Editing Ear (section)

==Development==
During [[embryogenesis]], the ear develops as three distinct structures: the inner ear, the middle ear and the outer ear.<ref name=moore2009>{{cite book |last=Moore |first=Keith L. |author-link=Keith L. Moore |year=2009 |title=Fundamentos de Anatomía con Orientación Clínica |pages=1021–1035}}</ref> Each structure originates from a different [[germ layer]]: the [[ectoderm]], [[endoderm]] and [[mesenchyme]].<ref name=sadler2012>{{cite book |last=Sadler |first=T.W. |author-link=T.W. Sadler |year=2010 |title=Embriología Médica|pages=321–327}}</ref><ref name=moore2008>{{cite book |last=Moore |first=Keith L. |year=2008 |title=Embriología Clínica |pages=477–482}}</ref>

===Inner ear===
[[File:G1. Otic placode (V07a).png|thumb|The [[otic placode]] on a developing embryo (about four weeks old)]]
[[File:Gray62.png|thumb|The ear develops in the lower neck region and moves upwards as the [[mandible]] develops (six weeks).]]

Around its second to third week, the developing embryo consists of three layers: ectoderm, [[mesoderm]], and endoderm. The first part of the ear to develop is the inner ear,<ref name=moore2008/> which begins to form from the ectoderm around the embryo's 22nd day,<ref name=sadler2012/> derived from two thickenings called [[otic placode]]s on either side of the head. Each otic placode recedes below the ectoderm, forms an [[otic pit]] and then an [[otic vesicle]].<ref name="GRAYS40th_38">{{cite book|last1=Standring|first1=Susan|editor1-last=Borley|editor1-first=Neil R.|title=Gray's Anatomy: The Anatomical Basis of Clinical Practice|date=2008|publisher=[[Churchill Livingstone]]/[[Elsevier]]|location=[[Edinburgh]]|isbn=978-0-443-06684-9|edition=40|pages=Chapter 38. "Development of the ear", 651–653}}</ref> This entire mass is eventually surrounded by mesenchyme to form the bony labyrinth.<ref name=GRAYS40th_38 /><ref name=UNSWembryology>{{cite book |title= UNSW Embryology. Hearing-Inner Ear Development |url= http://php.med.unsw.edu.au/embryology/index.php?title=Hearing_-_Inner_Ear_Development |access-date= 20 April 2013 |url-status=dead |archive-url= https://web.archive.org/web/20120930063158/http://php.med.unsw.edu.au/embryology/index.php?title=Hearing_-_Inner_Ear_Development |archive-date= 30 September 2012}}</ref>

Around the 28th day, parts of the otic vesicle begin to form the vestibulocochlear nerve.<ref name="GRAYS40th_38" /><ref name="drake2010">{{cite book |last1=Drake |first1=Richard L. |author-link=Richard L. Drake |title=GRAY Anatomía para estudiantes |last2=Wayne |first2=A. |author-link2=A. Wayne |last3=Mitchell |first3=Adam |author-link3=Adam Mitchell (scientist) |year=2010 |pages=854–871}}</ref> These form [[bipolar neuron]]s, which supply sensation to parts of the inner ear (namely the sensory parts of the semicircular canals, macular of the utricle and saccule, and organ of Corti).<ref name="GRAYS40th_38" />

Around the 33rd day, the vesicles begin to differentiate. Posteriorly, they form what will become the utricle and semicircular canals. Anteriorly, the vesicles differentiate into a rudimentary saccule, which eventually becomes the saccule and cochlea. Part of the saccule eventually gives rise and connects to the cochlear duct, which appears approximately during the sixth week and connects to the saccule through the [[ductus reuniens]].<ref name="sadler2012" />

As the cochlear duct's mesenchyme begins to differentiate, three cavities are formed: the [[scala vestibuli]], the [[scala tympani]] and the [[scala media]].<ref name="sadler2012" /><ref name="UNSWembryology" /> Both the scala vestibuli and the scala tympani contain an extracellular fluid called [[perilymph]], while the scala media contains endolymph.<ref name="UNSWembryology" /> The [[vestibular membrane]] and the [[basilar membrane]] develop to separate the cochlear duct from the vestibular duct and the tympanic duct, respectively.<ref name="sadler2012" />

;Molecular regulation
Most of the genes responsible for the [[Regulation of gene expression|regulation]] of inner ear formation and its [[morphogenesis]] are members of the [[homeobox gene]] family such as [[Pax genes|Pax]], Msx and Otx homeobox genes. The development of inner ear structures such as the [[cochlea]] is regulated by [[DLX5 (gene)|Dlx5]]/[[DLX6 (gene)|Dlx6]], [[OTX1 (gene)|Otx1]]/[[OTX2 (gene)|Otx2]] and [[PAX2|Pax2]], which in turn are controlled by the master [[SHH (gene)|gene Shh]]. Shh is secreted by the [[notochord]].<ref name=sumantra2010>{{cite journal |last1=Chatterjee |first1=Sumantra |author-link=Sumantra Chatterjee |last2=Kraus |first2=Petra |author-link2=Petra Krauss |last3=Luftkin |first3=Thomas |author-link3=Thomas Luftkin |year=2010 |title= A symphony of inner ear developmental control genes |journal=BMC Genetics |volume=11 |pages=68 |doi=10.1186/1471-2156-11-68 |pmid=20637105 |pmc=2915946 |doi-access=free }}</ref>

