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Clinical Morphology > Week 8: Eye and Ear Histology > Flashcards

Week 8: Eye and Ear Histology Flashcards

1
Q

Outer layer (fibrous tunic) of eyeball contains

A

sclera and cornea

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2
Q

middle layer (vascular tunic) of eyeball contains

A

choroid, ciliary body, and iris

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3
Q

Sclera

A
  • dense irregular CT
  • supports and maintains shape of eye
  • protects internal structures
  • attachment site for extraocular muscles
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4
Q

cornea function

A
  • Protects anterior surface of eye

* refracts (bends) incoming light into lens

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5
Q

Choroid

A
  • CT; highly vascularized
  • nourish retina
  • pigment absorbs extraneous light
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6
Q

ciliary body

A
  • smooth muscle + secretory epithelium
  • zonular fibers to lens
  • epithelium secretes aqueous humor
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7
Q

Iris

A

•sphincter pupillae and dilator pupillae + CT with central pupil

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8
Q

internal layer (retina) of eyeball contains

A

pigmented layer and neural layer

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9
Q

pigmented layer of retina

A
  • absorbs extraneous light
  • provides vitamin A for photoreceptors
  • recycles photoreceptor products
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10
Q

neural layer

A
  • neurons and glia cells
  • detects incoming light
  • converts light rays to nerve signals -> brain
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11
Q

anterior chamber of eyeball

A
  • between cornea and iris

* filled with aqueous humor

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12
Q

aqueous humor

A
  • liquid like blood plasma with less protein/glucose and more lactate/ascorbate
  • produced by secretory epithelium lining ciliary body
  • flows from posterior to anterior chamber via pupil
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13
Q

posterior chamber of eyeball

A
  • between iris and lens

* filled with aqueous humor

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14
Q

vitreous cavity of eyeball

A
  • surrounded by retina; posterior to the lens

* contains vitreous body = large transparent gelatinous mass -> hyaluronic acid

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15
Q

important details of cornea

A
  • colorless
  • transparent
  • highly innervated
  • completely avascular
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16
Q

5 layers of cornea

A
  1. corneal epithelium
  2. bowman’s layer
  3. corneal stroma
  4. descemets membrane
  5. corneal endothelium
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17
Q

corneal epithelium

A
  • non-keratinized stratified squamous
  • barrier to outside world
  • nerve endings -> blink reflex
  • continuous renewal from stem cells at corneal scleral junction (limbus)
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18
Q

bowman’s layer

A
  • CT that supports corneal epithelium

* additional protective barrier

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19
Q

corneal stroma

A
  • highly transparent layer; ~90% of thickness of cornea

* collagen fiber lattice -> highly resistant to deformations and trauma

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20
Q

keratocytes

A
  • cells of the corneal stroma

* produce/maintain the collagen matrix

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21
Q

descemets membrane

A

one of the thickest basement membranes in the body

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22
Q

corneal endothelium

A
  • simple squamous epithelium with impermeable junctions -> regulate influx of aqueous humor into corneal stroma
  • its structural and functional integrity is vital to maintenance of a proper hydration state of stroma and corneal transparency
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23
Q

What percent of eye’s total focusing power is contributed by cornea?

A

65-75%

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24
Q

myopia

A

(near-sightedness)
•eyeball that is too long, or cornea too curved
•light rays fall short of retina -> distant objects blurry

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25
Q

hyperopia

A

(far-sightedness)
•eyeball that is too short, or a cornea too flat
•light rays are focused behind retina -> close objects blurry

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26
Q

presbyopia

A

similar to hyperopia, but is due to change in elasticity of lens

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27
Q

conjunctiva

A

thin, transparent mucosa on exposed part of sclera and lining eyelids

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28
Q

primary functions of conjunctiva

A
  • lubricate anterior surface of eye
  • lubricate inner eyelids -> open/close w/o friction
  • protect eye
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29
Q

epithelia of conjunctiva

A

•stratified columnar with “goblet cells” that secrete mucous to add to tear film for cornea

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30
Q

conjunctivitis

A

=pink eye
•conjunctiva inflamed, usually due to bacterial infection or allergies
•inflammation increases the discharge of mucous and enlarges microvasculature of sclera -> reddish appearance
•bacterial and viral -> little effect on vision

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31
Q

2 layers of choroid

A
  1. choriocapillaries

2. bruch’s membrane

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32
Q

choriocapillaries

A

vascularized CT with pigment cells -> nourish outer retina and absorb scattered light

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33
Q

bruch’s membrane

A

thin CT between choriocapillaries and the pigmented layer of retina

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34
Q

site of Age-related macular degeneration (AMD)

A

choroid

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35
Q

AMD results from

A

damage to the macula that is required for central vision

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36
Q

Dry AMD

A

(nonexudative, >80%)
•diffuse or discrete deposits of lipid and protein (drusen) in Bruch’s membrane of choroid
•atrophy and degeneration of pigmented epithelium and associated photorecepters of retina -> vision loss
•no effective treatment

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37
Q

What may slow progression of Dry AMD?

