Editing Pain (section)

===Modern===
[[File:Schematic of cortical areas involved with pain processing and fMRI.jpg|thumb|right|Regions of the cerebral cortex associated with pain]]
Some sensory fibers do not differentiate between [[Noxious stimulus|noxious]] and non-noxious stimuli, while others (i.e., [[nociceptor]]s) respond only to noxious, high-intensity stimuli. At the peripheral end of the nociceptor, noxious stimuli generate currents that, above a given threshold, send [[action potential|signals]] along the nerve fiber to the spinal cord. The "specificity" (whether it responds to thermal, chemical, or mechanical features of its environment) of a nociceptor is determined by which [[ion channel]]s it expresses at its peripheral end. So far, dozens of types of nociceptor ion channels have been identified, and their exact functions are still being determined.<ref>{{cite journal | vauthors = Woolf CJ, Ma Q | title = Nociceptors{{snd}}noxious stimulus detectors | journal = Neuron | volume = 55 | issue = 3 | pages = 353–364 | date = August 2007 | pmid = 17678850 | doi = 10.1016/j.neuron.2007.07.016 | s2cid = 13576368 | doi-access = free }}</ref>

The pain signal travels from the periphery to the spinal cord along [[A delta fiber|A-delta]] and [[C fiber|C]] fibers. Because the A-delta fiber is thicker than the C fiber, and is thinly sheathed in an electrically insulating material ([[myelin]]), it carries its signal faster (5–30&nbsp;[[Metre per second|m/s]]) than the unmyelinated C fiber (0.5–2&nbsp;m/s).<ref name="Marchand">{{cite book | vauthors = Marchand S | veditors = Beaulieu P, Lussier D, Porreca F, Dickenson A |title=Pharmacology of pain |chapter=Applied pain neurophysiology |publisher=International Association for the Study of Pain Press |location=Seattle |year=2010 |pages=3–26 |isbn=978-0931092787}}</ref> Pain evoked by the A-delta fibers is described as sharp and is felt first. This is followed by a duller pain—often described as burning—carried by the C fibers.<ref name="Skevington9">{{cite book |vauthors=Skevington S |title=Psychology of pain |publisher=Wiley |location=New York |year=1995 |page=[https://archive.org/details/psychologyofpain0000skev/page/9 9] |isbn=978-0471957737 |url=https://archive.org/details/psychologyofpain0000skev/page/9 }}</ref> These A-delta and C fibers enter the spinal cord via [[Lissauer's tract]] and connect with spinal cord nerve fibers in the [[central gelatinous substance of the spinal cord]]. These spinal cord fibers then cross the cord via the [[anterior white commissure]] and ascend in the [[spinothalamic tract]]. Before reaching the brain, the spinothalamic tract splits into the [[lateral (anatomy)|lateral]], [[neospinothalamic tract]] and the [[medial (anatomy)|medial]], [[paleospinothalamic tract]]. The neospinothalamic tract carries the fast, sharp A-delta signal to the ventral posterolateral nucleus of the [[thalamus]]. The paleospinothalamic tract carries the slow, dull C fiber pain signal. Some of the paleospinothalamic fibers peel off in the brain stem—connecting with the reticular formation or midbrain periaqueductal gray—and the remainder terminate in the intralaminar nuclei of the thalamus.<ref name=Skevington1995>{{cite book |vauthors=Skevington SM |year=1995 |title=Psychology of pain |location=Chichester, UK |publisher=Wiley |page=[https://archive.org/details/psychologyofpain0000skev/page/18 18] |isbn=978-0471957737 |url=https://archive.org/details/psychologyofpain0000skev/page/18 }}</ref>

