Hearing - Outer Ear Development

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Introduction

Adult hearing embryonic origins.
Adult external ear

The outer ear or external ear is derived from 6 surface hillocks (auricular hillocks), three on each of pharyngeal arch 1 and 2.


The external auditory meatus is derived from the 1st pharyngeal cleft.


The postnatal human outer ear structure also selectively boosts frequencies around 3 kHz, by a sound pressure level of 30 to 100-fold, that correspond to frequencies associated with speech. The anatomical position, on either side of the head, also allows exquisite localization of sounds in space by neural comparison of signals reaching each ear.


Hearing Links: Introduction | inner ear | middle ear | outer ear | balance | placode | hearing neural | Science Lecture | Lecture Movie | Medicine Lecture | Stage 22 | hearing abnormalities | hearing test | sensory | Student project

  Categories: Hearing | Outer Ear | Middle Ear | Inner Ear | Balance

Historic Hearing Embryology 
Historic Embryology: 1880 Platypus cochlea | 1902 Development of Hearing | 1906 Membranous Labyrinth | 1910 Auditory Nerve | 1913 Tectorial Membrane | 1918 Human Embryo Otic Capsule | 1918 Cochlea | 1918 Grays Anatomy | 1922 Human Auricle | 1922 Otic Primordia | 1931 Internal Ear Scalae | 1932 Otic Capsule 1 | 1933 Otic Capsule 2 | 1936 Otic Capsule 3 | 1933 Endolymphatic Sac | 1934 Otic Vesicle | 1934 Membranous Labyrinth | 1938 Stapes - 7 to 21 weeks | 1938 Stapes - Term to Adult | 1942 Stapes - Embryo 6.7 to 50 mm | 1943 Stapes - Fetus 75 to 150 mm | 1948 Stapes - Fetus 160 mm to term | 1959 Auditory Ossicles | 1963 Human Otocyst | Historic Disclaimer

Some Recent Findings

  • Movement of the external ear in human embryo[1] "In all, 171 samples between Carnegie stage (CS) 17 and CS 23 were selected from MR image datasets of human embryos obtained from the Kyoto Collection of Human Embryos. The three-dimensional absolute position of 13 representative anatomical landmarks, including external and internal ears, from MRI data was traced to evaluate the movement between the different stages with identical magnification. Two different sets of reference axes were selected for evaluation and comparison of the movements. ...The results indicate that movement of all anatomical landmarks, including external and internal ears, can be explained by differential growth. Also, when the external ear is recognized as one of the facial landmarks and having a relative position to other landmarks such as the eyes and mouth, the external ears seem to move cranially."
  • Age- and sex-related changes in the normal human ear[2] "All ear dimensions were significantly larger in men than in women (p<0.001). A significant effect of age was found (p<0.001), with larger values in older individuals. The ear width-to-length ratio and the sagittal angle of the auricle significantly decreased as a function of age (p<0.001) but without sex-related differences. On average, the three-dimensional position of ears was symmetric, with symmetry coefficients ranging between 92% and 96%. Asymmetry was found in the sagittal angle of the auricle (both sexes), in the ear width-to-length ratio and ear width (men only)."
More recent papers  
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Search term: Outer Ear Development

Domenico Roberti, Renata Conforti, Teresa Giugliano, Barbara Brogna, Immacolata Tartaglione, Maddalena Casale, Giulio Piluso, Silverio Perrotta A Novel 12q13.2-q13.3 Microdeletion Syndrome With Combined Features of Diamond Blackfan Anemia, Pierre Robin Sequence and Klippel Feil Deformity. Front Genet: 2018, 9;549 PubMed 30524470

Sverre Morten Zahl, Arild Egge, Eirik Helseth, Anne-Britt Skarbø, Knut Wester Quality of life and physician-reported developmental, cognitive, and social problems in children with benign external hydrocephalus-long-term follow-up. Childs Nerv Syst: 2018; PubMed 30523438

Jenny X Chen, Elliott D Kozin, Jennifer O'Malley, Ivan Chebib, E Tessa Hedley-Whyte, William Faquin, Joseph Nadol, Alicia M Quesnel Otopathology in Angiosarcoma of the Temporal Bone. Laryngoscope: 2018; PubMed 30536838

Clara M Olcott, Patrick E Simon, Thomas Romo, William Louie Anatomy of the superficial temporal artery in patients with unilateral microtia. J Plast Reconstr Aesthet Surg: 2018; PubMed 30528867

Simerjit Nagra, Fatima Hussain, Isabel Alvarez, John Valdovinos Feasibility of a Post-Auricle Wireless Power System for Pediatric Mechanical Circulatory Support Pumps. Conf Proc IEEE Eng Med Biol Soc: 2018, 2018;1514-1517 PubMed 30440680

Pinna- Auricle

External ear stages-14-23-adult.jpg

Embryonic External Ear

Images of the lateral view of the human embryonic head from week 5 (stage 14) through to week 8 (stage 23) showing development of the auricular hillocks that will form the external ear. The adult ear is also shown indicating the part of the ear that each hillock contributes.


