Structural and functional unit nervous system is neuron(nerve cell). Intercellular tissue - neuroglia- represents cellular structures (glial cells) that perform supporting, protective, insulating and nutritional functions for neurons. Glial cells make up about 50% of the volume of the central nervous system. They divide throughout life and their number increases with age.
Neurons are capable to be excited - to perceive irritation, responding with the appearance of a nerve impulse and conduct the impulse. Basic properties of neurons: 1) Excitability– the property of generating an action potential to stimulation. 2) Conductivity – This is the ability of tissue and cells to conduct excitation.
In a neuron there are cell body(diameter 10-100 µm), a long process extending from the body, - axon(diameter 1-6 microns, length more than 1 m) and highly branched ends - dendrites. In the soma of the neuron, protein synthesis occurs and the body plays a trophic function in relation to the processes. The role of the processes is to conduct excitation. Dendrites conduct excitation into the body, and axons from the body of the neuron. The structures in which AP usually occurs (generator hillock) are the axon hillock.
Dendrites are susceptible to irritation due to existing nerve endings ( receptors), which are located on the surface of the body, in the senses, and in the internal organs. For example, in the skin there is great amount nerve endings that perceive pressure, pain, cold, heat; in the nasal cavity there are nerve endings that perceive odors; in the mouth and tongue there are nerve endings that perceive the taste of food; and in the eyes and inner ear there is light and sound.
The transmission of nerve impulses from one neuron to another is carried out using contacts called synapses. One neuron can have about 10,000 synaptic contacts.
Classification of neurons.
1. By size and shape neurons are divided into multipolar(have many dendrites), unipolar(have one process), bipolar(have two processes).
2. In the direction of excitation neurons are divided into centripetal, transmitting impulses from the receptor to the central nervous system, called afferent (sensory), and centrifugal neurons that transmit information from the central nervous system to effectors(to working bodies) - efferent (motor). Both of these neurons are often connected to each other through insertion (contact) neuron.
3. According to the mediator, released in axon terminals, adrenergic, cholinergic, serotonergic, etc. neurons are distinguished.
4. Depending on the part of the central nervous system secrete neurons of the somatic and autonomic nervous systems.
5. By influence secrete excitatory and inhibitory neurons.
6. By activity distinguish background-active and “silent” neurons that are excited only in response to stimulation. Background-active neurons generate impulses rhythmically, non-rhythmically, in bursts. They play a large role in maintaining the tone of the central nervous system and especially the cerebral cortex.
7. By perception of sensory information divided into mono- (neurons of the hearing center in the cortex), bimodal (in the secondary zones of the analyzers in the cortex - the visual zone reacts to light and sound stimuli), polymodal (neurons of the associative zones of the brain)
Functions of neurons.
1. Non-specific functions. A) Synthesis of tissue and cellular structures. B) Energy production to support life. Metabolism. C) Transport of substances from and into the cell.
2. Specific functions. A) Perception of changes in the external and internal environment of the body with the help of sensory receptors, dendrites, and neuron body. B) Signal transmission to other nerve cells and effector cells: skeletal muscles, smooth muscles internal organs, vessels, etc. using synapses. C) Processing of information entering the neuron through the interaction of excitatory and inhibitory influences of nerve impulses arriving at the neuron. D) Storing information using memory mechanisms. E) Providing communication (nerve impulses) between all cells of the body and regulating their functions.
The neuron changes during ontogenesis - the degree of branching increases, changes chemical composition the cell itself. The number of neurons decreases with age.
We are often nervous, constantly filtering incoming information, reacting to the world around us and trying to listen to our own body, and amazing cells help us with all this. They are the result of long evolution, the result of the work of nature throughout the development of organisms on Earth.
We cannot say that our system of perception, analysis and response is ideal. But we have come very far from animals. Understanding how such a complex system works is very important not only for specialists - biologists and doctors. A person from another profession may also be interested in this.
The information in this article is available to everyone and can be useful not only as knowledge, because understanding your body is the key to understanding yourself.
What is she responsible for?
Human nervous tissue is distinguished by a unique structural and functional diversity of neurons and the specificity of their interactions. After all, our brain is a very complex system. And to control our behavior, emotions and thinking, we need a very complex network.
