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.
Prescribing Nervous Regulation
For the first time, the nervous system appeared in living organisms with the need for more effective interaction with the environment. The development of the simplest network for transmitting pulses helped not only to perceive signals from outside. Thanks to it, it became possible to organize our own life processes for more successful functioning.
During evolution, the structure of the nervous system became more complicated: its task was not only the formation of an adequate response to external influences, but also the organization of their own behavior. I.P. Pavlov called this way of functioning higher nervous activity.
Interaction with the environment of unicellular
For the first time, the nervous system appeared in organisms consisting of more than one cell, as it transmits signals between the neurons that make up the network. But even in protozoa, one can observe the ability to respond to external stimuli provided by intracellular processes.
The multicellular nervous system differs qualitatively from a similar formation in protozoa. The last whole system of bonds is located within the metabolism of a single cell. Infusoria “learns” about the various processes that take place externally or internally due to changes in the composition of protoplasm and the activity of some other structures. Multicellular living beings have a system built of functional units, each of which is endowed with its own metabolic processes.
Thus, the first time the nervous system appears, who has not one but several cells, that is, in multicellular organisms. The prototype is the conduct of impulses in the simplest. At their level of vital activity, protoplasm production of structures with impulse conduction is detected. Similarly, in more complexly organized living beings, this function is performed by individual nerve cells.
Features of the nervous system of the intestinal
Multicellular animals living in colonies do not share functions, and they still do not have a neural network. It occurs at the stage when various functions in a multicellular organism are differentiated.
For the first time, the nervous system appears in hydra and other coelenterates. It is a network that conducts unfocused signals. The structure is not yet formed, it is diffusely distributed throughout the intestinal cavity. Ganglion cells and their Nisslev substance are not fully formed. This is the simplest version of the nervous system.
The type of animal motility is determined by the diffuse reticular nervous system. Hydra performs peristaltic movements, since it does not have special body parts for movement and other movements. For motor activity, it needs an uninterrupted connection of contracting elements, while it is required that the bulk of the conducting cells be located in the contractile part. Which animal first 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 of nervous regulation was associated with the development of bilateral symmetry instead of radial and the formation of clusters of neurons in various parts of the body.
In the form of strands, the nervous system first appears in 1 flatworms. At this stage, it is represented by paired head nerve nodes and formed fibers extending from them. Compared with the intestinal, such a system is much more complicated. In helminths, groups of nerve cells in the form of nodes and ganglia are detected. The prototype of the brain is the ganglion in the front of the body that performs regulatory functions. It is called the brain ganglion. From it along the whole body are two nerve trunks connected by jumpers.
All components of the system are not located outside, but are immersed in the parenchyma and thereby protected from injury. For the first time, the nervous system appears in flatworms along with the simplest sensory organs: touch, vision 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, the nervous system first appears in roundworms. The periopharyngeal ring is a single circular ganglion and serves as the basic organ of perception. A ventral cord and a dorsal nerve are associated with it.
Nerve trunks in nematodes are located intraepithelially, that is, in hypodermal ridges. The sensory organs act as sensory organs — bristles, papillas, complementary organs, amphids, and phasmids. All of them are endowed with mixed sensitivity.
The most complex organs of perception of nematodes are amphids. They are paired, can be different in shape and are 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 metanems.
Features of the nervous system of the annulus
The formation of ganglia in the nervous system subsequently develops in annelids. In most of them, ganglionization of the abdominal trunks occurs so 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 cerebral ganglion and a pair of cords extending from it. They stretch along the abdominal plane. The sensing elements are located in front and are represented by the simplest eyes, olfactory cells, ciliary fossae and locators. With paired nodes, the nervous system first appeared in annelids, but later on it develops in arthropods. They have an increase in the ganglia in the head and the combination of nodes in the body.
Elements of the diffuse network in the human nervous system
The peak of the evolutionary development of the nervous system is the appearance of the brain and spinal cord in humans. However, even with 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, the nervous system appears, who did not even have the opportunity to differentially perceive the environment.
Thanks to these “residual” structural units, a person has the opportunity to feel various influences even at microscopic sites. The body can respond to the appearance of the smallest alien agent by producing protective reactions. The presence of a diffuse network in the human nervous system is confirmed by laboratory research methods based on the introduction of a coloring matter.
The general line of development of the nervous system during evolution
The evolutionary processes of the nervous system took place in three stages:
- diffuse network;
- ganglia
- spinal cord and brain.
The structure and functioning of the central nervous system are very different from earlier types. In her sympathetic department, ganglionic and reticular elements are presented. In its phylogenetic development, the nervous system has become increasingly dissected and differentiated. The ganglionic stage of development from the reticular was distinguished by 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 the intestinal cavity, it was a diffuse network, providing elementary conduction of impulses.