We are often nervous, constantly filtering incoming information, reacting to the world around us and trying to listen to our own body, and amazing cells help us in all this. They are the result of a long evolution, the result of the work of nature throughout the development of organisms on Earth.
We cannot say that our system of perception, analysis and response is perfect. But we are very far removed from animals. Understanding how such a complex system works is very important not only for specialists - biologists and doctors. A person of another profession may also be interested in this.
The information in this article is available to everyone and can be useful not only as knowledge, because understanding your body is the key to understanding yourself.
What is she responsible for
The human nervous tissue is distinguished by a unique structural and functional diversity of neurons and the specifics of their interactions. After all, our brain is a very complex system. And to control our behavior, emotions and thoughts, we need a very complex network.
Nervoustissue, the structure and functions of which are determined by a set of neurons - cells with processes - and determine the normal functioning of the body, firstly, ensures the coordinated activity of all organ systems. Secondly, it connects the organism with the external environment and provides adaptive reactions to its change. Thirdly, it controls metabolism under changing conditions. All types of nervous tissues are the material component of the psyche: signaling systems - speech and thinking, behavioral features in society. Some scientists hypothesized that man greatly developed his mind, for which he had to "sacrifice" many animal abilities. For example, we do not have the sharp eyesight and hearing that animals can boast of.
Nervous tissue, whose structure and functions are based on electrical and chemical transmission, has clearly localized effects. Unlike the humoral system, this system acts instantly.
Many small transmitters
Nervous tissue cells - neurons - are structural and functional units of the nervous system. A neuron cell is characterized by a complex structure and increased functional specialization. The structure of a neuron consists of a eukaryotic body (soma), the diameter of which is 3-100 microns, and processes. The soma of a neuron contains a nucleus and a nucleolus with a biosynthetic apparatus that forms enzymes and substances inherent in the specialized functions of neurons. These are Nissl bodies - flattened tanks tightly adjacent to each otherrough endoplasmic reticulum, as well as a developed Golgi apparatus.
The functions of a nerve cell can be continuously carried out, thanks to the abundance in the body of "energy stations" that produce ATP - chondras. The cytoskeleton, represented by neurofilaments and microtubules, plays a supporting role. In the process of loss of membrane structures, the pigment lipofuscin is synthesized, the amount of which increases with the age of the neuron. The pigment melatonin is produced in stem neurons. The nucleolus is made up of protein and RNA, while the nucleus is made up of DNA. The ontogenesis of the nucleolus and basophils determine the primary behavioral responses of people, since they depend on the activity and frequency of contacts. Nervous tissue implies the main structural unit - the neuron, although there are other types of auxiliary tissues.
Features of the structure of nerve cells
The double-membrane nucleus of neurons has pores through which waste substances penetrate and are removed. Thanks to the genetic apparatus, differentiation occurs, which determines the configuration and frequency of interactions. Another function of the nucleus is to regulate protein synthesis. Mature nerve cells cannot divide by mitosis, and the genetically determined active synthesis products of each neuron must ensure functioning and homeostasis throughout the entire life cycle. Replacement of damaged and lost parts can occur only intracellularly. But there are also exceptions. In the epithelium of the olfactory analyzer, some animal ganglia are capable of division.
Nervous tissue cells are visually distinguished by a variety of sizes and shapes. Neurons are characterized by 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, whose role is to perceive sensory information, encode it through electrical impulses and transmit it to other differentiated cells, is able to provide a response. It's almost instantaneous. But some substances, including alcohol, greatly slow it down.
About axons
All types of nervous tissue function with the direct participation of processes-dendrites and axons. Axon is translated from Greek as "axis". This is an elongated process that conducts excitation from the body to the processes of other neurons. The axon tips are highly branched, each capable of interacting with 5,000 neurons and forming up to 10,000 contacts.
The locus of the soma from which the axon branches off is called the axon hillock. It is united with the axon by the fact that they lack a rough endoplasmic reticulum, RNA and an enzymatic complex.
A little about dendrites
This cell name means "tree". Like branches, short and strongly branching shoots grow from the catfish. 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 withoutcovers, axons are surrounded by myelin sheaths. Myelin is lipid in nature, and its action is similar to the insulating properties of a plastic or rubber coating on electrical wires. The point of excitation generation - the axon hillock - occurs at the place where the axon departs from the soma in the trigger zone.
The white matter of the ascending and descending tracts in the spinal cord and brain form axons through which nerve impulses are conducted, 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 communication between them. In this case, the executive organs can be connected to receptors. Gray matter forms the cerebral cortex. In the spinal canal there are centers of congenital reflexes (sneezing, coughing) and autonomic centers of reflex activity of the stomach, urination, defecation. Interneurons, motor bodies and dendrites perform a reflex function, carrying out motor reactions.
Features of nerve tissue due to the number of processes. Neurons are unipolar, pseudo-unipolar, bipolar. The human nervous tissue does not contain unipolar neurons with a single process. In multipolar ones, there is an abundance of dendritic trunks. Such branching does not affect the speed of the signal in any way.
Different cells - different tasks
The functions of a nerve cell are carried out by different groups of neurons. According to specialization in the reflex arc, afferent or sensory neurons are distinguished, conductingimpulses from organs and skin to the brain.
Intercalary neurons, or associative, are a group of switching or connecting neurons that analyze and make a decision, performing the functions of a nerve cell.
