Nerve tissue consists of nerve cells (neurons) and auxiliary satellite cells (glial cells). Nerve cells -the main structural and functional elements of the organs of the nervous system. They are able to perceive irritation, come into a state of excitement, generate and transmit nerve impulses. Glial cells (neuroglia) carry out supporting and delimiting functions, provide the existence and specific function of nerve cells. Nerve cells are characterized by the ability to synthesize biologically active substances (mediators). In some neurons, secretion becomes their main function. The neurons specialized for this function are called neurosecretory cells.

Nerve cells in different parts of the nervous system differ in size and shape. For example, the diameter of the body of some cells of the cerebellum is 4 - 6 microns, and the body of giant pyramidal cells of the cerebral cortex reaches 130 microns.

In each nerve cell, a body, processes and nerve endings are distinguished. A common morphological feature of all mature neurons is the presence of processes. Depending on the location and function of nerve cells, the length of the processes is very different, ranging from a few micrometers to 1 - 1.5 m.

There are two types of processes: axon and dendrites. Axon, or neuritis, a long process that conducts nerve impulses from the body nerve cell and transfers them to another neuron or to the cells of the working organ - muscles, glands. All neurons have only one axon. In most cases dendrites strongly branch, which determines their name (from the Greek. dendron - tree). One neuron can have from 1 to 15 dendrites. Dendrites conduct nerve impulses to the body of the nerve cell. According to the number of processes, neurons are divided into three groups (Fig. 42): cells with one process - unipolar neurons, cells with two processes - bipolar neurons and cells with three or more processes - multipolar neurons.

Figure: 42. Types of neurons (nerve cells):

1 - unipolar neuron, 2 - bipolar neuron, 3 - pseudo-unipolar neuron, 4 - multipolar neuron

Bifurcated neurons also include cells of sensory nodes located near the spinal cord and brain (nodes of the spinal and cranial nerves). From the body of such a cell, a cord departs, an outgrowth of its body, which has the form of a process, which is divided into a dendrite that goes to the periphery, and an axon that goes to the brain. Such sensitive cells, in which two processes branch off from the outgrowth of the body, are called pseudo-unipolar cells.

Depending on the function, nerve cells are divided into receptor(sensitive), efferent (outgoing) and associative (interlocking). Receptor neurons perceive irritations of the external or internal environment, participate in the formation nerve impulses and conducting these impulses to the brain. Efferent neurons (motor, secretory) conduct nerve impulses from the brain to the executive organs (muscles, glands). Intercalary neurons carry out communication between sensory and motor (secretory) neurons, participate in the formation of neural circuits.

The nerve cell is surrounded by a plasma membrane, which has a number of specific functions: 1) regulates the transport of substances that are associated with nerve signaling; 2) serves as a site of electrical activity underlying the conduction of a nerve impulse; 3) serves as a site of action of biologically active substances (mediators, peptides, etc.); 4) participates in the formation of specialized contacts (synapses) between neurons.

The body of a nerve cell contains a nucleus. Human neurons almost always contain one nucleus. The core is oval. The nucleolus is large. Chromatin in the nuclei is loosened, which is associated with its function as a regulator of active protein synthesis.

The cytoplasm of nerve cells is characterized by an abundance of various organelles, which is associated with their high functional activity. The cytoplasm of the neuron contains membrane and non-membrane organelles.

A neuron is characterized by the presence of special organelles in the cytoplasm: neurofibrils and chromatophilic substances. Neurofibrils -it is a set of fibrous structures of the cytoplasm, consisting of neurofilaments and microtubules. In the body of the neuron, they form a dense plexus; in the processes of nerve cells, they are oriented parallel to the length of the process. Neurofibrils perform supporting and transport functions in nerve cells,

Chromatophilic substance (granular endoplasmic reticulum) is localized in the body and dendrites of the neuron in the form of lumps various shapes and sizes. The significant development of the granular endoplasmic reticulum in neurons is associated with a high level of protein synthesis on its membranes.

Nerve fibers. The processes of nerve cells covered with membranes are called nerve fibers. Depending on the structure of the shells, there are pulpy(myelinated) and serene (myelin-free) nerve fibers. In the center of each nerve fiber (dendrite, axon) there is a process of a nerve cell, called axial cylinder. AT fleshy nerve fiber contains several (up to 10 - 20) axial cylinders, i.e. processes of various nerve cells. Pulpy nerve fiber contains one axial cylinder (dendrite or axon) of one nerve cell. The axial cylinder of nerve fibers consists of the cytoplasm of the nerve cell containing longitudinally oriented neurofilaments. Outside, the axial cylinder is covered with a membrane that ensures the conduction of a nerve impulse. Myelinated nerve fibers are much thicker than non-fleshy ones. In the sheath of myelinated nerve fibers there is a so-called myelin layer containing lipids. Myelinated nerve fibers conduct nerve impulses faster (5 - 120 m1s) than non-fleshy ones (1 - 2 m1s).

Nerve endings... All nerve fibers end with nerve endings. There are three types of nerve endings: sensory (receptor), motor, or secretory, and interneuronal (synaptic).

Sensitive nerve endings (receptors) - specialized terminal formations of dendrites of sensitive neurons. They are found in all organs and tissues of the human body and perceive various influences of factors of the external and internal environment, converting them into nerve impulses. Sensory endings are subdivided into free nerve endings and non-free nerve endings. Free nerve endings are the terminal branches of the dendrites of sensory neurons. Non-free sensory nerve endings have a sheath. which is formed with the participation of neuroglial cells. Non-free nerve endings that have a connective tissue sheath (capsule) are called encapsulated nerve endings, in the absence of a capsule - non-encapsulated nerve endings.

Effector nerve endings (effectors) are located in organs and tissues. With their participation, the nerve impulse is transmitted to the tissues of the working organs, causing the "effect" of movement, secretion or other action. Among the effectors, motor and secretory nerve endings are distinguished. The motor nerve endings are the terminal apparatus of the axons of the motor neurons of the anterior horns of the spinal cord, motor nuclei of the cranial nerves and autonomic nuclei. These endings are located on muscle fibers of skeletal muscles, smooth muscle cells of internal organs and blood vessels. Secretory nerve endings are located on the secretory cells of the glands of external and internal secretion.

The transmission of nerve impulses from one neuron to neighboring ones occurs at the points of contact of nerve cells with each other. Such specialized connections were named interneuronal contacts - synapses (fig. 43).

Figure: 43. Scheme of interneuronal contact (synapse): 1 - axon, 2 – microtubules, 3 – mitochondria, 4 – synaptic vesicle, 5 - presynaptic membrane, 6 – synaptic cleft, 7 - dendrite, 8 – postsynaptic membrane, 9 – mediator receptor

The word “synapse” (from the Greek synapsis - connection) was used to designate the junction (contact) of neurons, through which a nerve impulse passes from one neuron to another, making functional connections between neurons.

The section of the neuron through which impulses enter the synapse is called presynaptic department.In the presynaptic section there are presynaptic vesicles filled with a mediator, a chemical substance involved in the transmission of nerve impulses. The area of \u200b\u200bcontact of the neuron with the presynaptic department is called postsynaptic department, having a postsynaptic membrane. The postsynaptic membrane is thickened and has receptors for a transmitter. Between the presynaptic and postsynaptic membranes is synaptic cleft.

Synapses are dynamically polarized. In them, the transmission of a nerve impulse is carried out only in one direction: from the presynaptic membrane to the postsynaptic one, from the sensitive nerve endings to the body of the nerve cell, then along the axon of this cell to the dendrites or the body of another nerve cell. Conducting nerve impulses in such a strictly defined direction is explained dynamic polarization of neurons.

Depending on which parts of the nerve cells come into contact with each other, they distinguish axodendritic synapses (the end of the axon of one neuron makes contact with the dendrite of another neuron), axosomatic (the axon contacts the body of another neuron) and axoaxonal (the end of one axon makes contact with the axon of another neuron).

Synapses with chemical transmission of nerve impulses are distinguished - chemical synapses and synapses with electrical transmission of impulses - electrical synapses.

Chemical synapses conduct nerve impulses in only one direction. This is the most common type of connection in nervous system in a person. They are characterized by the transmission of a nerve impulse with the help of biologically active substances - neurotransmitters, secreted by the presynaptic ending into the synaptic cleft.

Distinguish between excitatory and inhibitory neurotransmitters. Excitatory neurotransmitters (acetylcholine, norepinephrine) alter the permeability of the postsynaptic membrane, causing the excitation potential. Inhibitory neurotransmitters (dopamine, glycine, gamma-aminobutyric acid) render the postsynaptic membrane unable to generate excitation.

Electrical (bubble-free) synapses are extremely rare. There are no synaptic vesicles in electrical synapses. The impulse in them can be transmitted in both directions.

