Sensory Development - Hearing

Introduction

We use the sense of balance and hearing to position ourselves in space, sense our surrounding environment, and to communicate. Portions of the ear appear very early in development as specialized region (otic placode) on the embryo surface that sinks into the mesenchyme to form a vesicle (otic vesicle = otocyst) that form the inner ear.

This region connects centrally to the nervous system and peripherally through specialized bones to the external ear (auricle). This organisation develops different sources forming the 3 ear parts: inner ear (otic placode, otocyst), middle ear (1st pharyngeal pouch and 1st and 2nd arch mesenchyme), and outer ear (1st pharyngeal cleft and 6 surface hillocks).

This complex origin, organisation, and timecourse means that abnormal development of any one system can impact upon the development of hearing.

Textbooks

Human Embryology (2nd ed.) Larson Chapter 12: p375-409
The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Chapter 19: p491-511

Objectives

Understanding of structures and functions of the auditory pathway
Understanding of inner, middle and external ear origins
Understanding of timecourse of auditory development
Understanding of abnormalities of auditory development
Brief understanding of central auditory pathway and molecular development

Development Timing

Week 3 - otic placode, otic vesicle

Week 5 - cochlear part of otic vesicle elongates (humans 2.5 turns)

Week 9 - Mesenchyme surrounding membranous labryinth (otic capsule) chondrifies

Week 12-16 - Capsule adjacent to membranous labryinth undegoes vacuolization to form a cavity (perilymphatic space) around membranous labrynth and fills with perilymph

Week 16-24 - Centres of ossification appear in remaining cartilage of otic capsule form petrous portion of temporal bone. Continues to ossify to form mastoid process of temporal bone.

3rd Trimester - Vibration acoustically of maternal abdominal wall induces startle response in fetus.

3 Sources:

Inner ear - epidermal otic placode at level of hindbrain.

Middle ear - cavity: 1st pharyngeal pouch, ossicles: mesenchyme 1st and 2nd pharyngeal arches.

Outer ear - external auditory meatus: 1st pharyngeal cleft, auricle: 6 hillocks 1st and 2nd pharyngeal arches.

Inner Ear

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.

Middle Ear

The middle ear ossicles (bones) are derived from 1st and 2nd arch mesenchyme.
The space in which these bones sit is derived from the 1st pharyngeal pouch.

Outer Ear

The external ear is derived from 6 surface hillocks, 3 on each of pharyngeal arch 1 and 2.
The external auditory meatus is derived from the 1st pharyngeal cleft.
The newborn external ear structure and position is an easily accessible diagnostic tool for potential abnormalities or further clinical screening.

Developmental Overview

Development of 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

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

Congenital malformations Statistics

Congenital sensorineural hereditary or acquired (see [#References 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

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.

References

Textbooks

Before We Are Born (5th ed.) Moore and Persaud Chapter 20: p460-479
Essentials of Human Embryology, Larson Chapter 12: p252-272

Online Textbooks

Developmental Biology (6th ed.) Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000. Evolution of the mammalian middle ear bones from the reptilian jaw | Chick embryo rhombomere neural crest cells | Some derivatives of the pharyngeal arches | Formation of the Neural Tube | Differentiation of the Neural Tube | Tissue Architecture of the Central Nervous System | Neuronal Types | Snapshot Summary: Central Nervous System and Epidermis

Neuroscience Purves, Dale; Augustine, George J.; Fitzpatrick, David; Katz, Lawrence C.; LaMantia, Anthony-Samuel; McNamara, James O.; Williams, S. Mark. Sunderland (MA): Sinauer Associates, Inc. ; c2001 The Auditory System | The Inner Ear | The Middle Ear | The External Ear | Early Brain Development | Construction of Neural Circuits | Modification of Brain Circuits as a Result of Experience

Molecular Biology of the Cell (4th Edn) Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter. New York: Garland Publishing; 2002. Neural Development | The three phases of neural development

Clinical Methods 63. Cranial Nerves IX and X: The Glossopharyngeal and Vagus Nerves | The Tongue | 126. The Ear and Auditory System | An Overview of the Head and Neck - Ears and Hearing | Audiometry

Health Services/Technology Assessment Text (HSTAT) Bethesda (MD): National Library of Medicine (US), 2003 Oct. Developmental Disorders Associated with Failure to Thrive

Eurekah Bioscience CollectionCranial Neural Crest and Development of the Head Skeleton

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Pubmed hearing development

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Course Content 2009

Cite this page: Hill, M.A. (2024, May 18) Embryology 2009 Lecture 17. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2009_Lecture_17

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