Auditory System Development Flashcards
mesoderm forms
ossicles, temporal bone and bony labyrinth
Ectoderm forms
outer ear (skin), inner ear (sense organs) & membranous labyrinth
endoderm forms
middle ear epithelial lining, aerated mastoid cavities & eustachian tube
During embryologic development, six hillocks of tissue form around both sides of the first branchial groove. What do these hillocks eventually become?
pinna of external ear
Which branchial arches play a major role in development of ear structures?
1 & 2
Embryologically, the central nervous system (including the brain and spinal cord), sense organs such as the cochlear and vestibular hair cells, and the skin are derived from which of the germ layers?
ectoderm
What is the generic term that describes defects of the spinal cord, during embryologic development when the caudal neuropore does not properly close?
spina bifida
With respect to neuroembryology, the term gastrulation refers to
formation of 3 germ layers
During embryologic development, which germ layer gives rise to the skeletal structures, circulation structures, meninges, and cartilage (including the ossicles and temporal bone)?
mesoderm
Embryologically, development of the inner ear begins with formation of…
otic placodes which are thickenings of ectoderm
During embryologic development, what does the tubotympanic recess eventually become?
ear canal and ™
Which branchial arches play a major role in development of ear/auditory structures?
1 & 2
describe inner ear formation in overview
First trimester
Ectoderm Auditory/otic placode on sides of neural tube—3rd week
Otic pits to auditory vesicle to otocyst
Saccular elongation grows and spirals into cochlea, SCC form,
SCC done first, cochlea last, cartilage first then ossifying
2.5 coils should be completed, the sensory and supporting cells and connections
Adult appearance by 20th to 23rd week (fetal midterm)
Statoacoustic ganglion
CNS development and neural connections and myelin continue to develop
inner ear development is mostly in ____ trimester with mature appearance by ____
first, 20-23 weeks
when does the otic placoe form
3rd week, 21 days
what is the otic placode
superficial thickening of surface ectoderm on either side of the open neural tube
ectoderm will become the____ of the inner ear
epithelium
the migrating neural cells aid in formation of
external ear
middle ear (ossicles)
inner ear (otic capsule and sensory neurons)
what happens on the 23rd day for inner ear
otic placod invaginates to become the otic pit
what happens by day 30 for inner ear
pit closes to form otocyst/auditory vesicle located dorsal to the 2nd pharyngeal cleft
neural tube closed now
otocyst differentiates into vestibular and cochlear portions
what is otic induction
time frame from the ectodermal thickening adjacent to the rhombencephalon on day 22-23 til complete invagination of the otic vesicle around day 26
what happens in the 4th week for inner ear
otic vesicle splits from the surface ectoderm dividing into the ventral and dorsal portion
what does the ventral portion of otic vesicle split into
saccule (part of vestib)
cochlear duct (future scala media and organ of corti)
what does the dorsal portion of otic vesicle split into
future utricle & semicircular canals (part of vestib system)
endolymphatic duct
what do we see in 6 week for inner ear
saccule forms tubular shaped pocket in lower pole
rudimentary cochlear duct, epnetrating surrounding mesenchyme in a spiral fashion to form the cochlea
cochlea completes its 2 3/4 turns by
end of 8th week
utricle and saccule communicate indirectly through
utriculosaccular duct
what system came first in inner ear
vestibular because cochlea develops from the saccule
what is significant of the otic capsule
necessary for proper development of the inner ear and for housing the perilymphatic fluid
cartilaginous otic capsule will eventually become the petrous portion of the temporal bone and called the bony labyrinth
what forms the cartilaginous otic capsule in week 9
the mesenchyme surrounding the inner ear membranous labyrinth
how does the auditory nerve form
from the neural crest cells
auditory nerve peirces the otic capsule where
two divisions
one for vestib and one for cochlea
cartilage surrouding cochlear duct forms
scala vestibuli
scala tympani
two perilymphatic spaces in the cochlea
scala vestibuli
scala tympani
The cochlear duct or scala media is separated from
scala vestibuli by the Reissner’s or vestibular membrane
scala tympani by the basilar membrane
when do sensory epithelia develop in cochlea
During week 7 to 8 of gestation, the cochlea exits the cell cycle and they begoin
2 ridges from epithelial cells of the cochlear duct
inner ridge will form the future spiral limbus
outer ridge will give rise to
about 3 rows of OHC
about 1 row of IHC
Epithelial cells of the spiral limbus form the ______ that lies over the tips of the outer hair cells
tectorial membrane
At about end of the ____ month of gestation, the human cochlea is developed and functional
5
when is the cochlea fully developed and functional
end of the 5th month
appear as flattened out-pockets of the utricular portion of the otic vesicle
semicircular canals, About the 6th week of development,
containing sensory cells for equilibrium and balance
crus ampullare
where are the crus ampullare
at the end of each canal
waht are filled with endolymph
semicircular canals, utricle and saccule
three canals are covered by
bone
Fluid between the outer bony covering and the semicircular canals
perilymph
three semicircular canals are sensitive to
angular motion or rotation as experienced when turning the head
macculae in the utricle and saccule are very sensitive to
linear acceleration as when the body or head is tilted
____ & ____ are gravistatic end organs (responsive to gravity)
utrticle and saccule
when you turn your head why dont you get dizzy?
