Chapter 9: The Eye Flashcards
(119 cards)
1
Q
Retina:
A
the back of the eye that contains photoreceptors specialized to convert light energy into neural activity
2
Q
What part of the eye is able to distinguish light intensity? How?
A
retina
contained two overlapping retinas; one specialized for low light and the other for high light color detection
3
Q
Light rays travel in straight lines until they interact with the atoms and molecules of the atmosphere:
- […]
- […]
- […]
A
- reflection
- absorption
- refraction
4
Q
Define the following:
Reflection–
Absorption–
Refraction–
A
Re: bouncing of light rays at angles
Ab: transfer of light energy to a particle or surface
Ra: bending of light rays that occurs
5
Q
Blue pigment absorbs long wavelengths but […]. This is because some compounds absorb light energy in only a […] range of wavelengths, and reflect the […] wavelengths.
A
reflects short waves; limited; remaining
6
Q
During refraction, different mediums change the […].
A
speed of light
7
Q
The greater the difference between the speed of light…
A
the greater the angle of refraction
8
Q
Optics:
A
the study of light rays and their interactions
9
Q
Pupil:
A
opening that allows light to enter the eye and reach the retina
10
Q
Why is the pupil dark?
A
because of the light-absorbing pigments
11
Q
The pupil is surrounded by the […].
A
iris
12
Q
Iris:
A
pigmentation provides eye color
13
Q
How does the pupil change size?
A
the iris contains two muscles which change the size
14
Q
Cornea:
A
glassy covering of the eye that covers both the iris and pupil
15
Q
The cornea is continuous with the […].
A
sclera
16
Q
Sclera:
A
white of the eye that forms a tough wall of the eyeball
17
Q
The sclera sits on the […]
A
eyes orbit (bony eye socket)
18
Q
Extraocular muscles:
A
consists of three pairs which move the eyeball in orbit
19
Q
The extraocular muscles are inserted into the […] and it lies behind the […].
A
sclera; conjuctive
20
Q
Cojunctiva:
A
membrane folds back from the inside the eyelids and attaches to the sclera
21
Q
Optic nerve: carrying […] from the […] and exits the back of the eye.
A
axons; retina
22
Q
The optic nerve passes through the […] and reaches the base of the brain near the […].
A
orbit; pituitary gland
23
Q
What is the optic disk? What is the significance of this region of the eye?
A
where the optic nerve fibers exit the retina
there are no photoreceptors and thus no perception of light
24
Q
The cross-sectional view shows the […] taken by light as it passes through the […] towards the retina.
A
path; cornea
25
Cornea lacks [...] so it receives nourishment from the [...] of the [...]..
blood vessels; fluid; aqueous humor
26
Aqueous humor description:
watery fluid that lies between the cornea and the lens
27
Vitreous humor description:
viscous, jellylike that lies between the lens and the retina
28
What is the significance of vitreous humor?
contains the pressure that keeps the eyeball spherical
29
What separates the two fluids of the eye?
lens
30
Lens:
transparent feature located behind the iris
31
The lens is suspended by [...] called [...] fibers that are attached to [...].
ligaments; zonule; ciliary muscles
32
Ciliary muscles are attached to the [...] and form a [...] inside the eye.
sclera; ring
33
Refraction is done by what eye feature?
cornea
34
As light passes into a medium where its speed is slowed it will...
bend towards a line that is perpendicular to the border, or interface between the media
35
Focal distance:
the distance from the refractive surface to the point where parallel light rays converge
36
Focal distance depends on the [...] of the [...]. The tighter the [...] the [...] the focal distance.
curvature; cornea/lens; curve; shorter
37
Diopter:
unit of measurement for refractive power
38
Formula: Refractive power:
1 / focal distance (m)
Units: diopter
39
The cornea has a refractive power of [...].
What is the focal distance? What does this mean in terms of focus?
42 diopters
0.024 m; the light rays will be focused 0.024 m behind the corneal surface
**distance from the cornea to the retina
40
Refractive power depends on the [...] of light at the [...] interface.
slowing; air-cornea
41
Besides the cornea, what other feature contributes to the eye's refraction? How so?
lens
accommodation
42
The lens is involved in forming crisp images of objects located...
closer than about 9 m from the eye
43
Accommodation:
process of changing the shape of the lens; adding greater refractory power to bring diverging rays into focus
44
How is accommodation accomplished?
contracting and relaxing of the ciliary muscles
45
During accommodation, the ciliary muscle [...] and [...] in size, thereby making the area inside the muscle [...] and [...] the tension in the suspensory ligaments.
Consequently, the lens becomes [...] because of its natural [...].
