We often get nervous, constantly filter incoming information, react to the world around us and try to listen to our own body, and amazing cells help us in all of 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 have gone very far from animals. Understanding how such a complex system works is very important not only for specialists - biologists and physicians. A person of another profession may be interested in this.
The information in this article is accessible to everyone and can benefit not only as knowledge, because understanding your body is the key to understanding yourself.
What is she responsible for
Human nervous tissue is characterized by a unique structural and functional diversity 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, you need a very complex network.
Nerve tissue, 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 body with the external environment and provides adaptive responses to its change. Thirdly, it controls the metabolism under changing conditions. All types of nerve tissue are the material component of the psyche: signaling systems - speech and thinking, behavior patterns in society. Some scientists have hypothesized that man greatly developed his mind, for which he had to “sacrifice” many animal abilities. For example, we do not have sharp eyesight and hearing, which animals can boast of.
Nerve 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 little transmitters
The cells of the nervous tissue - neurons - are structurally functional units of the nervous system. A neuron cell is characterized by a complex structure and increased functional specialization. The structure of the neuron consists of a eukaryotic body (soma), the diameter of which is 3-100 microns and processes. Neuron soma contains a nucleus and nucleolus with a biosynthesis apparatus, which forms enzymes and substances inherent in the specialized functions of neurons. These are Nissl bodies - flattened cisterns of a rough endoplasmic reticulum closely adjacent to each other, 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, chondras. The cytoskeleton, represented by neurofilaments and microtubules, plays a supporting role. In the process of loss of membrane structures, the lipofuscin pigment is synthesized, the amount of which increases with increasing age of the neuron. The pigment melatonin is formed in stem neurons. The nucleolus consists of protein and RNA, the core of DNA. The ontogenesis of the nucleolus and basophils determines the primary behavioral reactions of people, since they depend on the activity and frequency of contacts. Nerve tissue implies the main structural unit - a neuron, although there are still other types of auxiliary tissues.
Features of the structure of nerve cells
The two-membrane nucleus of neurons has pores through which waste substances penetrate and discharge. Thanks to the genetic apparatus, differentiation occurs, which determines the configuration and frequency of interactions. Another core function is to regulate protein synthesis. Ripen nerve cells cannot share mitosis, and genetically determined active products of the synthesis of each neuron must ensure functioning and homeostasis throughout the life cycle. Replacement of damaged and lost parts can only occur intracellularly. But there are exceptions. In the epithelium of the olfactory analyzer, some animal ganglia are capable of division.
Nerve cells visually differ in a variety of sizes and shapes. Irregular outlines are characteristic of neurons due to processes, often numerous and overgrown. These are the living conductors of electrical signals, through which reflex arcs are composed. Nerve 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 to other differentiated cells, is capable of providing a response. She is almost instantaneous. But some substances, including alcohol, greatly slow it down.
About axons
All types of nervous tissue function with the direct participation of the processes of dendrites and axons. Axon is translated from Greek as "axis". This is an elongated process, conducting excitation from the body to the processes of other neurons. The axon tips are highly branched, each able to interact with 5000 neurons and form up to 10 thousand contacts.
The locus of the soma, from which the axon branches, is called the axon knoll. It combines with the axon because they lack a rough endoplasmic reticulum, RNA, and an enzymatic complex.
A bit about dendrites
This cell name means "tree." Like branches, short and highly branching processes grow from the soma. They receive signals and serve as loci where synapses arise. 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 lipid nature, and its effect is similar to the insulating properties of a plastic or rubber coating of electrical wires. The point of generation of the excitation — the axon knoll — occurs at the site where the axon leaves the soma in the trigger zone.
The white matter of the ascending and descending paths in the spinal cord and brain is formed by axons, through which nerve impulses are carried out, performing a conduction function - transmission of a nerve impulse. Electrical signals are transmitted to various parts of the brain and spinal cord, making a connection between them. The executive organs in this case can connect with receptors. A gray matter forms the cerebral cortex. In the spinal canal are centers of congenital reflexes (sneezing, coughing) and autonomic centers of reflex activity of the stomach, urination, defecation. Insertion neurons, bodies and motor 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. Human nervous tissue does not contain unipolar neurons with one process. In multipolar - an abundance of dendritic trunks. This branching does not affect the speed of the signal.
