Ear Embryology Flashcards
What does the external ear develop from?
the 1st pharyngeal cleft, plus mesenchymal hillocks associated with the 1st and 2nd pharyngeal arches
What does the middle ear develop from?
the 1st pharyngeal pounch\
but the ossicles are from the 1st and 2nd pharyngeal arches
What does the inner ear devlop from?
the otic vessicle
How is the otic vesicle formed?
the otic placode is an area of thickened surface ectoderm aadjacent to eh hindbrain
it thickens, forms a depression and pinches off to sink into the surrounding mesenchyme
What will the otic vesicle induce the surrounding mesenchyme to form?
the bony labyrinth (meaning the otic vesicle transofrms into the membranous labyrinth)
What part of the brain takes care of induction of the otic placodes
the hindbrain
What ganglion does oart of the otic vesicle develop into?
the statoacoustic ganglion
THe otic vessicle sort of divides into what two sections?
the dorsal utricular part and the ventral saccular part
What does the utricular part of the otic vessicle give rise to?
the semicircular ducts utricle and endolymphatic duct
What does the saccular part of the otic vesicle give rise to?
the saccule, cochlear duct, ductus reuniens (connects the cochlea to the rest of the labyrinth)
HOw do the semicircular ducts for?
the utricular porition of the otic vesicle form plate-like outpocketings oriented at right angles to one another. The walls oppose one another and the cells in the middle portion will leave, leaving just hollow semicircular ducts
the wide areas are the ampulae, attached to the utricle
Besides the otic vesicle, what cells help to form the statoacoustic ganglion?
neural crest cells
What does the statoacoustic ganglion split to form?
the vestibular ganglion and the spiral ganglion
What organ develops in the wall of the cochlear duct?
organ of corti
THe otic vesicle induces condensation of the surorunding mesenchyme to form the otic capsule. The outer portion of this ossifies to form the bony labyrinth and the inner cartilage vacuolizes to form what three spaces?
scala vestibuli, scala tympani, and cochlear duct (scla media)
What does the vestibular membane separate? WHat does the basilar membrane separate
vestibulra separates scala vestibuli and cochlear duct (easy
basilar membrane is between the scala tympani and cochlear duct (it’s what the organ of corti rests on)
What forms the attachment of the cochlear duct tot he cartilage?
spiral ligament (on the inner aspect of the cochlea)
How is the tympanic membrane formed?
- the first pharyngel pouch evaginates while the firs tpharyngeal groove invaginates
- They grow towards each other until there’s only a small porion of second pharyngeal arch mesodemr between them.
During development, what do the ectodermal cells form outside the TM?
they proliferate and form a plug, which will eventually disappear
What forms the maleus and incus? WHat forms the stapes?
mesoderm from the 1st pharyngeal arch
mesoderm from the 2nd pharyngeal arch
What arch forms the tensor tympani? Innervation?
What arch forms the stapes? Innervation?
1st arch = tensor, trigeminal
2nd arch - stapes, facial
Describe development of the auricle.
you get six auricular hillocks developing by mesenchyme proliferation
the anteiror three are from the first arch and the posteior three are from the second arch
the center is the first pharyngeal cleft
These hillocks will eventually form the outer structures of the auricle
Although the pinna is formed by the 1st and 2nd pharyngeal arches aroudn the 1st pharyngeal cleft, whaat makes their innervation odd?
the anterior portion is supplied by the trigeminal as you’d espect from someone arising form the 1st pharyngeal arch, but the posterior half isn’t supplied by the facial, it’ supplied by the cervical plexus
