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. .then, [Mr Hammerhead Shark] his shirt covered in blood, spun around and hit his knee on the table, at which point he swore and yelled ‘My knee! My knee!’, the whole time unfussed about the hammer stuck in his neck.

G Lorimer Moseley, Painful Yarns. Metaphors and stories to help understand the biology of pain

Even the simplest biological organisms can protect themselves from threatening stimuli—by altering their path of movement away from the source of the threat.1 As evolution has honed us into more and more sophisticated creatures, we have also honed this fundamental capacity to protect ourselves from threat. Indeed, perhaps our most sophisticated protective strategy is pain. In this chapter, some of the ‘fearful and wonderful complexity’ of pain is conveyed, by:

  • outlining a contemporary definition of pain that is contrary to conventional definitions but which integrates the huge amount of research that has been undertaken since our conventional definitions were established

  • introducing the idea of nociception and describing some of what is known about the biological mechanisms that underpin nociception

  • providing a conceptual framework with which to make sense of pain within the context of clinical practice.


Almost everyone experiences pain. Those who do not experience pain, as the rest of us know it, are at a distinct disadvantage in life and are likely to die young without living fast. Pain is an unpleasant sensory and emotional experience that is felt in the body and motivates us to do something to escape it. These two characteristics of pain—its unpleasantness and its anatomical focus—are what makes it such an effective protector.

Pain alerts us to tissue damage or the threat thereof. Pain makes us seek care. Pain stops us competing, keeps us seeking a cure, compels us to prioritise pain relief above almost everything else. That’s the rub—pain changes our behaviour. In fact, if the brain concludes that there is something more important than protecting a body part then it makes the executive decision to not produce pain. Therein lies the key to really understanding pain; it is as simple and as difficult as this—if the brain concludes that a body part is in danger and needs protecting and you, the organism, ought to know about it, then the brain will make that body part hurt.2

There is a critical caveat here, one that was overlooked in the fourth edition of this book. This convention to ascribe pain to the brain is flawed, because a brain, on its own, almost certainly would not and probably could not, produce pain. This position has been criticised, with merit and additional pieces have been authored that critique it.3 The caveat, then, is this: to attribute it all ...

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