Embryology of the Eye and Ear

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

The eye is a highly specialized sensory organ derived from ______, mesoderm and surface ectoderm.

neural ectoderm

On the 22nd day of embryonic development, the region of the neural tube destined to form the ______ shows a linear thickened area.

prosencephalon

The optic vesacle is associated with the formation of the optic ______, which gives rise to the retina and optic nerve fibers.

cup

The surface ectoderm overlying the optic vesicle becomes thickened to form the ______ placode.

lens Signup and view all the answers

The proximal part of the optic vesicle becomes constricted and elongated to form the optic ______.

stalk Signup and view all the answers

The mesoderm contributes to the formation of the sclera, choroid, and ______ muscle.

ciliary Signup and view all the answers

As the optic vesicle grows laterally, its lateral walls make contact with the surface ______.

ectoderm Signup and view all the answers

After birth, the epithelium of the tympanic cavity invades bone of the developing ______ process.

mastoid Signup and view all the answers

The supporting ligament of the ossicles develops later within the ______.

mesenteries Signup and view all the answers

The structure that forms a partition between the external and middle ear is the tympanic ______.

membrane Signup and view all the answers

At birth, the cavities of the middle ear are filled with air via the ______ tube.

eustachian Signup and view all the answers

The part of the osseous labyrinth opposite the stapes remains thin and becomes the oval ______.

window Signup and view all the answers

The outer wall of the optic cup remains thin and becomes pigmented forming the ______ layer of the retina.

pigmented Signup and view all the answers

The inner layer of the optic cup forms the ______ layer of the retina.

neural Signup and view all the answers

The ______ vessels in this region are obliterated during fetal life.

hyaloid Signup and view all the answers

The ______ artery and vein of the retina develop from the hyaloid vessels within the optic stalk.

central Signup and view all the answers

The ______ body participates in the formation of the iris and the retina.

ciliary Signup and view all the answers

The inner neural layer of the retina can be divided into the anterior one-fifth and posterior ______ fifth.

four Signup and view all the answers

The ______ serrata is located in the eye and can be identified in the diagram.

Ora Signup and view all the answers

The ______ develops from the double layers of the optic cup.

retina Signup and view all the answers

The ______ of the retina is where the central artery and vein originate.

central Signup and view all the answers

The anterior part forms an epithelial covering for the ciliary body and ______.

iris Signup and view all the answers

The inner neural layer of the optic cup differentiates into matrix cells, mantle, and ______ layers.

marginal Signup and view all the answers

The cells of the matrix layer form the rods and ______.

cones Signup and view all the answers

The cells of the mantle layer differentiate into bipolar cells, the ganglion cells, and other ______ of the retina.

neurons Signup and view all the answers

The axons of the ganglion cells grow into the ______ layer to form the layer of nerve fibers.

marginal Signup and view all the answers

These nerve fibers in the marginal layer converge toward the ______ stalk.

optic Signup and view all the answers

The ciliary body and iris develop from the inner and outer layers of the ______ cup.

optic Signup and view all the answers

The ciliary body develops from the anterior part of the two layers of the optic ______.

cup Signup and view all the answers

The primary lens fibers create the ______ chamber.

anterior Signup and view all the answers

The ciliary epithelium consists of pigmented and ______ types.

non-pigmented Signup and view all the answers

The opening of these canaliculi on the eyelids are named the lacrimal ______.

puncta Signup and view all the answers

A dilatation of the nasolacrimal duct forms the lacrimal ______.

sac Signup and view all the answers

Coloboma results from non-closure of the lips of the ______ fissure.

choroidal Signup and view all the answers

In congenital cataracts, the lens becomes ______ during intrauterine development.

opaque Signup and view all the answers

Failure of the eyeball to develop is referred to as ______.

anophthalmia Signup and view all the answers

In microphthalmia, the eye is ______.

too small Signup and view all the answers

Cyclop refers to a condition involving a ______ eye.

single Signup and view all the answers

Congenital aphakia is the absence of the ______.

lens Signup and view all the answers

Microphthalmia may be associated with other ocular ______.

abnormalities Signup and view all the answers

Coloboma iridis is a common eye abnormality frequently associated with other eye ______.

defects Signup and view all the answers

Study Notes

Development of Sense Organs

The sense organs develop from multiple embryonic layers: neural ectoderm, mesoderm, and surface ectoderm.
Each sense organ part has a distinct embryonic origin.

