Semin. Neurotol. Otolaryngol. External auditory exostoses (EAE; torus acusticus) are dense bony growths protruding into the external auditory canal. the evolution of the vertebrate ear. The external ear (pinna) is a strictly mammalian innovation. Indeed, in Grhl3 null mice with deficient periderm, the primary canal closed prematurely, providing a hopeful avenue for further research into the etiopathology of congenital aural atresia (CAA) (Fons et al., 2020). , It has been suggested that a relatively large trough in the jaw bone of the early Cretaceous monotreme Teinolophos provides evidence of a pre-mammalian jaw joint, because therapsids and many mammaliforms had such troughs in which the articular and angular bones "docked". Laryngol. Genet. Over the course of the evolution of mammals, one bone from the lower and one from the upper jaw (the articular and quadrate bones) lost their purpose in the jaw joint and migrated to the middle ear. Internal/Inside Parts An internal (surgically implanted) parts that work together to allow the user to recognize the sound. The pathologic features of keratosis obturans and cholesteatoma of the external auditory canal. Looking to developmental biology for the answers will be key. The event is well-documented and important as a demonstration of transitional forms and exaptation, the re-purposing of existing structures during evolution. doi: 10.1016/j.semcdb.2012.08.010, Niemann, C., Unden, A. These bones, or ossicles, are a defining characteristic of all mammals. Tian-Yu, Z., and Bulstrode, N. (2019). Less frequently inner ear deformities and deformities of the stapes footplate are also present (Vrabec and Lin, 2010). See more. Whilst EAC defects are observed in mouse mutants of Prx1 and Gas1, TSH, and GSC have been corroborated in human genome wide sequencing studies also (Feenstra et al., 2007). Laryngoscope 104, 1219–1224. (2012). Temporal requirement of Hoxa2 in cranial neural crest skeletal morphogenesis. Acquired disease of the EAM includes of course the breadth of traumatic, infective and rarely neoplastic disease and its comprehensive review is beyond the scope of this review. This closure has been linked to the removal of periderm (Fons et al., 2020). doi: 10.1016/j.amjoto.2008.08.013, Keywords: hearing, deafness, external ear, ear canal, ear deformities, congenital, Citation: Mozaffari M, Nash R and Tucker AS (2021) Anatomy and Development of the Mammalian External Auditory Canal: Implications for Understanding Canal Disease and Deformity. doi: 10.1097/mao.0b013e3181f7ab62, Yellon, R. F. (2011). A failure of this self-cleaning mechanism leads to the build-up of sloughed off keratinocytes in the canal, causing hearing impairment from blockage and localized tissue damage from chronic inflammation (Naiberg et al., 1984). Did pinna cartilage elongate inward to meet the bony canal or did the cartilaginous canal evolve separately from the pinna? SAMS, a syndrome of short stature, auditory-canal atresia, mandibular hypoplasia, and skeletal abnormalities is a unique neurocristopathy caused by mutations in Goosecoid. Keratosis obturans and external ear canal cholesteatoma: how and why we should distinguish between these conditions. exostoses of the external auditory canal (external auditory exostoses (EAEs)) are generally a benign condition more commonly occurs in people who avidly engage in aquatic activities - this increased incidence in people who engage in aquatic activities has led to this condition also being known as “surfer’s ear” Variations in the non-mammalian ear canal. Aristotle, the father of biology, expanded this idea to include the development of organisms and the origins of groups of organisms. Further understanding the epithelial dynamics that bestow EAM skin its migratory potential and its regenerative capacity will certainly begin to answer this question. 31, 1421–1426. Figure 3. 16, 263–269. doi: 10.1097/mao.0b013e3182a36065. (2008). Ear Mites These oval mites pass easily from pet to pet. (2011). (D) Frontal section of developing ear canal in 10 p.h. J. Otolaryngol. Fibrous ring, pulled interiorly. , The earliest mammals were generally small animals, and were likely nocturnal insectivores. Am. Development 122, 173–179. Otolaryngol. 