The development of the inner ear explained in 15 minutes.
For the embryology of the middle and outer ear, tap here: kzfaq.info/get/bejne/n9aTn7p-xNS2nmw.html
If you are completely new to embryology and you want to understand it quickly, this should be the first video you watch:
- kzfaq.info/get/bejne/opuXiKSDzb67hI0.html
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SUMMARY OF THE VIDEO FOR YOUR NOTES
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The internal ear
- The otic placode is seen in the day 22 embryo as a thickened part of the ectoderm on both sides of the rhombencephalon (developing CNS / neural tube).
- the otic placode invaginates quickly forming the otic vesicles. Also known as auditory vesicles, or otocysts.
- the otic placode divides itself into both a ventral component and a dorsal component
- the ventral part gives rise to the saccule and the cochlear duct
- the dorsal part forms the utricle, semicircular canals, and endolymphatic duct.
- these are collectively the membraneous labyrinth
- by week 6, the saccule has an outgrowth that eventually forms the cochlear duct by growing and coiling 2.5 times around itself. It grows into the surrounding tissue to do this.
- the connection between the saccule and the cochlear duct is by the ductus reuniens
- the tissue that the cochlear duct penetrated will differentiate into cartilage
- some of this cartilage will become hollow, to allow for the development of the scala vestibuli and tympani, each having their own membrane.
- cochlear duct is attached to the rest of the cartilage by the spiral ligament
- epithelial cells of the cochlear duct differentiate
- these become the outer ridge and the inner ridge
- the outer ridge becomes the hair cells which are covered by the tectorial membrane
- the inner ridge becomes the spiral limbus
- the hair cells and the tectorial membrane are known as the Organ of Corti
- the Organ of Corti sends impulses to the brain via cranial verve VIII (CN8, vestibulocochlear nerve)
- by week 6 semicircular canals appear by walls that grow together
- the walls disappear leaving the three semicircular canals
- one of the ends become the crus ampullare that dilates and contains sensory cells, the other end doesn't dilate and is thus called the crus nonampullare
- the cells in the crus amopullare are known as the crista ampullaris and these maintain equilibrium
- inside the utricle and saccule , maculae acusticae develop, which send information about the bodies position in space to the brain for processing - this is done via the vestibular portion of CNVIII
- the statoacoustic ganglion is formed by both neural crest cells and by some cells that divide off the optic placode (so all ectoderm)
- the statoacoustic ganglion divides into both vestibular and cochlear segments (CNVIII)