovascular tract.
The nuclei of the trigeminal, glossopharyngeal, vagus and pontine nerves are associated with the grasping, chewing and swallowing of food.
Neurons of the reticular formation of the pons play a special role in activating the cerebral cortex and limiting the sensory influx of nerve impulses during sleep (Fig. 22, 23)
Rice. 22. Medulla oblongata and pons.
A. Top view (dorsal side).
B. Side view.
B. View from below (from the ventral side).
1 - uvula, 2 - anterior medullary velum, 3 - median eminence, 4 - superior fossa, 5 - superior cerebellar peduncle, 6 - middle cerebellar peduncle, 7 - facial tubercle, 8 - inferior cerebellar peduncle, 9 - auditory tubercle, 10 - brain stripes, 11 - band of the fourth ventricle, 12 - triangle of the hypoglossal nerve, 13 - triangle of the vagus nerve, 14 - areapos-terma, 15 - obex, 16 - tubercle of the sphenoid nucleus, 17 - tubercle of the tender nucleus, 18 - lateral cord, 19 - posterior lateral sulcus, 19 a - anterior lateral sulcus, 20 - sphenoid cord, 21 - posterior intermediate sulcus, 22 - tender cord, 23 - posterior median sulcus, 23 a - pons - base), 23 b - pyramid of the medulla oblongata, 23 c -olive, 23 g - decussation of pyramids, 24 - cerebral peduncle, 25 - lower tubercle, 25 a - handle of the lower tubercle, 256 - superior tubercle
1 - trapezoid body 2 - nucleus of the superior olive 3 - dorsal contains the nuclei of VIII, VII, VI, V pairs of cranial nerves 4 - medal part of the pons 5 - ventral part of the pons contains its own nuclei and pons 7 - transverse nuclei of the pons 8 - pyramidal tracts 9 - middle cerebellar peduncle.
Rice. 23. Diagram of the internal structure of the bridge in a frontal section
Cerebellum
The cerebellum is a part of the brain located behind the cerebral hemispheres above the medulla oblongata and the pons.
Anatomically, the cerebellum is divided into a middle part - the vermis, and two hemispheres. With the help of three pairs of legs (lower, middle and superior), the cerebellum is connected to the brain stem. The lower legs connect the cerebellum with the medulla oblongata and spinal cord, the middle ones with the pons, and the upper ones with the mesencephalon and diencephalon (Fig. 24).
1 - vermis 2 - central lobule 3 - vermis uvula 4 - anterior veslus cerebellum 5 - superior hemisphere 6 - anterior cerebellar peduncle 8 - peduncle flocculus 9 – flocculus 10 - superior semilunar lobule 11 - inferior semilunar lobule 12 - inferior hemisphere 13 - digastric lobule 14 - cerebellar lobule 15 - cerebellar tonsil 16 - vermis pyramid 17 - wing of the central lobule 18 - node 19 - apex 20 - groove 21 - vermis hub 22 - vermis tubercle 23 - quadrangular lobule.
Rice. 24. Internal structure of the cerebellum
The cerebellum is built according to the nuclear type - the surface of the hemispheres is represented by gray matter, which makes up the new cortex. The cortex forms convolutions that are separated from each other by grooves. Under the cerebellar cortex there is white matter, in the thickness of which the paired cerebellar nuclei are distinguished (Fig. 25). These include tent cores, spherical core, cork core, jagged core. The tent nuclei are associated with the vestibular apparatus, the spherical and cortical nuclei are associated with the movement of the torso, and the dentate nucleus is associated with the movement of the limbs.
1- anterior cerebellar peduncles; 2 - tent cores; 3 - dentate core; 4 - corky core; 5 - white substance; 6 - cerebellar hemispheres; 7 – worm; 8 globular nucleus
Rice. 25. Cerebellar nuclei
The cerebellar cortex is of the same type and consists of three layers: molecular, ganglion and granular, in which there are 5 types of cells: Purkinje cells, basket, stellate, granular and Golgi cells (Fig. 26). In the superficial, molecular layer, there are dendritic branches of Purkinje cells, which are one of the most complex neurons in the brain. Dendritic processes are abundantly covered with spines, indicating a large number of synapses. In addition to Purkinje cells, this layer contains many axons of parallel nerve fibers (T-shaped branching axons of granular cells). In the lower part of the molecular layer there are bodies of basket cells, the axons of which form synaptic contacts in the region of the axon hillocks of Purkinje cells. The molecular layer also contains stellate cells.
A. Purkinje cell. B. Granule cells.
B. Golgi cell.
Rice. 26. Types of cerebellar neurons.
Below the molecular layer is the ganglion layer, which contains the bodies of Purkinje cells.
The third layer - granular - is represented by the bodies of interneurons (granule cells or granular cells). In the granular layer there are also Golgi cells, the axons of which rise into the molecular layer.
Only two types of afferent fibers enter the cerebellar cortex: climbing and mossy, which carry nerve impulses to the cerebellum. Each climbing fiber has contact with one Purkinje cell. The branches of the mossy fiber form contacts mainly with granule neurons, but do not contact Purkinje cells. Mossy fiber synapses are excitatory (Fig. 27).
Excitatory impulses arrive to the cortex and nuclei of the cerebellum via both climbing and mossy fibers. From the cerebellum, signals come only from Purkinje cells (P), which inhibit the activity of neurons in nuclei 1 of the cerebellum (P). The intrinsic neurons of the cerebellar cortex include excitatory granule cells (3) and inhibitory basket neurons (K), Golgi neurons (G) and stellate neurons (Sv). The arrows indicate the direction of movement of nerve impulses. There are both exciting (+) and; inhibitory (-) synapses.
Rice. 27. Neural circuit of the cerebellum.
Thus, the cerebellar cortex includes two types of afferent fibers: climbing and mossy. These fibers transmit information from tactile receptors and receptors of the musculoskeletal system, as well as from all brain structures that regulate the motor function of the body.
