How do people feel pain and why does the body need it? We feel pain every day. It controls our behavior, shapes our habits and helps us survive. Thanks to the pain, we put on plaster on time, take sick leave, pull our hand away from the hot iron, fear dentists, run away from the wasp, sympathize with the characters in the Saw movie, and avoid the gang of hooligans.
Fish are the first organisms on Earth to feel pain. Living things evolved, became more complex, and their way of life too. And to warn them about the danger, a simple mechanism for survival appeared - pain.
Why do we feel pain?
Our body is made up of a huge number of cells. In order for them to interact, there are special proteins in the cell membrane - ion channels. With the help of them, the cell exchanges ions with another cell and contacts with the external environment. The solutions inside cells are rich in potassium but poor in sodium. Certain concentrations of these ions are maintained by a sodium-potassium pump, which pumps excess sodium ions out of the cell and replaces them with potassium.
The work of potassium-sodium pumps is so important that half of the food eaten and about a third of the oxygen inhaled goes to provide them with energy.
Ionic channels are the real gates of the senses, thanks to which we can feel warmth and cold, the scent of roses and the taste of our favorite food, and also feel pain.
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When something affects the cell membrane, the structure of the sodium channel is deformed and it opens. Due to a change in the ionic composition, electrical impulses arise that propagate through the nerve cells. Neurons consist of a cell body, dendrites and an axon - the longest process along which the impulse moves. At the end of the axon there are bubbles with a neurotransmitter, a chemical that is involved in the transmission of this impulse from a nerve cell to a muscle or other nerve cell. For example, acetylcholine transmits a signal from a nerve to a muscle, and there are many other mediators between neurons in the brain, such as glutamate and the "joy hormone" serotonin.
Cutting your finger while cooking salad - this has happened to almost everyone. But you do not go on cutting your finger, you pull your hand away. This happens because a nerve impulse runs along neurons from sensitive cells, pain detectors, to the spinal cord, where the motor nerve already transmits the command to the muscles: remove your hand! You put a band-aid on your finger, but you still feel pain: ion channels and neurotransmitters send signals to the brain. The pain signal passes through the thalamus, hypothalamus, reticular formation, areas of the midbrain and medulla oblongata.
And finally, pain reaches its destination - the sensitive areas of the cerebral cortex, where we are fully aware of it.
Life without pain
Life without pain is the dream of many people: no suffering, no fear. This is quite real, and there are people among us who do not feel pain. For example, in 1981, Stephen Peet was born in the United States, and when his teeth came out, he began to chew his tongue. Fortunately, his parents noticed this in time and took the boy to the hospital. There they were told that Stephen had a congenital insensitivity to pain. Steve's brother Christopher was soon born, and he was found to have the same thing.
Mom always told the boys: infection is a silent killer. Without knowing the pain, they could not see the symptoms of diseases in themselves. Frequent medical examinations were needed. Having no idea what pain is, the guys could fight to a pulp or, having received an open fracture, hobble with a protruding bone, without even noticing it.
Once, working with an electric saw, Steve ripped his arm from wrist to elbow, but sewed it up on his own, being too lazy to go to the doctor.
“We often skipped school because we ended up in a hospital bed with another injury. We spent more than one Christmas morning and birthday there,”says Stephen. A life without pain is not a life without suffering. Steve has severe arthritis and a sore knee - this threatens him with amputation. His younger brother Chris committed suicide after learning that he might end up in a wheelchair.
It turns out that the brothers have a defect in the SCN9A gene, which encodes the Nav1.7 protein, a sodium channel involved in pain perception. Such people distinguish cold from hot and feel touch, but the pain signal does not pass. This sensational news was published in the journal Nature in 2006. Scientists found this out by examining six Pakistani children. Among them was a magician who entertained the crowd by walking over the hot coals.
Another study published in Nature in 2013 focused on a little girl unfamiliar with the feeling of pain. German scientists at the University of Jena discovered a mutation in the SCN11A gene, which encodes the Nav1.9 protein, another sodium channel responsible for pain. Overexpression of this gene prevents the accumulation of ion charges, and the electrical impulse does not pass through the neurons - we do not feel pain.
It turns out that our heroes received their "superpower" due to the malfunction of sodium channels, which are involved in the transmission of a pain signal.
What makes us feel less pain?
When we are in pain, the body produces special "internal drugs" - endorphins, which bind to opioid receptors in the brain, dulling pain. Morphine, isolated in 1806 and renowned as an effective pain reliever, acts like endorphins - it binds to opioid receptors and inhibits neurotransmitter release and neuronal activity. When administered subcutaneously, morphine begins to act within 15–20 minutes and can last up to six hours. Only one should not get carried away with such "treatment", it can end badly, as in Bulgakov's story "Morphine". After several weeks of using morphine, the body stops producing endorphins in sufficient quantities, and dependence appears. And when the effect of the drug ends, many tactile signals that go to the brain, no longer protected by the anti-pain system,cause suffering - withdrawal occurs.
Alcoholic drinks also affect the endorphin system and increase the pain threshold. Alcohol in small doses, like endorphins, is euphoric and makes us less susceptible to being punched in the face after a wedding feast. The fact is that alcohol stimulates the synthesis of endorphins and suppresses the reuptake system of these neurotransmitters.
However, after the alcohol is removed from the body, the thresholds for pain sensitivity decrease due to the inhibition of the synthesis of endorphins and an increase in the activity of their capture, which does not alleviate the hangover typical of the next morning.
Who hurts more: men or women?
Women and men experience pain differently, according to a study by researchers at McGill University, who found that pain perception in female and male mice begins in different cells. To date, there have been a lot of studies on the nature of female and male pain, and most of them indicate that women suffer more from it than men.
In the course of a large-scale work in 2012, when scientists analyzed the records of more than 11 thousand patients of California hospitals, scientists found that women tolerate pain worse and face it more often than men. And plastic surgeons from the United States have found that women have twice as many nerve receptors per square centimeter on their face as men. Girls are already so sensitive from birth - according to a study published in the journal Pain, in newborn girls, facial reactions to injections in the foot were more pronounced than in boys. It is also known that women are more likely to complain of pain after surgery and feel worse in the dentist's chair.
Hormones come to the aid of poor women
For example, one of the female sex hormones, estradiol, decreases pain receptor activity and helps women cope with high levels of pain more easily.
For example, estradiol levels rise sharply before childbirth and acts as a kind of pain reliever. Unfortunately, after menopause, the level of this hormone in the body decreases, and women suffer more pain. By the way, men have a similar situation with testosterone. The level of this male sex hormone decreases with age, and some pain symptoms become more pronounced.
But pain is not only the transmission of nerve impulses to the brain, it is also the psychological perception of pain. For example, participants in one interesting study tripled their pain threshold after being shown how another participant calmly tolerated the same pain exposure. Boys are taught from birth to be courageous: “boys don't cry”, “you have to endure”, “it's shameful to cry”. And this makes a significant contribution: men endure pain steadily, and the brain "thinks" that it is not so painful for them.