  • develops from six aural hillocks: 3 on first pharyngeal arch and 3 on the second pharyngeal arch.
  • originally on neck, moves cranially during mandible development

Human embryo head week 6 to 8.jpg

Movement of the external ear in human embryo (week 6 to 8)[1]

Pharyngeal Contributions

External ear simplified anatomy
Pharyngeal Arch Hillock Auricle Component
Arch 1 1 tragus
2 helix
3 cymba concha
Arch 2 4 concha
5 antihelix
6 antitragus
  • Outer- external auditory meatus
  • derived from first pharyngeal cleft
  • ectodermal diverticulum
  • week 5 - extends inwards to pharynx
  • until week 18 has ectodermal plug - plug forms stratified squamous epithelia of canal and outer eardrum

Human Timeline

Time EAM Appearance
Embryonic period Ectodermal cells proliferate and fill the entire lumen forming a meatal plug
10 weeks Meatal plug extends in a disc-like fashion. In the horizontal plane the meatus is boot-shaped with a narrow neck and the sole of the meatal plug spreading widely to form the future tympanic membrane medially. Proximal portion of the neck starts to be resorbed.
13 weeks Disc-like plug innermost surface in contact with the primordial malleus, contributes to the formation of the tympanic membrane.
16.5 week Meatus is fully patent throughout its length, lumen is still narrow and curved.
18 week Meatus is already fully expanded to its complete form.

Based on data from[3]

Auricular Cartilage

Streeter1922-06-07.jpg Image shows the embryonic and fetal growth of the auricular cartilage within the pinna.[4]


Fig. 6. Lateral views of left auricular cartilage, taken from reconstructions of human embryos of the Carnegie Collection: No. 460 (21 mm.), No. 417 (32 mm.), No. 886 (43 mm.). X14.


Fig. 7. Reconstruction of left auricular cartilage of a 50 mm. fetus (No. 84, Carnegie Collection). X 14. A model of the external form of the auricle was made, in conjunction with the cartilage, to give the topographical relations. The edge of the helix in contact with the ectoderm is indicated by cross-lines.

Human Auricle Development

External Auditory Meatus

External Auditory Meatus
At Birth Adult
Keith1902 fig036b.jpg Keith1902 fig036a.jpg

Development of the human external auditory meatus (EAM) begins in the late embryo and continues through the fetal second trimester. The period the "metal plug" is present has been variously described. The best EAM developmental time course is described in two studies.[5][3]


External Auditory Meatus Timeline
Period Week Description
Embryo week 8 Funnel-shaped tube continues medially into mesenchymal tissue, forms a curved path.
Fetus (first trimester) week 9 Ectodermal cells proliferate, fill the meatus lumen and form the "meatal plug".
Fetus (first trimester) week 10 Meatal plug bottom extends in a disc-like fashion, so that in the horizontal plane the meatus is boot-shaped with a narrow neck and the sole of the meatal plug spreading widely to form the future tympanic membrane medially. At the same time, the plug in the proximal portion of the neck starts to be resorbed.
Fetus (second trimester) week 13 Meatal plug disc-like, innermost surface in contact with the primordial malleus, contributes to formation of tympanic membrane.
Fetus (second trimester) week 15 Meatal plug innermost portion splits, leaving a thin ectodermal cell layer of immature tympanic membrane. The neck of the boot forms the border between the primary and secondary meatus, and is the last part to split.
Fetus (second trimester) week 16.5 The meatus is fully patent throughout entire length. Lumen is still narrow and curved. Epithelium cornification commences.
Fetus (second trimester) week 18 The meatus is now fully expanded to its complete form.
Links: outer ear | hearing | timeline     Reference[3]


Fetal epithelium[5]

  1. originates as a tube derived from the epithelium of the fundus of the primary external canal
  2. composed of a thin, flat epithelium on the medial side
  3. continuous with a thicker epithelium on the lateral side
  4. then merges with the external epithelium of the primary external canal

Epithelium cornification begins in the second trimester, at week 16 (GA week 18), and is followed by clearing of keratinous debris to the exterior.

