Chapter 9: The Eye Flashcards
the retina contains () that convert light energy into neural activity and detect the differences in intensity of light
photoreceptors
Axons of retinal neurons are bundled into ()
optic nerves
vision is primarily mediated by the ()
retina
First synaptic relay in the primary visual pathway; from here visual information ascends to cortex where it is interpreted and remembered
lateral geniculate nucleus (LGN)
Electromagnetic radiation that is visible to our eyes
Light
the distance between successive peaks
Wavelength
the number of waves per second
frequency
the difference between trough and peak
amplitude
Light Energy is proportional to ().
frequency
Short wavelength (high frequency): Gamma radiation, X-rays and (1) colors—(2) energy
- cool
- high
Longer wavelength (lower frequency): Radio waves and (1) colors—(2) energy
- hot
- low
Study of light rays and their interactions
Optics
Bouncing of light rays off a surface
Reflection
Transfer of light energy to a particle or surface
Absorption
Bending of light rays from one medium to another
Refraction
opening where light enters the eye
Pupil
() : white of the eye
Sclera
() : gives color to eyes
Iris
() : glassy transparent external surface of the eye
Cornea
(): bundle of axons from the retina
Optic nerve
small device (in eye clinics) that enable one to peer into the eye structure from pupil to retina
Ophthalmoscope
Blood vessels that originate from the () – where optic nerve connects to eye from brain -> Technically a blind spot
optic disk
()– place where light Is focused by cornea and lens; detects images that is sent to the brain -> not in peripheral vision
Macula
()– dark spot in the center of macula; Used as a reference point (to distinguish between nasal vs temporal retina)
Fovea
macular degeneration without bleeding
dry macular degeneration
macular degeneration with bleeding
wet macular degeneration
Cornea is the site of most of the () of the eyes
refractive power
(): the distance from the refractive surface to the point where parallel light rays converge
Focal distance
() – refractive power of cornea
Diopters
Changing () provides extra focusing power.
shape of lens
Muscles around the lens make the lens flat ((1), for far objects) or fat ((2), for near objects)
- low refractive power
- high refractive power
Connections between retina and brain stem neurons that control muscles around pupil
pupillary light reflex
Pupil contributes to optical function by ()
continuously adjusting to different ambient light levels
the pupillary light reflex is (): shining a light into only one eye causes the constriction of the pupils of both eyes
Consensual
Pupil similar to the () of a camera
aperture
Amount of space viewed by retina when eye is fixated straight ahead
Visual field
ability to distinguish two nearby points; “resolution” of the eye
Visual acuity
direct (vertical) pathway of vision
photoreceptors -> bipolar cells -> ganglion cells
Retinal processing is also influenced by ()
lateral connections
Receive input from photoreceptors and project to other photoreceptors (laterally) and bipolar cells -> interaction between different fields of photoreceptors
Horizontal cells
Receive input from bipolar cells and project to ganglion cells, bipolar cells, and other amacrine cells; can also mediate and regulate the activity of neighboring photoreceptor signals during visual processing
Amacrine cells
The only light-sensitive cells in the retina are the ().
photoreceptors
The () are the only source of output from the retina and the only retinal neurons that fire an action potential.
ganglion cells
laminar organization of the retina: seemingly () layers
inside-out
Light passes through () before reaching photoreceptors.
ganglion cells and bipolar cells
outermost layer of retina: ()
retinal pigmental epithelium
() of the reitna: contains portion of photoreceptors embedded into RPE; major site of photoactivation
outer segment
Bipolar, horizonal, amacrine cells are located laterally in () of the retina
upper layers
retina’s Innermost layer: () -> project axons into forebrain
ganglionic cell layer
Many nocturnal animals have reflective layer beneath photoreceptors, specifically RPE: (), which bounces light back at the photoreceptors.
tapetum lucidum
nocturnal animals with tapetum lucidum are more sensitive to low light levels at the expense of ()
reduced acuity
4 main regions of photoreceptor structure
- outer segment
- inner segment
- cell body
- synaptic terminal
(1) of photoreceptors: a stack of membranous disks that absorb light, contains (2) -> trigger changes in membrane potential
- outer segment
- photopigment
the cell body of a photoreceptor is found in the ()
inner segment
types of photoreceptors
rods and cones
photoreceptor with long, cylindrical outer segment with many disks
rods
photoreceptors with shorter, tapering outer segment with fewer disks
cones
(1) over 1000 times more sensitive to light than (2)
- rods
- cones
Differences in rods and cones: “()”
duplex retina
for organisms with duplex retina: at night, only (1) are active -> (2)
- rods
- scotopic
for organisms with duplex retina: At intermediate light level: rods and cones are active ()
mesopic
for organisms with duplex retina: Mostly (1) are active (2) at daytime
- cones
- photopic
Rods are more sensitive because they have a lot more ()
photopigment
Cones recognize (1)
Rods recognize (2) signals
- colors
- black and white
in humans, there are (more/less) rods than cones
more
Only the () are responsible for our ability to see color
cones
():
Higher ratio of rods to cones and of photoreceptors to ganglion cells
More sensitive to low light, but less sensitive to color discrimination
peripheral retina
Most of the cone cells are located in the (1), while most rod cells are in the (2)
- fovea
- peripheral retina
in a (), there are no photoreceptors
blind spot
In (1) retina, information from many photoreceptors is processed together; in (2) retina, 1:1 ratio of photoreceptor to ganglion cells
- periphery
- central
cross-section of the fovea shows a pit in retina where outer layers are pushed aside -> maximizes ()
visual acuity
central fovea has only () -> area of highest visual acuity
cones
In peripheral fovea, light can be scattered -> less visual acuity because ()
light does not directly stimulate photoreceptors
Phototransduction in rods is analogous to activity at () to cause a change in second messengers
G-protein-coupled neurotransmitter receptor
phototransduction in rods starts when light energy interacts with ()
photopigment
G protein is also involved in phototransduction; however the main difference is that in phototransduction, there is an (increase/decrease) in second messengers
decrease
For phototransduction in particular, ion channel response is a decrease in ()
Na+ conductance
the consequence of () in a photoreceptor is signal amplification—> allows us to have sensitivity to small amounts of light.
