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
