Eye and Ear Histology LOs

Question 1

differentiate between the cornea, the limbus, and the sclera

Answer 1

cornea: clear

limbus: transition

sclera: white part of eye

Question 2

list the 5 layers of the cornea, moving anterior to posterior

Answer 2

1. corneal/anterior epithelium: stratified squamous non-cornified; much thicker than posterior epi
2. anterior limiting membrane: basement membrane to corneal epi
3. corneal stroma: thickest; type I collaged fibers arranged in layers intermixed with amorphous ground substance, avascular
4. posterior limiting membrane/Decsemet’s membrane: basement membrane to posterior epithelium
5. posterior epithelium: very low simple cuboidal epithelium, also called endothelium by opthamologists even though is avascular; much thinner than corneal epi

Question 3

what type of CT proper makes up the sclera?

Answer 3

dense irregular connective tissue that varies in thickness around the globe

Question 4

differentiate between the choroid, the ciliary body, and the iris

Answer 4

all part of middle layer of eye, called the uvea/vascular tunic

choroid: posterior surface of eye, contains the tapetum lucidum and the choriocapillary layer

Question 5

differentiate between a choroid with a tapetum and a choroid without a tapetum

Answer 5

with no tapetum, vascular layer/stroma of choroid connects right to choriocapillary layer (ex. pigs)

with a tapetum, this layer is in between vascular layer/stroma and choriopcapillary layer

pigmented layer cannot be pigmented on top of a tapeteum; will have nonpigmented regions in a choroid with a tapetum

Question 6

differentiate between a cellular (carnivore) and a fibrous (herbivore) tapetum

Answer 6

cellular: tapetal cells (fibrocytes) are arranged like stacked bricks

fibrous: thick, dense collagen fibers and fibrocytes

Question 7

what portion of the visual retina does the choriocapillary layer supply?

Answer 7

nourishes the pigmented epithelium of the retina (the pigmented epithelium then nourishes the rods and cones)

choriocapillary layer: layer of capillaries immediately adjacent to the pigmented epithelium of the retina

Question 8

differentiate between the flat and folded part of the ciliary body

Answer 8

flat part: pars plana
folded part: pars plicata, folds are called ciliary processes

Question 9

differentiate between ciliary processes and zonular fibers

Answer 9

ciliary processes are folds of the ciliary body, they are connected to the lens by elastic zonular fibers (stretched between capsule of lens and BM of inner ciliary epithelium); originate from ciliary body between bases of ciliary processes

Question 10

list the 2 major functions of the ciliary body

Answer 10

1. play a role in accomodation
2. produce aqueous humor

Question 11

differentiate between the inner and outer layers of the ciliary epithelium

Answer 11

inner non pigemented layer and outer pigmented layer; arranged face to face with a basement membrane on each side

Question 12

list the flow of aqueous humor between the ciliary epithelium and the trabecular meshwork of the iridocorneal angle

Answer 12

1. aqueous humor is secreted into posterior compartment (behind lens where vitreous body is located) AND into the anterior compartment (in front of the lens)
2. the anterior compartment is subdivided into the posterior chamber (between lens and iris) and the anterior chamber (between iris and cornea)
3. the aqueous fluid is pumped into the posterior chamber, flows through the pupil into the anterior chamber, and exits through the trabecular meshwork at the iridiocorneal angle; it is then drained by the scleral venous sinus (canal of Schlemm)

Question 13

what type of muscle is the ciliary muscle? if this muscle contracts, what happens to the lens and how does this affect vision?

