Vision Flashcards
name the two main processes involved in vision.
- light energy is transduced into neural activity
2. neural activity is processed by the brain
name the 4 things human visual systems permit light reflected off distant objects to be…
- localized relative to the individual within his or her environment
- identified based on size, shape, color, and past experience
- perceived to be moving (or not)
- detected in a wide variety of lighting conditions
light entering the eye is focused on the ________
retina
retina converts light energy into…
neural energy
axons of the retinal neurons are bundled to form the…
optic nerves
visual information is distributed to…
several brain structures that perform different functions
light rays must be ___ or ________ by the cornea
bent; refracted
what is the purpose of the refracting of light?
in order for it to focus on the retina
name the first sequence of event:
- light entering the eye is focused on the retina
name the second sequence of events:
retina converts light energy into neuronal activity
name the third sequence of events:
axons of the retinal neurons are bundled to form the optic nerves
name the fourth sequence of event:
visual information is distributed to several brain structures that perform different functions
define pupil
opening that allows light to reach retina
define iris
circular muscle that controls the diameter of the pupil
define aqueous humor
fluid behind the cornea
define sclera
the outermost layer of the eye
define extraocular muscles
attached to the eye and skull and allow movement
define conjunctiva
membrane inside the eyelid attached to the sclera
define optic nerve
axons of the retina leaving the eye
define cornea
transparent surface covering the iris and pupil
name the 6 muscles that surround the eye
superior rectus m. inferior rectus m. medial rectus m. lateral rectus m. superior oblique m. inferior oblique m.
another name for the optic disk is?
blind spot
the blood vessels of the eye originate where?
optic disk
the optic nerves leave through what?
optic disk
true or false: the optic disk contains photoreceptors.
false
define macula
area of the retina responsible for central vision
define fovea
center of the retina
where are most of the cones located at?
fovea
exactly where is the fovea located at?
the very center of the macula
the very center of the macula is located at
it’s the avascular zone just temporal to the optic nerve head
the fovea has a white dot called the…
foveal light reflex
name the things the fovea is responsible for.
for your color vision and the fine things you see
the small area just around the fovea is called the _____
foveola
define lens
transparent surface that contributes to the formation of images
what do ciliary muscles do?
change the shape of the lens and allow focusing
the vitreous humor is what than the aqueous humor?
more sticky than the aqueous humor
where is the vitreous humor located at?
between the lens and the retina
what is the main purpose of the vitreous humor?
to provide the eye with its spherical shape
the ______ is the innermost layer of cells at the back of the eye
retina
what is the main function of the retina?
transduces light energy into neural activity
name the 3 processes of image formation
- Refraction by the cornea
- Accommodation by the lens
- Pupillary light reflex
the refraction caused by the cornea aids in…
image formation
when refracting distant objects, light runs in…
parallel lines
light rays slow down because of what?
hitting the cornea and aqueous humor
describe how light bends when it hits the cornea
perpendicular to the angle (radius of the cornea) between the curve of the cornea and the plane they are traveling on
define focal distance
it is the distance between the refractive surface and where the light rays converge
the focal distance is dependant on what?
the curvature of the cornea
accommodations by the lens avoids what?
blurry vision
when viewing an object within 9 meters, light rays…
do not travel in parallel
when viewing objects within 9 meters, what is most likely to happen to the light rays?
they will eventually diverge
what does the lens add?
refractive power
how do the lens add refractive power?
by changing its shape
when the ciliary muscles’ tension on the suspensory ligaments is released, what happens?
the lens becomes rounded
why is having the lens rounded important?
because the greater the curvature the greater the refraction
what do the pupils contribute to?
the optical qualities of the eye
the pupil adjusts for what?
for different light levels
what does pupillary light reflex contribute to?
simultaneous focusing on near and distant objects
what does accommodation do exactly?
it alters light rays that would otherwise run in parallel
when accommodation occurs, what is happening regarding the light rays?
they are no longer focused on the retina by the cornea
when the aperture of the pupil closes, what happens?
only light rays that are primarily in the center of the cornea and lens are allowed in
True or False: the light is focused after the aperture of the pupil is closed
false
define visual field
total space that can be viewed by the retina
what is the total degree of vision?
