Fig. 2.

Schematic representation of the three phases of pain, proposed by Cervero & Laird (1991). Phase 1: an acute phase, with equally short-lived response in the central nervous system (CNS). Phase 2: prolonged noxious stimulation leading to an inflammatory response, and continued discharge of peripheral nociceptors, which in turn lead to changes in excitability of dorsal horn neurons. Phase 3: peripheral nerve damage may lead to spontaneous discharge, which modifies the behaviour of dorsal horn neurons, and allows non-nociceptive peripheral nerves (e.g. brush-sensitive Aβ fibres) access to the ascending pain system. Reproduced with permission from Cervero & Laird (1991).