de León-Casasola ÓA

Language: English
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Page: 133-138
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Neural processing of pain signals

Several neural steps are involved in the processing of noxious signals that can lead to the experience of pain.

• Transduction is the process by which noxious stimuli are converted to electrical signals in the nociceptors. Unlike other sensory receptors, nociceptors are not specialized from a structural point of view, but rather exist as free nerve endings. Nociceptors readily respond to different noxious modalities such as thermal, mechanical or chemical stimuli, but nociceptors do not respond to non-noxious stimuli. Also in contrast to other types of sensory receptors, nociceptors do not adapt–that is, continued stimulation results in continuous or repetitive firing of the nociceptor and, in some cases, continued stimulation actually results in a decrease in the threshold at which the nociceptors respond (ie, sensitization of nociceptors. Neurotransmitters that are produced within the cell body–ie, in the dorsal root ganglia (DRG) are the same at both the central and peripheral ends of the nerve fiber and are released at both ends, participating in producing the pain signal centrally, as well as in promoting events that lead to additional pain peripherally. The release of neurotransmitters from the peripheral terminals of the afferent fibers is actually an “efferent” function of these afferent neurons. Peripheral release of neurotransmitter substances lead to the classic “axon reflex”, a reflex that does not require the spinal cord–this reflex leads to peripheral changes that are well recognized to contribute to pain.