This rounding [...] the curvature of the [...] surface, and [...] refractory power.
contracts; swells; smaller; decreasing
rounder and thicker; elasticity
increases; lens; increases
46
Relaxation of the ciliary muscle [...] the tension in the suspensory ligaments, and the lens is [...] into a [...] shape.
increases; stretched; flatter
47
What does the pupil do for optical function?
continuously adjusts for different ambient light levels
48
Pupillary light reflex:
control of the pupils constricting muscles by the connections between the retina and the neurons of the brain stem
49
What does it mean by the pupillary light reflex is consensual?
both eyes will change in pupil size even though only one eye has light shined at it
50
When the pupillary light reflex is not consensual, what does it indicate?
neurological disorders (brainstem)
51
Constriction of the pupil effect increases...
depth of focus
52
Visual acuity:
ability of the eye to distinguish two nearby points
53
What greatly factors in on visual acuity?
the spacing of photoreceptors in the retina and the precision of the eye's refraction
54
Visual angle:
distance across the retina in degrees
55
What is the most direct pathway for visual information to exit the eye?
photoreceptors --- bipolar cells --- ganglion cells --- AP --- optic nerve --- brain
56
What other cell types influence the retinal process?
1. horizontal cells
| 2. amacrine cells
57
Horizontal cells receive input from the [...] and influence surrounding [...].
Amacrine cells receive input from the [...] and influence surrounding [...].
photoreceptors; bipolar cells and photoreceptors
bipolar cells; ganglion cells, bipolar cells, and other amacrine cells
58
The only light-sensitive cells in the retina are [...]. All others are influenced only by [...].
photoreceptors; direct/indirect synaptic transmission with photoreceptors
59
The [...] are the only source of output from the retina. No other retinal cell type projects an axon through the [...].
ganglion cells; optic nerve
60
Cells in the retina are organized in [...].
layers
61
Light must pass from the vitreous humor through the [...] and [...] before it reaches the [...].
ganglion cells; bipolar cells; photoreceptors
62
In order to reach the photoreceptors, light must pass through retinal cells. How come there is no distortion of images?
retinal cells are transparent
63
List the layer organization of the retinal cells (from innermost to outermost) and include amacrine/horizontal:
1. ganglion cell
2. inner plexiform
* *AMACRINE CELLS
3. inner nuclear layer
* *HORIZONTAL CELLS
4. outer plexiform layer
5. outer nuclear layer
6. layer of photoreceptor outer segments
7. pigmented epithelium
64
The inside-out arrangement is advantageous because...
1. [...]
a. [...]
b. [...]
* * [...]
1. pigmented epithelium is below the photoreceptors
a. plays a critical role in the maintenance of the photoreceptors
b. absorbs any light that passes entirely through the retina
* *minimizes reflection of the light
65
What is within the inner nuclear layer?
contains the cell bodies of bipolar cells, amacrine cells, and horizontal cells
66
What is within the outer nuclear layer?
cell bodies of the photoreceptors
67
What is within the layer of photoreceptor outer segments?
light-sensitive elements of the retina
68
What is within the inner plexiform layer?
contains synaptic contacts between bipolar cells, amacrine cells, ganglion cells
69
What is within the outer plexiform layer?
photoreceptors make synaptic contact with the bipolar and horizontal cells
70
Four regions of every photoreceptor:
1. outer segment
2. inner segment
3. cell body
4. synaptic terminal
71
What are the two types of photoreceptors? How do they differ from one another?
R (5)
C (4)
1. rods
2. cones
R:
1. greater number of disks
2. higher photopigment concentration
3. 1000 times more sensitive to light than cones
4. only contributor to nighttime lighting/scotopic conditions
5. same photopigment
C:
1. fewer number of disks
2. bulk of work during the daytime lighting/photopic conditions
3. responsible for seeing color
4. three different types of photopigments
72
Retina is [...]-- a scotopic retina using only [...] and photopic retina using mainly [...].
duplex; rods; cones
73
What two characteristics does the peripheral retina have that make this arrangement more sensitive to light? Why is this the case?
1. higher ratio of rods to cones
2. higher ratio of photoreceptors to ganglion cells
SENSITIVE BC
1. rods specialized in low light
2. there are more photoreceptors feeding information to each ganglion cell
74
The region of the retina most highly specialized for high resolution is the [...].
fovea
75
Fovea is a [...] of the retina at the center of the [...].
In cross-section, the fovea appears as a [...]. This is due to the [...]. of the cells above the photoreceptors, allowing light to strike the [...] without passing through the [...] cell layers.
This maximizes visual acuity by [...] other cells that might scatter light and blur the image. The central fovea also is unique because it contains no [...]; all the photoreceptors are [...].
thinning; macula
pit; lateral displacement; photoreceptors; retinal
pushing aside; rods; cones
76
TRANSDUCTION IN RODS
Light stimulation of the photopigment activates [...] which in turn activates [...] that changes the cytoplasmic concentration of a [...].
This change causes a membrane ion channel to [...] and the [...] to change.
G-protein; effector enzymes; second messengers
close; membrane potential
77
TRANSDUCTION IN RODS
In complete darkness, the membrane potential of a rod is [...]. The reason for this is due to [...] through special channels in the [...].
