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Special Senses: Vision
UCCS Bio 2020 Lykins- Exam 1, Chp. 15 S 3
177
Anatomy
Undergraduate 1
02/09/2014

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Term
Which structure, found along the inner margin of the lid, secretes a lipid-rich product that keeps the eyelids from sticking together?
Definition
tarsal (Meibomian) glands
Term
The cornea is part of which tunic?
Definition
fibrous
Term
Which color cones are most prevalent in the human eye?
Definition
red
Term
3 stages of eye development in embryo
Definition
1. optic vesicles
2. lateral bulges form optic cups
3. mesoderm isolates neural tissue from rest of body
Term
In the developing retina, ependymal cells on the outer wall of the optic cup develop into _________.
Definition
photoreceptors
Term
The site of sharpest vision is the
Definition
fovea
Term
Where do the photoreceptors of the eye synapse?
Definition
bipolar cells
Term
What comprises the innermost layer of cells in the retina?
Definition
ganglion cells
Term
The epithelia covering the inner surface of the eyelids and the anterior surface of the eye are called the palpebral and __________ conjunctivae, respectively.
Definition
ocular
Term
Circulation of the aqueous humor provides an important route for __________ in addition to forming a fluid _____.
Definition
nutrient and waste transport
cushion
Term
The __________ and transparency of the cornea are vital to eye function as it permits the entry of light into the eye.
Definition
clarity
Term
In the eye, light from each point of an image is focused on the retina, creating a miniature image of the original that is _________ and __________.
Definition
inverted
reversed
Term
The horizontal and __________ cells of the retina can facilitate or inhibit communication between photoreceptors and ganglion cells.
Definition
amacrine
Term
When light strikes a visual pigment, the retinal molecule changes shape, which changes the __________ of the outer segment.
Definition
permeability
Term
In the condition called __________, when the ciliary muscle is relaxed and the lens is flattened, the image of a distant object will be focused on the retina's surface.
Definition
emmetropia
Term
transparent area on the anterior surface of the eye
Definition
cornea
Term
Connection between the two eyelids on the lateral end
Definition
Lateral canthus
Term
A mucous membrane covered by a specialized stratified squamous epithelium
Definition
Conjunctiva
Term
Contains glands, which produce the thick secretions that contribute to the gritty deposits that sometimes appear after a good night's sleep
Definition
Lacrimal caruncle
Term
Through its continual blinking, it functions in keeping the surface of the eye lubricated, and it removes dust and debris
Definition
palpebra
Term
The gap that separates the free margins of the upper and lower eyelids
Definition
Palpebral fissure
Term
In the developing retina, ependymal cells on the inner wall of the optic cup develop into _________.
Definition
pigment cells
Term
Neural tissue of the outer wall of the optic cup forms layers of _____, _____, and _____.
Definition
neurons
ganglion cells
specialized glial cells
Term
The two palpebrae connect medially at the _____.
Definition
medial canthus
Term
pocket created where the two conjuctivae become continuous
Definition
fornix
Term
lacrimal apparatus
Definition
produces, distributes, and removes tears; the constant tear flow helps keep conjunctival surfaces moist and clean
Term
6 components of the lacrimal apparatus
Definition
lacrimal gland, tear ducts, lacrimal puncta, lacrimal canaliculi, lacrimal sac, and the nasolacrimal duct
Term
lacrimal gland
Definition
produces tears
Term
tear properties
Definition
slightly alkaline and contain antibacterial enzyme lysozyme and antibodies that attack pathogens before they enter the body
Term
tear duct properties
Definition
there are 10-12; deliver tears from lacrimal gland to the space behind the upper eyelid
Term
lacrimal puncta
Definition
2 small pores the drain the lacrimal lake
Term
lacrimal canaliculi
Definition
small canals that connect the lacrimal puncta to the lacrimal sac
Term
lacrimal sac
Definition
small chamber within the lacrimal sulcus of the orbit
Term
nasolacrimal duct
Definition
originates at the inferior tip of the lacrimal sac and passes through the nasolacrimal canal to deliver tears to the nasal cavity
Term
Where does the nasolacrimal duct empty?
