Editing Cilium (section)

{{Short description|Organelle found on eukaryotic cells}}
{{About|organelles|fine hairs on insect wings|Cilium (entomology)}}{{Distinguish|Cilium (computing)}}{{Distinguish|Psyllium}}
{{Use dmy dates|date=November 2018}}
{{Infobox microanatomy
| Name        = Cilium
| Latin       = cilium
| Image       = Bronchiolar epithelium 3 - SEM.jpg
| Caption     = [[Scanning electron microscope|SEM]] micrograph of motile cilia projecting from [[respiratory epithelium]] in the [[trachea]] 
| Width       = 
| Image2      = 
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{{wikt | cilium}}

The '''cilium''' ({{plural form}}: '''cilia'''; {{ety|la|cilium|[[eyelid]]}}; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like [[membrane protrusion]] from many types of [[eukaryotic cell]].<ref name="MW1">{{cite web | title=Definition of CILIUM |url=https://www.merriam-webster.com/dictionary/cilium | website=www.merriam-webster.com | access-date=15 April 2022 | language=en}}</ref><ref name="HHMIB2005"/> (Cilia are absent in [[bacteria]] and [[archaea]].) The cilium has the shape of a slender threadlike projection that extends from the surface of the much larger cell body.<ref name="HHMIB2005"/> Eukaryotic [[flagella]] found on [[sperm cell]]s and many [[protozoan]]s have a similar structure to motile cilia that enables swimming through liquids; they are longer than cilia and have a different undulating motion.<ref name="Haimo_JCB198112">{{cite journal |vauthors=Haimo LT, Rosenbaum JL |date=December 1981 |title=Cilia, flagella, and microtubules |journal=The Journal of Cell Biology |volume=91 |issue=3 Pt 2 |pages=125s–130s |doi=10.1083/jcb.91.3.125s |pmc=2112827 |pmid=6459327}}</ref><ref name="Alberts1">{{cite book | last1=Alberts | first1=Bruce |title =Molecular biology of the cell | year=2015 | location=New York, NY | isbn=9780815344643 | pages=941–942 | edition=6}}</ref>

There are two major classes of cilia: ''motile'' and ''non-motile'' cilia, each with two subtypes, giving four types in all.<ref name="Falk">{{cite journal | last1=Falk | first1=N | last2=Lösl | first2=M | last3=Schröder | first3=N | last4=Gießl | first4=A | title=Specialized Cilia in Mammalian Sensory Systems | journal=Cells | date=11 September 2015 | volume=4 | issue=3 | pages=500–19 | doi=10.3390/cells4030500 | pmid=26378583| pmc=4588048 | doi-access=free }}</ref> A cell will typically have one primary cilium or many motile cilia.<ref name="Wheatley">{{cite journal | last1=Wheatley | first1=DN | title=Primary cilia: turning points in establishing their ubiquity, sensory role and the pathological consequences of dysfunction | journal=Journal of Cell Communication and Signaling | date=September 2021 | volume=15 | issue=3 | pages=291–297 | doi=10.1007/s12079-021-00615-5 | pmid=33970456 |pmc=8222448 }}</ref> The structure of the cilium core, called the [[axoneme]], determines the cilium class. Most motile cilia have a central pair of single [[microtubule]]s surrounded by nine pairs of double microtubules called a [[9+2 axoneme]]. Most non-motile cilia have a [[9+0 axoneme]] that lacks the central pair of microtubules. Also lacking are the associated components that enable motility including the outer and inner [[dynein]] arms, and radial spokes.<ref name="Fisch">{{cite journal | last1=Fisch | first1=C | last2=Dupuis-Williams | first2=P | title=Ultrastructure of cilia and flagella - back to the future! | journal=Biology of the Cell | date=June 2011 | volume=103 | issue=6 | pages=249–70 | doi=10.1042/BC20100139 | pmid=21728999 |s2cid=7636387 | doi-access=free }}</ref> Some motile cilia lack the central pair, and some non-motile cilia have the central pair, hence the four types.<ref name="Falk"/><ref name="Fisch"/>