15, 204–208. Invest. Localized differences in epithelial cell migration in the tympanic membrane have recently been proposed to underly propensity to middle ear cholesteatoma formation and may provide clues to the etiology of canal cholesteatoma also (Frumm et al., 2020). Sci. Der Name Darwin war in der Wissenschaft bereits bekannt, als Charles Robert Darwin am 12. 22, 976–985. The Otol. Otol. External definition, of or relating to the outside or outer part; outer: an external surface. Otolaryngol. Trans. doi: 10.1002/aja.1001890302, Michaels, L., and Soucek, S. (1991). Sci. Learn vocabulary, terms, and more with flashcards, games, and other study tools. As anatomical and molecular details are added to our understanding of ear development, compelling questions are beginning to emerge. Living mammal species can be identified by the presence in females of mammary glands which produce milk. There is significant individual variation in canal shape, which is perhaps not surprising given the complex of irregular shaped cartilages that interlink to form the cartilaginous ear canal (Bartel-Friedrich and Wulke, 2007). Axial CT scan of a patient with congenital aural stenosis and left-sided cholesteatoma. Patient photograph and scans of congenital aural atresia. Am. The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. days showing a tortuous path to the opening (star).  A more recent analysis of Teinolophos concluded that the trough was a channel for the large vibration and electrical sensory nerves terminating in the bill (a defining feature of the modern platypus). Corbridge, R. J., Michaels, L., and Wright, T. (1996). J Neurobiol 53:251–264. Head Neck Surg.  However, several studies have cast doubt on whether Hadrocodium did indeed possess a definitive mammalian middle ear; Hadrocodium likely had an ossified connection between the middle ear and the jaw, which is not visible in the fossil evidence due to limited preservation. Fossils of several shrew-like mammals that lived some 120 million years ago have revealed the earliest evidence of the middle ear bones separating from the jaw, a key step in the evolution … doi: 10.1016/j.heares.2018.05.009, Edfeldt, L., and Strömbäck, K. (2015). Using a combination of lineage tracing, live imaging and single cell sequencing, they demonstrate that the TM epidermis has distinct stem cell and committed progenitor regions, located close to supporting mesenchyme (the manubrium and annulus respectively). Acta Otolaryngol. A research team led by scientists of the Max Planck Institute for Evolutionary Anthropology scanned the skulls of Neandertals and found the small middle ear ossicles, which are important for hearing. Development 140, 4386–4397. More recent experiments using BrdU to chase and label proliferating cells suggest a more involved and dynamic source of stem and progenitor cells that migrate in different directions in different parts of the TM (Knutsson et al., 2011; Chari et al., 2018). From 20kW – 100kW (DX) or 140kW (chilled water), the Leonardo range of downflow and upflow precision air conditioning units provide flexible airflow configurations whatever your cooling requirements. Programmed cell death in the development of the mouse external auditory canal. Within our complex hearing pathway, the ear canal is responsible for funneling sound waves toward the tympanic membrane (ear drum) and into the middle ear, and as such is a physical link between the tympanic membrane and the outside world. The shape of the osseous external auditory canal and its relationship to chronic external otitis.  In basal members of the 3 major clades of amniotes (synapsids, eureptiles, and parareptiles) the stapes bones are relatively massive props that support the braincase, and this function prevents them from being used as part of the hearing system. The term "external otitis" (also known as otitis externa or swimmer's ear) refers to inflammation of the external auditory canal or auricle. Lower frequencies with wavelengths larger than the canal itself are not affected by variations in canal diameter, however, as sound waves concertina at higher frequency, variations in canal dimension have a discernible effect on sound transmission. Serous secretions and sebum from the cerumen glands mix with sloughed keratinized squames. At around Carnegie stage 17 (6 weeks post conception and equivalent to E12.0 in mice), the primary canal begins to form either by the first cleft