The human brain consists of 10 12 nerve cells. The usual nervous cell receives information from hundreds and thousands of other cells and transmits hundreds and thousands, and the number of compounds in the brain exceeds 10 14 - 10 15. Open more than 150 years ago in the morphological studies R. Dutroshe, K. Erenberg and I. Purkinje, nerve cells do not cease to attract the attention of researchers. As independent elements of the nervous system, they were discovered relatively recently - in the XIX century. Golgi and Ramon-I-Kahal applied sufficiently perfect methods of coloring nervous tissue and found that cells of two types can be distinguished in brain structures: neurons and glius . Neurobiologist and Neuroanat Ramon-I-Kahal used Golgi coloring method for mapping the head and spinal cord. As a result, not only extreme difficulty, but also a high degree of orderliness of the nervous system was shown. Since then, new methods of studying the nervous tissue have emerged, allowing to perform a subtle analysis of its structure - for example, the use of historadiochemistry identifies the most complex links between the nerve cells, which makes it possible to put forward fundamentally new assumptions on the construction of neural systems.
The structures of microtubules are so complex that many of the mechanisms are not yet known. Recent research tools with extreme resolution have shown that these mechanisms are much more complicated than previously thought. Signal paths were found that regulate the construction, maintaining and restoring the structures of microtubules.
There are many versions of 7 species of tubulin molecules, called α, β, γ, δ, ε and ζ. For the launch of structures, the third type of γ-tubulin is necessary. γ-tubulin is combined with other large proteins for the formation of an annular complex, which is the original place for the structures.
Having an exceptionally complex structure, a nervous cell is a substrate of the most highly organized physiological reactions underlying the ability of living organisms to differentiated response to changes. external environment. To functions nervous cell Referring information about these changes inside the body and its memorization for long term, the creation of an appearance of the outside world and the organization of behavior is the most appropriate way to ensure a living being the maximum success in the struggle for its existence.
This origin is called nucleation. The structures are built, and then constantly separated from each other, while the microtubule goes into new regions, and then departs back when the situation changes or environment is not suitable for the structure under construction.
Two different events of the growing hollow tube are different. The positive end is growing rapidly and is also quickly broken. Another type adjusts the sections of the nucleation and where the structure begins. This group also destroys the structure. Another group is engines, such as kinesin and dyein, which create movement and mechanical forces related to building structures. Fifth are special proteins that affect the folding of tubulin molecules and modify the structures. This last group creates a lot different types unique structures.
Studies of the main and auxiliary functions of the nervous cell have currently developed into large independent areas of neurobiology. The nature of the receptor properties of sensitive nerve endings, the mechanisms of inter-line synaptic transmission of nerve influences, mechanisms for the appearance and propagation of the nerve impulse on the nervous cell and its processes, the nature of conjugation of excitation and contractor or secretory processes, the mechanisms of preserving traces in nerve cells - all of these cardinal problems, in solving which over the past decades has been achieved great progress due to widespread implementation newest methods structural, electrophysiological and biochemical analyzes.
Materials are marked for transport on the microtubule
One of the main functions of the microtubule is the regulation of all the vehicles along a very long axon, as well as body cells and dendrites with unique spikes. Specific material must be sent to each zone. Cells are very small compared to people - the size of a person compared to Everest. However, looking at the neuron scales, they may have axons a few feet long. Transport in this scale is the movement of a person walking along the wall of China.
The structures of microtubule form the entire cell
Neuron must be sent a large number of Specific labeled materials in certain places in the cage and along the axon. There are various types of tubules for axons and dendrites. For each there are special engines. When neuron migrates, it produces a process in front, moves the kernel to the front and then disassembles the process remaining back. Microtubule and actin forests direct all this.
2.1 Size and form
The dimensions of neurons can be from 1 (size of the photoreceptor) to 1000 μm (size of the giant neuron at the sea mollusk ApLysia) (see [Sakharov, 1992]). Neuron form is also extremely diverse. The most clear form of neurons is visible when the preparation of fully isolated nerve cells is prepared. Neurons most often have the wrong shape. There are neurons resembling a "leaf" or "flower". Sometimes the cell surface resembles the brain - it has "furrows" and "gyrus". Non-neurons membrane exhaustion increases its surface by more than 7 times.
Anchor in this process is a centrosome made from centrioles, which are made from specific structures of microtubule. It produces microtubule compounds in the processes moving forward. Centrosoma is the organizational center of the microtubule. This is an organella near the kernel. Two centrioles at right angles are surrounded large mass squirrel. This very complex car sends cell division by pulling all elements of division into many stages.
When the centrioles are connected, they do it at right angles, and these pairs move to the opposite ends of the kernel in the process of cell division. But the centrosome made from the centralines is also a critical way to which the neuron is organized by the spread and the constantly changing structure of microtubules. In fact, Centril determines where the core is in the cell, and also organizes spatial structure Organelle in the cage. In cages with cilia and flavors, central Centralol determines where it will be.
In the nerve cells are distinguishable the body and processes. Depending on the functional purpose of the processes and their quantity, monopolar and multipolar cells are distinguished. Monopolar cells have only one process - this is axon. According to classical ideas, neurons have one axon, according to which the excitation extends from the cell. According to the most new results obtained in electrophysiological studies using dyes that can spread from the body of the cell and to paint the processes, neurons have more than one axon. Multipolar (bipolar) cells have not only axons, but also dendrites. According to dendrites, signals from other cells come to neuron. Dendriti, depending on their localization, can be basal and apical. The dendritic tree of some neurons is extremely branched, and in dendrites there are synapses - structurally and functionally decorated places of contacts of one cell on the other.