Definition
into the inferior nasal meatus (narrow passageway inferior and lateral to the inferior nasal concha)
Term
pinkeye
Definition
conjunctivitis; results from damage to and irritation of the conjunctival surface
Term
The redness of pinkeye is due to what?
Definition
dilation of blood vessels deep to the conjunctival epithelium; the cornea isn't red because it's avascular
Term
6 extrinsic muscles of the eye and movements
Definition
superior rectus (elevates eye), inferior rectus (depresses eye), lateral rectus (moves eye laterally), medial rectus (moves eye medially), superior oblique (moves eye down and laterally), inferior oblique (moves eye up and laterally)
Term
sty
Definition
quick, painful, pimple-like infection on the eyelid
Term
chalazion
Definition
blocked gland that is irritated and red but not too painful, and it gets hard from secreted lipid
Term
tunics
Definition
the three layers of the eye (fibrous, vascular, and neural)
Term
fibrous tunic
Definition
outermost layer consisting of the cornea and sclera
Term
functions of the fibrous tunic
Definition
provides mechanical support and physical protection; serves as the attachment site for the eye muscles
Term
corneal limbus
Definition
the border of the continuous sclera and cornea
Term
Which part of the fibrous tunic aids in the focusing process?
Definition
the curvature of the cornea
Term
vascular tunic
Definition
aka uvea; contains numerous blood vessels and the intrinsic muscles of the eye
Term
functions of the vascular tunic
Definition
provides a route for the blood vessels and lymphatics that supply the tissues of the eye, regulates the amount of light that enters the eye, secretes and reabsorbs aqueous humor, and controls the shape of the lens (imp. in focusing)
Term
3 eye structures in the vascular tunic
Definition
iris, ciliary body, and choroid
Term
iris
Definition
colored part of the eye; visible through the transparent corneal surface; contains blood vessels, pigment cells, and layers of smooth muscle fibers
Term
What does the iris do?
Definition
contraction changes the diameter of the pupil
Term
ciliary body
Definition
thickened region that bulges into the interior of the eye that supports the lens and controls its shape
Term
What are the ligaments attached to the ciliary body, and what do they do?
Definition
suspensory ligaments that extend to the lens to hold it in place posterior to the pupil
Term
choroid
Definition
vascular layer right inside of the sclera that contains an extensive capillary network that delivers O2 and nutrients to neural tissue in the neural tunic
Term
neural tunic
Definition
aka retina; innermost layer of the eye consisting of a thin outer layer and thick inner layer
Term
outer layer of neural tunic
Definition
pigmented layer that absorbs light
Term
inner layer of neural tunic
Definition
neural layer, contains the photoreceptors
Term
The interior of the eye is divided into 2 _____ by the _____ and the _____.
Definition
cavities
ciliary body
lens
Term
anterior cavity
Definition
smaller, has aqueous humor, and is in front of lens; divided into the anterior chamber (cornea to iris) and posterior chamber (iris to ciliary body and lens)
Term
posterior cavity
Definition
large, behind the lens; most of the volume is taken up by the vitreous body or humor
Term
eye color is determined by
Definition
genes that influence density and distribution of melanocytes; density of pigmented epithelium (if light can pass through, eye appears blue)
Term
If there are an increased number of melanocytes on the iris, the eye appears _____.
Definition
darker- green, brown, and black have increasing numbers
Term
properties of the iris
Definition
body has highly vascular, pigmented, loose connective tissue; anterior surface has no epithelial covering; posterior surface covered by pigmented epithelium that's part of the neural tunic
Term
The anterior surface of the iris is covered by what?
Definition
an incomplete layer of fibroblasts and melanocytes
Term
What is the bulk of the ciliary body made of?
Definition
ciliary muscle- smooth muscular ring that projects into the interior surface of the eye
Term
ciliary processes
Definition
folds of epithelium covering the ciliary muscle
Term
ora serrata
Definition
jagged anterior edge of the thick inner portion of the neural tunic, part of the pigmented layer
Term
Which layer of the eye continues anteriorly across the posterior surface of the iris?
Definition
pigmented outer layer of the neural tunic
Term
aqueous humor circulation
Definition
ciliary body to posterior chamber through pupil to anterior chamber to canal of Schlemm to collecting channels and then delivered to veins of sclera
Term
The fluid pressure of which humor retains the eye's shape?