Light-activated biochemical cascade
in dark status, G proteins in the Light-activated biochemical cascade are coupled with () -> keeps G protein inactivated
rhodopsin
in a light status, G protein is activated due to conformational change in rhodopsin -> results in G protein being bound to ()
GTP
in rod phototransduction, bound GTP stimulates the activity of () -> breaks down cGMP to GMP and results in decreased cGMP level -> closes cGMP-gated Na+ channel and hyperpolarizes membrane potential of rod cell
phosphodiesterase
(): Rod outer segments are depolarized in the dark because of steady influx of Na+.
Dark current
Photoreceptors (depolarize/hyperpolarize) in response to light.
hyperpolarize
Types of photopigments in photoreceptors:
(1) – in rod cell
(2) – in cone cell
- Rhodopsin
- Opsin
Inside photopigments is a chemical called (), which is derived from vitamin A and undergoes conformational change under light stimulation -> causes activation (disruption) of photopigment and alters MP
retinal
Different opsins (correspond to different kinds of cone cells):
- Red (long wavelength)
- green (medium wavelength)
- blue (short wavelength)
Mediated by contributions of blue, green, and red cones to retinal signal
color perception
Mixing of red, green, and blue light causes () of the three types of cones -> perception of white
equal activation
Opponent colors:
red-green
yellow-blue
Opponent colors concept: Activation of red cones (activates/suppresses) activity of green cones and vice versa
suppresses
() -> allow us to see objects in a dark room more clearly
dark adaptation
factors in dark adaptation
- dilation of pupils
- regeneration of unbleached rhodopsin
- adjustment of functional circuitry
explain how adjustment of functional circuitry occurs
Ganglion cells get more input from rod cells instead of cone cells
Calcium’s role in light adaptation indirectly regulates levels of () -> regulation of ion channels
cGMP
specifically, Ca2+ that enters the photoreceptors via Na+ channels inhibits () -> synthesizes cGMP
guanylyl cyclase
closing of Na+ channels in photoreceptors decreases intracellular [Ca2+] -> activates guanylyl cyclase and ()
increases cGMP levels
inhibition of guanylyl cyclase serves as () that exists even without light stimulation
basal stimulation
when we move to a brighter environment, we are too sensitive to light -> Over time, MP is slowly () -> cells are able to respond to more light
depolarized and maintains a certain level
Effect of pupil size is the (different/same) on all photoreceptors
same
Area of retina where light changes neuron’s firing rate
receptive field
the receptive field changes in ()
shape and stimulus specificity
in a Receptive field: Stimulation in a small part of the visual field changes a cell’s ()
membrane potential.
role of horizontal cells in antagonistic relationship of center-surround receptive fields
responsible for inverting the response in the surround
ON bipolar cells have () receptors
metabotropic glutamate
bipolar cells that are depolarized by light in receptive field center and hyperpolarized by light in receptive field surround
ON bipolar cells
bipolar cells that are hyperpolarized by light in receptive field center and depolarized by light in receptive field surround
OFF bipolar cells
OFF bipolar cells have () receptors
ionotropic glutamate
Actual output from visual stimuli is interpreted as ()
ganglion cell response
types of ganglion cells
- M-type (magno, large) -5%
- P-type (parvo, small) - 90%
- nonM-nonP type - 5%
() is a specialized photopigment in ganglion cells -> can be stimulated by light directly -> direct depolarization
Melanopsin
melanopsin is found in (), and is involved in controlling circadian rhythms via SCN (subcortical visual area)
Intrinsically photosensitive retinal ganglion cells (ipRGCs)
different visual attributes are processed simultaneously using distinct pathways that are independent of each other
parallel processing
Different receptive fields and response properties of retinal ganglion cells: detecting subtle contrast, low resolution
M cells
Different receptive fields and response properties of retinal ganglion cells: small receptive field, discriminating fine details; red-green information
P cells
Different receptive fields and response properties of retinal ganglion cells: blue-yellow information
nonM–nonP cells
