Week 8: Eye and Ear Histology Flashcards
1
Q
Outer layer (fibrous tunic) of eyeball contains
A
sclera and cornea
2
Q
middle layer (vascular tunic) of eyeball contains
A
choroid, ciliary body, and iris
3
Q
Sclera
A
- dense irregular CT
- supports and maintains shape of eye
- protects internal structures
- attachment site for extraocular muscles
4
Q
cornea function
A
- Protects anterior surface of eye
* refracts (bends) incoming light into lens
5
Q
Choroid
A
- CT; highly vascularized
- nourish retina
- pigment absorbs extraneous light
6
Q
ciliary body
A
- smooth muscle + secretory epithelium
- zonular fibers to lens
- epithelium secretes aqueous humor
7
Q
Iris
A
•sphincter pupillae and dilator pupillae + CT with central pupil
8
Q
internal layer (retina) of eyeball contains
A
pigmented layer and neural layer
9
Q
pigmented layer of retina
A
- absorbs extraneous light
- provides vitamin A for photoreceptors
- recycles photoreceptor products
10
Q
neural layer
A
- neurons and glia cells
- detects incoming light
- converts light rays to nerve signals -> brain
11
Q
anterior chamber of eyeball
A
- between cornea and iris
* filled with aqueous humor
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
13
Q
posterior chamber of eyeball
A
- between iris and lens
* filled with aqueous humor
14
Q
vitreous cavity of eyeball
A
- surrounded by retina; posterior to the lens
* contains vitreous body = large transparent gelatinous mass -> hyaluronic acid
15
Q
important details of cornea
A
- colorless
- transparent
- highly innervated
- completely avascular
16
Q
5 layers of cornea
A
- corneal epithelium
- bowman’s layer
- corneal stroma
- descemets membrane
- corneal endothelium
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)
18
Q
bowman’s layer
A
- CT that supports corneal epithelium
* additional protective barrier
19
Q
corneal stroma
A
- highly transparent layer; ~90% of thickness of cornea
* collagen fiber lattice -> highly resistant to deformations and trauma
20
Q
keratocytes
A
- cells of the corneal stroma
* produce/maintain the collagen matrix
21
Q
descemets membrane
A
one of the thickest basement membranes in the body
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
23
Q
What percent of eye’s total focusing power is contributed by cornea?
A
65-75%
24
Q
myopia
A
(near-sightedness)
•eyeball that is too long, or cornea too curved
•light rays fall short of retina -> distant objects blurry
25
hyperopia
(far-sightedness)
•eyeball that is too short, or a cornea too flat
•light rays are focused behind retina -> close objects blurry
26
presbyopia
similar to hyperopia, but is due to change in elasticity of lens
27
conjunctiva
thin, transparent mucosa on exposed part of sclera and lining eyelids
28
primary functions of conjunctiva
* lubricate anterior surface of eye
* lubricate inner eyelids -> open/close w/o friction
* protect eye
29
epithelia of conjunctiva
•stratified columnar with "goblet cells" that secrete mucous to add to tear film for cornea
30
conjunctivitis
=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
31
2 layers of choroid
1. choriocapillaries
| 2. bruch's membrane
32
choriocapillaries
vascularized CT with pigment cells -> nourish outer retina and absorb scattered light
33
bruch's membrane
thin CT between choriocapillaries and the pigmented layer of retina
34
site of Age-related macular degeneration (AMD)
choroid
35
AMD results from
damage to the macula that is required for central vision
36
Dry AMD
(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
37
What may slow progression of Dry AMD?
diet, multivitamin supplements, and antioxidants
38
Wet AMD
(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
39
ciliary body is anterior expansion of___
| it encircles___
* choroid in the posterior chamber
| * it encircles the lens at the level of the limbus
40
ciliary processes
ridges extending from ciliary body and lined by a double layer of epithelium
41
inner layer of ciliary body is highly
pigmented
42
cells of outer layer of ciliary body are highly
specialized for secretion of aqueous humor into the posterior chamber
43
trabecular meshwork
* channels found at the corneoscleral junction (limbus)
| * pumps aqueous humor -> scleral venous sinus -> venous blood returning from eye
44
normal intraocular pressure
(about 15-22 mmHg)
•necessary for functioning optical system
•maintains smooth curvature of corneal surface
•keep photoreceptors in contact with pigmented epithelium
45
glaucoma
•intraocular pressure is elevated -> optic nerve constricted -> vision loss and blindness
46
What causes elevated intraocular pressure in glaucoma?
obstruction hampers normal drainage of aqueous humor
47
acute or closed-angle glaucoma
* iris tissue obstructs flow of aq. humor from post. to ant. compartment
* pushes portions of iris upward, blocking chamber angle
48
chronic or open-angle glaucoma
* chamber angle open, but drainage through trabecular meshwork impaired
* most common type of glaucoma that becomes more prevalent after age of 40
49
glaucoma versus ocular hypertension
* must have optic nerve damage and associated vision loss to be called glaucoma
* otherwise ocular hypertension
50
ciliary body and accommodation of lens
•zonular fibers/ suspensory ligaments extend from ciliary processes to capsule of lens
51
accommodation reflex
lens is flattened for far away objects and rounded for nearby objects
52
when ciliary muscle relaxes...
zonular fibers are put under increased tension -> lens flattens
53
when ciliary muscle contracts...
