Talk:2009 Lecture 17

From Embryology

Development of Hearing - 3 divisions of ear

outer - pinna (auricle, "ear") and external auditory meatus (ear canal) functions to collect sound and gude it to the tympanic membrane

middle - tympanic cavity functions to convert sound pressure waves into mechanical waves of typanic membrane. Ossicles reduce amplitude but increase force to drive fluid-filled inner ear and eustacian tube allows equalization of pressure (into oral cavity)

inner - duct system functions hearing and balance to convert hair displacement into neural signal

Table Embryonic Origins

External Ear

  • Auricle - Pharyngeal Arches 1 and 2 (ectoderm, mesoderm)
  • External Auditory Meatus - Pharyngeal Arch 1 groove (ectoderm)
  • Tympanic Membrane - Pharyngeal Arch 1 membrane (ectoderm, mesoderm, endoderm)

Middle Ear

  • Middle Ear Ossicles
    • Malleus and incus - Pharyngeal Arch 1 cartilage Neural crest (ectoderm)
    • Stapes - Pharyngeal Arch 2 cartilage Neural crest (ectoderm)
  • Middle Ear Muscles
    • Tensor tympani - Pharyngeal Arch 1 (mesoderm)
    • Stapedius - Pharyngeal Arch 2 (mesoderm)
  • Middle ear cavity - Pharyngeal Arch 1 cleft (endoderm)

Inner Ear

  • Inner Ear Labyrinth
    • Cochlea - Otic vesicle - Otic placode (ectoderm)
    • Semicircular canals - Otic vesicle - Otic placode (ectoderm)
    • Saccule and utricle - Otic vesicle - Otic placode (ectoderm)
  • Cranial Nerve VIII
    • Auditory component - Otic vesicle and neural crest (ectoderm)
    • Vestibular component - Otic vesicle and neural crest (ectoderm)

Table Pharyngeal arch contributions to external ear

Pharyngeal Arch Hillock Auricle Component
Arch 1 1 tragus
2 helix
3 cymba concha
Arch 2 4 concha
5 antihelix
6 antitragus
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}

Ear Development

Three divisions of the Ear
  • Ear Development
  • origins
  • otic placode
  • external, middle, inner ear
  • Abnormalities

Links: Systems Notes - Hearing | Systems Notes - Senses

2. Human Embryo External Appearance

File:600stage14.jpg File:600stage23.jpg
* Stage 14 * Stage 23

More: Externally the pharyngeal arches are initially the most obvious external feature. Sensory placodes are present on the surface (but not obvious). By this stage the sensory placode that contributes to hearing (otic placode) has already been lots from the surface and now lies in the mesenchyme in the neck region.

Links: Embryo Stages | Stage Comparison | Stage 14 | Stage 23

3. Three Ear Parts

  • inner ear
    • otic placode then otocyst
  • middle ear
    • 1st pharyngeal pouch
    • 1st and 2nd arch mesenchyme
  • outer ear
    • 1st pharyngeal cleft
    • 6 surface hillocks

4. Otocyst

  • pair of surface sensory placodes (otic placodes) in the head region
  • placodes fold inwards forming a depression
  • pinches off entirely from the surface
  • fluid-filled sac or vesicle (otic vesicle, otocyst)
  • vesicle sinks into the head mesenchyme
  • Stage 13 Embryo

5. Inner Ear Development

  • vesicle then extends and folds
  • membranous labrynth
  • cochlea
  • utricle and saccule
  • endolymphatic duct
  • semicircular canals
  • Then
    • innervated by CN VIII
    • embedded in developing temporal bone
File:Inner ear2 sm.jpgFile:Innerear sm.jpg
  • Stage 22

6. Middle Ear

* ossicles (bones)
  • arch 1 - malleus, incus
  • arch 2 - stapes
  • muscles (mesoderm)
  • arch 1 - tensor tympani
  • arch 2 - stapedius
  • tympanic cavity
  • first pharyngeal pouch
  • extends as tubotympanic recess
  File:Ear ossicles.jpg

7. Outer Ear

  • Surface hillocks (auricular hillocks)
    • three on pharyngeal arch 1
    • three on pharyngeal arch 2
  • external auditory meatus (canal)
    • 1st pharyngeal cleft (groove)
File:CSt17.gif* Stage 17

File:CSt18.gifFile:CSt19.gif* Stage 18 Stage 19 File:CSt20.gif
File:Hearingcartoon.jpg File:Externalearanatomy.gif

8. Postnatal Changes

Eustacian tube angle changes

Newborn to adult Eustachian (auditory, otopharyngeal or pharyngotympanic) tube.

  • Connects middle ear cavity to nasopharynx portion of pharynx


  • Ventilation - pressure equalization in the middle ear
  • Clearance - allow fluid drainage from the middle ear Tube is normally closed and opened by muscles

At birth

  • shorter (17-18 mm), narrower and runs almost horizontal Tube is opened by a single muscle, tensor palati muscle


  • longer (twice as long), wider and runs at approximately 45 degrees to the horizontal. Tube is opened by two separate muscles, tensor palati and levator palati

Ear Abnormalities

Fetal Alcohol Syndrome Face
  • Fetal Alcohol Syndrome - Abnormal position of ears (lower, uneven) can be an indicator of FAS.