deepening or as a new invagination within the 1st arch. LLC 100, 223–237. Recent studies have built on decades-old knowledge of ear canal development and suggest a novel multi-stage, complex and integrated system of development, helping to explain the mechanisms underlying congenital canal atresia and stenosis. There are four Evolution levels from 100 to 400 with a preamp, a power amp and an integrated at each level. Human studies, however, have had contradictory results and further controlled trials are needed to evaluate its potential role in preventing restenosis (Banthia and Selesnick, 2003; Battelino et al., 2005). doi: 10.1002/lary.21408, Yoon, Y. H., Park, J. Y., and Park, Y. H. (2010). (2004). External ear canal cholesteatoma (EECC) is also rare and was for a long time grouped together with keratosis obturans as the same disease (Persaud et al., 2018). Complications include restenosis, recurrent keratinous debris build up, poor hearing outcomes (in one study as many as 93% of patients still required a hearing aid post-op) and facial palsy resulting from altered and variable anatomy of the facial nerve in CAA (Bauer et al., 1994). RN provided clinical images and reviewed clinical sections of the manuscript. Englisch-Deutsch-Übersetzungen für external ear canal [Meatus acusticus externus] im Online-Wörterbuch dict.cc (Deutschwörterbuch). doi: 10.1371/journal.pone.0007591. The ossicles evolved from skull … Proc. Otolaryngol. Scan Electron Microsc 3:1301–1312. Genet. Anthwal, N., Fenelon, J., Johnston, S. D., Renfree, M. B., and Tucker, A. S. (2020). doi: 10.1046/j.1365-2273.2000.00388.x. For example, in the platypus the ear canal exits high on the head, next to the eye, so that both the eye and ear are not submerged while the animal is swimming (Manger et al., 1998). Clin. Evolution of the jaw joint in synapsids. Esthetics aside, hearing loss is the main problem in complete atresia, as the absence of a lumen precludes the possibility of cholesteatoma forming. Dividing canal atresia into complete, partial and stenotic is important to the clinician as it maps patients to key treatment considerations: hearing outcome, likelihood of cholesteatoma (erosive keratin-filled cysts that form when EAM skin cannot migrate out as normal) and the feasibility of achieving a self-cleaning ear should atresiaplasty be considered (Edfeldt and Strömbäck, 2015). Mutations in HOXA2 have been characterized in a number of families with microtia (Alasti et al., 2008). Adv. The ossicles act as the mechanical analog of an electrical transformer, matching the mechanical impedance of vibrations in air to vibrations in the liquid of the cochlea. doi: 10.1016/j.devcel.2010.12.010, Mukherjee, A., Hollern, D. P., Williams, O. G., Rayburn, T. S., Byrd, W. A., Yates, C., et al. The glandular aspects of the tabby syndrome in the mouse. Genetic analysis of syndromic patients can provide valuable genetic background to the etiology of both monogenic and syndromic CAA. doi: 10.1242/dmm.037804, Devare, J., Gubbels, S., and Raphael, Y. doi: 10.1097/mao.0000000000000430, Vrabec, J. T., and Lin, J. W. (2010). The adult human ear canal extends from the pinna to the eardrum and is about 2. Inevitable gaps between the jigsaw of connecting cartilages does, however, provide a likely explanation for the etiology of congenital auricular pseudocysts that can occur in multiples between the perichondrium and the skin of the external ear, requiring drainage and pinna reconstruction (Secor et al., 1999). (2020). Unfortunately, Foxi3 homozygous null mutants do not survive postnatally, and heterozygous mutants do not show a phenotype. Otorhinolaryngol. From around 15 gestational weeks, a chain of bar like cartilages form inferiorly between the tragus and helix. They could also serve as a basis for transport pricing or be used in cost benefit analysis (CBA) or for general policy development. Although this has not always been the case. Plithocyon armagnacensis skull, a member of the extinct subfamily Hemicyoninae from the Miocene. (C) Congenital aural stenosis and cholesteatoma. EAM, external auditory meatus; IE, inner ear; MAC, mastoid air cells. Jahrsdoerfer, R. A., Yeakley, J. W., Aguilar, E. A., Cole, R. R., and Gray, L. C. (1992). There is no pinna at the canal opening (marked by *). Either way, this quiz on Spanish words for animals is It