Education, The science
Nervous tissue: structure and function. Features of nerve tissues. Types of nerve tissue
We are often nervous, constantly filtering incoming information, reacting to the outside world and trying to listen to our own body, and in all this amazing cells help us. They are the result of a long evolution, the result of the work of nature throughout the development of organisms on Earth.
We can not say that our system of perception, analysis and response is ideal. But we are very far away from animals. To understand how such a complex system works, it is very important not only to specialists - biologists and physicians. And this person may be interested in another person's profession.
Information in this article is available to everyone and can benefit not only as knowledge, because understanding your body is the key to understanding yourself.
What is she responsible for?
The human nerve tissue is distinguished by the unique structural and functional variety of neurons and the specificity of their interactions. After all, our brain is a very complex system. And to control our behavior, emotions and thinking, we need a very complex network.
Nervous tissue, the structure and functions of which are determined by a combination of neurons - cells with processes - and determine the normal vital activity of the organism, firstly, it ensures the coordinated activity of all systems of organs. Secondly, it connects the body with the external environment and provides adaptive reactions to its change. Thirdly, it controls the metabolism under changing conditions. All kinds of nerve tissues are a material component of the psyche: signaling systems - speech and thinking, features of behavior in society. Some scientists have hypothesized that a person has developed his mind greatly, for which he had to "sacrifice" many animal abilities. For example, we do not have sharp eyesight and hearing, which animals can boast of.
Nervous tissue, the structure and functions of which are based on electrical and chemical transmission, has clearly localized effects. Unlike humoral, this system acts instantly.
Lots of small transmitters
Cells of nervous tissue - neurons - are structural-functional units of the nervous system. The cell of the neuron is characterized by a complex structure and increased functional specialization. The structure of the neuron consists of a eukaryotic body (soma), whose diameter is 3-100 microns and shoots. The neuron soma contains a nucleus and a nucleolus with a biosynthesis apparatus that forms enzymes and substances inherent in the specialized functions of neurons. This is Nissl's body - tightly adjacent flattened cisterns of a rough endoplasmic reticulum, as well as a developed Golgi apparatus.
The functions of the nerve cell can be continuously carried out, due to the abundance in the body of the "power stations" that produce ATP, the chondrasome. The cytoskeleton, represented by neurofilaments and microtubules, plays a supporting role. In the process of loss of membrane structures, pigment lipofuscin is synthesized, the amount of which grows with the age of the neuron. In the stem neurons, a pigment melatonin is formed. The nucleolus consists of protein and RNA, the nucleus of DNA. Ontogenesis of the nucleolus and basophils determine the primary behavioral reactions of people, since they depend on the activity and frequency of the contacts. Nerve tissue implies the main structural unit - the neuron, although there are other types of auxiliary tissues.
Features of the structure of nerve cells
The two-membrane nucleus of neurons has pores through which waste substances enter and leave. Due to the genetic apparatus, differentiation occurs, which causes the configuration and frequency of interactions. Another function of the nucleus is to regulate protein synthesis. Ripened nerve cells can not share mitosis, and the genetically determined active products of synthesis of each neuron should ensure functioning and homeostasis throughout the life cycle. Replacement of damaged and lost parts can occur only intracellularly. But there are exceptions. In the epithelium of the olfactory analyzer, certain ganglions of animals are capable of division.
Nerve cells are visually distinguished by a variety of sizes and shapes. Neurons have irregular outlines due to processes, often numerous and overgrown. These are living conductors of electrical signals, through which reflex arcs are composed. Nervous tissue, the structure and functions of which depend on highly differentiated cells, the role of which is to perceive sensory information, coding it through electrical impulses and transferring to the other differentiated cells, is capable of providing a response. It is almost instantaneous. But some substances, including alcohol, greatly slow it down.
About axons
All kinds of nervous tissue function with the direct participation of shoots-dendrites and axons. Axon is translated from Greek as an "axis". This is an elongated process that conducts excitation from the body to the processes of other neurons. The tips of the axon are highly branched, each capable of interacting with 5000 neurons and forming up to 10,000 contacts.
The locus of the catfish, from which the axon branches, is called the axon mound. It combines with the axon that in them there is no rough endoplasmic reticulum, RNA and enzymatic complex.
A little bit about dendrites
This name of the cells means "tree". Like branches, from soma grow short and strongly branching processes. They receive signals and serve as loci where synapses occur. Dendrites with the help of lateral processes - spines - increase the surface area and, accordingly, the contacts. Dendrites without integuments, axons are surrounded by myelin sheaths. Myelin has a lipidic nature, and its effect is similar to the insulating properties of a plastic or rubber coating of electrical wires. The point of excitation generation - the axon hillock - occurs at the point of axon's departure from the soma in the trigger zone.
The white matter of the ascending and descending pathways in the spinal cord and the brain form axons through which nerve impulses are carried out, carrying out a conductive function-the transmission of a nerve impulse. Electrical signals are transmitted to various parts of the brain and spinal cord, making a connection between them. At the same time, the executive organs can be connected to receptors. Gray matter forms the cortex of the brain. The centers of congenital reflexes (sneezing, coughing) and vegetative centers of reflex activity of the stomach, urination, defecation are located in the spinal canal. Insertion neurons, bodies and motor dendrites perform a reflex function, carrying out motor reactions.
Features of nerve tissue are determined by the number of processes. Neurons are unipolar, pseudo-unipolar, bipolar. The human nerve tissue does not contain unipolar ones with one process of neurons. In multipolar - an abundance of dendritic trunks. Such branching does not affect the speed of the signal.
