Hearing - Outer Ear Development

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Introduction

Adult hearing embryonic origins.
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

  • 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)."

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 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

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

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.

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.
Ear Length (mm +/-SD) Data [4]
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.

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.[5]

Minor structural anomalies have been shown to be corrected by appropriate splinting in the early neonatal period.[6]

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[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

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

References

  1. 1.0 1.1 <pubmed>22296782</pubmed>| PMC3286420 | Head Face Med.
  2. <pubmed>19356871</pubmed>
  3. <pubmed>1441991</pubmed>
  4. 4.0 4.1 <pubmed>18196763</pubmed>
  5. <pubmed>18261212</pubmed>| PMC2267455 | Head Face Med.
  6. <pubmed>18490209</pubmed>
  7. <pubmed>18394579</pubmed>
  8. <pubmed>18423520</pubmed>| PMC2427260
  9. <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

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Cite this page: Hill, M.A. (2019, August 19) 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