UNSW Embryology

• 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

• develops from six aural hillocks
• 3 on first arch
• 3 on second arch
• originally on neck, moves cranially during mandible development

• 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)

• derived from first pharyngeal pouch
• extends as tubotympanic recess
• during week 5 recess contacts outer ear canal

• develop from first and second pharyngeal arches
• tympanic cavity enlarges to incorporate
• coats with epithelia

• tensor tympani muscle
• malleus and incus

• stapedius muscle and stapes

• 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

• Human Stage 22
• Vestibular- Otoconia
• Otoconin- inner ear biominerals

• 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

• rare meatal atresia
• canal narrow or not formed
• part of first arch syndrome

• 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

• hereditary or acquired
• see recent reviews

• recessive- severe
• dominant- mild
• can be associated with abnormal pigmentation
• hair and irises

• rubella (German measles)
• maternal infection during 2nd month of pregnancy
• vaccination of young girls
• streptomycin
• antibiotic
• thalidomide

• 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