Ear Development Flashcards
What structures are a part of the external ear?
Auricle (pinna), external acoustic meatus, external layer of tympanic membrane
What structures are a part of the middle ear?
The three ossicles, the internal layer of the tympanic membrane, middle ear cavity
What structures are a part of the inner ear?
Vestibulocochlear organ
What is the auricle derived from?
1st and 2nd pharyngeal arches. Auricular hillocks (NCC) covered in surface ectoderm. Migrate and proliferate to make shape of outer ear
What are auricular appendages/skin tags?
Hillocks did not migrate properly, may or may not contain cartilage (NCC)
What is anotia?
No external ear due to abnormal migration/proliferation of NCC
What is microtia?
Small external ear, due to abnormal migration/proliferation of NCC
What is the meatal plug?
Comes from the 1st pharyngeal cleft/groove. Migrates in to meet up with the pouch, proliferation of surface ectoderm. Supposed to undergo apoptosis to create external auditory meatus
When does the inner ear form? What is it derived from?
Week 4, surface ectoderm
How does the inner ear form?
Thickening of surface ectoderm makes the otic placode which invaginates to make the otic pit. The pit rounds up to make the otic vesicle which migrates deeper into the head.
Gives rise to the primordium of the membranous labyrinth
What layer does the membranous labyrinth come from?
Surface ectoderm
What is the membranous labyrinth divided into?
The utricle (dorsal) and saccule (ventral)
What does the utricle give rise to?
Endolymphatic duct/sac, semicircular ducts and ampullae, and macula of utricle
What does the saccule give rise to?
Cochlear duct, ductus reunions, macula of saccule, organ of corti
What parts of the membranous labyrinth contain hair cells?
ampullae of semicircular ducts, macula of utricle, macula of saccule, organ of corti
What does the ampullae detect?
Rotational acceleration
What does the macula detect?
Gravity and linear acceleration
What does the organ of corti detect?
Sound vibration
What layer do the hair cells come from?
Surface ectoderm
What innervates the inner ear? What layer did it come from?
Vestibulocochlear nerve (CN VIII), surface ectoderm
What nerve do the cells of the spiral ganglion of the cochlea form?
Cochlear N
What nerve do the cells of the vestibular ganglion of the cochlea form?
Vestibular N
What is perilymph?
Similar to CSF (high NA, low K and protein), comes from periosteum
What is endolymph?
Similar to intracellular fluid (high K and protein, low NA), comes from stria vascularis, stored in endolymphatic sac
What fills the structures (ducts) of the membranous labyrinth?
Endolymph
What fills the space (canals) between the membranous labyrinth and the bone?
Perilymph
How can a chronic middle ear infection get dangerous?
If the infection erodes into the perilymph it can get into the subarachnoid space through the perilymphatic duct
Where is the bony labyrinth located? What layer is it from?
Petrous part of temporal bone, condensation of mesenchyme (mesoderm)
Where do ossicles come from?
NCC-derived, covered in endoderm
What muscle inserts onto the malleus and prevents loud sound from damaging ear? What is it innervated by?
Tensor tympani, trigeminal n (first arch mesoderm)
What muscle inserts on the stapes and prevents damage from loud sound? What is it innervated by?
Stapedius m, facial n (second arch mesoderm)
What causes congenital deafness?
Maldevelopment of sound-conduction apparatus in middle/external ears (ex: ossicles), neurosensory sensory structures of inner ear, infections
