UNSW Embryology

Development of the organs of Audition and Equilibrium

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Introduction

This section of notes relates to the sense of hearing and balance through the development of the specialized sense organ the ear. Portions of the ear appear very early in development as specialized region (placode) on the embryo surface, this region must be connected to the central nervous system by neural pathways that originate as extensions of the central nervous system.

Reading

Human Embryology (2nd ed.) Larson Ch12: p375-409

The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Ch19: p491-511

Essentials of Human Embryology Larson Ch12: p252-272

Before We Are Born (5th ed.) Moore and Persaud Ch20: p460-479

Human Embryology, Fitzgerald and Fitzgerald

Computer Activities

UNSW Embryology:

Human Systems

Head Set

Pig Head Set

Listed selected sections Ear

Embryo Images Unit: Ear Development

Embryology Overview- Hearing

Development of Hearing
- Larson- Ch12: p375-409
- Structures
- outer, middle inner
- Functions
- Origins
- Development
- Regulatory genes (mainly from KO studies)
- Abnormalities- congenital deafness
Hearing- 3 divisions of ear
- outer
  - 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
  - eustacian tube allows equalization of pressure (into oral cavity)
- inner
  - duct system
  - functions to convert hair displacement into neural signals
  - cochlear (sound)
  - semicircular canals (balance)
  - vestibulocochlear nerve
  - Organ of Corti
  - Hair Cells
Pinna- Auricle
- develops from six aural hillocks
- 3 on first arch
- 3 on second arch
- originally on neck, moves cranially during mandible development
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
- 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
Middle- tympanic cavity
- derived from first pharyngeal pouch
- extends as tubotympanic recess
- during week 5 recess contacts outer ear canal
mesoderm between 2 canals forms tympanic membrane
expands to form tympanic recess
stalk of recess forms eustacian tube
pharyngotympanic tube
Middle- Ossicles
- develop from first and second pharyngeal arches
- tympanic cavity enlarges to incorporate
- coats with epithelia
first arch mesoderm
- tensor tympani muscle
- malleus and incus
second arch mesoderm
- stapedius muscle and stapes
Middle Ear Genes
- gooscoid, RARs, Prx1, Otx2, Hoxa1, Hoxb1, endothelian related molecules
SEM
Inner- otocyst
- week 3 otic placode forms on surface ectoderm
- otic placode sinks into mesoderm
- forms otocyst (otic vesicle)
- Otic Vesicle to Labyrinth 1
- Pig stage 13/14 Otocyst
- Otocyst
- branches form and generate endolymphatic duct and sac
- forms vestibular and cochlear sac
Vestibular sac
- generates 3 expansions
- form semicircular ducts
- remainder forms utricle
- epithelia lining generates
- hair cells
- ampullary cristae
- utricular macula
Otic Vesicle to Labyrinth
- Human Stage 22
- Vestibular- Otoconia
- Otoconin- inner ear biominerals
Cochlear sac
- generates coiled cochlear duct
- humans 2 1/2 turns
- remainder forms saccule
- epithelia lining generates
- hair cells
- structures of organ of corti
- saccular macula
- Human Stage 22- cochlear
- Human Stage 22- cochlear
Bony Labyrinth
- formed from chrondified mesoderm
- Periotic Capsule
- mesenchyme within capsule degenerates to form space filled with perilymph
Vestibulocochlear Nerve
- forms beside otocyst
- from wall of otocyst and neural crest cells
- bipolar neurons
- vestibular neurons
  - outer end of internal acoustic meatus
  - innervate hair cells in membranous labyrinth
  - axons project to brain stem and synapse in vestibular nucleus
- cochlear neurons
  - cell bodies lie in modiolus
  - central pillar of cochlear
  - innervate hair cells of spiral organ
  - axons project to cochlear nucleus
Inner Ear Genes
- hindbrain segmentation occurs at same time placode arises
- otocyst adjacent to rhombomere 5
- may influence development
- Hoxa1, kreisler, Fgf3
- genes regulating neural crest cells (neural genes)
- Pax2 Ko affects cochlear and spiral ganglion, but not vestibular apparatus
- nerogenin 1 affects both ganglia
Semicircular canal
- Otx1- cochlear and vestibular normal
Hmx3, Prx1, Prx2
Sensory Organs
- thyroid hormone receptor beta
- Zebrafish-mindbomb mutant
  - excess hair cells but not supporting cells
    - Notch-Delta signaling
Gene Expression-inner ear
- Brn-3c and Hair cell development
- Supporting Cells- p27kip
- Thyroid Hormone
- Ganglion neurons require growth factors
- vestibular neurons- BDNF, NT3
  - survival not development
Congenital Deafness
- conductive- disease of outer and middle ear
- sensorineural- cochlear or central auditory pathway
Outer ear Malformation
- rare meatal atresia
- canal narrow or not formed
- part of first arch syndrome
Middle ear Malformation
- also rare
- can be part of first arch syndrome
- malformed maleus or incus
- congenital fixation of stapes
- stapes anchored to oval window
- annular ligament fails to develop
Congenital malformations Statistics
Congenital sensorineural
- hereditary or acquired
- see recent reviews
Hereditary
- recessive- severe
- dominant- mild
- can be associated with abnormal pigmentation
- hair and irises
Acquired
- rubella (German measles)
- maternal infection during 2nd month of pregnancy
- vaccination of young girls
- streptomycin
- antibiotic
- thalidomide
Conductive Hearing Loss
- produced by otitis media with effusion, is widespread in young children.
- temporary blockage of outer or middle ear
- See also: recent Ref and Senses WWW Link

