Vision Flashcards
(184 cards)
1
Q
name the two main processes involved in vision.
A
- light energy is transduced into neural activity
2. neural activity is processed by the brain
2
Q
name the 4 things human visual systems permit light reflected off distant objects to be…
A
- 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
3
Q
light entering the eye is focused on the ________
A
retina
4
Q
retina converts light energy into…
A
neural energy
5
Q
axons of the retinal neurons are bundled to form the…
A
optic nerves
6
Q
visual information is distributed to…
A
several brain structures that perform different functions
7
Q
light rays must be ___ or ________ by the cornea
A
bent; refracted
8
Q
what is the purpose of the refracting of light?
A
in order for it to focus on the retina
9
Q
name the first sequence of event:
A
- light entering the eye is focused on the retina
10
Q
name the second sequence of events:
A
retina converts light energy into neuronal activity
11
Q
name the third sequence of events:
A
axons of the retinal neurons are bundled to form the optic nerves
12
Q
name the fourth sequence of event:
A
visual information is distributed to several brain structures that perform different functions
13
Q
define pupil
A
opening that allows light to reach retina
14
Q
define iris
A
circular muscle that controls the diameter of the pupil
15
Q
define aqueous humor
A
fluid behind the cornea
16
Q
define sclera
A
the outermost layer of the eye
17
Q
define extraocular muscles
A
attached to the eye and skull and allow movement
18
Q
define conjunctiva
A
membrane inside the eyelid attached to the sclera
19
Q
define optic nerve
A
axons of the retina leaving the eye
20
Q
define cornea
A
transparent surface covering the iris and pupil
21
Q
name the 6 muscles that surround the eye
A
superior rectus m. inferior rectus m. medial rectus m. lateral rectus m. superior oblique m. inferior oblique m.
22
Q
another name for the optic disk is?
A
blind spot
23
Q
the blood vessels of the eye originate where?
A
optic disk
24
Q
the optic nerves leave through what?
A
optic disk
25
true or false: the optic disk contains photoreceptors.
false
26
define macula
area of the retina responsible for central vision
27
define fovea
center of the retina
28
where are most of the cones located at?
fovea
29
exactly where is the fovea located at?
the very center of the macula
30
the very center of the macula is located at
it's the avascular zone just temporal to the optic nerve head
31
the fovea has a white dot called the...
foveal light reflex
32
name the things the fovea is responsible for.
for your color vision and the fine things you see
33
the small area just around the fovea is called the _____
foveola
34
define lens
transparent surface that contributes to the formation of images
35
what do ciliary muscles do?
change the shape of the lens and allow focusing
36
the vitreous humor is what than the aqueous humor?
more sticky than the aqueous humor
37
where is the vitreous humor located at?
between the lens and the retina
38
what is the main purpose of the vitreous humor?
to provide the eye with its spherical shape
39
the ______ is the innermost layer of cells at the back of the eye
retina
40
what is the main function of the retina?
transduces light energy into neural activity
41
name the 3 processes of image formation
1. Refraction by the cornea
2. Accommodation by the lens
3. Pupillary light reflex
42
the refraction caused by the cornea aids in...
image formation
43
when refracting distant objects, light runs in...
parallel lines
44
light rays slow down because of what?
hitting the cornea and aqueous humor
45
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
46
define focal distance
it is the distance between the refractive surface and where the light rays converge
47
the focal distance is dependant on what?
the curvature of the cornea
48
accommodations by the lens avoids what?
blurry vision
49
when viewing an object within 9 meters, light rays...
do not travel in parallel
50
when viewing objects within 9 meters, what is most likely to happen to the light rays?
they will eventually diverge
51
what does the lens add?
refractive power
52
how do the lens add refractive power?
by changing its shape
53
when the ciliary muscles' tension on the suspensory ligaments is released, what happens?
the lens becomes rounded
54
why is having the lens rounded important?
because the greater the curvature the greater the refraction
55
what do the pupils contribute to?
the optical qualities of the eye
56
the pupil adjusts for what?
for different light levels
57
what does pupillary light reflex contribute to?
simultaneous focusing on near and distant objects
58
what does accommodation do exactly?
it alters light rays that would otherwise run in parallel
59
when accommodation occurs, what is happening regarding the light rays?
they are no longer focused on the retina by the cornea
60
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
61
True or False: the light is focused after the aperture of the pupil is closed
false
62
define visual field
total space that can be viewed by the retina
63
what is the total degree of vision?
