Pain threshold - what is pain for?
The feeling of pain is one of the most important instincts, thanks to which all life on earth exists. The ability to feel pain has been shaped by natural selection over millions of years.
Pain as a factor of protection makes animals and humans avoid the threat of damage to the body, eliminate the source of unpleasant sensations and escape from danger. This feeling is vital, since its absence can lead to dramatic, fatal consequences, the main of which is death.
Today on the planet there is only one type of highly organized creatures that are not able to feel pain. These are sharks.
The most terrible predators of the ocean, killer fish, fierce creatures that sow pain and fear everywhere, sharks simply do not perceive pain, just as people do not hear ultrasound. There is an explanation for this.
Sharks don't feel pain
In 2000, an international team of ichthyologists studied pain perception in fish. Using the example of some bony and cartilaginous species, scientists have shown that fish can also suffer from pain. For example, the application of weak current discharges to Atlantic trout, cod and stingray stingray caused a protective motor reaction, that is, the fish simply tried to escape.
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When the subjects were subjected to injections with a needle, strong squeezing of the skin or cauterization, a behavioral response immediately arose - shrinking, slipping, and fleeing. In some species of fish, the effect caused vocalization, that is, they screamed in pain!
The sound was generated by the movements of the swim bladder and lasted 490 milliseconds on average.
When the researchers applied the same experiments to sharks, it turned out that the toothy monsters practically did not respond to torture. Why? Finding the answer was not easy.
Pain receptors in most fish species are found throughout the body, including the fins. During pain exposure, nerve endings transmit an impulse to the cerebral cortex, and after that a behavioral response arises.
Causes of the high pain threshold in sharks
There are families that do not have a cortex, and then the response impulse is generated by the actual peripheral nerve fibers, as, for example, in horse mackerel, or by the spinal cord (in stingrays). The developed nervous system of sharks also reads more than a million nerve endings, but they are practically absent on the thick skin-armor.
Since this fact cannot explain the resistance to pain (apart from sharks, there are more than ten thousand species of fish with a small number of pain receptors on the planet), ichthyologists decided to investigate the biochemical processes of the shark brain.
This was the answer.
In the process of their vital activity, all living things, including fish, have to constantly face situations in which they should not react to painful influences for the sake of more important biological tasks - getting food, social contacts, reproduction, preservation of offspring, etc.
The suppression of pain impulses occurs due to special substances that block pain receptors - opioid peptides. Endogenous morphines bind to opioid receptors and control the endurance limit of organisms, ensuring its stable existence in the external environment.
The level of opioid peptides in sharks is hundreds of times higher than the average amount of the same substances in other fish species. That is, the arising pain impulses never reach the cortex, since they are suppressed even at the very beginning of the biochemical chain.
Fearless adrenaline sharks
By acting similarly to exogenous morphine and codeine, the main substances of the opium poppy, opioid peptides affect not only pain perception, but in general, sexual and social behavior, the nature of the motor activity of carnivorous fish. Simply put, sharks are constantly high-powered, without pain, fear and shame.
Exposure to these substances also disinhibits the hormonal systems of the body, thus provoking an increase in hormones in the blood. Among them - adrenaline and norepinephrine - hormones of risk, fearlessness and aggression.
Large concentrations of these substances also have a significant impact on the social behavior of sharks, and as a result, a peaceful creature turns into a ferocious predator, whose only pleasure is killing. It was bull sharks who became famous for their invulnerability and bloodthirstiness in relation to people.
The feeling of pain is one of the most important instincts, thanks to which all life on earth exists. However, for those who have nothing to fear, this feeling is basically unnecessary. An evolutionary experiment that took away the ability of sharks to suffer, turned them into the strongest predators on Earth, capable of surviving both short-term adverse environmental influences and global cataclysms.
It is the perfection of the shark as an organism that allowed it to remain the ruler of the world's oceans long before the appearance of mankind and, most likely, many centuries after us.