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.

Categories: Hearing | Outer Ear | Middle Ear | Inner Ear | Balance

Historic Embryology - Hearing
Historic Embryology: 1880 Platypus cochlea \| 1892 Vertebrate Ear \| 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 \| 1934 External Ear \| 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

Otic Placode

The sensory placode associated with hearing and balance.

Stage 13/14 embryo (shown below) 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.

Otocyst

Carnegie Stage 12 otic placode

Carnegie Stage 13 otic vesicle

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

Inner ear hair cells

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

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Cite this page: Hill, M.A. (2024, May 1) Embryology Hearing - Inner Ear Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Hearing_-_Inner_Ear_Development

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