Nervous center: properties and types

The nervous system has 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 central nervous system (CNS). It has its name - the nerve center. The properties with which it is characterized: occlusion, central relief, rhythm transformation. They and some others will be studied in this article.

The concept of the nerve center and its properties

Earlier we designated the main function of the nervous system - the integrating one. 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 (inspiration and expiration). It is located in the fourth ventricle, in the region of the reticular formation (oblong brain). According to the research of NA Mislavsky, it consists of symmetrically placed parts responsible for inhaling and exhaling.

In the upper zone of the variolium bridge is the pneumotaxic department, which regulates the above-named parts and structures of the brain responsible for respiratory movements. Thus, the general properties of nerve centers ensure the regulation of the physiological functions of the body: cardiovascular activity, secretion, respiration and digestion.

Theory of dynamic localization of functions IP Pavlova

According to the scientist, simple enough reflex actions have in the cerebral cortex, as well as in the spinal cord, stationary zones. Complex processes, such as memory, speech, thinking, are associated with certain areas of the brain and are an integrative result of the functions of many of its sites. The physiological properties of the nerve centers and cause the formation of the basic processes of higher nervous activity. In neurology, from the anatomical point of view, the parts of the central nervous system, consisting of the afferent and efferent parts of neurons, began to be called nerve centers. They, as the Russian scientist PK Anokhin thought, form functional systems (the union of neurons that perform similar functions and can be located in different parts of the central nervous system).

Irradiation of excitement

Continuing to study the basic properties of nerve centers, let us dwell on the form of the spread of the two main processes occurring in the nervous tissue - excitation and inhibition. It is called irradiation. If the strength of the stimulus and the time of its action are great, the nerve impulses diverge along the processes of the neurocytes, and also through the intercalary neurons. They combine afferent and efferent neurocytes, causing the continuity of the reflex arcs.

Consider inhibition (as a property 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 impede the spread of excitement. For example, the presence of inhibitory synapses and neurocytes. These structures perform important protective functions, as a result of which the risk of overexcitation of skeletal muscles that is capable of transitioning into convulsive state is reduced.

Having considered the irradiation of excitation, it is necessary to recall the following peculiarity of the nerve impulse. It moves only from the centripetal to the centrifugal neuron (for a two-neuron, reflex arc). If the reflex is more complex, 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, bioelectric impulses are also unidirectional: they move from the presynaptic membrane of the first nerve cell, then into the synaptic cleft, and from it into the postsynaptic membrane of another neurocyte.

Summation of nerve impulses

We continue to study the properties of nerve centers. The physiology of the main sections of the brain and spinal cord, being the most important and complex branch of medicine, studies the conduct of excitation through a set of neurons performing general functions. Their properties are summation, can be temporal or spatial. In both cases, weak nerve impulses caused by subthreshold stimuli add up (summed). This results in an abundant release of molecules of acetylcholine or another neurotransmitter, which generates an action potential in the neurocytes.

Transformation of the rhythm

This term indicates the change in the excitation frequency, which passes through the complexes of neurons of the central nervous system. Among the processes characterizing the properties of nerve centers is the transformation of the pulse rhythm, which can result from the distribution of excitation into several neurons, the long processes of which form the contact sites on one nerve cell (increasing the 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 decreasing rhythm transformation.

Divergence and convergence of excitation

They are interrelated processes characterizing the properties of nerve centers. Coordination of reflex activity is due to the fact that pulses from the receptors of various analyzers: the visual, olfactory and skin-muscular sensations come to the neurocyte at one and the same moment. In a nerve cell, they are analyzed and summed into bioelectric potentials. Those, in turn, are transferred 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 itself forms synapses with neighboring neurocytes. This phenomenon of divergence. Both properties provide propagation of excitation in the CNS. Thus, the aggregate of the nerve cells of the brain and spinal cord that perform general functions is a nerve center whose properties we are considering. It ensures the regulation of the work of all organs and systems of the human body.

Background Activity

The 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, is explained by the structural features of the nervous tissue itself. It is capable of self-generation of bioelectric excitation processes even in the absence of adequate stimuli. It is due to divergence and convergence of excitation, which we considered earlier, that neurocites receive impulses from excited nervous centers through postsynaptic connections of the same reticular formation of the brain.

Spontaneous activity can be caused by microdoses of acetylcholine, which enters 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 in both neurocytes and in neuroglia.

Types of summation of excitation

They were considered in the papers of IM Sechenov, who proved that the reflex can be induced by several weak (subthreshold) stimuli, which quite often act on the nerve center. The properties of its cells, namely: central relief and occlusion, and will be considered by us 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 an occlusion. It is the inverse property of 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 the threshold (central) zone and the subthreshold (peripheral) fringe.

Nervous tissue fatigue its role

The physiology of nerve centers, the definition, types and properties that we have already studied and inherent in neuron complexes, will be incomplete if we do not consider such a phenomenon as fatigue. Nerve centers are forced to conduct through themselves a continuous series of pulses, providing reflex properties of the central parts of the nervous system. As a result of intense metabolic processes, both in the body of the neuron and in the glia, accumulation of toxic metabolic wastes occurs. Deterioration of blood supply to nervous complexes also causes a decrease in their activity due to deficiency of oxygen and glucose. Their contribution to the development of fatigue of the nerve centers is also brought by the neuron contacts - synapses, which 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 body's activity undergo anatomical and physiological changes. They are explained by the complication of the physiological and psychological functions that arise during a person's life. The most important changes affecting the age features of the properties of nerve centers, we observe in the formation of such important processes as uprightness, speech and thinking that distinguish Homo sapiens from other representatives 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 proprioceptors of the muscles of the tongue, lips, vocal cords of the larynx and respiratory musculature. By the end of the third year of the child's life, they all combine in a functional system, which includes the cortical site, which lies at the base of the lower frontal gyrus. It was called the center of Brock.

In the formation of speech activity , the zone of the upper temporal gyrus (the Wernike center) also participates. 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.