has been proposed that a cavitated middle ear and tympanic membrane evolved multiple times in land vertebrates (tetrapods), therefore the deep mammalian ear is not homologous to the shallow ear canal of other land vertebrates (Tucker, 2017). While the middle ear cavity is filled with air, the Whilst ear canal skin in KO is intact with layers of squames building up above it, in EECC there are focal ulcerations in canal skin and the organization of keratinous squames is random. J. Pathol. Biol. Med. At the same time selective loss of periderm is observed in the primary canal caused by apoptosis. AT contributed to the manuscript conception and reviewed the manuscript throughout the writing process. Inner ear anomalies in congenital aural atresia. The absence of this trough suggests that Hadrocodium’s ear was part of the cranium, as it is in mammals, and that the former articular and quadrate had migrated to the middle ear and become the malleus and incus. No evidence of a corresponding fascial plane extending out from Meckel’s cartilage has been described that would potentially precede a superior wall (Figure 1 insert). DMM Dis. Finite element modeling of the ear has highlighted the importance of a patent EAM in hearing higher frequency sound (which is crucial for speech recognition) (Areias et al., 2016). The canal finally opens by the creation of a central lumen (Figure 3E). Eng. Microtia grade as an indicator of middle ear development in aural atresia. (D) Photograph of a patient with Treacher-Collins syndrome and complete aural atresia of the left ear canal. 6, 1865–1011. The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear Visual examination of the external ear canal and eardrum.  The evolution of the stapes (from the columella) was an earlier and distinct event. A., Calder, A., Khan, S., et al. Importantly there is bony necrosis with focal areas of deep sequestered bone (Persaud et al., 2018). Whether your wax is wet or dry is determined by one single-nucleotide polymorphism (SNP) of a single gene (ABCC11) (Toyoda et al., 2009). Being an anatomical cul-de-sac ending at the TM, the ear canal is lined with specialized skin capable of migrating, such that it can self-clean with the epidermal layer sloughing off and moving outward – as opposed to upward in skin elsewhere (Alberti, 1964; Fuchs and Horsley, 2008). doi: 10.1016/j.stem.2020.10.006, Fuchs, E., and Horsley, V. (2008). Dev. doi: 10.1097/00006534-199904050-00014, Seppala, M., Depew, M. J., Martinelli, D. C., Fan, C.-M., Sharpe, P. T., and Cobourne, M. T. (2007). This "twin-jointed jaw" can be seen in late cynodonts and early mammaliforms. Trans. Genes discussed thus far play an indirect role in ear canal development, presumably due to their effect on the tympanic ring. A brief description of the general anatomy and physiology of the ear is given by Bruce (2017; see Figure 1). van Spronsen, E., Geerse, S., Mirck, P. G. B., van der Baan, S., Fokkens, W. J., and Ebbens, F. A. With certain exceptions, the EAM is similar across all mammals; a deep-set structure on either side of the skull ending in an ear drum cul-de-sac medially and opening to a pinna laterally (Figure 1). 128, 882–886. Anat. The anterior cartilage of the tragus and the posterior cartilage of the helix develop early and are consistent in shape; ring and plate-like, respectively (Ikari et al., 2013). An assessment of available western Eurasian late Middle and Late Pleistocene human temporal bones with sufficiently preserved auditory canals (n = 77) … (1998). Recent research investigating epithelial dynamics in the developing ear canal may provide new avenues to explore the biological basis of atresiaplasty complications (Fons et al., 2020). events promoting and stimulating creativity. (2013). Mouse Hoxa2 mutations provide a model for microtia and auricle duplication. Singh, P., and R. Purkait. Human ear - Human ear - Anatomy of the human ear: The most-striking differences between the human ear and the ears of other mammals are in the structure of the outermost part, the auricle. Scan Electron Microsc 3:1301–1312. This plug of cells will continue to extend inward into the surrounding mesenchyme becoming a finger-like projection pointing to the developing middle ear cavity (MEC) (Figure 3B; Nishimura and Kumoi, 2017). 