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Ear II


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What bone is important for ear formation?
Temporal - houses the inner/middle ears and bony portion of outer meatus.
4 Parts of Temporal bone:
Styloid process
Squamous portion
Tympanic portion
What does the petromastoid portion develop from?
Otic capsule of the Chondrocranium
What does the styloid process develop from?
Pharyngeal arch 2 - Cartilage
What does the squamous portion develop from?
Pharyngeal arch 1 - Maxillary process
What does the Tympanic portion develop from?
Pharyngeal arch 1 - Maxillary process
How do the petromastoid and styloid process ossify?
How do the Squamous portion and Tympanic portion ossify?
What does the Aurical develop from?
Auricular Hillocks - hills on either side of the first pharyngeal cleft.
What pharyngeal arches contribute the auricular hillocks? What structures?
1 - tragus, part of helix

2 - remainder of auricle
When does the auricle reach its final position?
in the fetal period
What are the 2 portions of the External Auditory Meatus that must develop?
1. Cartilagenous portion
2. Osseous portion
What is the cartilagenous portion derived from?
1st pharyngeal cleft
What is the osseous portion derived from?
Medial extension of 1st pharyngeal cleft - MEATAL PLUG
What happens to the meatal plug?
It develops a lumen and extends; medial end flattens to form the Meatal Plate.
What is the Meatal plate?
Outer surface of the eardrum.
What structures need to be formed to make the middle ear?
-Tympanic cavity
-Auditory tube
-Internal covering of tymp memb
How does the Tympanic Cavity form?
By lateral evagination of pharyngeal pouch 1 - this forms the Tubotympanic recess
What does the Tubotympanic recess form?
Epithelial lining of Middle Ear and Auditory tube.
What arches are the Ossicles derived from?
Arch 1 = malleus and incus

Arch 2 = stapes
What is the Tympanic Membrane derived from?
The First Closing Plate (interface of cleft/pouch)
What composes the Tymp membrane?
-Fibrous CT
-Mucosal inner layer
Epidermis = meatal plug (ecto)
Fibrous CT= 1st arch mesenchyme
(probably neural crest)
Mucosal layer = endoderm tubotympanic recess
What size is the middle ear at birth?
Adult size!
What is the inner ear derived from?
the Otic Vesicle
What causes the otic vesicle to form?
Ectodermal thickening adjacent to the Rhombencephalon forms - Otic Placode
What does the Otic Placode become?
Otic Pit that disconnects from surface ectoderm and becomes the Otic Vesicle
What does the Otic Vesicle send signals to around it?
Periotic mesenchyme - and it sends reciprocal msgs to the otic vesicle.
What is the otic vesicle induced to do via reciprocal msgs?
Form parts of the membranous labrynth
What is the periotic mesenchyme induced to do?
Condense and form the otic capsule
What does the Otic capsule become?
Petrous part of the temporal bone.
So what develops from the otic vesicle?
-Membranous labrynth
-Cranial nerve 8
What develops from periotic mesenchym?
Osseous labyrinth - petrous part of the temporal bone
What does the otic vesicle divide into? (3 things)
1. Endolymphatic appendage
2. Dorsal portion
3. Ventral portion
What is the dorsal portion of the otic vesicle?
What develops from the utricle?
-Semicircular ducts
-Crista ampullaris
What is crista ampullaris for?
Sensory of fluid movement in semicircular canals (balance)
What is the Ventral portion of the otic vesicle?
What does the saccule develop?
-Cochlear duct
-Organ of Corti
What is the organ of corti for?
Detection of vibration in the cochlea - hearing
What is the Macula?
The sensory area that develops on the wall of the utricle and saccule.
What is anotia/microtia?
External ear defect - absent/small auricles
What causes auricular tags?
Tags = accesory auricule hillock

Sinus = abnormal 1st cleft devo
What is otocephaly? What arch?
Low-set ears; associated with a First arch problem
What is Meatal atresia caused by?
Failure of the meatal plug to canalize
What are problems that can develop in the Middle Ear?
-Congenital fixn of the stapes
-Defects of Ossicles
What is Cholesteatoma?
Benign growth of ENDODERM in tympanic cavity medial to eardrum
What is an anomaly of the inner ear?
Vestibular Cochlear Dysplasia
3 types of Congenital hearing loss:
What percent of all deafness is caused by congenital hearing loss?
What infection causes congenital hearing loss?
What drugs can cause it?

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