The adult stratified squamous epithelium lines the external auditory meatus and covers tympanic membrane.

Innervation

The auriculotemporal nerve supplies a large part of the pinna, some innervation may also arise from the trigeminus.

Postnatal Growth

Postnatally, human ears continue to grow throughout the entire lifetime and have a sexually dimorphic pattern, described in a large study.[6] Three anatomical features of the ear were found to not grow at all after birth; Concha auriculae width, Incisura intertragica width, and the helical brim diameter of the auricle.

  • birth - external ear bigger than the large head in proportion to the body
  • childhood - large yearly increases decrease by 8 or 10 years of age.
  • adult - male increases in all parameters were greater than for female ears.
Ear Length (mm +/-SD) Data[6]
Age Female Male
Birth 52 (4.3) 52 (4.1)
20 yrs 61 (3.9) 65 (4.0)
Older than 70 yrs 72 (4.6) 78 (4.8)

Ear Features

  • Darwin's tubercle - (Woolnerian tip) is a tubercle is seen along the upper, posterior portion of the helix (upper and middle thirds).
  • "railroad track" - associated with fatal alcohol syndrome, the curve at top part of outer ear is underdeveloped and folded over parallel to curve beneath.

Lobe Attachment

In the normal population, free earlobes have been described as dominant.[7] With some researchers suggesting that "attached" would be better described as "lobeless". There have been several historic studies identifying attached ear lobes in some population groups (Indian[8], Malaysian). There are a number of syndromes and genetic disorders associated with variation in lobe attachment.


Links: OMIM 128900 | PMID 14277139

Molecular

Outer Ear Genes

  • controlled by genes that regulate arch 1 and 2 development
  • related to hindbrain segmentation (rhombomere 4)
  • Mouse - Hoxa1/Hoxb1, goosecoid, Endothelin1, dHAND

Abnormalities

Facial appearance of fetal alcohol syndrome. Ear curve at top part of outer ear is underdeveloped and folded over parallel to curve beneath and gives the appearance of a "railroad track"

There are a range of external ear abnormalities relate to final structure, size and position. In some cases these abnormalities relate directly to pharyngeal arch development or may be part of a wider spectrum of abnormalities associated with a genetic or environmental (fetal alcohol syndrome) disorders. Some known abnormalities include: anotia, microtia, prominent ear, lop ear, cup ear, cryptotia and Stahl's ear. Other associated external ear abnormalities include the formation of the external auditory meatus (canal) and pre-auricular fistulae (pits) and appendages. Finally, a range of abnormalities can be found associated with the overlying skin of both the external ear and the ear canal.{#pmid:18261212|PMID18261212}}

Minor structural anomalies have been shown to be corrected by appropriate splinting in the early neonatal period.{#pmid:18490209|PMID18490209}}

Links: Sensory - Hearing Abnormalities

Anotia

Anotia 01.jpg

Upper Auricular Detachment

Upper auricular detachment 02.jpg Upper auricular detachment 01.jpg

Microtia

Microtia.jpg

Microtia (autosomal-recessive) - A mutation has been identified in HoxA2 (https://www.omim.org/entry/604685 HOXA2] 7p15.2){#pmid:18394579|PMID18394579}}


Links: Hox

Cleft Lobule

Oculo-auricular syndrome - A mutation in the NKX5-3 (HMX3 10q26.13) human homeobox gene.{#pmid:18423520|PMID18423520}}

Stahl's Ear

A rare ear abnormality, where the rim of the ear is flattened and the upper portions deformed. More common in Oriental background and can occur from mild to severe. The skin and cartilage are both folded to different degrees that can result in a pointed upper edge. This pointed ear has been said to resemble the Star Trek television character "Vulcan" ear shape.

External Auditory Meatus

The external auditory meatus (canal) can also fail to canalise leading to a range of malformation including membranous and/or bony atresia and stenosis.

External Auditory Meatus Stenosis[9]

  • Type A - a marked narrowing of the canal with an intact skin layer.
  • Type B - a partial development of the canal with an atresia plate at the medial part.
  • Type C - a complete bony canal atresia.

Pre-auricular Fistulae and Appendages

Preauricular sinus
Preauricular tag
Preauricular tag

There are also a range of pre-auricular fistulae (pits) and appendages that generally occur in a specific region beside the tragus and crus helicis.

Pre-auricular fistulae and appendage locations.jpg

Auricular Pit

Beckwith-Wiedemann syndrome posterior helix pit.jpg

Posterior helix pit associated with Beckwith-Wiedemann syndrome.