References

Recent Reviews Abnormal Development

Webster WS. [See Related Articles] Teratogen update: congenital rubella. Teratology. 1998 Jul;58(1):13-23. Review. PMID: 9699240; UI: 98364396.
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.PMID: 9279630; UI: 97425580.
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. PMID: 8893214; UI: 97048378.
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. MID: 7747785; UI: 95266633.
Strasnick B, et al [See Related Articles] Teratogenic hearing loss. J Am Acad Audiol. 1995 Jan;6(1):28-38. Review. PMID: 7696676; UI: 95210704.
Kossowska E, et al. [See Related Articles] Prenatal and neonatal prophylaxis in otorhinolaryngology. Int J Pediatr Otorhinolaryngol. 1980 Jun;2(2):85-98. Review. PMID: 6765128; UI: 84160924.
Gottlieb G. [See Related Articles] Conceptions of prenatal development: behavioral embryology. Psychol Rev. 1976 May;83(3):215-34. Review. No abstract available.
PMID: 188059; UI: 77079452.
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.

Human Genes

LocusID

Symbol

Description

Position

Links

1678

DFN1

deafness, X-linked 1, progressive

Xq22

1679

DFN2

deafness, X-linked 2, perceptive, congenital

Xq22

1680

DFN4

deafness, X-linked 4, congenital sensorineural

Xp21.2

1701

DFNB9

deafness, autosomal recessive 9

2p23-p22

1729

DIAPH1

diaphanous (Drosophila, homolog) 1

5q31

2706

GJB2

gap junction protein, beta 2, 26kD (connexin 26)

13q11-q12

4647

MYO7A

myosin VIIA (Usher syndrome 1B (autosomal recessive, severe))

11q13.5

5459

POU4F3

POU domain, class 4, transcription factor 3

5q31

Conductive Hearing Loss

Conductive Hearing Loss Produces a Reversible Binaural Hearing Impairment David R. Moore, Jemma E. Hine, Ze Dong Jiang, Hiroaki Matsuda, Carl H. Parsons, and Andrew J. King J. Neurosci. 1999;19 8704-8711
- http://www.jneurosci.org/cgi/content/abstract/19/19/8704
- tested ferrets by lon-term plugging of ear canal
- Repeated testing during the 22 months after unplugging revealed a gradual return to normal levels of unmasking.
- Results show that a unilateral conductive hearing loss, in either infancy or adulthood, impairs binaural hearing both during and after the hearing loss.
- Show scant evidence for adaptation to the plug and demonstrate a recovery from the impairment that occurs over a period of several months after restoration of normal peripheral function.

Terms

About Notes

These lecture notes from the Embryology Program compiled and written by Dr M. Hill.
Some notes derived from historic class notes.
This updated section of notes is still being developed Mar99 and is not yet complete.
Note Links to OMIM Entries are copies of originals for computers without internet access. Computers with internet access can directly access the database.

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Date Last Modified: 11/3/99
This site maintained by Dr M. Hill