The efferent influence of the cerebellum is carried out through the axons of Purkinje cells, which are inhibitory. The axons of Purkinje cells exert their influence either directly on motor neurons of the spinal cord, or indirectly through neurons of the cerebellar nuclei or other motor centers.
In humans, due to upright posture and work activity, the cerebellum and its hemispheres reach their greatest development and size.
When the cerebellum is damaged, imbalances and muscle tone are observed. The nature of the violations depends on the location of the damage. Thus, when the tent cores are damaged, the balance of the body is disrupted. This manifests itself in a staggering gait. If the worm, cork and spherical nuclei are damaged, the work of the muscles of the neck and torso is disrupted. The patient has difficulty eating. If the hemispheres and dentate nucleus are damaged, the work of the muscles of the limbs (tremor) becomes difficult, and his professional activities become difficult.
In addition, in all patients with cerebellar damage due to impaired coordination of movements and tremor (shaking), fatigue quickly occurs.
Midbrain
The midbrain, like the medulla oblongata and the pons, belongs to the stem structures (Fig. 28).
1 - commissure of leashes
2 - leash
3 - pineal gland
4 - superior colliculus of the midbrain
5 - medial geniculate body
6 - lateral geniculate body
7 - inferior colliculus of the midbrain
8 - superior cerebellar peduncles
9 - middle cerebellar peduncles
10 - inferior cerebellar peduncles
11- medulla oblongata
Rice. 28. Hindbrain
The midbrain consists of two parts: the roof of the brain and the cerebral peduncles. The roof of the midbrain is represented by the quadrigemina, in which the superior and inferior colliculi are distinguished. In the thickness of the cerebral peduncles, paired clusters of nuclei are distinguished, called the substantia nigra and the red nucleus. Through the midbrain there are ascending pathways to the diencephalon and cerebellum and descending pathways from the cerebral cortex, subcortical nuclei and diencephalon to the nuclei of the medulla oblongata and spinal cord.
In the lower colliculus of the quadrigemina there are neurons that receive afferent signals from auditory receptors. Therefore, the lower tubercles of the quadrigeminal are called the primary auditory center. The reflex arc of the indicative auditory reflex passes through the primary auditory center, which manifests itself in turning the head towards the acoustic signal.
The superior colliculus is the primary visual center. The neurons of the primary visual center receive afferent impulses from photoreceptors. The superior colliculus provides an indicative visual reflex - turning the head towards the visual stimulus.
The nuclei of the lateral and oculomotor nerves take part in the implementation of orientation reflexes, which innervate the muscles of the eyeball, ensuring its movement.
The red nucleus contains neurons of different sizes. The descending rubrospinal tract begins from the large neurons of the red nucleus, which affects motor neurons and finely regulates muscle tone.
The neurons of the substantia nigra contain the pigment melanin and give this nucleus its dark color. The substantia nigra, in turn, sends signals to neurons in the reticular nuclei of the brain stem and subcortical nuclei.
The substantia nigra is involved in complex coordination of movements. It contains dopaminergic neurons, i.e. releasing dopamine as a mediator. One part of these neurons regulates emotional behavior, the other plays an important role in the control of complex motor acts. Damage to the substantia nigra, leading to degeneration of dopaminergic fibers, causes the inability to begin performing voluntary movements of the head and arms when the patient sits quietly (Parkinson's disease) (Fig. 29 A, B).
Rice. 29A. 1 - colliculus 2 - aqueduct of the cerebellum 3 - central gray matter 4 - substantia nigra 5 - medial sulcus of the cerebral peduncle
Rice. 29B. Diagram of the internal structure of the midbrain at the level of the inferior colliculi (frontal section)
1 - nucleus of the inferior colliculus, 2 - motor tract of the extrapyramidal system, 3 - dorsal decussation of the tegmentum, 4 - red nucleus, 5 - red nucleus - spinal tract, 6 - ventral decussation of the tegmentum, 7 - medial lemniscus, 8 - lateral lemniscus, 9 - reticular formation, 10 - medial longitudinal fasciculus, 11 - nucleus of the midbrain tract of the trigeminal nerve, 12 - nucleus of the lateral nerve, I-V - descending motor tracts of the cerebral peduncle
Rice. 29. Diagram of the internal structure of the midbrain
Diencephalon
The diencephalon forms the walls of the third ventricle. Its main structures are the visual tuberosities (thalamus) and the subtuberculous region (hypothalamus), as well as the supratubercular region (epithalamus) (Fig. 30 A, B).
Rice. 30 A. 1 - thalamus (visual thalamus) - the subcortical center of all types of sensitivity, the “sensory” of the brain; 2 - epithalamus (supratubercular region); 3 - metathalamus (foreign region).
Rice. 30 B. Circuits of the visual brain ( thalamencephalon ): a - top view b - rear and bottom view.
Thalamus (visual thalamus) 1 - anterior burf of the visual thalamus, 2 - cushion 3 - intertubercular fusion 4 - medullary strip of the visual thalamus
Epithalamus (supratubercular region) 5 - triangle of the leash, 6 - leash, 7 - commissure of the leash, 8 - pineal body (epiphysis)
Metathalamus (external region) 9 - lateral geniculate body, 10 - medial geniculate body, 11 - III ventricle, 12 - roof of the midbrain
Rice. 30. Visual Brain
Deep in the brain tissue of the diencephalon, the nuclei of the external and internal geniculate bodies are located. The outer border is formed by the white matter that separates the diencephalon from the telencephalon.
Thalamus (visual thalamus)
The neurons of the thalamus form 40 nuclei. Topographically, the nuclei of the thalamus are divided into anterior, median and posterior. Functionally, these nuclei can be divided into two groups: specific and nonspecific.
Specific nuclei are part of specific pathways. These are ascending pathways that transmit information from sensory organ receptors to the projection zones of the cerebral cortex.