A

diet, multivitamin supplements, and antioxidants

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38
Q

Wet AMD

A

(exudative, 10-15%)
•angiogenesis from the choriocapillaries -> penetrate through buch’s membrane and RPE
•vessels leak -> scarring
•treatment= injection of VEGF antagonists into vitreous cavity to inhibit angiogenesis and leaking OR laser treatment

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39
Q

ciliary body is anterior expansion of___

it encircles___

A
  • choroid in the posterior chamber

* it encircles the lens at the level of the limbus

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40
Q

ciliary processes

A

ridges extending from ciliary body and lined by a double layer of epithelium

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41
Q

inner layer of ciliary body is highly

A

pigmented

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42
Q

cells of outer layer of ciliary body are highly

A

specialized for secretion of aqueous humor into the posterior chamber

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43
Q

trabecular meshwork

A
  • channels found at the corneoscleral junction (limbus)

* pumps aqueous humor -> scleral venous sinus -> venous blood returning from eye

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44
Q

normal intraocular pressure

A

(about 15-22 mmHg)
•necessary for functioning optical system
•maintains smooth curvature of corneal surface
•keep photoreceptors in contact with pigmented epithelium

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45
Q

glaucoma

A

•intraocular pressure is elevated -> optic nerve constricted -> vision loss and blindness

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46
Q

What causes elevated intraocular pressure in glaucoma?

A

obstruction hampers normal drainage of aqueous humor

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47
Q

acute or closed-angle glaucoma

A
  • iris tissue obstructs flow of aq. humor from post. to ant. compartment
  • pushes portions of iris upward, blocking chamber angle
48
Q

chronic or open-angle glaucoma

A
  • chamber angle open, but drainage through trabecular meshwork impaired
  • most common type of glaucoma that becomes more prevalent after age of 40
49
Q

glaucoma versus ocular hypertension

A
  • must have optic nerve damage and associated vision loss to be called glaucoma
  • otherwise ocular hypertension
50
Q

ciliary body and accommodation of lens

A

•zonular fibers/ suspensory ligaments extend from ciliary processes to capsule of lens

51
Q

accommodation reflex

A

lens is flattened for far away objects and rounded for nearby objects

52
Q

when ciliary muscle relaxes…

A

zonular fibers are put under increased tension -> lens flattens

53
Q

when ciliary muscle contracts…

A

zonular fibers become more lax -> lens becomes more round

54
Q

ciliary body innervated by

A

parasympathetic fibers of occulomotor nerve

55
Q

posterior surface of iris has

A
  • 2-layered epithelium continuous with covering of ciliary processes
  • heavily filled with melanin
56
Q

2 layers of smooth muscle in iris

A
  • outer radial layer called dilator pupillae

* inner circular bundle near pupil called sphincter pupillae

57
Q

innervation of dilator pupillae

A
  • sympathetic to enlarge pupil

* contraction increases pupillary aperture

58
Q

innervation of sphincter pupillae

A
  • parasympathetic fibers of oculomotor nerve to constrict pupil
  • contraction decreases pupillary aperture
59
Q

layers of retina in order

A
  • nerve fiber layer
  • ganglion cell layer
  • inner nuclear layer
  • outer nuclear layer
  • pigmented epithelium
60
Q

retinal pigmented epithelium (RPE)

A
  • cuboidal epithelial cells in close association with photorecepters of the retina
  • convert and store retinoid
  • phagocytose shed photorecepters
  • absorb scattered light
  • iron and fluid transport
61
Q

dysfunction of RPE can result in

A

photoreceptor cell death and blindness

62
Q

outer nuclear layer of retina

A
  • cell bodies and nuclei of photoreceptors (rods and cones)

* generate a signal in response to a photon of light and transmit it to the neurons of inner nuclear layer

63
Q

rods contain___ and are responsible for ___

A
  • visual pigment rhodopsin

* responsible for vision in low light

64
Q

cones responsible for

A

color vision (site of color blindness)

65
Q

ganglion cell layer of retina

A

has neurons with very long axons that make up the nerve fiber layer, which come together to form optic nerve

66
Q

inner nuclear layer consists of

A
  • bipolar cells, amacrine cells, and horizontal cells

* all responsible to integrate signals produced by photoreceptors and transmit it to ganglion cell layer

67
Q

muller glial cells

A
  • support retinal neurons

* extend full thickness of neurosensory retina

68
Q

microglial cells

A
  • support retinal neurons

* phagocytic and other immune functions

69
Q

cells that support retinal neurons

A
  • muller glial cells

* microglial cells

70
Q

production of visual image that is transmitted to the brain via the optic nerve requires

A

light rays to pass through full thickness of retina

71
Q

optic disc

A
  • axons from ganglion cells of retina exit eye to form the optic nerve
  • retinal blood vessels enter and leave the eye
72
Q

macula

A

•6mm oval shaped, highly pigmented spot near center of retina

73
Q

fovea

A
  • small pit in the center of macula

* responsible for high resolution/high acuity vision

74
Q

ears consist of

A
  • auditory system

* vestibular system

75
Q

auricle consists of

A

(pinna)