Different cells - different tasks
Nerve cell functions are carried out 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 decisions by 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.
The peculiarities of nerve tissues are that neurons perform complex and jewelry work in the body, therefore, everyday primitive work - providing food, removing decay products, and the protective function is assigned to auxiliary neuroglia or supporting Schwann cells.
The process of nerve cell formation
Differentiation occurs in the cells of the neural tube and ganglion plate, which determines the characteristics of nerve tissues in two directions: large ones become neuroblasts and neurocytes. Small cells (spongioblasts) do not increase and become gliocytes. Nerve tissue, tissue types of which are composed of neurons, consists of primary and secondary. 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 neurolemmmocytes - Schwann cells. Ependymocytes line the cavities of the ventricles of the brain and the spinal canal and secrete cerebrospinal fluid. Types of nerve tissue - 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 structurally functional border passes between the fluid connective and nervous tissues.
Tissue evolution
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 complicated in the process of evolution. All organisms require certain parameters of internal coordination and regulation, the proper interaction between the stimulus for homeostasis and physiological state. The nervous tissue of animals, especially multicellular organisms, the structure and functions of which 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 finest processes intertwined. This type of nerve tissue is called diffuse.
The nervous system of the flat and round worms of the stem, staircase type (orthogon) consists of paired brain ganglia - clusters of nerve cells and longitudinal trunks (connecting lines) extending from them, connected by transverse commissures. In the annuli, the abdominal nerve chain departs from the peri-pharyngeal ganglion, connected by strands, in each segment of which there are two closely connected nerve nodes connected by nerve fibers. In some soft-bodied nerve ganglia are concentrated with the formation of the brain. Arthropod instincts and spatial orientation are determined by the cephalization of the ganglia of the paired brain, the periglottic nerve ring, and the abdominal nerve chain.
In chordates, nerve tissue, the types of tissues of which are strongly expressed, is complex in structure, 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. In vertebrates, it differentiates into the brain and spinal cord. With the formation of the brain at the front end of the tube, swellings form. 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 in higher mammals, has undergone significant changes. This is the progressive development of the cerebral cortex and all parts of the nervous system, which cause complex adaptation to environmental conditions, and the regulation of homeostasis.
Center and periphery
Departments of the nervous system are classified according to the functional and anatomical structure. The anatomical structure is similar to toponymy, where the central nervous system and peripheral are distinguished. The brain and spinal cord enter the central nervous system , 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, conduct electrical signals. Dendrites of sensitive neurons form sensitive nerves, axons - motor nerves.
The combination of long and short processes forms mixed nerves. Accumulating and concentrating, the bodies of neurons constitute nodes that extend beyond the central nervous system. Nerve endings are divided into receptor and effector. Dendrites through terminal branches transform irritations into electrical signals. And the efferent endings of axons - in the working organs, muscle fibers, glands. Classification by functionality involves the division of the nervous system into somatic and autonomous.
Something we control, but something beyond our control
The properties of the nervous tissue explain the fact that the somatic nervous system obeys the will of the 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 man. Based on our own requests, it is impossible to accelerate or slow down the heartbeat or intestinal motility. Since the location of the autonomic centers is the hypothalamus, the autonomic nervous system monitors the work of the heart and blood vessels, the endocrine apparatus, and abdominal organs.
Nerve tissue, the photo of which you can see above, forms the sympathetic and parasympathetic parts of the autonomic nervous system, which allow them to act as antagonists, exerting 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 heart chambers, narrowing of blood vessels, jumps in blood pressure, as noradrenaline is released. Parasympathetics, releasing acetylcholine, helps to weaken the rhythms of the heart, increase the lumen of the arteries, lower the pressure. Balancing these groups of mediators normalizes heart rate.
The sympathetic nervous system acts during intense tension with fear or stress. Signals occur in the area of the thoracic and lumbar vertebrae. The parasympathetic system is activated during rest and digestion of food, in the process of 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 shape with many branching dendrites, you can see how the impulse is transmitted and reveal the mechanism of successive stages of the process.