Answer 13

ciliary muscle: smooth muscle

when these muscle fibers contract, the ciliary body rounds up, releasing tension on the zonular fibers and the lens thickens/becomes rounder, allowing the animal to focus on a close object (accomodation, parasympathetic innervation)

Question 14

differentiate between the pupillary dilator muscle and the pupillary sphincter muscle

Answer 14

pupillary sphincter muscle: is arranged circumferentially around the free border or the iris in round pupils (canines and pigs), or the fibers cross laterally and medially in oval pupils (horses and ruminants), or fibers cross dorsally and ventrally in animals with slitlike pupils (felines); contraction decreases the diameter of the pupil and this muscle has parasympathetic innervation

pupillary dilator muscle: a myoepithelium because the anterior epithelial layer is partially differentiated into cells with contractile properties; radially oriented fibers along outer peripheral border; contraction increases the diameter of the pupil and this muscle has sympathetic innervation

Question 15

what type of muscle are the sphincter muscles?

Answer 15

both are smooth muscle

Question 16

what happens to the pupil when the dilator muscle contracts?

Answer 16

this muscle is longitudinally oriented and radially arranged around the pupil, so it increases the diameter (widens the aperture) when it contracts

Question 17

what happens to the pupil when the sphincter muscle contracts?

Answer 17

this muscle is circumferentially arranged around the pupil so it decreases the diameter (narrows the aperture) of the pupil when it contracts

Question 18

differentiate between the lens capsule, the lens epithelium, and the lens fibers

Answer 18

capsule: thickened basement membrane

epithelium: confined to anterior (cuboidal cells) and equatorial (elongated cells) surfaces of the lens

lens fibers: elongated lens epithelial cells, U-shaped; at equator of lens; fibers are added to the lens throughout the life of the animal

Question 19

which part of the ANS innervates the sphincters?

Answer 19

autonomic

Question 20

differentiate between the visual retina (retina) and the nonvisual retina (ciliary epithelium and iridial epithelium)

Answer 20

retina: 2 layers
1. pigmented epithelium: pigment quenches light photons, but this layer is NOT pigmented where it overlays a tapetum so that light photons can be reflected off the tapetum back onto phororeceptor cells
2. photoreceptor layer: the first neurons of the visual pathway! contains rods (low light ad night vision) and cones (bright light and color vision)

nonvisual retina:

Question 21

the ora serrata is the junction between which portions of the neuroepithelial tunic?

Answer 21

visual and nonvisual retina

Question 22

the inner and outer plexiform layers are where the 3 basic neurons of the visual pathway synapse; which two neurons synapse at the outer plexiform layer? which two neurons of the visual pathway synapse at the inner plexiform layer?

Answer 22

rods and cone cells synapse with bipolar and horizontal cells at the outer plexiform layer

bipolar neurons synapse with ganglion cells and amarcrine cells at the inner plexiform layers

Question 23

the axons of which specific neurons join together and exit the eye at where (the blind spot), pass through the sclera, and form what nerve?

Answer 23

axonal processes of ganglionic cells (3rd neuron in visual pathway) come together to form optic nerve which gather at the posterior medial pole of the globe (optic disc)
optic disc = blind spot

Question 24

list the 2 types of photoreceptor cells in the retina and indicate which of these is most abundant in the retina of the domestic species

Answer 24

cones and rods; rods predominate in domestic species

Question 25

list the 3 subdivisions of the bony labyrinth

Answer 25

1. semicircular canals
2. vestibule
3. cochlea

Question 26

list the 3 subdivisions of the membranous labyrinth

Answer 26

1. semicircular ducts: housed within semicircular canals
2. utricle and saccule: housed within vestibule
3. cochlear duct: housed within cochlea

Question 27

list the sensory epithelial housed within each subdivision of the membranous labyrinth and the basic functions of each

Answer 27

1. semicircular ducts contain a christa ampullaris that detects ANGULAR acceleration and deceleration
2. each utricle and saccule contain a macula (macula of utricle and macula of saccule) that provide awareness of static equilibrium based upon detection of head’s orientation in space and detection of LINEAR acceleration and deceleration
3. each cochlear ducts contains a spiral organ (organ of Corti) with the 3 subdivisions of scala vestibuli, scala media/cochlear duct, and scala tympani that detect sound vibrations