Ear development Flashcards
Critical period for ear development
Week 4-8
External ear:
Auricle, external acoustic meatus, external tympanic membrane
Middle ear:
Three ossicles, internal tympanic and middle ear cavity
Internal ear:
Vestibulocochlear organs
Auricle development:
Which pharyngeal arch?
PA 1 and 2 Auricular hillocks (neural crest) are mesenchymal swelling covered with surface ectoderm > migrate and give the ear its shape
nnervation of the external ear:
Great Auricular
V3 - Auriculotemporal (PA 1)
CN VII (PA 2)
CN X (auricular branches)
Abnormal auricle shape:
Cartilage present = Hillocks did not migrate properly
Skin only - surface ectoderm did not migrate properly
Anotia
Microtia
- No ear. No hillocks. Neural crest did not migrate.
- Small ears. Abnormal hillock and neural crest migration
Development of the external auditory meatus:
Which part of the pharyngeal arches?
Derived from first pharyngeal cleft
1st pharyngeal cleft (surface ectoderm) and tubotympanic recess (1st arch pouch) forms the middle ear
Cleft meets the pouch > surface ectoderm proliferates > meatal plus (external auditory meatus) forms and fills up with these cells > the meatal plug will undergo apoptosis and form the shape of the outer ear
Inner ear development:
Derived from?
Forms when?
Derived from ectoderm, first one to form at week 4
Surface ectoderm thickens and forms the otic placode > this invaginates and forms the otic pit > rounds up to see the vesicle which will migrate into the head
-These structures give rise to the primordium of membranous labyrinth
Draw the developmental process of the inner ear:
Refer to drawings
Draw the development of the membranous labyrinth of the inner ear:
Refer to drawings
Membranous labyrinth is derived from:
Surface ectoderm
Structures developing from the utricle (dorsal):
Endolymphatic sac and duct
Semicircular ducts and ampullae, lateral canal
Macula of utricle
Structures developing from the saccule (ventral):
Cochlear duct, ductus reunions, macula of saccule, organ of corti
What do these hair cells detect?
Ampullae
Macula
Organ of corti
- rotational acceleration
- gravity and linear acceleration
- sound vibration
All come from surface ectoderm
What innervates the inner ear ?
Cranial nerve VIII (surface ectoderm, specifically the otic placode)
Forms the vestibular ganglion which forms the Vestibular N. and the spiral (cochlear ganglion) which forms the Cochlear N.
Perilymph:
Drainage: passes through the perilymphatic duct from subarachnoid space into inner ear
Similar in ion content to CSF (high Na, low K and protein
Separates the endolymph from the bony labyrinth
Derived from mesoderm
Endolymph:
Produced by stria vascularis
Similar ion content to intracellular fluid (High K and protein, low Na)
Stored by endolymphatic sac
Fills the structures of the membranous labyrinth
Perilymph and subarachnoid space
Perilymph drains to the subarachnoid space. Inner ear infections can get into the perilymph and drain to the subarachnoid space (meningitis
Development of the bony labyrinth of the inner ear:
Formed by the condensation of mesenchyme (mesoderm) > ossifies and forms the petrous part of the temporal bone
Scala vestibuli and scala tympani are filled with …
Scala Media is filled with…
Perilymph
Endolymph
Draw the development of the bony labyrinth
Refer to drawings
Middle ear development: External auditory meatus Tubotympanic recess Tympanic membrane Malleus and Incus Stapes Ossicles
1st pharyngeal cleft (ectoderm)
1st pharyngeal pouch (endoderm)
1st arch Ectoderm (external layer), 1st arch mesoderm and 1st arch endoderm
1st arch neural crest
2nd arch neural crest
Derived from neural crest, but are covered with endodermal epithelium
Draw the development of the middle ear
Refer to drawings
What cell type are these muscles from?
Tensor Tympani
Stapedius
1st arch mesoderm (innervated by V3)
2nd arch mesoderm (innervated by CN VII)
Congenital deafness:
Cause: Genetic. Maldevelopment of sound conduction apparatus of middle and external ear. First arch syndrome, abnormalities of malleus and incus, congenital fixation of the stapes
-Neurosensory deafness (for inner ear derived problems)
Rubella infection
Cytomegalovirus
- Infection during 7-8th week can cause defects in the spiral organ and deafness
- leading cause of congenital sensorineural hearing loss
Cytomegalovirus infection causes….
Herpes simplex virus causes….
Human parovirus B19 causes …
Sensorineural hearing loss
Hemolytic anemia
Fetal anemia
Rubella causes ….
Toxoplasma gondii causes …
Treponema pallidum causes …
Cardiac abnormalities, sensorineural deafness, cataract, micropthalmos, glaucoma, pigmented retinopathy, neonate bleeding
- microphthalmia, hearing loss
- congenital deafness
Venezuelan equine encephalitis virus causes…
Varicella virus causes…
- microphthalmia
- cataracts, microphthalmia, optic atrophy