Development of the Eye

The eye is a complex sensory organ comprised of multiple parts like the retina, iris, ciliary body, lens, optic nerve, sclera, choroid, cornea, and pupil.
The neural ectoderm gives rise to: optic vesicle, optic cup, retina, optic nerve fibers, and iris.
The surface ectoderm gives rise to: lens, lacrimal and tarsal glands, epithelium of the cornea, conjunctiva, and epidermis of the eyelid.
The mesoderm gives rise to: cornea stroma, sclera, choroid, ciliary muscle, parts of the vitreous, and muscles lining the anterior chamber.
The optic vesicle forms the optic cup.
The optic cup develops into two layers: outer and inner.
The outer wall forms the pigmented layer of the retina.
The inner layer forms the neural layer of the retina.
The margins of the optic cup grow over the lens to enclose it.
A deficiency in the inferior aspect of the cup is called the choroidal or fetal fissure.
The mesoderm surrounding the optic cup becomes the superficial fibrous layer and deeper vascular layer (corresponding to pia-arachnoid and dura).
The mesoderm forms hyaloid vessels within the choroid fissure which supply the lens and retina.
The hyaloid vessels are obliterated leaving the hyaloid canal.
The inner neural layer of the retina is divided into anterior one-fifth and posterior four-fifths.
The anterior part forms an epithelial covering for the ciliary body and iris.
The posterior part differentiates into matrix cells, mantle, and marginal layers.
Matrix cells form the rods and cones.
The mantle layer differentiates to form bipolar cells, ganglion cells, and supporting elements of the retina.
The axons of ganglion cells form the nerve fibers which converge into the optic stalk to form the optic nerve.

Ciliary Body & Iris

The ciliary body develops from the anterior part of the optic cup's two layers.
Stroma of the ciliary body, ciliary muscle (smooth muscle), and blood vessels originate from vascular mesenchyme around the optic cup.
The iris is formed by the marginal region of the optic cup. The stromal layer and blood vessels of the iris develop from mesenchyme in front of the anterior part of the optic cup. The sphincter and dilator muscles develop from neuroectoderm around the optic cup.

Lens

The lens develops from the lens vesicle which is lined by a single layer of cuboidal cells.
Cells in the anterior wall of the vesicle remain cuboidal.
The cells in the posterior wall elongate and lose their nuclei to form the lens fibers.
The anterior layer forms the epithelium which covers the lens surface.

Choroid & Sclera

The mesoderm surrounding the optic cup forms the inner pigmented vascular layer (choroid) and an outer fibrous layer (sclera).
The choroid contacts the outer pigmented layer of the optic cup.
The sclera is continuous with the dura mater, connecting to the optic nerve at the optic foramen of the skull.

Vitreous Body

Loose mesenchyme tissue surrounding the optic cup migrates into the cavity between the retina and lens to form the vitreous body, a network of fibers.
The interstitial spaces of this network fill with a transparent gelatinous substance.

Anterior Chamber

Cavuolation occurs in the mesenchymal cells between the lens and surface ectoderm, forming the anterior chamber.
The anterior chamber splits the mesenchyme into two layers.
The outer layer of the chamber is continuous with the sclera; the inner layer with the choroid.
The outer layer of the mesoderm gives rise to the substantia propria and mesothelium of the cornea.
The outer epithelial layer of the cornea arises from surface ectoderm.
The inner layer, in front of the lens and iris, forms the irido-pupillary membrane in contact with the lens's anterior surface.

Mesenchymal Tissue

Mesenchymal tissue in the anterior portion contributes to the connective tissue of the iris and the dilator and sphincter muscles of the pupil.
The region of the non-visual retina between the iris and the visual retina folds to form the ciliary processes.
Mesenchymal cells between the ciliary processes and the lens form the suspensory ligament of the lens.