Thus, chemical interneuronal synapses ensure the transmission of nerve signals in only one direction, which is the basis for the reliability of the nervous system; postsynaptic neurons, receiving signals from a large number of nerve cells, summarize them and provide a coordinated response.

Similar information.

The structure of the heart tissue is somewhat different in animals of different species. Of domestic animals, in a horse, muscle fibers are laid most compactly, have a ribbon-like shape, lateral bridges are rare, endomysium is poorly developed, blood supply is abundant, myocytes are narrow (10-21 microns) and long (110-130 microns), with a large number of myofibrils, which are often lie in the center of the cells, pushing long narrow nuclei to the periphery. The transverse striation is clearly visible. In cattle, the fibers are polygonal, myocytes are shorter and wider, lateral bridges are more common, and the number of myofibrils is less than in a horse. They are located on the periphery of myocytes. The pig has a reticular heart muscle tissue the most pronounced, the fibers are rounded, the endomysium is well developed, but capillaries are less common than in the horse, myofibrils are smaller, the transverse striation is poorly expressed.

The peculiarity of the cardiac muscle tissue is that it, being essentially a symplast and contracting as a whole, at the same time suffers little when individual myocytes are damaged. Cardiac muscle tissue does not have cambial elements and responds to training or injury with physiological hypertrophy of myocytes. Damaged myocytes die and are replaced by connective tissue.

The intensity and frequency of contractions of the heart muscle are regulated by nerve impulses. However, the heart muscle also has its own system of movement regulation. True, without external regulation, the heart rate is halved. The automatism of contractions is provided by the conductive muscles built from atypical muscle fibers(Purkinje). They consist of large cells with a small number of myofibrils and form the conducting system of the heart,which makes consistent contraction of the atria and ventricles of the heart, provides a rhythmic change in the working act (systole and diastole) with a recovery period (relaxation of the heart muscle).

Questions for self-control.1. What is the origin, structure, distribution, features of the functioning of smooth muscle tissue? 2. The origin and structure of striated skeletal muscle tissue? 3. The structure of the muscle fiber. 4. What is a sarcomere, what is its structure and function? 5. What are the features of the structure and functions of the cardiac striated muscle tissue?

Chapter 10. NERVOUS TISSUE

The nervous tissue is highly specialized; the entire nervous system is built from it. In the central nervous system, it forms a gray and white substance

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in the brain and spinal cord, in the peripheral - ganglia, nerves, nerve endings. The nervous tissue is able to perceive irritations from the external and internal environment, be excited under their influence, develop, conduct

and transmit impulses, organize responses. The sum of these properties of the nervous tissue manifests itself in the main function of the nervous system: regulation and coordination of the activity of various tissues, organs and systems of the body.

Nervous tissue develops from the neuroectoderm. From it is formed first neural plate,and then the neural tube, along which the neural crests (ridges) lie on both sides. All cells of the neural tissue are formed in the neural tube and crests. The structure of the nervous tissue in different parts of the nervous system varies greatly. Nevertheless, it everywhere consists of neurons and neuroglia. Between them there are intercellular spaces filled with tissue fluid. The intercellular spaces of the brain make up 15-20% of its volume. Diffusion of substances between the capillaries and cells of the nervous tissue occurs in the tissue fluid. Neurons are nerve cells capable of producing and conducting nerve impulses. The neuroglia consists of cells that perform auxiliary functions.

The structure and types of neurons. Neuron (neurocyte) - the main structural

and functional unit of nervous tissue (Fig. 32). It distinguishesbody

Pericarion and processes. Neurons of different parts of the nervous system differ from each other in function, shape, size, number and nature of branching of the processes, according to the released mediator. By function, neurons are sensitive (receptor, or afferent), motor (effector, or efferent) and intercalary (associative). The sizes of neurocytes range from 4 microns in cerebellar granule cells to 130 microns (in giant pyramidal cells of the cortex).

Neurons are basically mononuclear cells. The nucleus is large, rounded, usually located in the center of the cell. The karyoplasm is light, since chromatin does not form large lumps. Contains 1-2 large nucleoli. The Golgi complex is located around the core. There are many mitochondria, microtubules, there is a centrosome, lysosomes. The protein synthesis apparatus is well represented: ribosomes and granular cytoplasmic reticulum. The adsorption of basic dyes on clusters of these organelles forms a characteristic pattern in the form of large lumps, resembling a tiger's skin (when examined under a light microscope),

for which it is called tigroid (basophilic) substance or Nissl substance (named after the histologist who described it). There are also specialorga-nella

Neurofilaments. Bunches of neurofilaments and microtubules (neurotubules), due to the adsorption of dyes on them, are visible in a light microscope in the form of neurofibrils. These organelles are involved in the formation of the cytokeleton, in the movement of substances through the cell and its processes.

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Figure: 32. Scheme of the structure of a neuron:

A - at the light-optical level and B - at the ultramicroscopic level:

1 - perikarion; 2 - core; 3 - nucleolus; 4 - dendrites; 5 - axon; 6 - terminal branches of the axon; 7- Golgi complex; 8 - granular endoplasmic reticulum; 9 - mitochondria; 10 - neurofibrils.

The shape of the perikarion is largely determined by the number of processes. Distinguish between unipolar - with one process, pseudo-unipolar, bipolar - with two processes and multipolar neurons - with several (3-20) processes. The bodies of unipolar and pseudo-unipolar cells are round, bipolar - fusiform, multipolar - diverse. Processes are a mandatory accessory of neurons. Without them, neurocytes cannot perform their functions, since the processes provide the conduction of a nerve impulse from one part of the body to another. Their length ranges from a few micrometers to 1-2 m. In terms of morphological and functional properties, the processes are unequal. In a neuron, dendrites and an axon (neurite) are distinguished. There is always one axon in a cell; there can be a different number of dendrites. Excitation spreads along the axon from the body, along the dendrite to the body of the nerve cell. Dendrites, as a rule, are strongly branched and they contain all the organelles that are also present in the cell body. The axon does not branch, but it can give off collaterals - branches running in parallel. There is no basophilic substance in it. Neurofilaments and neurotubules are arranged in order - along the axon. Undifferentiated nerve cells are considered to be unipolar at an early stage of development, when dendrites have not yet formed. Among differentiated cells, unipolar neurons are rare.

From the body pseudo-unipolar neuronone process departs, which T-shaped branches into dendrite and neurite. Such cells are common in the spinal nodes (ganglia). These are sensitive neurons, the dendrites of which go to the periphery, where they end in organs with sensitive nerve endings (receptors), and neurites carry excitation from the cell body to the central nervous system. As you can see, these cells in their own

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structural and functional properties approach bipolar neurons,which are found in the organ of vision, smell and among associative neurons. The most common are multipolar neurons.These are all motor (motor) and most associative neurons. Among their processes, only one axon, and the rest are dendrites. In associative neurons, the axon does not leave the central nervous system, in motor neurons, it goes to the periphery - to the organs (muscles, glands), where it ends with a motor nerve ending.

Nerve cells differentiate early in ontogenesis, lose the ability to divide, normally their life expectancy is equal to that of an individual. To maintain vital activity and the ability to perform functions for such a long time, a system of intracellular regeneration is developed in neurons. In this case, macromolecules and their ensembles are constantly destroyed and created again. Protein syntheses take place mainly in the cell body. A high level of vital activity of the processes is maintained by constant such cytoplasm in the processes and back.

Plasmolemma of a neuron performs all the functions inherent in it in any cells. In addition, it is capable of excitation during depolarization (decrease in the amount of charge) as a result of the movement of Na + ions into the cell. Depolarization occurs locally (in one place) and moves in waves from the dendrite to the body and axon. At what speed the wave of depolarization moves, at the same speed the nerve impulse is transmitted. Inhibition occurs with the opposite phenomenon: an increase in the membrane charge under the influence of ionic fluxes (O- - into the cell and K + - from the cell). In the nervous tissue, neurons form ensembles characteristic of certain parts of the nervous system. The nature of their location is called cytoarch-

tectonics.

Figure: 33. Synapse:

1 - presynaptic pole; 2 - synaptic vesicles; 3- mitochondria; 4 - presynaptic membrane; 5 - synaptic cleft; 6 - postsynaptic pole; 7- postsynaptic membrane.

The transmission of a nerve impulse from one neuron to another is carried out in the place of their contact - the synapse (sinapsis - connection) (Fig. 33). Depending on which parts of the neurons come into contact, they distinguish axodendritic(the axon of one neuron contacts the dendrite of another neuron), axosomatic(the axon contacts the body of another neuron) and

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axoaxonal(the axons of two neurons are in contact) synapses. Also described dendrosomaticand dendrodendriticsynapses. Approximately flat

the fault of the surface of the body of the neuron and almost the entire surface of its dendrites is occupied by synapses.

