Chapter 2 Flashcards
light
the spectrum of electromagnetic radiation that can be detected by a visual system
light can be conceptualized as a ______ (when moving around the world) or as a stream of _____ (when absorbed)
wave; photon
photons
quantum of electromagnetic radiation that has both particle and wave like properties
light obeys properties of _____ made up of ______
waves; photons
our visible portion is _____ when compared to the electromagnetic spectrum
tiny
absorbed
light is taken up and is not transmitted further
scattered
light is dispersed in an irregular/random fashion
how does scattered light gives the sky its color?
blue during the day as the sun is direct and not a lot of blue light is scattered
reddish orange at dawn/dusk as the sun is not direct and therefore scatters more
reflected
light is redirected, generally back the way it came
ex) mirror or lake on a calm day
transmitted
light is passed through a surface (without being reflected or absorbed)
ex) light through a glass window
refracted
light is altered as it passes through a medium
ex) light through the eye!
white light is made up of
all colors
cornea
the transparent “window” to the eye
first part of eye light hits
no blood vessels = clear
pupil
hole in musculature/iris that lets light through into the eye
iris
colored portion of the eye
muscular diaphragm surrounding the pupil that controls the amount of light by dilating or contracting
lens
curved structure that bends/focuses light onto the back of the eye
crystalline but also flexible
aqueous humor
fluid between the cornea and the lens
provides oxygen and nutrients to the cornea and lens while also removing waste
vitreous chamber/humor
the large open space of the eye is the chamber, filled with humor
80% of the eye
gel-like fluid that helps maintain eye shape
retina
light sensitive membrane at the back of the eye where photoreceptors are, which transduce light to electrochemical signals
where seeing begins
optic disc
the point on the eye where the optic nerve exits the eye
blind spot as it has no photoreceptors!
layers of the eye
sclera
- outer layer of the eye/the “white” of the eye
- supportive of vision
choroid
- middle layer filled with blood vessels to supply oxygen and nutrients to the retina
- supportive of vision
retina
- inner layer where photoreceptors are found
- contributed to vision
fundus
back part of the eye made up of:
retina
macula and fovea
optic disc
the path of light
1) cornea
2) pupil
3) lens
- image is flipped at this point
4) retina/macula/fovea
- here transduction occurs
the lens uses _______ to focus light onto the retina
refraction
the lens can be adjusted by the ______ _______ to alter is refractive power in a process called __________
ciliary muscle; accommodation
presbyopia
“old sight”
the age-related loss of accommodation, which makes it hard to focus on near objects
how the ciliary muscle works for close and far sight
for distance objects, the muscle relaxes making the zonules tighten and lens become thin
for near objects, the muscles contracts, zonules loosen and lens becomes thicker
emmetropia
eye correctly refracts light onto the retina
myopia
nearsightedness
light is focused in front of the retina and distant objects cannot be seen sharply
shape of eye with myopia
elongated eye
hyperopia
farsightedness
light is focused behind the retina and near objects cannot be seen sharply
shape of eye with hyperopia
shortened eye
astigmatism
unequal curving of one or more of the refractive surfaces of the eye, usually the cornea
resulting in multiple focal points on the retina instead of just one
spot in the eye with the highest concentration/densest of photoreceptors and highest acuity
fovea
acuity
sharpest detail
rods
specialized for night vision
respond well in low luminance conditions
do not process color
cones
specialized for color vision and acuity
respond well in daytime conditions
can remember C for Color
once transduced, neural signal travels back up from (1), to (2), to (3), to (4)
rods/cones
bipolar cells
ganglion cells
optic nerve
what shape does the fovea appear as and why?
divot, upper layers bend away from focal point which means fewer layers to travel through and a higher density of cones
where are cones and rods most present?
cones: fovea
rods: peripheral vision
the visual angle of an object is a function of both its _________ and _____ from the observer
actual size; distance
the fovea has ____ acuity while the periphery has _____ acuity
high; low
macular degreneration
a disease associated with aging that affects the macula/fovea and gradually destroys sharp central vision
causes central vision loss, resulting in a blind spot in the visual field called a scotoma
the fovea has ____ light sensitivity while the periphery has ____ light sensitivity
low; high
4 mechanisms for dark and light adaption
pupil dilation
photoreceptors and their replacement
duplex retina - rods/cones
neural circuitry beyond rods/cones
pupil dilation
the pupils size changes to adjust how much light is being let in
only a small part of light adaption, slow and only does so much
range of brightness
scotopic
cone threshold between
- no color vision and poor acuity
mesopic
rod saturation begins
- good color vision and best acuity
photopic
photopigments
class of proteins in rods and cones that absorb light and trigger a biochemical cascade that alters the electrical properties of the photoreceptors
finite in the moment but replenished over time
bleached
when photopigments are used, can’t detect light until replenished
when there are few photons available, we _________________. When there is a ton of light, we _________________
have lots of photoreceptors to process whats there; only process part and ignore the rest
cones replenish ______ and are _____ sensitive in the dark when compared to rods
faster; less
rods replenish ______ and are ______ sensitive in the dark when compared to cones
slower; more
why did pirates wear eye-patches?
to have a dark adapted eye for below deck!
if we were to rank portions of the retina from worst to best acuity, what relationship would be correct?