Links: Sensory - Hearing Abnormalities

Additional Images

Historical Images

References

  1. 1.0 1.1 Kagurasho M, Yamada S, Uwabe C, Kose K & Takakuwa T. (2012). Movement of the external ear in human embryo. Head Face Med , 8, 2. PMID: 22296782 DOI.
  2. Sforza C, Grandi G, Binelli M, Tommasi DG, Rosati R & Ferrario VF. (2009). Age- and sex-related changes in the normal human ear. Forensic Sci. Int. , 187, 110.e1-7. PMID: 19356871 DOI.
  3. 3.0 3.1 3.2 Nishimura Y & Kumoi T. (1992). The embryologic development of the human external auditory meatus. Preliminary report. Acta Otolaryngol. , 112, 496-503. PMID: 1441991
  4. Streeter GL. Development of the auricle in the human embryo. (1922) Carnegie Instn. Wash. Publ. 277, Contrib. Embryol., 14: 111-138.
  5. 5.0 5.1 Michaels L & Soucek S. (1989). Development of the stratified squamous epithelium of the human tympanic membrane and external canal: the origin of auditory epithelial migration. Am. J. Anat. , 184, 334-44. PMID: 2756906 DOI.
  6. 6.0 6.1 Niemitz C, Nibbrig M & Zacher V. (2007). Human ears grow throughout the entire lifetime according to complicated and sexually dimorphic patterns--conclusions from a cross-sectional analysis. Anthropol Anz , 65, 391-413. PMID: 18196763
  7. DUTTA P & GANGULY P. (1965). FURTHER OBSERVATIONS ON EAR LOBE ATTACHMENT. Acta Genet Stat Med , 15, 77-86. PMID: 14277139
  8. Sharma A, Sidhu NK, Sharma MK, Kapoor K & Singh B. (2007). Morphometric study of ear lobule in northwest Indian male subjects. Anat Sci Int , 82, 98-104. PMID: 17585565 DOI.
  9. Kösling S, Omenzetter M & Bartel-Friedrich S. (2009). Congenital malformations of the external and middle ear. Eur J Radiol , 69, 269-79. PMID: 18054456 DOI.


Reviews

Anthwal N & Thompson H. (2016). The development of the mammalian outer and middle ear. J. Anat. , 228, 217-32. PMID: 26227955 DOI.

Alasti F & Van Camp G. (2009). Genetics of microtia and associated syndromes. J. Med. Genet. , 46, 361-9. PMID: 19293168 DOI.

Torban E & Goodyer P. (2009). The kidney and ear: emerging parallel functions. Annu. Rev. Med. , 60, 339-53. PMID: 18976115 DOI.

Wood-Jones F & I-Chuan W. (1934). The Development of the External Ear. J. Anat. , 68, 525-33. PMID: 17104502

Articles

Michaels L & Soucek S. (1989). Development of the stratified squamous epithelium of the human tympanic membrane and external canal: the origin of auditory epithelial migration. Am. J. Anat. , 184, 334-44. PMID: 2756906 DOI.

Sforza C, Grandi G, Binelli M, Tommasi DG, Rosati R & Ferrario VF. (2009). Age- and sex-related changes in the normal human ear. Forensic Sci. Int. , 187, 110.e1-7. PMID: 19356871 DOI.

Nishimura Y & Kumoi T. (1992). The embryologic development of the human external auditory meatus. Preliminary report. Acta Otolaryngol. , 112, 496-503. PMID: 1441991

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May 2010 "Outer Ear Development" All (1478) Review (120) Free Full Text (215)

