Hearing - Outer Ear Development

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Hearing cartoon.jpg

Introduction

External ear stages 14-23 and adult (not to scale)

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.


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 
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 | 1940 Stapes | 1942 Stapes - Embryo 6.7 to 50 mm | 1943 Stapes - Fetus 75 to 150 mm | 1946 Aquaductus cochleae and periotic (perilymphatic) duct | 1946 aquaeductus cochleae | 1948 Fissula ante fenestram | 1948 Stapes - Fetus 160 mm to term | 1959 Auditory Ossicles | 1963 Human Otocyst | Historic Disclaimer

Some Recent Findings

  • Age- and sex-related changes in the normal human ear[1] "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)."

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


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
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.

(Nishimura, 1992}

External Auditory Meatus

Gray0908.jpg

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.

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

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.[2]

Minor structural anomalies have been shown to be corrected by appropriate splinting in the early neonatal period.[3]

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 in HOXA2[4]

Cleft Lobule

Oculo-auricular syndrome - A mutation in the NKX5-3 human homeobox gene.[5]

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[6]

  • 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


Links: Sensory - Hearing Abnormalities

References

  1. <pubmed>19356871</pubmed>
  2. <pubmed>18261212</pubmed>| PMC2267455 | Head Face Med.
  3. <pubmed>18490209</pubmed>
  4. <pubmed>18394579</pubmed>
  5. <pubmed>18423520</pubmed>| PMC2427260
  6. <pubmed>18054456</pubmed>


Reviews

<pubmed>17104502</pubmed>

Articles

Search PubMed

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

Search Pubmed: Outer Ear Development Pinna Development

External Links

Glossary Links

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Cite this page: Hill, M.A. (2019, September 20) 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 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G