spiral wave
{{main|Autowave reverberator}}
Spiral waves are travelling waves that rotate outward from a center in a spiral. They are a feature of many excitable media. Spiral waves have been observed in various biological systems{{cite book|author=Winfree AT. |authorlink=Arthur Winfree|title=The Geometry of Biological Time|publisher=Springer-Verlag|location=New York|year=2001}}{{cite book|author=Murray JD.|authorlink=James D. Murray|title=Mathematical Biology II: Spatial models and biomedical applications|publisher=Springer-Verlag|location=New York|year= 2003}} including systems such as heart ventricular fibrillation,{{cite journal|vauthors=Davidenko JM, Pertsov AV, Salomonsz R, Baxter W, Jalife J |title=Stationary and drifting spiral waves of excitation in isolated cardiac muscle|journal=Nature|year=1992|volume=355|issue=6358 |pages=349–351|pmid=1731248|doi=10.1038/355349a0|bibcode=1992Natur.355..349D }} Dictyostelium cAMP waves,{{cite journal|vauthors= Ford HZ, Manhart A, Chubb JR |title=Controlling periodic long-range signalling to drive a morphogenetic transition|journal=eLife|year=2023|volume=12|pages=e83796|pmid=36856269|doi=10.7554/eLife.83796|doi-access=free |pmc=10027319}} retinal spreading depression,{{cite journal|vauthors=Gorelova NA, Bures J |title=Spiral waves of spreading depression in the isolated chicken retina|journal=J Neurobiol|year=1983|volume=14|issue=5 |pages=353–363|pmid=6619832|doi=10.1002/neu.480140503}} Xenopus oocyte calcium waves,{{cite journal|vauthors=Lechleiter J, Girard S, Peralta E, Clapham D |title=Spiral calcium wave propagation and annihilation in Xenopus laevis oocytes|journal=Science|year=1991|volume=252|issue=5002 |pages=123–126|pmid=2011747|doi=10.1126/science.2011747|bibcode=1991Sci...252..123L }} and glial calcium waves in cortical tissue culture.{{cite journal|vauthors=Verkhratsky A, Orkand RK, Kettenmann H |title=Glial calcium: homeostasis and signaling function|journal=Physiol. Rev. |year=1998|volume=78|pages=99–141|pmid=9457170|doi=10.1152/physrev.1998.78.1.99}}