Inner Ear Embryology Flashcards
List the very beginning inner ear structures in order (start with otic placode
Otic placode (ectoderm thickens and folds inward –> Otic pit –> Otic vessicle/Otocyst (fluid filled sac) –> Otic capsule (Mesenchyme surrounds otocyst)
What structure do all inner ear structures form from?
Otocyst
List the 3 stages of development of the Otic capsule (bony labyrinth) in order
1: Chondrification
2: Peri-lymphatic (peri-otic) sac forms
3: Ossification
Where does the organ of Corti form from and when does it begin?
Ventral Otocyst, begins 9-10 fetal weeks
List the developmental gradients in the cochlea
- Base to Apex
2. Inner to Outer
What is the Sliding Place Principle?
Change in place of responsiveness. The base initially responds to low frequencies, mature base responds to high frequencies.
When is there an adult # of hair cells?
22 Fetal wks
Which hair cells are chaotic and uneven during initial development?
OHCs
During stereociliogenesis, when do IHCs have adult configuration & U-Shaped?
12-13 fetal wks
When are the stereocilia adult-like on both IHCs and OHCs?
20-21st fetal wks
When is the stria vascularis mature by?
19 fetal wks
Cochlear nerve fibers: Type I innervate _____
Type II innervate ________
Type I : IHCs
Type II: OHCs
When does the space between the tectorial membrane major and minor form?
~18 weeks
Describe Michel’s Aplasia
Complete failure of inner ear development. Absent cochlea, vestibule, SCC & likely the nerve. Problem with Otic placode formation
Cochlear aplasia
Absent cochlea, vestibule & SCC present
Common cavity
Cochlea and vestibule in a common cavity
Incomplete Partition I
No bony modiolus & no interscalar septum
Incomplete Partition II (Mondini Dysplasia)
1.5 cochlear turns instead of 2.5-2.75
Cochlear Hypoplasia
Underdeveloped cochlea
Hair cell innervation: Penetration starts when?
Week 11 GA
Hair cell innervation: Fibers contact OHCs
Week 14 GA
Name 2 syndromes that cause abnormalities of the 1st pharyngeal arch
- Treacher Collins
2. Pierre Robin
When are hair cells differentiated by?
10-11 wks
When does a fetus reasonably respond to sound by?
25 fetal wks
Where do spiral ganglia develop from?
Otic Vessicle
When is the cochlea mature by?
25 wks
When does the cochlea have 2 3/4 turns developed?
10-11 wks
