The nervous system has a rather complex histological structure. It consists of neurons (nerve cells), nerve fibers, neuroglia and connective tissue elements. Neurons are the main structural and functional part of the nervous system. The size and shape of the neuron depends on the length and number of its processes. Sprouts are usually divided into dendrites (cytoplasmic) and axons, or neurites (axial cylindrical). Dendrites, tree-branching outgrowths of the cytoplasm of the neuron, conduct stimulation toward the body of the neuron. Axon is a axial cylindrical long single process that carries pulses from the nerve cell; it ends in short branches.
The body of a neuron consists of a cytoplasm and a nucleus. In the cytoplasm, there is a chromatophilic (tiger) substance and neurofibrils, which are specific components of nerve cells. Chromatophilic substance is present in the body of a neuron and large dendrites in the form of lumps of different sizes. It varies with different functional states of the neuron, so its study may have a certain diagnostic value. Neurofibrils in the form of the finest filaments are found in the body of the cell and its processes. In addition, the neuron contains the Golgi mesh apparatus, mitochondria and other organelles, as well as the nucleolus that enters the nucleus, rich in nucleic acids.
Nerve fibers are formed by the processes of the neurons. Depending on whether they have a layer of myelin, they are divided into bezmielinovye (non-confluent) and myelin (moth). The former predominate in the vegetative, and the latter predominate in the somatic part of the nervous system.
Myelin nerve fiber consists of an axial cylinder that is a continuation of the neuron axon, myelin layer and neurilemocyte layer of the neurilemma (Schwann’s membrane).
Axial cylinder consists of axoplasm and neurofibrils, which play an important role in the regeneration of nerve fibers. If the axial cylinder becomes damaged, the axoplasm begins to flow out from the end of the central segment, resulting in the formation of its inflow into which the neurofibrils grow. The myelin layer (myelin, or mya-cotal, envelope) enveloping the axial cylinder has a significant thickness throughout the entire nerve fiber and contains a large amount of myelin, consisting of fat-like substances. Thinning out in separate areas, it forms intersegmentary nodes of nerve fiber (Ranvier intercepts). In the myelin layer also there are deep funnel-shaped depressions visible on longitudinal sections like tubules reaching the axial cylinders in an oblique direction – incisions of myelin (notches of Schmidt-Lanterman).
The cytoplasm of neurolemocytes (Schwann cells), protruding into such funnels, forms sprouts that also reach the axial cylinders. Thanks to such processes, neuro-lemocytes, according to BS Doinikov, carry out the regulation of trophic processes in the axial cylinder of the nerve fiber. A distinctive feature of nerve fibers in the central nervous system is that they do not have nodes of nerve fiber and neurolemmy and axial cylinders are accompanied by glial elements.
Neurolematocytes perform the role of peripheral glia. Outer layer Neurolematocyte with its nucleus and most of the cytoplasm is a neurolemma. The inner layer of the cytoplasm contains maminin plates. If the nerve fiber is damaged, the neurolemocytes proliferate and form bridges (Bünger-Herow ribbons) between its central and peripheral segments, thus playing an important role in regeneration.
Neuroglia plays the role of connective tissue of the central nervous system. There are macro and microglia. In turn, macroglia consists of astrocyte glia and oligodendroglia.
Astrocyte glia-syncytial formation, consisting of large multistep astrocytes. Appendages of some astrocytes, connecting with the processes of other astrocytes, form beams, between which there are nerve cells.
Oligodendroglia performs a supporting function mainly for shoots neurons, accompanying them all the way to the end devices. In the peripheral nervous system, as noted above, it is represented by neurolematocytes.
Microglia consists of small otroschatyh cells that perform a protective function.
In addition to supporting glia, the forest and protective function. Glial cells participate in a variety of reactions in response to the action of harmful factors on the nervous system. In this case, glial cells first increase in volume, then multiply, astrocytes and oligodendroglia cells replace the perishing nerve tissue in the form of a gliotic scar. Along with the regenerative processes, glia can undergo, in pathological conditions, degenerative changes. Some authors attribute the neuroglia to a vnutrikretornuyu function, as well as participation in the storage of information.