Pain Relief - Introduction

Pain may be unpleasant but it is essential for survival. If cuts did not hurt, we might not cover our wounds. Walking with a broken leg would cause untold damage. All mammals feel and respond to pain in similar ways.

Epidurals ease the pain of childbirth [BSIP, Laurent/Science Photo Library].

Inflammation, disease, or a malfunctioning nervous system can all cause pain, but it may seemingly have no cause at all. The pain sensation can be described in many ways: throbbing, shooting, dull-ache, pounding, stabbing, wrenching, stinging, and cutting. It can cause crying and fainting. Special nerve cell receptors are involved in detection of pain whether it comes from a burn, cut or swelling. These receptors send signals to the brain, which interprets whether the signal constitutes pain.

Pain is incredibly hard to treat because precise medical evaluation of pain and its causes is often difficult. Moreover, people have different pain thresholds, so the type and amount of medication needed differs. In the UK, use of over the counter painkillers such as aspirin, paracetamol and ibuprofen is increasing every year; but the uptake of alternative treatments such as acupuncture are also growing.

Unlikely as it may sound, research into pain does not have to be painful for the animals used. For example, scientists can investigate whether a new chemical is likely to dampen down pain using very mild procedures. On the other hand, some animal studies undoubtedly cause a degree of suffering. This is unlikely to be as severe or as prolonged as for human patients and is not allowed to continue unchecked.

What causes pain?

Consider what happens when you put your hands close to a fire. You need to know they are in danger of being damaged. Specialised nerves in the skin called sensory neurones are the early warning system. They have proteins called receptors, which are activated by the heat of the fire. This in turn causes electrical impulses to be sent along the length of the nerve cell - which can be up to a metre long - to the spinal cord. The impulses activate yet more receptors on nearby spinal nerve cells. It is like a baton being passed between relay runners. The newly-activated neurones in the spinal cord then signal directly to parts of the brain that are involved in pain perception. And once the brain has interpreted the pain message - a somewhat mysterious process - appropriate action is taken to prevent further damage occurring: in this case, moving your hands away from the fire. Sensory nerves respond in a similar way to chemicals, pressure and all the other sources of pain.

As well as receiving the warning signs and initiating the required action, the spinal cord and brain send messages back to the sensory nerves to damp down pain. This is necessary when we need to tough it out and get on with things, childbirth for example. Failure to send these inhibitory messages is one cause of chronic pain - pain that continues after the injury is healed. Diseases such as arthritis that disrupt normal tissue function also cause chronic pain. Pain is generated too by our nervous system generating spurious pain messages when there is actually no tissue injury. This is what happens in neuropathic pain. The most dramatic and mysterious example of neuropathic pain is "phantom limb syndrome" - where even though an arm or leg has been removed, the brain still gets pain messages from nerves that originally carried impulses from the missing limb.

Thanks are due to Professor Paul Flecknell (University of Newcastle upon Tyne), Professor Peter McNaughton (University of Cambridge) and Professor John Wood (University College London).

FURTHER INFORMATION LINK: Understanding pain

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