This central mother is also called basal body as the starting point of the entire microtubule process of the cell. Microtubule form a large structure that surrounds the entire core in the cell. This cell extends from the centrosome around the kernel and to the leading process. These microtubule contribute to the migration of neurons. Then the structure of the tubules is pulling the centrosome with the kernel into the front edge.
When the axon begins and grows, the cell form becomes polar and asymmetric. Neulet grows with bunches of microtubules and a very active actin growth cone. This complex process includes mechanical actions of both. When neuron becomes a specific type, microtubule acquire a very specific forms and must support them with unique stabilizing molecules. This is due to the very active transfer of these stabilizing molecules by kinesine engines. As directed, it is unclear.
What cells are more perfect - unipolar or bipolar? Unipolar neurons can be a certain step in the development of bipolar cells. At the same time, mollusks, which in the evolutionary stairs occupy not the top floor, unipolar neurons. New histological studies showed that even a person in the development of the nervous system of the cell of some structures of the brain from unipolar "turn" into bipolar. A detailed study of ontogenesis and phylogenesis of nerve cells convincingly showed that the unipolar structure of the cell is a secondary phenomenon and that during the embryonic development it is possible to traverse the gradual conversion of bipolar forms of nerve cells into unipolar. Consider the bipolar or unipolar type of structure of the nervous cell as a sign of complexity of the structure of the nervous system is hardly true.
Perhaps the centrosoma and Golgi are involved. From time to time, the entire beam of many microtubules is moved by mechanical forces from engines, which allows you to change the form. When damage to the axon occurs, the microtubule is again critically involved in recovery.
Microtubules have many different roles in the formation and stabilization of synapses. In the previous article, dynamic changes of dendritic spikes and various shapes. This happens through the actions of microtubules. These microtubules bring material to change the form of the spine with the help of special engines.
Explorer processes give the nervous cells the ability to unite into nervous networks of various complexity, which is the basis for creating elementary nerve cells of all brain systems. To actuate this basic mechanism and its use, nerve cells must have auxiliary mechanisms. The appointment of one of them is the conversion of the energy of various external influences in the type of energy that can enable the process of electrical excitation. In receptor nerve cells, such auxiliary mechanism are special sensory membrane structures that allow you to change its ionic conductivity under the action of certain or other external factors (mechanical, chemical, light). In most other nerve cells, it is the chemoch-sensitive structures of those areas of the surface membrane, to which the end of the processes of other nerve cells (postsynaptic areas) and which can change the ionic conductivity of the membrane when interacting with chemicalssecreted by nerve endings. Arising from such a variation local electricity It is a direct stimulus, which includes the main mechanism of electrical excitability. The purpose of the second auxiliary mechanism is the transformation of the nerve impulse into a process that allows the use of information brought by this signal to start certain forms of cellular activity.
Organization and structure of the cytoskeleton
Axans may have up to 100 microtubule bundles in one axon cross section. There are many variations in these lattices with various types of stabilizing molecules, various orientations and many different bound molecules and related factors. It is so difficult that most of the structure is not clear, despite extensive studies with electron microscopes and subtle cuts.
Therefore, the minus ends are not always in the centrosome. The very first structures begin in the centrosome, but then when it becomes more complex and more across the axon, this direction seems to disappear, and others raise it. The previous message described the critical cell cilia with their numerous functions in alarm and motion. These cilia are highly organized by microtubes of a certain form, and they occur from the centrosome.
2.2 Color Neurons
Next external characteristic Nervous cells are their color. It is also diverse and may indicate the cell function - for example, neuroendocrine cells have white color. Yellow, orange, and sometimes brown color Neurons is explained by pigments that are contained in these cells. The placement of pigments in the cell is uneven, so its painting is different over the surface - the most colored areas are often focused near the axonny holly. Apparently, there is a certain relationship between the function of the cell, its color and its shape. The most interesting data was obtained in studies on the nerve clams of mollusks.
But most microtubules are not fixed at both ends. Orientation are different, as well as when starting from different sources. In dendrites, the orientation of the plus and minus is half and half, whereas in the Axone it is mainly the lead. Microtubules are constantly expanding and compressed both in the axes and in dendrites even in the ripe axonovsky synapse. It seems that some of them are stable in these mature situations, while others are not. Areas that are more stable have much more related proteins and connections.
Types of microtubule structures
There are various tubulin molecules that build a microtubule, and the main structural α-tubulin and β-tubulin have options that make it more complex. These options are called isoforms and produced by various genes, various changes that occur in protein when they are produced, and different structure threads. One of the differences is the sequence of amino acids in the molecule section, which sticks out of the structure in the form of a tail in different formsthat form the pattern and code.
2.3. Sinapsy
Biophysical and cellular biological approach to the analysis of neural functions, the possibility of identifying and cloning genes essential for alarm, revealed a close relationship between the principles that underlie the synaptic transmission and interaction of cells. As a result, the conceptual unity of neurobiology with cell biology was provided.
These differences in the sequence seem to have functions in different types of cells. Mutations in these tails are associated with brain diseases. There are also special chaperone molecules that help a tubulin protein molecule in folding. One particular mutation in Chaperone causes a destructive human disease with serious development symptoms.
Modifications of tubulin tails may occur after they are part of the lattice. Some of these modifications can help with the stability of the structure over time. They can attract special molecules that stabilize the structure and stop the decomposition of the tube. There are many modifications of these tails, including the removal of amino acid, section section and acetyl, phosphorylation, glycylation and polyglutamine. There are special enzymes that work with these tags for certain purposes.
