12. Ear Development (KEIM) Flashcards
What does the spiral organ differentiate from?
Cells of the cochlear duct itself.
Tissues of the Middle Ear Derivatives
external auditory meatus and external TM
tubotympanic recess
tympanic membrane
malleus and incus
stapes
covering the ossicles
1st pharyngeal groove, surface ectoderm
1st pharyngeal pouch, endoderm
ectoderm, mesoderm, endoderm from PA1
NCC from PA1
NCC PA2
endodermal epithelium
Tensor Tympani
Insertion
Action
Derived from
handle of malleus
dampen sounds
PA1 mesoderm, CN V
Stapedius
Insertion
Action
Derived from?
neck of stapes
pulls posteriorly, dampens sounds
PA 2 mesoderm, CN VII
Inner Ear
Derived from?
forms how and when
surface ectoderm, 1st part to form
4th wk
otic placode from surface endoderm invaginates to form otic pit which rounds up to form the vesicle which will migrate and become primordium of membranous labyrinth
External Ear
Derived from
Innervated by
1st and 2nd PA NCC with mesencymal swellings covered with ectoderm
Great auricular, CN V3, VII, and X
How is the tympanic cavity formed?
The first pharyngeal pouch foms the tubotympanic recess, which forms the pharyngotympanic tube (proximally) and the tympanic cavity (distally).
From what structures is the external ear derived?
The auricular hillocks surrounding the first pharyngeal groove.
What structure connects the cochlea to the saccule?
The ductus reuniens.
What embryological tissue is the otic placode made of?
Surface ectoderm.
What is the external auditory meatus derived from?
The 1st pharyngeal groove.
What is the tympanic membrane derived from?
Three parts:
Ectoderm from the 1st pharyngeal groove.
Mesenchyme from pharyngeal arches 1 and 2.
Endoderm from the tubotympanic recess (1st pharyngeal pouch)
Where does the stapedius insert?
Where does the tensor tympani insert?
Tensor tympani inserts onto the handle of the malleus.
Stapedius inserts on the neck of the stapes.
What forms the endolymphatic duct and sac?
What trascription factor regulates this differentiation?
A diverticulum from the dorsal utricular part of the otic vesicle.
SOHOL
What are the tensor tympani and stapedius muscles derived from respectively?
Tensor tympani: 1st pharyngeal arch mesoderm.
Stapedius: 2nd pharyngeal arch mesoderm.
What is formed by the dorsal part of the otic vesicle?
The endolymphatic ducts, the semicircular canals, and the utricles.
What does the cochlea differentiate from?
The ventral (cochlear) part of the otic vesicle.
What is microtia?
Small or rudimentary auricle, resulting from supressed mesenchymal proliferation
abnormal migration of NCC and hillocks
What is a meatal plug?
The proliferated of surface ectoderm between the external auditory meatus and tympanic cavity does not undergo apoptosis.
Describe the components of the membranous labyrinth
Made of the dorsal utricle and the ventral saccule
What are the components of the utricle?
endolymphatic duct and sac
semicircular ducts and ampullae (hair cells)
macula of utricle (hair cells)
What are the components of the saccule?
cochlear duct
ductus reunions
macula of saccule, organ of corti (hair cells)
What is the specific function of the hair cells in each of these locations:
Ampullae
Macula (utricle and saccule)
Organ of Corti
rotational acceleration
gravity and linear acceleration
sound vibration
Inn: CN VIII, Hair cells do not regenerate, come from surface ectoderm
Describe perilymph
Duct?
ion content?
found?
duct is patent, can flow from subarachnoid space and inner ear (opportunity for meningitis)
similar to CSF, high Na, low K and protein
found within the bony canal system
Describe Endolymph
Produced?
Ion content?
stored?
stria vascularis
High K and protein, low Na
stored in endolympatic sac within membranous labyrinth
What causes auricular appendages?
skin tages/cartialginous components around ear
Abnormal migration of NCC (if cartilage) or surface ectoderm hillocks (if skin)
Describe Anotia
No outer ear
abnormal migration of NCC, no hillocks form.
inner ear likely uneffected
What is a possible complication of prolonged middle ear infection?
Can erode into perilymph and get into subarachnoid space and get into meninges
The bony labyrinth is made of what?
mesenchyme
contains vacuoles (scala vestibuli and tympani full of perilymph)
bony elements ossify and locate within the petrous part of the temporal bone
Describe congenital deafness
usually genetic
maldevelopment of sound conduction by 1st and 2nd arch issues, Treacher-Collins, PRS, or abnormal malleus and incus; fixation of the stapes
Sensorineural Deafness can occur in utero by the following teratogens
rubella in 7-8wk causes defect in spiral organ and deafness
CMV-leading cause of sensorneural hearing loss
toxoplasmosis (toxoplasma gandii), Syphilis (treponema pallidum) can also cause hearing deficits