===Middle ear===
The middle ear and its components develop from the first and second [[pharyngeal arch]]es.<ref name=GRAYS40th_38 /> The tympanic cavity and auditory tube develop from the first part of the [[pharyngeal pouch (embryology)|pharyngeal pouch]] between the first two arches in an area which will also go on to develop the [[pharynx]]. This develops as a structure called the [[tubotympanic recess]].<ref name=GRAYS40th_38 /> The ossicles (malleus, incus and stapes) normally appear during the first half of fetal development. The first two (malleus and incus) derive from the first pharyngeal arch and the stapes derives from the second.<ref name=sadler2012/> All three ossicles develop from the [[neural crest]].<ref name=GRAYS40th_38 /> Eventually, cells from the tissue surrounding the ossicles will experience [[apoptosis]] and a new layer of endodermal epithelial will constitute the formation of the tympanic cavity wall.<ref name=sadler2012/><ref name=moore2008/>

===Outer ear===

Unlike structures of the inner and middle ear, which develop from pharyngeal pouches, the ear canal originates from the dorsal portion of the first [[pharyngeal cleft]].<ref name=sadler2012/><ref name=GRAYS40th_38 /> It is fully expanded by the end of the 18th week of development.<ref name=UNSWembryology/> The eardrum is made up of three layers (ectoderm, endoderm and connective tissue). The auricle originates as a fusion of six hillocks. The first three hillocks are derived from the lower part of the first pharyngeal arch and form the tragus, crus of the helix, and helix, respectively. The final three hillocks are derived from the upper part of the second pharyngeal arch and form the antihelix, antitragus, and earlobe.<ref name=sadler2012/><ref name=GRAYS40th_38 /><ref name=UNSWembryology/> The outer ears develop in the lower [[neck]]. As the [[mandible]] forms, they move towards their final position level with the eyes.<ref name=moore2009/><ref name=drake2010/>

===Growth===
The ears of newborn humans are proportionally very large, even more so than the head's largeness as compared to the body. Ears grow quickly until about the age of nine, then continue to grow steadily in circumference (about 0.5 millimeters a year) throughout life, with the increase in length more extreme in males.<ref>{{Cite journal |last1=Niemitz |first1=Carsten |last2=Nibbrig |first2=Maike |last3=Zacher |first3=Vanessa |date=December 2007 |title=Human ears grow throughout the entire lifetime according to complicated and sexually dimorphic patterns--conclusions from a cross-sectional analysis |url=https://pubmed.ncbi.nlm.nih.gov/18196763/#:~:text=At%20the%20time%20of%20birth,volunteers%20aged%20over%2085%20yrs. |journal=Anthropologischer Anzeiger; Bericht Uber die Biologisch-Anthropologische Literatur |volume=65 |issue=4 |pages=391–413 |doi=10.1127/anthranz/65/2007/391 |issn=0003-5548 |pmid=18196763}}</ref><ref>{{Cite journal |last1=Tan |first1=R |last2=Osman |first2=V |last3=Tan |first3=G |date=1997-10-01 |title=Ear size as a predictor of chronological age |url=https://www.sciencedirect.com/science/article/pii/S0167494397000101 |journal=Archives of Gerontology and Geriatrics |volume=25 |issue=2 |pages=187–191 |doi=10.1016/S0167-4943(97)00010-1 |pmid=18653105 |issn=0167-4943|url-access=subscription }}</ref>

=== Uniqueness ===
Ears are individually very unique, with the odds of two people having matching ears very low.<ref>{{Cite web |date=2023-07-14 |title=Ears as effective as DNA in identifying people - new study |url=https://www.rnz.co.nz/national/programmes/checkpoint/audio/2018898315/ears-as-effective-as-dna-in-identifying-people-new-study |access-date=2024-06-04 |website=[[RNZ]] |language=en-nz}}</ref> Additionally, the ear's proportions are normally retained for life, and have thus been employed for [[forensic identification]] since the 1950s.<ref>{{Cite web |last=Tangalakis-Lippert |first=Katherine |date=2023-03-19 |title=Is Putin using a body double? Listen here: Skeptics say spotting a decoy is all in the ears. |url=https://www.businessinsider.com/vladimir-putin-ukraine-trip-body-double-conspiracy-theories-ears-2023-3 |access-date=2023-03-22 |website=[[Business Insider]] |language=en-US}}</ref>