When it turned out that the brain tissues consist of separate cells connected by theity of the process, the question arose: how the joint work of these cells ensures the functioning of the brain as a whole? For decades, disputes caused the question of the method of transmission of excitation between neurons, i.e. What way it is carried out: electric or chemical. By the mid-20s. Most scientists took the point of view that the excitement of muscles, regulation heart Rhythm and other peripheral organs - the result of the influence of chemical signals arising in nerves. Experiments of the English pharmacologist Dale and the Austrian biologist O. Levi were recognized as decisive confirmations of hypothesis about chemical transmission.
Modifications are noted in certain sections of neurons, which, obviously, have a specific function. It seems to be another complex code that is not yet understood. Enzymes with other functions appear to act on the tails of microtubules. The initial neuron segment organizes the stream of material in Akson, not allowing diffusion of many proteins that remain in the body of the cell. This allows some types of transport in Axone, not different. In this area, an unusual beam of several microtubules, which can be associated with the initiation of the action potential are detected.
The complication of the nervous system develops along the path of establishing links between cells and complications of the compounds themselves. Each neuron has many connections with target cells. These targets can be neurons of different types, neurosecretory cells or muscle cells. The interaction of nerve cells is largely limited to specific places in which the connections may come are synapses. This term occurred from the Greek word "stamping" and was introduced by Ch. Sherngton in 1897. And for half a century, K. Bernard has already noted that contacts that form neurons with target cells, specialized, and, as a result, the nature of signals, spreading between neurons and target cells, somehow changes in the place of this contact. Critical morphological data on the existence of synapses appeared later. They received S. Ramon-I-Kahal (1911), which showed that all synapses consist of two elements - the presynaptic and postsynaptic membrane. Ramon-and-kahul predicted the existence of a third element of synapse - synaptic slit (space between the presynaptic and postsynaptic elements of synaps). The joint work of these three elements and underlies communication between neurons and synaptic information transmission processes. Complex forms of synaptic bonds that are formed as the brain development make up the basis of all functions of nerve cells - from sensory perception to training and memory. Synaptic transmission defects are based on many diseases of the nervous system.
Formation of the structure of microtubule
They have a lot of cross references to a structure called a beam. They are also apparently related to the regulation of the flow of Tau molecule between the axon and the body of the cell. Many various factors, engines and protein complexes regulate a complex three-dimensional dynamic microtubule grille. γ-tubulin forms a complex complex to start a process that becomes a template for building a structure at the beginning. It can start in the centrosome or not. It was believed that these incentric structures were cut out from the source complex, but there is no real evidence for this.
Synaptic transmission through most The brain synapses are mediated in the interaction of chemical signals coming from the presynaptic terminal, with postsynaptic receptors. For more than 100 years of studying Synaps, all data was viewed from the point of view of the concept of dynamic polarization, extended by S. Ramon-I-Kahal. In accordance with the generally accepted point of view, synaps transmits information only in one direction: the information flows from the presynaptic to the postsynaptic cell, an anterographed directional transmission of information provides a final step in formed neural communications.
Some organisms have active lattices without any centrosome. The original centrosome is separated after the differentiation of the neuron. Recently some γ-tubulin was discovered in axons and dendrites. The initiation sites were potentially discovered in Golgi, on the plasma membrane and in other places.
Golgi creates its own complex grille of microtubules, sending material in the direction of the front part of the moving neuron. It seems that Golges have a mechanism for running structures related to other purposes. Golgi has its own basic operations in the body of the cell, but in some dendrites there are other outposts that help create forms of dendrites. But, apparently, there are other γ-tubulin and other sources for the start of the scaffolding. New grilles can also move away from existing ones.
An analysis of new results makes it imply that a substantial part of the information is transmitted and retrograded - from postsynaptic neuron to the presynaptic nerve terminals. In some cases, molecules were identified that mediate the retrograde transmission of information. This is a number of substances from moving small nitrogen oxide molecules to large polypeptides, such as nerve growth factor. Even if signals that transmit information retrograde are different in their molecular nature, principles on the basis of which these molecules act may be similar. The bidirectionality of the transmission is also provided in an electrical synapse in which the slot in the connecting channel forms a physical connection between two neurons, without using the neurotransmitter to transmit signals from one neuron to another. This allows the bidirectional transmission of ions and other small molecules. But reciprocal transmission also exists in dendrodritic chemical synapses, where both elements have devices for the release of the transmitter and response. Since these transmission forms are often difficult to differentiate in complex brain networks, cases of bidirectional synaptic communication may be significantly more than it seems now.
Special proteins were found that bind to microtubules, and then attract γ-tubulin to start another frame. Special enzymes cut a part of the microtubule lattice and use it to create a new lattice. There are three family of enzymes that provide this service: Katanan, spastin and phigenin, which are part of a large group of enzymes that distinguish protein structures. These enzymes are apparently especially important to create branches in the Axone with the formation of several buds and dendrites forming multiple spikes.
Bediographic transmission of signals in Sinapse plays an important role in any of the three main aspects of the work of the nervous network: synaptic transmission, plasticity of synapses and the ripening of synapses during development. The plasticity of synapses is the basis for the formation of links, which are created in the development of the brain and when learning. In both cases, retrograde transmission of signals from the post-presuginable cell, the network effect of which is to maintain or potent active synapses. The synaps ensemble involves the coordinated effect of proteins released from the presence of a postsynaptic cell. The primary protein function is to induce the biochemical components required to release the transmitter from the presynaptic terminal, as well as to organize a device for transmitting an external signal of the postsynaptic cell.