As a result, each neuron has extensive contacts. So, on one piriform cell of the cerebellum, there are up to 200,000 synapses. Synapses are both excitatory and inhibitory.

All synapses have general principles of structure: the terminal branches of the axon, which transmits the impulse of the neuron at the site of the synapse, form flask-shaped thickenings - this is presynaptic pole.It contains many mitochondria and synaptic vesicles,which differ in type and size depending on the mediator contained in them - the substance that excites the second neuron. It can be serotonin, acetylcholline, adrenaline and other substances. The section of the second neuron that receives the impulse is called postsynaptic pole.It lacks synaptic vesicles and mitochondria. There is a narrow synap between the two poles.

tic gap (about 20 them), limitedcontacting membranes of two poles: presynaptic and postsynaptic. These membranes have thickenings and other special structural adaptations that ensure the successful transmission of a nerve impulse in only one direction. A nerve impulse arriving at the presynaptic pole leads to the release of a transmitter into the synaptic cleft. The nervous impulse caused by it - the pulse goes to the second neuron.

Neuroglia fills all the spaces between neurons, their processes, and blood capillaries in the nervous tissue. Closely adjoins the listed structures, forming their shells. It performs various functions: supporting, isolating, delimiting, trophic, protective, metabolic, homeostatic. Neuroglial cells - gliocytes

They are called auxiliary cells of the nervous tissue, since they do not conduct a nerve impulse. Nevertheless, their functions are vital, since the absence or damage of the neuroglia makes it impossible for the neurons to function. There are two types of neuroglia: macroglia and microglia.

Macroglia (gliocytes), like neurons, develop from neural tube cells. Among the gliocytes are distinguished: ependymocytes, astrocytes, oligodendrocytes.

Ependymocytes are cubic or cylindrical glial cells with cilia at their apical pole; a long process extends from the basal pole, which permeates the entire thickness of the brain. They fit tightly to each other, lining the walls of the ventricles of the brain and the spinal canal with a continuous layer. The movements of the cilia create a flow of cerebrospinal fluid. In some ependymocytes, secretory granules are found. It is assumed that ependymocytes secrete secretions into the cerebrospinal fluid and regulate its composition.

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Astrocytes are the main type of gliocytes in the central nervous system. These are cells with a body diameter of 10-25 microns, with rounded or oval nuclei, with numerous processes diverging in different directions. Distinguish between plasma and fibrous astrocytes. Plasma astrocytes lie in gray matter the brain (that is, where the neuron bodies are located). They have light cytoplasm, short and thick processes, which, adjoining the bodies of neurons and vessels, partially spread out and take the form of plates. Fibrous astrocytes lie in the white matter of the brain, that is, where the nerve fibers are. In these cells, the cytoplasm is darker, longer, thinner and weakly branching processes in comparison with plasma astrocytes. They also form extensions in the form of plates on the walls of blood vessels and nerve fibers, delimiting them from each other and at the same time holding them in a certain position. Both types of astrocytes perform supporting and delineating functions. There is evidence that they are involved in water metabolism and transport of substances from capillaries to neurons.

Oligodendrocytes- a large and rather diverse group of gliocytes. These are small cells of an angular or oval shape with a small number of short thin processes. They surround the bodies and processes of neurons, accompanying them all the way to the nerve endings. Their functions are varied. They are involved in the formation of membranes around dendrites and axons, in the nutrition of neurons. With strong excitement, they transfer part of their RNA into the body of the neuron. They are able to accumulate in themselves a large amount of liquid and other substances, maintaining the homeostasis of the nervous tissue. Consequently, oligodendrocytes perform demarcation, trophic and homeostatic functions.

Microglia (glial macrophages) are small cells derived from the mesenchyme and then from blood cells, apparently by transformation of monocytes. Their number is small - about 5% of glial cells. In a resting state, they have an elongated body and a small number of branching processes. When excited, the processes are drawn in, the cells are rounded, increase in volume, acquire mobility and the ability to phagocytosis.

Nerve fibers - processes of nerve cells (axons and dendrites), covered with gliocyte sheaths. In the brain and spinal cord, the sheath of the fibers is formed by oligodendrocytes, in the remaining parts, their variety, called lemmocytes (Schwann cells).

Depending on the structural features, myelinic and nonmyelinated nerve fibers are distinguished. Myelin-free fibers are distributed in the autonomic nervous system and in the gray matter of the brain, myelin-free - in the peripheral (somatic) nervous system and in the white matter. When the fiber is formed, oligodendroglial cells are located along the process of the neuron, tightly adhering to both the process and to each other. The process of the nerve cell, which is part of the fiber, is called axial cylinder.

Myelin-free nerve fibers. In the case of the formation of a non-myelinated nerve fiber, the process of the neuron pushes in the place of attachment to the lem-

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mocyte its membrane in the form of a groove. As the process descends, the groove becomes deeper, the plasmolemma of the lemmocyte dresses it from all sides in the form of a sleeve. In the end, the axial cylinder, immersed in the lemmocyte, seems to hang in the fold (mesaxon) of its plasmolemma. Mesaxon and lemmocyte plasmolemma surrounding the axial cylinder are visible only through an electron microscope. As a rule, several axial cylinders (3-20) pass in mielene-free fibers. They can be immersed in the lemmocyte at different depths and have different mesaxon lengths. These fibers are called fibers. cable type.Their thickness is 1-5 microns. The nuclei of lemmocytes are located both laterally and in the center of the fiber. The insulation of the axial cylinders inside the cable-type fibers is small, the nerve impulse can propagate diffusely - to all the axial cylinders of the fiber. Axial cylinders pass from one myelin-free fiber to another, which also contributes to the propagation of a nerve impulse along the fibers. The speed of the nerve impulse is relatively low - 0.2-2 m / s.

Figure: 34. Diagram of the structure of myelinated nerve fiber:

1 - axial cylinder; 2 - neurilemma:

3 - nuclei and 4- processes of the lemmocyte;

5 - myelin sheath; 6 - nodal interception; 7- inter-node segment.

Myelinated nerve fibers are more complex (Fig. 34). In the center of each myelin fiber, there is an axial cylinder covered with a myelin sheath. The top layer of the fiber is called neurilemma. The myelin sheath and neurilemma are the constituent parts of the lemmocytes surrounding the axial cylinder. When the myelin fiber is formed, the lemmocytes adjacent to the process of the neuron are flattened and wound around the axial cylinder, wrapping it several times. In this case, the cytoplasm is squeezed out of the wound area of \u200b\u200bthe lemmocyte into free areas, and the plasmolemma collapses, sticks together and forms a layer of the myelin sheath. In the process of winding on the axial cylinder, the lemmocyte grows, stretches more and more, the number of myelin layers increases. The remaining unwound part of the cell with the nucleus and cytoplasm is on top. This will be neurilemma

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(neurolemma). Lemmocytes are incomparably smaller than the axial cylinder. They are located in the fiber alternately, connecting to each other with finger-like outgrowths. At the point of contact of neighboring lemmocytes, the fiber sharply becomes thinner, since the myelin sheath is absent here and the fiber is covered only with neurilemma - nodal interceptions.Areas of fiber covered by the myelin sheath are called inter-site segments.

Myelin fibers are thicker than myelin fibers. Their diameter is 7-20 microns. The nerve impulse passes through them much faster (5-120 m / s). The thicker the fiber, the faster the impulse travels through it. The myelin sheath plays an important role in accelerating the passage of a nerve impulse. In the nodal interceptions, the plasmolemma (axolemma) of the axial cylinder is excited, as in myelin-free nerve fibers, as a result of depolarization under the influence of ion currents. In the area of \u200b\u200bthe inter-nodal segments, the myelin sheath, acting as an insulator, facilitates the lightning-fast passage of a nerve impulse, just as it happens in an electrical conductor. As a result, the nerve impulse, as it were, jumps from one nodal interception to another and thus moves at high speed.

Myelin-free and myelinated nerve fibers outside the central nervous system are clad with a basement membrane, similar to the basement membrane of the epithelium. In the nerve tissue, nerve fibers form ensembles that are characteristic of a particular part of the nervous system. The nature of the arrangement of nerve fibers is called myeloarchitectonics.In the central nervous system, fibers form pathwayson the periphery - nerve

trunks or nerves.

Nerve. Nerve fibers, united by connective tissue, form a nerve, and the thinnest layers of connective tissue located between nerve fibers - endoneurium. It is closely associated with the basement membranes of the fibers, capillaries lie in it. Endoneurium binds nerve fibers into a bundle. The bundles of nerve fibers are dressed with perineurium - wider layers of connective tissue with an ordered arrangement of fibers and with vessels passing through it. Outside, the nerve is covered with epineurium - a fibrous connective tissue rich in fibroblasts, macrophages, and fat cells. In it, the blood and lymphatic vessels and nerves branch out.