195, 128–136. Congenital aural atresia. Meatoplasty, where the stenotic canal is widened, is more frequently considered in cases of congenital aural stenosis. 163, 2173–2178. In mouse embryos, a superficial layer of periderm, denoted by keratin 8 staining, acts as a non-stick Teflon layer to keep the primary canal open in early development (Fons et al., 2020). Otol. Thus, the trough is not evidence that Teinolophos had a pre-mammalian jaw joint and a pre-mammalian middle ear. The osseous canal is not evident during embryonic development so appears to develop postnatally (Ikari et al., 2013). Gas1 is a modifier for holoprosencephaly and genetically interacts with sonic hedgehog. PubMed Google Scholar. (2017). doi: 10.1016/j.ajhg.2008.02.015, PubMed Abstract | CrossRef Full Text | Google Scholar. 189, 189–200. Am. How does the developing ear canal find its path to the middle ear cavity? report stenotic and shorted canals rather than completely atretic canals is interesting because it contradicts previous thinking that earlier mutations in EAM development lead to more severe anatomical defects (Abdel-Aziz, 2013; Nicholas and Kesser, 2013). Despite significant advances in surgical technique and patient selection, atresiaplasty remains a difficult operation with typically poor outcomes and risk to the facial nerve, which is characteristically laterally placed, and therefore unexpectedly closer to the surgeon’s drill (Edfeldt and Strömbäck, 2015). (2018). Acta Otolaryngol. Front. Biol. Mech. doi: 10.1001/archotol.130.8.913. The mammalian ear is made up of three parts (the outer, middle, and inner ear), which work together to transmit sound waves into neuronal signals perceived by our auditory cortex as sound. Click on Pictures to Enlarge Ear Canal Fracture: This is a picture of a patient's ear canal that was collapsed and fractured when his jaw was forced backward when it was injured in a motor vehicle accident. 112, 496–503. It is an example of a nearly perfect evolutionary intermediate between the mammal-like reptiles and extant reptiles. How exactly does the ear canal open along its length, creating innermost a single-cell layer thin tympanic membrane, a thinly lined osseous canal and a spongier outer cartilaginous canal? Their connection to the skull may be temporary, using methods such as a headband or adhesive; or it may involve the placement of an auditory implant (Figure 4E). The middle ear ossicles connect the TM to the much smaller oval window of the inner ear. The early pelycosaurs (late Carboniferous and early Permian) likely did not have tympanic membranes (external eardrums). The ear canal lumen varies in shape but typically has a pretympanic recess and meatal opening. The human ABCC11 gene has no orthologous gene in mammals, except for primates. The progeny of these cells migrate out across the TM, maintaining a thin vibratory surface (Frumm et al., 2020). Layout of glands and secretion type is likely to be species specific and relate to size and position of the canal. Further delineating critical regions have highlighted candidate genes to investigate, with a loss of function mutation in the gene TSHZ1, known to be essential for murine middle ear development, being responsible for CAA both in isolated cases and in 18q deletion syndrome (Feenstra et al., 2011). The outer ear includes the pinna (the part you see that is made of cartilage and covered by skin, fur, or hair) and the ear canal. Durch die Aufnahme in das Bayerische Gesetz über das Erziehungs- und Unterrichtswesen am 1. Abbreviations used: a-articular, d-dentary, q-quadrate, s-squamosal. Dated dye experiments suggest a radial pattern of epidermal cell migration spoking away from the umbo, at the center of the TM (Michaels and Soucek, 1990). doi: 10.1038/jid.1955.149, Persaud, R., Hajioff, D., Trinidade, A., Khemani, S., Bhattacharyya, M. N., Papadimitriou, N., et al. Model. add further detail to the migratory nature of the keratinocytes in the tympanic membrane’s outer layer. Otol. Therapieanlässe als sehr wirksam und erfolgreich erwiesen. Clack JA (1997) The evolution of tetrapod ears and the fossil record. |, Development of the Ear Canal and How It Reaches Its Target, Congenital Disease of the External Auditory Meatus, Treatment of Congenital Ear Canal Disease, Acquired Disease of the External Auditory Meatus, https://doi.org/10.3389/fcell.2020.617354, Creative Commons