Nervous tissue, the structure and functions of which are determined by a set of neurons - cells with processes - and determine the normal functioning of the body, firstly, ensures the coordinated activity of all organ systems. Secondly, it connects the body with the external environment and provides adaptive reactions to its changes. Thirdly, it controls metabolism under changing conditions. All types of nerve tissue are a material component of the psyche: signaling systems- speech and thinking, behavioral characteristics in society. Some scientists hypothesized that man greatly developed his mind, for which he had to “sacrifice” many animal abilities. For example, we do not have the keen vision and hearing that animals can boast of.
Nervous tissue, whose structure and functions are based on electrical and chemical transmission, has clearly localized effects. Unlike the humoral system, this system acts instantly.
Many small transmitters
Nervous tissue cells - neurons - are the structural and functional units of the nervous system. The neuron cell is characterized by a complex structure and increased functional specialization. The structure of a neuron consists of a eukaryotic body (soma), the diameter of which is 3-100 microns, and processes. The soma of a neuron contains a nucleus and a nucleolus with a biosynthetic apparatus that forms enzymes and substances inherent in the specialized functions of neurons. These are Nissl bodies - tightly adjacent flattened cisterns of the rough endoplasmic reticulum, as well as a developed Golgi apparatus.
The functions of a nerve cell can be continuously carried out due to the abundance of “energy stations” in the body that produce ATP - chondrasomes. The cytoskeleton, represented by neurofilaments and microtubules, plays a supporting role. In the process of loss of membrane structures, the pigment lipofuscin is synthesized, the amount of which increases with increasing age of the neuron. The pigment melatonin is formed in stem neurons. The nucleolus consists of protein and RNA, the nucleus of DNA. The ontogeny of the nucleolus and basophils is determined by the primary behavioral reactions of people, since they depend on the activity and frequency of contacts. Nervous tissue refers to the basic structural unit, the neuron, although there are other types of supporting tissues.
Features of the structure of nerve cells
The double-membrane nucleus of neurons has pores through which waste substances penetrate and are eliminated. Thanks to the genetic apparatus, differentiation occurs, which determines the configuration and frequency of interactions. Another function of the nucleus is to regulate protein synthesis. Mature nerve cells cannot divide by mitosis, and genetically determined active synthesis products of each neuron must ensure functioning and homeostasis throughout life cycle. Replacement of damaged and lost parts can only occur intracellularly. But there are also exceptions. In the epithelium, some animal ganglia are capable of division.
Nervous tissue cells are visually distinguished by a variety of sizes and shapes. Neurons have irregular outlines due to their processes, which are often numerous and overgrown. These are living conductors of electrical signals through which reflex arcs are formed. Nervous tissue, the structure and functions of which depend on highly differentiated cells, whose role is to perceive sensory information, encode it through electrical impulses and transmit it to other differentiated cells, is capable of providing a response. It's almost instantaneous. But some substances, including alcohol, greatly slow it down.
About axons
All types of nervous tissue function with the direct participation of dendritic processes and axons. Axon is translated from Greek as “axis”. This is an elongated process that conducts excitation from the body to the processes of other neurons. The tips of the axon are highly branched, each is capable of interacting with 5000 neurons and forming up to 10 thousand contacts.
The locus of the soma from which the axon branches is called the axon hillock. What it has in common with the axon is that they lack rough endoplasmic reticulum, RNA and enzyme complex.
A little about dendrites
This cell name means "tree". Like branches, short and strongly branching processes grow from the soma. They receive signals and serve as loci where synapses occur. Dendrites, with the help of lateral processes - spines - increase the surface area and, accordingly, contacts. Dendrites are unsheathed, while axons are surrounded by myelin sheaths. Myelin is a lipid in nature, and its action is similar to the insulating properties of the plastic or rubber coating of electrical wires. The point of generation of excitation - the axon hillock - appears at the point where the axon departs from the soma in the trigger zone.
The white matter of the ascending and descending tracts in the spinal cord and brain is formed by axons, through which nerve impulses are carried out, performing a conductor function - the transmission of a nerve impulse. Electrical signals are transmitted to various parts of the brain and spinal cord, communicating between them. Executive bodies at the same time they can connect with receptors. Gray matter forms the cerebral cortex. In the spinal canal there are centers of innate reflexes (sneezing, coughing) and vegetative centers of reflex activity of the stomach, urination, and defecation. Interneurons, motor bodies and dendrites perform a reflex function, carrying out motor reactions.
