Hearing - Inner Ear Development
Introduction
The inner ear is derived from a pair of surface sensory placodes (otic placodes) in the head region. These placodes fold inwards forming a depression, then pinch off entirely from the surface forming a fluid-filled sac or vesicle (otic vesicle, otocyst). The vesicle sinks into the head mesenchyme some of which closely surrounds the otocyst forming the otic capsule. The otocyst finally lies close to the early developing hindbrain (rhombencephalon) and the developing vestibulo-cochlear-facial ganglion complex.
Some Recent Findings
- Tbx1 and Brn4 regulate retinoic acid metabolic genes during cochlear morphogenesis. [1]"These results indicate that Tbx1 expression in the POM regulates cochlear outgrowth potentially via control of local retinoic acid activity."
Otic Placode
The embryonic surface sensory placode associated with hearing and balance. This will be lost from the embryo surface to form the otocyst or otic vesicle.
- Stage 13/14 embryo - the otic placode has sunk from the surface ectoderm to form a hollow epithelial ball, the otocyst, which now lies beneath the surface surrounded by mesenchyme (mesoderm).
- The epithelia of this ball varies in thickness and has begun to distort, it will eventually form the inner ear membranous labyrinth.
Sensory Placodes
- week 4 a series of thickened surface ectodermal patches form in pairs rostro-caudally in the head region.
- Recent research suggests that all sensory placodes may arise from common panplacodal primordium origin around the neural plate, and then differentiate to eventually have different developmental fates. (More? Schlosser G.)
- sensory placodes will later contribute key components of each of our special senses (hearing, vision, smell and taste).
- Otic Placode - one of the first to form and contributes inner ear structures.
- Optic (Lens) Placode - lies on the surface, adjacent to the outpocketing of the nervous system (which will for the retina) and will form the lens.
- Nasal Placode - 2 components (medial and lateral) and will form the nose olefactory epithelium.
- Other species have a number of additional placodes which form other sensory structures (fish, lateral line receptor).
- Note that their initial postion on the developing head is significantly different to their final position in the future sensory system.
- Links: Placodes
Otocyst
- week 3 otic placode forms on surface ectoderm
- otic placode sinks into mesoderm
- forms otocyst (otic vesicle)
- branches form and generate endolymphatic duct and sac
- forms vestibular (dorsal) and cochlear (ventral) regions
- differentiation of otic vesicle to membranous labyrinth
Vestibular Sac
- generates 3 expansions - form semicircular ducts
- remainder forms utricle
- epithelia lining generates - hair cells, ampullary cristae, utricular macula
- 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
Cochlea
Magnetic Resonance images of the adult Cochlea | |
---|---|
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 has 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
Sox9 20346939 Sox2 20071536
References
- ↑ <pubmed>19476657</pubmed>
Reviews
Articles
- Development of the mouse cochlea database (MCD). Santi PA, Rapson I, Voie A. Hear Res. 2008 Sep;243(1-2):11-7. Epub 2008 May 25. PMID:18603386 | PMC2628570
Search PubMed
May 2010 "Inner Ear Development" All (4027) Review (452) Free Full Text (750)
Search Pubmed: Inner Ear Development Cochlea Development
External Links
- Neuroscience Neuroscience - The Inner Ear
Glossary Links
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Cite this page: Hill, M.A. (2024, June 15) Embryology Hearing - Inner Ear Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Hearing_-_Inner_Ear_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G