I always enjoy a good pain mechanism article. Here are some block quotes in bold from this one. Give it a read.
Over one-third of the world's population suffers from persistent or recurrent pain, costing the American public alone approximately $100 billion each year in health care, compensation, and litigation (1). Chronic pain is associated with conditions such as back injury, migraine headaches, arthritis, herpes zoster, diabetic neuropathy, temporomandibular joint syndrome, and cancer. Many of the currently available pain therapies are either inadequate or cause uncomfortable to deleterious side effects. Chronic pain results not just from the physical insult but also from a combination of physical, emotional, psychological, and social abnormalities. Because many pains persist after an insult is healed, the ongoing pain rather than the injury underlies the patient's disability. Untreated pain may become self-perpetuating because pain has immunosuppressive effects that leave patients susceptible to subsequent diseases. It is now clear that if we can effectively treat the pain despite the underlying cause, it will be possible for patients to regain normal functioning. The key to more successful pain treatment is to understand the mechanisms that generate and maintain chronic pain. Mechanisms of pain
Plasticity is a term used to refer to changes that occur in the established nervous system. Changes in neuronal structure; connections between neurons; and alterations in the quantity and properties of neurotransmitters, receptors, and ion channels can ultimately result in increased functional activity of neurons in the pain pathway. Conversely, plasticity can decrease the body's own pain inhibitory systems, resulting ultimately in increased pain. Injury, inflammation, and disease can all cause neuronal plasticity and increased pain by means of increased excitatory or decreased inhibitory mechanisms. Plasticity can result in short-term changes that last minutes to hours, or long-term changes which may be permanent. Mechanisms of pain