The most important of the specific nuclei are the lateral geniculate body, which is involved in transmitting signals from photoreceptors, and the medial geniculate body, which transmits signals from auditory receptors.
The nonspecific ribs of the thalamus are classified as the reticular formation. They act as integrative centers and have a predominantly activating ascending effect on the cerebral cortex (Fig. 31 A, B)
1 - anterior group (olfactory); 2 - posterior group (visual); 3 - lateral group (general sensitivity); 4 - medial group (extrapyramidal system; 5 - central group (reticular formation).
Rice. 31B. Frontal section of the brain at the level of the middle of the thalamus. 1a - anterior nucleus of the visual thalamus. 16 - medial nucleus of the visual thalamus, 1c - lateral nucleus of the visual thalamus, 2 - lateral ventricle, 3 - fornix, 4 - caudate nucleus, 5 - internal capsule, 6 - external capsule, 7 - external capsule (capsula extrema), 8 - ventral nucleus thalamus optica, 9 - subthalamic nucleus, 10 - third ventricle, 11 - cerebral peduncle. 12 - bridge, 13 - interpeduncular fossa, 14 - hippocampal peduncle, 15 - inferior horn of the lateral ventricle. 16 - black substance, 17 - insula. 18 - pale ball, 19 - shell, 20 - Trout N fields; and b. 21 - interthalamic fusion, 22 - corpus callosum, 23 - tail of the caudate nucleus.
Figure 31. Diagram of groups of thalamus nuclei
Activation of neurons in the nonspecific nuclei of the thalamus is especially effective in causing pain signals (the thalamus is the highest center of pain sensitivity).
Damage to the nonspecific nuclei of the thalamus also leads to impairment of consciousness: loss of active communication between the body and the environment.
Subthalamus (hypothalamus)
The hypothalamus is formed by a group of nuclei located at the base of the brain. The nuclei of the hypothalamus are the subcortical centers of the autonomic nervous system of all vital functions of the body.
Topographically, the hypothalamus is divided into the preoptic area, the areas of the anterior, middle and posterior hypothalamus. All nuclei of the hypothalamus are paired (Fig. 32 A-D).
1 - aqueduct 2 - red nucleus 3 - tegmentum 4 - substantia nigra 5 - cerebral peduncle 6 - mastoid bodies 7 - anterior perforated substance 8 - oblique triangle 9 - infundibulum 10 - optic chiasm 11. optic nerve 12 - gray tubercle 13 - posterior perforated substance 14 - external geniculate body 15 - medial geniculate body 16 - cushion 17 - optic tract
Rice. 32A. Metathalamus and hypothalamus
a - bottom view; b - mid sagittal section.
Visual part (parsoptica): 1 - terminal plate; 2 - visual chiasm; 3 - visual tract; 4 - gray tubercle; 5 - funnel; 6 - pituitary gland;
Olfactory part: 7 - mamillary bodies - subcortical olfactory centers; 8 - the subcutaneous region in the narrow sense of the word is a continuation of the cerebral peduncles, contains the substantia nigra, the red nucleus and the Lewis body, which is a link in the extrapyramidal system and the vegetative center; 9 - subtubercular Monroe's groove; 10 - sella turcica, in the fossa of which the pituitary gland is located.
Rice. 32B. Subcutaneous region (hypothalamus)
Rice. 32V. Main nuclei of the hypothalamus
1 - nucleus supraopticus; 2 - nucleus preopticus; 3 - nucliusparaventricularis; 4 - nucleus in fundibularus; 5 - nucleuscorporismamillaris; 6 - visual chiasm; 7 - pituitary gland; 8 - gray tubercle; 9 - mastoid body; 10 bridge.
Rice. 32G. Scheme of the neurosecretory nuclei of the subthalamic region (Hypothalamus)
The preoptic area includes the periventricular, medial and lateral preoptic nuclei.
The anterior hypothalamus group includes the supraoptic, suprachiasmatic and paraventricular nuclei.
The middle hypothalamus makes up the ventromedial and dorsomedial nuclei.
In the posterior hypothalamus, the posterior hypothalamic, perifornical and mamillary nuclei are distinguished.
The connections of the hypothalamus are extensive and complex. Afferent signals to the hypothalamus come from the cerebral cortex, subcortical nuclei and thalamus. The main efferent pathways reach the midbrain, thalamus and subcortical nuclei.
The hypothalamus is the highest center for the regulation of the cardiovascular system, water-salt, protein, fat, and carbohydrate metabolism. This area of the brain contains centers associated with the regulation of eating behavior. An important role of the hypothalamus is regulation. Electrical stimulation of the posterior nuclei of the hypothalamus leads to hyperthermia, as a result of increased metabolism.
The hypothalamus also takes part in maintaining the sleep-wake biorhythm.
The nuclei of the anterior hypothalamus are connected to the pituitary gland and transport biologically active substances that are produced by the neurons of these nuclei. Neurons of the preoptic nucleus produce releasing factors (statins and liberins) that control the synthesis and release of pituitary hormones.
Neurons of the preoptic, supraoptic, paraventricular nuclei produce true hormones - vasopressin and oxytocin, which descend along the axons of neurons to the neurohypophysis, where they are stored until released into the blood.
Neurons of the anterior pituitary gland produce 4 types of hormones: 1) somatotropic hormone, which regulates growth; 2) gonadotropic hormone, which promotes the growth of germ cells, the corpus luteum, and enhances milk production; 3) thyroid-stimulating hormone – stimulates the function of the thyroid gland; 4) adrenocorticotropic hormone - enhances the synthesis of hormones of the adrenal cortex.
The intermediate lobe of the pituitary gland secretes the hormone intermedin, which affects skin pigmentation.
The posterior lobe of the pituitary gland secretes two hormones - vasopressin, which affects the smooth muscles of the arterioles, and oxytocin, which acts on the smooth muscles of the uterus and stimulates milk secretion.
The hypothalamus also plays an important role in emotional and sexual behavior.