Search Pubmed: Outer Ear Development | Pinna Development


Hearing Terms

Hearing Terms  
Hearing and Balance Development
  • altricial animal - Term used to describe an animal born in a helpless state, with incomplete development of sensory systems at birth. For example rats and mice are born with incomplete development of visual and auditory systems. (More? Animal Development)
  • ampulla - Term used to describe an anatomical dilation of a tube or canal lumen. Anatomical description of the opening end of the uterine tube lying above the ovary and the enlarged initial segmeny of the semicircular canals of the inner ear vestibular system. (More? inner ear)
  • aneurism - (Greek, aneurysma = a widening, aneurysm) A term used to describe an abnormal widening of a vessel or anatomical tubal structure.
  • aquaeductus vestibuli - see vestibular aqueduct (More? inner ear)
  • auditory neuropathy - (AN) abnormality of transmission of sound information to the brain.
  • auditory tube - (eustachian tube) between the middle ear and oral cavity, has a bony (tympanic 1/3) and cartilaginous (pharyngeal 2/3) portion. The main role is equalization of pressure and fluid drainage in the middle ear. (More? middle ear)
  • auricular hillock - see hillock (More? middle ear)
  • atresia - narrowing, usually of an anatomical tube or cavity.
  • autophagocytosis - (Greek, auto = self, phagy = eating, also called autophagy) a cell death mechanism that uses the cell's own lysosomes to self digest.
  • border cells - columnar cells within the organ of Corti on the medial portion of the basilar membrane. (More? inner ear)
  • canalis reuniens - (ductus reuniens, canaliculus reuniens, canalis reuniens, Hensen's canal, Hensen's duct, uniting canal, canalis reuniens of Hensen) short narrow canal connecting the cochlea duct to the saccule. (Victor Hensen, 1835-1924) (More? inner ear)
  • cerumen - (ear wax) produced by glands in the skin of the outer portion of the ear canal. (More? Outer Ear)
  • chondrified - the developmental differentiation of cartilage from mesenchye, an embryonic connective tissue.
  • cristae ampullaris - located in the ampulla of the membranous semicircular canals a region with both supporting and hair cells. The hair cell cilia are embedded in the gelatinous cupula. (More? inner ear)
  • claudius cells - (cells of Claudius) columnar cells with microvilli overlying the basilar membrane and extend from Hensen's cells to the spiral prominence. Barrier cells that lie external to the organ of corti in endolymph. (More? inner ear)
  • cochlear sac - embryonic structure, which will form the coiled cochlear duct and contribute to the saccule. (More? inner ear)
  • cochlear aqueduct - a bony channel containing the fibrous periotic duct. It connects the basal turn of the cochlea perilymphatic space with the subarachnoid space of the posterior cranial cavity. (More? inner ear)
  • cochlin - major constituent of the inner ear extracellular matrix. (More? inner ear)
  • collagen type II - major constituent of the inner ear extracellular matrix. (More? inner ear)
  • conductive loss - term used to describe one of the two major classes of hearing loss involving external and middle ear abnormalities (other form is Sensorineural loss).
  • connexins - channel proteins of the gap junctions that allow rapid communication between adjacent cells. The two connexins Cx26 and Cx30 are the major proteins of cochlear gap junctions.
  • connexin 26 - A strikingly high proportion (50%) of congenital bilateral nonsyndromic sensorineural deafness cases have been linked to mutations in the GJB2 coding for the connexin26
  • cupular deposits - basophilic material on the cupulae of the semicircular ducts, an postnatal ageing phenomenon seen in some vestibular labyrinth. (More? inner ear)
  • clinical weeks - taken from last menstrual period (LMP) and therefore approximately two weeks before fertilization occurs.
  • Deiters' cells - (outer phalangeal cells)
  • discoidin domain receptor 1 - (DDR1) a tyrosine kinase receptor activated by native collagen, expressed in the basement membrane and with fibrillar collagens. Found in basal cells of the stria vascularis, type III fibrocytes, and cells lining the basilar membrane of the organ of Corti. {Meyer zum Gottesberge, 2008 #1877}
  • ductus utriculosaccularis - (More? inner ear)
  • endochondral ossification - the process of bone formation from a pre-existing cartilage template. (More? middle ear)
  • endoderm - One of the initial 3 germ cell layers (ectoderm, mesoderm and endoderm) formed by the process of gastrulation. The endoderm forms as a cuboidal epithelium and contributes not only to the trilaminar embryo, but also lines the yolk sac. It will form the entire epithelial lining of the gastrointestinal tract (GIT), contribute to the accessory organs of GIT and also forms the epithelial lining of the respiratory tract.
