ABSTRACT
Pain is a physiological experience, designed to alert us from potential damages to our body, so it has a clear protective role. Ideally, the sensation we perceive should be unpleasant enough, so it cannot be ignored, and the sensation should continue as long as the stimulus is present. The unmyelinated C nociceptive afferents can be divided into two major subpopulations, the peptidergic and the nonpeptidergic. The peptidergic nociceptors express substance P (SP) and calcitonin gene-related peptide, and the nonpeptidergic ones possess fluoride-resistant acid phosphatase activity, bind the lectin IB4 and express purinergic P2X3 receptors. The peripheral terminal of the nociceptor, embedded in the tissue, is where the noxious stimuli are detected and transduced into electrical impulses. The transduction of the nociceptive information starts in the periphery, where a stimulus is able to activate the nociceptor endings, by stretching or bending the nociceptor surface or by activating ion channels present in its membrane.
