Nociception and Pain

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Pain is a complex experience that not only involves transduction of noxious stimuli, but also emotional and cognitive processing by the brain. In order to avoid painful and potentially harmful stimuli, our bodies instigate coordinated and elaborate responses (Snider and McMahon, 1998). Primary sensory neurons detect pain-producing stimuli in a process called nociception. Nociceptors, excited by different modes of stimuli such as mechanical, thermal, conductive, chemical, and radiant for example, are the mediators of these protective reflexes. These nociceptors differ from other neurons due to the fact that they have appropriately tuned receptive properties, where they detect stimuli such as noxious heat, intense pressure, or irritant chemicals, but not innocuous stimuli such as light touch or warming (Julius and Basbaum, 2001). Unmyelinated, slowly conducting C Fibers and thinly myelinated, more rapidly conducting Aδ fibers establish the pain response. C fiber nociceptors are the ones sensitive to noxious chemical stimuli such as capsaicin, the ingredient in hot chili peppers, which gives a burning sensation when eaten; this involves the receptor that is the focus of this paper (Tominaga and Julius, 2000). Nociceptors have a large repertoire of transduction devices in order to detect a wide range of stimulus modalities. Figure 1.1 shows that different stimuli can activate the TRPV1 receptor; it also illustrates the redundancy of nociception, where a single stimulus can interact with multiple detectors at the same time, such as TRPV1 and ASIC’s (acid sensing ion channels).

Fig. 1.1. This diagram shows how TRPV1 (the light blue ion channel) is activated by various different stimuli and also illustrates the redundancy ion pain sensation showing that ASIC’s (the red ion channel) also respond to pH (Julius and Basbaum, 1998).

Nociceptors not only signal acute pain, but also contribute to persistent pathological pain conditions such as rheumatoid...
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