The nervous system plays a leading role in ensuring the integrity of the body, as well as in its regulation. These processes are carried out by an anatomical and physiological complex, including the departments of the central nervous system (central nervous system). It has its own name - the nerve center. The properties it is characterized by: occlusion, central relief, rhythm transformation. These and some others will be explored in this article.
The concept of the nerve center and its properties
Earlier, we identified the main function of the nervous system - integrating. It is possible due to the structures of the brain and spinal cord. For example, the respiratory nerve center, the properties of which are the innervation of respiratory movements (inhalation and exhalation). It is located in the fourth ventricle, in the region of the reticular formation (medulla oblongata). According to the research of N. A. Mislavsky, it consists of symmetrically placed parts responsible for inhalation and exhalation.
In the upper zone of the pons there is a pneumotaxic department that regulates the above-mentioned parts and structures of the brain responsible for respiratory movements. SoThus, the general properties of the nerve centers ensure the regulation of the physiological functions of the body: cardiovascular activity, excretion, respiration and digestion.
Theory of dynamic localization of functions by I. P. Pavlov
According to the views of the scientist, rather simple reflex actions have stationary zones in the cerebral cortex, as well as in the spinal cord. Complex processes, such as memory, speech, thinking, are associated with certain areas of the brain and are the integrative result of the functions of many of its areas. The physiological properties of the nerve centers determine the formation of the main processes of higher nervous activity. In neurology, from an anatomical point of view, sections of the central nervous system, consisting of the afferent and efferent parts of neurons, began to be called nerve centers. They, according to the Russian scientist P. K. Anokhin, form functional systems (a combination of neurons that perform similar functions and can be located in different parts of the central nervous system).
Irradiation of excitation
Continuing to study the basic properties of the nerve centers, let us dwell on the form of distribution of the two main processes occurring in the nervous tissue - excitation and inhibition. It's called irradiation. If the strength of the stimulus and the time of its action are large, the nerve impulses diverge through the processes of neurocytes, as well as through the intercalary neurons. They unite afferent and efferent neurocytes, causing the continuity of reflex arcs.
Consider braking (asproperty of nerve centers) in more detail. The reticular formation of the brain provides both irradiation and other properties of the nerve centers. Physiology explains the reasons that limit or prevent the spread of excitation. For example, the presence of inhibitory synapses and neurocytes. These structures perform important protective functions, thereby reducing the risk of overexcitation of the skeletal muscles, which can go into a convulsive state.
Having considered the irradiation of excitation, you need to remember the following feature of the nerve impulse. It moves only from centripetal to centrifugal neuron (for a two-neuron, reflex arc). If the reflex is more complex, then interneurons are formed in the brain or spinal cord - intercalary nerve cells. They receive excitation from the afferent neurocyte and then transmit it to the motor nerve cells. In synapses, bioelectrical impulses are also unidirectional: they move from the presynaptic membrane of the first nerve cell, then to the synaptic cleft, and from it to the postsynaptic membrane of another neurocyte.
Summation of nerve impulses
Let's continue to study the properties of nerve centers. The physiology of the main parts of the brain and spinal cord, being the most important and complex branch of medicine, studies the conduction of excitation through a set of neurons that perform common functions. Their properties are summation, it can be temporal or spatial. In both cases, weak nerve impulses caused by subthreshold stimuliadd up (combine). This results in a copious release of acetylcholine molecules or another neurotransmitter, which generates an action potential in neurocytes.
Rhythm transformation
This term refers to a change in the frequency of excitation that passes through the complexes of CNS neurons. Among the processes that characterize the properties of nerve centers is the transformation of the rhythm of impulses, which can occur as a result of the distribution of excitation to several neurons, the long processes of which form contact points on one nerve cell (increasing transformation). If a single action potential appears in the neurocyte, as a result of the summation of the excitation of the postsynaptic potential, they speak of a downward transformation of the rhythm.