The epithalamus (pineal gland) includes the pineal gland. The pineal gland hormone, melatonin, inhibits the formation of gonadotropic hormones in the pituitary gland, and this in turn delays sexual development.
Forebrain
The forebrain consists of three anatomically separate parts - the cerebral cortex, white matter and subcortical nuclei.
In accordance with the phylogeny of the cerebral cortex, the ancient cortex (archicortex), old cortex (paleocortex) and new cortex (neocortex) are distinguished. The ancient cortex includes the olfactory bulbs, which receive afferent fibers from the olfactory epithelium, the olfactory tracts - located on the lower surface of the frontal lobe, and the olfactory tubercles - secondary olfactory centers.
The old cortex includes the cingulate cortex, hippocampal cortex, and amygdala.
All other areas of the cortex are neocortex. The ancient and old cortex is called the olfactory brain (Fig. 33).
The olfactory brain, in addition to functions related to smell, provides reactions of alertness and attention, and takes part in the regulation of the autonomic functions of the body. This system also plays an important role in the implementation of instinctive forms of behavior (eating, sexual, defensive) and the formation of emotions.
a - bottom view; b - on a sagittal section of the brain
Peripheral department: 1 - bulbusolfactorius (olfactory bulb; 2 - tractusolfactories (olfactory path); 3 - trigonumolfactorium (olfactory triangle); 4 - substantiaperforateanterior (anterior perforated substance).
Central section - convolutions of the brain: 5 - vaulted gyrus; 6 - hippocampus is located in the cavity of the lower horn of the lateral ventricle; 7 - continuation of the gray vestment of the corpus callosum; 8 - vault; 9 - transparent septum - conductive pathways of the olfactory brain.
Figure 33. Olfactory brain
Irritation of the structures of the old cortex affects the cardiovascular system and breathing, causes hypersexuality, and changes emotional behavior.
With electrical stimulation of the tonsil, effects associated with the activity of the digestive tract are observed: licking, chewing, swallowing, changes in intestinal motility. Irritation of the tonsil also affects the activity of internal organs - kidneys, bladder, uterus.
Thus, there is a connection between the structures of the old cortex and the autonomic nervous system, with processes aimed at maintaining the homeostasis of the internal environments of the body.
Finite brain
The telencephalon includes: the cerebral cortex, white matter and the subcortical nuclei located in its thickness.
The surface of the cerebral hemispheres is folded. Furrows - depressions divide it into lobes.
The central (Rolandian) sulcus separates the frontal lobe from the parietal lobe. The lateral (Sylvian) fissure separates the temporal lobe from the parietal and frontal lobes. The occipito-parietal sulcus forms the boundary between the parietal, occipital and temporal lobes (Fig. 34 A, B, Fig. 35)
1 - superior frontal gyrus; 2 - middle frontal gyrus; 3 - precentral gyrus; 4 - postcentral gyrus; 5 - inferior parietal gyrus; 6 - superior parietal gyrus; 7 - occipital gyrus; 8 - occipital groove; 9 - intraparietal sulcus; 10 - central groove; 11 - precentral gyrus; 12 - inferior frontal sulcus; 13 - superior frontal sulcus; 14 - vertical slot.
Rice. 34A. Brain from the dorsal surface
1 - olfactory groove; 2 - anterior perforated substance; 3 - hook; 4 - middle temporal sulcus; 5 - inferior temporal sulcus; 6 - seahorse groove; 7 - roundabout groove; 8 - calcarine groove; 9 - wedge; 10 - parahippocampal gyrus; 11 - occipitotemporal groove; 12 - inferior parietal gyrus; 13 - olfactory triangle; 14 - straight gyrus; 15 - olfactory tract; 16 - olfactory bulb; 17 - vertical slot.
Rice. 34B. Brain from the ventral surface
1 - central groove (Rolanda); 2 - lateral groove (Sylvian fissure); 3 - precentral sulcus; 4 - superior frontal sulcus; 5 - inferior frontal sulcus; 6 - ascending branch; 7 - anterior branch; 8 - postcentral groove; 9 - intraparietal sulcus; 10 - superior temporal sulcus; 11 - inferior temporal sulcus; 12 - transverse occipital groove; 13 - occipital groove.
Rice. 35. Grooves on the superolateral surface of the hemisphere (left side)
Thus, the grooves divide the hemispheres of the telencephalon into five lobes: the frontal, parietal, temporal, occipital and insular lobe, which is located under the temporal lobe (Fig. 36).
Rice. 36. Projection (marked with dots) and associative (light) zones of the cerebral cortex. Projection areas include the motor area (frontal lobe), somatosensory area (parietal lobe), visual area (occipital lobe), and auditory area (temporal lobe).
There are also grooves on the surface of each lobe.
There are three orders of furrows: primary, secondary and tertiary. The primary grooves are relatively stable and the deepest. These are the boundaries of large morphological parts of the brain. Secondary grooves extend from the primary ones, and tertiary ones from the secondary ones.
Between the grooves there are folds - convolutions, the shape of which is determined by the configuration of the grooves.
The frontal lobe is divided into the superior, middle and inferior frontal gyri. The temporal lobe contains the superior, middle and inferior temporal gyri. The anterior central gyrus (precentral) is located in front of the central sulcus. The posterior central gyrus (postcentral) is located behind the central sulcus.
In humans, there is great variability in the sulci and convolutions of the telencephalon. Despite this individual variability in the external structure of the hemispheres, this does not affect the structure of personality and consciousness.
