Eye and Ear

MULTIPLE CHOICE

Directions: Each group of questions below consists of a numbered list of descriptive words or phrases accompanied by a diagram with certain parts indicated by letters or by a list of lettered headings. For each numbered word or phrase, select the lettered part or heading that matches it correctly and then insert the letter in the space to the right of the appropriate number. Sometimes more than one numbered word or phrase may be correctly matched to the same lettered part or heading.

        1.  

________ Becomes the pigmented layer of the retina

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   B

The external layer of the optic cup differentiates into the pigmented layer of the retina. The pigmented epithelium consists of a single layer of cells that reinforces the light-absorbing properties of the choroid membrane to reduce scattering of light within the eye.

        2.  

________ Retinal fissure

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   E

The retinal fissure (optic fissure) develops on the inferior surface of the optic cup and along the optic stalk. The hyaloid blood vessels pass into the optic cup along this cleft and supply the lens and the developing neural layer of the retina.

        3.  

________ Becomes specialized for sensitivity to light

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   C

The inner layer of the optic cup becomes the neural layer of the retina. It differentiates into the visual receptive portion of the adult retina. The inner layer of the optic cup also gives rise to the ciliary and the iridial parts of the retina.

        4.  

________ Gives rise to the lens

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   D

The lens develops from the lens vesicle, a derivative of the surface ectoderm. The anterior wall of this vesicle becomes the anterior epithelium of the adult lens. Cells of the posterior wall lengthen to form lens fibers, which grow into and gradually obliterate the cavity of the lens vesicle.

        5.  

________ Future optic nerve

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   A

The optic stalk, connecting the optic cup to the brain, becomes the optic nerve as axons of ganglion cells in the neural layer of the retina pass into the inner wall of the stalk. As a result of the continually increasing number of optic nerve fibers, the inner wall of the stalk increases in thickness and fuses with the outer wall, obliterating the lumen of the optic stalk.

        6.  

________ Differentiates into the nonpigmented portion of the ciliary epithelium

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   C

Most of the inner layer of the optic cup becomes the neural layer of the retina. The anterior part becomes the nonpigmented portion of the ciliary epithelium (ciliary part of the retina) and the iridial portion of the retina. Toward the root of the iris, on the anterior surface of the ciliary processes, the cells of the inner layer of the cup gradually accumulate pigment granules.

        7.   ________ Tunica vasculosa lentis

a.
Scleral venous sinus
b.
Optic nerve
c.
Corneal epithelium
d.
Central artery of retina
e.
Pupillary membrane

ANS:   E

The anterior part of the tunica vasculosa lentis, a vascular layer around the embryonic lens, is called the pupillary membrane. When the distal part of the hyaloid artery degenerates, the tunica vasculosa lentis, including the pupillary membrane, also degenerates. Remnants of this membrane often appear as tissue strands in normal eyes of infants, but these strands usually cause little disturbance of vision and tend to disappear in old age.

        8.   ________ Ganglion cells of retina

a.
Scleral venous sinus
b.
Optic nerve
c.
Corneal epithelium
d.
Central artery of retina
e.
Pupillary membrane

ANS:   B

As the neural layer of the retina develops from the inner layer of the optic cup, the axons of ganglion cells in the retina pass into the inner wall of the optic stalk and gradually convert it into the optic nerve.

        9.   ________ Hyaloid artery

a.
Scleral venous sinus
b.
Optic nerve
c.
Corneal epithelium
d.
Central artery of retina
e.
Pupillary membrane

ANS:   D

The hyaloid artery passes along the retinal fissure to the optic cup, where it supplies blood to the developing neural layer of the retina and to the embryonic lens. The distal portion of this artery usually degenerates, but the proximal part persists as the central artery of the retina. Persistence of the distal part of the hyaloid artery is a fairly common abnormality. It may persist in whole or in part, but it usually is not patent. The hyaloid arterial remnant appears as a thin line or thick cord in the vitreous humor.

      10.   ________ Surface ectoderm

a.
Scleral venous sinus
b.
Optic nerve
c.
Corneal epithelium
d.
Central artery of retina
e.
Pupillary membrane

ANS:   C

The corneal epithelium is derived from the surface ectoderm. The lens functions as an inductor and influences the surface ectoderm to develop into the epithelium of the cornea. The substantia propria of the cornea is derived from mesenchyme.

