Editing Blinking (section)

==Function and anatomy==
[[File:Bird blink-edit.jpg|thumb|right|Birds, reptiles and sharks blink with a [[nictitating membrane]] from one side of the eye to the other.]]
Blinking provides moisture to the eye by irrigation using tears and a lubricant the eyes secrete. The eyelid provides suction across the eye from the tear duct to the entire eyeball to keep it from drying out.
[[File:Closed human eye, superior view.jpg|thumb|Closed eye of a human, displaying [[eyelashes]] which function to catch irritants when the eye is blinked.]]
Blinking also protects the eye from irritants. [[Eyelash]]es are hairs which grow from the edges of the upper and lower [[Eyelid|eyelids]] that create a line of defense against dust and other elements to the eye. The eyelashes catch most of these irritants before they reach the eyeball.

There are multiple muscles that control reflexes of blinking. The main muscles, in the upper eyelid, that control the opening and closing are the [[orbicularis oculi]] and [[levator palpebrae superioris muscle]]. The orbicularis oculi closes the eye, while the contraction of the levator palpebrae muscle opens the eye. The Müller's muscle, or the [[superior tarsal muscle]], in the upper eyelid and the inferior palpebral muscle in the lower 3 eyelid are responsible for widening the eyes. These muscles are not only imperative in blinking, but they are also important in many other functions such as squinting and winking.  The inferior palpebral muscle is coordinated with the inferior rectus to pull down the lower lid when one looks down.

The correlation between human eyelid blink behavior and [[psychological stress]] was also demonstrated by means of a laboratory study.<ref>N Reßut (2021): ''Das Lidschlagverhalten als Indikator psychischer Belastung'', Wiesbaden: Springer Vieweg, 2021. DOI: https://doi.org/10.1007/978-3-658-36052-8 – ISBN 978-3-658-36051-1</ref><ref>N Reßut & A Hoppe (2019): ''Erfassung von individuellem Beanspruchungserleben bei kognitiven Belastungssituationen mittels Mustererkennung im Lidschlagverhalten.'' In: Zeitschrift für Arbeitswissenschaft 65 (2019), S. 1–13. DOI: https://doi.org/10.1007/s41449-019-00165-y. – ISSN 0340-2444</ref> Lying may affect the rate of blinking.<ref>{{Cite journal|url=https://link.springer.com/article/10.1007/s10919-008-0051-0|doi = 10.1007/s10919-008-0051-0|title = Blinking During and After Lying|year = 2008|last1 = Leal|first1 = Sharon|last2 = Vrij|first2 = Aldert|journal = Journal of Nonverbal Behavior|volume = 32|issue = 4|pages = 187–194|s2cid = 43996756|url-access = subscription}}</ref> 

Blinking is used for communication in humans,<ref name="p574">{{cite journal |last1=Hömke |first1=Paul |last2=Holler |first2=Judith |last3=Levinson |first3=Stephen C. |date=2018 |title=Eye blinks are perceived as communicative signals in human face-to-face interaction |journal=PLOS ONE |volume=13 |issue=12 |page=e0208030 |doi=10.1371/journal.pone.0208030 |issn=1932-6203 |doi-access=free|pmid=30540819 |pmc=6291193 |bibcode=2018PLoSO..1308030H |hdl=21.11116/0000-0002-7F3D-D |hdl-access=free }}</ref> some primates,<ref name="o381">{{cite journal |last1=Tada |first1=Hideoki |last2=Omori |first2=Yasuko |last3=Hirokawa |first3=Kumi |last4=Ohira |first4=Hideki |last5=Tomonaga |first5=Masaki |date=2013 |title=Eye-Blink Behaviors in 71 Species of Primates |journal=PLOS ONE |volume=8 |issue=5 |page=e66018 |doi=10.1371/journal.pone.0066018 |issn=1932-6203 |doi-access=free|pmid=23741522 |bibcode=2013PLoSO...866018T }}</ref> in human interactions with cats,<ref name="e356">{{cite journal |last1=Humphrey |first1=Tasmin |last2=Proops |first2=Leanne |last3=Forman |first3=Jemma |last4=Spooner |first4=Rebecca |last5=McComb |first5=Karen |date=2020-10-05 |title=The role of cat eye narrowing movements in cat–human communication |journal=Scientific Reports |volume=10 |issue=1 |page= 16503|doi=10.1038/s41598-020-73426-0 |issn=2045-2322 |doi-access=free|pmid=33020542 |pmc=7536207 |bibcode=2020NatSR..1016503H }}</ref>  and by female concave-eared torrent frogs to initiate mating with males.<ref name="s453">{{cite journal |last1=Chen |first1=Pan |last2=Liu |first2=Shuwen |last3=Wu |first3=Yatao |last4=Liu |first4=Guoqing |last5=Jin |first5=Yingying |last6=Zhang |first6=Fang |year=2024 |title=Female frogs communicate with males through blinking |journal=Current Biology |volume=34 |issue=5 |pages=R191–R192 |doi=10.1016/j.cub.2024.01.023 |pmid=38471444 |bibcode=2024CBio...34.R191C |issn=0960-9822}}</ref> 

