ch. 9 - eye Flashcards
wavelength
distance between peaks
frequency
waves per second
amplitude
peak minus through
what is the visual range for humans?
400-700 nm
higher frequency equals…
higher energy
optics
the study of light rays and their interactions
ray
wave of electromagnetic radiation in vacuum traveling as a straight line
reflection
the bouncing of light rays off a surface; this is most of the light we see
absorption
transfer of light energy to a particle or surface
refraction
the bending of light rays that can occur when they travel from one transparent medium to another
pupil
opening that allows light to enter the eye and reach the retina; dark because of retinal pigments
iris
pigmentation provides the eye color
muscles around iris
control pupil size
cornea
transparent external surface that contains NO blood vessels
sclera
the white of the eye, forms the tough wall of the eyeball
extraocular muscles
move the eyeball in orbit (three pairs)
conjunctiva
a membrane that folds back from the inside of the eyelids and attaches to the sclera
optic nerve
carries axons from the retina and exits the back of the eye, passes through the orbit, and reaches the base of the brain by the pituitary gland
optic disc
where the optic nerve fibers exit the retina; there are blood vessels here; form blind spot
macula
the part of the retina for central vision
fovea
retina is the most thin here; good reference point
ophthalmoscope
a device that enables one to peer into the eye through the pupil to the retina
ciliary muscles
attached to the sclera; controls shape of the lens
aqueous humor
watery fluid that lies between the cornea and the lens
vitreous humor
lies between the lens and the retina; its pressure serves to keep the eyeball spherical
esotropia
cross-eyed
exotropia
wall-eyed
extraocular muscle disorders
input from one eye is suppressed
cataract
clouding of lens
glaucoma
increased intraocular pressure
retinitis pigmentosa
loss of peripheral and night vision
macular degeneration
loss of central vision
where is the site of most of the refractive power of the eyes?
cornea
what is the reactive power of the cornea?
42 diopters
what is the focal distance of the cornea?
2.4 cm (or 0.024m)
focal distance
the distance from the refractive surface to the point where parallel light rays converge
the tighter the curve of the cornea, the _____ the distance.
shorter
what does refractive power depend on?
the slowing of light at the air-cornea interface
accommodation
changing the shape of the lens; ciliary muscles contract, lens becomes more round, more curved
hyeropia
far-sightedness, convex
myopia
near-sightedness, concave
detached retina
retina pulls away from underlying wall of the eye from a blow to the head or by shrinkage of the vitreous humor
pupillary light reflex
produced by retina-brain stem connections
* consensual
construction of pupil…
increases depth of focus
visual acuity
ability to distinguish between near by points
20/20 = 0/083 degrees
left visual field is imaged on what side of the retina?
RIGHT
right visual field is imaged on what side of the retina?
left
what is the most direct pathway for visual info. to exit the eye?
photoreceptors to bipolar cells to ganglion cells
horizontal cells
receive input from photoreceptors and project neuritis laterally to influence surrounding bipolar cells and photoreceptors
amacrine cells
receive input from bipolar cells and project laterally to influence surrounding ganglion cells, bipolar cells, and other amacrine cells
what are the ONLY light sensitive cells in the retina?
photoreceptors
what are the ONLY source of output from the retina?
ganglion cells
how is the retina organized?
in layers (laminar)
how does light pass?
from vitreous humor through ganglion and bipolar cells BEFORE it reaches photoreceptors
what is the innermost layer of the retina?
ganglion cell layer
what is the second layer of the retina?
inner nuclear layer: bipolar, horizontal, and amacrine cells
what is the third layer of the retina?
outer nuclear layer: cell bodies of photoreceptors
what is the last layer of the retina?
layer of photoreceptor outer segments: light sensitive elements
pigmented epithelium
lies below the photoreceptors, plays a critical role in the maintenance of the photoreceptors and photopigments
inner plexiform layer
between the ganglion cell and inner nuclear cell layers, contains the synaptic contacts between bipolar, amacrine, and ganglion cells
outer plexiform layer
between the outer and inner nuclear layers, where photoreceptors make synaptic contact with the bipolar and horizontal cells
rod photoreceptors
long, cylindrical outer segment, containing many discs
cone photoreceptors
shorter, tapering outer segment with fewer discs
night vision (scotopic)
rods bc they are 1000X more sensitive
dayligt (photopic)
cones
does the peripheral retina have more rods or cones?