scc are there to keep head and body upright
looking down and bending over?
utricle and saccule
where are the otoliths?
utricle and saccule
hearing loss can either be
isolated condition (non-syndromic) or associated with other abnormalities/disorders (syndromic)
isolated condition
non syndromic
associated with other abnormalities/disorders
syndromic
undergo complex development because of the actions of a myriad of genes
inner ear
both cochlea and vestib
In many instances the hearing and or vestibular problems in the embryologic phase are caused by
single gene (monogenic) mutations and/or interactions between multiple genes
why is our knowledge in molecular basis of inner ear development important
It is incomplete but necessary to some day fully understand how the inner ear develops and perhaps prevent/treat gene mutations that can lead to auditory/vestibular disorders
Describe the inner ear formation at week 3
The first part of the inner ear to form is the otic placode (superficial thickening of surface ectoderm located on either side of the open neural tube).
Otic placodes sink inward and become otic pits. The otic pit is located dorsal to the second pharyngeal cleft.
Describe inner ear formation at week 4
The neural tube should be closed by now.
The otic pit closes with its edges fused to form the otocyst.
The otocyst turns into the membranous labyrinth.
what happens during week 6-8 of inner ear
Otocyst continues to divide into the vestibular and cochlear portions.
Ventral part of the otocyst gives rise to the saccule and cochlear duct.
Dorsal part of the otocyst gives rise to the utricle, semicircular canals, and endolymphatic duct.
Cochlea begins to coil.
what happens to inner ear during week 7-12
Cochlea’s 2.5 coils are completed and the 3 semicircular canals have formed.
Sensory and supporting cells are developing in vestibular and cochlear sensory end organs.
By month 3, the otic capsule begins ossifying. The vestibular end organs are primary and complete before the cochlea. This is why we see more cochlea developmental deviations than in the vestibular.
gives rise to the stapes
arch 2
gives rise to the mandible
arch 1
external humps
arches
external
clefts/grooves
internal
pouches
clefts grooves
ectoderm
mesenchyme
core
pouches
endoderm
Each arch will have its own
cartilage, nerve, muscle and artery
endoderm invaginates and creates
eustachian tube
ectoderm invaginates and creates
EAC
site where the canal and pouch meet is the
TM
branchial arches form at ___ days post conception
22
critical for face outer and middle ear development
1 and 2 arch
formsexternal and middle ear
1 and 2 pharyngeal arches, pouches and clefts and neural crest cells
develops into facial and auditory muscles
mesoderm of arches
endoderm =
pouches
ectoderm =
clefts/grooves
formation begins during week 6 with invagination of the 1st pharyngeal cleft
EAC
is the ear canal fully formed when baby is born?
no takes about 6-7 years until it is fully developed
2nd 3rd and 4th clefts/grooves form the_______, later disappears
cervical sinus
If the cervical sinus persists, it forms the
lateral or branchial cysts or fistulas
marks boundary between outer and middle ear
TM
outer layer is formed by the
ectodermal meatual plug of the EAC
middle layer is mesoderm derived from
neural crest cells
inner layer is endoderm the
epithelial lining of the tympanic cavity
formed by the tubotympanic recess - extension of the first pharyngeal pouch
tympanic cavity and ET
extension of the first pharyngeal pouch
tubotympanic recess
tubotympanic recess is derived from
endoderm
proximal extension of the first pouch
future eustachian tube
distal extension of first pouch
future tympanic cavity
what clears mucus and pathogens out of the ME cavity?
