Editing Cilium (section)

== Function ==
The [[dynein]] in the axoneme – [[axonemal dynein]] forms bridges between neighbouring microtubule doublets. When [[Adenosine triphosphate|ATP]] activates the motor domain of dynein, it attempts to walk along the adjoining microtubule doublet. This would force the adjacent doublets to slide over one another if not for the presence of [[nexin]] between the microtubule doublets. And thus the force generated by dynein is instead converted into a bending motion.<ref>{{Cite book |url = https://www.ncbi.nlm.nih.gov/books/NBK26888/|title = Molecular Biology of the Cell|last = Alberts|first = Bruce| chapter=Molecular Motors |year = 2002| publisher=Garland Science }}{{ISBN?}}{{page needed|date=April 2020}}</ref><ref name="King">{{cite journal |last1=King |first1=SM |title=Axonemal Dynein Arms. |journal=Cold Spring Harbor Perspectives in Biology |date=1 November 2016 |volume=8 |issue=11 |pages=a028100 |doi=10.1101/cshperspect.a028100 |pmid=27527589|pmc=5088525 }}</ref>

===Sensing the extracellular environment===
Some primary cilia on [[epithelial]] cells in eukaryotes act as ''cellular antennae'', providing [[Molecular sensor|chemosensation]], [[thermosensation]] and [[mechanosensation]] of the extracellular environment.<ref name="Adams2008"/><ref name="Singla 629–633"/> These cilia then play a role in mediating specific signalling cues, including soluble factors in the external cell environment, a [[Secretion|secretory]] role in which a soluble protein is released to have an effect downstream of the fluid flow, and mediation of fluid flow if the cilia are [[Motility|motile]].<ref name=Adams2008>{{cite journal | vauthors = Adams M, Smith UM, Logan CV, Johnson CA | title = Recent advances in the molecular pathology, cell biology and genetics of ciliopathies | journal = Journal of Medical Genetics | volume = 45 | issue = 5 | pages = 257–67 | date = May 2008 | pmid = 18178628 | doi = 10.1136/jmg.2007.054999 | doi-access = free }}</ref>

Some [[epithelial]] cells are ciliated, and they commonly exist as a sheet of polarized cells forming a tube or tubule with cilia projecting into the [[Lumen (anatomy)|lumen]]. This sensory and signalling role puts cilia in a central role for maintaining the local cellular environment and may be why [[Ciliopathy|ciliary defects]] cause such a wide range of human diseases.<ref name="Reiter 533–547"/>

In the embryo, [[nodal cilia]] are used to direct the flow of extracellular fluid.  This leftward movement is to generate [[left-right asymmetry]] across the midline of the embryo.  Central cilia coordinate their rotational beating while the immotile cilia on the sides sense the direction of the flow.<ref name="Larsen"/><ref>{{cite book|last1=Wolpert|first1=Lewis|title=Principles of Development|last2=Tickle|first2=Cheryll|last3=Martinez Arias|first3=Alfonso|date=2015|publisher=Oxford University Press|edition=5th|page=227}}</ref><ref>[https://www.science.org/doi/10.1126/science.abq7317 Cilia function as calcium-mediated mechanosensors that instruct left-right asymmetry], Science, 5 January 2023, Vol 379, Issue 6627, pp. 71-78; DOI: 10.1126/science.abq7317</ref> Studies in mice suggest a biophysical mechanism by which the direction of flow is sensed.<ref name=science20230105>[https://www.science.org/doi/10.1126/science.abq8148 Immotile cilia mechanically sense the direction of fluid flow for left-right determination], Science, 5 January 2023, Vol 379, Issue 6627, pp. 66-71; DOI: 10.1126/science.abq8148</ref>

===Axo-ciliary synapse===
With axo-ciliary [[synapse]]s,<!-- first reported in 2022,--> there is communication between [[Serotonin|serotonergic]] [[axon]]s and <!--at least the -->primary cilia of [[Hippocampus anatomy#Basic hippocampal circuit|CA1]] [[Pyramidal cell|pyramidal]] [[neuron]]s that alters the neuron's [[epigenetic]] state in the [[Cell nucleus|nucleus]] – "a way to change what is being transcribed or made in the nucleus" via this signalling distinct from that at the [[plasma membrane]] which also is longer-term.<ref>{{cite news |last1=Tamim |first1=Baba |title=New discovery: Synapse hiding in the mice brain may advance our understanding of neuronal communication |url=https://interestingengineering.com/science/new-discovery-synapse-hiding-in-mice-brain |access-date=19 October 2022 |work=interestingengineering.com |date=4 September 2022}}</ref><ref>{{cite journal |last1=Sheu |first1=Shu-Hsien |last2=Upadhyayula |first2=Srigokul |last3=Dupuy |first3=Vincent |last4=Pang |first4=Song |last5=Deng |first5=Fei |last6=Wan |first6=Jinxia |last7=Walpita |first7=Deepika |last8=Pasolli |first8=H. Amalia |last9=Houser |first9=Justin |last10=Sanchez-Martinez |first10=Silvia |last11=Brauchi |first11=Sebastian E. |last12=Banala |first12=Sambashiva |last13=Freeman |first13=Melanie |last14=Xu |first14=C. Shan |last15=Kirchhausen |first15=Tom |last16=Hess |first16=Harald F. |last17=Lavis |first17=Luke |last18=Li |first18=Yulong |last19=Chaumont-Dubel |first19=Séverine |last20=Clapham |first20=David E. |title=A serotonergic axon-cilium synapse drives nuclear signaling to alter chromatin accessibility |journal=Cell |date=1 September 2022 |volume=185 |issue=18 |pages=3390–3407.e18 |doi=10.1016/j.cell.2022.07.026 |pmid=36055200 |pmc=9789380 |s2cid=251958800 |language=English |issn=0092-8674}}
* University press release: {{cite news |title=Scientists discover new kind of synapse in neurons' tiny hairs |url=https://phys.org/news/2022-09-scientists-kind-synapse-neurons-tiny.html |access-date=19 October 2022 |work=Howard Hughes Medical Institute via phys.org |language=en}}</ref>