Cytoarchitecture and myeloarchitecture of the neocortex
In accordance with the division of the hemispheres into five lobes, five main areas are distinguished - frontal, parietal, temporal, occipital and insular, which have differences in structure and perform different functions. However, the general plan of the structure of the new cortex is the same. The new crust is a layered structure (Fig. 37). I - molecular layer, formed mainly by nerve fibers running parallel to the surface. Among the parallel fibers there is a small number of granular cells. Under the molecular layer there is a second layer - the outer granular one. Layer III is the outer pyramidal layer, layer IV is the inner granular layer, layer V is the inner pyramidal layer and layer VI is multiform. The layers are named after the neurons. Accordingly, in layers II and IV, the neuron somas have a rounded shape (granular cells) (outer and internal granular layers), and in layers III and IV, the somas have a pyramidal shape (in the outer pyramidal there are small pyramids, and in the inner pyramidal layers there are large ones). pyramids or Betz cells). Layer VI is characterized by the presence of neurons of various shapes (fusiform, triangular, etc.).
The main afferent inputs to the cerebral cortex are nerve fibers coming from the thalamus. Cortical neurons that perceive afferent impulses traveling along these fibers are called sensory, and the area where sensory neurons are located is called projection zones of the cortex.
The main efferent outputs from the cortex are the axons of layer V pyramids. These are efferent, motor neurons involved in the regulation motor functions. Most cortical neurons are intercortical, involved in information processing and providing intercortical connections.
Typical cortical neurons
Roman numerals indicate cell layers I - molecular layer; II - outer granular layer; III - outer pyramidal layer; IV - internal granular layer; V - inner primamide layer; VI-multiform layer.
a - afferent fibers; b - types of cells detected on preparations impregnated using the Goldbrzy method; c - cytoarchitecture revealed by Nissl staining. 1 - horizontal cells, 2 - Kees stripe, 3 - pyramidal cells, 4 - stellate cells, 5 - outer Bellarger stripe, 6 - inner Bellarger stripe, 7 - modified pyramidal cell.
Rice. 37. Cytoarchitecture (A) and myeloarchitecture (B) of the cerebral cortex.
While maintaining the general structural plan, it was found that different sections of the cortex (within one area) differ in the thickness of the layers. In some layers, several sublayers can be distinguished. In addition, there are differences cellular composition(diversity of neurons, density and their location). Taking into account all these differences, Brodman identified 52 areas, which he called cytoarchitectonic fields and designated in Arabic numerals from 1 to 52 (Fig. 38 A, B).
And the side view. B midsagittal; slice
Rice. 38. Field layout according to Boardman
Each cytoarchitectonic field differs not only cellular structure, but also by the location of nerve fibers, which can run in both vertical and horizontal directions. The accumulation of nerve fibers within the cytoarchitectonic field is called myeloarchitectonics.
Currently, the “columnar principle” of organizing the projection zones of the cortex is becoming increasingly recognized.
According to this principle, each projection zone consists of large quantity vertically oriented columns, approximately 1 mm in diameter. Each column unites about 100 neurons, among which there are sensory, intercalary and efferent neurons, interconnected by synaptic connections. A single “cortical column” is involved in processing information from a limited number of receptors, i.e. performs a specific function.
Hemispheric fiber system
Both hemispheres have three types of fibers. Through projection fibers, excitation enters the cortex from receptors along specific pathways. Association fibers connect different areas of the same hemisphere. For example, the occipital region with the temporal region, the occipital region with the frontal region, the frontal region with the parietal region. Commissural fibers connect symmetrical areas of both hemispheres. Among the commissural fibers there are: anterior, posterior cerebral commissures and the corpus callosum (Fig. 39 A.B).
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Rice. 39A. a - medial surface of the hemisphere;
b - upper-alteral surface of the hemisphere;
A - frontal pole;
B - occipital pole;
C - corpus callosum;
1 - arcuate fibers of the cerebrum connect neighboring gyri;
2 - belt - a bundle of the olfactory brain lies under the vaulted gyrus, extends from the region of the olfactory triangle to the hook;
3 - the lower longitudinal fasciculus connects the occipital and temporal regions;
4 - the superior longitudinal fasciculus connects the frontal, occipital, temporal lobes and the inferior parietal lobe;
5 - the uncinate fascicle is located at the anterior edge of the insula and connects the frontal pole with the temporal one.
Rice. 39B. Cerebral cortex in cross section. Both hemispheres are connected by bundles of white matter that form the corpus callosum (commissural fibers).
Rice. 39. Scheme of associative fibers
Reticular formation
The reticular formation (reticular substance of the brain) was described by anatomists at the end of the last century.
The reticular formation begins in the spinal cord, where it is represented by the gelatinous substance of the base of the hindbrain. Its main part is located in the central brain stem and diencephalon. It consists of neurons of various shapes and sizes, which have extensive branching processes running in different directions. Among the processes, short and long nerve fibers are distinguished. Short processes provide local connections, long ones form the ascending and descending paths of the reticular formation.
Clusters of neurons form nuclei that are located at different levels of the brain (dorsal, medulla, middle, intermediate). Most of the nuclei of the reticular formation do not have clear morphological boundaries and the neurons of these nuclei are united only by functional characteristics (respiratory, cardiovascular center, etc.). However, at the level of the medulla oblongata, nuclei with clearly defined boundaries are distinguished - the reticular giant cell, reticular parvocellular and lateral nuclei. The nuclei of the reticular formation of the pons are essentially a continuation of the nuclei of the reticular formation of the medulla oblongata. The largest of them are the caudal, medial and oral nuclei. The latter passes into the cell group of nuclei of the reticular formation of the midbrain and the reticular nucleus of the tegmentum of the brain. The cells of the reticular formation are the beginning of both ascending and descending pathways, giving numerous collaterals (endings) that form synapses on neurons of different nuclei of the central nervous system.
Fibers of reticular cells traveling to the spinal cord form the reticulospinal tract. Fibers of the ascending tracts, starting in the spinal cord, connect the reticular formation with the cerebellum, midbrain, diencephalon and cerebral cortex.
There are specific and nonspecific reticular formations. For example, some of the ascending pathways of the reticular formation receive collaterals from specific pathways (visual, auditory, etc.), along which afferent impulses are transmitted to the projection zones of the cortex.