Divergence and Convergence of Excitation
They are interconnected processes that characterize the properties of the nerve centers. The coordination of reflex activity occurs due to the fact that the neurocyte simultaneously receives impulses from the receptors of various analyzers: visual, olfactory and musculoskeletal sensitivity. In the nerve cell, they are analyzed and summarized into bioelectric potentials. Those, in turn, are transmitted to other parts of the reticular formation of the brain. This important process is called convergence.
However, each neuron not only receives impulses from other cells, but also forms synapses with neighboring neurocytes. This phenomenondivergence. Both properties ensure the spread of excitation in the central nervous system. Thus, the totality of nerve cells of the brain and spinal cord that perform common functions is the nerve center, the properties of which we are considering. It provides regulation of the work of all organs and systems of the human body.
Background activity
Physiological properties of nerve centers, one of which is spontaneous, that is, the background formation of electrical impulses by neurons, for example, the respiratory or digestive center, are explained by the structural features of the nervous tissue itself. It is capable of self-generation of bioelectric processes of excitation even in the absence of adequate stimuli. It is due to the divergence and convergence of excitation, discussed earlier, that neurocytes receive impulses from excited nerve centers through postsynaptic connections of the same reticular formation of the brain.
Spontaneous activity can be caused by microdoses of acetylcholine entering the neurocyte from the synaptic cleft. Convergence, divergence, background activity, as well as other properties of the nerve center and their characteristics directly depend on the level of metabolism both in neurocytes and in neuroglia.
Types of excitation summation
They were considered in the works of I. M. Sechenov, who proved that the reflex can be caused by several weak (subthreshold) stimuli, which quite often act on the nerve center. The properties of its cells, namely: the centralrelief and occlusion, and will be discussed further.
With simultaneous stimulation of the centripetal processes, the response is greater than the arithmetic sum of the strength of the stimuli acting on each of these fibers. This property is called central relief. If the action of pessimal stimuli, regardless of their strength and frequency, causes a decrease in the response, this is occlusion. It is the inverse property of the summation of excitation and leads to a decrease in the strength of nerve impulses. Thus, the properties of nerve centers - central relief, occlusion - depend on the structure of the synaptic apparatus, consisting of a threshold (central) zone and a subthreshold (peripheral) border.
Fatigue of the nervous tissue its role
Physiology of nerve centers, definition, types and properties, already studied by us earlier and inherent in complexes of neurons, will be incomplete if we do not consider such a phenomenon as fatigue. The nerve centers are forced to conduct continuous series of impulses through themselves, providing the reflex properties of the central parts of the nervous system. As a result of intense metabolic processes, carried out both in the body of the neuron and in the glia, there is an accumulation of toxic metabolic wastes. The deterioration of the blood supply to the nerve complexes also causes a decrease in their activity due to a lack of oxygen and glucose. The sites of neuron contacts, synapses, also contribute to the development of fatigue of nerve centers.rapidly reduce the release of neurotransmitters into the synaptic cleft.
Genesis of nerve centers
Complexes of neurocytes located in the central nervous system and performing a coordinating role in the activity of the body undergo anatomical and physiological changes. They are explained by the complication of physiological and psychological functions that arise during a person's life. We observe the most important changes affecting the age-related features of the properties of nerve centers in the formation of such important processes as bipedalism, speech and thinking, which distinguish Homo sapiens from other members of the mammalian class. For example, the formation of speech occurs in the first three years of a child's life. Being a complex conglomerate of conditioned reflexes, it is formed on the basis of stimuli perceived by the proprioreceptors of the muscles of the tongue, lips, vocal cords of the larynx and respiratory muscles. By the end of the third year of a child's life, all of them are combined into a functional system, which includes a section of the cortex that lies at the base of the inferior frontal gyrus. It has been called Broca's center.
The zone of the superior temporal gyrus (Wernicke's center) also takes part in the formation of speech activity. Excitation from the nerve endings of the speech apparatus enters the motor, visual and auditory centers of the cerebral cortex, where speech centers are formed.