150 degrees
64
150 degrees can be divided into:
90 on temporal side
| 60 on the nasal side
65
the image on the back of the retina is...
reversed and inverted
66
define emmetropia
parallel light rays are focused on the retina without accommodation
67
emmetropia can also be called
normal vision
68
define hyperopia
the image is focused at a point behind the retina because the eyeball is too short
69
what is another term for hyperopia
farsightedness
70
hyperopia can be corrected how?
with a convex lens
71
define myopia
light rays converge in front of the retina because the eyeball is too long
72
how can myopia be corrected?
with concave lens
73
specialized cells of the retina do what?
convert light energy into neural activity
74
name the five main cell types found in the retina
1. photoreceptors
2. bipolar cells
3. ganglion cell
4. horizontal cells
5. amacrine cells
75
define photoreceptors
the only light sensitive cells in the retina
76
photoreceptors are either...
rods or cones
77
what do bipolar cells do?
connect photoreceptors to ganglion cells
78
what do ganglion cells do?
fire action potential and send axons to the brain
79
what do horizontal cells do?
receive inputs from photoreceptors and project laterally to bipolar cells
80
what do amacrine cells do?
receive inputs from bipolar cells and project laterally to ganglion cells
81
name the 5 layers of the retina from innermost to outermost
1. ganglion cell layer
2. inner plexiform layer
3. bipolar layer (inner nuclear)
4. outer plexiform layer
5. photoreceptor layer (outer nuclear)
pigmented layer
82
the ganglion cell layer contains
cell bodies of the ganglion cells
83
the inner nuclear layer contains
cell bodies of the bipolar cells
84
the outer nuclear layer contains
cell bodies of the photoreceptors
85
___________ are the only output cells
ganglion cells
86
what can ganglion cells only do?
produce action potentials
87
light travels through the other cell layers in order to...
reach the photoreceptors
88
at the back of the eye is a pigmented epithelium that...
absorbs any light not absorbed by the photoreceptors
89
there are two kind of photoreceptors based on
appearance and function
90
name the two kinds of photoreceptors
rods and cones
91
rods are...
long, cylindrical and have many disks
92
cones are
shorter, tapering outer segment, and has relatively fewer disks
93
rods are _____ to colors
not sensitive
94
rods are sensitive to
shades of grey and low light vision
95
where can rods be found?
macula
96
rods have a much higher...
pigment concentration
97
rods are ________________ to light than cones
1000x more sensitive
98
rods function in what kind of condition?
scotopic conditions
99
scotopic means
nighttime
100
name the pigment all rods have
rhodopsin
101
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
102
cones are used in what kind of condition
photopic
103
there are ___ types of cones
3
104
the three types of cones see what colors
blue
green
red
105
where can cones be found?
primarily in the fovea centralis and macula
106
cones use the visual pigment of __________
iodopsin
107
in the central retina, there is correspondence between...
photoreceptor and ganglion
108
in the peripheral retina, many photoreceptors do what?
converge on a single output ganglion cell
109
which is more sensitive to light: central or peripheral retina?
peripheral retina
110
photoreceptors transduce what?
light energy into changes in membrane potential
111
the first step in phototransduction, starts with events at...
G-protein coupled receptors
112
the binding of a neurotransmitter activates what?
G-proteins
113
G-protein activation stimulates...
various effector enzymes
114
the enzymes alters what?
the intracellular concentration of cytoplasmic second messengers
115
the 2nd messengers either directly or indirectly alters...
membrane ion channels which alter membrane potential
116
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
117
in complete darkness there is a steady influx of
Na+
118
the steady flow of Na+ does what?
depolarizes the photoreceptor membrane and thus NT is released
119
what is a general term for this?
dark current
120
Na+ channels responsible for this current are gated by...
cGMP (cyclic guanosine monophosphate)
121
where is cGMP produced?
in photoreceptors
122
thus, Na+ stays open in the ___
dark
123
why is it that in the dark, the Na+ stay open?