The characteristics of nerve tissue are determined by the number of processes. Neurons are unipolar, pseudounipolar, bipolar. Human nervous tissue does not contain unipolar with one. In multipolar, there is an abundance of dendritic trunks. This branching does not in any way affect the speed of the signal.
Different cells - different tasks
The functions of the nerve cell are carried out different groups neurons. By specialization in reflex arc distinguish between afferent or sensory neurons that conduct impulses from organs and skin to the brain.
Intercalary neurons, or associative neurons, are a group of switching or connecting neurons that analyze and make decisions, performing the functions of a nerve cell.
Efferent neurons, or sensory neurons, carry information about sensations - impulses from the skin and internal organs to the brain.
Efferent neurons, effector, or motor, conduct impulses - “commands” from the brain and spinal cord to all working organs.
The peculiarities of nervous tissues are that neurons perform complex and precious work in the body, so everyday primitive work - providing nutrition, removing decay products, the protective function goes to auxiliary neuroglial cells or supporting Schwann cells.
The process of formation of nerve cells
In the cells of the neural tube and ganglion plate, differentiation occurs, which determines the characteristics of nervous tissues in two directions: large ones become neuroblasts and neurocytes. Small cells (spongioblasts) do not enlarge and become gliocytes. Nervous tissue, the types of tissues of which are composed of neurons, consists of primary and auxiliary tissues. Supporting cells (“gliocytes”) have a special structure and function.
The central one is represented by the following types of gliocytes: ependymocytes, astrocytes, oligodendrocytes; peripheral - ganglion gliocytes, terminal gliocytes and neurolemmocytes - Schwann cells. Ependymocytes line the cavities of the ventricles of the brain and the spinal canal and secrete cerebrospinal fluid. Types of nerve tissue - star-shaped astrocytes form gray and white matter tissues. The properties of nervous tissue - astrocytes and their glial membrane contribute to the creation of a blood-brain barrier: a structural-functional boundary passes between the liquid connective and nervous tissues.
Evolution of fabric
The main property of a living organism is irritability or sensitivity. The type of nervous tissue is determined by the phylogenetic position of the animal and is characterized by wide variability, becoming more complex in the process of evolution. All organisms require certain parameters of internal coordination and regulation, proper interaction between stimulus for homeostasis and physiological state. The nervous tissue of animals, especially multicellular ones, the structure and functions of which have undergone aromorphoses, contributes to survival in the struggle for existence. In primitive hydroids, it is represented by stellate, nerve cells scattered throughout the body and connected by thin processes intertwined with each other. This type of nerve tissue is called diffuse.
The nervous system of flat and roundworms is a stem, scalene type (orthogonal) system consisting of paired cerebral ganglia - clusters of nerve cells and longitudinal trunks extending from them (connectives), interconnected by transverse cords-commissures. In the rings, from the peripharyngeal ganglion, connected by cords, the abdominal nerve chain departs, in each segment of which there are two close nerve ganglia connected by nerve fibers. In some soft-bodied animals, nerve ganglia are concentrated to form the brain. Instincts and spatial orientation in arthropods are determined by the cephalization of the ganglia of the paired brain, the peripharyngeal nerve ring and the ventral nerve cord.
In chordates, the nervous tissue, the types of tissues of which are strongly expressed, is complex, but such a structure is evolutionarily justified. Different layers arise and are located on the dorsal side of the body in the form of a neural tube, the cavity is the neurocoel. In vertebrates, it differentiates into the brain and spinal cord. As the brain forms, swellings form at the anterior end of the tube. If in lower multicellular organisms the nervous system plays a purely connecting role, then in highly organized animals it stores information, retrieves it when necessary, and also ensures processing and integration.
In mammals, these cerebral swellings give rise to the main parts of the brain. And the rest of the tube forms the spinal cord. Nervous tissue, the structure and functions of which are unique in higher mammals, has undergone significant changes. This is the progressive development of the cerebral cortex and all parts that determine complex adaptation to conditions external environment, and regulation of homeostasis.
Center and periphery
The parts of the nervous system are classified according to their functional and anatomical structure. The anatomical structure is similar to toponymy, where the central and peripheral nervous systems are distinguished. The central nervous system includes the brain and spinal cord, and the peripheral is represented by nerves, nodes and endings. Nerves are represented by clusters of processes outside the central nervous system, covered with a common myelin sheath, and conduct electrical signals. Dendrites of sensory neurons form sensory nerves, axons form motor nerves.
