Regulation of nervous activity is a process of excitation and inhibition in the central nervous system. Initially, it arises as an elementary reaction to stimulation. In the course of evolution there was a complication of neurohumoral functions, leading to the formation of the main parts of the nervous and endocrine systems. In this article, we will study one of the main processes - inhibition in the central nervous system, the types and mechanisms of its implementation.
Nervous tissue, its structure and functions
One of the varieties of animal tissues, called the nervous one, has a special structure that provides both the excitation process and activates the functions of inhibition in the central nervous system. Nerve cells consist of a body and processes: short (dendrites) and long (axon), which provides the transfer of nerve impulses from one neurocyte to another. The end of the axon of the nerve cell contacts the dendrites of the next neurocyte in places called synapses. They ensure the transfer of bioelectric impulses along the nerve tissue. And the excitation always moves in one direction - from the axon to the body or dendrites of another neurocyte.
Another property, except for excitation, which flows in the nervous tissue, is inhibition in the central nervous system. It is the response of the body to the action of the stimulus leading to a reduction or complete cessation of motor or secretory activity, in which centrifugal neurons participate. Braking in the nervous tissue can occur without prior stimulation, but only under the influence of the inhibitory mediator, for example, GABA. He is one of the main transmitters of inhibition. Here you can name a substance such as glycine. This amino acid is involved in the enhancement of inhibitory processes and stimulates the production of gammaaminobutyric acid molecules in synapses.
IM Sechenov and his work in neurophysiology
An outstanding Russian scientist, the creator of the theory of reflex activity of the brain, proved the presence in the central sections of the nervous system of special cell complexes capable of inactivating bioelectric processes. The discovery of centers of inhibition in the central nervous system became possible thanks to I. Sechenov's application of three types of experiments. These include: cutting sections of the cortex in different areas of the brain, stimulation of individual loci of gray matter by physical or chemical factors (electric current, sodium chloride solution), as well as the method of physiological excitation of the brain centers. IM Sechenov was an excellent experimenter, conducting superficial incisions in the zone between the visual hillocks and directly in the frog's thalamus itself. He observed a decrease and complete cessation of the motor activity of the animal's limbs.
So, a special kind of nervous process was discovered by the neurophysiologist - inhibition in the central nervous system. The types and mechanisms of its formation will be discussed in more detail in the following sections, and now we will once again focus attention on this fact: in such departments as the medulla oblongata and visual hillocks, there is a site called the inhibitory center or the "sechen" center. The scientist also proved his presence not only in mammals, but also in humans. Moreover, IM Sechenov discovered the phenomenon of tonic excitation of inhibitory centers. He understood by this process a slight excitement in centrifugal neurons and associated muscles, as well as in the nerve centers of inhibition themselves.
Do the nervous processes interact?
Studies of outstanding Russian physiologists IP Pavlov and IM Sechenov have proved that the work of the central nervous system is characterized by the coordination of the reflex reactions of the organism. The interaction of the processes of excitation and inhibition in the central nervous system leads to a coordinated regulation of the body's functions: motor activity, respiration, digestion, excretion. Bioelectric processes simultaneously occur in the nerve centers and can consistently vary in time. This ensures correlation and timely passage of response reflexes to signals of the internal and external environment. Numerous experiments conducted by neurophysiologists have confirmed the fact that excitation and inhibition in the central nervous system are key nervous phenomena, which are based on certain patterns. Let us dwell on them in more detail.
Nerve centers of the cerebral cortex are able to propagate both types of processes throughout the nervous system. This property is called irradiation of excitation or inhibition. The opposite phenomenon is the reduction or restriction of the area of the brain that propagates bioimpuls. It is called concentration. Both types of interactions are observed by scientists during the formation of conditioned motor reflexes. During the initial stage of formation of motor skills, due to the irradiation of excitation, several groups of muscles are simultaneously contracted, not necessarily participating in the performance of the motor act being formed. Only after repeated repetitions of the formed complex of physical movements (skating, skiing, bicycle), as a result of the concentration of excitation processes in specific nerve pockets of the cortex, all human movements become highly coordinated.