2.4. Electrical excitability
All features peculiar nervous systemare associated with the presence of structural nervous cells functional featuresproviding the possibility of generating under the influence external influence A special signal process is a nervous pulse (the main properties of which are the unsuccessful propagation along the cell, the possibility of transmitting the signal in the required direction and exposure to its help to other cells). The ability to generate a non-cellular nervous pulse is determined by a special molecular device of the surface membrane, which allows you to perceive changes in the electrical field passing through it, to change almost instantly its ion conductivity and create a transmembrane ionic current due to the driving force that are constantly existing between an out-and-cellular medium as a driving force. ion gradients.
This complex of processes united under the general title "Electrical Ecurity Mechanism" is the bright functional characteristic of the nervous cell. The possibility of the directional propagation of the nerve impulse is ensured by the presence of branching processes in the nerve cell, often extending for significant distances from its soma and possessing the signal transmission mechanism in the area of \u200b\u200btheir endings through the intercellular slot to subsequent cells.
The use of microelectrode equipment made it possible to perform subtle dimensions characterizing the main electrophysiological characteristics of nerve cells [Kostyuk, Worsttal, 1981; OX, 1974; Khodorov, 1974]. Measurements have shown that each nervous cell has a negative charge, the value of which is -40 - -65 mV. The main difference between the nerve cell from any other lies in the fact that it is able to quickly change the charge value until the opposite. The critical level of neuron depolarization, when the achievement of which arises a rapid discharge, is called the actions of the action potential generation (PD). The duration of the potential of action is different in vertebrates and invertebrate animals - in invertebrates it is equal to 0.1 ms, and in the invertebrates 1-2 ms. A series of action potentials distributed over time is the basis for spatial-temporal coding.
The outer membrane of neurons is sensitive to the action of special substances that are allocated from the presynaptic terminal to neurotransmitters. Currently, about 100 substances that perform this function are identified. On the outside Membranes are located specialized protein molecules - receptors, which interact with the neurotransmitter. As a result, the channels of specific ion permeability occurs - only certain ions can be massate into a cell after the mediator's action. Local depolarization or hyperpolarization of the membrane develops, which is called postsynaptic potential (PSP). PSPs may be excitable (VSP) and brake (TPSP). The PSP amplitude can reach 20 mV.
2.5. PaceMeker
One of the amazing types of electrical activity of neurons registered by the intracellular microelectrode is pacemeration potentials. A. Arvanitaki and N. Khalazonitis first described the oscillating potentials of the nerve cell that are not associated with the flow of synaptic effects. These fluctuations in some cases can acquire such a scope, which exceed the critical level of the potential necessary to activate the electrical excitability mechanism. The presence of such waves of the membrane potential in the soma cells was detected on mollusc neurons. They were regarded as a manifestation of spontaneous, or autoitmic activity having endogenous origin.
Similar rhythmic oscillations were then described in many other types of neurons. The ability to long-term rhythmic activity remains in some cells for a long time after their complete selection. Consequently, it is based on endogenous processes, leading to a periodic change in the ion permeability of the surface membrane. An important role is played by changes in the ion permeability of the membrane under the action of some cytoplasmic factors, such as cyclic nucleotide exchange systems. Changes in the activity of this system under action on the somatic membrane of some hormones or other incompatible chemical influences can modulate the rhythmic activity of the cell (endogenous modulation).
Launch the generation of oscillations of membrane potential can be synaptic and incompatible influences. L. Tauz and G.M. Gershchenfeld found that the somatic membrane of mollusc neurons, which does not have synaptic endings on its surface, has a high sensitivity to the media substances and, therefore, has molecular chem controlled structures inherent in the postsynaptic membrane. The presence of an incompatible reception show shows the possibility of modulating the pacemener activity by the diffuse effect of the mediator substances.
The current concept of two types of membrane structures - electrically excutable and electronically visible, but chemically excitable, laid the foundation for the neuron submissions as a threshold, which has the property of the amount of exciting and braking synaptic potentials. Fundamentally new, which makes endogenic pacemener potential into the functioning of the neuron, is as follows: the pacemecker potential turns the neuron from the adapter potential adder into the generator. The imaging about neuron as a managed generator makes it in a new one to take a look at the organization of many functions of the neuron.
PaceMegery potentials in the proper sense of the word are called close to sinusoidal oscillations with a frequency of 0.1-10 Hz and a 5-10 mV amplitude. It is this category of endogenous potentials associated with the active transport of ions, forms the mechanism of an internal neuron generator, providing a periodic achievement of the PD generation threshold in the absence of an external excitation source. In very general Neuron consists of an electroplated membrane, a chemically excitable membrane and the locus of the generation of pacemeker activity. It is the pacemecker potential that interacts with the chemis-duty and electrol-free membrane makes the neuron with a device with an "built-in" controlled generator.
If the local potential is a special case of a PD generation mechanism, then the pacemener potential belongs to a special class of potentials - the electrical effect of the active transport of ions. The features of the ionic mechanisms of electrical excitability of the somatic membrane underlie the important properties of the nerve cell, first of all its ability to generate rhythmic discharges of nerve impulses. The electrical effect of active transport arises as a result of unbalanced ions transfer in different directions. The hyperpolarization permanent potential is widely known as the result of the active output of sodium ions, summarizing the potential of Nernst [Khodorov, 1974]. The additional inclusion of the active sodium ion pump creates a phase-slow wave of hyperpolarization (negative deviations from the level of the membrane resting potential), usually arising after the high-frequency PD group, which leads to excess sodium accumulation in neuron.