Efferent neurons, or sensitive 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.
Features of nerve tissues is that neurons perform complex and jewelry work in the body, therefore everyday primitive work - providing nutrition, removing decay products, the protective function goes to auxiliary neuroglia cells or supporting Schwann cells.
The process of formation of nerve cells
In the cells of the neural tube and ganglionic plate, differentiation occurs, which determines the characteristics of nerve tissues in two directions: large ones become neuroblasts and neurocytes. Small cells (spongioblasts) do not enlarge and become gliocytes. Nervous tissue, the types of tissues of which are composed of neurons, consists of basic and auxiliary. Auxiliary cells ("gliocytes") have a special structure and function.
The central nervous system is represented by the following types of gliocytes: ependymocytes, astrocytes, oligodendrocytes; peripheral - ganglion gliocytes, terminal gliocytes and neurolemmocytes - Schwann cells. Ependymocytesline the cavities of the ventricles of the brain and the spinal canal and secrete cerebrospinal fluid. Types of nerve tissues - star-shaped astrocytes form tissues of gray and white matter. The properties of the nervous tissue - astrocytes and their glial membrane contribute to the creation of a blood-brain barrier: a structural-functional boundary passes between the liquid connective and nervous tissues.
Evolution of fabric
The main property of a living organism is irritability or sensitivity. The type of nervous tissue is justified by the phylogenetic position of the animal and is characterized by wide variability, becoming more complex in the process of evolution. All organisms require certain parameters of internal coordination and regulation, a proper interaction between the stimulus for homeostasis and physiological state. The nervous tissue of animals, especially multicellular ones, whose structure and functions have undergone aromorphoses, contributes to survival in the struggle for existence. In primitive hydroids, it is represented by stellate, nerve cells scattered throughout the body and connected by the thinnest processes, intertwined with each other. This type of nervous tissue is called diffuse.
The nervous system of flat and roundworms is a stem, ladder type (orthogon) consists of paired brain ganglia - clusters of nerve cells and longitudinal trunks (connectives) extending from them, interconnected by transverse commissure cords. In the rings, from the peripharyngeal ganglion, connected by strands, the abdominal nerve chain departs, in each segment of which there are two adjacent nerve nodes,connected by nerve fibers. In some soft-bodied nerve ganglia are concentrated with the formation of the brain. Instincts and orientation in space in arthropods are determined by the cephalization of the ganglia of the paired brain, the peripharyngeal nerve ring and the ventral nerve cord.
In chordates, the nervous tissue, the types of tissues of which are strongly expressed, is 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 neurocoel. In vertebrates, it differentiates into the brain and spinal cord. During the formation of the brain, swellings form at the anterior end of the tube. If the lower multicellular nervous system plays a purely connecting role, then in highly organized animals information is stored, retrieved if necessary, and also provides 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 functions of which are different in higher mammals, has undergone significant changes. This is the progressive development of the cerebral cortex and all parts of the nervous system, causing complex adaptation to environmental conditions, and the regulation of homeostasis.
Center and periphery
Departments of the nervous system are classified according to their functional and anatomical structure. The anatomical structure is similar to toponymy, where the central and peripheral nervous systems are distinguished. To the central nervousthe system includes the brain and spinal cord, and the peripheral is represented by nerves, nodes and endings. Nerves are represented by clusters of processes outside the central nervous system, covered with a common myelin sheath, and conduct electrical signals. Dendrites of sensory neurons form sensory nerves, axons form motor nerves.
The combination of long and short processes forms mixed nerves. Accumulating and concentrating, the bodies of neurons form nodes that extend beyond the central nervous system. Nerve endings are divided into receptor and effector. Dendrites, through terminal branches, convert irritations into electrical signals. And the efferent endings of axons are in the working organs, muscle fibers, and glands. Classification by functionality implies the division of the nervous system into somatic and autonomous.
Some things we control and some things we can't
The properties of the nervous tissue explain the fact that the somatic nervous system obeys the will of a person, innervating the work of the supporting system. The motor centers are located in the cerebral cortex. Autonomous, which is also called vegetative, does not depend on the will of a person. Based on your own requests, it is impossible to speed up or slow down the heartbeat or intestinal motility. Since the location of the autonomic centers is the hypothalamus, the autonomic nervous system controls the work of the heart and blood vessels, the endocrine apparatus, and abdominal organs.
Nervous tissue, the photo of which you can see above,forms the sympathetic and parasympathetic divisions of the autonomic nervous system, which allow them to act as antagonists, providing a mutually opposite effect. Excitation in one organ causes inhibition processes in another. For example, sympathetic neurons cause a strong and frequent contraction of the chambers of the heart, vasoconstriction, jumps in blood pressure, as norepinephrine is released. Parasympathetic, releasing acetylcholine, contributes to the weakening of heart rhythms, an increase in the lumen of the arteries, and a decrease in pressure. Balancing these groups of neurotransmitters normalizes the heart rate.
The sympathetic nervous system operates during times of intense tension in fear or stress. Signals arise in the region of the thoracic and lumbar vertebrae. The parasympathetic system is activated during rest and digestion of food, during sleep. The bodies of neurons are in the trunk and sacrum.
By studying in more detail the features of Purkinje cells, which are pear-shaped with many branching dendrites, it is possible to see how the impulse is transmitted and to reveal the mechanism of the successive stages of the process.