Switchings in the work of nerve centers can also occur due to induction. It manifests itself when the following condition is met: first, there is a concentration of inhibition or excitation, and these processes must be of sufficient strength. In science, two types of induction are known: the S-phase (central inhibition in the central nervous system enhances excitation) and a negative form (excitation causes the inhibition process). There is also a consistent induction. In this case, the nervous process changes to the opposite in the nerve center itself. Studies of neurophysiologists have proved the fact that the behavior of higher mammals and humans is determined by the phenomena of induction, irradiation and concentration of nervous processes of excitation and inhibition.
Let us consider in more detail the types of inhibition in the central nervous system and dwell on its form, which is inherent in both animals and man. The term was proposed by I. Pavlov. The scientist considered this process one of the innate properties of the nervous system and identified two of its types: dying and permanent. Let us dwell on them in more detail.
Let us assume that there is a focus of excitation in the cortex that generates impulses to the working organ (to the muscles, secretory gland cells). Due to changes in the conditions of the external or internal environment, another excited region of the cerebral cortex arises. It produces bioelectric signals of higher intensity, which inhibits the excitation in the previously active nerve center and its reflex arc. Extinguishing inhibition in the central nervous system leads to the fact that the intensity of the orienting reflex gradually decreases. The explanation for this is the following: the primary stimulus no longer causes the excitation process in the receptors of the afferent neuron.
Another kind of inhibition observed both in humans and animals is demonstrated by the experience conducted by the Nobel Prize winner in 1904 by IP Pavlov. During the feeding of the dog (with the fistula removed from the cheek), the experimenters included a sharp sound signal - the salivary discharge from the fistula ceased. This kind of braking scientist called the beyond.
Being an innate property, inhibition in the central nervous system proceeds through an unconditionally reflex mechanism. It is passive enough and does not cause a large amount of energy consumption, leading to the cessation of conditioned reflexes. Constant unconditioned inhibition accompanies many psychosomatic diseases: dyskinesia, spastic and flaccid paralysis.
What is a dying brake
Continuing to study the mechanisms of inhibition in the central nervous system, we will consider what is one of its species, called a dying brake. It is well known that the orienting reflex represents the body's reaction to the impact of a new foreign signal. In this case, a nerve center is formed in the cerebral cortex, which is in a state of excitation. It also forms a reflex arc, which is responsible for the reaction of the organism and is called the orienting reflex. This reflex act causes the inhibition of the conditioned reflex, which occurs at the moment. After repeated repetition of an extraneous stimulus, the reflex, called the orientation reflex, gradually decreases and finally disappears. So, it does not cause more inhibition of the conditioned reflex. This signal is called the dying brake.
Thus, the external inhibition of conditioned reflexes is associated with the influence of an external signal on the body and is a congenital property of the central and peripheral nervous system. A sudden or new stimulus, for example, a pain sensation, an extraneous sound, a change in illumination, not only causes an orienting reflex, but also contributes to the weakening or even complete cessation of the conditioned-reflex arc that is active at the moment. If an extraneous signal (other than the pain signal) acts repeatedly, inhibition of the conditioned reflex manifests itself less. The biological role of the unconditioned form of the nervous process consists in carrying out the body's response to the stimulus, the most important at the moment.
Its other name, used in the physiology of higher nervous activity, is conditioned inhibition. The main prerequisite for the emergence of such a process is the lack of reinforcement of signals coming from the outside world, congenital reflexes: digestive, salivary. The processes of inhibition that arise under these conditions in the central nervous system require a certain time interval. Let's consider their types in more details.
For example, differentiation inhibition occurs as a response to environmental signals, which coincide in amplitude, intensity, and strength with the conditioned stimulus. This form of interaction of the nervous system and the surrounding world allows the body to more subtly distinguish between stimuli and isolate from their totality the one that receives reinforcement by an innate reflex. For example, the sound of a bell with a strength of 15 Hz, backed by a food trough, the dog developed a conditioned salivation reaction. If another sound signal is applied to the animal, by force of 25 Hz, without backing it with food, in the first series of experiments the dog from the fistula saliva will be allocated to both conditioned stimuli. After a while, the animal will differentiate these signals, and the sound, with a force of 25 Hz, saliva from the fistula will cease to be allocated, that is, differentiation inhibition will develop.