There is no doubt that some of the components of the mechanism of electrical excitability of the somatic membrane, namely electrofluid calcium canalsHowever, there are a factor that conjugates membrane activity with cytoplasmic processes, in particular with the processes of protoplasmic transport and nervous trophic. A detailed clarification of this important issue requires further experimental study.
PaceMecret mechanism, being endogenous by origin, can be activated and inactivated on for a long time As a result of afferent impacts on the neuron. Plastic neuron reactions can be provided by changes in the effectiveness of the synaptic transmission and excitability of the pacemaker (Sokolov, Tauchelidze, 1975).
Pacesecker potential is a compact method of transmitting intaternal genetic information. Having obtained to generate PD, it provides the possibility of outgoing signals to other neurons, including effector, providing the reaction. The fact that the genetic program includes a pacemaker management link, allows neuron to implement the sequence of its genetic programs. Finally, the pacemener potential can be subjected to synaptic influences to one degree or another. This path allows you to integrate genetic programs with current activity, providing flexible management of sequential programs. Plastic changes in the pacemeration potential are even more expanding the possibility of adapting hereditary fixed forms to the needs of the body. Plastic changes are developing in this case not in the genome, but on the way out of the hereditary program to implement (at the level of generation of PD).
The human brain consists of 10 in the 12th nervous cells. The usual nervous cell receives information from hundreds and thousands of other cells and transmits hundreds and thousands, and the number of compounds in the brain exceeds 10 in 14-10 in the 15th. Open more than 150 years ago in the morphological studies R. Dutroshe, K. Erenberg and I. Purkinje, nerve cells do not cease to attract the attention of researchers. As independent elements of the nervous system, they were discovered relatively recently - in the XIX century. Golgji and Ramon-I-Kahal applied sufficiently perfect methods of color of the nervous tissue and found that cells of two types can be distinguished in brain structures: neurons and glius. The neurobiologist and Neuroanat Ramon-I-Kahal used the Golgi coloring method for mapping the portions of the head and spinal cord. As a result, not only extreme difficulty, but also a high degree of orderliness of the nervous system was shown. Since then, new methods of studying the nervous tissue have emerged, allowing to perform a subtle analysis of its structure - for example, the use of historadiochemistry identifies the most complex links between the nerve cells, which makes it possible to put forward fundamentally new assumptions on the construction of neural systems.
Having an exceptionally complex structure, the nervous cell is a substrate of the most highly organized physiological reactions underlying the ability of living organisms to differentiated response to changes in the external environment. The functions of the nervous cell include the transfer of information on these changes inside the body and its memorization for long terms, the creation of an image of the outside world and the organization of behavior is the most appropriate way to ensure a living being the maximum success in the struggle for their existence.
This origin is called nucleation. The structures are built, and then constantly separated from each other, while the microtubule goes into new regions, and then departs back when the situation changes or environment is not suitable for the structure under construction.
Two different events of the growing hollow tube are different. The positive end is growing rapidly and is also quickly broken. Another type adjusts the sections of the nucleation and where the structure begins. This group also destroys the structure. Another group is engines, such as kinesin and dyein, which create movement and mechanical forces related to building structures. Fifth are special proteins that affect the folding of tubulin molecules and modify the structures. This last group creates many different types of unique structures.
Studies of the main and auxiliary functions of the nervous cell have currently developed into large independent areas of neurobiology. The nature of the receptor properties of sensitive nerve endings, the mechanisms of inter-line synaptic transmission of nerve influences, mechanisms for the appearance and propagation of the nerve impulse on the nervous cell and its processes, the nature of conjugation of excitation and contractor or secretory processes, the mechanisms of preserving traces in nerve cells - all of these cardinal problems, in solving Which over the past decades has been achieved by large successes due to the widespread introduction of the latest methods of structural, electrophysiological and biochemical analyzes.
Materials are marked for transport on the microtubule
One of the main functions of the microtubule is the regulation of all the vehicles along a very long axon, as well as body cells and dendrites with unique spikes. Specific material must be sent to each zone. Cells are very small compared to people - the size of a person compared to Everest. However, looking at the neuron scales, they may have axons a few feet long. Transport in this scale is the movement of a person walking along the wall of China.
The structures of microtubule form the entire cell
Neuron should send a large number of specific labeled materials in certain places in the cell and along the axon. There are various types of tubules for axons and dendrites. For each there are special engines. When neuron migrates, it produces a process in front, moves the kernel to the front and then disassembles the process remaining back. Microtubule and actin forests direct all this.
Size and form
The dimensions of neurons can be from 1 (size of the photoreceptor) to 1000 μm (size of the giant neuron at the sea mollusk ApLysia) (see [Sakharov, 1992]). Neuron form is also extremely diverse. The most clear form of neurons is visible when the preparation of fully isolated nerve cells is prepared. Neurons most often have the wrong shape. There are neurons resembling a "leaf" or "flower". Sometimes the cell surface resembles the brain - it has "furrows" and "gyrus". Non-neurons membrane exhaustion increases its surface by more than 7 times.
In the nerve cells are distinguishable the body and processes. Depending on the functional purpose of the processes and their quantity, monopolar and multipolar cells are distinguished. Monopolar cells have only one process - this is axon. According to classical ideas, neurons have one axon, according to which the excitation extends from the cell. According to the most new results obtained in electrophysiological studies using dyes that can spread from the body of the cell and to paint the processes, neurons have more than one axon. Multipolar (bipolar) cells have not only axons, but also dendrites. According to dendrites, signals from other cells come to neuron. Dendriti, depending on their localization, can be basal and apical. The dendritic tree of some neurons is extremely branched, and in dendrites there are synapses - structurally and functionally decorated places of contacts of one cell on the other.