The nerves include both myelinated and non-myelinated fibers. There are sensory nerves, formed by dendrites of sensory neurons (sensory cranial nerves), motor nerves - formed by the axons of motor neurons (motor cranial nerves) and mixed - which include processes of neurons of different function and structure (spinal nerves). The size of the nerves and their composition depend largely on the size and functional activity of the organs innervated by them. It is noticed that the nerves of the muscles of the dynamic type

from active motor function are composed of thick myelin fibers

from a small amount of myelin-free. The ventral branches of the spinal nerves are also arranged. In the dorsal branches of the spinal nerves

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and in the nerves innervating the dynamostatic muscles, thinner myelin and more myelin-free fibers.

Figure: 35. Types of nerve endings:

I - sensitive nerve endings - non-encapsulated: A - in the corneal epithelium; B - in the epithelium of the pig's patch; B - in the horse's pericardium; encapsulated: G- phaterpacin's body; D - Meissner's little body; E - a body from a sheep's nipple; 11 - motor nerve endings; W - in a cross-striped fiber; 3 - in a smooth muscle cell; 1 - epithelium; 2 - connective tissue; 3 - nerve endings: 4 - Merkel's cell; 5 - discoidal terminal expansion of the nerve ending; 6 - nerve fiber; 7 - bifurcation of the axial cylinder; 8 - capsule; 9 - the nucleus of the lemmocyte; 10 - muscle fiber.

Nerve endings (Fig. 35). The nerve ending is the place of contact of the process of the nerve cell with various structures of a non-nervous nature. These can be muscle fibers, cells of the glandular or integumentary epithelium, etc. Depending on the functional orientation, there are sensory (receptor, afferent) and motor (effector, efferent) nerve endings.

Sensory nerve endings - receptors are formed by the final branching of the dendrites of sensitive neurons and perceive irritations coming to them from different parts of the body or from the outside. They are scattered throughout the body. Depending on where the receptors get irritated from, they are divided into exteroreceptors,perceiving irritations from the external environment, proprioceptors,carrying excitations from the organs of motion, and interoreceptors,perceiving irritations from internal organs.

Receptors are sensitive only to certain types of stimuli. In this regard, mechano-, thermo-, photo-, baro-, chemo- and other receptors are distinguished. The most common mechanoreceptors. They are present in the skin, muscles, and internal organs. Pain sensations are perceived both by pain receptors, and, apparently, by any other receptor

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ramis when they are excessively irritated. By structure, receptors are divided into free and non-free. Non-free receptors, in turn, are encapsulated and non-encapsulated.

Free nerve endingsthey are formed only by the terminal ramifications of dendrites, which are not covered with anything, and in the form of bushes, glomeruli, loops, rings are located between the cells of the innervated tissue. Most often, free nerve endings are found in the epithelium and connective tissue. There are many of them in the epidermis of the nasal mirror in sheep and horses, in the nasolabial mirror in the cow, around the hair follicles. They have a variety of sensitivities.

Non-free nerve endings represent the terminal branching of the dendrite, surrounded by special receptor cells. Unencapsulated nerve endings are a type of non-free receptor in which the branches of the axial cylinder (dendrite) are surrounded by epithelial or glial cells. Such nerve endings are well developed in the pig's patch. These are tactile menisci (Merkel discs) in which the terminal branches of the dendrite are entwined with special cells in the stratified epithelium that are sensitive to touch and pressure.

Encapsulated nerve endings arranged the most complex. AT

their axial cylinder is surrounded not only by glial cells, but also by a connective tissue capsule. There are many types of encapsulated nerve endings: tactile bodies (Meissner) -tactile receptors, lamellar bodies (Fatera-Pacini) -baroreceptors, bulbous bodies (Golgi-Mazzoni), genital bodies (Dogel), end-flasks (Krause) muscle spindles, etc. The lamellar body (Fatera-Pacini) and the neuromuscular spindle have been studied better than others.

In the lamellar body, the terminal branches of the dendrite (telodendria) are surrounded by glial cells, which, spreading out and densely layering on top of each other, form inner flask(onion). The inner flask is covered with layers of spreading fibroblast-like cells, which together form outer capsulecalf. Between the inner bulb and the outer capsule, and near the nerve endings, there is a space in which sensitive process (ciliary) cells are found. Lamellar bodies react to any changes in pressure in tissues (pressure of liquids, when supported, pressed, hit, etc.), while coding the direction, frequency of the irritating stimulus and the type of its energy. They are very common in the body - they lie in the connective tissue of the organs of the musculoskeletal system, internal organs, blood vessels, nerve trunks, they are found in the lymph nodes, autonomic ganglia, and endocrine glands. Their number and size vary depending on age, location and frequency of excitation (0.1-6 mm).

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Other encapsulated receptors are built on the same principle, differing in the nature of the branching of the axial cylinder, the number and arrangement of plates in the inner flask and capsule. Structural features determine the nature of the sensitivity of one or another nerve ending. In the striated muscle tissue, the branches of the axial cylinder braid from above a group of modified muscle fibers, forming a kind of spindle. From above, the neuromuscular spindle is covered with a connective tissue capsule.

Motor nerve endings - effectors in smooth muscle tissue and glands are usually built like free nerve endings. In striated muscle tissue, they have a complex structure and

are called neuromuscular synapses, or motor plaques. Come on-

for a muscle fiber, the nerve fiber changes. Its axial cylinder, which is an axon of a motor neuron, branches into terminals that are pressed into the muscle fiber and form a contact with its plasmolemma, similar to a synapse. The plasmolemma of the axon at the point of contact is presynaptic membraneneuromuscular synapse, plasmolemma of muscle fiber - postsynaptic.Between them is synoptic gapabout 50 nm wide. The basement membranes of the nerve and muscle fibers join, passing one into the other and cover the motor plaque on top. The plasmolemma of the muscle fiber forms numerous folds at the point of contact. It is assumed that the rate of muscle contraction is associated with their development. One motor neuron (and its axon), together with the muscle fibers innervated by it, creates a motor unit - the mion. The strength of muscle contraction depends on how many motor units are involved in the contraction.

Figure: 36. Reflex arc:

1 spinal cord; 2 - dorsal and 3 - ventral horn of gray matter; 4- spinal ganglion; 5 - sensitive and 6 - motor roots of the spinal nerve; 7 - mixed spinal nerve; 8 - leather; 9 - muscle; 10 - sensitive nerve ending: 11-dendrite; 12 - body and 13 - axon of a sensitive neuron; 14 - insertion neuron and its (15) axon; 16 - motor neuron and its (17) axon; 18 - motor nerve ending.

It includes from 3 to 2000 muscle fibers. Muscle fibers belonging to one motor unit are distributed throughout the muscle. As a result, when a small number of neurons are excited, the entire muscle contracts, and not just any part of it.

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Reflex arc (fig. 36). Excitation in the nervous tissue and in the nervous system does not spread chaotically, but along certain paths - reflex arcs. The reflex arc is formed by a sensitive, one or more associative and motor neurons. Excitation in the reflex arc always goes in a strictly defined direction: from the receptor (sensory nerve endings) along the centripetal process of the sensitive neuron (usually the dendrite) to its body located in the ganglion (nerve node), from where along its centrifugal process (axon) - to the dendrite associative neuron. A synapse is formed between the axon of the sensitive neuron and the dendrite of the associative neuron, which passes the nerve impulse in only one direction: from the presynaptic pole to the postsynaptic pole. The nerve impulse sequentially passes to the dendrite, body and axon of the associative neuron, and from there

Through the synaptic connection to the dendrite, body and axon of the motor neuron. Associative neurons with processes, dendrites and bodies of motor neurons are located in the central nervous system. The axons of motor neurons leave it and go to the innervated tissues and organs, where their terminal ramifications form motor nerve endings - effectors. Receptor irritation (for example, pressure on the skin excites lamellar

corpuscles) leads to a wave of excitation, which travels along the reflex arc and, having reached the effector, organizes a response called a reflex. (In our example, muscle contraction in response to pressure and, as a consequence, movement.)

Age-related and reactive changes in the nervous tissue. The new

in born animals, the structural elements of the nervous tissue are differentiated to such an extent that they can perform all the functions inherent in the nervous system (especially in mature ungulates): reception, integration of the receptor signal, transmission of a nerve impulse, secretion of a transmitter into the synaptic cleft, and the organization of an effector reaction. Nevertheless, in the postnatal period of ontogenesis, there is an increase in the size and complexity of the structure of neurons, which, apparently, is associated with the specifics of their functioning. The sizes of the bodies and nuclei of neurons proportionally increase, the basophilic substance accumulates. In sheep, an increase in its quantity was traced up to 3 years of age, and from 5-6 years - an age-related decrease. The myelin sheath and the size of the lemmocytes that form this membrane thicken.

