Development of the Ear Flashcards
When does the ear begin to develop
starts at the 4th week
What consists of the External ear
Consists of auricle (pinna)
ecternal acoustic meatus
external layer of tympanic membrane
What consists of the middle ear
Three ossicles: malleus, incus, stapes
internal layer of tympanic membrane
middle ear cavity
What consisits of the internal ear
Consists of the vestibulocochlear organ
what does the auricle derive from and its innervation
Derived from the 1st and 2nd PA and neuro crest
Auricular hillocks are mesenchymal swellings covered with surface ectoderm with a neural crest component
innervated by Great auricular
Auriculotemporal (V3)
CN VII
CN X auricular branches
what happens if a baby is born with lack or missing parts of ears (Anotia), (Microtia)
the Auricular hillocks did not develop
usually from abnormal Neural crest migratory
microtia= small ears anotia= no ear
what does the external auditory meatus arise from and what fills the hole that must dissenegrate
First paharyngeal cleft (groove) (surface ectoderm)
Meatal plug which will apoptosis (Surface ectoderm)
what does the inner ear derive from
Derived from surface ectoderm
What is the sequential embryologic structures of the inner ear and when does this start
in the 4th week
otic placode
then to otic pit
then to otic vesicle
begin to start the primordium of membranous labyrinth (surface ectoderm)
In the Membranous labyrinth, what develops from the utricle portion of the otocyst
dorsal
Endolymphatic duct and sac
semicircular ducts and ampullae and lateral canal
In the membranous labyrinth, what develops from the saccule portion of the otocyst
ventricle
Cochlear duct
ductus reunions
macula of saccule
organ of corti
What is the innervation of the inner ear
Hair cells found in the ampulla, macula, and the organ of corti
What does the ampulla detect
Rotational acceleration
What does the macula detect
gravity of linear acceleration
What does the organ of corti detect
Sound vibration
What does the innervation of the inner ear
Cranial nerve VIII
vestibular ganglion
spiral (cochlear) ganglion
What is perilymph and where does it come from
comes from the perilymphatic duct from the subarachnoid space
may also come from filtration of blood in perilymphatic space
similar in ion content to CSF
High Na, low K, and protein
What is endolymph and where does it come from
Produced by the stria vascularis
similar in ion content to intracellular fluid
high K and protein, low K
Endolymphatic sac stores endolymph
whats the clinical significance of the perilymphatic duct getting into the subarachnoid space
the spread of infection can travel through the perilymph in the perilymphatic duct to the subarachnoid space and this is a common way people get memningitis
What fills the canal, and what fills the duct
The canal is filled with perilymph
the duct is filled with endolymph
What embrylogical type cell makes up the organ of corti
surface ectoderm
arised from the cochlear duct
What lymph is found in the scala vestibuli, sclera media
scala tympani
scala vestibuli = perilymph
sclera media = endolymph
scala tympani = perilymph
what makes up the vacuoles
condensation of mesenchyme
semicircular ducts
scala vestibuli
scala tympani
Where does the bony labyrinth come from
ossification
petrous part of temporal bone
What forms the external auditory meatus
1st Pharyngeal cleft/groove (ectoderm)
what forms the tubotympanic recess
1st pharyngeal pouch (endoderm)
later turns into the tympanic cavity, mastoid antrum, and the pharyngotympanic tube
What forms the tympanic membrane
ectoderm, mesoderm, and endoderm
1st Pharyngeal membrane
What makes the malleus and incus
1st PA which is Neural crest
what makes the stapes
2nd PA which is Neural crest
What are the ossicles covered with
endodermal epithelium
What gives rise to the tensor tympani and whats this muscles action
the 1st pharyngeal arch mesoderm
muscle inserts on the handle of the malleus
action prevents damage from loud sounds
What gives rise to the stapedius muscle and what is ists function
2nd Pharyngeal arch mesodern
inserts on neck of stapes
pulls the stapes posteriorly and tilts its base in the oval window
action prevents damage from the loud sounds
Congenital Deafness
Inner ear forms independently from middle and external ears
causes: most genetic
maldevelopment of sound-conduction apparatus of middle and external ears
first arch syndrom
abnormalities of mallus or incus
congenital fixation of the stapes
Neurosensory sensory structures of inner ear
infections
- rubella during 7-8 week can cause defects to spiral organ and deafness
- cytomegalovirus-leading cause of congenital sensorineural hearing loss
- toxoplasmosis
- syphilis (toxoplasma pallidum)
- zika