Pain-related activity in the thalamus spreads to the [[insular cortex]] (thought to embody, among other things, the feeling that distinguishes pain from other [[homeostatic emotion]]s such as itch and nausea) and [[anterior cingulate cortex]] (thought to embody, among other things, the affective/motivational element, the unpleasantness of pain),<ref name= Craig2003a>{{cite journal | vauthors = Craig AD | title = Pain mechanisms: labeled lines versus convergence in central processing | journal = Annual Review of Neuroscience | volume = 26 | pages = 1–30 | year = 2003 | pmid = 12651967 | doi = 10.1146/annurev.neuro.26.041002.131022 | s2cid = 12387848 }}</ref> and pain that is distinctly located also activates the [[primary somatosensory cortex|primary]] and [[secondary somatosensory cortex]].<ref name="Romanelli P, Esposito V.">{{cite journal | vauthors = Romanelli P, Esposito V | title = The functional anatomy of neuropathic pain | journal = Neurosurgery Clinics of North America | volume = 15 | issue = 3 | pages = 257–268 | date = July 2004 | pmid = 15246335 | doi = 10.1016/j.nec.2004.02.010 }}</ref>

Spinal cord fibers dedicated to carrying A-delta fiber pain signals and others that carry both A-delta and C fiber pain signals to the [[thalamus]] have been identified. Other spinal cord fibers, known as [[wide dynamic range neuron]]s, respond to A-delta and C fibers and the much larger, more heavily myelinated A-beta fibers that carry touch, pressure, and vibration signals.<ref name=Marchand/>

[[Ronald Melzack]] and [[Patrick David Wall|Patrick Wall]] introduced their [[gate control theory]] in the 1965 [[Science (journal)|''Science'']] article "Pain Mechanisms: A New Theory".<ref name="pmid5320816">{{cite journal | vauthors = Melzack R, Wall PD | title = Pain mechanisms: a new theory | journal = Science | volume = 150 | issue = 3699 | pages = 971–979 | date = November 1965 | pmid = 5320816 | doi = 10.1126/science.150.3699.971 | url = https://www.hnehealth.nsw.gov.au/__data/assets/pdf_file/0012/70122/pain_mechanisms_20100315013844.pdf | author-link = Ronald Melzack | url-status = dead | bibcode = 1965Sci...150..971M | archive-url = https://web.archive.org/web/20120114141747/https://www.hnehealth.nsw.gov.au/__data/assets/pdf_file/0012/70122/pain_mechanisms_20100315013844.pdf | archive-date = 14 January 2012 | author-link2 = Patrick David Wall | accessdate = 7 March 2022 }}</ref> The authors proposed that the thin C and A-delta (pain) and large diameter A-beta (touch, pressure, vibration) nerve fibers carry information from the site of injury to two destinations in the [[posterior horn of spinal cord|dorsal horn]] of the spinal cord, and that A-beta fiber signals acting on inhibitory cells in the dorsal horn can reduce the intensity of pain signals sent to the brain.<ref name="MelzackKatz"/>

====Three dimensions of pain====
In 1968, [[Ronald Melzack]] and [[Kenneth L. Casey|Kenneth Casey]] described chronic pain in terms of its three dimensions:
* "sensory-discriminative" (sense of the intensity, location, quality, and duration of the pain),
* "affective-motivational" (unpleasantness and urge to escape the unpleasantness) and
* "cognitive-evaluative" (cognitions such as appraisal, cultural values, distraction, and hypnotic suggestion).

They theorized that pain intensity (the sensory discriminative dimension) and unpleasantness (the affective-motivational dimension) are not simply determined by the magnitude of the painful stimulus, but "higher" cognitive activities can influence perceived intensity and unpleasantness. Cognitive activities may affect both sensory and affective experience, or they may modify primarily the affective-motivational dimension. Thus, excitement in games or war appears to block both the sensory-discriminative and affective-motivational dimensions of pain, while suggestion and placebos may modulate only the affective-motivational dimension and leave the sensory-discriminative dimension relatively undisturbed.<ref name=M&C>{{cite book|last1=Melzack|first1=Ronald|author-link1=Ronald Melzack|last2=Casey|first2=Kenneth|author-link2=Kenneth L. Casey|editor-last=Kenshalo|editor-first=Dan|year=1968|chapter=Sensory, Motivational, and Central Control Determinants of Pain|title=The Skin Senses|publisher=Charles C Thomas|publication-place=Springfield, Illinois|url=https://www.researchgate.net/publication/233801589}}</ref> (p.&nbsp;432)

The paper ends with a call to action: "Pain can be treated not only by trying to cut down the sensory input by anesthetic block, surgical intervention and the like, but also by influencing the motivational-affective and cognitive factors as well."<ref name=M&C/> (p.&nbsp;435)