•elastic cartilage covered by keratinized stratified squamous epithelium with hairs, sebaceous glands, and sweat glands

76
Q

external auditory meatus

A
  • from auricle to tympanic membrane of middle ear
  • outer 1/3 is elastic cartilage that is continuous with auricle
  • inner 2/3 is temporal bone
77
Q

external auditory meatus lined by

A

stratified squamous epithelium with hairs, sebaceous glands, and ceruminous glands

78
Q

cerumen

A

(earwax)

the combination of secretions from sebaceous glands and ceruminous glands

79
Q

tympanic cavity is

A

an irregular space that lies within the temporal bones between the tympanic membrane and bony surface of the internal ear

80
Q

anteriorly, the tympanic cavity communicates with

A

pharynx via the auditory tube (Eustachian)

81
Q

posteriorly, the tympanic cavity communicates with

A

the smaller, air-filled mastoid cavities of the temporal bone

82
Q

primary function of auditory (eustachian) tube

A

•equalize air pressure between tympanic cavity and external environment

83
Q

Walls of eustachian tube…

A

during swallowing and yawning, walls separate to allow air to enter tympanic cavity

84
Q

tympanic cavity lined with

A

mainly simple cuboidal epithelium, thin lamina propria -> strongly adherent to periosteum

85
Q

oval and round windows

A
  • found in the medial bony wall of the middle ear

* membrane covered regions completely devoid of bone

86
Q

tympanic membrane indirectly connected to

A

oval window by auditory ossicles

87
Q

auditory ossicles transmit

A

vibrations of the TM to the internal ear

88
Q

tensor tympani

A

small skeletal muscle attached to malleus -> restrict movement to protect inner ear from loud noise

89
Q

stapedius

A

small skeletal muscle attached to stapes -> restrict movement to protect internal ear from loud noise

90
Q

internal ear located

A

completely within temporal bone

91
Q

bony labyrinth

A

houses set of continuous fluid-filled epithelium lined tubes and chambers (membranous labyrinth)

92
Q

vestibule

A
  • central cavity of the bony labyrinth

* contains utricle and saccule

93
Q

semicircular canals

A

(superior, lateral, and posterior)
•extend posteriorly from vestibule
•oriented at right angles to one another
•has ampulla at one end

94
Q

what mediates sense of equilibrium

A

vestibule and semicircular canals

95
Q

cochlea

A
  • coils like a snail shell around a central pillar of bone containing the cochlear duct
  • mediates sense of hearing
96
Q

hair cells

A
  • columnar sensory mechanoreceptors
  • each contains numerous sterocilia and a kinocilium that respond to motion
  • found lining utricle, saccule, and semicircular canals
97
Q

kinocilium

A
  • found in hair cells

* detects motion and conveys signals to the brain via a branch of the vestibular nerve

98
Q

cochlear duct surrounded by

A

scala vestibuli and scala tympani, which contain perilymph

99
Q

perilymph

A

•similar in iconic composition to CSF and extracellular fluid of other tissues, but contains little protein

100
Q

What does perilymph do?

A

suspends and supports closed membranous labyrinth -> protect from bony labyrinth

101
Q

What is cochlear duct filled with?

A

endolymph

102
Q

endolymph

A

also contains few proteins, but has high K+ (150 mM) and low Na+ (16 mM), similar to that of intracellular fluid

103
Q

endolymph is generated by

A

capillaries in the stria vascularis in the wall of the cochlear duct

104
Q

endolymph is drained

A

from the vestibule into venous sinuses of the dura mater

105
Q

perilymph emerges

A

emerges from microvasculature of periosteum

106
Q

perilymph is drained

A

by a perilymphatic ducts into adjoining subarachnoid space

107
Q

vestibular membrane

A

runs along the length of the cochlea and separates it from scala vestibuli

108
Q

organ of corti

A
  • spiral organ found in the wall that separates the cochlear duct from the scala tympani
  • rest on thick basal lamina, the basilar membrane
109
Q

organ of corti contains

A

special auditory receptors in the form of hair cells that respond to different sound frequencies

110
Q

tectorial membrane

A

an acellular layer extending over organ of corti that has tips of tallest hair cells embedded in it

111
Q

base of each hair cell is innervated by

A
  • a branch of the cochlear division of CN VIII

* the nerve endings transmit impulses to the bipolar neurons of the spiral ganglion

112
Q

how does hearing work?

A

sound wave collected in auricle -> vibrate TM -> moves ossicles ->fluid waves in perilymph begin at oval window and move along scala vestibuli -> causes momentary movement of vestibular and/or basilar membranes and endolymph surrounding organ of corti -> fluid displacement causes hair cells embedded in tectorial membrane to bend -> neurotransmitters released from basal portion of hair cells -> neural impulses

113
Q

high-frequency sounds produce maximal movement where

A

nearest to the oval window

114
Q

sounds of progressively lower frequency produce fluid waves that

A

move further along the scala vestibuli and displace the spiral organ at a point further away . from the oval window

115
Q

sound of lowest frequency that can be detected produce

A

movement of the basilar membrane at the apex or helocotrema of the cochlea

Clinical Morphology (25 decks)

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