150 degrees
150 degrees can be divided into:
90 on temporal side
60 on the nasal side
the image on the back of the retina is…
reversed and inverted
define emmetropia
parallel light rays are focused on the retina without accommodation
emmetropia can also be called
normal vision
define hyperopia
the image is focused at a point behind the retina because the eyeball is too short
what is another term for hyperopia
farsightedness
hyperopia can be corrected how?
with a convex lens
define myopia
light rays converge in front of the retina because the eyeball is too long
how can myopia be corrected?
with concave lens
specialized cells of the retina do what?
convert light energy into neural activity
name the five main cell types found in the retina
- photoreceptors
- bipolar cells
- ganglion cell
- horizontal cells
- amacrine cells
define photoreceptors
the only light sensitive cells in the retina
photoreceptors are either…
rods or cones
what do bipolar cells do?
connect photoreceptors to ganglion cells
what do ganglion cells do?
fire action potential and send axons to the brain
what do horizontal cells do?
receive inputs from photoreceptors and project laterally to bipolar cells
what do amacrine cells do?
receive inputs from bipolar cells and project laterally to ganglion cells
name the 5 layers of the retina from innermost to outermost
- ganglion cell layer
- inner plexiform layer
- bipolar layer (inner nuclear)
- outer plexiform layer
- photoreceptor layer (outer nuclear)
pigmented layer
the ganglion cell layer contains
cell bodies of the ganglion cells
the inner nuclear layer contains
cell bodies of the bipolar cells
the outer nuclear layer contains
cell bodies of the photoreceptors
___________ are the only output cells
ganglion cells
what can ganglion cells only do?
produce action potentials
light travels through the other cell layers in order to…
reach the photoreceptors
at the back of the eye is a pigmented epithelium that…
absorbs any light not absorbed by the photoreceptors
there are two kind of photoreceptors based on
appearance and function
name the two kinds of photoreceptors
rods and cones
rods are…
long, cylindrical and have many disks
cones are
shorter, tapering outer segment, and has relatively fewer disks
rods are _____ to colors
not sensitive
rods are sensitive to
shades of grey and low light vision
where can rods be found?
macula
rods have a much higher…
pigment concentration
rods are ________________ to light than cones
1000x more sensitive
rods function in what kind of condition?
scotopic conditions
scotopic means
nighttime
name the pigment all rods have
rhodopsin
rhodopsin is a
purple pigment that when the eye is exposed to right light, it becomes bleached (inactive), after interval of darkness, it returns to color
cones are used in what kind of condition
photopic
there are ___ types of cones
3
the three types of cones see what colors
blue
green
red
where can cones be found?
primarily in the fovea centralis and macula
cones use the visual pigment of __________
iodopsin
in the central retina, there is correspondence between…
photoreceptor and ganglion
in the peripheral retina, many photoreceptors do what?
converge on a single output ganglion cell
which is more sensitive to light: central or peripheral retina?
peripheral retina
photoreceptors transduce what?
light energy into changes in membrane potential
the first step in phototransduction, starts with events at…
G-protein coupled receptors
the binding of a neurotransmitter activates what?
G-proteins
G-protein activation stimulates…
various effector enzymes
the enzymes alters what?
the intracellular concentration of cytoplasmic second messengers
the 2nd messengers either directly or indirectly alters…
membrane ion channels which alter membrane potential
name the events during phototransduction
light stimulation of photopigment activates G-proteins
G-proteins activate various effector enzymes
enzymes decrease intracellular concentrations of 2nd messengers (cGMP)
change in 2nd messenger concentration closes a Na+ channel
in complete darkness there is a steady influx of
Na+
the steady flow of Na+ does what?
depolarizes the photoreceptor membrane and thus NT is released
what is a general term for this?
dark current
Na+ channels responsible for this current are gated by…
cGMP (cyclic guanosine monophosphate)
where is cGMP produced?