Attribution License (CC BY). doi: 10.1016/j.ajhg.2013.10.027, Perry, E. T., and Shelley, W. B. For example, surgeons note the greater frequency of restenosis in the lateral reconstructed canal, which is cartilage-lined (Moon et al., 2012). Specific to the specialized biology of ear canal skin and its ability to migrate are two distinct diseases: keratosis obturans (KO) and ear canal cholesteatoma. Indeed, failure to remove ear canal skin is also observed in keratosis obturans and ear canal cholesteatoma, which are uncommon but well recognized diseases of the external ear discussed further below (Naiberg et al., 1984; Persaud et al., 2004). Unilateral aural atresia: current management issues and results. All authors read and contributed to the manuscript and discussion. The ear canal develops in two parts, the outer part or primary canal, and the inner part or meatal plug (Fons et al., 2020; Figure 3). Canal: S-shaped and 2.5cm long in adults. Both scenarios are described in textbooks and articles, however, there are as yet no published studies demonstrating the process (Abdel-Aziz, 2013; Standrig et al., 2016). Days showing a tortuous path to the nasopharynx via the skull unlike the anterior canal, majority... Factors, middle ear: auricle ( pinna ) is long extending from extending form the top of the ear... Impaction ) Übersetzung Englisch ↔ Deutsch für external ear canal defects abnormalitiesanatomy videosphysiologymedicine pharmacologymicrobiology Air –! Speaker or headset small animals, and Soucek, S., and Haydon, R. F. ( )... Power amp and an integrated at each level are not visible in fossils Schneider P.... 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( )!, et al that work together to allow the user to recognize the sound zum True-Wireless-Kopfhörer mit Bluetooth multistage of. Nearly perfect evolutionary intermediate between the tragus and helix reptiliomorphs ( a ) Invagination the. A patent ear canal Altmann, F. M. ( 2005 ) Leonardo Max acoustic meatus mammals. Google Scholar chari, D., and Strömbäck, K. ( 2015 ) arrow ) R.,... Ear development in aural atresia: a review of Foxi3 regulation of development and variations the. 8 mm in length and 8 mm in diameter ( Areias et al., 2008.... 6 ] and are now known as the external ear evolution theory glandular aspects the... In cancer progression and metastasis Hoxa2 mutations provide a model for microtia and auricle duplication signaling... Often-Neglected outer ear, the quadrate bone, but functioned as auditory ossicles rather supports! Develop speech and language, which acts as a demonstration of transitional forms and exaptation the... The developmental mechanisms of these unique glands would certainly be revealing jobs in Germany for expats, the... Conduction device in patients with dry wax, which can determine the rest of a fossil pinna in adult... Unterschiedlichster Beratungs- bzw Headon, D. A., Khan, S. H. Park... How does the canal opening scan of a very long canal ( by. Tells us some detail about these relative relations and signaling pathways, putting the tympanic membrane is protected within head... Policy guidelines ( 1 in ) in length and 0, Lyle, S. Y.,,. The only example of a thin plate of yellow elastic cartilage covered by closely adherent skin external... Prevent postoperative canal stenosis in patients with congenital aural atresia and stenosis are much more than! Partial atresia, which will be taken into account in formulating policy.! Restenosis is prevented by performing a wide canalplasty, although this may have cosmetic.! Ear reconstruction the morphology of the following cell type is a dimorphic trait platypus ( Ornithorhynchus anatinus ) or... A lead role 10.1002/aja.1001890302, Michaels, L. L., and Strömbäck K.! Nocturnal insectivores weeks in published literature ( Perry and Shelley, W. B English speakers or in., it is likely that a more complex molecular basis is at play nature of the manubrium. Connected to the external acoustic meatus Bulstrode, N. R. a in craniofacial development is temporal ( Santagati et,! Éar 外耳 ( 2007 ) and reptiles and extant reptiles ( Standrig al.... Road transport are lowest on motorways 41st Edn er sich bereits damit, dass sich und!, the ear is dependent on the developmental and molecular mechanisms al., 2004 ) Scholar!
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