Definition
aqueous
Term
tonometry
Definition
procedure that measures the eye's intraocular pressure within the anterior chamber
Term
normal intraocular pressure
Definition
12-21 mmHg
Term
How and at what rate does aqueous humor form?
Definition
through active secretion by epithelial cells of ciliary body's cell processes at the rate of 1-2 microliters/min.
Term
What does the aqueous humor resemble?
Definition
CSF
Term
The canal of Schlemm is also called what?
Definition
the scleral venous sinus
Term
canal of Schlemm
Definition
passageway extending completely around the eye at the level of the corneal limbus
Term
glaucoma
Definition
when aqueous humor isn't adequately reabsorbed, internal pressure builds, and the retina is eventually damaged, sometimes to the point of blindness
Term
Which structure permits the entry of light into the eye?
Definition
the cornea
Term
The lens has a _____ layer of cells surrounded by _____.
Definition
concentric
dense fibrous capsule
Term
The cells of the lens are _______.
Definition
slender, elongate, and filled with crystallines
Term
crystallines
Definition
transparent proteins of the lens responsible for both clarity and focusing power of the lens
Term
What is the primary function of the lens, and how is this accomplished?
Definition
to focus the visual image on the photoreceptors by changing its shape
Term
The tension in the suspensory ligaments resists the tendency of the lens to do what?
Definition
have a spherical shape
Term
The retina contains what types of cells?
Definition
photoreceptors, pigment cells, supporting cells, and neurons
Term
Where are the blood vessels that provide nutrients to all structures within the eye located?
Definition
the choroid
Term
What is the sclera made up of?
Definition
dense fibrous connective tissue containing collagen and elastic fibers
Term
Where is the sclera thickest and thinnest?
Definition
thickest over posterior surface of the eye, near the exit of the optic nerve; thinnest over the anterior surface
Term
What is the function of the sclera?
Definition
stabilizes the shape of the eye during eye movements
Term
Where do the extrinsic muscles of the eye insert?
Definition
On the sclera, blending their collagen fibers together
Term
What control the amount of light entering the eye and passing through the lens?
Definition
the 2 layers of the iris' pupillary muscles
Term
The intrinsic eye muscles are controlled by which part of the nervous system?
Definition
the ANS
Term
The pupils _____ during parasympathetic activation and _____ during sympathetic activation.
Definition
constrict
dilate
Term
pupillary dilator muscles
Definition
activate in dim light; extend radially away from the edge of the pupil
Term
pupillary constrictor muscles
Definition
activate in bright light; form concentric circles around pupils
Term
Where is the highest concentration of photoreceptors?
Definition
on the fovea (site of sharpest vision, where an image falls when we are looking directly at it)
Term
When is light refracted?
Definition
When it passes between mediums of different densities
Term
When does the greatest amount of refraction occur, and what is this called?
Definition
when light passes from air to the corneal tissues (density like water); static refraction
Term
dynamic refraction
Definition
more refraction that occurs at the lens when light has passed from the aqueous humor (b/c lens is relatively dense)
Term
focal distance
Definition
distance between the center of the lens and an objects focal point (specific point of intersection on the retina), determined by the distance from and object to the lens and the shape of the lens
Term
A closer light source = _____ focal distance.
Definition
longer
Term
A rounder lens = _____ focal distance.
Definition
shorter
Term
accomodation
Definition
images are focused on the retina by the changing shape of the lens to keep the focal distance constant
Term
For close vision, the ciliary muscle is _____, and the lens is _____.
Definition
contracted
rounded
Term
When the ciliary muscle contracts, the ciliary body does what?
Definition
moves toward the lens the reduce the tension in the suspensory ligaments
Term
What does the lens do for close vision?
Definition
its elastic capsule pulls it into a more spherical shape, which increases its refractive power, which gives it the ability to focus light from nearby objects onto the retina
Term
For distance vision, the ciliary muscle is _____, and the lens is _____.
Definition
relaxed
flattened
Term
When the ciliary muscle is relaxed, the ciliary body does what?
Definition
pulls the suspensory ligaments at the circumference of the lens, which flattens it
Term
Is the greatest amount of refraction required near or far objects?