levels of cGMP rise, and keep the gates open
124
when light enters, cGMP is converted to
GMP (phosphodiesterase hydrolyxes cGMP)
125
the membrane ______________ in response to light
repolarizes
126
thus in the light, Na+ channels do what?
close
127
rhodopsin is
a photopigment
128
where is rhodopsin located?
in stacked disks in the outer segment of the rods
129
what is rhodopsin comprised of?
retinal and opsin
130
what does opsin do?
absorbs light
131
photoreceptors no longer respond at...
particular light intensities
132
the activation of rods by light does what to photopigment?
it bleaches it
133
cones are contain what?
opsin
134
the 3 kinds of opsin found in cones can be activated by
blue, green, red
135
what results from equal activation of all three
white
136
only _______ cells fire action potentials
ganglion
137
axons of ganglion cells form the ______
optic nerve
138
in response to dark, photoreceptors are depolarized and release NT called
glutamate
139
photoreceptors make _______ contact with bipolar cells
synaptic
140
how do photoreceptors contact bipolar cells?
through horizontal cells
141
bipolar cells, in response to the glutamate released by photoreceptors are either...
depolarized or hyperpolarized
142
so in darkness, the glutamate released by the photoreceptor causes...
EPSP in bipolar cell
143
if the bipolar cell is classified as "ON" it
hyperpolarizes when there is no light and depolarize when there is light
144
name the 2 types of ganglion cells
M type ganglion (large)
| P-type ganglion (small)
145
the signals goes from the retina to the
LGN (lateral geniculate nucleus) of the thalamus
146
the signal moves from the LGN towards
primary visual cortex
147
the signals moves from the primary visual cortex to
other cortical areas
148
name the 3 connections between the eyes and brain
optic nerve
optic chiasm
optic tract
149
left and right visual worlds are processed
contralaterally
150
information about the left visual field is processed by the
right side of the brain
151
information about the left that is seen by the right eye
does not cross over
152
the image is...
inverted and reversed
153
objects in the temporal part of the left hemifield are focused onto the
nasal retina of the left eye
154
objects in the nasal part of the right hemifield are focused on the
temporal retina of the left eye
155
fibers from the nasal retinas always...
cross over at the optic chiasm
156
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
157
if ultimately seen by the temporal retinas, they...
do not cross over because they are already viewing the opposite world
158
thus, when you view something from the nasal visual field, the image will be seen by the...
opposite eye's temporal retina
159
if an image is seen by the temporal visual field, the image will be seen by the....
same side's nasal retina
160
the primary target of the optic tract is
the LGN
161
10% of the optic tract goes to the
superior colliculus in the midbrain
162
name the other 2 places the optic tract will travel to.
hypothalamus (SCN-circadian rhythm)
| pretectum-reflex control of the pupil and lens
163
the lateral geniculate nucleus (LGN) is part of the
dorsal thalamus
164
the LGN is arranged in ___ layers
6
165
Layers 1 + 2 are the most
ventral
166
layers 1 + 2 contain....
large neurons
167
layers 1 + 2 are referred to as
magnocellular LGN layers
168
Layers 3 -6 contain what?
small neurons
169
what are layers 3-6 referred to as?
parvocellular LGN layers
170
how is the information from the 2 eyes kept separate?
they are projected to different layers of the LGN
171
the nasal retinal sees the temporal part of the hemifields and the information...
crosses over
172
Nasal retina projects to which layers?
1,4,and 6
173
temporal retina projects to which layers?
2, 3, and 5
174
Layer IV is subdivided into 3 separate layers....
IV A, B, and C
175
LGN projects primarily to which layer?
layer IVC
176
Layer IVC is divided into 2 tiers:
Alpha
| Beta
177
alpha corresponds with
movement
178
beta corresponds with
color
179
Magnocellular LGN layers project to
IVC alpha
180
Parvocellular LGN layers project to
IVC beta
181
Beta = blue =
color
182
Beta = blue = color = pigment =
P type
183
M type cells are large and they project to the magnocellular layers:
1 or 2
184
P type cells are small and they project to the parvocellular layers:
3, 4, 5, or 6
