Physiology and Pathophysiology of Chronic Pain

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. The experience of pain serves as one of the most important protective mechanisms of the body. Consistent with its important role, the physiology of pain spans the entire nervous system, from peripheral nociceptors to central thalamocortical loops. In this chapter we describe the physiology and pathophysiology of pain. After a brief summary of treatment strategies, featured in detail elsewhere in this chapter, we examine the flow and modulation of pain signals from the periphery to the center. Pain transmission is a complex process involving many levels of endogenous modulation. However, at each level the process can become pathologic and lead to development of chronic pain. These pathological processes and strategies for treatment are also discussed.