2. Pathophisiology of acute pain
A number of theories have been formulated to explain noxious perception: The specificity
theory by Descartes, the intensity theory by Sydenham, and recently the gate control theory
by Melzack and Wall where they suggested that sensory fibers of differing specificity
stimulate second-order spinal neurons fire at a different intensity.5 Pain perception is
dependent on the degree of noxious stimulation, local descending inhibition from CNS
centers, and responses of second order transmissions cells. Woolf and coworkers have
proposed a new theory to explain pain-processing, suggesting that primary and secondary
hyperalgesia as well as qualitative differences among physiologic, inflammatory, and
neuropathic pain reflect sensitization of both peripheral nociceptors and spinal neurons.
Noxious perception is the result of several distinct processes that begin in the periphery,
extended up the neuraxis, and terminate at supraspinal regions responsible for
interpretation and reaction.