      11.   ________ Congenital glaucoma

a.
Scleral venous sinus
b.
Optic nerve
c.
Corneal epithelium
d.
Central artery of retina
e.
Pupillary membrane

ANS:   A

Absence or incomplete development of the scleral venous sinus results in congenital glaucoma or buphthalmos. This abnormality usually is caused by recessive mutant genes, but sometimes it results from a maternal rubella infection during early pregnancy. The embryological basis of blockage or incomplete development of the scleral venous sinus is abnormal persistence of mesenchymal tissue in the angle of the anterior chamber. As a result of inadequate drainage of the aqueous humor through the canal, intraocular tension rises, the eye gradually enlarges, and the cornea becomes hazy. Retinal damage causes visual impairment.

      12.   ________ Neuroectoderm

a.
Scleral venous sinus
b.
Optic nerve
c.
Corneal epithelium
d.
Central artery of retina
e.
Pupillary membrane

ANS:   B

The optic vesicle is an outgrowth of the brain. Hence, the retina and the optic nerve are derived from neuroectoderm of the embryonic brain. The adult structure of the retina and optic nerve shows a marked resemblance to the brain, and the coats of the eyeball and the optic nerve show resemblances to the coverings of the brain. The central artery and vein of the retina pass in the meningeal sheaths and are included in the anterior part of the optic nerve. This relation is of clinical significance because an increase in pressure of cerebrospinal fluid around the optic nerve interferes with venous return from the eye, and edema of the optic disc (papilledema) results. This is an important indicator of an increase in intracranial pressure.

      13.  

________ Gives rise to a semicircular duct

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   C

This flat, disclike diverticulum of the utricular portion of the otic vesicle is the primordium of one of the three semicircular ducts. They are attached to the utricle and later are enclosed in the semicircular canals of the bony labyrinth. The sensory areas (cristae ampullares), which develop in these ducts, respond to changes in the direction of movement of the head.

      14.  

________ Absorption focus

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   E

The central parts of the walls of the disclike diverticula from the utricular portion of the otocyst fuse and later disappear. Degeneration of tissue proceeds peripherally from the absorption focus, but peripheral portions of the diverticula remain as the semicircular ducts.

      15.  

________ Endolymphatic duct

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   D

The endolymphatic duct appears as a hollow diverticulum from the dorsal utricular part of the otocyst. Its distal end expands to form the endolymphatic sac.

      16.  

________ Primordium of the cochlea

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   A

The cochlear duct develops as a tubular diverticulum from the saccular part of the otocyst. The cochlear duct grows and makes two and a half turns around the developing modiolus, a bony pillar or core that contains nerves and vessels. The coiled cochlear duct is called the membranous cochlea. It is contained in the bony cochlea, which develops from the surrounding mesenchyme.

      17.  

________ Saccular part of the otic vesicle

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   B

The saccular part of the otic vesicle—the saccule—is an endolymph-containing dilation of the membranous labyrinth. The saccule contains a specialized area of sensory epithelium, the macula sacculi, and together with the macula utriculi signals the orientation of the head in space.

      18.  

________ Gives rise to the spiral organ

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   A

The spiral organ (of Corti) differentiates from cells in the wall of the cochlear duct. Ganglion cells of the eighth cranial nerve migrate along the coils of the cochlea and form the cochlear ganglion. Nerve processes grow from this ganglion to the spiral organ.

      19.   ________ External acoustic meatus

a.
Conjunctival epithelium
b.
Neuroectoderm
c.
First pharyngeal pouch
d.
First pharyngeal groove
e.
Mesenchyme

ANS:   D

The external acoustic meatus is the adult derivative of the dorsal part of the first pharyngeal groove. It grows inward as a funnel-shaped tube until it reaches the endodermal tubotympanic recess, primordium of the tympanic cavity, tympanic antrum, pharyngotympanic (auditory) tube, and mastoid cells.

