Embryology Of The Eye And Ear Flashcards
What causes the formation of the lens placodes and what are the steps of the eye folding?
He diencephalon causes the formation of the lens placode
The optic grooves form into the optic vesicles which form into the optic cups
When does the eye begin to form?
Before the rostal neural tube closes
A little neural tube begins to evaginate and push through the wall
What vessels enter into the developing stack of the eye?
He hyaloid arteries
What are hyaloid vessels and where do hey come from?
Branches of the Opthalmic vessels that supply the eye, retina, and posterior aspect of the lens capsule
What normally happens to the optic fissure?
The fissure closes the hyaloid vessels
At the same time, the folded edge of the optic cup folds inward and covers the lens. These edges will be the edges of the pupil
What happens at the same time of the pupil edges development?
The neurons on the back of the eye start to thicken and develop into photoreceptors
What is the sheath surrounding the optic nerve am extension of?
The meninges
What can happen to the hyaloid artery?
Normally is disappears by apoptosis but sometimes that doesn’t happen and you can see it behind the lens
What is comgenital coloboma?
Defective closure of the choroid or optic fissure
Can just have a split in the iris or one in the retina also
It is positioned in the infero-nasal quadrant reflective of the optic fissure during fetal development
What are the two layers of the optic cup formed by the diencephalon?
Two layers with an intraretinal space
The top layer thickens to form ganglion cells
What layer of the optic cup has neural cells?
The inner retina
What does the outer layer of the retina become?
The retinal pigmented epithelium
Outer with the ear medial
What do the axons of the ganglion cells leave the eye through?
The lamina cribrosa
The arteries actually lie on the photoreceptors
What are the ciliary body and iris formed from?
Anterior part of the optic cup
What are the two layers of the iris?
Pigmented area and muscle
Where do the sphincter pupillae and the dilater pupillae develop from?
The iris mesenchyme not mesoderm
From the optic cup
What is responsible for forming aqueous humor?
The ciliary body
What induces the surface extoderm to form the lens placode?
The neuroectoderm which it itself forms the retina, iris, and ciliary body
Where are the major lens fibers coming from?
The posterior wall
What happens anterior to the mexenchyme forming the eye?
Parts of the mesenchyme apoptosis and become the anterior chamber
What can fail to apoptosis and give blurry visions
The irido-pupillary membrane
How is the vitreous humor formed?
Entirely from the mesenchyme
What induces the formation of the choroid and sclera?
The RPE
What are the three layers of the cornea?
Epithelium (surface ectoderm)
Stroma (mesenchyme)
Endothelium (associated with the sclera, neural crest cells from the optic cup)
When do the eyelids open?
26 day
Where is the skeletal muscle of the eyelids from?
2nd arch
The levator palpebrae superioris is from myotomes
Where are the tarsal muscles developed from?
Mesenchyme
What is the etiology of a congenital cataract?
Rubella infection of mom 4-9weeks Hereditary Malnutrition Radiation Galactosemia
What causes congenital Ptosis?
Abnormal development of levator palpebrae superioris, localized myogenic dysgenesis Occularmotor nerve palsy Autosomal dominant Does not affect vision Surgically correctable
What is anophthalmia and microphthalmia?
Absent or small eye
What are the three different areas the ear comes from?
Pharyngeal arches
Pharyngeal pouches
Otic placodes
What induces the descent of the otic placodes?
The phombencephalon
What forms the structures of he inner ear?
The otic placode
What does the dorsal part of the otic vesicle gove rise to?
Semicircular ducts
Utricle
Endolymphatic duct/sac
What does the ventral part of the otic vesicle give rise to?
Saccule
Cochlear duct
Ductus reuniens
What are the two parts of the otic placode?
Dorsal (utricular)
Ventral (saccular)
Where does the cochlear duct come from?
The dorsal otic placode?
What are the semicircular ducts filled with?
Endolymph
Where are the sensory receptors of the semicircular ducts?
The ampulla (crista ampullaris)
What are the sensory receptors that develop from the utricular portion of the otic placode?
Macula utriculi
What is the precursor the the spiral and vestibular ganglion?
The statoacoustic ganglion
How is the statoacoustic ganglion formed?
From the cells of the wall of the otic vesicle and neural crest cells
What type of cells are in the vestibular ganglion?
Primary afferent bipolar neurons
What induces the cochlear duct area to grow and then ossify?
The otic vesicle
What is the stria Vascularis?
The blood supply area of the cochlear
Derived from neural crest cells
What is the middle ear lined by?
Endoderm
What is the origin of the tympanic cavity and the Eustachian tube?
The first pharyngeal pouch
What becomes the ear drum?
Mesoderm
Where do the ossicles develop from?
Mesenchyme
What become the mastoid air cells?
The tympanic cavity
What is the stapedius muscle derived from and what nerve supplies it?
Second arch
The nerve of the second arch - facial
What is the tensor tympani derived from and what nerve supplies it?
First pharyngeal arch
Supplied by the nerve of the first pharyngeal arch, the mandibular branch of the trigeminal
What is the meatal plug?
Ultimately disappears to form the tympanic membrane
Where is the auricle or pinna derived from?
Mesoderm from either side of the firstmoharyngeal groove
Where does facial innervate?
Only the inner ear
So you do not see the sensory dermatome
What happens when the hillocks do not fuse?
Per auricular cyst
What does first arch syndrome?
Persistent meatal plug
