Lec.11 DEV'T OF EYE AND EAR Flashcards
Eyes develop from three sources:
the ____ of the forebrain (retina, iris and optic nerve)
the ____ of the head (lens)
the ____ of neural crest origin between these layers (vascular and fibrous coats)
neuroectoderm
surface ectoderm
head mesenchyme
*Optic Cup & Lens Vesicle
Formation of the eye begins in the medially near the anterior margin of the ____
Interactions of this area with the underlying ____ will eventually lead to lateral eye-forming regions.
future prosencephalon.
mesoderm
*Optic Cup & Lens Vesicle
At the ____ week of gestation in most species, shallow grooves are formed on the sides of the forebrain.
These grooves will then expand as the ____
It has been shown in the mouse that the transcription factor Rx is expressed very early in the optic field.
In its absence, the optic vesicles fail to form.
third week
optic vesicles.
*Optic Cup & Lens Vesicle
Each optic vesicle grows laterally until it comes into contact with the ____
This will induce thickening of the ectoderm, creating the ____
surface ectoderm.
lens placode.
*Optic Cup & Lens Vesicle
The ;lens placode invaginates and forms a ____, which loses its contact with the surface ectoderm.
As the lens vesicles develop, the optic vesicles invaginate and become the ____
lens vesicle
optic cups.
*Optic Cup & Lens Vesicle
The inner layer of the optic cup later develops into the ____ that function in visual perception.
The outer layer of the optic cup becomes the pigmented layer of the retina.
The outer lips of the optic cup give rise to the _____
neural retina
iris and ciliary body.
*Optic Cup & Lens Vesicle
In ____, retinal differentiation and maturation is completed at birth.
In ____, they continue for up to 5 weeks after birth.
The last retinal cells to differentiate are the ____ – the rod and cone cells.
ungulates
carnivores
bipolar neurons and receptor cells
*Optic Axon
The ____ connects the retina with the diencephalon.
On its ventral surface the stalk has a groove, the ____, that contains the hyaloid vessels.
Later, the choroid fissure closes and a tunnel is formed inside the optic stalk.
optic stalk
choroid fissure
*Optic Axon
A number of nerve fibers in the inner wall of the stalk _____.
Eventually the inside and outside walls of the stalk fuse, transforming the optic stalk into the ____
The optic nerve carries the central artery of the retina.
increases
optic nerve
*Iris & Ciliary Body
Differentiation of the iris and ciliary body occurs at the ____, where the neural and pigment layers of the retina meet.
The iris consists of an inner ____ and an _____.
lip of the optic cup
non-pigmented epithelial layer
outer pigmented layer
*Iris & Ciliary Body
The levels and distribution of pigmentation in the iris determine eye color.
The _____ color is caused by the pigmentation of the outer pigmented layer of the iris.
Pigment cells also appear in the stroma of the iris; the greater the density of pigment cells in the stroma, the _____ is the eye color.
bluish
browner
*Iris & Ciliary Body
The ciliary body, containing the ciliary muscle, takes shape between the iris and the neural retina.
_____ of the ciliary muscle results in a more spherical, relaxed shape of the lens, which is needed in the focusing of the lens.
Contraction
*Lens
When the optic vesicles come in contact with the surface ectoderm, the ectoderm thickens to form the _____
This will then invaginate and form the _____, which break away from the surface ectoderm.
lens placodes
lens vesicles
*Lens
Cells of the posterior wall of the vesicles elongate to form ____.
The fibers will fill the hollow lens vesicle cavity and transform it into a ____.
In the lens, all cell organelles gradually disappear, leaving only an intact ____, an ____ and ____ filled with crystalline proteins.
primary lens fibers
solid lens
outer membrane, inner cytoskeleton, transparent cytoplasm
*Lens
The development of the lens is strongly influenced by the ____.
Fibroblast growth factor secreted by the retina accumulates in the vitreous humour behind the lens and stimulates the formation of ____.
retina
lens fibers
The vitreous body arises from a ____ that invades the cavity of the optic cup where it forms a loose fibrillar mesh.
The interstitial spaces later fill with transparent gelatinous substance, the ____
loose mesenchyme
vitreous humor
*Choroid, Sclera & Cornea
During early development, the ____ is surrounded by a layer of loose mesenchyme.