Questions for self-control.1. What is the origin and principles of the structure of nervous tissue? 2. What is a neuron, what are neurons in structure and function? 3. What is a synapse, its types and structure? 4. What cells of neuroglia do you know, how they differ from each other? 5. What is a nerve fiber, how is it arranged, what is the difference and where are myelinated and nonmyelinated fibers found? 6. What is a nerve ending? 7. Classification and structure of nerve endings. 8. Composition of the reflex arc.

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Section four. MORPHOLOGY OF ORGANS AND THEIR SYSTEMS

Chapter 11. GENERAL PRINCIPLES OF BUILDING AND DEVELOPING THE ORGANISM

Modern morphology, which stands on the positions of dialectical materialism, considers the organism - the object of its study - as a single whole, all parts of which are interconnected, interdependent and interdependent. In addition, the organism is considered not statically, but in the process of its growth and development (in ontogeny), in the light of evolutionary transformations (in phylogeny), depending on the living conditions and the influence of functions.

Such a comprehensive approach to (The study of an organism with the help of a number of sciences and directions included as constituent parts of morphology gave the basis to V.A. Dombrovsky (1946) to define it as an integral morphology. a historically formed system, which has its own special structure and development, due to hereditary properties, the interaction of its parts and the influence of the environment.The organism consists of organs combined into systems and apparatus that provide all manifestations of its life: reactivity, metabolism, reproduction, growth and development ...

Organ (organon - tool) - a part of the body, built of regularly interconnected tissues; has a certain shape, occupies a certain position in the body and performs a specific function. Organs of a single origin, of a similar structure, as a rule, are morphologically closely related and interdependent, perform a common function, constitute an organ system, for example, the nervous, vascular, bone, muscular and other systems. Organs providing a certain life process, but having a different structure and origin, are combined into an apparatus. For example, the apparatus of movement, digestion, respiration, blood, lymph formation, etc. Organ systems can be included in the apparatus as their component.

Organ systems and apparatus, depending on their morphological and functional characteristics, are divided into three groups: somatic, visceral and integrating. AT somatic groupincludes the skeleton, musculature (combined in the movement apparatus) and organs of the skin. They form the soma - the walls of the body. AT visceral (splanchnic) groupin-

they feed the digestive, respiratory and genitourinary apparatus. Together, they make up the insides (Greek splanchna, Latin viscera), located mostly in the natural cavities of the body. AT group of integrating systemsincludes the endocrine, cardiovascular and nervous systems with sensory organs. The cardiovascular system permeates all organs and tissues of the body (with rare exceptions), performs a transport function and unites all systems. Through it, humoral regulation is carried out. The nervous system regulates and coordinates the activity of all systems, including the vascular system, ensuring the harmonious integrity of the organ-

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ism and its adequate connection with the environment with the help of the senses.

All chordates are characterized by common principles of body construction: a) bipolarity (uniaxiality) - the body has two poles - head (cranial) and caudal (caudal); b) bilaterality - bilateral symmetry - the right and left sides of the body are mirror images of each other; c) segmentation (metamerism) - nearby segments are close to construction; d) four-legged (tetrapody); e) the location of most unpaired organs along the main axis of the body.

The direction of the gravity forces of a four-legged animal coincides with the anatomical boundaries dividing the skeleton into its natural sections: skull, cervical, thoracic, lumbar, sacral and caudal, and on the extremities it passes through the sections of the limbs (belt, stylopodia, zeigopodia, autopodia). The general center of gravity passes through the liver, which in cattle corresponds to the level of the 11th thoracic vertebra.

The relationship of the body with the environment. The organism cannot exist in isolation from the environment, as it constantly exchanges matter and energy with it. The body responds to changes in the external environment with adaptive reactions. However, they are not unlimited and are always within the normal range of a given reaction.

The reaction rate is the limits of the body's ability to respond by changing its morphological and physiological properties to changes in the environment without disturbing the main morphological and functional systems.

The structure norm is considered the most common variant of the structure of the body. Animals of different species, sex, age, constitution have their own structural norms that distinguish them from other groups (age, sex, etc.). So, young ungulates are characterized by relative high legs, and adults - by elongation of the body. The norm of the structure is fixed in the genotype more rigidly than the physiological norm. Consequently, structural changes under the influence of the environment will be less pronounced than functional ones. But the structures are also genetically determined to varying degrees. So, the size of the head, the length of the tubular bones, the shape of the muscles in to a greater extent is determined by the genotype, than, for example, the size of the lower back, the thickness of the tubular bones, the mass of the muscles. The individual variability of the organism and organs, if it does not disturb their vital functions, is within the normal range of reaction and structure. If changes in the environment exceed the adaptive capabilities of the organism, pathology develops, which is expressed in diseases, deformities, premature death, etc.

Ontogenesis as a dialectical process. The organism naturally changes during the entire period of its existence. The process of individual development - ontogenesis - begins with the appearance of the zygote and ends with the death of the organism. The development of an organism is a dialectic process, that is, a process in which contradictory phenomena are interconnected and interdependent. Inconsistency is inherent in ontogeny - this is its driving force. So, the contradiction of heredity and variability of op-

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reduces the entire course of individual development; assimilation (anabolism) and dissimilation (catabolism) are inextricably linked in the course of metabolism (energy released during catabolism is spent in the process of anabolic synthesis); the interaction between dying and nascent structures, between progressive and regressive processes is observed at all stages of development (the appearance of daughter cells on the basis of the maternal one, bone formation in place of resorbing cartilage, etc.).

The development of an individual is a reflection of the development of a species, which was formulated by E. Haeckel in the form of a biogenetic law, which states that ontogeny repeats phylogeny. C. Darwin wrote in 1842 that the embryo is, as it were, a witness to the past centuries through which the species passed. A.N.Severtsov supplemented and expanded this provision, showing that ontogeny is not only the result, but also the basis of phylogenesis, since phylogeny is a series of ontogenesis and changes occurring in the genotype of an individual, transmitted to offspring, affect the direction of phylogenesis. Changes in the development of an individual that occur under the influence of the environment are considered adaptive. The severity of the changes depends on the individual reactions of the organism, and then natural selection begins to operate, preserving the individuals whose changes turned out to be the most adaptive, increased their viability, promoted active reproduction, etc. The wider the norm of reaction and structure, the wider the geno- and phenotypic variability , the greater the possibility of morphofunctional adaptation, and, consequently, the prosperity and evolution of the species. The influence of the external environment on the morphofunctional organization of an animal is clearly seen in the process of domestication: in red foxes, after a few generations, polyesterity, variegated coat color appear, behavior changes, the ability to wag its tail appears; in sheep, the length and structure of the gastrointestinal tract, the quality of the wool change.

Ontogenesis is carried out according to a certain plan: pigs are born in a pig, from which pigs grow, and not, say, barks. The regularity and direction of ontogenesis are determined by the genetic program, the mutual influence of parts of the organism in the process of development and functioning, and the completeness of its implementation depends on the influence of the external environment and is manifested in the phenotype.

The interaction of parts of the body is carried out by regulation and occurs at all levels - from molecular to systemic. Regulatory processes are always based on the principle of negative feedback and are self-regulating: the regulated body by the accumulation of the products of its activity suppresses the activity of the regulator. At the cell level, regulation is carried out through cellular metabolism and intercellular interactions. At the organ and organism level - with the help of the endocrine and nervous systems.

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Growth and differentiation are two sides of a single developmental process. Individual development (ontogenesis) includes qualitative (differentiation) and quantitative (growth) sides.

Differentiation, or differentiation, is the emergence in the process of development of the organism of biochemical, morphological and functional differences between cells, tissues and organs. As a result, the whole is divided into parts, various cells, tissues, organs are formed and acquire specialization. In the ontogeny of multicellular animals, specialization occurs at the stage of several blastomeres. In the process of differentiation, organelles, cells, tissues, organs acquire specific structural features and their inherent function. It turns out that the more specialized a part of the body is, the more it depends on other parts.

R about with t - an increase in the mass and size of the body and its parts, organically associated with formative processes. In biology, there is still no unified theory of growth, although the process itself is well studied in animals. different types, classes, types. Growth is a quantitative indicator of changes in structures, therefore, it is easier to express it in mathematical form than other characteristics of ontogeny. The growth patterns in animals of different species and even in one animal at different stages of ontogenesis are not the same.

The vast majority of warm-blooded animals (except rats), having reached a certain size, stop growing. This growth is called limited. Most cold-blooded chordates (including fish) have unlimited growth. These animals grow throughout their lives.

