Ear Development Flashcards
When does the ear begin to develop?
week 4 (goes to week 20)
*if a problem does occur, it’ll probably be b/t week 4-8
What is in the external Ear?
– Consists of auricle (pinna), external acoustic meatus, external layer of tympanic membrane
What is in the middle Ear?
– Consists of three ossicles, internal layer of tympanic membrane, and middle ear cavity
What is coming from inner Ear?
– Consists of vestibulocochlear organ
Where do the external and middle ear come from? inner ear?
- Pharyngeal arches
- develops independently
*can have problems with E/M and I is fine
What arches does the external ear come from? Innervation?
- pharyngeal arches 1 +2
2. CNV3 (auriculotemporal), CN X (auricular branches), CN VII, Great Auricular (C2 + C3)
What covers the external ear?
Covered with ectoderm that becomes the skin, and underneath made of auricular hillocks
mesenchymal swellings covered with ECTODERM (NC component)
What are auricular hillocks?
mesenchymal swellings (NC cells) covered by surface ectoderm; NC cells migrate to pull external ectoderm which gives rise to different aspects of the external ear
What part of the external ear came from the first arch?
half of ear attached to body
rest comes from arch 2
What nerve innervates arch 1? 2?
- CN 5
2. CN 7
How do Auricular Skin tags form?
problem with migration of surface ectoderm, and if cartilage is there, then abnormal migration of NC cells too
*always will have skin
How do we get Anotia?
NC and Auricular hillocks do not form/migrate
*NC cells of arch 1 + 2 did not migrate properly
What are pharyngeal arches made of?
Ectoderm, mesoderm, endoderm, + NC components
What causes Microtia?
NC cells form arches 1 + 2 migrate abnormally
How does the external auditory meatus form?
the 1st pharyngeal cleft (ectoderm) invaginate in
*it fills in with cells to form the meatal plug, and at 6 months they go through apoptosis to open up the EAM
What is the inner ear developed? what is it derived from?
week 4 (first to develop) surface ectoderm
What structures to help with inner ear development form in week 4?
- Otic placode - forms near hindbrain, surface ectoderm; invaginate to from otic pit
- Otic Pit - connects to itself, and migrates in to form otic vesicle
- Otic vesicle - own little pouch, gives rise to membranous labyrinth
What does the membranous labyrinth come from/form?
comes from otic vesicle, and forms utricle (dorsal) and saccule (ventral)
What is the utricle? Where does it come from? What controls its development?
- Utricle + Semicircular Canal
- Membranous Labyrinth
- Dlx5 + Dlx6
What is the saccule? Where does it come from? What controls its development?
- Cochlear Duct, Ductus reunions, Macula of saccule, organ of corti
- Membranous Labyrinth
- Pax6 (cochlear duct is dependent on Pax 2)
How do the semicircular canal/ducts form?
endo lymphatic duct/sac–>developing semi –> functional semi
*lateral canal dependent on Otx1
What is the function of the ducts reunions?
connects saccule (from saccule) to the utricle (from utricle)
Where do we find hair cells? What do they do?
- Ampullae - acceleration
- Macula - gravity
- Organ of cortical - sound vibration
- come from SURFACE ECTODERM
- *when they bend, it leads to innervation of the inner ear
- **do not regrow (if lost, you go deaf)
What is the innervation of the inner ear?
CN 8 - goes to hair cells
comes from two sources:
- vestibular ganglion
- spiral (cochlear) ganglion
- both have contributions from surface ectoderm via otic placode
- Vestibular ganglion also has neural crest contribution
Where does perilymph come from? What is it made of?
- From perilymphatic duct or filtration of blood in perilymphatic space
- Similar content to CSF
*b/t duct and bone
Where does endolymph come from? what is it made of?
- Stria vascularis
- similar to ICF
- endolymphatic sac stores it
- found within duct
If we get an infection in the middle ear, and it eroded through the round/oval window, what happens?
offers a direct route to the subarachnoid space and you get meningitis
What is the bony labyrinth? function?
- condensation of mesenchyme (mesoderm)
- protects membranous labyrinth
*vacuoles around cochlear duct called scala tympani + vestibuli
How does the bony labyrinth form?
mesoderm around cochlear duct –> as it grows you get vacuoles which develop sacral vestibuli and scala tympani –> ends with bony around the ST/SV/scala media and cochlea
*week 5-8
What surrounds the spiral ganglion?
bony labyrinth
*send its nerve fibers into basal membrane to be discharged to pick up impulses for sound
Of the 1st pharyngeal cleft, what does the ectoderm form? endoderm?
- External Auditory Meatus
2. Tubotympnaic recess (and eventually tympanic cavity)
What is the tympanic membrane derived from?
ecto, meso, and endo
- external surface (N: Auriclotemporal + Vagus)
- *blood supply to TM
- **internal surface (N: CN 9)
What are the ear bones made of?
NC
Malleus and include are form 1st arch NC
Stapes is from 2nd arch NC
*covered with endodermal epithelium from 1st pharyngeal pouch
Where does the Tensor Tympani come from?
Pharyngeal arch 1 -mesoderm
-Innervated by CN 5
Where does anything innervated by CN 5 come from?
arch 1
Where does stapedius come from?
Pharyngeal arch 2 - mesoderm
-Innervated by CN 7
Why do you sound different than you hear your voice as?
Stapedius + Tympani tense to ensure your voice doesn’t damage your ears
Congenital Deafness Causes
- Most times genetic
- Maldevelopment of sound conduction apparatus of middle and external ears (arch 1 + 2)
a. First arch syndrome
b. Abnormalities of malleus and incus (1st arch)
c. Congenital fixation of stapes - Neurosensory sensory structures of inner ear
- Rubella infection during week 7-8 can cause defects of spiral organ and deafness
