EMB: Ear Development Flashcards
What week does the ear start to develop?
4
What germ layer does the middle + external ear come from?
external: auricle (pinna), external acoustic meatus, tympanic membrane (external layer)
Middle: 3 ossicles, tympanic membrane (internal) + middle ear cavity
Pharyngeal arches
What germ layer does the inner ear come from?
-vestibulocochlear organ
Surface Ectoderm (develops independently)
The auricular hillocks of the external ear are __________ cells.
Neural Crest
What is the importance of the neural crest cells in the auricular hillock?
The neural crest cells migrate and move to form the weird looking external part of the ear.
What is the innervation of the external ear?
Great Auricular N (C2 = C3) and Auriculotemporal N.
(+ a litle vagus and facial)
What causes microtia?
NC cells did not migrate appropriately
What causes Skin Tags?
Problem with migration of surface ectoderm + NC cells
What does the external auditory meatus come from?
First pharyngeal cleft of ectoderm
What does the Auricle come from?
1st and 2nd pharyngeal arches (NC)
What fails to happen leading to no ear at all and no external auditory meatus?
Auricular hillocks + NC cells did not migrate/form
What causes this?
Surface ectoderm cells did not undergo apoptosis, so we still have a metal plug.
In the inner ear, how does this development work, in stages?
Otic placode –> Otic pit –> Otic vesicle –> membranous labyrinth
What are the 2 parts of the membranous labyrinth?
Utricle (dorsal)
Saccule (ventral)
In the membranous labyrinth, what is the utricle dependent on and its subpart the lateral canal of semicircular duct?
Dlx5 + Dlx6
lateral canal –> Otx1
What components are in the Utricle part of the membranous labyrinth?
Semicircular ducts + utricle
In the membranous labyrinth, the saccule part is dependent on?
Pax6
What are the derivatives of the saccule part of the membranous labyrinth?
Cochlear duct (Pax 6) + ductus reunions + saccule + organ of corti (cochlea)
The inner ear has hair cells that come from surface ectoderm, what are the 3 parts and function?
Ampullae - acceleration
Macula - gravity
Organ of Corti - sound vibration
What nerve innervates the inner ear?
Vestibulocochlear
What are the two parts of the vesitubularcochlear N. and their orgin?
Vestibular ganglion = SE + NC
Spiral (cochlear) ganglion = SE
Perilymph is from the bone and surrounds the endolymph (endo = in). What does it mimic?
CSF
What is endolymph similar to?
Intracellular fluid
Where does perilymph come from?
A patent perilymphatic duct –> allows free passage from subarachnoid space (which is why it is smilar to CSF)
Where does endolymph come from?
Stria vascularis
What protects the membranous labyrinth?
Bony labyrinth
What is the bony labyrinth made of?
Mesenchyme (mesoderm)
In the bony labyrith, which spaces hold perilymph?
Scala vestibuli + scala tympani
What space houses the endolymph?
Scala media
In the middle ear, the 1st pharyngeal cleft (ectoderm) forms _________.
External auditoy meatus
In the middle ear the 1st pharyngeal pounch (endoderm) forms ________.
Tubotympanic recess
In the middle ear, the tympanic membrane is formed by?
Everything!
Ectoderm, Mesoderm, Endoderm
In the middler ear, the ossicles (malleus + incus) are formed from?
NC!!! = bone
Malleus = 1st arch
Stapes = 2nd arch
What nerve innervates the tensor tympani muscle of the ear?
CN V
*Anything innervated by 5 = 1st arch*
What innervates the stapedius M. of the ear?
CN VII
The tensor tympani comes from the _________.
1st pharngeal arch mesoderm
The stapedius M. comes from the _________.
2nd pharyngeal arch mesoderm
What causes congenital deafness?
genetic
Maldevelopment of sound-conduction apparatus of middle + external ears (which come from pharyngeal arches).
Could be due to: first arch syndrome, mallus/incus abnormalities, stapes doesn’t move, hair cells didn’t form, etc.
and
*rubella infection during 7-8th week can cause defects of spiral organ and deafness*