zonular fibers become more lax -> lens becomes more round
54
ciliary body innervated by
parasympathetic fibers of occulomotor nerve
55
posterior surface of iris has
* 2-layered epithelium continuous with covering of ciliary processes
* heavily filled with melanin
56
2 layers of smooth muscle in iris
* outer radial layer called dilator pupillae
| * inner circular bundle near pupil called sphincter pupillae
57
innervation of dilator pupillae
* sympathetic to enlarge pupil
| * contraction increases pupillary aperture
58
innervation of sphincter pupillae
* parasympathetic fibers of oculomotor nerve to constrict pupil
* contraction decreases pupillary aperture
59
layers of retina in order
* nerve fiber layer
* ganglion cell layer
* inner nuclear layer
* outer nuclear layer
* pigmented epithelium
60
retinal pigmented epithelium (RPE)
* 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
dysfunction of RPE can result in
photoreceptor cell death and blindness
62
outer nuclear layer of retina
* 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
rods contain___ and are responsible for ___
* visual pigment rhodopsin
| * responsible for vision in low light
64
cones responsible for
color vision (site of color blindness)
65
ganglion cell layer of retina
has neurons with very long axons that make up the nerve fiber layer, which come together to form optic nerve
66
inner nuclear layer consists of
* bipolar cells, amacrine cells, and horizontal cells
| * all responsible to integrate signals produced by photoreceptors and transmit it to ganglion cell layer
67
muller glial cells
* support retinal neurons
| * extend full thickness of neurosensory retina
68
microglial cells
* support retinal neurons
| * phagocytic and other immune functions
69
cells that support retinal neurons
* muller glial cells
| * microglial cells
70
production of visual image that is transmitted to the brain via the optic nerve requires
light rays to pass through full thickness of retina
71
optic disc
* axons from ganglion cells of retina exit eye to form the optic nerve
* retinal blood vessels enter and leave the eye
72
macula
•6mm oval shaped, highly pigmented spot near center of retina
73
fovea
* small pit in the center of macula
| * responsible for high resolution/high acuity vision
74
ears consist of
* auditory system
| * vestibular system
75
auricle consists of
(pinna)
| •elastic cartilage covered by keratinized stratified squamous epithelium with hairs, sebaceous glands, and sweat glands
76
external auditory meatus
* 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
external auditory meatus lined by
stratified squamous epithelium with hairs, sebaceous glands, and ceruminous glands
78
cerumen
(earwax)
| the combination of secretions from sebaceous glands and ceruminous glands
79
tympanic cavity is
an irregular space that lies within the temporal bones between the tympanic membrane and bony surface of the internal ear
80
anteriorly, the tympanic cavity communicates with
pharynx via the auditory tube (Eustachian)
81
posteriorly, the tympanic cavity communicates with
the smaller, air-filled mastoid cavities of the temporal bone
82
primary function of auditory (eustachian) tube
•equalize air pressure between tympanic cavity and external environment
83
Walls of eustachian tube...
during swallowing and yawning, walls separate to allow air to enter tympanic cavity
84
tympanic cavity lined with
mainly simple cuboidal epithelium, thin lamina propria -> strongly adherent to periosteum
85
oval and round windows
* found in the medial bony wall of the middle ear
| * membrane covered regions completely devoid of bone
86
tympanic membrane indirectly connected to
oval window by auditory ossicles
87
auditory ossicles transmit
vibrations of the TM to the internal ear
88
tensor tympani
small skeletal muscle attached to malleus -> restrict movement to protect inner ear from loud noise
89
stapedius
small skeletal muscle attached to stapes -> restrict movement to protect internal ear from loud noise
90
internal ear located
completely within temporal bone
91
bony labyrinth
houses set of continuous fluid-filled epithelium lined tubes and chambers (membranous labyrinth)
92
vestibule
* central cavity of the bony labyrinth
| * contains utricle and saccule
93
semicircular canals
(superior, lateral, and posterior)
•extend posteriorly from vestibule
•oriented at right angles to one another
•has ampulla at one end
94
what mediates sense of equilibrium
vestibule and semicircular canals
95
cochlea
* coils like a snail shell around a central pillar of bone containing the cochlear duct
* mediates sense of hearing
96
hair cells
* columnar sensory mechanoreceptors
* each contains numerous sterocilia and a kinocilium that respond to motion
* found lining utricle, saccule, and semicircular canals
97
kinocilium
* found in hair cells
| * detects motion and conveys signals to the brain via a branch of the vestibular nerve
98
cochlear duct surrounded by
scala vestibuli and scala tympani, which contain perilymph
99
perilymph
•similar in iconic composition to CSF and extracellular fluid of other tissues, but contains little protein
100
What does perilymph do?
suspends and supports closed membranous labyrinth -> protect from bony labyrinth
101
What is cochlear duct filled with?
endolymph
102
endolymph
also contains few proteins, but has high K+ (150 mM) and low Na+ (16 mM), similar to that of intracellular fluid
103
endolymph is generated by
capillaries in the stria vascularis in the wall of the cochlear duct
104
endolymph is drained
from the vestibule into venous sinuses of the dura mater
105
perilymph emerges
emerges from microvasculature of periosteum
106
perilymph is drained
by a perilymphatic ducts into adjoining subarachnoid space
107
vestibular membrane
runs along the length of the cochlea and separates it from scala vestibuli
108
organ of corti
* spiral organ found in the wall that separates the cochlear duct from the scala tympani
* rest on thick basal lamina, the basilar membrane
109
organ of corti contains
special auditory receptors in the form of hair cells that respond to different sound frequencies
110
tectorial membrane
an acellular layer extending over organ of corti that has tips of tallest hair cells embedded in it
111
base of each hair cell is innervated by
* a branch of the cochlear division of CN VIII
| * the nerve endings transmit impulses to the bipolar neurons of the spiral ganglion
112
how does hearing work?
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
high-frequency sounds produce maximal movement where
nearest to the oval window
114
sounds of progressively lower frequency produce fluid waves that
move further along the scala vestibuli and displace the spiral organ at a point further away . from the oval window
115
sound of lowest frequency that can be detected produce
movement of the basilar membrane at the apex or helocotrema of the cochlea