RODS
T or F: peripheral retina has more receptors per ganglion cell
true
is the peripheral retina more sensitive to light?
yes, bc rods are specialized for low lights and there are more photoreceptors feeding info to each ganglion cell
what area is specialized for high resolution?
fovea bc there are no rods
is the peripheral retina good for details?
NO, it is poor for details
__X more rods than cones
20
what is the Vm of the rod outer segment?
-30 mV
dark current
Vm due to special Na+ channels, opened by cGMP, made by guanylate cyclase
in light
light reduces levels of cGMP, Na+ channels close, photoreceptor cells hyperpolarize
what is light absorbed by in rod outer segment?
rhodopsin
receptor is phototransduction
opsin
- 7 TM G-protein receptor
- retinal bound
retinal
a derivative of vitamin A
bleaching
the absorption of light causes a change in the conformation of retinal so that it activates opsin
what does bleaching stimulate?
the G-protein transductin, which then activates phosphodiesterase (PDE) - which breaks down cGMP
amplification
allows detection of single photon
at what wavelength do rods respond to light?
500 nm
what does it mean when light becomes saturated?
additional light causes no more hyperpolarization
at what wavelength are blue cones maximally activated?
430 nm
at what wavelength are green cones maximally activated?
530 nm
at what wavelength are red cones maximally activated?
560 nm
what did young show about colors?
all colors of the rainbow, including white, could be created by mixing the proper ratio of red, green, and blue light
young-helmholtz trichromacy theory
the brain assigns colors based on comparison of the readout of the three cone types
dark adaptation
getting used to the dark, takes about 20-25 mins
what is dark adaptation due to?
- pupil dilation
- adjustment of retinal circuitry
- making new unbleached rhodopsin
light adaptation
reversing the changes in the retina that were accomplished by dark adaptation, takes 5-10 mins
what is Ca2+ role in light adaptation?
- inhibits guanylyl cyclase
- decreases PDE and photopigments response to light
who were the neuropysiologists behind retinal processing?
Hartline, Kuffler, and Barlow (1950)
what did they find with retinal processing?
ONLY ganglion cells fire action potentials
what did Dowling find in 1970s?
how retinal ganglion cells responses were affected by horizontal and bipolar cells
OFF-type bipolar cells
glutamate gated cation channels mediate a classical depolarizing EPSP from the influx of Na+
- “sign conserving”
- depolarize in dark
- hyperpolarize in light
ON-type bipolar cells
have G-protein-coupled receptors and respond to less glutamate
- “sign inverting”
- depolarize in light
- hyperpolarize in dark
receptive field
area of retina that when stimulated with light changes the cell’s membrane potential
receptive field center
a circular area of retina providing direct photoreceptor input
receptive field surround
surrounding area of retina providing input via horizontal cells
1 mm on the retina is how many degrees?
3.5
ON response
illumination of the center causes depolarization, while illumination of the surround will causes antagonistic hyoerpolarization
OFF response
cell is depolarized by a spot turning from light to dark in the center, it will be hyperpolarized by the same stimulus to the surround
ON center ganglion cells
is depolarized and responds with a barrage of action potentials when a small spot of light is projected onto the middle of its receptive field
what are ganglion cells most responsive to?
differences in illumination that occur within their receptive field
uniform illumination
the center and surround cancel to yield some low level response
P ganglion cells
- 90%
- contact one to a few cone bipolar cells
- small cells
- small concentric receptive field
- sustained
- slowly adapting response
- weak response to movement
M ganglion cells
- 5%
- synapse with many bipolar cells
- color insensitive
- large concentric receptor field
- transient
- rapid adapting response
- responds to movement across field
non M - non P cells
other 5%
which ganglion cells are sensitive to color?
P and some nonM-nonP
color-opponent cells
response in center to one wavelength is canceled by other wavelength in surround
red-green
P cells
blue-yellow
nonM-nonP
parallel processing
- information about depth
- light and dark information
- ganglion cells have different receptive fields and response properties
low resolution, large field
M cells
small fields, fine detail
P cells
