3: Eye & Ear Development Flashcards
when does the eye first appear
22 days
appears as optic grooves on sides of forebrain
steps to form optic cup and vesicle
- neural tube closes and grooves form the out-pocketings called OPTIC VESICLES
- vesicles contact surface ectoderm and LENS INDUCTION begins
- vesicle starts to invaginate and double-walled OPTIC CUP forms
- cells of surface ectoderm, in contact with optic vesicle, elongate and form LENS PLACODE
- placode develops into LENS VESICLE, which loses contact w/surface ectoderm and rests in mouth of optic cup
- layers of optic cup are initially separated by INTRARETINAL SPACE (which quickly disappears)
- inferior aspect of cup invaginates, forming CHOROID FISSURE allowing HYALOID A. to reach inner chamber of eye
- 7th week: edge of choroid fissure fuse and optic cup mouth becomes round opening –>future pupil
coloboma
key hole appearance of iris due to failure of retinal fissure to close in 7th week
eye at 7 weeks
outer layer of optic cup=retinal pigment layer
neural layer of retina is complex
pars optica retinae
posterior 4/5s of retina
rods and cones
mantle layer of retina
generates neurons & glia of outer and inner nuclear layers and ganglion layer
axons in retina
axons from neurons of deeper layers collect on retinal surface in a fiber layer
converge to form optic stalk and optic nerve
iris & ciliary body
aka pars ceca retinae
anterior 1/5 of inner layer
divides into pars iridica retinae and pars ciliaris retinae
pars iridica retinae
forms inner layer of iris
pars ciliaris retinae
helps form ciliary body
sphincter & dilator pupillae
region btwn optic cup and overlying surface epithelium
contains mesenchyme
forms sphincter & dilator pupillae mm.
ciliary muscle
formed by mesenchyme on outside of pars ciliaris retinae
controls lens curvature
connected to lens from inside, by elastic fiber network called suspensory ligament or zonula
suspensory ligament
aka zonula
elastic fiber network that connects ciliary body to lens
lens
after lens vesicle forms, cells along posterior wall elongate anteriorly and form long fibers that fill lumen of vesicle
reach anterior wall of lend by 7th week
choroid
inner layer like pia
vascularized pigmented layer
emerges from loose mesenchyme that forms around eye in 5th week
sclera
outer layer like dura
continuous with dura of optic nerve
emerges from loose mesenchyme that forms around eye in 5th week
cornea formation
anterior chamber of mesenchyme, formed by vacuolization
inner layer of cornea
in front of lens & iris
aka iridopupillary membrane (disappears)
outer layer of cornea
substantia propria
cornea contents
epithelial layer from surface ectoderm
substantial propria, aka stroma, continuous with sclera
epithelial layer that borders anterior chamber
anterior & posterior chambers of cornea
filled w/fluid, aqueous humor, produced by ciliary body
how do the anterior & posterior chambers of cornea communicate
thru pupil
fluid flows from posterior to anterior chamber, providing nutrients for avascular cornea & lens
where does fluid thru pass after anterior chamber
Canal of Schlemm at iridocorneal angle
what causes glaucoma
blockage of Canal of Schlemm
vitreous body
gelatinous material that fills interstitial space in the fine network of fibers btwn lens & retina
hyloid vessels
formed by mesenchyme surrounding eye primordium and invading optic eye via choroid fissure
support lens in utero and form a vascular layer on inner retina
how is optic cup connected to brain
by optic stalk, with choroid fissure on ventral surface
what does the choroid fissure contain
hyaloid vessels
where do retinal nerve fibers going into the brain lie
along inner wall of the optic stalk
when does optic stalk become optic nerve
7th week, when choroid fissure closes
hyaloid artery is now central artery of the retina
external ear function
collects sound
middle ear function
conducts sound
internal ear function
converts sound waves to nerve impulses & detects changes in equilibrium converting them into nerve impulses
internal ear development
22 days: otic placode
thickening of surface ectoderm on each side of rhombencephalon
otic placodes invaginate and form otic/auditory vesicles
otic vesicle development
ventral component: saccule and cochlear duct
dorsal component: utricle, semicircular canals, endolymphatic duct
beginning of saccule & cochlea development
week 6
saccule forms tubular outpocketing aka cochlear duct
cochlear duct penetrates mesenchyme while it spirals thru 2.5 turns
ductus reuniens
connection btwn cochlear duct and saccule
saccule, cochlea & Organ of Corti development (8-10 weeks)
- mesenchyme around cochlear duct –> cartilage
- cartilage becomes vacuolated; perilymphatic spaces arise (scala vestibuli & scala tympani)
- vestibular membrane separates cochlear duct & scala vestibuli. basilar membrane separates cochlear duct & scala tympani
- modiolus supports medial cochlear duct –> becomes axis of future bony cochlea
2 ridges of cochlear duct epithelial cells
inner ridge: future spiral limbus
outer ridge: forms 1 row of inner and 3 rows of outer hair cells (sensory cells of auditory system)
tectorial membrane
gelatinous material attached to spiral limbus and rests on top of hair cells
what is the Organ of Corti made of
hair cells and tectorial membrane
where are impulses from Organ of Corti sent
to spiral ganglion and then to brain via CN VIII
when do semicircular canals appear
6th week
as outpocketings of utricle
which end of the canals dilates
crus ampullare
which end of the canals does not dilate
crus nonampullare
crista ampullaris
crest formed by ampullae cells
important for angular acceleration (equilibrium)
macule acusticae
develop in walls of utricle and saccule
important for linear acceleration
where are impulses from cristae and maculae sent
to brain by CN VIII (body position)
tympanic cavity
endoderm from 1st pharyngeal pouch
tympanic cavity & auditory tube development
1st pharyngeal pouch expands
distal aspect = tubotympanic recess –> primitive tympanic cavity
proximal pouch = auditory (eustachian) tube
ossicles
incus & malleus=cartilage of 1st pharyngeal arch
stapes=cartilage of 2nd pharyngeal arch
ossicles development
embedded in mesenchyme until 8th month, after which the endodermal lining connects them to the wall of the cavity via ligaments
epithelial lining of primitive tympanic cavity extends into this new space
development of external auditory meatus
dorsal portion of 1st pharygeal cleft
- cells at bottom of meatus proliferate and form MEATAL PLUG in 3rd month
- in 7th month, plug dissolves and epithelium in floor of meatus contributes to eardrum formation
sometimes plug persists and results in CONGENITAL DEAFNESS
eardrum consists of
ectodermal lining at bottom of meatus
endodermal lining of tympanic cavity
intermediate layer of connective tissue (fibrous striatum)
auricle development
from 6 mesenchymal proliferations at dorsal end of 1st and 2nd pharyngeal arches surrounding 1st cleft
–formed from NEURAL CREST
3 hillocks on each side of meatus fuse and form auricle
ear starts in LOWER NECK and ASCENDS as mandible develops
top of ear should be at eye level, complications are common
anotia
absent external ear
microtia
small ear
preauricular appendages
accessory hillocks
preauricular pit
abnormal hillocks