  • endolymphatic fluid - (endolymph, Scarpa's fluid) fluid that fills all the membranous labyrinth of the inner ear, except for the cochlea scala tympani and scala vestibuli which are filled with perilymph.
  • endolymphatic sac - inner ear structure that has anatomically both an intraosseous and extraosseous component. Th e sac has functions regulating endolymph that are both secretory and absorptive. Also the site of endolymphatic sac tumors either sporadical occurring or associated with the autosomal-dominant von Hippel-Lindau (VHL) disease, due to a germ line mutation. (More? inner ear)
  • embryological weeks - taken from the time of fertilization which typically occurs around the middle (day 14), or just after, of the typical 28 day menstrual cycle. (More? Embryonic Development)
  • Emx2 - homeobox gene affecting middle ear and inner ear development.
  • eustachian tube - (auditory tube) A cavity linking the pharynx to the middle ear, which develops from the first pharyngeal pouch. Named after Bartolomeo Eustachi (1500 - 1574) an Italian anatomist. (More? middle ear)
  • external auditory meatus - (ear canal) develops from the first pharyngeal cleft. (More? Outer Ear)
  • espins - calcium-resistant actin-bundling proteins enriched in hair cell stereocilia and sensory cell microvilli and spiral ganglion neurons (SGNs)
  • eustachian tube - (auditory tube) between the middle ear and oral cavity, equalization of pressure in the middle ear. (More? middle ear)
  • external auditory meatus - (EAM, ear canal) cavity connecting the external ear to the tympanic membrane. The adult human ear canal is about 2.5 cm long and 0.7 cm in diameter. (More? Outer Ear)
  • fenestra ovalis - (oval window) separates the tympanic cavity from the vestibule of the osseous labyrinth. (More? inner ear)
  • fenestra rotunda - (round window) separates the tympanic cavity from the scala tympani of the cochlea. (More? inner ear)
  • fetus - (foetus) term used to describe human development after the 8th week (10th clinical week, LPM) and covers the developmental periods of second and third trimester.
  • fibroblast growth factor 1 - (Fgf-1) a growth factor released from cochlea sensory epithelium which stimulates spiral ganglion neurite branching.
  • fibroblast growth factor 8 - (Fgf-8) a growth factor released by inner hair cells which regulates pillar cell number, position and rate of development.
  • fibroblast growth factor receptor 3 - (Fgfr-3) a tyrosine kinase receptor with a role in the commitment, differentiation and position of pillar cells in the organ of corti
  • fundamental frequency - (natural frequency) the lowest frequency in a harmonic series, for the female voice this is about 225 Hz.
  • Glaserian fissure - (petrotympanic fissure, squamotympanic fissure) the fissure in the temporal bone that runs between the temporomandibular joint to the tympanic cavity. Named after Johann Glaser (1629–1675) a Swiss anatomist.
  • helicotrema - term used to describe the cochlear apex. (More? inner ear)
  • Hes - (hairy and enhancer of split) family of factors, which has been shown to be a general negative regulator of neurogenesis (Zheng, 2000).
  • hillock - a small hill, used to describe the six surface elevations on pharyngeal arch one and two. (More? Outer Ear)
  • Incus - (anvil) auditory ossicle (More? middle ear)
  • inner phalangeal cells - in the cochlea a single row of cells, that along with and three rows of outer phalangeal cells (Deiter's cells), are the hair cell supporting cells. (More? inner ear)
  • inner pillar cells - organ of Corti cells arranged in rows and form a boundary between the single row of inner hair cells and three rows of outer hair cells. These cells have surface-associated microtubule bundles. (More? inner ear)
  • inner sulcus - area of the cochlear duct. (More? inner ear)
  • internal auditory meatus - (internal acoustic meatus, IAM) Anatomical canal in which CN VII and CN VIII ganglia reside and pass through to the brainstem. This bony canal lies between the posterior surface of the petrous pyramid and the bony labyrinth within the dense petrous bone. Also associated clinically with the site where acoustic neuromas may occur. (More? inner ear)
  • kinocilium - inner ear hair cell specialised type of cilium on the cell apex.
  • Kolliker's organ - (Kollicker's organ, greater epithelial ridge) Developing cochlear structure consisting of columnar-shaped supporting cells filling the inner sulcus and lying directly under the tectorial membrane. This transient organ regresses and generates the space of the inner sulcus. Rudolph Albert von Kolliker (1817-1905)?? (More? inner ear