in photoreceptors
thus, Na+ stays open in the ___
dark
why is it that in the dark, the Na+ stay open?
levels of cGMP rise, and keep the gates open
when light enters, cGMP is converted to
GMP (phosphodiesterase hydrolyxes cGMP)
the membrane ______________ in response to light
repolarizes
thus in the light, Na+ channels do what?
close
rhodopsin is
a photopigment
where is rhodopsin located?
in stacked disks in the outer segment of the rods
what is rhodopsin comprised of?
retinal and opsin
what does opsin do?
absorbs light
photoreceptors no longer respond at…
particular light intensities
the activation of rods by light does what to photopigment?
it bleaches it
cones are contain what?
opsin
the 3 kinds of opsin found in cones can be activated by
blue, green, red
what results from equal activation of all three
white
only _______ cells fire action potentials
ganglion
axons of ganglion cells form the ______
optic nerve
in response to dark, photoreceptors are depolarized and release NT called
glutamate
photoreceptors make _______ contact with bipolar cells
synaptic
how do photoreceptors contact bipolar cells?
through horizontal cells
bipolar cells, in response to the glutamate released by photoreceptors are either…
depolarized or hyperpolarized
so in darkness, the glutamate released by the photoreceptor causes…
EPSP in bipolar cell
if the bipolar cell is classified as “ON” it
hyperpolarizes when there is no light and depolarize when there is light
name the 2 types of ganglion cells
M type ganglion (large)
P-type ganglion (small)
the signals goes from the retina to the
LGN (lateral geniculate nucleus) of the thalamus
the signal moves from the LGN towards
primary visual cortex
the signals moves from the primary visual cortex to
other cortical areas
name the 3 connections between the eyes and brain
optic nerve
optic chiasm
optic tract
left and right visual worlds are processed
contralaterally
information about the left visual field is processed by the
right side of the brain
information about the left that is seen by the right eye
does not cross over
the image is…
inverted and reversed
objects in the temporal part of the left hemifield are focused onto the
nasal retina of the left eye
objects in the nasal part of the right hemifield are focused on the
temporal retina of the left eye
fibers from the nasal retinas always…
cross over at the optic chiasm
if its seen by the nasal world, it __________________ cause it already did switched by being seen by the opposite eye’s temporal retina
never decussates
if ultimately seen by the temporal retinas, they…
do not cross over because they are already viewing the opposite world
thus, when you view something from the nasal visual field, the image will be seen by the…
opposite eye’s temporal retina
if an image is seen by the temporal visual field, the image will be seen by the….
same side’s nasal retina
the primary target of the optic tract is
the LGN
10% of the optic tract goes to the
superior colliculus in the midbrain
name the other 2 places the optic tract will travel to.
hypothalamus (SCN-circadian rhythm)
pretectum-reflex control of the pupil and lens
the lateral geniculate nucleus (LGN) is part of the
dorsal thalamus
the LGN is arranged in ___ layers
6
Layers 1 + 2 are the most
ventral
layers 1 + 2 contain….
large neurons
layers 1 + 2 are referred to as
magnocellular LGN layers
Layers 3 -6 contain what?
small neurons
what are layers 3-6 referred to as?
parvocellular LGN layers
how is the information from the 2 eyes kept separate?
they are projected to different layers of the LGN
the nasal retinal sees the temporal part of the hemifields and the information…
crosses over
Nasal retina projects to which layers?
1,4,and 6
temporal retina projects to which layers?
2, 3, and 5
Layer IV is subdivided into 3 separate layers….
IV A, B, and C
LGN projects primarily to which layer?
layer IVC
Layer IVC is divided into 2 tiers:
Alpha
Beta
alpha corresponds with
movement
beta corresponds with
color
Magnocellular LGN layers project to
IVC alpha
Parvocellular LGN layers project to
IVC beta
Beta = blue =
color
Beta = blue = color = pigment =
P type
M type cells are large and they project to the magnocellular layers:
1 or 2
P type cells are small and they project to the parvocellular layers:
3, 4, 5, or 6