Nonspecific ascending and descending pathways of the reticular formation affect the excitability of various parts of the brain, primarily the cerebral cortex and the spinal cord. These influences, according to their functional significance, can be both activating and inhibitory, therefore they are distinguished: 1) ascending activating influence, 2) ascending inhibitory influence, 3) descending activating influence, 4) descending inhibitory influence. Based on these factors, the reticular formation is considered as a regulating nonspecific brain system.
The most studied is the activating influence of the reticular formation on the cerebral cortex. Most of the ascending fibers of the reticular formation diffusely end in the cerebral cortex and maintain its tone and ensure attention. An example of inhibitory descending influences of the reticular formation is a decrease in the tone of human skeletal muscles during certain stages of sleep.
Neurons of the reticular formation are extremely sensitive to humoral substances. This is an indirect mechanism of influence of various humoral factors and the endocrine system on the higher parts of the brain. Consequently, the tonic effects of the reticular formation depend on the state of the whole organism (Fig. 40).
Rice. 40. The activating reticular system (ARS) is a nervous network through which sensory excitation is transmitted from the reticular formation of the brain stem to the nonspecific nuclei of the thalamus. Fibers from these nuclei regulate the level of activity of the cortex.
Subcortical nuclei
The subcortical nuclei are part of the telencephalon and are located inside the white matter of the cerebral hemispheres. These include the caudate body and the putamen, united under common name the “striatum” (striatum) and the globus pallidus, consisting of the lentiform body, husk and tonsil. The subcortical nuclei and nuclei of the midbrain (red nucleus and substantia nigra) make up the system of basal ganglia (nuclei) (Fig. 41). The basal ganglia receives impulses from the motor cortex and cerebellum. In turn, signals from the basal ganglia are sent to the motor cortex, cerebellum and reticular formation, i.e. There are two neural loops: one connects the basal ganglia with the motor cortex, the other with the cerebellum.
Rice. 41. Basal ganglia system
The subcortical nuclei take part in the regulation of motor activity, regulating complex movements when walking, maintaining a posture, and when eating. They organize slow movements (stepping over obstacles, threading a needle, etc.).
There is evidence that the striatum is involved in the processes of memorizing motor programs, since irritation of this structure leads to impaired learning and memory. The striatum has an inhibitory effect on various manifestations of motor activity and on the emotional components of motor behavior, in particular on aggressive reactions.
The main transmitters of the basal ganglia are: dopamine (especially in the substantia nigra) and acetylcholine. Damage to the basal ganglia causes slow, writhing, involuntary movements accompanied by sharp muscle contractions. Involuntary jerky movements of the head and limbs. Parkinson's disease, the main symptoms of which are tremor (shaking) and muscle rigidity (a sharp increase in the tone of the extensor muscles). Due to rigidity, the patient can hardly begin to move. Constant tremor prevents small movements. Parkinson's disease occurs when the substantia nigra is damaged. Normally, the substantia nigra has an inhibitory effect on the caudate nucleus, putamen and globus pallidus. When it is destroyed, the inhibitory influences are eliminated, as a result of which the excitatory effect of the basal ganglia on the cerebral cortex and reticular formation increases, which causes the characteristic symptoms of the disease.
Limbic system
The limbic system is represented by sections of the new cortex (neocortex) and diencephalon located on the border. It unites complexes of structures of different phylogenetic ages, some of which are cortical, and some are nuclear.
The cortical structures of the limbic system include the hippocampal, parahippocampal and cingulate gyri (senile cortex). The ancient cortex is represented by the olfactory bulb and olfactory tubercles. The neocortex is part of the frontal, insular and temporal cortices.
The nuclear structures of the limbic system combine the amygdala and septal nuclei and anterior thalamic nuclei. Many anatomists consider the preoptic area of the hypothalamus and the mammillary bodies to be part of the limbic system. The structures of the limbic system form 2-way connections and are connected to other parts of the brain.
The limbic system controls emotional behavior and regulates endogenous factors that provide motivation. Positive emotions are associated primarily with the excitation of adrenergic neurons, and negative emotions, as well as fear and anxiety, are associated with a lack of excitation of noradrenergic neurons.
The limbic system is involved in organizing orienting and exploratory behavior. Thus, “novelty” neurons were discovered in the hippocampus, changing their impulse activity when new stimuli appear. The hippocampus plays a significant role in maintaining the internal environment of the body and is involved in the processes of learning and memory.
Consequently, the limbic system organizes the processes of self-regulation of behavior, emotion, motivation and memory (Fig. 42).
Rice. 42. Limbic system
Autonomic nervous system
The autonomous (autonomic) nervous system provides regulation of internal organs, strengthening or weakening their activity, carries out an adaptive-trophic function, regulates the level of metabolism (metabolism) in organs and tissues (Fig. 43, 44).
1 - sympathetic trunk; 2 - cervicothoracic (stellate) node; 3 – middle cervical node; 4 - upper cervical node; 5 - internal carotid artery; 6 - celiac plexus; 7 - superior mesenteric plexus; 8 - inferior mesenteric plexus
Rice. 43. Sympathetic part of the autonomic nervous system,
III - oculomotor nerve; YII - facial nerve; IX - glossopharyngeal nerve; X - vagus nerve.
1 - ciliary node; 2 - pterygopalatine node; 3 - ear node; 4 - submandibular node; 5 - sublingual node; 6 - parasympathetic sacral nucleus; 7 - extramural pelvic node.
Rice. 44. Parasympathetic part of the autonomic nervous system.
The autonomic nervous system includes parts of both the central and peripheral nervous systems. Unlike the somatic nervous system, in the autonomic nervous system the efferent part consists of two neurons: preganglionic and postganglionic. Preganglionic neurons are located in the central nervous system. Postganglionic neurons are involved in the formation of autonomic ganglia.
The autonomic nervous system is divided into sympathetic and parasympathetic divisions.
In the sympathetic division, preganglionic neurons are located in the lateral horns of the spinal cord. The axons of these cells (preganglionic fibers) approach the sympathetic ganglia of the nervous system, located on both sides of the spine in the form of a sympathetic nerve chain.