The combination of long and short processes forms mixed nerves. Accumulating and concentrating, the cell bodies of neurons form nodes that extend beyond the central nervous system. Nerve endings are divided into receptor and effector. Dendrites, through terminal branches, convert stimuli into electrical signals. And the efferent endings of axons are in working organs, muscle fibers, and glands. Classification by functionality implies the division of the nervous system into somatic and autonomic.
Some things we control, some things we cannot control.
The properties of nervous tissue explain the fact that it obeys the will of a person, innervating the work of the support system. Motor centers are located in the cerebral cortex. Autonomous, which is also called vegetative, does not depend on the will of a person. Based on your own requests, it is impossible to speed up or slow down your heartbeat or intestinal motility. Since the location of the autonomic centers is the hypothalamus, the autonomic nervous system controls the functioning of the heart and blood vessels, endocrine apparatus, and abdominal organs.
The nervous tissue, a photo of which you can see above, forms the sympathetic and parasympathetic divisions, which allow them to act as antagonists, producing a mutually opposite effect. Excitation in one organ causes inhibition processes in another. For example, sympathetic neurons cause strong and frequent contractions of the heart chambers, vasoconstriction, and surges in blood pressure, as norepinephrine is released. Parasympathetic activity, releasing acetylcholine, helps to weaken heart rhythms, increase the lumen of arteries, and lower blood pressure. Balancing these groups of mediators normalizes heart rhythm.
The sympathetic nervous system operates during times of intense tension such as fear or stress. Signals arise in the area of the thoracic and lumbar vertebrae. The parasympathetic system is activated when resting and digesting food, during sleep. The cell bodies of neurons are in the trunk and sacrum.
By studying in more detail the features of Purkinje cells, which are pear-shaped with many branching dendrites, one can see how impulse transmission occurs and reveal the mechanism of successive stages of the process.
The modern understanding of the structure and function of the central nervous system is based on the neural theory.
The nervous system is built from two types of cells: nerve and glial, and the number of the latter is 8-9 times higher than the number of nerve cells. However, it is neurons that provide all the variety of processes associated with the transmission and processing of information.
A neuron, a nerve cell, is a structural and functional unit of the central nervous system. Individual neurons, unlike other cells in the body that act in isolation, “work” as a single unit. Their function is to transmit information (in the form of signals) from one part of the nervous system to another, to exchange information between the nervous system and different parts of the body. In this case, transmitting and receiving neurons are combined into nerve networks and circuits.
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Neurons have a number of characteristics common to all cells of the body. Regardless of its location and functions, any neuron, like any other cell, has a plasma membrane that defines the boundaries of the individual cell. When a neuron communicates with other neurons, or senses changes in the local environment, it does so through the membrane and the molecular mechanisms it contains. It is worth noting that the membrane of a neuron has significantly higher strength than other cells in the body.
Everything that's inside plasma membrane(except for the nucleus) is called cytoplasm. It contains the cytoplasmic organelles necessary for the neuron to exist and do its job. Mitochondria provide the cell with energy by using sugar and oxygen to synthesize special high-energy molecules that the cell uses as needed. Microtubules - thin supporting structures - help the neuron maintain a certain shape. A network of internal membrane tubules through which the cell distributes chemical substances necessary for its functioning is called the endoplasmic reticulum.