This central mother is also called basal body as the starting point of the entire microtubule process of the cell. Microtubule form a large structure that surrounds the entire core in the cell. This cell extends from the centrosome around the kernel and to the leading process. These microtubule contribute to the migration of neurons. Then the structure of the tubules is pulling the centrosome with the kernel into the front edge.
When the axon begins and grows, the cell form becomes polar and asymmetric. Neulet grows with bunches of microtubules and a very active actin growth cone. This complex process includes mechanical actions of both. When neuron becomes a specific type, microtubule acquire very specific forms and must support them with unique stabilizing molecules. This is due to the very active transfer of these stabilizing molecules by kinesine engines. As directed, it is unclear.
What cells are more perfect - unipolar or bipolar? Unipolar neurons can be a certain step in the development of bipolar cells. At the same time, mollusks, which in the evolutionary stairs occupy not the top floor, unipolar neurons. New histological studies showed that even a person in the development of the nervous system of the cell of some structures of the brain from unipolar "turn" into bipolar. A detailed study of ontogenesis and phylogenesis of nerve cells convincingly showed that the unipolar structure of the cell is a secondary phenomenon and that during the embryonic development it is possible to traverse the gradual conversion of bipolar forms of nerve cells into unipolar. Consider the bipolar or unipolar type of structure of the nervous cell as a sign of complexity of the structure of the nervous system is hardly true.
Perhaps the centrosoma and Golgi are involved. From time to time, the entire beam of many microtubules is moved by mechanical forces from engines, which allows you to change the form. When damage to the axon occurs, the microtubule is again critically involved in recovery.
Microtubules have many different roles in the formation and stabilization of synapses. In the previous article, dynamic changes in dendritic spikes and various forms were shown. This happens through the actions of microtubules. These microtubules bring material to change the form of the spine with the help of special engines.
Explorer processes give the nervous cells the ability to unite into nervous networks of various complexity, which is the basis for creating elementary nerve cells of all brain systems. To actuate this basic mechanism and its use, nerve cells must have auxiliary mechanisms. The appointment of one of them is the conversion of the energy of various external influences in the type of energy that can enable the process of electrical excitation. In receptor nerve cells, such auxiliary mechanism are special sensory membrane structures, which make it possible to change its ionic conductivity under the action of certain external factors (mechanical, chemical, light). In most other nervous cells, these are the chemo-sensitive structures of those areas of the surface membrane, to which the end of the processes of other nerve cells (postsynaptic areas) and which can change the ionic conductivity of the membrane when interacting with chemicals secreted by nerve endings. The local electric current occurs with such a change is the immediate stimulus, which includes the main mechanism of electrical excitability. The purpose of the second auxiliary mechanism is the transformation of the nerve impulse into a process that allows the use of information brought by this signal to start certain forms of cellular activity.
Organization and structure of the cytoskeleton
Axans may have up to 100 microtubule bundles in one axon cross section. There are many variations in these lattices with various types of stabilizing molecules, various orientations and many different bound molecules and related factors. It is so difficult that most of the structure is not clear, despite extensive studies with electron microscopes and subtle cuts.
Therefore, the minus ends are not always in the centrosome. The very first structures begin in the centrosome, but then when it becomes more complex and more across the axon, this direction seems to disappear, and others raise it. The previous message described the critical cell cilia with their numerous functions in alarm and motion. These cilia are highly organized by microtubes of a certain form, and they occur from the centrosome.
The color of neurons
The next external characteristic of nerve cells is their color. It is also diverse and may indicate the cell function - for example, neuroendocrine cells have white color. Yellow, orange, and sometimes brown neurons are explained by pigments that are contained in these cells. The placement of pigments in the cell is uneven, so its painting is different over the surface - the most colored areas are often focused near the axonny holly. Apparently, there is a certain relationship between the function of the cell, its color and its shape. The most interesting data was obtained in studies on the nerve clams of mollusks.
Sinapsy
Biophysical and cellular biological approach to the analysis of neural functions, the possibility of identifying and cloning genes essential for alarm, revealed a close relationship between the principles that underlie the synaptic transmission and interaction of cells. As a result, the conceptual unity of neurobiology with cell biology was provided.
When it turned out that the brain tissues consist of separate cells connected by theity of the process, the question arose: how the joint work of these cells ensures the functioning of the brain as a whole? For decades, disputes caused the question of the method of transmission of excitation between neurons, i.e. What way it is carried out: electric or chemical. By the mid-20s. Most scientists took the point of view that the excitation of muscles, the regulation of cardiac rhythm and other peripherals - the result of the impact of chemical signals arising in nerves. Experiments of the English pharmacologist Dale and the Austrian biologist O. Levi were recognized as decisive confirmations of hypothesis about chemical transmission.
Modifications are noted in certain sections of neurons, which, obviously, have a specific function. It seems to be another complex code that is not yet understood. Enzymes with other functions appear to act on the tails of microtubules. The initial neuron segment organizes the stream of material in Akson, not allowing diffusion of many proteins that remain in the body of the cell. This allows some types of transport in Axone, not different. In this area, an unusual beam of several microtubules, which can be associated with the initiation of the action potential are detected.