  • lateral semicircular duct


  • limbus -


  • LMP - acronym for last menstrual period, used to clinically measure gestation.


  • malleus - (hammer) auditory ossicle (More? middle ear)
  • mastoid process - of temporal bone (More? middle ear)
  • Math1 - homolog of the Drosophila proneural gene atonal, necessary and sufficient for the production of hair cells in the mouse inner ear. Negatively regulated by Hes1 and Hes5
  • meatal plug - temporary blockage of the external auditory meatus which forms at the end of the embryonic period and remains present until the seventh month.
  • meatus - anatomical opening, cavity or space (external acoustic meatus, internal auditory meatus)
  • mechano-electrical transduction - (MET) occurs within the cochlear hair cells hair bundle. A mechanical stimulus of the hair bundle causes the tip-links to be tensioned, opening ion channels, resulting in the generation of the cell receptor potential. (More? inner ear)
  • Meckel's cartilage - first pharyngeal ach cartilage, located within the mandibular prominence. This cartilage first appears at stage 16, stage 20 the beginning of membranous ossification. Named after Johann Friedrich Meckel, (1781 - 1833) a German anatomist. (http://www.whonamedit.com/doctor.cfm/1840.html) (More? middle ear)
  • mucopolysaccharidosis - (MPS IIIB, Sanfilippo Syndrome type B) abnormality caused by a deficiency in the lysosomal enzyme N-acetyl-glucosaminidase (Naglu). Children with MPS IIIB develop abnormal hearing, and mental functioning culminating in early death.
  • netrin-1 - secreted growth factor, expressed in the organ of Corti and spiral ganglion cells, role in process outgrowth. (More? inner ear)
  • otoacoustic emissions testing - (OET) hearing test measures sounds generated by the outer hair cells of the cochlea in response to clicks or tone bursts emitted and recorded by a tiny microphone placed in the infant’s external ear canal. (More? Hearing test)
  • olivocochlear - brainstem cholinergic and GABAergic efferent system that innervates sensory cells and sensory neurons of the inner ear.
  • organ of Corti protein II - (OCP-II) cytosolic protein or transcription factor? (More? inner ear)
  • otolithic membrane - extracellular matrix that cover the sensory epithelia of the inner ear. (More? inner ear)
  • ossicle - (small bone) the individual bone of the three middle ear bones (auditory ossicles), which reduce vibrational amplitude but increase force to drive fluid-filled inner ear. (More? middle ear)
  • otic capsule -
  • otic cup -
  • otic placode - Embryonic ectodermal epithelium giving rise to inner ear structures. (More? inner ear | Placodes)
  • otoconin - inner ear biominerals required for vestibular apparatus function. (More? inner ear)
  • otogelin - (Otog) an inner ear specific glycoprotein expressed in cochlea cells at different developmental times. (More? inner ear)
  • otolithic membrane - a membrane within the utricle and saccule containing embedded hair cell cilia and small crystalline bodies of calcium carbonate (otoliths). Functions to detect head motion.
  • otoliths - small crystalline bodies of calcium carbonate found within the otolitic membrane of the utricle and saccule. (More? inner ear)
  • ototoxic - compound or drug causing temporary or permanent hearing loss.
  • outer hair cells - (OHCs) three rows of hair cells that function to increase basilar membrane motion through a local mechanical feedback process within the cochlea, the " cochlear amplifier".
  • outer pillar cells - arranged in rows and form a boundary between the single row of inner hair cells and three rows of outer hair cells. (More? inner ear)
  • paratubal musculature - muscles lying beside the auditory (Eustachian) tube. The tensor veli, palatini (TVP) and tensor tympani muscles. (More? middle ear)
  • perilymph - perilymphatic space - Periotic Capsule - petrous portion - of temporal bone
  • pejvakin gene - in humans, two missense mutations in this gene cause nonsyndromic recessive deafness (DFNB59) by affecting the function of auditory neurons.
  • petrotympanic fissure - (Glaserian fissure, squamotympanic fissure) the fissure in the temporal bone that runs between the temporomandibular joint to the tympanic cavity.
  • pharyngeal arch - (More? Outer Ear) pharyngeal pouch pharyngeal membrane Pharynx
  • pillar cells - (PC) form an inner and outer row of support cells that form a boundary between inner and outer hair cells. (More? inner ear)
  • preyer reflex - ear flick in mouse in response to sound.
  • presbyacusis
  • prestin - a motor protein structurally similar to the anion transporter family expressed in cochlear outer hair cells. (More? inner ear)
  • preauricular tag - skin tags located in front of the external ear opening, are common in neonates and in most cases are normal, though in some cases are indicative of other associated abnormalities.
  • protocadherin 15 - (Pcdh15) required for initial formation of stereocilia bundles and changes in the actin meshwork within hair cells. The Ames waltzer (av) mouse mutant has both auditory and vestibular abnormalities from a mutation in this gene.
  • Reichert's cartilage - pharyngeal arch 2 cartilage, named after Karl Bogislaus Reichert (1811 - 1883) a German anatomist. (More? middle ear | pharyngeal arch)
  • Reissner's membrane - (vestibular membrane, vestibular wall) is a membrane located inside the cochlea separating the scala media from scala vestibuli. Named after Ernst Reissner (1824-1878) a German anatomist. It primarily functions as a diffusion barrier, allowing nutrients to travel from the perilymph to the endolymph of the membranous labyrinth.
