10. Ear Slide Flashcards
What is our external ear made up of?
- auricle ear
- external acoustic meatus
- external layer. of. te. TM
What is the middle ear made up of?
- 3 ossicles
- Internal layer of tympanic membrane
- Tympanic cavity
What makes up our internal ear?
Vestibulocochlear organ
What pharyngeal arches is our auricle derived from?
1st and 2nd pharyngeal arches
How is our auricle formed?
Auricle is derived from six auricular hillocks from the first and second pharyngeal arches; swellings of mesenchyme (NCC) that is covered with surface ectoderm.
What innervates the external ear?
- CN V3: Auriculotemporal N.
- CN X: Auricular branch
- Great Auricular N (C2-C3)
- Facial N (CN VII)
If a patient as a auricular appendage (skin tag) how did this occur?
result from the development of accessory auricular hillocks; thus, there was a problem with the migration of surface ectoderm.
If a patient has microtia, what i s this a. result of?
Microtia has a small auricle that is formed d/t abnormal proliferation of NCC (mesenchyme) from the 1st. and 2nd pharyngeal arch.
What is anotia and how do we get it?
Anotia: no ear.
D/t NCC in the auricular hillox did not form or migrate.
External Auditory Meatus is derived from what pharyngeal arch?
1st
How do we form the External Auditory Meatus?
- External acoustic meatus develops from dorsal part of 1st pharyngeal groove
- It. will begin to invagine inward -> and ectodermal cells proliferate, creating a meatal plug.
- Around 6 months, meatal plug will undergo apoptosis and form our external auditory meatus.
What part of our ear develops first and when?
INNER EAR at week 4.
What. is. the inner ear derived from?
- Surface ectoderm
How do we form our inner ear?
- Week 4: Otic placode (surface ectoderm) will form
- Will invaginate into underlying mesenchyme, forming the otic pit
- Edges of the pit fuse→ otic vesicle
- Otic vesicle will create the primordium of the membranous labyrinth. It has parts (dorsal and ventral part)
- will then coil to make vestibules, semicircular canals and cochlea.
Once we have gone from:
Otic placode -> otic pit -> otic vesicle -> primordium of membranous labyrinth.
What do they form?
Dorsal part of the primordium of membranous labyrinth forms the utricle.
Ventral part of the primordium of membranous labyrinth forms the saccule
Dorsal part of the primordium of membranous labyrinth forms the utricle.
- This is dependent on:
Ventral part of theprimordium of membranous labyrinth forms the saccule
- This is dependent on:
Utricle: DlX5/6
Saccule: PAX6
What is our membranous labyrinth?
Sac that forms our utricle and saccule.
Dorsal part. of membranous labryrinth will form what?
forms the
- endolymphatic ducts,
- utricles
- 3 semicircular canals with dilations on each end called ampulae.
- lateral canal of the semicular duct
- Macula of the utricle
• Lateral canal of semicircular duct is dependent on ____.
Otx-1
Ventral part of membranous labyrinth forms what?
- Cochlear duct, which grows and coils to become the membranous cochlea.
- Ductus reunions
- saccule
- Macula of saccule and organ of corti
How does the ventral part of membranous labryrinth differentiate into products?
- Tail of ventral part of membranous labryrinth will curl to make cochlear duct
- Cochlear duct grows and coild to make the membranous cochlea
- Ductus reuniens will form to connect the cochlea to the vestibular aparatus (saccule, utricle and semicircular ducts.
________ differentiates from cells in the wall of the cochlear duct.
How then, do we form the innervation to our inner ear?
Spiral organ/organ of corti
- Ganglion cells of CN VIII (vestibulocochlear) migrate along the coils of membranous cochlea -> form spiral ganglion
- Nerve processes extend to the -> basilar membrane -> spiral organ/organ of Corti, where they terminate on hair cells
What nerve innervates our inner ear?
CN VIII (vestibulocochlear), which comes from vestibular ganglion & spiral ganglion.
What cells is the vestibular ganglion from?
NCC and surface extroderm via the otic placode.
What cells is the spiral (cochlear) ganglion from?
Surface ectoderm via otic placode
What is perilymph from?
- Perilymphatic duct
- Filtration of blood in perilymphatic space
What is the Perilymphatic duct?
Perilymphatic duct is a free passage from subarachnoid space -> inner ear. It is usually patent.
What is the difference between perilymph and endolymph?
- Perilymph has ion content to CSF: high Na, [low K and protein]
- Endolymph has similar ion content to intracellular fluid: [High K and protein], low Na+
What produces endolymph?
What stores endolymph?
