12-Embryology of the eye and ear brainscape Flashcards
Coloboma
incomplete closure of optic fissure. Often associated with Pax-2 abnormalities and kidney disease
Crystallins
proteins in primary lens fibers that allow for refraction & focusing of light rays
Describe the initial development of the ear
FGF3 + FGF 10 –> Thickening of ectoderm to produce the otic placode
Development of the Ciliary Body
*Neuroectoderm & mesoderm *Located between the iris & neural retina, arises from point where the neural and pigment retinas meet at outer rim of optic cup
Development of the Iris
arises from point where neural and pigment retinas meet (it is therefore mesoderm & neuroectoderm) *Through contraction & relaxation, controls amount of light that passes through the pupil
Differentiation of the Cornea
Induced by the formation of the lens at week 8 *Outer epithelial layer from surface ectoderm and inner layer from NC cells
Formation of the eyelids
*From ectodermal-mesenchymal folds *Fuse at 10 weeks, lead to formation of conjunctival sac underneath *Reopen at beginning of third trimester
Formation of the Otic Pit
otic placode invaginates into the mesenchyme
From what tissue does the optic groove form?
Neuroectoderm
From which location do eye fields develop?
from cells in the anterior neural plate - in the prosencephalon
How do we have separate eyes?
Eye fields develop in areas that express Pax-6 BUT: cells in midline express SHH which represses Pax -6 so we have separate optic fields
How does the bony labyrinth form?
membranous labyrinth is initially surrounded by NC cells that form mesenchymal covering. Mesenchyme becomes cartilaginous, then ossifies. Mesenchyme closest to labyrinth degenerates, forming the perilymphatic space that contains the perilymph
How does the lens placode form and from what tissue?
FGF & BPM from neuroectoderm of optic vesicle + Sox 2 + Pax 6 –> Thickening of the surface ectoderm –> Lens placode
Hyaloid vessels
located within the choroid fissure in the optic stalk - supply the neural retina & developing lens *Past 10 weeks the vessels degenerate, but the central artery of the retina is left behind (branch off the opthalamic artery off the ICA)
Location of the Otic Vesicle
Dorsal to the second pharyngeal cleft Adjacent to the rhombencephalon Very close to the neural tube
Optic Chiasm
nerve fibers from each half of the retina cross over–> allows each half of brain to receive visual signals from visual fields of both eyes
Outer vs Inner Layer of the Optic Cup
Outer Layer= Pigmented epithelium Inner Layer= Neural retinal cells
Perilymph
Located in the perilymphatic space which floats the membranous labyrinth within the bony labyrinth. Communicates with the subarachnoid space via the perilymphatic duct
Persistent Pupillary Membrane
can interfere with vision by reducing the amount of light passing through the eye or cause stimulus deprivation (ambylopia)
Pigmented epithelium
monolayer of pigmented cells that helpt o reduce scattered light. Secretes growth factors, and is the reason why pupils are black
Primary Lens Fibers
cells at posterior surface of the lens vesicle. Elongate, lose their pigment, and express crystallins *Lose nuclei, form lifeless cell and remain at center of lens for life *SIze of lens determined by cell proliferation at lens vesicle’s equator
Pupillary membrane
membrane located between the anterior & posterior chambers *Will atrophy between time of birth and 4-6 weeks postnatal
Secondary Lens Fibers
*Form after 8th week, simple epithelium at anteiror wall form these new fibers. Contribute to the growth and maintenance throughout life
What does Pharyngeal Arch 1 give rise to in the middle ear?
Malleus, Incus (both from Meckel’s cartilage) and Tensor Tympani Muscle