Nerve tissue consists of nerve cells - neurons and auxiliary neuroglial cells, or companion cells. Neuron is an elementary structural and functional unit of nervous tissue. The main functions of a neuron: generation,
conduction and transmission of a nerve impulse, which is a carrier of information in the nervous system. A neuron consists of a body and processes, and these processes are differentiated in structure and function. The length of the processes of different neurons varies from several micrometers to 1-1.5 m. The long process (nerve fiber) of most neurons has a myelin sheath, consisting of a special fat-like substance - myelin. It is formed by one of the types of neuroglial cells - oligodendrocytes. Based on the presence or absence of the myelin sheath, everything
fibers are divided respectively into pulpy (myelinated) and non-pulpate (non-myelinated). The latter are immersed in the body of a special neuroglial cell, the neurolemmocyte. The myelin sheath has White color, which allowed
divide the matter of the nervous system into gray and white. The cell bodies of neurons and their short processes form Gray matter brain, and fibers - white matter. The myelin sheath helps insulate the nerve fiber. A nerve impulse is conducted along such a fiber faster than through one without myelin. Myelin does not cover the entire fiber: at a distance of approximately 1 mm there are gaps in it - nodes of Ranvier, which are involved in the rapid conduction of nerve impulses. The functional difference in neuron processes is associated with the conduction of nerve impulses. The process along which the impulse travels from the neuron body is always one and is called an axon. The axon practically does not change in diameter throughout its entire length. In most nerve cells this is a long process. An exception is the neurons of the sensory spinal and cranial ganglia, in which the axon is shorter than the dendrite. The axon may branch at the end. In some places (myelinated axons - in the nodes of Ranvier), thin branches - collaterals - can extend perpendicularly from the axons. The process of a neuron along which the impulse travels to the cell body is a dendrite. A neuron may have one or more dendrites. Dendrites move away from the cell body gradually and branch under acute angle. Clusters of nerve fibers in the central nervous system are called tracts, or pathways. They carry out a conducting function in various parts of the brain and spinal cord and form white matter there. In the peripheral nervous system, individual nerve fibers are collected into bundles surrounded by connective tissue, which also contains blood and lymphatic vessels. Such bundles form nerves - clusters of long processes of neurons covered with a common membrane. If information along a nerve comes from peripheral sensory formations - receptors - to the brain or spinal cord, then such nerves are called sensory, centripetal or afferent. Sensory nerves are nerves consisting of dendrites of sensory neurons that transmit excitation from the sensory organs to the central nervous system. If information along the nerve goes from the central nervous system to the executive organs (muscles or glands), the nerve is called centrifugal, motor or efferent. Motor nerves are nerves formed by the axons of motor neurons that conduct nerve impulses from the center to the working organs (muscles or glands). Mixed nerves contain both sensory and motor fibers. In the case when nerve fibers approach an organ, ensuring its connection with the central nervous system, it is customary to speak of the innervation of this organ by a fiber or nerve. The bodies of neurons with short processes are located differently relative to each other. Sometimes they form quite dense clusters, which are called nerve ganglia, or nodes (if they are located outside the central nervous system, i.e., in the peripheral nervous system), and nuclei (if they are located in the central nervous system). Neurons can form a cortex - in this case they are arranged in layers, and in each layer there are neurons that are similar in shape and perform a specific function (cerebellar cortex, cortex cerebral hemispheres). In addition, in some areas of the nervous system (reticular formation), neurons are located diffusely, without forming dense clusters and representing a mesh structure penetrated by white matter fibers. Signal transmission from cell to cell occurs in special formations - synapses. This is a specialized structure that ensures the transmission of a nerve impulse from a nerve fiber to any cell (nerve, muscle). Transmission is carried out using special substances - mediators.
Diversity
The bodies of the largest neurons reach a diameter of 100-120 microns (giant pyramids of Betz in the cerebral cortex), the smallest - 4-5 microns (granular cells of the cerebellar cortex). Based on the number of processes, neurons are divided into multipolar, bipolar, unipolar and pseudounipolar. Multipolar neurons have one axon and many dendrites; these are the majority of neurons in the nervous system. Bipolar ones have one axon and one dendrite, unipolar ones have only an axon; they are typical for analyzer systems. One process emerges from the body of a pseudounipolar neuron, which immediately after exit is divided into two, one of which functions as a dendrite, and the other as an axon. Such neurons are located in sensory ganglia.
Functionally, neurons are divided into sensory, interneurons (relay and interneurons) and motor. Sensitive neurons are nerve cells that perceive stimuli from the external or internal environment of the body. Motor neurons are motor neurons that innervate muscle fibers. In addition, some neurons innervate the glands. Such neurons, together with motor neurons, are called executive neurons.
Some interneurons (relay, or switching, cells) provide
connection between sensory and motor neurons. Relay cells are usually quite large, with a long axon (Golgi type I). Another part of the interneurons are small in size and have relatively short axons (interneurons, or Golgi type II). Their function is related to controlling the state of relay cells.
