Regulation of nervous activity is a process of excitation and inhibition in the central nervous system. Initially, it occurs as an elementary reaction to irritation. In the process of evolution, neurohumoral functions became more complex, leading to the formation of the main divisions 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 nervous, has a special structure that provides both the process of excitation and actuates the functions of inhibition in the central nervous system. Nerve cells consist of a body and processes: short (dendrites) and long (axon), which ensures the transmission of nerve impulses from one neurocyte to another. The end of the axon of a nerve cell contacts the dendrites of the next neurocyte at places called synapses. They provide the transmission of bioelectric impulses through the nervous tissue. And the excitementalways moves in one direction - from the axon to the body or dendrites of another neurocyte.
One more property, in addition to excitation, occurring in the nervous tissue, is inhibition in the central nervous system. It is a response of the body to the action of an irritant, leading to a decrease or complete cessation of motor or secretory activity, in which centrifugal neurons participate. Inhibition in the nervous tissue can also occur without prior excitation, but only under the influence of an inhibitory mediator, such as GABA. It is one of the main transmitters of braking. Here you can also name such a substance as glycine. This amino acid is involved in enhancing inhibitory processes and stimulates the production of gamma-aminobutyric acid molecules in synapses.
I. M. 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 parts 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 the use of three types of experiments by I. Sechenov. 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 brain centers. I. M. Sechenov was an excellent experimenter, making ultra-precise cuts in the area between the visual tubercles and directly inthe frog thalamus itself. He observed a decrease and complete cessation of the motor activity of the limbs of the animal.
Thus, a neurophysiologist discovered a special type of nervous process - inhibition in the central nervous system. We will consider the types and mechanisms of its formation in more detail in the following sections, and now we will once again focus on this fact: in such departments as the medulla oblongata and visual tubercles, there is a site called the inhibitory, or "Sechenov" center. The scientist also proved its presence not only in mammals, but also in humans. Moreover, I. M. Sechenov discovered the phenomenon of tonic excitation of inhibitory centers. He understood by this process a slight excitation in the centrifugal neurons and the muscles associated with them, as well as in the nerve centers of inhibition themselves.
Do neural processes interact?
Research by prominent Russian physiologists I. P. Pavlov and I. M. Sechenov proved that the work of the central nervous system is characterized by the coordination of reflex reactions of the body. The interaction of the processes of excitation and inhibition in the central nervous system leads to a coordinated regulation of body functions: motor activity, respiration, digestion, excretion. Bioelectrical processes simultaneously occur in the nerve centers and can consistently change over time. This ensures the correlation and timely passage of response reflexes to signals from the internal and external environment. Numerous experiments conducted by neurophysiologists have confirmed the fact that excitation and inhibition in the central nervous system arekey nervous phenomena, which are based on certain regularities. Let's dwell on them in more detail.
Nerve centers of the cerebral cortex are able to distribute both types of processes throughout the nervous system. This property is called irradiation of excitation or inhibition. The opposite phenomenon is a reduction or limitation of the area of the brain that propagates bio-impulses. It's called concentration. Scientists observe both types of interactions during the formation of conditioned motor reflexes. During the initial stage of the formation of motor skills, due to the irradiation of excitation, several muscle groups simultaneously contract, 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, cycling), as a result of the concentration of excitation processes in specific nerve foci of the cortex, all human movements become highly coordinated.
Switching 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: S-phase (central inhibition in the central nervous system enhances excitation) and negative form (excitation causes the process of inhibition). There is also sequential induction. In this case, the nervous process is reversed in the nerve center itself. Researchneurophysiologists 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.
Unconditional inhibition
Let's 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 humans. The term itself was proposed by I. Pavlov. The scientist considered this process to be one of the innate properties of the nervous system and singled out two types of it: fading and constant. Let's dwell on them in more detail.
Assume that there is a focus of excitation in the cortex that generates impulses to the working organ (muscles, secretory cells of the glands). Due to changes in the conditions of the external or internal environment, another excited area of the cerebral cortex arises. It produces bioelectrical signals of greater intensity, which inhibits excitation in the previously active nerve center and its reflex arc. Fading inhibition in the central nervous system leads to the fact that the intensity of the orientation reflex gradually decreases. The explanation for this is as follows: the primary stimulus no longer causes the process of excitation in the receptors of the afferent neuron.
Another kind of inhibition, observed both in humans and in animals, is demonstrated by the experiment conducted by the Nobel Prize winner in 1904 IP Pavlov. While feeding the dog (with the fistula removed from the cheek), the experimenters turned on a sharp sound signal - the release of saliva from the fistula stopped. The scientist called this type of inhibition transcendental.
Being an innate property, inhibition in the central nervous systemproceeds by an unconditional reflex mechanism. It is quite passive and does not cause the consumption of a large amount of energy, leading to the cessation of conditioned reflexes. Constant unconditional inhibition accompanies many psychosomatic diseases: dyskinesias, spastic and flaccid paralysis.
