Development Of The Ear Flashcards
What is the first indication of the developing ear?
In embryos 22 days a thickening of the surface ectoderm on each side
of the rhombencephalon
How are the auditory vesicles (otocysts) formed?
The thickening of the surface ectoderm, the otic placodes, pits ,invaginate rapidly and form the otic or auditory vesicles (otocysts)
• Otic pit, otic vesicle, loses connection from surface ectoderm
The inner ear is under inductive influence by?
- Notochord
- Paraxial mesoderm
Name the embryonic structure tires that develop into the inner ear?
• Otic placode - thickening of ectoderm
• Otic pit
• Otic vesicle = otocyst
Note: Epithelium of membranous labyrinth incl. sensory epithelium originate from ectoderm
Each auditory vesicle divided into?
- Ventral component that gives rise to the saccule and cochlear duct .
- Dorsal component that forms the utricle, semicircular canals, and endolymphatic duct
- Together these epithelial structures form the membranous labyrinth.
Describe the development of the saccule?
• in the sixth week of development, the saccule forms a tubular outpocketing at its lower pole.
• This outgrowth, the cochlear duct, penetrates the surrounding mesenchyme in a spiral fashion until at the end of the eighth week it has completed 2.5 turns.
• The ductus reuniens connects the remaining portion of the saccule with utricle.
What is the cochlear duct?
Outgrowth of the saccule at its lower pole
How does the cochlear duct develop?
Penetrates surrounding mesenchyme in a spiral fashion
- completes 2.5 turns at the end of week 8
What connects the remaining portion of the saccule with the utricle?
Ductus reuniens
What happens to the mesenchyme surrounding the cochlear duct?
Differentiates into cartilage
What happens to the cartilaginous shell?
In the 10th week, this cartilaginous shell undergoes vacuolization, and forms two perilymphatic spaces
1. the scala vestibuli
2. scala tympani
What separates the cochlear duct from the scala vestibuli?
Vestibular membrane
What separates the cochlear duct from the scala tympani?
Basilar membrane
Function of spiral ligament?
Attaches lateral wall of cochlear duct to the surrounding cartilage
What is the Modiolus?
The median angle of the cochlea angle is connected to and partly supported by a long cartilaginous process know as the modiolus
- the future axis of the bony cochlea
Ossification of cartilaginous she’ll happens by?
25 weeks
The epithelial cells of the cochlear duct form what 2 ridges?
- The inner ridge, the future spiral limbus,
- The outer ridge which forms the sensory cells, hair cells, of the auditory system
- They are covered by the tectorial membrane
- The sensory cells and tectorial membrane together constitute the organ of Corti
- Impulses received by this organ are transmitted to the spiral ganglion and then to the nervous system by the auditory fibers of cranial nerve VIll
