What is this thing called pain?
“Pain is like love, is all-consuming: when you have it not much else matters and there is nothing you can do about it.” (Woolf 2010)
There are three different pain types we all experience
1 Nociceptive pain: When we touch something too hot or cold, too sharp or blunt, we reflexively withdraw from that stimulus. Specialist nerve endings detect and alert us to get out of harms way. Nociceptive pain tells is what to avoid now, and when activated, it overrules most other neural functions. Nociceptive pain is essential for maintaining body integrity and care must be taken to not blunt its protective role
2 Inflammatory pain: Also known as adaptive or protective pain. Pain is one of the five cardinal features of inflammation and as a result of inflammation the wound site, eg post operation, post accident /insult, the area becomes inflamed and swollen leading to tenderness and restricted movement. We adapt our movement patterns to avoid aggravating the injured site and to allow healing to occur.
(5 cardinal signs of inflammation: rubor (redness), calor (increased heat), tumor (swelling), dolor (pain), and functio laesa (loss of function)
3 Pathological pain: Also known as maladaptive pain resulting from abnormal functioning of the nervous system. It exists where there is no nociceptive or inflammatory pain. It is a disease state of the nervous system where there is damage to the nervous system itself as in “neuropathic pain” or where there is no inflammation or damage; it is “dysfunctional pain”. For example, irritable bowel syndrome, fibromyalgia, TMJ pain and interstitial cystitis syndromes are examples.
Treatment should be directed at the type of presenting pain.
Pain is not just a switch in the periphery that results in transmission of signals to the cortex of the brain where the sensation of pain manifests. Inhibitory and excitatory circuits in the central nervous system also control pain. These circuits can either diminish or exaggerate pain depending on mood, cognitive function, and even memory. These increases and decreases, particularly the latter, are the basis of “suggestion” or “placebo” and the basis of some treatments that “work” such acupuncture. They are also the basis of some pharmaceutical analgesics such as opioids that increase inhibitory tone.
Chronic pain Different areas of the brain make up the brain pain matrix and are activated by nociceptive pain’s location, intensity, duration, quality and emotional association and show how pain can be affected by mood, attention and distraction. Regarding the pain locations, there can be structural changes in the brain suggesting that chronic pain is a disease of the nervous system.
Inflammatory and pathological pain does not require noxious stimuli (hot cold sharp blunt etc.) to generate pain. Pain may arise spontaneously without any stimulus. Nociceptors in the periphery may become sensitized during inflammation and become sufficiently hyper excitable and generate spontaneous action potentials. Synapses in the spinal cord can change their strength and undergo structural change. These changes can also take place in the spinal cord and brain leading to central sensitization resulting in a fall in the threshold for generating pain and an increase in its duration, amplitude and spatial distribution increase. So the difference between inflammatory pain and pathological pain is inflammatory pain is hypersensitivity in relation to a defined peripheral pathology and pathological pain is the result of altered neural processing.
Finally the susceptibility to having pain and the conversion of acute to chronic pain may be heritable.