In 1995, the British Medical Journal published an astonishing report about a 29-year-old builder. He accidentally jumped onto a 15-centimeter nail, which pierced straight through his steel-toed boot. He was in such agonizing pain that even the smallest movement was unbearable. But when the doctors took off his boot, they faced a surprising sight: the nail had never touched his foot at all.
1995. godine British Medical Journal objavio je zapanjujuće izvješće o 29-godišnjem graditelju. On je slušajno skočio na čavao dug 15 centimetara koji je probio njegovu čizmu s čeličnom kapicom. Osjećao je tako očajničku bol da je i najmanji pokret bio nepodnošljiv. Ali kada su mu liječnici skinuli čizmu, dočekao ih je iznenađujuć prizor: čavao nije ni dotaknuo njegovo stopalo.
For hundreds of years, scientists thought that pain was a direct response to damage. By that logic, the more severe an injury is, the more pain it should cause. But as we’ve learned more about the science of pain, we’ve discovered that pain and tissue damage don’t always go hand in hand, even when the body’s threat signaling mechanisms are fully functioning. We’re capable of experiencing severe pain out of proportion to an actual injury, and even pain without any injury, like the builder, or the well-documented cases of male partners of pregnant women experiencing pain during the pregnancy or labor.
Stotinama godina znanstvenici su mislili da je bol izravan odgovor na ozljedu. Po toj logici, što je ozljeda ozbiljnija, uzrokovat će veću bol. Ali kako smo učili sve više o znanosti boli, otkrili smo da bol i oštećenje tkiva ne idu uvijek ruku pod ruku, čak i kada mehanizmi koji tijelu signaliziraju opasnost odlično rade. U stanju smo iskusiti opaku bol uzrokovanu stvarnom ozljedom, ali također i bol bez ikakve ozljede, poput graditelja, ili dobro dokumentirani slučajevi kada muški partneri trudnih žena iskuse bol tijekom trudnoće ili poroda.
What’s going on here? There are actually two phenomena at play: the experience of pain, and a biological process called nociception. Nociception is part of the nervous system’s protective response to harmful or potentially harmful stimuli. Sensors in specialized nerve endings detect mechanical, thermal, and chemical threats. If enough sensors are activated, electrical signals shoot up the nerve to the spine and on to the brain. The brain weighs the importance of these signals and produces pain if it decides the body needs protection. Typically, pain helps the body avoid further injury or damage. But there are a whole set of factors besides nociception that can influence the experience of pain— and make pain less useful.
Što se ovdje događa? Zapravo postoje dva fenomena na snazi: iskustvo boli i biološki proces pod nazivom nocicepcija. Nocicepcija je dio zaštitnog odgovora živčanog sustava na štetni ili potencijalno štetni podražaj. Senzori u specijaliziranim završecima živaca otkrivaju mehaničke, termalne i kemijske prijetnje. Ako se dovoljno senzora aktivira, električni signali odlaze živcima do kralježnične moždine te potom do mozga. Mozak procjenjuje važnost tih signala i stvara bol ako dođe do zaključka da je tijelu potrebna zaštita. Obično bol pomaže tijelu da izbjegne daljnje ozljede ili oštećenje, ali postoje različiti skupovi faktora uz nocicepciju koji utječu na iskustvo boli i čine bol manje korisnom.
First, there are biological factors that amplify nociceptive signals to the brain. If nerve fibers are activated repeatedly, the brain may decide they need to be more sensitive to adequately protect the body from threats. More stress sensors can be added to nerve fibers until they become so sensitive that even light touches to the skin spark intense electrical signals. In other cases, nerves adapt to send signals more efficiently, amplifying the message. These forms of amplification are most common in people experiencing chronic pain, which is defined as pain lasting more than 3 months. When the nervous system is nudged into an ongoing state of high alert, pain can outlast physical injury. This creates a vicious cycle in which the longer pain persists, the more difficult it becomes to reverse.
Prvo, tu su biološki faktori koji pojačavaju nociceptivne signale prema mozgu. Ako se živčana vlakna opetovano aktiviraju, mozak može odlučiti da trebaju biti osjetljivija kako bi na prikladan način zaštitila tijelo od opasnosti. Više senzora stresa može biti dodano živčanim vlaknima dok ne postanu toliko osjetljiva da čak i lagani dodir kože potiče snažne električne signale. U ostalim slučajevima, živci se prilagode kako bi djelotvornije slali signale pojačavajući poruku. Ovi oblici pojačavanja najčešći su kod ljudi koji doživljavaju kroničnu bol, koja se definira kao bol u trajanju duljem od 3 mjeseca. Kad je živčani sustav ponukan u stanje stalne visoke uzbune, bol može trajati dulje od fizičke ozljede. Ovo stvara začarani krug u kojemu što dulje bol traje, to ju je teže suzbiti.
Psychological factors clearly play a role in pain too, potentially by influencing nociception and by influencing the brain directly. A person’s emotional state, memories, beliefs about pain and expectations about treatment can all influence how much pain they experience. In one study, children who reported believing they had no control over pain actually experienced more intense pain than those who believed they had some control. Features of the environment matter too: In one experiment, volunteers with a cold rod placed on the back of their hand reported feeling more pain when they were shown a red light than a blue one, even though the rod was the same temperature each time. Finally, social factors like the availability of family support can affect perception of pain. All of this means that a multi-pronged approach to pain treatment that includes pain specialists, physical therapists, clinical psychologists, nurses and other healthcare professionals is often most effective.
Psihološki faktori očito također igraju ulogu u boli, potencijalno utječući na nocicepciju i utječući izravno na mozak. Osobno emocionalno stanje, uspomene, uvjerenja o boli i očekivanja u vezi liječenja mogu također utjecati na to koliko boli osoba doživljava. U jednom istraživanju djeca koja su iznijela uvjerenja kako ona nemaju kontrolu nad boli zapravo su doživljavala intenzivniju bol od djece čija su uvjerenja bila kako imaju nešto kontrole. Značajke okoline također su važne. U jednom ekperimentu volonterima kojima je prislonjen ledeni štap na stražnju stranu ruke izjavili su kako osjećaju jaču bol kada im je pokazano crveno svjetlo nego plavo, iako je štap svaki puta bio iste temperature. Konačno, društveni faktori poput dostupnosti obiteljske podrške mogu utjecati na percepciju boli. Sve ovo znači da višestruki pristup liječenju boli koji uključuje specijaliste za bol, terapeute, kliničke psihologe, medicinske sestre i ostale zdravstvene radnike često je najučinkovitiji.
We’re only beginning to uncover the mechanisms behind the experience of pain, but there are some promising areas of research. Until recently, we thought the glial cells surrounding neurons were just support structures, but now we know they have a huge role in influencing nociception. Studies have shown that disabling certain brain circuits in the amygdala can eliminate pain in rats. And genetic testing in people with rare disorders that prevent them from feeling pain have pinpointed several other possible targets for drugs and perhaps eventually gene therapy.
Tek počinjemo otkrivati mehanizme koji stoje u podlozi doživljavanja boli, ali postoje obećavajuća područja istraživanja. Donedavno se mislilo kako glija stanice koje okružuju živce samo podupiru strukture, ali sada znamo da one imaju ogromnu ulogu u utjecanju na nocicepciju. Istraživanja su pokazala kako onespo- sobljavanje određenih moždanih krugova u amigdali može ukloniti bol kod štakora. I genetska testiranja ljudi s rijetkim poremećajima zbog kojih ne osjećaju bol ukazala su na nekoliko mogućih opcija lijekova i s vremenom možda gensku terapiju.