The nervous system in a living organism is represented by a network of communications that ensure its connection with the outside world and its own processes. Its basic element is a neuron - a cell with processes (axons and dendrites) that transmits information electrically and chemically.
Assignment of nervous regulation
For the first time, the nervous system appeared in living organisms in need of more effective interaction with the environment. The development of a simple network for transmitting impulses helped not only to receive signals from the outside. Thanks to her, it became possible to organize their own life processes for more successful functioning.
During evolution, the structure of the nervous system became more complicated: its task was not only to form an adequate response to external influences, but also to organize its own behavior. IP Pavlov called this way of functioning higher nervous activity.
Interaction with the environment of unicellular organisms
For the first time, the nervous system appeared in organisms consisting of more than one cell, as it transmits signalsbetween neurons that form a network. But already in protozoa one can observe the ability to respond to external stimuli provided by intracellular processes.
The nervous system of multicellular organisms is qualitatively different from that of protozoa. The latter have the entire system of connections within the metabolism of a single cell. About the various processes that take place outside or inside, the infusoria "learns" due to changes in the composition of the protoplasm and the activity of some other structures. Multicellular living beings have a system built from functional units, each of which is endowed with its own metabolic processes.
Thus, for the first time, the nervous system appears in someone who has not one, but several cells, that is, in multicellular organisms. The prototype is the conduction of impulses in protozoa. At their level of vital activity, the production by the protoplasm of structures with the conductivity of impulses is revealed. Similarly, in more complex living beings, this function is performed by individual nerve cells.
Features of the nervous system of the coelenterates
Multicellular animals living in colonies do not share functions among themselves, and they do not yet have a neural network. It occurs at the stage when various functions in the multicellular organism are differentiated.
For the first time, the nervous system appears in hydra and other coelenterates. It is a network that conducts non-targeted signals. The structure has not yet been formalized, it is diffuselydistributed throughout the body of the intestinal cavity. Ganglion cells and their Nissl substance are not fully formed. This is the simplest version of the nervous system.
The type of animal motility is determined by the diffuse reticulum nervous system. Hydra performs perist altic movements, as it does not have special body parts for movement and other movements. For motor activity, it needs a continuous connection of contracting elements, while it is required that the bulk of the conducting cells be located in the contractile part. Which of the animals for the first time the nervous system appears in the form of a diffuse network? Those who are the founders of the human regulation system. This is evidenced by the fact that gastrulation is present in the development of the animal embryo.
Features of the nervous system of helminths
Subsequent improvement in nervous regulation was associated with the development of bilateral symmetry instead of radial symmetry and the formation of clusters of neurons in various parts of the body.
For the first time, the nervous system appears in the form of strands in 1 flatworms. At this stage, it is represented by paired head nerve nodes and formed fibers extending from them. In comparison with the intestinal cavity, such a system is much more complicated. In helminths, groups of nerve cells are found in the form of nodes and ganglia. The prototype of the brain is a ganglion in the anterior part of the body that performs regulatory functions. It is called the brain ganglion. From it along the whole body are twonerve trunks connected by jumpers.
All components of the system are not located outside, but are immersed in the parenchyma and thus protected from injury. For the first time, the nervous system appears in flatworms along with the simplest sense organs: touch, sight and a sense of balance.
Features of the nervous system of nematodes
The next stage of development is the formation of an annular formation near the pharynx and several long fibers extending from it. With such characteristics, for the first time, the nervous system appears in roundworms. The peripharyngeal ring is a single circular ganglion and performs the functions of a basic organ of perception. It is connected to the ventral cord and the dorsal nerve.
Nerve trunks in nematodes are located intraepithelial, that is, in hypodermal ridges. The organs of perception are sensilla - setae, papillae, supplementary organs, amphids and phasmids. They all have mixed sensibilities.
The most complex organs of perception of nematodes are amphids. They are paired, can be different in shape and are located in front. Their main task is to recognize chemical agents located far from the body. Some roundworms also have receptors that perceive internal and external mechanical influences. They are called metanemes.
Features of the nervous system of the annulus
The formation of ganglia in the nervous system further develops inringed worms. In most of them, ganglionization of the abdominal trunks occurs in such a way that each segment of the worm has a pair of nerve nodes that are connected by fibers to neighboring segments. Annelids have an abdominal nerve chain formed by the brain ganglion and a pair of cords coming from it. They stretch along the abdominal plane. The perceiving elements are located in front and are represented by the simplest eyes, olfactory cells, ciliary pits and locators. With paired nodes, the nervous system first appeared in annelids, but later it develops in arthropods. They have an increase in the ganglia in the head part and the combination of nodes in the body.
Elements of the diffuse network in the human nervous system
The pinnacle of the evolutionary development of the nervous system is the emergence of the human brain and spinal cord. However, even in the presence of such complex structures, the original diffuse organization is retained. This network entangles every cell of the body: skin, blood vessels, etc. But with such characteristics, for the first time, a nervous system appears in someone who did not even have the opportunity to perceive the environment in a differentiated way.
Thanks to these "residual" structural units, a person has the opportunity to feel various effects even in microscopic areas. The body can react to the appearance of the smallest foreign agent by developing protective reactions. The presence of a diffuse network in the human nervous system is confirmed by laboratory methodsstudies based on the introduction of a dye.
The general line of development of the nervous system in the course of evolution
Evolutionary processes of the nervous system took place in three stages:
- diffuse network;
- gangillia;
- spinal cord and brain.
The structure and function of the CNS is very different from earlier types. Its sympathetic division contains ganglionic and reticular elements. In its phylogenetic development, the nervous system acquired more and more dissection and differentiation. The ganglion stage of development differed from the reticular stage in the presence of neurons still located above the conduction system.
Any living organism is essentially a monolith, consisting of various organs and their systems, which constantly and continuously interact with each other and with the external environment. For the first time, the nervous system appeared in coelenterates, it was a diffuse network that provides elementary conduction of impulses.