What is a fading brake
Continuing to study the mechanisms of inhibition in the central nervous system, let's consider what is one of its types, called an extinguishing brake. It is well known that the orienting reflex is the body's reaction to the impact of a new extraneous signal. In this case, a nerve center is formed in the cerebral cortex, which is in a state of excitation. It forms a reflex arc, which is responsible for the reaction of the body and is called the orientation reflex. This reflex act causes inhibition of the conditioned reflex that is taking place at the moment. After repeated repetition of an extraneous stimulus, the reflex, called indicative, gradually decreases and finally disappears. This means that it no longer causes inhibition of the conditioned reflex. This signal is called the fading brake.
Thus, external inhibition of conditioned reflexes is associated with the influence of an extraneous signal on the body and is an innate 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 conditionedreflex arc that is currently active. If an extraneous signal (except for pain) acts repeatedly, inhibition of the conditioned reflex manifests itself less. The biological role of the unconditional form of the nervous process is to carry out the body's response to the stimulus, the most important at the moment.
Internal braking
Its another 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 with innate reflexes: digestive, salivary. The processes of inhibition in the central nervous system that have arisen under these conditions require a certain time interval. Consider their types in more detail.
For example, differential inhibition occurs as a response to environmental signals that match in amplitude, intensity and strength to the conditioned stimulus. This form of interaction between 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, to the sound of a call with a strength of 15 Hz, supported by a feeder with food, the dog developed a conditioned salivary reaction. If another sound signal is applied to the animal, with a strength of 25 Hz, without reinforcing it with food, in the first series of experiments in a dog, saliva will be released from the fistula to both conditioned stimuli. After some time, the animal will differentiate these signals, and the sound, with a force of 25 Hz, will stop salivating from the fistula, that is,differential inhibition will develop.
Free the brain from information that has lost its vital role for the body - this function is precisely performed by inhibition in the central nervous system. Physiology has empirically proven that conditioned motor responses, well fixed by developed skills, can persist throughout a person's life, for example, skating, cycling.
Summing up, 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 of great importance, since all reflexes of the body are corrected in accordance with the changed conditions, and if the conditioned signal has lost its value, then they can even completely disappear. Various types of inhibition in the central nervous system are basic for such abilities of the human psyche as maintaining self-control, distinguishing stimuli, and expectation.
Delayed view of the nervous process
Empirically, you can create a situation in which the body's response to a conditioned signal from the external environment manifests itself even before exposure to an unconditioned stimulus, such as food. With an increase in the time interval between the onset of exposure to a conditioned signal (light, sound, for example, metronome beats) and the moment of reinforcement up to three minutes, the release of saliva to the above conditioned stimuli is more and more delayed and manifests itself only at the moment when a feeder with food appears in front of the animal. The delay in response to a conditioned signal characterizes the processes of inhibition in the central nervous system, called delayeda form in which its flow time corresponds to the delay interval of an unconditioned stimulus, such as 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 many reflexes. Their nerve centers and arcs are formed in the brain and spinal cord. The overload of the nervous system with a huge number of excited centers in the cerebral cortex negatively affects the mental he alth of a person, and also reduces his performance.
Biological basis of human behavior
Both types of activity of the nervous tissue, both excitation and inhibition in the CNS, are the basis of higher nervous activity. It determines the physiological mechanisms of human mental activity. The doctrine of higher nervous activity was formulated by IP Pavlov. Its modern interpretation is as follows:
Excitation and inhibition in the central nervous system, occurring in interaction, provide complex mental processes: memory, thinking, speech, consciousness, and also form complex human behavioral reactions
To compose a scientifically grounded mode of study, work, rest, scientists apply the knowledge of the laws of higher nervous activity.
The biological significance of such an active nervous process as inhibition can be determined as follows. Changes in the conditions of the external and internal environment (lack of reinforcementconditioned signal by an innate reflex) entails adequate changes in the adaptive mechanisms in the human body. Therefore, the acquired reflex act is inhibited (extinguishes) or disappears altogether, as it becomes inappropriate for the body.
What is sleep?
I. P. Pavlov in his works experimentally proved the fact that the processes of inhibition in the central nervous system and sleep are of the same nature. During the period of wakefulness of the body, against the background of the general activity of the cerebral cortex, its individual sections covered by internal inhibition are still diagnosed. During sleep, it radiates over the entire surface of the cerebral hemispheres, reaching the subcortical formations: visual tubercles (thalamus), hypothalamus, reticular formation and limbic system. As the outstanding neurophysiologist P. K. Anokhin pointed out, all of the above parts of the central nervous system, responsible for the behavioral sphere, emotions and instincts, reduce their activity during sleep. This entails a decrease in the generation of nerve impulses coming from under the cortex. Thus, the activation of the cortex is reduced. This provides the possibility of rest and restoration of metabolism both in the neurocytes of the large brain and throughout the body as a whole.
Experiences of other scientists (Hess, Economo) established special complexes of nerve cells included in the non-specific nuclei of the visual tubercles. 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(waking) to sleep. Studies of such parts of the brain as the aqueduct of Sylvius and the third ventricle prompted scientists to the idea of a sleep regulation center. It is anatomically related to the part 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 conditions of insomnia. We also note the fact that the regulation of such a vitally important process of inhibition for the body as sleep is carried out by the nerve centers of the diencephalon and subcortical nuclei: caudate, almond-shaped, fence and lenticular.
