The nervous system is a complex network of structures that permeate the system and provide self-regulation of its vital activity due to the ability to respond to external and internal influences. The main functions of the nervous system are receiving, storing, and processing information from the external and internal environment, regulation, and coordination of all organs and organ systems. In humans, as in all mammals, the nervous system includes three components:
- nerve cells (neurons);
- associated glial cells, neuroglia cells, as well as cells that form neurilemma;
- connective tissue.
Neurons carrying nerve impulses; trophic functions of neuroglia both in the brain and in the spinal cord, neurilemma, consisting mainly of operators, the so-called. Schwann cells, participate in the formation of the sheaths of the fibers of the peripheral nerves; connective tissue supports and connects various parts of the nervous system.
General characteristics of the nervous system
One of the functions of the nervous system is the perception of various signals (stimuli) of the external and internal environment of the body. Let’s remind, any cells can perceive various signals from the environment of existence with the help of specialized cellular receptors. However, they are not adapted to the perception of a number of vital signals and cannot instantly transmit information to other cells, which function as regulators of the body’s integral adequate responses.
Exposure to stimuli is perceived by specialized sensory receptors. Examples of such stimuli include:
- mechanical influences (gravity, pressure changes, vibration, acceleration, compression, tension);
- signals of a complex nature (color, complex sounds, word).
In order to assess the biological significance of the perceived signals and organize an adequate response to them in the receptors of the nervous system, they are converted – they create a universal form of signals understandable to the nervous system – into nerve impulses, conductive, from which they must be analyzed along nerve fibers and paths to nerve centers.
Signals and the results of their analysis are used by the nervous system to organize a reaction to changes in the external or internal environment, to regulate and coordinate the functions of cells and supracellular structures of the body. Such responses are carried out by the effector organs. The most frequent variants of responses to stimuli are motor reactions of skeletal or smooth muscles, changes in the secretion of epithelial (exocrine, endocrine) cells initiated by the nervous system. Taking a direct part in the formation of responses to changes in the environment of existence, the nervous system performs the functions of regulating homeostasis, ensuring the functional interaction of organs and tissues and their integration into a single whole organism.
Thanks to the nervous system, an adequate interaction of the body with the environment are carried out not only through the organization of response reactions by the effector systems but also through its own mental reactions:
- higher cognitive and creative processes.
The human brain contains over 100 billion nerve cells (neurons). Clusters of nerve cells that perform or control the same functions form nerve centers in the central nervous system. The structures of the brain, represented by the bodies of neurons, form the gray matter of the central nervous system, and the processes of these cells, combining into pathways, form a white matter. In addition, the glial cells that form the neuroglia are a structural part of the central nervous system. The number of glial cells is about 10 times the number of neurons, and these cells make up most of the mass of the central nervous system.
The structure of the nervous system
The nervous system is divided into several sections, primarily into the peripheral and central. The peripheral nervous system (its very name suggests that it serves the peripheral regions of the body) is subdivided into the somatic and autonomic nervous systems. The voluntary movements of the muscles in the body are controlled by the somatic nervous system. The vegetative (autonomic) nervous system is associated with the control of the involuntary functions of the body. It consists of two antagonistic divisions:
- The sympathetic nervous system, when there is intense work or the body is in a stressful situation, stimulates the expenditure of energy.
- The parasympathetic nervous system is responsible for ensuring that the body accumulates and restores energy reserves during sleep, and rest.
The central nervous system consists of the spinal cord and brain, which are actually a collection of several different structures. The spinal cord, protected by the spine, serves as a conductor of impulses from bottom to top and top to bottom, i.e. connects the brain with the peripheral nervous system. In addition, at the level of the spinal cord, the simplest unconditioned reflexes (for example, the knee) are closed.
Nervous system functions
Central nervous system functions.
- Large hemispheres. Carries out higher nervous activity (thinking, speech, the second signaling system, memory, imagination, the ability to write, read). Communication with the external environment occurs with the help of analyzers located in the occipital lobe (visual zone), in the temporal lobe (auditory zone), along the central sulcus (musculocutaneous zone), and on the inner surface of the cortex (gustatory and olfactory zone). Regulates the work of the whole organism through the peripheral nervous system.
- Cerebellum. Muscle tone regulates and coordinates body movements. Carries out the unconditional reflex activity (centers of congenital reflexes).
- Brain stem. Connects the brain with the spinal cord into a single central nervous system. In the medulla oblongata, there are centers: respiratory, digestive, cardiovascular. The bridge connects both halves of the cerebellum. The midbrain controls reactions to external stimuli, muscle tone (tension). The diencephalon regulates metabolism, body temperature, connects body receptors with the cerebral cortex.
- Spinal cord. Functions under the control of the brain. Arcs of unconditioned (innate) reflexes pass through it, carrying out excitation and inhibition during movement. The pathways are white matter that connects the brain to the spinal cord; is a conductor of nerve impulses. It regulates the work of internal organs through the peripheral nervous system. The spinal nerves are used to control voluntary body movements.
Peripheral nervous system functions.
- Cranial nerves. Provide the body’s connection with the external environment, quick reactions to its change, orientation in space, body movements (purposeful), sensitivity, hearing, smell, touch, taste, facial expressions, speech. The activity is carried out under the control of the brain.
- Spinal nerves. They carry out movements with all parts of the body, limbs, determine the sensitivity of the skin. Skeletal muscles innervate, causing voluntary and involuntary movement. Voluntary movements are carried out under the control of the brain, involuntary movements under the control of the spinal cord (spinal reflexes)
- Sympathetic nerves. They innervate internal organs. The postnodal ones exist as part of the mixed nerve from the spinal cord and pass to the internal organs. Nerves form plexuses – solar, pulmonary, cardia – stimulate the work of the heart, sweat glands, metabolism. They slow down the activity of the digestive tract, constrict blood vessels, relax the walls of the bladder, dilate the pupils, etc.
- Parasympathetic nerves. Innervate the internal organs, exerting an influence on the opposite to the action of the sympathetic nervous system. The largest nerve is the vagus nerve. Its branches are located in many internal organs – the heart, blood vessels, stomach, since the nodes of this nerve are located there.
The main functions of the nervous system are the control of the activity of various organs and apparatuses that make up the whole organism, the implementation of the connection of the organism, depending on the state of the external and internal environment. It also coordinates the processes of metabolism, blood circulation, lymph drainage, which in turn affect the functions of the nervous system.
A person has two different, but interconnected systems of coordination – nervous and endocrine. The nervous system acts very quickly, its effects are clearly localized, and its activity is based on electrical and chemical transmission. The endocrine system acts more slowly, its effects are diffuse, and its action is based on chemical signal transmission through the circulatory system.
The nervous system regulates relations with the external environment and body functions. Provides adaptation of the body to the effects of the external environment and the implementation of its reactions in general. The irritation received by the receptor causes a nerve impulse that is processed in the central nervous system and transmitted to the working organ. The nervous system regulates the activity of various organs and tissues, adapting their work to changing conditions both at certain times and throughout the life of the organism.