Hearing - Outer Ear Development
- 1 Introduction
- 2 Some Recent Findings
- 3 Pinna- Auricle
- 4 External Auditory Meatus
- 5 Innervation
- 6 Molecular
- 7 Abnormalities
- 8 References
- 9 External Links
- 10 Glossary Links
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.
Some Recent Findings
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
|Pharyngeal Arch||Hillock||Auricle Component|
- 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
|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.|
External Auditory Meatus
External auditory meatus and the outer ear.
The auriculotemporal nerve supplies a large part of the pinna, some innervation may also arise from the trigeminus.
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
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.
Upper Auricular Detachment
Microtia (autosomal-recessive) - A mutation in HOXA2
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
- 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.
May 2010 "Outer Ear Development" All (1478) Review (120) Free Full Text (215)
- Neuroscience Neuroscience - The External Ear
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Cite this page: Hill, M.A. (2019, December 5) Embryology Hearing - Outer Ear Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Hearing_-_Outer_Ear_Development
- © Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G