Definition
near
Term
near point of vision
Definition
the inner limit clear vision that is determined by the degree of elasticity in the lens; increases in distance with age (7-9 cm for children, 15-20 cm for young adults, 83 cm for 60 yr olds)
Term
retinal pigmented epithelia
Definition
pigmented part of the retina that absorbs light that passes through the neural part, preventing light from bouncing back and producing visual echoes
Term
The RPE also has important _____ with the retina's light receptors that are located in the neural part.
Definition
biochemical reactions
Term
The neural part of the retina contains what types of cells that do what?
Definition
photoreceptors, supporting cells, and neurons that perform preliminary processing and integration of visual info
Term
Which part of the retina (specifically) contains the photoreceptors?
Definition
the outermost layer of the neural part, closest to the pigmented part
Term
ganglion cells
Definition
form the innermost layer of cells in the neural part of the retina; receive visual info from bipolar cells and amacrine cells and transmit it to the brain
Term
Ganglion axons converge at the _____ to form the _____.
Definition
optic disc
optic nerve (CNII)
Term
blind spot
Definition
the optic disc has no photoreceptors, so an image falling here can't be detected
Term
rods
Definition
photoreceptors that don't discriminate among colors of light (monochromatic) and are highly sensitive, so they see in dim light
Term
cones
Definition
photoreceptors for color vision that give us sharper, clearer images than rods do, but they require more intense light
Term
Photoreceptors synapse with _____ on _____.
Definition
neurons called bipolar cells
ganglion cells
Term
What do horizontal and amacrine cells do?
Definition
facilitate or inhibit communication between photoreceptors and ganglion cells, leading to altered sensitivity of the retina; play important role in eye's adjustment to dim or brightly lit environments
Term
Where are horizontal cells located?
Definition
a network of them extends across the outer portion of the retina at the level of the synapses between photoreceptors and bipolar cells
Term
Where are amacrine cells located?
Definition
a layer of them occurs where bipolar cells synapse with ganglion cells
Term
How many cones and rods does the retina have?
Definition
6 million cones and 125 million rods
Term
Where are the densities of cones and rods at a max?
Definition
cones: fovea, rods: lateral and nasal borders
Term
Where are there no rods?
Definition
at the fovea
Term
visual acuity
Definition
sharpness of vision, directly correlated with cone density
Term
macular degeneration
Definition
macula doesn't work the best, and the photoreceptors start to die, leading to lesions and loss of vision; dry: RPE isn't working, wet: blood vessels are growing in
Term
Where does photoreception occur?
Definition
at the outer segment of rods and cones
Term
Light energy is in the form of _____.
Definition
radiant energy
Term
What wavelengths are our eyes sensitive to?
Definition
400-700 nm (spectrum of visible light)
Term
The outer segments of rods and cones have _____ that contain _____.
Definition
membranous plates and discs
visual pigments (special organic compounds)
Term
What absorbs photons that aren't absorbed by visual pigments?
Definition
pigment epithelium
Term
The pigment epithelium has _____.
Definition
melanin granules
Term
The outer segment of the pigment epithelium has what (having to do with cones and rods)?
Definition
cones with infolding discs of the plasma membrane and rods that are independent entities
Term
The inner segment of the pigment epithelium contains what?
Definition
major organelles
Term
The inner segment of the pigmented epithelium is responsible for what?
Definition
all cell functions other than photoreceptors
Term
What are visual pigments derived from?
Definition
the compound rhodpsin, which is visual purple (which is made of the protein opsin bound to the pigment retinal)
Term
In photoreception, when light strikes a visual pigment, retinal molecule does what?
Definition
changes shape, which leads to a change in permeability of outer segment
Term
What is the key to transduction in the eye?
Definition
permeability because it converts light energy into a nerve impulse
Term
Part 1 of the photoreception process
Definition
1. light is absorbed -> retina changes to a more linear shape -> activation of opsin
2. opsin activation changes the permeability of the outer segment to Na+ -> rate of neurotransmitter release by inner segment at its synapse with a bipolar cell
3. change in bipolar cell activity are detected by 1+ ganglion cells
Term
What does the location of the stimulated ganglion cells indicate?