  • Template:Rhombomere - hindbrain rostrocaudal segmentation established by expression of Hox homeodomain transcription factors. Histologically rhombomeres are visible as undulating folds (scalloping) of the neural tube in the hindbrain region and have associated cranial nerves.
  • saccular macula - (macula of saccule) thickened anterior part of the saccule containing the saccular filaments of the acoustic nerve. (More? balance)
  • Saccule - (Latin, sacculus = a small pouch) (More? balance)
  • sacculocollic reflex -
  • scala tympani - one of the three cochlea cavities, it is filled with perilymph.
  • Scarpa's ganglion - (vestibular ganglion) primary afferent vestibular neuron ganglion of the vestibular nerve. Located within the internal auditory meatus. (More? inner ear)
  • semicircular canals - series of fluid-filled loops of the inner ear required for balance and sensing acceleration. (More? inner ear)
  • sensorineural - term used to describe one of the two major classes of hearing loss involving the central pathway from the cochlear (other form is conductive loss).
  • space of Nuel - within the cochlea, an organ of Corti space between the outer pillar cells and the phalangeal and hair cells. Named after Jean-Pierre Nuel (1847-1920) a Belgian ophthalmologist. (More? inner ear)
  • spiral ganglion neurons - (SGN) innervate the inner (Type I) and outer (Type II) hair cells of the cochlea. (More? inner ear)
  • stapedius muscle - (innervated by CN VII tympanic branch) one of the two muscles in the middle ear, contraction of this muscle pulls the stapes and dampens auditory ossicle movement. (More? middle ear)
  • stapes - (stirrup) a middle ear auditory ossicle (bone) (More? middle ear)
  • startle response - {Moro reflex)
  • stereocilia -finger-like projections from the apical surface of sensory hair cells forming the hair bundle in the cochlea. Formed by tightly cross-linked parallel actin filaments in a paracrystalline array with cell surface specializations (tip links, horizontal top connectors, and tectorial membrane attachment crowns).
  • stratified squamous epithelia - classification of epithelium which transiently forms a plug in external ear canal to the outer eardrum.
  • stria vascularis - forms the outer wall of the cochlear duct of the mammalian cochlea is composed primarily of three types of cells. Marginal cells line the lumen of the cochlear duct and are of epithelial origin. Basal cells also form a continuous layer and they may be mesodermal or derived from the neural crest. Intermediate cells are melanocyte-like cells, presumably derived from the neural crest, and are scattered between the marginal and basal cell layers. The stria forms endolymph and also contains a rich supply of blood vessels. (More? inner ear)
  • sulcus -
  • synostotically - anatomically normally separate skeletal bones fused together. (More? middle ear)
  • tectorial membrane - within the cochlea an extracellular matrix produced by interdental cells, that covers the sensory epithelial hair cells of the organ of corti. (More? inner ear)
  • alpha-tectorin and beta- (TECTA, TECTB) major non-collagenous protein component of the tectorial membrane forming a striated-sheet matrix. Synthesized as glycosylphosphatidylinositol-linked, membrane bound precursors.
  • tensor tympani - (innervated by CN V mandibular nerve) one of the two muscles in the middle ear, contraction of this muscle pulls the malleus and tenses the tympanic membrane, dampening auditory ossicle movement. The muscle arises from auditory tube (cartilaginous portion) and is inserted into the malleus (manubrium near the root).
  • teratogens -
  • tonotopy - term describing the mapping along the tectorial membrane within the cochlea of the different sound frequencies. (More? inner ear)
  • tympanic membrane - (ear drum)
  • utricle -
  • vacuolization -
  • vesicle -
  • vestibular apparatus -
  • vestibular evoked myogenic potential - (VEMP) a test for vestibular disorders (utricle and superior nerve) response elicited by loud clicks or tone bursts recorded from the tonically contracted sternocleidomastoid muscle.
  • vestibular ganglion - (Scarpa's ganglion) primary afferent vestibular neuron ganglion of the vestibular nerve. Located within the internal auditory meatus. (More? inner ear)
  • vestibular membrane - (Reissner's) extends from the spiral lamina to the outer wall and divides the cochlea into an upper scala vestibuli, a lower scala tympani. (More? inner ear)
  • Vestibulocochlear Nerve - Cranial Nerve VIII CN VIII
  • Whirlin - A PDZ scaffold protein expressed in hair cells at the stereocilia tips, essential for the stereocilia elongation process. The DFNB31 gene mutations cause hearing loss in human and mouse. This protein can interact with membrane-associated guanylate kinase (MAGUK) protein, erythrocyte protein p55 (p55). (More? inner ear)
  • Wnt7a - signaling through the Wnt pathway regulates the development of hair cell unidirectional stereociliary bundle orientation. (More? inner ear)
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Cite this page: Hill, M.A. (2018, December 15) Embryology Hearing - Outer Ear Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Hearing_-_Outer_Ear_Development

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© Dr Mark Hill 2018, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G