a) periphery is worse than fovea and macula. Fovea and macula are equal
b) periphery is worse than macula which is worse than fovea
c) periphery is worse than fovea which is worse than. the macula
d) periphery is similar to the macula, and both are worse than the fovea
b) periphery is worse than macula which is worse than fovea
structural/support features of the eye
sclera
choroid
aqueous humor
vitreous chamber/humor
what controls the lens shape?
ciliary muscle, connected to lens by the Zonules of Zinn (white strings)
passing on light parts of the eye
cornea
pupil
lens
transduction parts of the eye
retina
macula and fovea
optic disc
optic nerve
what does the inner segment of rods/cones do? outer segment?
inner - produces photopigments
outer - stores photopigments for transduction
photopigments contain opsins, which
determine the wavelength of light the photoreceptor responds to
action potentials are driven by __________ of the cell, allowing for _____________
depolarization; longer range communication
graded potentials
measuring amount of depolarization/hyperpolarization
found in photoreceptors and
the more depolarized the cell is, the _____ neurotransmitter it releases
more
photoreceptors release a neurotransmitter called
glutamate
when light is present, the photoreceptor is always _______
hyperpolarized
when the photoreceptor is hyperpolarized, there will be ____ glutamate released to the bipolar cells
less
bipolar cells
intermediary cell between photoreceptors and ganglion cells
graded potentials
divided by:
convergence/divergence
off/on
diffuse bipolar cell
periphery, receives input from many photoreceptors (usually rods)
high convergence (many photoreceptors are converging on a singular bipolar cell)
high: sensitivity and convergence
low: acuity
midget bipolar cell
fovea, receives input from a single cone and passes it on to a single ganglion
divergence/low convergence, 1:1 ratio
high: acuity
low: sensitivity and convergence
off bipolar cells
deactivate in the presence of light
receptors are excited by glutamate
photoreceptors are depolarized
more active in the dark
on bipolar cells
active in the presence of light
receptors are inhibited by glutamate
photoreceptors are hyperpolarized
more active in light
in on cells, light on –> (less/more) glutamate —> (depolarized/hyperpolarized) cell
less; hyperpolarized
when a photoreceptor is exposed to light, becomes hyperpolarized, and releases less glutamate to an ON bipolar cell, the bipolar cell becomes depolarized due to …
release from inhibition
on cells are inhibited by glutamate so if there is less glutamate they are released from their inhibition, allowing the cell to act
if a cone is in the dark, the photoreceptor is depolarized and releases more glutamate, which bipolar cell will release a signal?
off bipolar cell
if a cone is in the light, the photoreceptor is hyperpolarized and releases less glutamate, which bipolar cell will release a signal?
on bipolar cell
ganglion cells
final layer of the retina
uses action potential
primary divisions:
P vs. M cells
on-center vs. off-center
3 ways P and M ganglion cells differ
1) by the region of the brain they send their signal
2) by their size
3) by the type of bipolar providing input
M ganglion cells
large in size as they receive input from diffuse bipolar cells (same convergence (+), sensitivity (+) and acuity (-))
M means Massive
P ganglion cells
small in size as they receive input from midget bipolar cells (same convergence (-), sensitivity (-), and acuity (+))
P means Petite
makes up most ganglion cells as you need more since they are 1:1 ratio with bipolar cells
each layer of neural communication in the eyes through cones
photoreceptors, midget bipolar cells, P ganglion cells, small receptive fields (fovea)
each layer of neural communication in the eyes through rods
photoreceptors, diffuse bipolar cells, M ganglion cells, large receptive fields (periphery)
receptive fields
influence space that can influence a neuron
larger receptive fields = ___ acuity
lower
ganglion receptive fields are particularly coded to detect differences in the intensity of light, hence the need for …
“center-surround” receptive field
center-surround focuses on
contrast (differences between luminance of adjacent regions)
horizontal cells
part of lateral connection between photoreceptor cells + bipolar cells
allows the surround photoreceptors to inhibit whatever information it was getting from center (center-surrond)
on-center for lateral inhibition
if the light is hitting the center, the surround fails to inhibit it = light is perceived
if the light is hitting the surround, the center will be inhibited = light will not be perceive
off-center for lateral inhibition
if the light is hitting the center, the surround fails to inhibit it = light will not be perceived
if the light is hitting the surround, the center will be inhibited = light will be perceived
lateral inhibition
adjacent cells at the same level blocking/inhibiting each other’s effects
emphasizes priority of contrasts
explain why we can see dots in between black boxes
both eyes open:
- can see the dot when looking directly at the cross point and in your periphery b/c the periphery has larger receptive fields. the center is saying on but the surround are also being hit, causing lateral inhibition and perceived dots to appear
one eye open:
- receptive field shrinks causing you to not see dots directly at the cross section but still in your periphery
amacrine cells
horizontal connection between bipolar and ganglion cells
Which cells are responsible for lateral inhibition in the retina?
horizontal cells
when light hits a photoreceptor, it _________ and releases _____ glutamate
hyperpolarizes; less
which of the following is NOT an example of convergence?
1) multiple photoreceptors feeding input to a single bipolar cell
2) multiple bipolar cells feeding input to a single ganglion cell
3) multiple bipolar cells receiving input from a single photoreceptor
4) All are examples of convergence
3) convergence needs to be going from a single source to multiple
which of the following are not characteristics of cells in the fovea?
1) Show generally low convergence
2) Have relatively small receptive fields
3) have generally smaller bipolar and ganglion cells
4) all of the above are characteristic of foveal cells
4)
