Editing Nociception (section)

==Detection of noxious stimuli==
[[File:Nociceptive pain.jpg|thumb|upright=2|Mechanism of nociception via [[sensory afferents]]]]
Potentially damaging mechanical, thermal, and chemical stimuli are detected by nerve endings called nociceptors, which are found in the [[skin]], on internal surfaces such as the [[periosteum]], [[joint]] surfaces, and in some internal [[organ (anatomy)|organ]]s. Some nociceptors are unspecialized [[free nerve ending]]s that have their cell bodies outside the [[spinal column]] in [[dorsal root ganglia]].<ref>{{cite book |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK10965/ |chapter=Nociceptors |last=Purves |first=D. |title=Neuroscience |editor1-first=MA. |editor1-last=Sunderland |publisher=Sinauer Associates |year=2001 |access-date=2017-09-06 |archive-date=2020-08-14 |archive-url=https://web.archive.org/web/20200814091452/https://www.ncbi.nlm.nih.gov/books/NBK10965/ |url-status=live }}</ref> Others are specialised structures in the skin such as nociceptive [[Schwann cells]].<ref>{{Cite journal|last1=Doan|first1=Ryan A.|last2=Monk|first2=Kelly R.|date=16 August 2019|title=Glia in the skin activate pain responses|journal=Science|volume=365|issue=6454|pages=641–642|doi=10.1126/science.aay6144|issn=1095-9203|pmid=31416950|bibcode=2019Sci...365..641D|s2cid=201015745}}</ref> Nociceptors are categorized according to the [[axon]]s which travel from the receptors to the [[spinal cord]] or brain. After nerve injury, it is possible for touch fibers that normally carry non-noxious stimuli to be perceived as noxious.<ref>{{Cite journal|last1=Dhandapani|first1=Rahul|last2=Arokiaraj|first2=Cynthia Mary|last3=Taberner|first3=Francisco J.|last4=Pacifico|first4=Paola|last5=Raja|first5=Sruthi|last6=Nocchi|first6=Linda|last7=Portulano|first7=Carla|last8=Franciosa|first8=Federica|last9=Maffei|first9=Mariano|last10=Hussain|first10=Ahmad Fawzi|last11=de Castro Reis|first11=Fernanda|date=2018-04-24|title=Control of mechanical pain hypersensitivity in mice through ligand-targeted photoablation of TrkB-positive sensory neurons|journal=Nature Communications|language=en|volume=9|issue=1|page=1640|doi=10.1038/s41467-018-04049-3|pmid=29691410|pmc=5915601|bibcode=2018NatCo...9.1640D|issn=2041-1723|doi-access=free}}</ref>

Nociceptive pain consists of an adaptive alarm system.<ref>{{Cite journal|last1=Woolf|first1=Clifford J.|last2=Ma|first2=Qiufu|date=2007-08-02|title=Nociceptors--noxious stimulus detectors|journal=Neuron|volume=55|issue=3|pages=353–364|doi=10.1016/j.neuron.2007.07.016|issn=0896-6273|pmid=17678850|s2cid=13576368 |doi-access=free}}</ref> Nociceptors have a certain threshold; that is, they require a minimum intensity of stimulation before they trigger a signal. Once this threshold is reached, a signal is passed along the neuron's axon into the spinal cord.

Nociceptive threshold testing deliberately applies a noxious stimulus to a human or animal subject to study pain. In animals, the technique is often used to study the efficacy of [[analgesic drugs]] and to establish dosing levels and periods of effect. After establishing a baseline, the drug under test is given, and the elevation in threshold is recorded at specified times. The threshold should return to the baseline (pretreatment) value when the drug wears off. In some conditions, the excitation of pain fibers increases as the pain stimulus continues, leading to a condition called [[hyperalgesia]].