motile silica push it out into the throat through the eustachian tube
clears ME of mucus and pathogens through the eustachian tube to the mouth
cilia
neural crest cells play a role in development of these
cilia
ME infection arises when
cilia breaks down and there is not movement of fluid in the ME
develop independently from each other from tubotympanic recess with neural cell contribution
ossicles
derived from the 1st and 2nd pharyngeal arches
ossicles
are the 3 ossicles from the same arches?
no from different arches
ossicles are made up of
cartilage and embedded in mesenchyme adjacent to the tympanic cavity
during ____ month of gestation, tympanic cavity envelops the ossicles
8
what is the lever system form the ossicles
diminish the force of sound waves in the ME and increase force of sound waves on the inner ear
Most of the head and neck develops from
the pharyngeal arches
Each arch has _____ on the outside, ____ on the inside, and a ____ core
ecto, endo, meso
The mesodermal core develops a cartilage/boney component after being invaded by
neural crest cells, a cranial nerve component, and a vascular component (aortic arch arteries)
Externally, there is a pharyngeal ____ between each pair of pharyngeal arches
cleft/groove
The clefts go through a sequence of development that when goes awry, can lead to
cervical or branchial fistulas and cysts
Internally, there is a pharyngeal ____ between each pair of pharyngeal arches
pouch
These endodermal pouches contribute to development of the
tympanic membrane, tonsils, thymus gland, parathyroid glands and parafollicular cells of thyroid gland
explains the sensory innervation of the face
relationships of these prominences to the trigeminal nerve
explain the varieties of cleft lip and cleft palate
Failures of fusion of pairs of these prominences
what are bony, muscle and nerve derivatives of the first arch
Bony: Maxillary bone, zygomatic bone, temporal bone, mandible, malleus, and incus
Muscle: Muscles of mastication, mylohyoid muscle, anterior belly of digastric, tensor tympani, tensor palatine muscle
Trigeminal nerve (V)
what are bony, muscle and nerve derivatives of the second arch
Bony:Stapes, styloid process, lesser horn of the hyoid bone, and upper portion of body of the hyoid bone
muscle: Muscles of facial expression, posterior belly of digastric, stylohyoid, stapedius
Facial nerve (VII)
what are bony, muscle and nerve derivatives of the third arch
bony:Greater horn of the hyoid bone, lower portion of body of the hyoid bone
Muscle: Stylopharyngeus muscle
Glossopharyngeal nerve (IX)
what are bony, muscle and nerve derivatives of the fourth arch
Bony: Laryngeal cartilages
Muscle: Cricothyroid muscle, levator palatine muscle, pharyngeal constrictors, intrinsic muscles of the larynx
Vagus nerve (X)
what are the derivatives of the first pouch
eustachian tube and middle ear cavity
what are the derivatives of the second pouch
lining of palatine tonsils
what are the derivatives of the first cleft/groove
develops into external auditory meatus
defects here can result in preauricular cysts or fisutulas
Ectoderm forms
skin covering
Mesoderm forms
cartilage of external ear
Most of auricle from the ____ branchial arch
second
Tragus from the ____ branchial arch
first
Pinna continues to grow until about
age 9
hillocks are located between ___ and ___ arches, 3 on each side of the ear canal
fisrt, second
During the 5th week the hillocks arise on the
branchial clefts
By the 7th week the hillocks enlarge and fuse to form ______
auricle/pinna
Pinna formation is completed at
~ 30 weeks
stem cells, can develop into anything, on sides of neural tube
neural crest cells
why can human babies not walk/talk when they are born?
maturation - they dont do these because cns and pns haven’t matured yet, synapses and schwann is not fully developed yet
why we see so many deviations of pinna
there is a multitude of genes that form the pinna
no two pinnas are the same
true
3 projections on the 1st pharyngeal cleft
tragus, helix, cymba concha
3 projections from the 2nd pharyngeal cleft
antitragus antihelix, concha