The complication of the nervous system develops along the path of establishing links between cells and complications of the compounds themselves. Each neuron has many connections with target cells. These targets can be neurons of different types, neurosecretory cells or muscle cells. The interaction of nerve cells is largely limited to specific places in which the connections may come are synapses. This term occurred from the Greek word "stamping" and was introduced by Ch. Sherngton in 1897. And for half a century, K. Bernard has already noted that contacts that form neurons with target cells, specialized, and, as a result, the nature of signals, spreading between neurons and target cells, somehow changes in the place of this contact. Critical morphological data on the existence of synapses appeared later. They received S. Ramon-I-Kahal (1911), which showed that all synapses consist of two elements - the presynaptic and postsynaptic membrane. Ramon-and-kahul predicted the existence of a third element of synapse - synaptic slit (space between the presynaptic and postsynaptic elements of synaps). The joint work of these three elements and underlies communication between neurons and synaptic information transmission processes. Complex forms of synaptic bonds that are formed as the brain development make up the basis of all functions of nerve cells - from sensory perception to training and memory. Synaptic transmission defects are based on many diseases of the nervous system.
Formation of the structure of microtubule
They have a lot of cross references to a structure called a beam. They are also apparently related to the regulation of the flow of Tau molecule between the axon and the body of the cell. Many different factors, engines and protein complexes regulate a complex three-dimensional dynamic grille of microtubules. γ-tubulin forms a complex complex to start a process that becomes a template for building a structure at the beginning. It can start in the centrosome or not. It was believed that these incentric structures were cut out from the source complex, but there is no real evidence for this.
The synaptic transmission through most of the brain synapses is mediated by the interaction of chemical signals coming from the presynaptic terminal, with postsynaptic receptors. For more than 100 years of studying Synaps, all data was viewed from the point of view of the concept of dynamic polarization, extended by S. Ramon-I-Kahal. In accordance with the generally accepted point of view, synaps transmits information only in one direction: the information flows from the presynaptic to the postsynaptic cell, an anterographed directional transmission of information provides a final step in formed neural communications.
Some organisms have active lattices without any centrosome. The original centrosome is separated after the differentiation of the neuron. Recently some γ-tubulin was discovered in axons and dendrites. The initiation sites were potentially discovered in Golgi, on the plasma membrane and in other places.
Golgi creates its own complex grille of microtubules, sending material in the direction of the front part of the moving neuron. It seems that Golges have a mechanism for running structures related to other purposes. Golgi has its own basic operations in the body of the cell, but in some dendrites there are other outposts that help create forms of dendrites. But, apparently, there are other γ-tubulin and other sources for the start of the scaffolding. New grilles can also move away from existing ones.
An analysis of new results makes it imply that a substantial part of the information is transmitted and retrograded - from postsynaptic neuron to the presynaptic nerve terminals. In some cases, molecules were identified that mediate the retrograde transmission of information. This is a number of substances from moving small nitrogen oxide molecules to large polypeptides, such as nerve growth factor. Even if signals that transmit information retrograde are different in their molecular nature, principles on the basis of which these molecules act may be similar. The bidirectionality of the transmission is also provided in an electrical synapse in which the slot in the connecting channel forms a physical connection between two neurons, without using the neurotransmitter to transmit signals from one neuron to another. This allows the bidirectional transmission of ions and other small molecules. But reciprocal transmission also exists in dendrodritic chemical synapses, where both elements have devices for the release of the transmitter and response. Since these transmission forms are often difficult to differentiate in complex brain networks, cases of bidirectional synaptic communication may be significantly more than it seems now.
Special proteins were found that bind to microtubules, and then attract γ-tubulin to start another frame. Special enzymes cut a part of the microtubule lattice and use it to create a new lattice. There are three family of enzymes that provide this service: Katanan, spastin and phigenin, which are part of a large group of enzymes that distinguish protein structures. These enzymes are apparently especially important to create branches in the Axone with the formation of several buds and dendrites forming multiple spikes.
Bediographic transmission of signals in Sinapse plays an important role in any of the three main aspects of the work of the nervous network: synaptic transmission, plasticity of synapses and the ripening of synapses during development. The plasticity of synapses is the basis for the formation of links, which are created in the development of the brain and when learning. In both cases, retrograde transmission of signals from the post-presuginable cell, the network effect of which is to maintain or potent active synapses. The synaps ensemble involves the coordinated effect of proteins released from the presence of a postsynaptic cell. The primary protein function is to induce the biochemical components required to release the transmitter from the presynaptic terminal, as well as to organize a device for transmitting an external signal of the postsynaptic cell.
Electrical excitability
All functions peculiar to the nervous system are associated with the presence of structural and functional features in nerve cells, providing the possibility of generating under the influence of the external effects of a special signal process - a nervous pulse (the main properties of which are the unsophisticate propagation along the cell, the possibility of transmitting the signal in the required direction and exposure to Its help on other cells). The ability to generate a non-cellular nervous pulse is determined by a special molecular device of the surface membrane, which allows you to perceive changes in the electrical field passing through it, to change almost instantly its ion conductivity and create a transmembrane ionic current due to the driving force that are constantly existing between an out-and-cellular medium as a driving force. ion gradients.
This complex of processes united under the general title "Electrical Ecurity Mechanism" is the bright functional characteristic of the nervous cell. The possibility of the directional propagation of the nerve impulse is ensured by the presence of branching processes in the nerve cell, often extending for significant distances from its soma and possessing the signal transmission mechanism in the area of \u200b\u200btheir endings through the intercellular slot to subsequent cells.