All of these neurons form aggregates - nerve circuits and networks that conduct, process and store information. At the ends of the processes there are
Neurons contain nerve endings (terminal apparatus of the nerve fiber). According to the functional division of neurons, receptor, effector and interneuron endings are distinguished. Receptor endings are called the endings of the dendrites of sensory neurons that perceive irritation; effector - the endings of the axons of executive neurons, forming synapses on a muscle fiber or on a glandular cell; interneuronal - endings of axons of intercalary and
sensory neurons that form synapses on other neurons.
Nervous tissue. Peripheral nerve.
Evolutionarily the youngest tissue of the human body
Participates in the construction of nervous system organs
Together with the endocrine system it provides neurohumoral regulation activity of tissues and organs, correlates and integrates their functions within the body. And adapts them to changing environmental conditions.
Nerve tissue perceives irritation, comes into a state excitement, forms and conducts nerve impulses.
It is in provisional condition. Didn't reach definitive(not fully formed) development And does not exist as such, since the process of its formation occurred simultaneously with the formation of the organs of the nervous system.
Pharmacist
The vitality of nervous tissue is confirmed by apoptosis, i.e. programmed death large quantity cells. Every year we lose up to 10 million nerve tissue cells.
1) Nerve cells (neurocytes/neurons)
2) Supporting cells (neuroglia)
The process of development of nervous tissue in the embryonic period is associated with the transformation of the neural anlage. It stands out as part of the dorsal ectoderm and is separated from it in the form neural plate.
Neural plate sags By midline, forming the neural groove. Its edges close, forming the neural tube.
Part of the cells The neural plate is not part of the nerve tube and is located on the sides of it ,forming neural crest.
Initially, the nerve tube consists of one layer of cylindrical cells, then becomes multilayer.
There are three layers:
1) Internal/ependymal- cells have long shoot, cells penetrate the thickness neural tube, at the periphery they form a dividing membrane
2) Mantle layer- also cellular, two types of cells
- neuroblasts(from which nerve cells are formed)
- spongeoblasts(of which - cells of astrocytic neuroglia and aligodendroglia)
Based on this zone, a gray matter of the spinal cord and head brain
The processes of the cells of the mantle zone extend into the marginal veil.
3) Outer (edge veil)
It has no cellular structure. Based on it, it is formed white matter of the spinal cord and brain brain
Cells of the ganglion plate are involved in the formation of nerve cells of the autonomic and spinal ganglia of the adrenal medulla and pigment cells.
Characteristics of nerve cells
Nerve cells are structural and functional unit nervous tissue. They provide her ability perceive irritation, be excited, form and carry out nerve impulses. Based on the function they perform, nerve cells have a specific structure.
In a neuron there are:
1) Cell body (perikareon)
2) Two types of processes: axon and dendrite
1) Included pericoreon included cell membrane, nucleus and cytoplasm with organelles and cytoskeletal elements.
Cell membrane provides the cell protective f functions. Fine permeable for various ions, has high excitability, fast conducts wave of depolarization (nerve impulses)
Cell nucleus - large, lies eccentrically (in the center), light-colored, with an abundance of dusty chromatin. The nucleus has a round nucleolus, which makes the nucleus resemble an owl's eye. The core is almost always the same.
In the nerve cells of the ganglion of the prostate gland in men and the wall of the uterus in women, up to 15 nuclei are found.
IN cytoplasm all cellular organelles are present, especially well developed protein-synthesizing organelles.
In the cytoplasm there are local clusters granular EPS With high content ribosomes and RNA. These areas are colored in tolluidine blue color (Nissel) and look like granules(tigroid). Availability tigroids in a cage - indicator high degree his maturity or differentiation and indicator high f functional activity.
Golgi complex most often located in the place of the cytoplasm where the axon leaves the cell. There is no tigroid in its cytoplasm. Plot with K. Golgi - axon hillock. Presence of Golgi connection - active transport of proteins from the body cells into the axon.
Mitochondria form large clusters at points of contact neighboring nerve cells etc.
The metabolism of nerve cells is aerobic in nature, therefore they are especially sensitive to hypoxia.
Lysosomes provide the process intracellular regeneration, lyse aged cellular organelles.
Cell center lies between core And dendrites. Nerve cells don't share. The main mechanism of regeneration is intracellular regeneration.
Cytoskeleton presented neurotubules and and neurofibrils, form a dense network of pericoreoni and keep fit cells. They lie longitudinally in the axon, guide transport flows between the body and processes nerve cell.