Growth and differentiation are interconnected inversely: the more differentiated the organism, the lower the rate of its growth. The highest growth rate is observed in the embryo, less in the fetus, even less after birth, and with the achievement of physiological and morphological maturity, growth stops. Consequently, in ontogeny, there is a constant decrease in the growth rate. However, this decrease is uneven, since the periods of active growth and differentiation alternate, as a result of which growth has the character of dying fluctuations, and differentiation also increases stepwise until the period of morphofunctional maturity.

In different animals, the growth rate and duration are not the same, and there is an inverse relationship between these growth indicators: the faster the growth rate, the shorter its duration, and vice versa. Birds have a particularly high growth rate and short duration. In mammals, a relationship has been noted between the size of the animal, the rate and duration of growth. Species of small animals usually grow intensively, but not for a long time; species of large animals grow less intensively, but for a long time. The body weight that a particular species reaches is not random, but is determined by the relationship between the surface of the body, its volume, the surface of the intestinal mucosa and the intensity of metabolic processes. These relationships place strict limits on the size of the animal. If the body does not change shape during growth, such growth is called

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proportional. It is characteristic only for the earliest stages of the cleavage of the embryo and in the period close to the end of growth (from the period of puberty to morphophysiological maturity). All other periods are characterized by disproportionate growth, when some organs grow faster than others. At the same time, the proportions of the body, the ratio of tissues in organs change.

Uneven growth is determined by the time of organ laying (some organs are laid early, for example, eyes, brain, others much later - intestines, muscles), the size of the bookmark (in the eyes, brain - more, in the lungs, muscles - relatively less), the timing and duration of histological differentiation ... If an organ has a large anlage and this anlage is formed early, such an organ is characterized by a slow rate of embryonic and postnatal growth (eye, brain). In addition, such organs are genetically highly determined, that is, their morphological development is determined mainly by the genotype. If the anlage of an organ is formed late, but its histological differentiation proceeds quickly, such an organ is characterized by rapid embryonic and short postnatal growth (for example, the liver). If the anlage of an organ is formed late, and its histological differentiation is slow, such an organ is characterized by rapid embryonic and long postnatal growth (apparatus of movement, reproduction). Moreover, the later the organ is laid, the more its development depends on environmental conditions. And since bones, muscles and skin are one of the most late differentiating organs, this gives the animal engineer the key to control the formation of meat and wool production.

Periodization of development. In the process of individual development, certain stages are distinguished when, as a result of increasing quantitative changes, the body passes into a new qualitative state. The periods of intrauterine development have been traced by us in the section "Embryology". In postnatal ontogenesis, the periods of neonatal, lactic, growth and development of young animals, puberty, morphophysiological maturity, the flowering of functional activity (adulthood), aging are distinguished. In the process of individual development, there are critical periods when certain organs are most sensitive to external influences. It turned out that the critical period for an organ is the time of its most intensive growth, as well as the moments of periodic (rhythmic) increases in the growth rate during ontogenesis. In rhythm, the uneven nature of growth is manifested. Yearly rhythms associated with the change of seasons have long been known. In wild animals, and from domestic animals in reindeer, camel, growth stops in winter and resumes in the warm season. Circa monthly, circadian and circadian rhythms were found in all mammals, as well as 12-day cycles of activity and growth decay in calves and chickens. The use of differentiated feeding in accordance with the detected rhythms made it possible to increase productivity by 20-30% with 20% savings in feed. Knowledge of growth patterns

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and their use in the practice of animal husbandry makes it possible to manage not only the growth processes of the animal, but also its development in general, which is one of the reserves for the intensification of animal husbandry.

BODY PLANES AND TERMS FOR DESIGNATION OF ORGAN LOCATION

For a more accurate determination of the location of organs and parts, the body of the animal is dismembered by three imaginary mutually perpendicular planes - sagittal, segmental and frontal (Fig. 37). Median sagittalThe (median) plane is drawn vertically along the middle of the animal's body from the mouth to the tip of the tail and dissecting it into two symmetrical halves. The direction in the body of the animal to the median plane is called medial, and from it - lateral (lateralis - lateral).

Figure: 37. Planes and directions in the body of the animal.

Planes: I - segmental; II - sagittal; III - frontal. Directions: 1 - cranial; 2 - caudal; 3 - dorsal; 4 - ventral; 5 - medial; 6 - lateral; 7 - rostral (oral); 8

Aboral; 9 - proximal; 10 - distal; 11 - dorsal (dorsal, dorsal); 12 - palmar; 13 - plantar.

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Segmental planeis carried out vertically across the body of the animal. The direction from it towards the head is called cranial (cranium

Skull), towards the tail - caudal (cauda - tail). On the head, where everything is cranial, since the direction to the nose - nasal or proboscis -

rostral and the opposite iscaudal. Frontal flat

bone (Irons - forehead) is carried out horizontally along the body of the animal (with a horizontally extended head), that is, parallel to the forehead. The direction in this plane towards the back is called dorsal (dorsum - back), towards the stomach - ventral (venter - stomach).

To determine the position of the limbs, there are the terms proximus (proximus) - a closer position to the axial part of the body and distal (distalus - distant) - a more distant position from the axial part of the body. To designate the anterior surface of the limbs, the terms cranial or dorsal (for the paw) are adopted, and for the posterior surface - caudal, as well as palmar or volar

(palma, vola - palm) - for the hand and plantar (planta - foot) - for the foot.

DEPARTMENTS AND AREAS OF ANIMAL BODY AND THEIR BONE BASE

The body of vertebrates is divided into an axial part and limbs. In fish, the axial part consists of the head, body and tail. Starting with amphibians, in animals, the axial part of the body is divided into the head, neck, trunk and tail. The neck, trunk and tail together make up the trunk of the body. Each of the body parts, in turn, is divided into sections and areas (Fig. 38). In most cases, they are based on the bones of the skeleton, which have the same names as the regions.

The head (Latin caput, Greek cephale) is divided into a skull (brain) and a face (facial).

The skull (cranium) is represented by the following areas: occipital (occiput), parietal (crown), frontal (forehead) with the horn area in cattle, temporal (temple) and parotid (ear) with the auricle area.

On the face (fades), the following areas are distinguished: the orbital, (eyes) with the areas of the upper and lower eyelids, the infraorbital, the zygomatic with the area of \u200b\u200bthe large chewing muscle (in a horse - ganache), the intermaxillary, chin, nasal (nose) with the area of \u200b\u200bthe nostrils, the oral (mouth ), which includes the areas of the upper and lower lips and cheeks. Above the upper lip (in the area of \u200b\u200bthe nostrils) there is a nasal speculum; in large ruminants, it extends to the area of \u200b\u200bthe upper lip and becomes nasolabial.

The neck (cervix, collum) extends from the occipital region to the scapula and is divided into regions: the upper cervical, lying over the bodies of the cervical vertebrae; lateral cervical (area of \u200b\u200bthe brachiocephalic muscle), running along the vertebral bodies; the lower cervical, along which the jugular groove stretches, and

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laryngeal and tracheal (on its ventral side). Ungulates have a relatively long neck due to the need to feed on pasture. Therefore, they also have a direct correlation between the length of the limbs and the length of the neck. The longest neck in high-legged, fast-paced horses. The shortest is in the pig. The shape of the neck in herbivores is oval, elongated in the dorsoventral direction, in a pig (omnivore) it is more rounded.

Figure: 38. Areas of the body of cattle:

1 - frontal; 2 - occipital; 3 - parietal; 4 - temporal; 5 - parotid; 6 - auricle; 7 - nasal; 8 - areas of the upper and lower lips; 9 - chin; 10 - buccal; 11 - intermaxillary; 12 - infraorbital; 13 - zygomatic; 14 - eye area; 15 - large chewing muscle; 16 - upper cervical; 17 - lateral cervical; 18 - lower cervical; 19 - withers; 20 - backs; 21 - costal; 22 - pre-sternal; 23 - sternal; 24 - lumbar; 25 - hypochondrium; 26 - xiphoid cartilage; 27 - peri-lumbar (hungry) fossa; 28 - lateral area; 29 - inguinal; 30 - umbilical; 31 - pubic; 32 - maklok; 33- sacral; 34 - gluteal; 35

- tail root; 36 - sciatic region; 37 - scapula; 38- shoulder; 39

- forearm; 40 - brush; 41- wrist; 42 - metacarpus; 43 - fingers; 44 - thigh; 45 - shin; 46 - foot; 47 - tarsus; 48 - metatarsus.

The trunk (truncus) consists of the thoracic, abdominal and pelvic regions. The thoracic region includes the areas of the withers, back, lateral costal, pre-sternal and sternal. It is durable and mobile at the same time. In the caudal direction, the strength decreases, and the mobility increases due to the different degrees of development of the bones of the skeleton and the peculiarities of their connection. The bones of the withers and back are the thoracic vertebrae. In the region

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these withers have the highest spinous processes. The higher and longer the withers, the larger the area of \u200b\u200battachment of the muscles of the spine and the girdle of the chest limb, the more sweeping and more elastic the movements. There is an inverse relationship between the length of the withers and back. The longest withers and the shortest back are in a horse, in a pig, on the contrary.