- Stria vasculari
- Endolymphatic sac
Why is an infection of the middle ear bad?
- Go through oval/round winder -> inner ear -> infection can go into the subarachnoid space and cause meningitis
What is the role of the bony. labyrthing?
Protexts the membranous labyrith
How do we develop bony. labyritnth?
- Membranous labyrinth enlarges & vacuoles appear in the capsule
- Join & form perilymphatic space (semicircular ducts).
- Now, the membranous labyrinth is surrounded by perilymph.
- Perilymphatic space divides, causing the otic vacuoles to form our scala tympani & scala vestibuli
- Carilagionous otic capsule ossifies, condensing the mesenchyme (mesoderm) -> forms bony labryrinth, located in the petrous portion of temporal bone.
What suspends the cochlear duct?
Spiral ligament
Inner ear is is filled with hair cells. Where do they come from?
Surface ectorderm that arise in the otic vesicle.
Hair cells in ________ detect accerleration
Hair cells in ________ detect gravity
Hair cells in __________ detect sound vibration.
Hair cells in ampullae detect accerleration
Hair cells in macula of utricle and saccule detect gravity
Hair cells in organ of corti detect sound vibration.
How do we form our middle ear?
- Ectoderm from the 1st pharyngeal cleft/arch/cleft (formed our external auditory meatus) fuses with endoderm from 1st pharyngeal pouch (formed our tubotympanic recess)
- Before these meet, in the middle of them is mesoderm forming our B.V to supply tympanic membrane.
- Eventually, the endoderm from the 1st pharyngeal POUCH will form the typanic cavity
- MEANWHILE; otic vesicle is makign the inner ear NEAR the ossicles
What. is tymapnic membrane derived from?
- 1. Ectoderm (external surface of TM)
- 2. Mesoderm
- 3. Endoderm (internal surface of TM)
What tissue and arches arches do malleus, incus and stapes come from?
- Malleus and incus are from 1st arch NC.
- Stapes are from 2nd arch NC.
What covers the ossicles?
endodermal (Endoderm) epithelium
Tensor Tympani M
- Muscle inserts into the:
- Cell type:
- Axn:
- Innervation
- Muscle inserts into the: handle of malleus
- Cell type: 1st pharyngeal arch mesoderm
- Axn: prevent damage from loud sounds
- Innervation: CN 5
Stapedius M
Muscle inserts into the:
Cell type:
Axn:
Innervation
Muscle inserts into the: Neck of stapes
Cell type: 2nd pharyngeal arch mesoderm
Axn: Prevent damage from loud sounds
Innervation: CN 7
________ ear forms. independent of ______ and _____ ears
INNER ear forms independently
of external and middle ear.
Congenital deafness can be associated. with what?
-
Mostly genetic; abnormal development of the sound-counducting sytem of the middle and external ear. For example
- first arch syndrome: causes abnormalities of malleus and incus; often times will lack an auricle
- Congenital fixation of stapes to the bony labyrinth
- Rubella infection during weeks 7-8 can cause defect of spiral organ -> deafness.
The epithelium covering the ossicles in the middle ear is derived from:
A. Endoderm of the first pharyngeal pouch
B. Endoderm of the second pharyngeal pouch C. Ectoderm of the first pharyngeal cleft
D. Ectoderm of the second pharyngeal cleft
E. None of the above
A
The fibrous stratum of the tympanic membrane carries blood vessels and supporting tissue. This layer is derived from the:
A. Endoderm of the first pharyngeal pouch
B. Mesoderm of the first pharyngeal pouch
C. Ectoderm of the otic placode
D. Ectomesoderm of the neural crest origin
E. Ectoderm of the first pharyngeal clef
B
Which of the following structures gives rise to the semicircular ducts?
Perilymphatic duct
Endolymphatic duct
Utricular region of the otic vesicle
Ductus reunions
Cochlear duct
C
Which of the following structures is derived from the otic vesicle?
Cochlear duct
Auditory tube
Stapes
Pinna
A
Which embryonic portion of the inner ear is formed first?
Vestibular duct
Semicircular ducts
Saccule
Cochlear duct
Otic vesicle
otic vesicle
Which of the following neuroepithelial regions is not involved in equilibrium and balance?
Ampullae of the semicircular ducts
Macula of the utricle
Macula of the saccule
Organ of Corti
D
Which of the following structures is not needed to detect sound?
Utricle
Cochlear duct
Eardrum
Ossicles
A
Which of the following structures is derived from neural crest?
Malleus
Auditory tube
External ear canal
Membranous labyrinth of the inner ear
A malleus
