An international team of scientists has established the existence in the rat body of a system of a kind of "mini-brains" capable of suppressing the feeling of pain by blocking the excitation of individual neurons. If it can be confirmed that similar mechanisms exist in the human body, this will lead to the creation of new effective pain relievers.
Modern concepts say that the sensation of pain occurs when the central nervous system (spinal cord and brain) perceives certain signals. However, in a new study, scientists were able to prove that the peripheral nervous system plays an important role in this process.
The peripheral nervous system includes the cranial nerves that branch out from the brain, as well as the spinal or spinal nerves that originate in the spine. One of the main tasks of the peripheral nervous system is to provide communication between the body and the outside world. The main role in this process belongs to sensory neurons, which are called afferent. They transmit information to the central nervous system from receptors located in the sense organs.
At the same time, the body also contains specialized neurons or nociceptors, which are activated only when stimuli can damage or damage the tissues of the human body. They are located in internal organs or in the skin and are activated when the external influence exceeds a certain threshold of excitability. After receiving a signal of a dangerous effect from nociceptors, the central nervous system processes this signal and triggers somatic, autonomic and behavioral responses that provide adaptive responses to pain stimuli.
Pain impulses are carried by sensory neurons to a specific part of the brain called the thalamus. This is a kind of staging post in which the process of redistribution of information that comes from the senses takes place. The thalamus contains several nuclei. In the event that information about pain, before entering the sensory cortex of the cerebral hemispheres, enters specific sensory nuclei, and then a person can determine exactly where he is in pain. In the event that information passes through non-specific nuclei, the pain is dull and poorly localized.
The impulses enter specific sensory nuclei through myelin fibers, and into nonspecific ones, respectively, through nonmyelin fibers. The first method was named neospinothalamic and it is younger in terms of evolution.
In one of the specialized scientific publications in 1965, the work of the Canadian psychologist Ronald Melzak was published in co-authorship with the neuroscientist Patrick Wall. In the article, the authors tried to formulate a theory of control gates. According to scientists, the impulse is transmitted by sensory neurons of the spinal cord not only to cells that lead to the thalamus, but also to inhibitory neurons, which prevent the signal from moving further. In the event that the strength of the pain impulse is powerful enough, inhibitory neurons are blocked, and the signal enters the brain. At the same time, the excitation of these neurons occurs in the case of receiving other types of impulses by touch, vibration or pressure. The more a person feels pressure or touch, the more the pain dulls.
In the peripheral nervous system, similar logic circuits exist. Certain parts of the spinal cord include not only C and Aδ fibers, but also Aβ-fibers that conduct non-painful impulses. They block the functions of nociceptors, preventing signals from passing further, or everything happens exactly the opposite. Control gate theory thus explains how pain sensations can be reduced. For example, if you rub a bruised place, then the discomfort dulls. Anesthetic electrical stimulation is based on this principle, which is carried out using electrodes.
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In addition, Melzak suggested that the brain itself is able to control the feeling of pain. Due to the activation of the sylvian aqueduct, analgesia occurs, which provokes the activation of the descending nerve pathways, which suppress the excitation of nociceptors in the spinal cord. The brain can determine which pain impulses to respond to and which can be ignored.
In a new study, published relatively recently, scientists tried to prove that nerve nodes in the peripheral system can also control the transmission of pain impulses. These nodes, called ganglia of the peripheral system, are clusters of neurons that perform specific functions, in this case, sensory ones. Researchers have found that in the ganglia, nerve cells are involved in the synthesis of proteins necessary for the synthesis of a special amino acid GABA.
γ-Aminobutyric acid or GABA is the most important neurotransmitter of the central nervous system, which performs the function of inhibition. When this acid hits the site of contact of neurons, impulse blocking occurs between these cells. It was previously believed that this acid is characteristic only of the central nervous system, but now it has become obvious that it also performs neurotransmitter functions in the peripheral nervous system. As Nikita Gamper notes, ganglia are a kind of “mini-brains” that decide whether to send pain signals further to the brain or block them.
Studies in rats have shown that aminobutyric acid dramatically reduces the level of inflammatory and neuropathic pain. However, it remains unclear whether something similar exists in the human body. If such a system exists, it will allow scientists to apply it in the development of new pain relieving drugs.