The abdominal region includes the lower back (lumbus) and the abdomen (abdomen), or belly (venter), therefore it is also called the lumbar-abdominal region. Loin - an extension of the back to the sacral region. It is based on the lumbar vertebrae. The abdomen has soft walls and is divided into a number of areas: the right and left hypochondria, xiphoid cartilage, the upper border of which runs along the costal arch; paired lateral (iliac) with a hungry fossa, adjacent to the bottom of the lower back, in front of the last rib, and behind - passes into the groin; umbilical, lying below the abdomen behind the region of the xiphoid cartilage to the front of the pubic region. The mammary glands are located on the ventral surface of the xiphoid cartilage, umbilical and pubic regions of females. The horse has the shortest loin and the less extensive abdominal region. Pigs and cattle have a longer loin. The most voluminous abdominal region in ruminants.

The pelvic region (pelvis) is divided into areas: sacral, gluteal, including the umbilical, ischial and perineal with an adjacent scrotal region. In the tail (cauda), a root, body and tip are distinguished. The areas of the sacral, two gluteal and the root of the tail in a horse form the croup.

The limbs (membra) are divided into thoracic (front) and pelvic (rear). They consist of belts, which are connected to the trunk of the body, and free limbs. The free limbs are divided into a main support post and a leg. The pectoral limb consists of the shoulder girdle, upper arm, forearm and hand.

Shoulder girdle areasand the shoulder is adjacent to the lateral chest region. The bony base of the shoulder girdle in ungulates is the scapula, therefore it is often called the scapula region.

The shoulder (brachiuni) is located below the shoulder girdle and has the shape of a triangle. The bone base is the humerus.

The forearm (antebrachium) is located outside the cutaneous trunk sac. Its bone base is the radius and ulna.

The hand (marius) consists of the wrist (carpus), the metacarpus (metacarpus) and the fingers (digiti). The latter are called serial numbers, they are counted from the inside. In animals of different species there are from 1 to 5. Each finger (except for the first) consists of three phalanges: proximal, middle and distal (which in ungulates are called, respectively, in ungulates, in a horse

Grandma), crown and hoofed (in the horse - hoofed).

The pelvic limb consists of the pelvic girdle, thigh, lower leg, and foot. Pelvic girdle area(pelvis) is part of the axial part of the body as

in the gluteal region. The bone base is the pelvic or anonymous bone.

Nervous system controls, coordinates and regulates the coordinated work of all organ systems, maintaining the constancy of the composition of its internal environment (thanks to this, the human body functions as a single whole). With the participation of the nervous system, the body is connected with the external environment.

Nerve tissue

The nervous system is formed nerve tissuewhich consists of nerve cells - neurons and small satellite cells (glial cells), which are about 10 times more than neurons.

Neurons provide the basic functions of the nervous system: transmission, processing and storage of information. Nerve impulses are electrical in nature and propagate along the processes of neurons.

Cells satellites perform nutritional, support and protective functions, promoting the growth and development of nerve cells.

Neuron structure

The neuron is the basic structural and functional unit of the nervous system.

The structural and functional unit of the nervous system is a nerve cell - neuron... Its main properties are excitability and conductivity.

A neuron consists of body and offshoots.

Short, highly branched processes - dendrites, through them nerve impulses come to the body nerve cell. There can be one or several dendrites.

Each nerve cell has one long process - axonwhere the impulses are directed from the cell body... The length of the axon can reach several tens of centimeters. Combining into bundles, axons form nerves.

Long processes of a nerve cell (axons) are covered myelin sheath... Clusters of such appendages covered myelin (fatty substance white), in the central nervous system form the white matter of the brain and spinal cord.

The short processes (dendrites) and bodies of neurons do not have a myelin sheath, therefore they are gray in color. Their clusters form the gray matter of the brain.

Neurons connect to each other in this way: the axon of one neuron connects to the body, dendrites or axon of another neuron. The place of contact of one neuron with another is called synapse... On the body of one neuron, there are 1200-1800 synapses.

Synapse is the space between neighboring cells, in which chemical transmission of nerve impulses from one neuron to another is carried out.

Each the synapse consists of three sections:

1. the membrane formed by the nerve ending ( presynaptic membrane);
2. cell body membranes ( postsynaptic membrane);
3. synaptic cleft between these membranes

The presynaptic part of the synapse contains a biologically active substance ( mediator), which ensures the transmission of a nerve impulse from one neuron to another. Under the influence of a nerve impulse, the mediator enters the synaptic cleft, acts on the postsynaptic membrane and causes excitation in the cell of the next neuron. So through the synapse, excitation is transmitted from one neuron to another.

The spread of excitement is associated with such a property of the nervous tissue as conductivity.

Types of neurons

Neurons vary in shape

Depending on the function performed, the following types of neurons are distinguished:

• Neurons, transmitting signals from the senses to the central nervous system (spinal cord and brain) are called sensitive... The bodies of these neurons are located outside the central nervous system, in the nerve nodes (ganglia). A nerve node is a collection of nerve cell bodies outside of the central nervous system.
• Neurons, transmitting impulses from the spinal cord and brain to muscles and internal organs called motor. They provide the transmission of impulses from the central nervous system to the working organs.
• The connection between sensory and motor neurons carried out by intercalary neurons through synaptic contacts in the spinal cord and brain. Intercalary neurons lie within the CNS (i.e., the bodies and processes of these neurons do not go outside the brain).

The accumulation of neurons in the central nervous system is called core (nuclei of the brain, spinal cord).

The spinal cord and brain are connected to all organs nerves.

Nerves - sheathed structures composed of bundles of nerve fibers formed mainly by axons of neurons and neuroglia cells.

Nerves provide a connection between the central nervous system and organs, blood vessels and the skin.

Functions of the National Assembly.

1) regulatory and coordinating, i.e. NS regulates and coordinates the work of all organs and systems of the body, therefore, a lot depends on its state,

2)integrating - unites all organs and systems into a single whole - an organism,

3) reflex, i.e. it provides the body's relationship with the external environment, responding to all stimuli of the external and internal environments.

4) provides mental functions human (sensation, perception, speech, memory, ...)

Departments of the National Assembly.

Anatomical division of the NA

Central NS Peripheral NS

(spinal, brain) (nerves, nerve fibers, endings, nodes, plexuses)

Functional division of the NS

Somatic NS Vegetative NS (autonomous)

(innervates skin, bones, (innervates internal organs, glands,

skeletal muscle) smooth muscle)

Sympathetic NS Parasympathetic NS

(strengthens the work of all (weakens the activity of all

internal organs, except for the digestive tract) organs, except for the digestive tract)

I. Microstructure of NT.

The main fabric in NS - nervous tissue.

Although there are other tissues in the NS, for example, the lining of the brain is formed connective tissue, and the brain cavities are lined with a special type of epithelial tissue - ependyma.

NT differs from other fabrics in that there is no intercellular substance in it.

NT consists of two types of cells:

Cellular neuroglia Neurons

(auxiliary cells, help (the main nerve cells, due to which

neurons to carry out their functions), all the functions of the central nervous system are carried out)

The structural functional unit of the NS is neuron.

Each neuron has:

· Soma (body), in which the nucleus and most of the organelles are located,

· Scionsextending from the catfish are strongly branching - dendrites, and little branching - axons.

The axon has lateral branchwhich is called collateral, and at the end there is final ramifications - terminal.

By dendrites excitement is directed to catfish neuron, and from the soma axon.

The place of origin of the axon from the soma is called axonal mound.

More often dendrites are short branchesalthough they can be long in sensory neurons. Tzh and axons are most often long, but can be short (in the central nervous system).

In relation to the processes, catfish perform a trophic function, regulating the exchange in-in.

As in any cell, the following parts are distinguished in the nervous one:

· Shell - neurolemma,

· Core,

· Cytoplasm, in which the organelles are located.

There are organelles in neurons general and special destination.

General purpose organelles include:

· EPS (smooth and rough) - this system of tubules and tubules that permeates the entire cytoplasm.

In addition, Y and Zh are synthesized on smooth EPS membranes, and B on a rough EPS membrane.

With special staining, rough EPS is visible under a light microscope in the form of blue lumps and is called tigroid (Nissl substance).

· Golgi apparatus is a system of cisterns and membrane sacs located around the nucleus and closely related to the EPS.

It receives synthesized substances in EPS - BJU, where they mature and are surrounded by a membrane. Thus, lysosomes are formed and separated in the Golgi apparatus.

· Lysosomes - most play the role of digestive vacuoles, because they contain secrets that break down nutrients, i.e. enzymes, or break down the remains of dead organelles.

