Hockenbury Discovering Psychology 5th txtbk

The Chemical and Body Senses1111. Pain source 2. Fast A-delta fibers andslow C fibers transmittheir messages to thespinal cord, and thento the brain.3. Slow pain messages travelto the hypothalamus andthalamus, then to limbicsystem structures, suchas the amygdala.AmygdalaHypothalamusSomatosensorycortex4. Fast pain messages travelto the thalamus, then to thesomatosensory cortex.ThalamusHippocampusA-delta fibers(fast pain system)C fibers (slowpain system)Figure 3.11 Fast and Slow PainPathways The fast pain pathway consistsof myelinated A-delta fibers,shown in red, which project first to thethalamus and then on to the somatosensorycortex. Signals carriedalong this pathway produce the sensoryaspects of pain—the sharp butshort-lived pain of an immediate injury.In contrast, the slow pain pathway consistsof unmyelinated C fibers, shown inblue. The slow pain pathway is muchmore involved with the emotional aspectsof pain. The C fibers project tothe thalamus and hypothalamus, thento limbic system structures, includingthe amygdala.factors, and cultural learning experiences about the meaning of pain and howpeople should react to it (Gatchel & others, 2007; Raichle & others, 2007). Inthe chapter section on Enhancing Well-Being with Psychology, we discuss somehelpful strategies that you can useto minimize pain.Psychological factors also influencethe release of endorphins andenkephalins, the body’s naturalpainkillers (see Chapter 2). Endorphinsand enkephalins are producedin the brain and spinal cord. Theyare released as part of the body’soverall response to physical pain orstress. In the brain and spinal cord,endorphins and enkephalins inhibitthe transmission of pain signals, includingthe release of substance P.Red-Headed Women and Pain Genderdifferences in pain have been extensivelyresearched (see Fillingim, 2000). Ingeneral, women are more sensitive topain than men. Studies also show thatwomen respond better than men tosome morphine-like pain medicationscalled “kappa opioids” (Gear & others,1996). Psychologist Jeffrey Mogil and hiscolleagues (2003) found that a geneassociated with red hair and fair skinwas implicated in the response to thesepain medications. Women with twocopies of this gene, like the three sistersin the photo here, experience muchgreater pain relief from kappa opioidsthan men or other women.Sensitization: Unwarranted Pain One of the most frustrating aspects of pain managementis that it can continue even after an injury has healed, such as after recoveringfrom a spinal cord injury or severe burns. A striking example of this phenomenon isphantom limb pain, in which a person continues to experience intense painful sensationsin a limb that has been amputated (Flor & others, 2006).How can phantom limb pain be explained? Basically, the neurons involved in processingthe pain signals undergo sensitization. Earlier in the chapter, we discussed sensoryadaptation, in which sensory receptors become gradually less responsive tosteady stimulation over time. Sensitization is the opposite of adaptation. In sensitization,pain pathways in the brain become increasingly more responsive over time. It’slike a broken volume control knob on your stereo that you can turn up, but notdown or off.