Lecture 15: Ear Development Flashcards
When is the critical period for embryological development of the ear?
Weeks 4-8
When does development of the ear occur?
Week 4-20
What is found in the external, middle, and inner ear?
External Ear
- Auricle
- External Acoustic Meatus
- External Layer of Tympanic Membrane
Middle Ear
- Auditory Ossicles (3)
- Internal Layer of Tympanic Membrane
- Middle Ear Cavity
Inner Ear
- Vestibulocochlear Organ
- Develops separately from external and internal ear
The medial part of the external ear came from what pharyngeal arch?
1st Pharyngeal Arch
The lateral part of the external ear came from what pharyngeal arch?
2nd Pharyngeal Arch
The mesenchymal swellings located within the pharyngeal arches are known as what?
Auricular Hillocks
What are the cells that migrate and pull the surface ectoderm around to form the external ear?
Neural crest cells of the auricular hillocks
Auricular skin tags that may contain cartilage are a result of what?
Abnormal migration of surface ectoderm and neural crest cells
Abnormal or absent migration of the NCCs and auricular hillocks can result in what disorders?
Anotia
Microtia
What embryonic layer does the meatal plug arise from?
Surface ectoderm
1st Pharyngeal Cleft
What embryonic layer forms the tubotympanic recess?
Endoderm: 1st Pharyngeal Pouch
What embryonic layer does the inner ear arise from?
Surface ectoderm
How does the inner ear form from surface ectoderm?
- Otic Placode thickens
- Invaginates to form Otic Pit
- Becomes Otic Vesicle that migrates to the head
What embryonic structure gives rise to the membranous labyrinth?
Otic vesicle
Also Surface Ectoderm
What does the dorsal side of the otocyst give rise to?
Utricle
- Endolymphatic duct and sac
- Semicircular ducts and ampullae
- Macula of utricle
What does the ventral side of the otocyst give rise to?
Saccule
- Cochlear duct
- Ductus reuniens
- Maccula of saccule
- Organ of Corti
What structure connects the cochlea to the vestibular apparatus?
Ductus reunions
What is the embryonic layer that gives rise to the hair cells of the inner ear?
Surface ectoderm
Where are hair cells located in the inner ear?
What does the respective hair cells sense?
- Ampullae of Semicircular Canals
- Rotational Acceleration
- Macula of utricle and saccule
- Linear Acceleration
- Organ of Corti (cochlea)
- Sound Vibration
What nerve is responsible for innervation to the inner ear?
Where did this nerve come from?
CN VIII: Vestibulocochlear Nerve
Otic Placode
What are the embryonic contributions to the vestibular ganglion?
What cell bodies contribute to this?
Neural crest cells and surface ectoderm
Cell bodies from macula and ampullae
What is the embryonic contribution to the spiral (cochlear ganglion)?
Surface ectoderm
What structures does the perilymphatic duct provide passage between?
Subarachnoid space to inner ear
What is the ion content of perilymph?
High Na+
Low K+ and Protein
(Similar to CSF)
What is the ion content of endolymph?
High K+ and Protien
Low Na+
(Similar to ICF)
What produces endolymph?
Stria Vascularis
What embryonic layer does the bony labyrinth arise from?
Mesoderm
Condensation of Mesenchyme
What are the vacuoles of the bony labyrinth?
Scala Vestibuli
Scala Tympani
Semicircular Ducts (Perilymphatic Space)
What suspends the cochlear duct within the bony labyrinth and attaches it to the wall?
Spiral Ligament
What bones of the middle ear arise from the 1st pharyngeal arch?
What is their embryonic origin?
Malleus and Incus
Neural Crest Cells
The stapes bone arises from what arch?
What is the embryonic origin?
2nd Pharyngeal Arch
Neural crest cells
What embryonic layer does the epithelium covering the ossicles arise from?
Endoderm
What are the embryonic layers making up the tympanic membrane?
Arive from 1st Pharyngeal Membrane
- Ectoderm: from 1st Pharyngeal Cleft
- Mesoderm
- Endoderm: from 1st Pharyngeal Pouch
What pharyngeal arch does the Tensor Tympani Muslce arise from?
What embryonic layer?
What innervates this muscle?
1st Pharyngeal arch
Mesoderm
CN V3
What pharyngeal arch does the Stapedius Muslce arise from?
What embryonic layer?
What nerve innervates it?
2nd Pharyngeal Arch
Mesoderm
CN VII
What part of the fetal ear is affected if there is a maternal Rubella infection?
Inner ear: Spiral Organ/Organ of Corti defects
What is the leading cause of congenital sensorineural hearing losss?
Cytomegalovirus