Free the brain from information that has lost a vital role for the body - this function is just doing braking in the central nervous system. Physiology has experimentally proved that conditioned motor reactions, well fixed by the developed skills, can persist throughout the life of a person, for example, skating, cycling.
Summarizing, we can say that the processes of inhibition in the central nervous system is the weakening or cessation of certain reactions of the body. They are very important, since all the reflexes of the body are corrected in accordance with the changed conditions, and if the conditioned signal has lost its meaning, then even completely can disappear. Different types of inhibition in the central nervous system are basic for such abilities of the human psyche as the preservation of self-control, the discrimination of stimuli, and anticipation.
Delayed kind of nervous process
Experienced you can create a situation in which the response of the body to the conditioned signal from the external environment is manifested even before the action of the unconditioned stimulus, for example, food. When the time interval between the onset of the action of the conditioned signal (light, sound, for example, the metronome beats) and the moment of reinforcement to three minutes increase, the saliva is more and more delayed by the above-mentioned conditioned stimuli and manifests itself only at the moment when a feeding bowl appears before the animal. Lagging response to the conditioned signal characterizes the inhibition processes in the central nervous system, called a delayed species, in which its flow time corresponds to the lag interval of the unconditioned stimulus, for example, food.
The value of inhibition in the central nervous system
The human body, figuratively speaking, is "under the gun" of a huge number of factors of the external and internal environment, to which it is forced to react and form a multitude of reflexes. Their nerve centers and arcs form in the brain and spinal cord. The congestion of the nervous system by a huge number of excited centers in the cerebral cortex negatively affects the mental health of a person, and also reduces its efficiency.
Biological basis of human behavior
Both types of activity of the nervous tissue, both excitation and inhibition in the central nervous system, are the basis of higher nervous activity. It determines the physiological mechanisms of a person's mental activity. The teaching of higher nervous activity was formulated by IP Pavlov. Its modern interpretation is as follows:
- Excitation and inhibition in the CNS, occurring in the interaction, provide complex mental processes: memory, thinking, speech, consciousness, and also form complex behavioral reactions of a person.
To make a scientifically based mode of study, work, rest, scientists apply knowledge of the laws of higher nervous activity.
The biological significance of such an active nervous process as inhibition can be defined as follows. Changes in the conditions of the external and internal environment (the absence of reinforcement of the conditioned signal by an innate reflex) entails adequate changes in the adaptive mechanisms in the human body. Therefore, the acquired reflex act is oppressed (extinguished) or completely disappears, since it becomes inappropriate for the organism.
What is a dream?
IP Pavlov in his works experimentally proved the fact that the processes of inhibition in the central nervous system and sleep are of a unified nature. During the wakefulness of the organism against the background of the general activity of the cerebral cortex, some of its areas are covered, which are covered by internal inhibition. During sleep, it radiates across the entire surface of the cerebral hemispheres, reaching subcortical formations: visual bumps (thalamus), hypothalamus, reticular formation and limbic system. As pointed out by the outstanding neurophysiologist PK Anokhin, all the above-mentioned parts of the central nervous system, responsible for the behavioral sphere, emotions and instincts, during sleep, reduce their activity. This entails a decrease in the generation of nerve impulses coming from under the crust. Thus, the activation of the cortex is reduced. This provides an opportunity for rest and recovery of the metabolism both in brain neurocytes and in the whole organism.
Experiments of other scientists (Hess, Ekonomo) have established special complexes of nerve cells that are part of the nonspecific nuclei of the visual hillocks. Excitation processes diagnosed in them cause a decrease in the frequency of cortical biorhythms, which can be regarded as a transition from an active state (wakefulness) to sleep. Studies of such areas of the brain, as Silviev water pipe and the third ventricle, pushed scientists to the idea of a center for sleep regulation. It is anatomically linked to the area of the brain responsible for wakefulness. The defeat of this locus of the cortex due to trauma or as a result of hereditary disorders in humans leads to pathological states of insomnia. Also note the fact that the regulation of such a vital process of inhibition, like sleep, is performed by the nerve centers of the intermediate brain and subcortical nuclei: caudate, almond-shaped, fence and lenticular.