===Central nervous system's control===
Though one may think that the stimulus triggering blinking is dry or irritated eyes, it is most likely that it is controlled by a "blinking center" of the [[globus pallidus]] of the [[lenticular nucleus]]—a body of nerve cells between the base and outer surface of the brain.  Nevertheless, external stimuli can contribute. The orbicularis oculi is a facial muscle; therefore its actions are translated by the [[facial nerve]] root. The levator palpebrae superioris' action is sent through the [[oculomotor nerve]]. The duration of a blink is
on average 100–150 milliseconds according to UCL researcher<ref>{{cite web|url=https://www.ucl.ac.uk/news/2005/jul/blink-and-you-miss-it|title=Blink and you miss it|date=2005-08-03}}</ref> and between 100 and 400 ms according to the Harvard Database of Useful Biological Numbers.<ref>{{cite web|url=http://bionumbers.hms.harvard.edu/bionumber.aspx?s=y&id=100706&ver=0|title=Average duration of a single eye blink – Human Homo sapiens – BNID 100706}}</ref> Closures in excess of 1000 ms were defined as [[microsleep]]s.

Greater activation of  dopaminergic pathways dopamine production in the [[striatum]] is associated with a higher rate of spontaneous eye blinking.<ref>{{cite journal | last1 = Taylor | first1 = JR | last2 = Elsworth | first2 = JD | last3 = Lawrence | first3 = MS | last4 = Sladek Jr | first4 = JR | last5 = Roth | first5 = RH | last6 = Redmond Jr | first6 = DE | title = Spontaneous blink rates correlate with dopamine levels in the caudate nucleus of MPTP-treated monkeys | journal = Experimental Neurology | volume = 158 | issue = 1 | pages = 214–20 | year = 1999 | pmid = 10448434 | doi = 10.1006/exnr.1999.7093 | s2cid = 43504305 | doi-access = free }}</ref><ref>{{cite journal | last1 = Colzato | first1 = LS | last2 = Van Den Wildenberg | first2 = WP | last3 = Van Wouwe | first3 = NC | last4 = Pannebakker | first4 = MM | last5 = Hommel | first5 = B | title = Dopamine and inhibitory action control: evidence from spontaneous eye blink rates | journal = Experimental Brain Research. Experimentelle Hirnforschung. Experimentation Cerebrale | volume = 196 | issue = 3 | pages = 467–74 | year = 2009 | pmid = 19484465 | pmc = 2700244 | doi = 10.1007/s00221-009-1862-x }}</ref> Conditions in which there is reduced dopamine availability such as [[Parkinson's disease]] have reduced eye blink rate,<ref>{{cite journal | last1 = Deuschl | first1 = G | last2 = Goddemeier | first2 = C | title = Spontaneous and reflex activity of facial muscles in dystonia, Parkinson's disease, and in normal subjects | journal = [[Journal of Neurology, Neurosurgery, and Psychiatry]] | volume = 64 | issue = 3 | pages = 320–4 | year = 1998 | pmid = 9527141 | pmc = 2169979 | doi=10.1136/jnnp.64.3.320}}</ref> while conditions in which it is raised such as [[schizophrenia]] have an increased rate.<ref>{{cite journal | last1 = Freed | first1 = WJ | last2 = Kleinman | first2 = JE | last3 = Karson | first3 = CN | last4 = Potkin | first4 = SG | last5 = Murphy | first5 = DL | last6 = Wyatt | first6 = RJ | title = Eye-blink rates and platelet monoamine oxidase activity in chronic schizophrenic patients | journal =[[Biological Psychiatry (journal)|Biological Psychiatry]] | volume = 15 | issue = 2 | pages = 329–32 | year = 1980 | pmid = 7417620 }}</ref> Blink rate is associated with dopamine-related executive function and creativity.<ref>{{Cite journal|last1=Jongkees|first1=Bryant J.|last2=Colzato|first2=Lorenza S.|date=December 2016|title=Spontaneous eye blink rate as predictor of dopamine-related cognitive function—A review|url=https://linkinghub.elsevier.com/retrieve/pii/S0149763416302846|journal=Neuroscience & Biobehavioral Reviews|language=en|volume=71|pages=58–82|doi=10.1016/j.neubiorev.2016.08.020|pmid=27555290|s2cid=25094074|url-access=subscription}}</ref><ref>{{Cite journal|last1=Chermahini|first1=Soghra Akbari|last2=Hommel|first2=Bernhard|date=2010-06-01|title=The (b)link between creativity and dopamine: Spontaneous eye blink rates predict and dissociate divergent and convergent thinking|url=https://www.sciencedirect.com/science/article/pii/S0010027710000715|journal=Cognition|language=en|volume=115|issue=3|pages=458–465|doi=10.1016/j.cognition.2010.03.007|pmid=20334856|s2cid=14791691|issn=0010-0277|url-access=subscription}}</ref><ref>{{Cite journal|last1=Kuwamizu|first1=Ryuta|last2=Suwabe|first2=Kazuya|last3=Damrongthai|first3=Chorphaka|last4=Fukuie|first4=Takemune|last5=Ochi|first5=Genta|last6=Hyodo|first6=Kazuki|last7=Hiraga|first7=Taichi|last8=Nagano-Saito|first8=Atsuko|last9=Soya|first9=Hideaki|date=July 2021|title=Spontaneous Eye Blink Rate Connects Missing Link between Aerobic Fitness and Cognition|url=https://journals.lww.com/10.1249/MSS.0000000000002590|journal=Medicine & Science in Sports & Exercise|language=en|volume=53|issue=7|pages=1425–1433|doi=10.1249/MSS.0000000000002590|pmid=33433152|s2cid=231585782|issn=1530-0315|url-access=subscription}}</ref>