· MTX - cell power plants. There is a lot of MTX in neurons, the cell of a neuron is very active, and MTX is present not only in the soma, but also in the processes.

· Ribosomes - collect proteins from amino acids.

However, in the neuron no cell center, mk neuron - non-dividing cell.

Special purpose organelles:

· Microfilaments (microfilaments) - organelles from B, represents the internal skeleton of a neuron and is located mainly in the soma.

· Microtubules- organelles from B, stretching from the soma to the processes, in particular, reaching the end of the axon.

Biologically active substances, in particular mediators, are distributed through them.

After special coloring with salts of silver or other heavy metals, microtubules and microfilaments are glued together, forming threads - neurofibrils, which are visible under the light of a microscope in the catfish and in the processes.

· The nucleus is the main compartment of any cell that stores hereditary information in the form of DNA.

The nucleus is the main manager of all vital processes of the cell. When the nucleus is destroyed, the cell dies.

· Neurolemma (neuron membrane) - according to the mosaic model, it consists of a bilayer of lipids and surface proteins built into the bilayer and penetrating the bilayer.

Performs many important functions:

Protective

Provides selective permeability of substances into and out of the cell

Receptor

Exchange

Excretory

Participates in the conduct of arousal

There are several classifications of neurons based on different traits:

1. By the shape of the catfish:

Granular

Star-shaped

Pear-shaped

Fusiform

Triangular

Pyramidal

2. By the number of processes:

Unipolar

Pseudo-unipolar

Bipolar

Multipolar

3. By function:

· Sensitive (afferent, centripetal, sensory) - carry impulses from receptors in the central nervous system, are pseudo-unipolar, their somas are located outside the central nervous system and are granular in shape, form sensitive ganglia (spinal and cranial),

· Interlocking (central, interneurons, intermediate) - located in the central nervous system, receive and process information from the periphery, store it in memory, form a response program, communicate between sensory and motor neurons, basically these are multipolar neurons of various shapes, except for granular, make up the bulk brain,

· Motor (motornerons, efferent, centrifugal) - carry information from the central nervous system to the working organ (muscles and glands).

4. By effectto other neurons:

Excitatory, which activate other neurons,

· Inhibitory, which inhibit the activity of other neurons.

II. Neuroglia

Neuroglia (nerve glue) is an analogue of the intercellular substance of other tissues. It was opened in 1846 by Rudolf Virchow.

Unlike neurons, neuroglial cells divide throughout a person's life.

Nerve tissue (textus nervosus) - a set of cellular elements that form the organs of the central and peripheral nervous system. Possessing the property of irritability, the nervous tissue provides for the receipt, processing and storage of information from the external and internal environment, regulation and coordination of the activities of all parts of the body. The nervous tissue contains two types of cells: neurons (neurocytes) and glial cells (gliocytes). The first type of cells organizes complex reflex systems through a variety of contacts with each other and generates and propagates nerve impulses. The second type of cells performs auxiliary functions, ensuring the vital activity of neurons. Neurons and glial cells form glioneural structural and functional complexes.

Nerve tissue is of ectodermal origin. It develops from a neural tube and two ganglion plates that arise from the dorsal ectoderm during its immersion (neurulation). From the cells of the neural tube is formed nervous tissue, forming the organs of c.ns. - the brain and spinal cord with their efferent nerves (see. Brain, Spinal cord), from ganglion plates - nervous tissue various parts of the peripheral nervous system. Cells of the neural tube and ganglion lamina, as they divide and migrate, differentiate in two directions: some of them become large processes (neuroblasts) and turn into neurocytes, others remain small (spongioblasts) and develop into gliocytes.

The basis of the nervous tissue is made up of neurons. Auxiliary cells of the nervous tissue (gliocytes) are distinguished by their structural and functional features. In the central nervous system there are the following types of gliocytes: ependymocytes, astrocytes, oligodendrocytes; in the peripheral - ganglion gliocytes, terminal gliocytes and neurolemmocytes (Schwann cells). Ependymocytes form ependyma - the integumentary layer lining the cavities of the cerebral ventricles and the central canal of the spinal cord. These cells are involved in the metabolism and secretion of certain components cerebrospinal fluid.

Astrocytes are part of the gray and white matter tissue of the brain and spinal cord; have a stellate shape, numerous processes, the spreading terminals of which are involved in the creation of gliosis membranes. On the surface of the brain and under the ependymus, they form the outer and inner border gliosis membranes. Around all blood vessels in the brain tissue, astrocytes form the perivascular gliosis membrane. Together with the components of the blood vessel wall itself, this gliosis membrane creates the blood-brain barrier - the structural and functional border between blood and nervous tissue.

Oligodendrocytes in the gray matter of the brain are neuronal satellite cells; in white matter, they form sheaths around their axons. Peripheral glial cells create barriers around neurons in the peripheral nervous system. Glyocytes of ganglia (satellite cells) surround their perikarion, and neurolemmocytes accompany the processes and participate in the formation of nerve fibers.

Nerve fibers - pathways for the propagation of a nerve impulse; they form the white matter of the brain and spinal cord and peripheral nerves. In the nerve fiber there is a central part, forming an axon of a nerve cell, and a peripheral part - meningeal glial cells, or lemmocytes. In c.n.s. the role of lemmocytes is played by oligodendrocytes, and in the peripheral nervous system - neurolemmocytes. The axon of the nerve fiber, as part of the nerve cell, has an outer membrane (axolemma) and contains organelles: neurofilaments, microtubules, as well as mitochondria, lysosomes, and non-granular endoplasmic reticulum. The axon transport of organelle proteins is carried out along the axon from the body of the neuron. In axonal transport, a slow flow is distinguished (at a speed of about 1 mm per day), ensuring the growth of axons, and a fast flow (about 100 mm per day), related to synaptic function. The transport processes in the axial cylinder are associated with the microtubule system.

Depending on the method of organizing the sheath around the axon, myelin (pulp) and myelin-free (non-pulp) nerve fibers are distinguished. In the latter, the axon is immersed in the cytoplasm of the lemmocyte, therefore it is surrounded only by its double cytomembrane. Fleshy fibers are thin (0.3-1.5 μm), are characterized by a low speed of the impulse (0.5-2.5 m / s). Such fibers are typical for the autonomic nervous system. In the myelin (pulp) nerve fibers, the cytomembrane of the lemmocyte, due to repeated twisting around the axon (myelogenesis), forms a multilayer structure of alternating bilipid and glycoprotein layers. This layered, lipid-rich material is called myelin. Myelinated nerve fibers differ in the thickness of the myelin sheath (from 1 to 20 μm), which affects the pulse propagation speed (from 3 to 120 m / s). The myelin coating along the length of the fiber has a segmental structure, depending on the length of the lemmocyte (from 0.2 to 1.5 μm). On the border of two lemmocytes there are areas of myelin-free constrictions - nerve fiber nodes (Ranvier interceptions). Therefore, the propagation of the impulse in the myelin fibers has a saltatory (abrupt) character. Myelin fibers are typical of the somatic nerves, as well as the pathways of the brain and spinal cord. The leading role of the axon as a part of the neuron in the structural and functional organization of the nerve fiber is manifested when it is damaged. If even a small area perishes, then the nerve fiber dies along its entire further length, because turns out to be separated from the cell body, on which its existence depends. The death of the distal portion of the axon is accompanied by degeneration and disintegration of its myelin sheath (Wallerian degeneration). In this case, macrophages absorb the decaying myelin and the remains of the axon, and then are removed from the focus. The further recovery process is associated with the reaction of neurolemmocytes, which begin to proliferate from the proximal end of the damaged nerve fiber, forming tubes. Axons grow into these tubes at a rate of 1-3 mm per day. This process is characteristic of the peripheral nerves after they have been compressed and cut.

Interneuronal communication is carried out through their processes using intercellular contacts - synapses.

Nerve fibers end not only on neurons, but also on the cells of all other tissues, especially muscle and epithelial, forming efferent nerve endings, or neuroeffector synapses. The motor nerve endings on the striated musculature - motor plaques - are especially numerous and complexly developed.

Perceiving (receptor) nerve endings - the terminal apparatus of the dendrites of sensitive neurons - generate a nerve impulse under the influence of various stimuli from the external and internal environment. By their structural features, the receptor nerve endings can be "free", ie. located directly between the cells of the innervated tissue; "Non-free" and even encapsulated, i.e. surrounded by special receptor cells of an epithelial or glial nature, as well as a connective tissue capsule.

Bibliography:Ham A. and Cormac D. Histology, trans. from English. t 3 with 163, M., 1983; Shepherd G. Neurobiology, trans. from English, t. 1-2, M., 1987; Shubnikova E.A. Functional morphology of tissues, M., 1981.