Definition
the specific portion of the retina stimulated by arriving photons
Term
Part 2 of the photoreception process
Definition
4. rhodopsin absorbs photon and begins to breakdown into retinal and opsin (bleaching)
5. retinal converted to original shape (requires ATP)
6. retinal recombines with opsin -> rhodopsin now ready to repeat cycle
Term
What happens to photoreceptors during regeneration?
Definition
they are inactivated (after exposure to bright light)
Term
What are the three types of cones and their abundance?
Definition
blue (16%), green (10%), and red (74%)
Term
What is different about each type of cone?
Definition
they each have a different form of opsin that is sensitive to a different range of wavelength
Term
What is perceived when all three types of cones are stimulated?
Definition
white
Term
If rods but not cones are stimulated, what is perceived?
Definition
white
Term
What does color blindness result from?
Definition
lack of 1 of more cone pigments
Term
The most common forms of color blindness are _____.
Definition
sex linked
Term
What type of color blindness is very rare?
Definition
total
Term
partial color blindness
Definition
lack either red or green cones; 2% of males
Term
visual pathways
Definition
distribute info from each eye to both cerebral hemispheres
Term
Where do visual pathways begin?
Definition
at photoreceptors in the retina
Term
What does each photoreceptor do, and what happens when they're stimulated?
Definition
monitors a specific receptor field
passes the info through a bipolar cell and to a ganglion cell
Term
How many ganglion cells are there?
Definition
~ 1 million
Term
After the optic nerve penetrates the wall of the eye, where does it go?
Definition
the diencephalon (the optic nerves reach it at the optic chiasm)
Term
How do the fibers proceed from there?
Definition
Half go to the lateral geniculate nucleus on the same side of the brain, and half cross over to opposite side
Term
Where does the visual info go from the lateral geniculate nucleus?
Definition
the occipital cortex of the cerebral hemisphere on that side
Term
optic radiation
Definition
the bundle of projection fibers linking each lateral geniculate nucleus with the visual cortex
Term
The fovea of each eye are about ____ cm apart, so _____.
Definition
5-7.5
each eye receives a slightly different image and the visual images overlap
Term
The left cortex gets ____, and vice versa.
Definition
the right visual field
Term
The basic (3 way) visual path is what?
Definition
receptors -> bipolar cells -> ganglion cells
Term
What can accommodation problems result from?
Definition
abnormalities in the cornea, lens, or the shape of the eye
Term
What is normal vision called?
Definition
emmatropia
Term
myopia
Definition
nearsightedness; the image of a distant object is projected in front of the retina due to a deep eyeball or too great of a lens curvature
Term
How is myopia treated?
Definition
diverging lenses (concave surface that spreads light rays apart as if the object were closer)
Term
hyperopia
Definition
farsightedness; too shallow of an eyeball or too flat of a lens, so the ciliary muscle must contract to focus even a distant object on the retina, and at close range the lens can't provide enough refraction to focus an image on the retina
Term
How is hyperopia treated?
Definition
with a converging lens (convex surface that provides additional refraction needed for focusing on a close object)
Term
photorefractive keratectomy (PTK)
Definition
computer-guided laser shapes the cornea to exact specifications; tissue is removed down to about 10% of the cornea, and it takes < 1 minute
Term
laser-assisted in-situ keratomiteusis (LASIK)
Definition
interior layers of the cornea are reshaped and covered by a flap of the normal corneal epithelium; most common refractive surgery, and ~70% of patients achieve normal vision
Term
cataract
Definition
lens loses transparency (opaque) from injury, radiation, or a reaction to drugs
Term
senile cataracts
Definition
most common type; due to old age
Term
How can a damaged lens from cataracts be fixed?
Definition
it can be replaced by a synthetic lens
Term
bleaching
Definition
a process in photoreception where rhodopsin absorbs photon and begins to breakdown into retinal and opsin
Term
astigmatism
Definition
irregularities/unequal curvature of the lens or cornea that causes blurred vision
Term
presbyopia
Definition
elasticity of the lens decreases with age, which makes it harder to focus for near vision
Term
accommodation
Definition
alteration in the curvature of the lens to focus an image on the retina
Term
cranial nerve of each extrinsic eye muscle
Definition
superior rectus (III), inferior rectus (III), medial rectus (III), lateral rectus (VI), superior oblique (IV), inferior oblique (III)
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