The pigmented epithelium of the retina, influences the inner layer of these cells to differentiate into the highly vascularized pigmented layer of the ____.
optic cup
choroid
*Choroid, Sclera & Cornea
The outer cells form the white, densely collagenous sclera that provides mechanical support for the eye.
Formation of the cornea results from the transformation of the ____ into a transparent structure that allows light to pass towards the retina.
surface ectoderm
*Eyelids & Lacrimal Glands
Each eyelid is formed from a _____
Once their formation starts, the eyelids grow rapidly towards each other over the developing cornea until they meet and fuse with one another.
fold of ectoderm
*Eyelids & Lacrimal Glands
Separation of the eyelids occurs:
before birth in humans (around the ____ month of gestation), horses, and ruminants
after birth in carnivores (at about the ____ days postnatally in pups and kittens, respectively)
seventh month
eight and tenth days
*Eyelids & Lacrimal Glands
Before the eyelids reopen, ____ and modified ____ along the margins of the lids (the tarsal glands) begin to form.
Each lash also has its own modified sweat gland.
In what animal? , no eyelashes develop in the lower eyelids.
eyelashes
sebaceous glands
dogs
*Eyelids & Lacrimal Glands
The space between the eyelids and the front of the eyeball is known as the ____.
In domestic animals, a fold of mesenchyme covered by conjunctiva develops into the ____.
conjunctival sac
third eyelid
*Eyelids & Lacrimal Glands
Around the time when the eyelids fuse, the ____ develop from solid buds from the surface ectoderm.
These buds branch and become canalized to form the ____ and ____ of the glands.
lacrimal glands
ducts
alveoli
*Eyelids & Lacrimal Glands
Soon after birth they produce a watery secretion that lubricates the outer surface of the cornea.
The lacrimal glands do not function fully at birth in humans; newborn babies do not produce tears when crying during the first __ weeks.
six weeks
The outer and middle ear are derived from the ____ as well as the ____
The inner ear develops from a ____ at the level of the hindbrain.
first and second pharyngeal arches
first pharyngeal cleft and pharyngeal pouch.
thickened ectodermal placode
*Inner Ear Dev’t
The inner ear originates from the ____, bilateral thickenings of the surface ectoderm adjacent to the myelencephalon.
The otic placodes invaginate to form the ____
The pits will make contact with the wall of the ____.
otic placodes
otic pits
myelencephalon
*Inner Ear Dev’t
The lips of the pit will then close, separating the otic vesicle from the surface ectoderm.
The otic vesicle itself soon begins to elongate and differentiates into two distinct parts: the ____ dorsally, and the ____ ventrally.
utricle
saccule
*Inner Ear Dev’t
Both of the utricle and saccule (sacculus) contain a sensory epithelium, the ____, which consists of hair cells and associated supporting cells.
A gelatinous layer, and above this is a fibrous structure, the otolithic membrane embedded with crystals of calcium carbonate called ____ can also be seen.
macula
otoconia
*Inner Ear Dev’t
The cochlear diverticulum evaginates from the ventral part of the saccule.
The cochlear duct curls as it elongates and forms the membranous cochlea.
The ____ is fluid-filled and transforms soundwaves to electrical signals.
cochlea
*Middle Ear Dev’t
Development of the middle ear occurs in association with the developmental changes of the ____
The tympanic cavity and the auditory tube (Eustachian tube) arise from an expansion of the ____
first and second pharyngeal arches.
first pharyngeal pouch.
*Middle Ear Dev’t
A ____ (connective tissue) is present in the developing middle ear.
Later, the thickness of this mesenchymal layer decreases significantly and will later establish the ____ (eardrum).
mesenchyme
tympanic membrane
*Middle Ear Dev’t
Just dorsal to the first pharyngeal pouch, ____ (bones) start to form.
The malleus and incus arises from ____ of the first pharyngeal arch, whereas the stapes originates from the ____
auditory ossicles
neural-crest-derived mesenchyme
second pharyngeal arch mesenchyme.
*Outer Ear Dev’t
The external auditory meatus arises from an inward expansion of the ____.
Sebaceous and modified sweat glands responsible for cerumen production, begin their development at the middle of gestation in the outer portion of the ____.
first pharyngeal cleft
external canal
*Outer Ear Dev’t
Development of the auricles is a lengthy and complex process that extends from early embryonic life until the postnatal period.
The auricles are formed from mesenchymal tissue of the ____
first and second pharyngeal arches.