      20.   ________ Sclera and choroid

a.
Conjunctival epithelium
b.
Neuroectoderm
c.
First pharyngeal pouch
d.
First pharyngeal groove
e.
Mesenchyme

ANS:   E

The sclera and choroid develop from mesenchyme that surrounds the optic cup. The mesenchyme differentiates into an inner vascular layer, the choroid, and an outer fibrous layer, the sclera. Toward the margin of the optic cup, the choroid becomes modified to form the cores of the ciliary processes, which consist chiefly of capillaries supported by delicate connective tissue.

      21.   ________ Has same origin as the cornea

a.
Conjunctival epithelium
b.
Neuroectoderm
c.
First pharyngeal pouch
d.
First pharyngeal groove
e.
Mesenchyme

ANS:   A

The conjunctival epithelium, like the corneal epithelium, is derived from the surface ectoderm. The substantia propria of the conjunctiva and cornea consists of connective tissue derived from mesenchyme. The conjunctiva is a thin, transparent mucous membrane that covers the sclera and lines the eyelid. At the lid margin, the epithelium of the conjunctiva becomes continuous with the epidermis of the skin, another derivative of the surface ectoderm.

      22.   ________ Mastoid cells

a.
Conjunctival epithelium
b.
Neuroectoderm
c.
First pharyngeal pouch
d.
First pharyngeal groove
e.
Mesenchyme

ANS:   C

The mastoid cells begin to develop near term as the endodermal lining of the tympanic cavity, a derivative of the first pharyngeal pouch, induces erosion of the bone around the ear. The epithelium lining the mastoid cells formed by this process, called pneumatization, is derived from endoderm. Most mastoid cells develop after birth.

      23.   ________ Bipolar cells of the retina

a.
Conjunctival epithelium
b.
Neuroectoderm
c.
First pharyngeal pouch
d.
First pharyngeal groove
e.
Mesenchyme

ANS:   B

The bipolar cells of the neural part of the retina are derived from neuroectoderm of the brain. These cells are true neurons interposed between photoreceptor cells and ganglion cells.

      24.   ________ Tympanic cavity

a.
Conjunctival epithelium
b.
Neuroectoderm
c.
First pharyngeal pouch
d.
First pharyngeal groove
e.
Mesenchyme

ANS:   C

The tympanic cavity develops from the expanded distal end of the tubotympanic recess, a derivative of the first pharyngeal pouch. The tympanic cavity is a tiny epithelium-lined cavity in bone that communicates with the nasopharynx through the pharyngotympanic tube, another derivative of the first pharyngeal pouch.

      25.  

________ Continuous with the pigmented epithelium of the retina

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   B

The outer wall of the optic stalk is continuous with the outer wall of the optic cup, which gives rise to the pigmented epithelium of the retina.

      26.  

________ Gradually obliterates

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   A

The lumen of the optic stalk gradually obliterates as the optic nerve forms. As the number of axons of ganglion cells from the retina increases in the inner wall of the optic stalk, the lumen gradually disappears and the optic nerve forms.

      27.  

________ Continuous with the neural layer of the retina

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   D

The internal layer of the optic stalk is continuous with the inner layer of the optic cup, which gives rise to the neural layer of the retina. The internal layer of the optic stalk thickens as axons of ganglion cells pass through it on their way to the brain.

      28.  

________ Hyaloid vessels

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   E

The hyaloid vessels supply blood to and return blood from the inner layer of the optic cup (future neural layer of retina) and the embryonic lens. The distal parts of these vessels usually degenerate and the remaining parts become the central artery and vein of the retina. When the retinal fissure closes, these vessels are incorporated into the optic nerve.

      29.  

________ Continuous with the cranial meninges

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   C

The sheath of the optic nerve is continuous with the meninges of the brain and with the choroid and sclera. When the optic vesicles develop as outgrowths of the brain, they carry the layers of the meninges with them.

      30.  

________ Contains axons of ganglion cells

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   D

The internal layer of the optic stalk contains axons of ganglion cells in the neural layer of the retina. About 1 million fibers eventually pass through the optic nerve, the adult derivative of the optic stalk. The optic nerve fibers are myelinated by oligodendrocytes instead of by Schwann cells because the optic nerve is comparable to a tract within the brain. The neuroepithelial cells in the walls of the optic stalk differentiate into oligodendrocytes and other neuroglial cells.

      31.  