Links: Head and Neck Abnormalities | Hearing Abnormalities | Abnormal Development - Fetal Alcohol Syndrome |


Werner LA. Issues in human auditory development. J Commun Disord. 2007 Mar 13;

Barald KF, Kelley MW. From placode to polarization: new tunes in inner ear development. Development. 2004 Sep;131(17):4119-30. Review.

Morsli H, Choo D, Ryan A, Johnson R, Wu DK. Development of the mouse inner ear and origin of its sensory organs. J Neurosci. 1998 May 1;18(9):3327-35. J Neuroscience Link


Villa-Cuesta E, Modolell J. Mutual repression between msh and Iro-C is an essential component of the boundary between body wall and wing in Drosophila. Development. 2005 Aug 10

Goto M, Piper Hanley K, Marcos J, Wood PJ, Wright S, Postle AD, Cameron IT, Mason JI, Wilson DI, Hanley NA. In humans, early cortisol biosynthesis provides a mechanism to safeguard female sexual development. J Clin Invest. 2006 Apr;116(4):953-60.

Jones JM, Montcouquiol M, Dabdoub A, Woods C, Kelley MW. Inhibitors of differentiation and DNA binding (Ids) regulate Math1 and hair cell formation during the development of the organ of Corti. J Neurosci. 2006 Jan 11;26(2):550-8.

"Basic helix-loop-helix (bHLH) transcription factor Math1 (Mouse homolog of ATH1, also called Atoh1) is both necessary and sufficient for hair cell development in the mammalian cochlea. The bHLH-related inhibitors of differentiation and DNA binding (Id) proteins negatively regulate many bHLH transcription factors including Math1. Progenitor cells expressing Ids during the time of hair cell differentiation were inhibited from developing as hair cells. Role for Ids in the regulation of expression of Math1 and hair cell differentiation in the developing cochlea." (text edited from abstract) (More? OMIM ATONAL)

Rodriguez-Vazquez JF. Development of the stapes and associated structures in human embryos. J Anat. 2005 Aug;207(2):165-73.

"The stapedial anlage is a unique formation with two distinct parts: the superior part that will comprise the base and the inferior part that will be crossed by the stapedial artery during embryonic development and will constitute the limbs and the head of the stapes. According to the results, the otic capsule is not involved in formation of the base of the stapes."

Kiernan AE, Pelling AL, Leung KK, Tang AS, Bell DM, Tease C, Lovell-Badge R, Steel KP, Cheah KS. Sox2 is required for sensory organ development in the mammalian inner ear. Nature. 2005 Apr 21;434(7036):1031-5.

"Sensory hair cells and their associated non-sensory supporting cells in the inner ear are fundamental for hearing and balance. They arise from a common progenitor, but little is known about the molecular events specifying this cell lineage."

Molecular Normal Development

Jones JM, Montcouquiol M, Dabdoub A, Woods C, Kelley MW. [See Related Articles ] Inhibitors of differentiation and DNA binding (Ids) regulate Math1 and hair cell formation during the development of the organ of Corti. J Neurosci. 2006 Jan 11;26(2):550-8.

Kawamoto K, Ishimoto S, Minoda R, Brough DE, Raphael Y. [See Related Articles ] Math1 gene transfer generates new cochlear hair cells in mature guinea pigs in vivo. J Neurosci. 2003 Jun 1;23(11):4395-400.

Zine A, de Ribaupierre F. [See Related Articles ] Notch/Notch ligands and Math1 expression patterns in the organ of Corti of wild-type and Hes1 and Hes5 mutant mice. Hear Res. 2002 Aug;170(1-2):22-31.

List of [../Refer/senses/ear_rev.htm Ear Development Reviews (1998)]

Reviews Abnormal Development (1998)

 Webster WS. [See Related Articles ] Teratogen update: congenital rubella. Teratology. 1998 Jul;58(1):13-23. Review.

Yates JA, et al. [See Related Articles] Isolated congenital internal auditory canal atresia with normal facial nerve function. Int J Pediatr Otorhinolaryngol. 1997 Jul 18;41(1):1-8. Review.

Lambert PR, et al. [See Related Articles] Congenital malformations of the external auditory canal. Otolaryngol Clin North Am. 1996 Oct;29(5):741-60. Review.

Lin AE, et al.  [See Related Articles] Further delineation of the branchio-oculo-facial syndrome. Am J Med Genet. 1995 Mar 13;56(1):42-59. Review.

Strasnick B, et al  [See Related Articles] Teratogenic hearing loss. J Am Acad Audiol. 1995 Jan;6(1):28-38. Review.

Kossowska E, et al. [See Related Articles] Prenatal and neonatal prophylaxis in otorhinolaryngology. Int J Pediatr Otorhinolaryngol. 1980 Jun;2(2):85-98. Review.

Gottlieb G. [See Related Articles] Conceptions of prenatal development: behavioral embryology. Psychol Rev. 1976 May;83(3):215-34. Review.

Holme RH, Steel KP Genes involved in deafness. Curr Opin Genet Dev 1999 Jun;9(3):309-314

"Remarkable progress has been made over the past few years in the field of hereditary deafness. To date, mutations in at least 35 genes are known to cause hearing loss. We are now beginning to understand the function of many of these genes, which affect diverse aspects of ear development and function.


Note: books are listed for educational and information purposes only and does not suggest a commercial product endorsement.

Molecular and Cellular Approaches to Neural Development

The Embryonic Human Brain: An Atlas Of Developmental Stages, 3rd Edition

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