Pain is a really interesting topic because it combines scientific objectivity and the subjectivity of emotion into one area. Nearly all of us feel pain and pain has developed to keep us alive and safe from harm. However evidence (anecdotal and scientific) shows that we all experience pain differently. Pain can be separated into ‘higher’ psychological pain such as anxiety, fear and anger or more ‘basic’ physical pain, such as our body withdrawing from a painful stimulus. These are of course interlinked and work upon a spectrum, but to put it basically pain is there to keep us out of trouble. However when things go wrong, chronic or maladaptive pain, it can actually get us into quite a bit of trouble too.
Before I go on, I will give you a quick run of how pain works. First we need to take a look at a few of the key pain players.
- Painful stimuli – grabbing something hot, cutting yourself or even hot chilli’s
- C-fibres – specialised peripheral fibres found in the muscle, skin and various other cells.
- Nociceptors – specialised sensory receptors, found within C-fibres.
- Multiple different types which can detect mechanical (pressure), thermal (hot) and chemical (Chilli) stimuli
- COX-1/2 enzymes form inflammatory prostaglandins
- Dorsal horn – areas of the spinal cord where nerves carrying pain signals converge and allow communication to the central nervous system.
Okay so now you know a bit more about the major players, lets move onto how pain signals work.
- Painful stimuli activates nociceptors
- If the painful stimulus damages surrounding tissues, surrounding cells will release a cocktail of chemicals. One of these chemicals is prostaglandin these act to cause inflammation.
- Inflammation, caused by the release of chemicals (prostaglandins), is a major cause of increased nociceptor sensitivity. Inflammation acts to reduce the threshold required to activate C-fibres. The biological aim of this is so that you avoid and take action to prevent further damage to the damaged area.
- Nociceptor activation opens various ionic channels within the C-fibre
- This ionic change activates an electrical impulse within the C-fibre
- Nerves carrying pain signals from the periphery converge at the dorsal horn in the central nervous system (Spinal cord)
- Here the pain signal can be amplified so to prolong the stimulus
- Calcium release from peripheral nerves activates the release of a chemical transmitter called glutamate in the dorsal horn
- The release of Glutamate causes the activation of thousands of nerves which terminate in multiple different regions of the brain
10. This allows the brain to locate pain and describe its intensity
11. Pain can reach brain areas which control sleep, appetite and our attention to the outside world
Through this, simplified, pathway pain stimuli can be converted into perceptions. These tell us about the location and intensity of the pain stimuli. This system is brilliant because if we didn’t know about pain (this is called congenital analgesia) our bodies would be at severe risk. However it does not always run smoothly. When pain becomes chronic or maladaptive it is a very serious problem. Maladaptive pain has a larger influence than just a constant feeling of pain it also can lead to depression and changes in behaviour.
One example is neuropathic pain this results from nerve injuries and can lead to allodynia (sensations which shouldn’t cause pain, causing pain) and hyperalgesia (heightened pain response to standard painful stimuli). Neuropathic pain strangely can be seen in conditions where nerve damage is not clear, such as: diabetes, shingles, HIV and cancer. The changes, which are taking place, suggest changes are occurring within the nervous system. On going pain in damaged nerves is attributed to an increase in the number of sodium channels (these channels initiate nervous impulses). Therefore pain impulses will be generated in the absence of appropriate stimulation. As well as this spontaneous pain can be felt. This is attributed to an increased sensitivity to chemicals, which are released by other nerves.
Another major change is called ‘wind up’, this is where persistent pain causes amplification and prolongation of response to pain by nerves in the dorsal horn (area of pain transmission). Wind up occurs upon activation of NMDA receptors. NMDA receptors are associated with our memory and the ‘acquisition’ of memories can be caused by long-term potentiation of these receptors. The same occurs with pain, upon repeated NMDA receptor stimulation our spinal cord becomes hypersensitive to pain and it remembers the pain stimulus as being more intense than it is. This results in allodynia.
Pain although following initially simple pathways, can have far reaching affects. This is because pain pathways interact with various parts of the brain, which are key to our everyday behaviour. So pain can cause sleep problems, make us more fearful and anxious. Also because it activates areas responsible for attention and our response to the outside world our social interactions and work can suffer.
We have drugs to treat pain but treatment needs to take a more holistic nature. We need to look at the emotional side, the ability not to give into pain, learning to cope and distractions all have a positive impact. This can be brought about through movement and exercise. Which does seem strange because our bodies are screaming at us to protect the injury. You can understand why people don’t do things, which are painful. However this ‘protection’ could be more harmful.
So in conclusion chronic pain is often incurable, pain often goes undiagnosed and can be un-diagnosable. Other people don’t realise its real and don’t understand how hard it is to live with pain. Rather than a cure, holistic therapy is given from physiotherapy to psychotherapy. This has not been seen to reduce pain but instead it allows people to manage their pain and to live fuller lives. This has a positive impact on their psychological well-being and consequently their pain.