Nerve fiber is a process of the neuron, which is covered with glial membrane. What is it for? What functions does it perform? How is it arranged? You will learn about this from the article.
Fibers of the nervous system have different structures. In accordance with their structure, they can be of one of two types. Thus, moth-fiber and myelin fibers are isolated. The first consist of the process of the cell, which is located in the center of the structure. It is called the axon (axial cylinder). This process is surrounded by myelin sheath. Given the nature of the intensity of the functional load, there is the formation of nerve fibers of one type or another. The structure of the structures directly depends on the department in which they are located. For example, in the somatic department of the nervous system, myelinic nerve fibers are located, and in the vegetative system, there are no maternal fibers. At the same time, it should be said that the process of formation of these and other structures is similar.
How does a thin nerve fiber appear?
Consider the process in more detail. At the stage of formation of structures of the demyelin-free type, the axon deepens into a lump consisting of lemocytes, in which cytolemmas begin to bend and encircle the process by the principle of a coupling. Edges at the same time close above the axon, and a duplication of the cell membrane is formed, which is called "mezakson." Lemmatocytes located in the neighborhood, form with their cytolymph simple contacts. Bezmielin fibers due to weak insulation are able to transmit a nerve impulse in the area of mesaxone, and in the area of contacts between lemocytes. As a result, it passes from one fiber to another.
Formation of thick structures
Myelin-type nerve fibers are significantly thicker than mothillin. In the process of forming shells, they are the same. Nevertheless, the accelerated growth of neurons in the somatic department, which is associated with the development of the whole organism, promotes the extension of mesacsons. After that, lemmocytes turn around the axons several times. As a result, concentric type layers are formed, and the nucleus with the cytoplasm is moved to the last turn, which is the outer membrane of the fiber (neurilemoma). The inner layer consists of a mezacson, entangled several times, and called myelin. Over time, the number of turns and the size of the mezaxone gradually increase. This is due to the passage of the myelination process during the growth of axons and lemocytes. Each next turn is wider than the previous one. The widest is the one that contains the cytoplasm with the nucleus of the lemocyte. In addition, the thickness of myelin differs throughout the length of the fiber. In those places where the lemmocytes contact each other, the lamination disappears. Only the outer layers enter into contact, the composition of which includes the cytoplasm and the nucleus. Such places are formed in connection with the absence of myelin in them, thinning of the fiber and are called nodal interceptions.
Growth of structures in the central nervous system
Myelination in the system proceeds as a result of the girth of the oligodendrocytes of the axons. Myelin consists of a lipid base and when it interacts with oxides it becomes darker. The remaining components of the membrane and its gaps remain bright. Such encountered strips are called notches of myelin. They correspond to insignificant interlayers in the cytoplasm of the lemocyte. And in the axon cytoplasm there are neurofibrils and mitochondria located longitudinally. The largest number of them - closer to the interceptions and in the end apparatus of fibers. The axon cytolemma (axolemma) promotes a nerve impulse. It is manifested by the wave of its depolarization. In the case when the neurite is presented as the axial cylinder, it does not contain the granules of the basophilic substance.
Myelinated nerve fibers consist of:
- Axon, which is in the center.
- Myelin sheath. It is covered with an axial cylinder.
- Schwann shell.
In the axial cylinder there are neurofibrils. Myelin sheath consists of many lipoid substances forming myelin. This compound is of great importance in the activity of the central nervous system. In particular, the speed with which excitation is carried out along nerve fibers depends on it. The shell formed by the junction closes the axon in such a way that gaps are formed, which are called Ranvier intercepts. In their region, the axial cylinder is in contact with the Schwann shell. The fiber segment is its span, which is between two Ranvier intercepts. In it one can consider the core of the Schwann shell. It is located approximately at the center of the segment. It is surrounded by protoplasm Schwann cells with myelin content in loops. In the intervals of the Ranvier interceptions, the myelin sheath is not homogeneous. In it there are oblique incisions of Schmidt-Lanterman. The cells of the Schwannian membrane begin to develop from the ectoderm. Below them is the Axon of the fibers of the peripheral nervous system, due to what they can be called its glial cells. The nerve fiber in the central system is devoid of Schwann's shell. Instead, there are elements of oligodendroglia. Bezmielin fiber has only an axon and Schwann's shell.
The main task that the nerve fiber performs is innervation. This process can be of two types: impulse and pulseless. In the first case, transmission occurs due to electrolyte and neurotransmitter mechanisms. Myelin plays the main role in innervation, so the speed of this process is much higher in myelin fibers than in maternal fibers. The process of the pulseless type occurs by the axoplasmic current passing through the special microtubules of the axon, which contain trophogens (substances that have a trophic effect).