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Theouter ear,external ear, orauris externa is the external part of theear, which consists of theauricle (also pinna) and theear canal.[1] It gathers sound energy and focuses it on the eardrum (tympanic membrane).
The visible part is called theauricle, also known as thepinna, especially in other animals. It is composed of a thin plate of yellowelastic cartilage, covered with integument, and connected to the surrounding parts by ligaments and muscles; and to the commencement of theear canal by fibrous tissue. Manymammals can move the pinna (with the auriculares muscles) in order tofocus their hearing in a certain direction in much the same way that they can turn theireyes. Most humans do not have this ability.[2]
From the pinna, thesound waves move into theear canal (also known as theexternal acoustic meatus) a simple tube running through to themiddle ear. This tube leads inward from the bottom of the auricula and conducts the vibrations to the tympanic cavity and amplifies frequencies in the range 2 kHz to 5 kHz.[3]
Thehelicis major is a narrow vertical band situated upon the anterior margin of thehelix. It arises below, from thespina helicis, and is inserted into the anterior border of the helix, just where it is about to curve backward.
Thetransverse muscle is placed on the cranial surface of thepinna. It consists of scattered fibers, partly tendinous and partly muscular, extending from theeminentia conchae to the prominence corresponding with thescapha.
Theoblique muscle also on the cranial surface, consists of a few fibers extending from the upper and back part of theconcha to the convexity immediately above it.
The intrinsic muscles contribute to the topography of the auricle, while also function as a sphincter of the external auditory meatus. It has been suggested that during prenatal development in the womb, these muscles exert forces on the cartilage which in turn affects the shaping of the ear.[4]
The superior muscle is the largest of the three, followed by the posterior and the anterior.
In some mammals these muscles can adjust the direction of the pinna. In humans these muscles possess very little action.The auricularis anterior draws the auricula forward and upward, the auricularis superior slightly raises it, and the auricularis posterior draws it backward. The superior auricular muscle also acts as a stabilizer of theoccipitofrontalis muscle and as a weak brow lifter.[5] The presence of auriculomotor activity in the posterior auricular muscle causes the muscle to contract and cause the pinna to be pulled backwards and flatten when exposed to sudden, surprising sounds.[6]
One consequence of the configuration of the outer ear is selectively to boost thesound pressure 30- to 100-fold for frequencies around 3 kHz. This amplification makes humans most sensitive to frequencies in this range—and also explains why they are particularly prone to acoustical injury and hearing loss near this frequency. Most human speech sounds are also distributed in the bandwidth around 3 kHz.[7]
An important function of the pinna and concha is to selectively filter different sound frequencies in order to provide cues about the elevation of the sound source. The convolutions of the pinna are shaped so that the outer ear transmits more high-frequency components from an elevated source than from the same source at ear level.[8]
Malformations of the external ear can be a consequence ofhereditary disease, or exposure to environmental factors such asradiation,infection. Such defects include:
Goldenhar syndrome, a combination of developmental abnormalities affecting the ears, eyes, bones of the skull, and vertebrae, inherited in anautosomal dominant manner.[15]
Treacher Collins syndrome, characterised by dysplasia of the auricle, atresia of the bony part of the auditory canal, hypoplasia of the auditory ossicles and tympanic cavity, and 'mixed' deafness (bothsensorineural and conductive), inherited in an autosomal dominant manner.[16][17]
The outer ear's cartilage is homologous to the cartilage ingills of amphibians, fishes, and invertebrates such as thehorseshoe crab. The extracolumella cartilage of reptiles is likely also homologous.[20]
^Chon, Brian H.; Blandford, Alex D.; Hwang, Catherine J.; Petkovsek, Daniel; Zheng, Andrew; Zhao, Carrie; Cao, Jessica; Grissom, Nick; Perry, Julian D. (February 2021). "Dimensions, Function and Applications of the Auricular Muscle in Facial Plastic Surgery".Aesthetic Plastic Surgery.45 (1):309–314.doi:10.1007/s00266-020-02045-x.ISSN1432-5241.PMID33258010.S2CID227236615.
^Purves, Dale, George J. Augustine, David Fitzpatrick, William C. Hall, Anthony-Samuel LaMantia, James O. McNamara, and Leonard E. White (2008). "Chapter 13".Neuroscience. 4th ed. Sinauer Associates. p. 317.ISBN978-0-87893-697-7.{{cite book}}: CS1 maint: multiple names: authors list (link)
^Dale Purves, George J Augustine, David Fitzpatrick, Lawrence C Katz, Anthony-Samuel LaMantia, James O McNamara, and S Mark williams (2001). "Chapter 13".Neuroscience. 2nd edition. Sinauer Associates.ISBN0-87893-742-0.{{cite book}}: CS1 maint: multiple names: authors list (link)
^Thiruppathy, Mathi; Teubner, Lauren; Roberts, Ryan R.; Lasser, Micaela; Moscatello, Alessandra; Chen, Ya-Wen; Hochstim, Christian; Ruffins, Seth; Sarkar, Arijita; Tassey, Jade; Evseenko, Denis; Lozito, Thomas P.; Willsey, Helen Rankin; Gillis, J. Andrew; Crump, J. Gage (9 January 2025). "Repurposing of a gill gene regulatory program for outer ear evolution".Nature.639 (8055):682–690.Bibcode:2025Natur.639..682T.doi:10.1038/s41586-024-08577-5.PMID39788155.
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This article incorporates text in thepublic domain frompage 1033 of the 20th edition ofGray's Anatomy(1918)
Media related toOuter ear at Wikimedia Commons
