Philosophical transactions of the Royal Society of London. Series B, Biological sciences
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Philos. Trans. R. Soc. Lond., B, Biol. Sci. · Feb 1985
Visceral nociception: peripheral and central aspects of visceral nociceptive systems.
Discomfort and pain are the sensations most commonly evoked from viscera. Most nociceptive signals that originate from visceral organs reach the central nervous system (c.n.s.) via afferent fibres in sympathetic nerves, whereas parasympathetic nerves contain mainly those visceral afferent fibres concerned with the non-sensory aspects of visceral afferent function. Noxious stimulation of viscera activates a variety of specific and non-specific receptors, the vast majority of which are connected to unmyelinated afferent fibres. ⋯ Visceral pain is the consequence of the diffuse activation of somato-sensory nociceptive systems in a manner that prevents accurate spatial discrimination or localization of the stimuli. Noxious stimulation of visceral receptors triggers general reactions of alertness and arousal and evokes unpleasant and poorly localized sensory experiences. This type of response may be a feature of sensory systems dominated by unmyelinated afferent inputs.
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Philos. Trans. R. Soc. Lond., B, Biol. Sci. · Feb 1985
Spinal processing: anatomy and physiology of spinal nociceptive mechanisms.
The processing of nociceptive input that occurs at the spinal level represents the first stage of effective control over its access to higher regions of the central nervous system. Recent developments in both the anatomy and physiology of nociceptive processing pathways at this level are beginning to yield an integrated understanding of structure and function. Most small afferent axons terminate in the more superficial laminae of dorsal horn, but technical difficulties have, until recently, prevented analysis of the functional properties of identified small fibres. ⋯ The mechanisms of such descending controls and the importance of their interaction with segmental control systems, such as those involving the dynorphin opioids, are just beginning to be understood. Many somatosensory neurons in dorsal horn, both the large cells, some of which project supraspinally, and the small cells of superficial laminae, receive convergent nociceptive and non-nociceptive inputs. Although solely nociresponsive neurons are clearly likely to fill a role in the processing and signalling of pain in the conscious central nervous system, the way in which such useful specificity could be conveyed by multireceptive neurons is difficult to appreciate.(ABSTRACT TRUNCATED AT 400 WORDS)
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A role for thalamic structures in the processing of signals of nociception and pain has been suggested on the basis of clinical data since the turn of the century. Searches for a 'pain centre' by lesion or stimulation were often disappointing and the electrophysiological data were rare and usually contradictory. ⋯ The eventual respective roles of these thalamic structures are considered. Electrophysiological recordings from thalamic structures in a model of experimental pain, arthritic rats, are also presented.