________ Derived from the first pharyngeal arch cartilage

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   C

The malleus, one of the middle ear bones—auditory ossicles—is derived from the first pharyngeal arch cartilage. It develops by endochondral ossification of the dorsal end of the cartilage. The incus and stapes, the other two ossicles, are derived in a similar manner from the first and second pharyngeal arch cartilages, respectively.

      32.  

________ Gives rise to the utricle

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   D

The dorsal or utricular portion of the otic vesicle gives rise to the utricle. Like the saccule, it is a dilation of the membranous labyrinth that contains a specialized area of sensory epithelium, the macula utriculi. The utricle and saccule are sensors of head movements.

      33.  

________ External acoustic meatus

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   B

The external acoustic meatus is the adult derivative of the dorsal end of the first pharyngeal groove. This canal leads to the tympanic membrane, and its function (along with the auricle) is to collect sound waves, which cause resonant vibration of the tympanic membrane.

      34.  

________ Meatal plug

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   A

The ectodermal cells at the bottom of the developing external acoustic meatus proliferate and grow caudally as a solid epithelial plate—the meatal plug. Late in fetal life, the central cells of this plug degenerate, forming the inner part of the external acoustic meatus. Failure of the meatal plug to canalize results in atresia of the external acoustic meatus and deafness. This condition usually is caused by genetic factors.

      35.  

________ Derived from the tubotympanic recess

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   E

The pharyngotympanic tube is derived from the tubotympanic recess, the derivative of the first pharyngeal pouch. This tube makes possible adjustments of pressure in the middle ear. When the tube opens during swallowing, the pressure in the middle ear is equalized with the atmospheric pressure.

      36.  

________ Membranous labyrinth

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   D

The membranous labyrinth develops from the otic vesicle, a derivative of the surface ectoderm. It gives rise to the utricle, saccule, endolymphatic duct and sac, semicircular ducts, and cochlea. The internal ear, which has a dual function (hearing and equilibrium), consists of the membranous labyrinth derived from the otic vesicle. It is enclosed in the bony labyrinth derived from the surrounding mesenchyme.

      37.  

________ Only derived from surface ectoderm

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   D

The lens develops from the lens vesicle, a derivative of the surface ectoderm. The anterior wall of the hollow lens vesicle, composed of cuboidal epithelium, becomes the anterior lens epithelium. The tall columnar cells of the posterior wall of the vesicle lengthen to form highly transparent primary lens fibers that gradually fill the cavity of the vesicle. The corneal epithelium is derived from surface ectoderm, but its stroma is derived from mesenchyme, probably of neural crest origin.

      38.  

________ Ciliary body

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   B

The pigmented region of the epithelium of the ciliary body is derived from the outer region of the optic cup. It is continuous with the retinal pigment epithelium. The nonpigmented part of the ciliary epithelium represents the interior prolongation of the neural retina in which no neural elements differentiate. The ciliary muscle and connective tissue in the ciliary body develop from mesenchyme or early fibroblasts found at the edge of the optic cup.

      39.  

________ Develops from mesenchyme

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   E

The mesenchyme surrounding the optic cup differentiates into an inner vascular layer, the choroid, and an outer fibrous tunic, the sclera. The sclera develops from a condensation of the mesenchyme external to the choroid. It is continuous with the substantia propria of the cornea and with the dura mater that surrounds the optic nerve.

      40.  

________ Composed of vitreous humor

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   A

The vitreous body forms within the cavity of the optic cup, between the lens and retina. It is composed of vitreous humor, an avascular mass of intercellular substance. The primary vitreous forms from mesenchymal cells and hyaloid blood vessels. The mesenchymal cells are probably of neural crest origin. The primary vitreous becomes surrounded by a gelatinous secondary vitreous that probably arises from the inner layer of the optic cup. The secondary vitreous is formed from primitive hyalocytes, compact collagenous fibrillar material, and hyaluronic acid.

      41.  

________ Cornea

a.
A
b.
B
c.
C
d.
D
e.
E

ANS:   C

The lens induces formation of the cornea, which develops following separation of the lens vesicle from the surface ectoderm. The anterior surface of the cornea, which is covered by a stratified squamous, nonkeratinizing epithelium, forms from the surface ectoderm. The other layers of the cornea are probably derived from neural crest cells.