Most non-motile cilia, termed ''primary cilia'' or ''sensory cilia'', serve solely as sensory organelles.<ref name="Prevo">{{cite journal | last1=Prevo | first1=B | last2=Scholey | first2=JM | last3=Peterman | first3=EJG | title=Intraflagellar transport: mechanisms of motor action, cooperation, and cargo delivery | journal=The FEBS Journal | date=September 2017 | volume=284 | issue=18 | pages=2905–2931 | doi=10.1111/febs.14068 | pmid=28342295| pmc=5603355 }}</ref><ref name ="Elliott">{{Cite journal |last1=Elliott |first1=Kelsey H. |last2=Brugmann |first2=Samantha A. |date=1 March 2019 |title=Sending mixed signals: Cilia-dependent signaling during development and disease |journal=Developmental Biology |volume=447 |issue=1 |pages=28–41 |doi=10.1016/j.ydbio.2018.03.007 |issn=1095-564X |pmc=6136992 |pmid=29548942}}</ref> Most vertebrate cell types possess a single non-motile primary cilium, which functions as a cellular antenna.<ref name="Singla 629–633">{{Cite journal |last1=Singla |first1=Veena |last2=Reiter |first2=Jeremy F. |date=2006-08-04 |title=The primary cilium as the cell's antenna: signaling at a sensory organelle |url=https://www.ncbi.nlm.nih.gov/pubmed/16888132 |journal=Science |volume=313 |issue=5787 |pages=629–633 |doi=10.1126/science.1124534 |issn=1095-9203 |pmid=16888132 |bibcode=2006Sci...313..629S |s2cid=29885142}}</ref><ref name="Patel">{{cite journal | last1=Patel | first1=MM | last2=Tsiokas | first2=L | title=Insights into the Regulation of Ciliary Disassembly | journal=Cells | date=1 November 2021 | volume=10 | issue=11 | page=2977 | doi=10.3390/cells10112977 | pmid=34831200 |pmc=8616418 | doi-access=free }}</ref> [[Olfactory neuron]]s possess a great many non-motile cilia. Non-motile cilia that have a central pair of microtubules are the [[Kinocilium|kinocilia]] present on [[hair cell]]s.<ref name="Falk"/>

Motile cilia are found in large numbers on [[Respiratory epithelium|respiratory epithelial cells]] – around 200 cilia per cell, where they function in [[mucociliary clearance]], and also have [[Mechanosensation|mechanosensory]] and [[Chemoreceptor|chemosensory]] functions.<ref name=Horani>{{Cite journal |last1=Horani |first1=A |last2=Ferkol |first2=T |date=May 2018 |title=Advances in the Genetics of Primary Ciliary Dyskinesia |journal=Chest |volume=154 |issue=3 |pages=645–652 |pmid=29800551 |pmc=6130327 |doi=10.1016/j.chest.2018.05.007}}</ref><ref name="2012-Enuka" /><ref name="Bloodgood">{{cite journal | last1=Bloodgood | first1=RA | title=Sensory reception is an attribute of both primary cilia and motile cilia | journal=Journal of Cell Science | date=15 February 2010 | volume=123 | issue=Pt 4 | pages=505–9 | doi=10.1242/jcs.066308 | pmid=20144998 |s2cid=207165576 }}</ref> Motile cilia on [[ependymal cells]] move the [[cerebrospinal fluid]] through the [[ventricular system]] of the [[brain]]. Motile cilia are also present in the [[oviduct]]s ([[fallopian tube]]s) of female ([[theria]]n) mammals, where they function in moving [[egg cell]]s from the [[ovary]] to the [[uterus]].<ref name="2012-Enuka" /><ref name="Panelli"/> Motile cilia that lack the central pair of microtubules are found in the cells of the embryonic [[primitive node]]; termed ''nodal cells'', these nodal cilia are responsible for the [[left-right asymmetry]] of [[bilaterians]].<ref name="Desgrange">{{cite journal | last1=Desgrange | first1=A | last2=Le Garrec | first2=JF | last3=Meilhac | first3=SM | title=Left-right asymmetry in heart development and disease: forming the right loop | journal=Development | date=22 November 2018 | volume=145 | issue=22 | doi=10.1242/dev.162776 | pmid=30467108 | s2cid=53719458 |url=https://hal.archives-ouvertes.fr/hal-03094768/file/dev162776.full.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://hal.archives-ouvertes.fr/hal-03094768/file/dev162776.full.pdf | archive-date=2022-10-09 | url-status=live}}
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