Even if the feeling of "pain" may be unpleasant, it is absolutely indispensable for the purpose of life itself and for a good health. It seems an absolute contradiction: to feel good you have to feel bad.
"Pain" by Nick Youngson CC BY-SA 3.0 Alpha Stock Images
The pain, as most of our biological functions, is a mechanism that has evolved and perfected over the millennia of our existence just to safeguard us from numerous dangers.
Pain 101
Although we all know the feeling of pain, only few of us know that the mechanism behind it, it's extremely complex and it's highly regulated. We can describe "pain" as an unpleasant feeling, but it's way more that this: it signal to our conscience that something "is not ok". It is not a "defect" of human being, but one of the most important alarm systems that our body has. Our body perceives pain through receptors (nociceptors) located in some tissues, the most important (and most extensive) is skin that allow us to interact with the outside world. Nociceptors are also present in the muscles, joints and some membranes (serous) that cover the organs of our body. These receptors consists in nerve cells that are highly specialized in responding to particular types of stimuli. Without going too much into detail, the nociceptors can respond to mechanical, thermal and chemical stimuli; in order to get activated and transmit signals to the brain, the stimulus must be of a certain intensity or involve different nociceptors at the same time. Once an appropriate stimulus activate these nerve cells, an electrical impulse is transmitted via the spinal cord to reach the nuclei of thalamus and from there to the brain, in an specific area dedicated to reception and processing of painful stimuli (postcentral convolution or primary somatosensory cortex). In reality, the pain circuit is much more complex than that: in the brain, there are numerous connections between the primary somatosensory area, the secondary somatosensory are and the limbic system, which is dedicated to the processing of memories and feelings. For this reason, a painful sensation can be amplified if it associated to our fear or if it's charged by a strong bad emotion; on the other hand if we are distracted by something else, we feel the pain with some delay, as we can see in the TV shows where the hero on duty realizes that he was wounded by a bullet only at the end of a firefight.
Pain: why does it even exists?
Our body is a formidable machine: resistant, agile, able to protect our internal organs and with some regenerative capacities. Why something so perfectly made, does offer us such a bad sensation as pain? Let's do a little imaginary experiment. Let's consider an extremely long nail, which goes through the center of our body very gradually. This is a bit "macabre", but that gives a good idea on how we are made and why pain is so essential to us.
First, we feel a simple pinch as soon as the nail hit our skin. We have injured the most superficial layers of our skin, not a big deal: our regenerative capacity will repair the damage in a few hours. Proceeding deeper with the nail, we begin to bleed, we feel a warm sensation and a more intense pain: we are in the subcutaneous layer, which is rich in blood vessels that bring nourishment to both the most superficial and deeper layers of our skin. The damage at this level begins to be tangible: the formation of new blood vessels can take hours and this kind of damage can trigger a severe infectious process that can compromise the whole organism. If we go deeper, the nail will then touches the muscles: the pain that was previously punctiform, begins to be wider and less defined and the bleeding becomes way more conspicuous due to the abundance of blood vessels in the muscles. The damage in this case can be repaired over a period of months, sometimes leaving permanent dysfunctions. The pain at this point, is much more intense and almost unbearable. However, as we go deeper, the pain feeling changes: when the damage is to the internal organs, the pain is felt as deep, badly localizable, intense but in some ways more bearable. Our body begins to give us other warning signs: the blood vessels contract, the blood pressure is altered, we start to sweat, to agitate and to be confused. The journey of our nail ends at the level of the spinal cord, which is made by the nerve cells responsible for the transfer of informations from the periphery of the body to the brain. At this point, the pain just disappear because we have damaged the main conduction system of painful information (and not only). Now, you have a severe damage all over your body but you feel no pain: are you starting to get the point?
I do not know if you got it by example above, but the truth is that pain serves as a defense mechanism to external harmful stimuli. When we feel the pin that touches us, the initial nuisance makes us react in a reflexive manner, leading us to move away from the source of the damage. In fact, the pain is a spy system of damage that is happening in our body: the more it is intense, the more we quickly adapt to flee from the harmful stimulus: this is why the pain is more precise on the superficial layers of our body, so we can quickly locate its source.
When not experiencing pain it is lethal: analgesic syndromes
CIPA (Congenital Insensitivity to Pain with Anhidrosis) is a very rare condition of natural analgesia (pain suppression): a pathology in which the patient is immune to pain and does not feel neither cold nor hot. The etiology of CIPA is a very rare autosomal recessive mutation of the NTRK1 gene, which codes for a protein essential for the proper functioning of sensory neurons, which just do not work in these patients. The literature on the subject is extremely poor: just about 100 publications for a disease that affects less than 500 people worldwide (mostly in Japan). What seems a very happy life without pain is actually a real nightmare: children with CIPA generally do not survive infancy and there are only few cases of those arriving in the adulthood. Death usually occurs due to hyperthermia, recurrent infections or internal bleeding. Children affected by CIPA can face severe falls, break bones or get head damage without having any symptoms until it is too late; they die from hyperthermia because they can not sweat to expel excess heat. The most devastating symptom, however, are the self-mutilations: without pain, babies just gnaw their fingers or toes to completely detach them: this is why they are often removed all the milk teeth.
There are no therapies for this disease given the extremely small number of cases to be studied (moreover, almost all cases are about children). The only possible approaches are to control all the activities of the child, preventing him from performing too dangerous activities and continuously monitor the temperature to prevent hypo and hyperthermia.
Another recently discovered analgesic syndrome is entirely Italian: the Marsili Syndrome, from the name of the affected family. Also in this case, it is a mutation of a gene, * ZFHX2 *, which regulates the transcription of genes involved in the sensory process, whose details have not yet been discovered. Experiments on mice to which the gene has been eliminated, have shown the development of an insensitivity to pain and heat, which proves that the gene plays an important role in regulating pain. The mutation is dominant: the Marsili family has six individuals affected by this disease, for three generations. Similar to CIPA, they easily develop fractures and severe bodily injuries due to trauma and injuries that do not cause them pain; however, it seems that these deficits develop after childhood and that some types of pain, such as headaches, are fully felt.
Pain as a mechanism of physical preservation ... and much more
Now it should be easy to understand why physical pain exists: it allows us to safeguard the integrity of our body and to identify and move away from an harmful stimulus. The safeguarding of our health is also protected by various "innate" mechanisms, which are beyond our "conscious" control. For example, if you accidentally touch a hot object, your hand quickly moves away; as if you hear a sudden noise, you automatically turn your head and eyes to look at the source of the noise. In both cases, I described some reflex arcs or in other words, reflex behaviors that are given by the activation of much shorter nervous circuits than the "standard" one we have seen previously.
In the example in the figure, we take into consideration the withdrawal refles, in which a painful stimulus (heat source or just a nail pinch) activates pain receptors. The impulse reaches the spinal cord and from there it splits: an impulse will go to the brain to make us realize what is happening while another one will go directly to the effector muscle, the biceps, making it to contract, causing the withdrawal of the hand by the flexion of the arm.
We can therefore say with absolute certainty that pain is essential to our life and is part of it: it's a mechanism that serves to protect us from what can destroy us. Likewise, emotional pain has an even more tangible role on the growth of the individual: amorous disappointment, betrayals, dissatisfaction that we receive in life and that make us suffer, make us more attentive and stronger to deal with relationships with next one.
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