===Evolutionary origins===
Blinking is present in all major [[tetrapod]] [[crown group]]s. The soft tissues involved in blinking have not been preserved in the fossil record, but study of [[mudskipper]]s (a group of amphibious fish species that evolved blinking [[Convergent evolution|independently]] from other tetrapod species, but for similar purposes), suggest that blinking (which involves the eye retracting in mudskippers) may have arose in response to [[Natural selection|selective pressures]] upon species shifting from aquatic to terrestrial habitats. For example, compared to an aquatic environment, in a terrestrial environment, the corneal cells must be kept moist such that vital substances like oxygen can more easily diffuse into them, detritus may adhere to the eye in dry conditions, and objects may move towards the eye at faster and more dangerous speeds in air than in water. Additionally, when at their fully aquatic juvenile stage of development, their eyes are not in the positioning with which they blink, but as adults, their eyes elevate to a position that can blink, which they do when they are not submerged or bump into a surface, suggesting blinking emerged as an adaptation to terrestrial life as opposed to aquatic life.<ref name="mudskipper">{{cite journal |last1=Aiello |first1=Brett R. |last2=Bhamla |first2=M. Saad |last3=Gau |first3=Jeff |last4=Morris |first4=John G. L. |last5=Bomar |first5=Kenji |last6=da Cunha |first6=Shashwati |last7=Fu |first7=Harrison |last8=Laws |first8=Julia |last9=Minoguchi |first9=Hajime |last10=Sripathi |first10=Manognya |last11=Washington |first11=Kendra |last12=Wong |first12=Gabriella |last13=Shubin |first13=Neil H. |last14=Sponberg |first14=Simon |last15=Stewart |first15=Thomas A. |date=April 24, 2023 |title=The origin of blinking in both mudskippers and tetrapods is linked to life on land |journal=[[PNAS]] |volume=120 |issue=18 |pages=e2220404120 |doi=10.1073/pnas.2220404120 |pmid=37094121 |pmc=10160996 |doi-access=free|bibcode=2023PNAS..12020404A }}</ref>

Early tetrapods in the transition to land, which would later yield all non-mudskipper blinking species, possessed similar characteristics regarding eye positioning that suggest blinking arose in response to aerial vision and terrestrial lifestyle.<ref name="mudskipper" />