The use of microelectrode equipment made it possible to perform subtle dimensions characterizing the main electrophysiological characteristics of nerve cells [Kostyuk, Worsttal, 1981; OX, 1974; Khodorov, 1974]. Measurements have shown that each nervous cell has a negative charge, the value of which is -40 - -65 mV. The main difference between the nerve cell from any other lies in the fact that it is able to quickly change the charge value until the opposite. The critical level of neuron depolarization, when the achievement of which arises a rapid discharge, is called the actions of the action potential generation (PD). The duration of the potential of action is different in vertebrates and invertebrate animals - in invertebrates it is equal to 0.1 ms, and in the invertebrates 1-2 ms. A series of action potentials distributed over time is the basis for spatial-temporal coding.
The outer membrane of neurons is sensitive to the action of special substances that are allocated from the presynaptic terminal to neurotransmitters. Currently, about 100 substances that perform this function are identified. On the outside of the membrane, specialized protein molecules are located - receptors, which interact with the neurotransmitter. As a result, the channels of specific ion permeability occurs - only certain ions can be massate into a cell after the mediator's action. Local depolarization or hyperpolarization of the membrane develops, which is called postsynaptic potential (PSP). PSPs may be excitable (VSP) and brake (TPSP). The PSP amplitude can reach 20 mV.
PaceMeker
One of the amazing types of electrical activity of neurons registered by the intracellular microelectrode is pacemeration potentials. A. Arvanitaki and N. Khalazonitis first described the oscillating potentials of the nerve cell that are not associated with the flow of synaptic effects. These fluctuations in some cases can acquire such a scope, which exceed the critical level of the potential necessary to activate the electrical excitability mechanism. The presence of such waves of the membrane potential in the soma cells was detected on mollusc neurons. They were regarded as a manifestation of spontaneous, or autoitmic activity having endogenous origin.
Similar rhythmic oscillations were then described in many other types of neurons. The ability to long-term rhythmic activity remains in some cells for a long time after their complete selection. Consequently, it is based on endogenous processes, leading to a periodic change in the ion permeability of the surface membrane. An important role is played by changes in the ion permeability of the membrane under the action of some cytoplasmic factors, such as cyclic nucleotide exchange systems. Changes in the activity of this system under action on the somatic membrane of some hormones or other incompatible chemical influences can modulate the rhythmic activity of the cell (endogenous modulation).
Launch the generation of oscillations of membrane potential can be synaptic and incompatible influences. L. Tauz and G.M. Gershchenfeld found that the somatic membrane of mollusc neurons, which does not have synaptic endings on its surface, has a high sensitivity to the media substances and, therefore, has molecular chem controlled structures inherent in the postsynaptic membrane. The presence of an incompatible reception show shows the possibility of modulating the pacemener activity by the diffuse effect of the mediator substances.
The current concept of two types of membrane structures - electrically excutable and electronically visible, but chemically excitable, laid the foundation for the neuron submissions as a threshold, which has the property of the amount of exciting and braking synaptic potentials. Fundamentally new, which makes endogenic pacemener potential into the functioning of the neuron, is as follows: the pacemecker potential turns the neuron from the adapter potential adder into the generator. The imaging about neuron as a managed generator makes it in a new one to take a look at the organization of many functions of the neuron.
PaceMegery potentials in the proper sense of the word are called close to sinusoidal oscillations with a frequency of 0.1-10 Hz and a 5-10 mV amplitude. It is this category of endogenous potentials associated with the active transport of ions, forms the mechanism of an internal neuron generator, providing a periodic achievement of the PD generation threshold in the absence of an external excitation source. In the most general form, neuron consists of an electrophrol-free membrane, a chemically excitable membrane and locus of the generation of pacemeker activity. It is the pacemecker potential that interacts with the chemis-duty and electrol-free membrane makes the neuron with a device with an "built-in" controlled generator.
If the local potential is a special case of a PD generation mechanism, then the pacemener potential belongs to a special class of potentials - the electrical effect of the active transport of ions. The features of the ionic mechanisms of electrical excitability of the somatic membrane underlie the important properties of the nerve cell, first of all its ability to generate rhythmic discharges of nerve impulses. The electrical effect of active transport arises as a result of unbalanced ions transfer in different directions. The hyperpolarization permanent potential is widely known as the result of the active output of sodium ions, summarizing the potential of Nernst [Khodorov, 1974]. The additional inclusion of the active sodium ion pump creates a phase-slow wave of hyperpolarization (negative deviations from the level of the membrane resting potential), usually arising after the high-frequency PD group, which leads to excess sodium accumulation in neuron.
There is no doubt that some of the components of the mechanism of electrical excitability of the somatic membrane, namely electrotable calcium channels, at the same time, are a factor that conjugates membrane activity with cytoplasmic processes, in particular with the processes of protoplasmic transport and nervous trophic. A detailed clarification of this important issue requires further experimental study.
A pacemecker mechanism, being endogenous by origin, can be activated and inactivated for a long time as a result of afferent impacts on neuron. Plastic neuron reactions can be provided by changes in the effectiveness of the synaptic transmission and excitability of the pacemaker (Sokolov, Tauchelidze, 1975).
Pacesecker potential is a compact method of transmitting intaternal genetic information. Having obtained to generate PD, it provides the possibility of outgoing signals to other neurons, including effector, providing the reaction. The fact that the genetic program includes a pacemaker management link, allows neuron to implement the sequence of its genetic programs. Finally, the pacemener potential can be subjected to synaptic influences to one degree or another. This path allows you to integrate genetic programs with current activity, providing flexible management of sequential programs. Plastic changes in the pacemeration potential are even more expanding the possibility of adapting hereditary fixed forms to the needs of the body. Plastic changes are developing in this case not in the genome, but on the way out of the hereditary program to implement (at the level of generation of PD).
Loading ...