Development of the Ear Flashcards
What is contained in the external ear?
Auricle (pinna)
External acoustic meatus
External layer of the tympanic mebrane
What is contained in the middle ear?
Ossicles
Internal layer of tympanic membrane
Middle ear cavity
What is contained in the internal ear?
Vestibulocochlear
develops independently of external and middle
Where is the auricle derived from? What are the auricular hillocks made of? How does it form?
1st and 2nd pharyngeal arches
Mesenchyme (NCC) swellings covered with surface ectoderm
NCC migrate and proliferate to form shape of ear
What innervates the external ear?
Great Auricular n.
CN V3: auriculotmeproal (arch 1)
CN VII (arch 2)
CN X auricular branches
What can cause external ear defects?
If have skin tags with just skin no cartilage= surface ectoderm issue
Everything else aka anotia and microtia is abnormal migration of NCC
Where does the external auditory meatus come from? How does this occur?
First pahryngeal cleft/groove (ectoderm)
Groove migrates up and meets pouch –> proliferation of surface extoderm –> meatal plug –> external acoustic meatus
What is the inner ear derived from? How does this process occur?
Surface ectoderm
Otic placode (thickening of ectoderm) invaginates –> otic plate which migrates –> otic vesicle which migrates into head as mandibular prominence grows
All of these structures lead to the formation of the primordium of membranous labyrinth
What structures come from the dorsal/utricle portion of the membranous labyrinth? What layer are they from?
Endolymphatic duct and sac
Semicircular ducts and ampullae –> lateral canal
Macula of utricle
Surface ectoderm
What structures arise from the saccule/ ventral portion of the membranous labyrinth? What layer are they from?
Cochlear duct
Ductus reunions
Macula of saccule, organ of Corti
surface ectoderm
What do hair cells of the ampullae sense?
rotational acceleration
What do hair cells of the macula sense?
Gravity and linear acceleration
What do hair cells of the organ of corti sense?
Sound vibration
What innervates the inner ear?
Cranial nerve VIII which has vestibular ganglion for macula and ampullae and spiral cochlear ganglion
Where is perilymph found? Where can it travel to? What is its ion concentration similar to?
From periosteum between membranous labyrinth and bone
Into the subarachnoid space via the perilymphatic duct
Where is endolymph found? What is it produced by? Where is it stored? What is it similar in ion concentration to?
Fills membranous labyrinth duct structures
stria vascularis
endolymphatic sacs
intracellular fluid
Why is perilymph clinically significant?
If get ear infection in middle ear can erode spread the infection to perilymph –> infection of subarachnoid space –> meningitis
What is the bony labyrinth?
Condensation of mesenchyme
Ossifies and becomes petrous part of the temporal bone
How do the vacules develop?
Cochlear duct surrounded by cartilaginous otic capsule –> apoptosis cause development of vacules in perilymphatic space and development of organ of corti –> bony cochlea with scala vestibuli, scala tympani, cochlear duct with organ of corti, and spiral ganglion
What is contained in the scala vestibuli and scala tympani? What are these structures derived from?
perilymph
mesenchyme
What is contained in the cochlear duct aka scleramedia? What is this structure derived from?
Enodlymph
Also has organ of corti sitting inside
ectoderm
What forms the external auditory meatus?
1st pharyngeal cleft (ectoderm)
What forms the tympanic recess?
1st pharyngeal puch (endoderm)
What forms the tympanic membrane?
1st Pouch and groove meet up= ecto endo and mesoderm
What does the malleus and incus form from?
1st arch NCCs (bones are neural crest but covered with endoderm epithelium)
What does the stapes form from?
2nd arch NCCs (bones are neural crest but covered with endoderm epithelium)
Where does the tensor tympani come from? What is its action?
1st pharyngeal arch mesoderm so innervated by trigeminal
prevents damage from loud sounds, inserts into handle of the malleus
Where does the stapedius come from?
2nd pharyngeal arch mesoderm so innervated by facial n.
prevent damage from loud sounds by pulling the stapes posteriorly and tilting its base in the oval window
What can cause maldevelopment of sound sound conduction?
Issue with apparatus of middle and external ear
Causes:
- 1st arch syndrome
- Abnormalities in mallus and incus (first arch)
- congenital fixation of stapes (2nd arch)
What infections can cause issues in the inner ear?
Rubella (during week 7-8) cause defects of spiral organ and deafness, sensorineural
Cytomegalovirus –> sensorineural hearing loss
Toxoplasmosis
Syphilis
Zika
What can toxoplasma gondia cause? Treponema pallidum?
hearing loss
congenital deafness
