19. Developmental Anatomy: Neural Crest, Eye, Ear Flashcards
Where do neural crest cells come from?
Lateral edge of neural ectoderm
Where do neural crest cells migrate once the neural fold is closed?
Into mesenchyme
Enter mesoderm
Which disease is due to the failure of neural crest cells to migrate into the bowel wall?
Hirschsprung’s disease
Why are there no bowel reflexes in Hirschsprung’s disease?
No parasympathetic plexus
Which parts of the bowel are most affected by Hirschsprung’s?
Sigmoid colon
Rectum
What does Hirschsprung’s disease present as?
Constipation
Vomiting
Abdominal distension
What is the first sign of eye development on day 22?
Pair of shallow grooves at the side of the forebrain
What are the outpocketings of forebrain known as?
Optic vesicles
What causes the changes needed for lens formation?
Vesicles come in contact with surface ectoderm
What is the optic cup formed by?
Invagination of the optic vesicle
What are the layers of the optic cup separated by?
Intraretinal space
What gap allows the hyaloid artery to reach the inner chamber of the eye?
Choroid fissure
What will eventually form the pupil?
Fused lips of the choroid fissure, which form a round opening in the optic cup
What forms the lens placode?
Elongated cells of the surface ectoderm
What happens at the canal of Schlemm?
Aqueous humour drains into venous circulation
What are the retina, iris and optic nerve derived from?
Neuroectoderm
What are the lens and corneal epithelium derived from?
Surface ectoderm
What does the mesoderm between the neuroectoderm and surface ectoderm form?
Fibrous and vascular coats of the eye
What are the choroid, sclera and corneal endothelium derived from?
Neural crest cells
What is a coloboma?
Choroid fissure fails to close
What are the causes of congenital cataracts?
Genetics
Maternal rubella
What is cyclopia?
Fusion of eyes due to loss of midline tissue
What is the first sign of ear development?
Thickening of surface ectoderm on each side of rhombencephalon (Otic placodes)
What are otic placodes known as once they invaginate?
Otic or auditory vesicles
What does each otic vesicle divide into?
Ventral and dorsal parts
Differentiation forms ganglion cells for vestibulocochlear ganglia
What is derived from the ventral part of the otic vesicle?
Saccule and Organ of Corti
What is derived from the dorsal part of the otic vesicle?
Utricle
Semicircular canals
Endolymphatic duct
What is the collective names for the structures formed by the ventral and dorsal vesicles?
Membranous labyrinth
What happens to the otic vesicle in the 4th week?
Detaches from surface ectoderm
What role do neural crest cells have in the ear?
Form bony labyrinth in temporal bone
What forms the perilymphatic space?
Connective tissue closest to the membranous labyrinth degenerates
What is the tympanic cavity derived from?
1st pharyngeal pouch
What comes from the distal part of the 1st pharyngeal pouch?
Tubotympanic recess > primitive tympanic cavity
What comes from the proximal part of the 1st pharyngeal pouch?
Eustachian tube
Which pharyngeal arch do the malleus and incus come from?
1st
Which pharyngeal arch does the stapes come from?
2nd
What is the tympanic membrane made up of?
Ectodermal epithelium lining at bottom of auditory meatus and tympanic cavity
Connective tissue
What is the filling of the external auditory meatus with ectodermal cells called?
Meatal plug
What does the pinna develop from?
6 auricular hillocks surrounding the 1st pharyngeal cleft
