UNSW Embryology

Development of the Organs of Audition and Equilibrium - Stage 13/14 Embryo

© Dr Mark Hill (2008)

Acknowledgements

Introduction

Page under construction

Stage 13/14 Embryo

A2: Otocyst (R). Apex of otocyst (primordium of L endolymphatic sac).

A3: Otocyst; surrounding mesenchyme = otic capsule. Note proximity of otocyst to wall of rhombencephalon. Superior glossopharyngeal ganglion. Vestibulo-cochlear-facial ganglion complex (R). Trigeminal ganglion (not in image excerpt).

A4: Indentation in rostral margin of otocyst = primordium of utriculosaccular canal. Note alignment of superior cardinal vein (LS) in relation to the nerve trunks (XS). Trigeminal ganglion (not in image excerpt). Note variation in height of cells of L otocyst wall. Dorsal end of 1st pharyngeal arch and groove (not in image excerpt).

A5: Facial ganglion (R). "Floor" of L otocyst. Note on R, the former position of the otocyst in relation to the 2nd pharyngeal arch.

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 labrynth (otic capsule) chondrifies

Week 12-16 - Capsule adjacent to membranous labrynth 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 respone in fetus.

(These are Human embryonic timings, not clinical which is based on last menstral period +2 weeks)

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.

Developmental Overview

  • Hearing- 3 divisions of ear
  • Pinna- Auricle
  • Outer- external auditory meatus
  • 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
  • first arch mesoderm
  • second arch mesoderm
  • Inner- otocyst
  • Vestibular sac - generates 3 expansions, form semicircular ducts, remainder forms utricle, epithelia lining generates hair cells, ampullary cristae, utricular macula
  • Otic Vesicle to Labyrinth
  • 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
  • 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

    • Hearing Development Terms

    ampulla

    auricle - "external ear"

    Cranial Nerve VIII

    cristae ampularis

    Equilibrium

    Eustacian tube

    Hillock

    ossicles

    Otic vesicle

    - otocyst

    Pharyngeal arch

    Pharyngeal cleft

    Pharyngeal pouch

    Pharynx

    Placode

    Semicircular canals

    tympanic membrane

    - "eardrum"

    Glossary of Terms

    A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

    Quick Links

    UNSW Embryology ISBN: 978 0 7334 2609 4

    UNSW CRICOS Provider Code No. 00098G