Basic mechanisms and pathophysiology

Abstract

The ability to experience pain is essential for survival and wellbeing and the pathological consequences of the inability to experience pain are particularly well-illustrated by the extensive injuries experienced by children with congenital insensitivity to pain. In this chapter, the authors focus on the molecules and cell types that underlie normal pain sensation, with specific emphasis on the nociceptor and on second order neurons in the spinal cord. They also discuss how these circuits are altered following tissue or nerve injury and in persistent pain states. In the setting of injury, complementary and sometimes contemporaneous mechanisms underlie the process of sensitization that leads to allodynia and hyperalgesia. One involves peripheral sensitization usually of the nociceptor itself. Another, central sensitization, can result from increased excitability of CNS circuits in the nociceptive pathway.