ABSTRACT
The pathophysiological mechanisms of chronic pain may be split fairly neatly into two main groups: the first underpinned by functional plasticity, involving biochemical alterations within and between neurons and other cell types; and the second, structural plasticity, involving anatomical changes within the system. Nociceptors are normally small-diameter sensory neurons involved in the transduction and transmission of damaging or potentially damaging stimuli. Nociceptors terminate in the dorsal horn of the spinal cord. The cord is highly arranged, consisting of several distinct layers. Primary afferent fibers show a marked preference for specific lamina, e.g., C-fibers terminate in the outer laminae I and II while larger myelinated fibers penetrate deeper within the horn, e.g., Ad synapse preferentially in lamina V. While the spinothalamic is best known as the main nociceptive pathway, noxious inputs ascend via several spinal cord tracts. These pathways have been broadly grouped into medial and lateral systems.