Postganglionic neurons are located in the sympathetic ganglia. Their axons emerge as part of the spinal nerves and form synapses on the smooth muscles of internal organs, glands, vascular walls, skin and other organs.
In the parasympathetic nervous system, preganglionic neurons are located in the nuclei of the brainstem. The axons of preganglionic neurons are part of the oculomotor, facial, glossopharyngeal and vagus nerves. In addition, preganglionic neurons are also found in the sacral spinal cord. Their axons go to the rectum, bladder, and to the walls of the vessels that supply blood to the organs located in the pelvic area. Preganglionic fibers form synapses on postganglionic neurons of the parasympathetic ganglia located near or within the effector (in the latter case, the parasympathetic ganglion is called intramural).
All parts of the autonomic nervous system are subordinate to the higher parts of the central nervous system.
Functional antagonism of the sympathetic and parasympathetic nervous systems was noted, which is of great adaptive importance (see Table 1).
SECTION I V . DEVELOPMENT OF THE NERVOUS SYSTEM
The nervous system begins to develop in the 3rd week of intrauterine development from the ectoderm (outer germ layer).
On the dorsal (dorsal) side of the embryo, the ectoderm thickens. This forms the neural plate. The neural plate then bends deeper into the embryo and a neural groove is formed. The edges of the neural groove close together to form the neural tube. The long, hollow neural tube, which first lies on the surface of the ectoderm, is separated from it and plunges inward, under the ectoderm. The neural tube expands at the anterior end, from which the brain later forms. The rest of the neural tube is transformed into the brain (Fig. 45).
Rice. 45. Stages of embryogenesis of the nervous system in a transverse schematic section, a - medullary plate; b and c - medullary groove; d and e - brain tube. 1 - horny leaf (epidermis); 2 - ganglion cushion.
From cells migrating from the side walls of the neural tube, two neural crests are formed - nerve cords. Subsequently, spinal and autonomic ganglia and Schwann cells are formed from the nerve cords, which form the myelin sheaths of nerve fibers. In addition, neural crest cells participate in the formation of the pia mater and arachnoid membrane of the brain. In the inner part of the neural tube, increased cell division occurs. These cells differentiate into 2 types: neuroblasts (precursors of neurons) and spongioblasts (precursors of glial cells). Simultaneously with cell division, the head end of the neural tube is divided into three sections - the primary brain vesicles. Accordingly, they are called the forebrain (I vesicle), middle (II vesicle) and hindbrain (III vesicle). In subsequent development, the brain is divided into the telencephalon (cerebral hemispheres) and diencephalon. The midbrain is preserved as a single whole, and the hindbrain is divided into two sections, including the cerebellum with the pons and the medulla oblongata. This is the 5-vesical stage of brain development (Fig. 46, 47).
a - five brain tracts: 1 - first vesicle (end brain); 2 - second bladder (diencephalon); 3 - third bladder (midbrain); 4- fourth bladder (medulla oblongata); between the third and fourth bladder there is an isthmus; b - brain development (according to R. Sinelnikov).
Rice. 46. Brain development (diagram)
A - formation of primary blisters (up to the 4th week of embryonic development). B - E - formation of secondary bubbles. B, C - end of the 4th week; G - sixth week; D - 8-9 weeks, ending with the formation of the main parts of the brain (E) - by 14 weeks.
3a - isthmus of the rhombencephalon; 7 end plate.
Stage A: 1, 2, 3 - primary brain vesicles
1 - forebrain,
2 - midbrain,
3 - hindbrain.
Stage B: the forebrain is divided into the hemispheres and basal ganglia (5) and diencephalon (6)
Stage B: The rhombencephalon (3a) is divided into the hindbrain, which includes the cerebellum (8), the pons (9) stage E and the medulla oblongata (10) stage E
Stage E: spinal cord is formed (4)
Rice. 47. The developing brain.
The formation of nerve vesicles is accompanied by the appearance of bends due to different rates of maturation of parts of the neural tube. By the 4th week of intrauterine development, the parietal and occipital curves are formed, and during the 5th week, the pontine curve is formed. By the time of birth, only the bend of the brain stem remains almost at a right angle in the area of the junction of the midbrain and diencephalon (Fig. 48).
Lateral view illustrating curves in the midbrain (A), cervical (B), and pons (C).
1 - optic vesicle, 2 - forebrain, 3 - midbrain; 4 - hindbrain; 5 - auditory vesicle; 6 - spinal cord; 7 - diencephalon; 8 - telencephalon; 9 - rhombic lip. Roman numerals indicate the origin of the cranial nerves.
Rice. 48. The developing brain (from the 3rd to the 7th week of development).
At the beginning, the surface of the cerebral hemispheres is smooth. At 11-12 weeks of intrauterine development, the lateral sulcus (Sylvius) is formed first, then the central (Rollandian) sulcus. The laying of grooves within the lobes of the hemispheres occurs quite quickly; due to the formation of grooves and convolutions, the area of the cortex increases (Fig. 49).
Rice. 49. Side view of the developing cerebral hemispheres.
A- 11th week. B- 16_ 17 weeks. B- 24-26 weeks. G- 32-34 weeks. D - newborn. The formation of the lateral fissure (5), the central sulcus (7) and other sulci and convolutions is shown.
I - telencephalon; 2 - midbrain; 3 - cerebellum; 4 - medulla oblongata; 7 - central groove; 8 - bridge; 9 - grooves of the parietal region; 10 - grooves of the occipital region;
II - furrows of the frontal region.
By migration, neuroblasts form clusters - nuclei that form the gray matter of the spinal cord, and in the brain stem - some nuclei of the cranial nerves.
