Talk:2009 Lecture 17
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
- 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 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 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|
|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.|
- Ear Development
- otic placode
- external, middle, inner ear
2. Human Embryo External Appearance
|* 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.
3. Three Ear Parts
5. Inner Ear Development
6. Middle Ear
|* ossicles (bones)
7. Outer Ear
||File:CSt17.gif* Stage 17
|File:CSt18.gifFile:CSt19.gif* Stage 18 Stage 19||File:CSt20.gif|
8. Postnatal 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
- 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
- Fetal Alcohol Syndrome - Abnormal position of ears (lower, uneven) can be an indicator of FAS.
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.
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)
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.
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Search Mar2007 "hearing development" 7,453 reference articles of which 900 were reviews.