Posterior Chamber

The irido-pupillary membrane breaks down to form the posterior chamber bounded by the lens, suspensory ligament, and iris.
Ciliary muscles control tension in the suspensory ligament, thereby regulating lens shape for accommodation.

Eyelid

The eyelid forms by reduplication of the surface ectoderm above and below the cornea.
Ectodermal folds contain mesoderm that gives rise to muscles and tarsal plates.
The eyelid margins fuse together temporarily and separate later.
The fusion of the lids makes the conjunctiva of ectodermal origin.

Lacrimal Gland

The lacrimal gland develops from a number of buds arising from the upper conjunctiva.
Soon after birth, the lacrimal gland secretes a watery fluid into the conjunctival sac, lubricating the cornea.
Both deep and superficial lacrimal glands relate to the third eyelid.

Nasolacrimal Duct

Superficial rod-like cords of ectoderm extend from the medial canthi of the eyelids to the developing nasal pit.
As these cords move deeper, they become the naso-lacrimal ducts.
Each duct opens into the developing nasal cavity.
The proximal part of the duct bifucates towards the eyelids — these ducts are the lacrimal canaliculi.
The lacrimal glands and associated duct system make up the lacrimal apparatus.

Anomalies of the Eye

Non-closure of the choroidal fissure leads to coloboma in the eyeball's ventral surface.
Coloboma iridis is an eye abnormality often associated with other eye defects.
Coloboma of the eyelids may also occur.
Corneal opacity is a result of persistent iridopupillary membrane.
Congenital cataracts occur during intrauterine development and can result from German measles exposure during pregnancy, making the lens opaque.
Anophthalmia is the failure of the eyeball to develop due to a problem with the optic vesicle.
Microphthalmos is an abnormally small-sized eye.
Hyaloid artery may persist.
Congenital aphakia (no lens) and aniridia (no iris) are rare anomalies.
Cyclopia involves a single eye and/or a fusion of the eyes.
Holoprosencephaly—a possible associated defect—involves partial or complete fusion of the cerebral hemispheres.
Some people have blue sclera, a thin sclera that shows the pigment of the choroid, or anomalies of pigmentation/albinism.

Development of the Ear

The ear develops into three parts: external, middle, and inner ear, each with distinct embryonic origins
The external ear is formed from the first pharyngeal cleft and surrounding mesoderm. The structure comprises the auricle (pinna), external auditory meatus, and outer lining of the tympanic membrane.
The middle ear is formed from the first pharyngeal pouch and its surrounding mesoderm. Its components include the auditory/Eustachian tube, tympanic cavity, and auditory ossicles.
The inner ear develops from the otic placodes in the 4th week of development. The otic placode sinks below the surface ectoderm into the mesoderm, forming the otic pit. The pit's edges fuse to form the otic vesicle, and this becomes the primordium of the membranous labyrinth
The otic vesicle develops into the saccule, cochlear duct, and spiral ganglion, and the utricle and semicircular canals, and endolymphatic duct and sac.
The perilymphatic space forms between the cartilaginous shell and the membranous labyrinth in the 10th week.
The spiral organ develops from cells in the cochlear duct walls. Ganglion cells of the vestibulocochlear nerve migrate along the membranous cochlear duct and form the spiral ganglion. Nerve processes extend from the ganglion to the spiral organ, where they end on the hair cells.
The membranous labyrinth is now suspended within perilymph in the cochlear region.
The perilymphatic space is divided into the scala vestibuli and the scala tympani.
The cochlear duct separates from the scala vestibuli by the vestibular membrane and the scala tympani by the basilar membrane
The lateral wall of the cochlear duct is attached to the cartilaginous shell by the spiral ligament, connected to and supported by a cartilaginous process, the modiolus.
The cartilaginous capsule surrounding the membranous labyrinth is replaced by bone—the osseous labyrinth— within the petrous temporal bone

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz covers key aspects of the embryological development of the eye and ear. Questions focus on the formation of various structures such as the optic vesicle, retina, and tympanic cavity. It's ideal for students studying developmental biology or medical students focusing on anatomy.