Neuroblast somata have a round shape. The development of a neuron is manifested in the appearance, growth and branching of processes (Fig. 50). A small short protrusion forms on the neuron membrane at the site of the future axon - a growth cone. The axon extends and delivers nutrients to the growth cone. At the beginning of development, a neuron develops a larger number of processes compared to the final number of processes of a mature neuron. Some of the processes are retracted into the soma of the neuron, and the remaining ones grow towards other neurons with which they form synapses.
Rice. 50. Development of a spindle-shaped cell in human ontogenesis. The last two sketches show the difference in the structure of these cells in a child aged two years and an adult
In the spinal cord, axons are short in length and form intersegmental connections. Longer projection fibers form later. Somewhat later than the axon, dendritic growth begins. All branches of each dendrite are formed from one trunk. The number of branches and length of dendrites is not completed in the prenatal period.
The increase in brain mass during the prenatal period occurs mainly due to an increase in the number of neurons and the number of glial cells.
The development of the cortex is associated with the formation of cellular layers (in the cerebellar cortex there are three layers, and in the cerebral cortex there are six layers).
The so-called glial cells play an important role in the formation of the cortical layers. These cells take a radial position and form two vertically oriented long processes. Neuronal migration occurs along the processes of these radial glial cells. The more superficial layers of the bark are formed first. Glial cells also take part in the formation of the myelin sheath. Sometimes one glial cell participates in the formation of the myelin sheaths of several axons.
Table 2 reflects the main stages of development of the nervous system of the embryo and fetus.
Table 2.
The main stages of development of the nervous system in the prenatal period.
| Fetal age (weeks) | Nervous system development |
| 2,5 | A neural groove is outlined |
| 3.5 | The neural tube and nerve cords are formed |
| 4 | 3 brain bubbles are formed; nerves and ganglia form |
| 5 | 5 brain bubbles form |
| 6 | The meninges are outlined |
| 7 | The hemispheres of the brain reach a large size |
| 8 | Typical neurons appear in the cortex |
| 10 | The internal structure of the spinal cord is formed |
| 12 | General structural features of the brain are formed; differentiation of neuroglial cells begins |
| 16 | Distinct lobes of the brain |
| 20-40 | Myelination of the spinal cord begins (week 20), layers of the cortex appear (week 25), sulci and convolutions form (week 28-30), myelination of the brain begins (week 36-40) |
Thus, the development of the brain in the prenatal period occurs continuously and in parallel, but is characterized by heterochrony: the rate of growth and development of phylogenetically older formations is greater than that of phylogenetically younger formations.
Genetic factors play a leading role in the growth and development of the nervous system during the prenatal period. The average weight of a newborn's brain is approximately 350 g.
Morpho-functional maturation of the nervous system continues in the postnatal period. By the end of the first year of life, the weight of the brain reaches 1000 g, while in an adult the brain weight is on average 1400 g. Consequently, the main increase in brain weight occurs in the first year of a child’s life.
The increase in brain mass in the postnatal period occurs mainly due to an increase in the number of glial cells. The number of neurons does not increase, since they lose the ability to divide already in the prenatal period. Overall Density neurons (the number of cells per unit volume) decreases due to the growth of the soma and processes. The number of branches of dendrites increases.
In the postnatal period, myelination of nerve fibers also continues both in the central nervous system and the nerve fibers that make up the peripheral nerves (cranial and spinal).
The growth of spinal nerves is associated with the development of the musculoskeletal system and the formation of neuromuscular synapses, and the growth of cranial nerves with the maturation of sensory organs.
Thus, if in the prenatal period the development of the nervous system occurs under the control of the genotype and is practically independent of the influence of the external environment, then in the postnatal period external stimuli play an increasingly important role. Irritation of the receptors causes afferent impulse flows that stimulate the morpho-functional maturation of the brain.
Under the influence of afferent impulses, spines are formed on the dendrites of cortical neurons - outgrowths that are special postsynaptic membranes. The more spines, the more synapses and the more involved the neuron is in information processing.
Throughout postnatal ontogenesis up to puberty, as well as in the prenatal period, brain development occurs heterochronously. Thus, the final maturation of the spinal cord occurs earlier than the brain. The development of stem and subcortical structures, earlier than the cortical ones, the growth and development of excitatory neurons overtakes the growth and development of inhibitory neurons. These are general biological patterns of growth and development of the nervous system.
Morphological maturation of the nervous system correlates with the characteristics of its functioning at each stage of ontogenesis. Thus, earlier differentiation of excitatory neurons compared to inhibitory neurons ensures the predominance of flexor muscle tone over extensor tone. The arms and legs of the fetus are in a bent position - this determines a position that provides minimal volume, due to which the fetus takes up less space in the uterus.
Improving the coordination of movements associated with the formation of nerve fibers occurs throughout the preschool and school periods, which is manifested in the consistent development of sitting, standing, walking, writing, etc. postures.
The increase in the speed of movements is caused mainly by the processes of myelination of peripheral nerve fibers and an increase in the speed of excitation of nerve impulses.
The earlier maturation of subcortical structures compared to cortical ones, many of which are part of the limbic structure, determines the characteristics of the emotional development of children (greater intensity of emotions and the inability to restrain them are associated with the immaturity of the cortex and its weak inhibitory influence).
In old age and senility, anatomical and histological changes in the brain occur. Atrophy of the cortex of the frontal and superior parietal lobes often occurs. The fissures become wider, the ventricles of the brain enlarge, and the volume of white matter decreases. Thickening of the meninges occurs.
With age, neurons decrease in size, but the number of nuclei in cells may increase. In neurons, the content of RNA necessary for the synthesis of proteins and enzymes also decreases. This impairs the trophic functions of neurons. It has been suggested that such neurons fatigue more quickly.
In old age, the blood supply to the brain is also disrupted, the walls of blood vessels thicken and cholesterol plaques are deposited on them (atherosclerosis). It also impairs the functioning of the nervous system.
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Tissue is a collection of cells and intercellular substance, similar in structure, origin and functions.
Some anatomists do not include the medulla oblongata in the hindbrain, but distinguish it as an independent section.