Lec.11 DEV'T OF EYE AND EAR

Question 1

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)

Answer 1

neuroectoderm

surface ectoderm

head mesenchyme

Question 2

*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.

Answer 2

future prosencephalon.

mesoderm

Question 3

*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.

Answer 3

third week

optic vesicles.

Question 4

*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 ____

Answer 4

surface ectoderm.

lens placode.

Question 5

*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 ____

Answer 5

lens vesicle

optic cups.

Question 6

*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 _____

Answer 6

neural retina

iris and ciliary body.

Question 7

*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.

Answer 7

ungulates

carnivores

bipolar neurons and receptor cells

Question 8

*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.

Answer 8

optic stalk

choroid fissure

Question 9

*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.

Answer 9

increases

optic nerve

Question 10

*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 _____.

Answer 10

lip of the optic cup

non-pigmented epithelial layer

outer pigmented layer

Question 11

*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.

Answer 11

bluish

browner

Question 12

*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.

Answer 12

Contraction

Question 13

*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.

Answer 13

lens placodes

lens vesicles

Question 14

*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.

Answer 14

primary lens fibers

solid lens

outer membrane, inner cytoskeleton, transparent cytoplasm

Question 15

*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 ____.

Answer 15

retina

lens fibers

Question 16

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 ____

Answer 16

loose mesenchyme

vitreous humor

Question 17

*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 ____.

Answer 17

optic cup

choroid

Question 18

*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.

Answer 18

surface ectoderm

Question 19

*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.

Answer 19

fold of ectoderm

Question 20

*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)

Answer 20

seventh month

eight and tenth days

Question 21

*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.

Answer 21

eyelashes

sebaceous glands

dogs

Question 22

*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 ____.

Answer 22

conjunctival sac

third eyelid

Question 23

*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.

Answer 23

lacrimal glands

ducts

alveoli

Question 24

*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.

Answer 24

six weeks

Question 25

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.

Answer 25

first and second pharyngeal arches

first pharyngeal cleft and pharyngeal pouch.

thickened ectodermal placode

Question 25

*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 ____.

Answer 25

otic placodes

otic pits

myelencephalon

Question 26

*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.

Answer 26

utricle

saccule

Question 27

*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.

Answer 27

macula

otoconia

Question 28

*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.

Answer 28

cochlea

Question 29

*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 ____

Answer 29

first and second pharyngeal arches.

first pharyngeal pouch.

Question 30

*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).

Answer 30

mesenchyme

tympanic membrane

Question 31

*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 ____

Answer 31

auditory ossicles

neural-crest-derived mesenchyme

second pharyngeal arch mesenchyme.

Question 32

*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 ____.

Answer 32

first pharyngeal cleft

external canal

Question 33

*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 ____

Answer 33

first and second pharyngeal arches.