Different cells - different tasks
Nerve cell functions are performed by different groups of neurons. By specialization in the reflex arc, afferent or sensitive neurons that conduct impulses from organs and skin to the brain are distinguished.
Insertion neurons, or associative ones, are a group of switching or binding neurons that analyze and make a decision, carrying out the functions of the nerve cell.
Efferent neurons, or sensory ones, carry information about sensations - impulses from the skin and internal organs to the brain.
Efferent neurons, effector, or motor, conduct impulses - "commands" from the brain and spinal cord to all working organs.
The characteristics of neural tissues are that neurons perform complex and jewelry work in the body, so everyday primitive work - providing food, removing decay products, a protective function is given to the auxiliary cells of neuroglia or basic Schwann cells.
The process of nerve cells formation
In the cells of the neural tube and ganglionic plate, there is a differentiation that determines the characteristics of the nerve tissues in two directions: the large ones become neuroblasts and neurocytes. Small cells (spongioblast) do not increase and become gliocytes. Nervous tissue, the types of tissues of which are composed of neurons, consists of basic and auxiliary ones. Auxiliary cells ("gliocytes") have a special structure and functions.
Evolution of tissue
The main property of a living organism is irritability or sensitivity. The type of nervous tissue is grounded in the phylogenetic position of the animal and differs in its wide variability, becoming more complicated in the process of evolution. All organisms require certain parameters of internal coordination and regulation, proper interaction between the stimulus for homeostasis and the physiological state. Nervous tissue of animals, especially multicellular, whose structure and functions underwent aromorphosis, promotes survival in the struggle for existence. The primitive hydroids are represented by stellate, nerve cells scattered throughout the body and connected by the finest processes intertwined. This type of nerve tissue is called diffuse.
The nervous system of flat and round worm stem, staircase type (orthogon) consists of paired brain ganglia - accumulations of nerve cells and the longitudinal trunks (connectives) that leave from them, connected by transverse strands-commissures. In the rings from the okolothriangular ganglion connected by strands, the ventral neural chain departs, in each segment of which there are two closely spaced nerve nodes connected by nerve fibers. In some benign nerves, the nerve ganglia are concentrated with the formation of the brain. Instincts and orientation in space in arthropods are determined by cephalization of the ganglions of the twin brain, the peripheral nerve ring and the abdominal neural chain.
In chordates, the nervous tissue, the types of tissues of which are strongly pronounced, are complex, but such a structure is evolutionarily justified. Different layers arise and are located on the dorsal side of the body in the form of a neural tube, the cavity is a neurocele. Vertebrates differentiate into the brain and spinal cord. When the brain is formed at the anterior end of the tube, swellings form. If the nervous system plays a purely binding role in the lower multicellular systems, highly organized animals store information, extract it if necessary, and also provide processing and integration.
In mammals, these cerebral swellings give rise to the main parts of the brain. And the rest of the tube forms the spinal cord. Nervous tissue, the structure and function of which in its higher mammals, has undergone significant changes. This is a progressive development of the cerebral cortex and all parts of the nervous system that cause complex adaptation to environmental conditions, and the regulation of homeostasis.
Center and periphery
The departments of the nervous system are classified according to the functional and anatomical structure. Anatomical structure is similar to toponymy, where the central nervous system and peripheral are isolated. The central nervous system includes the brain and spinal cord, and the peripheral nervous system is represented by nerves, nodes and termini. Nerves are represented by clusters of processes outside the central nervous system, covered with a common myelin sheath, and electrical signals. Dendrites of sensitive neurons form sensitive nerves, axons are motor nerves.
The totality of long and short processes forms mixed nerves. Accumulating and concentrating, the bodies of neurons make up nodes that go beyond the central nervous system. Nerve endings are divided into receptor and effector. Dendrites by means of terminal branches transform irritations into electrical signals. A efferent end of axons - in the working organs, muscle fibers, glands. Classification by functionality implies the division of the nervous system into somatic and autonomic.
We control something, but something is beyond our control
The properties of nervous tissue are explained by the fact that the somatic nervous system is subject to the will of man, innervating the work of the support system. The motor centers are located in the cerebral cortex. Autonomous, which is also called vegetative, does not depend on the will of man. Based on their own requests, it is impossible to accelerate or slow heart rate or intestinal motility. Since the location of autonomic centers is the hypothalamus, the autonomic nervous system controls the work of the heart and vessels, the endocrine apparatus, and the cavity organs.
Nerve tissue, the photo of which you can see above, forms the sympathetic and parasympathetic parts of the nervous system of the vegetative, which allow it to act as antagonists, providing an opposite effect. Excitation in one organ causes the processes of inhibition in the other. For example, sympathetic neurons cause a strong and frequent reduction of the chambers of the heart, narrowing of blood vessels, jumps of arterial pressure, since norepinephrine is secreted. Parasympathetic, releasing acetylcholine, contributes to weakening heart rhythms, increasing the lumen of the arteries, and lowering the pressure. Balancing these groups of mediators normalizes the heart rhythm.
The sympathetic nervous system acts during intense stress during fright or stress. Signals occur in the area of the thoracic and lumbar vertebrae. Parasympathetic system is included when resting and digesting food, during sleep. The bodies of neurons are in the trunk and sacrum.
Having studied in more detail the features of Purkinje cells, which have a pear-shaped form with a multitude of branching dendrites, one can see how the impulse is transferred and uncover the mechanism of successive stages of the process.
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