Hearing - Outer Ear Development: Difference between revisions
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May 2010 "Outer Ear Development" All (1478) Review (120) Free Full Text (215) | May 2010 "Outer Ear Development" All (1478) Review (120) Free Full Text (215) | ||
'''Search Pubmed:''' [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Outer | '''Search Pubmed:''' [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Outer+Ear+Development Outer Ear Development] | [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=pinna+Development Pinna Development] | ||
==External Links== | ==External Links== |
Revision as of 23:11, 16 May 2012
Introduction
The 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 external 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.
Some Recent Findings
|
Pinna- Auricle
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
Movement of the external ear in human embryo (week 6 to 8)[1]
Pharyngeal Contributions
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]
Human Auricle Development
External Auditory Meatus
External auditory meatus and the outer ear.
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.[4] 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.
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) |
Molecular
Outer Ear Genes
- controlled by genes that regulate arch 1 and 2 development
- related to hindbrain segmentation (rhombomere 4)
- Mouse - Hox a1/Hoxb1, goosecoid, Endothelin1, dHAND
Abnormalities
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.[5]
Minor structural anomalies have been shown to be corrected by appropriate splinting in the early neonatal period.[6]
Anotia
Upper Auricular Detachment
Microtia
Microtia (autosomal-recessive) - A mutation in HOXA2[7]
Cleft Lobule
Oculo-auricular syndrome - A mutation in the NKX5-3 human homeobox gene.[8]
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
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.
Auricular Pit
Posterior helix pit associated with Beckwith-Wiedemann syndrome.
References
- ↑ 1.0 1.1 <pubmed>22296782</pubmed>| PMC3286420 | Head Face Med.
- ↑ <pubmed>19356871</pubmed>
- ↑ <pubmed>1441991</pubmed>
- ↑ 4.0 4.1 <pubmed>18196763</pubmed>
- ↑ <pubmed>18261212</pubmed>| PMC2267455 | Head Face Med.
- ↑ <pubmed>18490209</pubmed>
- ↑ <pubmed>18394579</pubmed>
- ↑ <pubmed>18423520</pubmed>| PMC2427260
- ↑ <pubmed>18054456</pubmed>
Reviews
<pubmed>19293168</pubmed> <pubmed>18976115</pubmed> <pubmed>17104502</pubmed>
Articles
<pubmed>19356871</pubmed>
Search PubMed
May 2010 "Outer Ear Development" All (1478) Review (120) Free Full Text (215)
Search Pubmed: Outer Ear Development | Pinna Development
External Links
External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.
- Neuroscience Neuroscience - The External Ear
Glossary Links
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Cite this page: Hill, M.A. (2024, May 19) Embryology Hearing - Outer Ear Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Hearing_-_Outer_Ear_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G