-30 mV; steady Na+ influx; outer segment
78
TRANSDUCTION IN RODS
Dark current:
movement of positive charge across the membrane during the dark
79
TRANSDUCTION IN RODS
Dark current is [...] by the intracellular second messenger called [...] and is continually produced in the photoreceptor by [...] keeping [...] channels open.
gated; cyclic guanosine monophosphate; enzyme guanylyl cyclase; Na+
80
TRANSDUCTION IN RODS
In rods: Light [...] cGMP, cause the Na+ channels to [...] and the membrane potential becomes [...].
reduces; close; more negative
81
TRANSDUCTION IN RODS
Photoreceptors [...] in response to light.
hyperpolarize
82
TRANSDUCTION IN RODS
The hyperpolarizing response to light is initiated by...
the absorption of electromagnetic radiation by the photopigment in the membrane of the stacked disks in the rod outer segments
83
TRANSDUCTION IN RODS
In rods the photopigment that initiates the hyperpolarizing response is [...].
rhodopson
84
TRANSDUCTION IN RODS
Rhodopsin:
receptor protein with a pre-bound chemical agonist
85
TRANSDUCTION IN RODS
What is the receptor protein for rhodopsin?
What is the prebound agonist?
opsin
retinal
86
TRANSDUCTION IN RODS
Retinal:
derivative of vitamin A
87
TRANSDUCTION IN RODS
The absorption of light causes a change in the conformation of [...] so that it activates the [...] in opsin. This process is called [...].
retinal; G-protein complex; bleaching
88
TRANSDUCTION IN RODS
The bleaching of rhodopsin stimulates the G-protein [...] in the disk membrane which in turn activates the effect enzyme [...].
transducin; phosphodiesterase
89
TRANSDUCTION IN RODS
Phosphodiesterase:
effector enzyme that breaks down the cGMP
90
TRANSDUCTION IN RODS
The amplification consequence of transduction allows our visual system the ability to detect as little as...
a single photon
91
TRANSDUCTION IN CONES
Saturation causes...
no more hyperpolarization
92
Vison during the day depends entirely on the [...] whose photopigments require [...] to become [...].
cones; more energy (than rods); bleached
93
What is the major difference between the phototransduction in cones vs rods?
type of opsins in the membranous disks of the cone outer segments
94
TRANSDUCTION IN CONES
What are the three different types of opsins/photopigments for cones?
blue, green, red
95
TRANSDUCTION IN CONES
When are the cone opsins maximally activated?
B: 430 nm
G: 530 nm
R: 560 nm
96
TRANSDUCTION IN CONES
Young-Helmholtz trichromacy theory:
the theory that the brain assigns colors based on a comparison of the readout of the three types of cone photoreceptors
97
TRANSDUCTION IN CONES
The peak sensitivity of the rods is to a wavelength of about [...] perceived as [...].
500 nm; blue-green
98
The transition from all-cone daytime vision to all-rod nighttime vision is not [...] it takes about [...] minutes.
instantaneous; 20-25
99
Dark adaption:
getting used to the dark
100
How can dark adaption be explained?
1. dilation of the pupil allows more light to enter
| 2. light adaption
101
Light adaption:
reversing the changes in the retina that accompanied dark adaption
102
What concentration is a factor in the eye's ability to adapt to changes in light?
calcium
103
When you step out into bright light from a dark theater, initially the cones are [...].
The [...] helps a bit in reducing the light entering the eye. However, the most important change is the gradual [...] of the membrane back to about [...].
hyperpolarized
constriction of the pupil; depolarization; -35 mV.
104
Only [...] cells fire action potentials in the retina. All other cells respond to [...] when [...] changes in membrane potential.
ganglion; stimulations; graded
105
The most direct path for information flow in the retina:
cone photoreceptor---bipolar cell---ganglion cell
106
At each synaptic relay, the responses are modified by... (2)
1. lateral connections of horizontal cells
| 2. lateral connections of amacrine cells
107
What NT is released when a photoreceptor is depolarized?
AA glutamate
108
Photoreceptors are [...] in the dark and are [...] in the light.
depolarized; hyperpolarized
109
In the outer plexiform layer, each photoreceptor is in synaptic contact with two types of retinal neuron:
How is each significant?
1. bipolar cells
2. horizontal cells
B: creat direct pathway from photoreceptors to ganglion cells
H: influence laterally in the plexiform layer; influence neighbors
110
What are the two classifications of bipolar cells? What is this based on?
1. OFF bipolar cells
2. ON bipolar cells
their responses to the glutamate released by photoreceptors
111
In OFF bipolar cells what occurs?
glutamate-gated cation channels mediate a classical depolarizing EPSP from the influx of Na+
112
In ON bipolar cells, what occurs?
G-protein coupled receptors respond to glutamate hyperpolarizing
113
Light off means [...] glutamate. More light means [...] glutmate.
more; less
114
The number of photoreceptors in this cluster ranges from... (2)
1. one at the center of the fovea
| 2. thousands in the peripheral retina
115
Receptive field:
is the area of retina that, when stimulated with light, changes the cell's membrane potential
116
What are the two parts of the receptive field of a bipolar cell?
1. receptive field center: circular area providing direct photoreceptor input
2. receptive field surround: surrounding area of retina providing input via horizontal cells
117
One mm of the retina corresponds with a visual angle of ...
about 3.5
118
Which group of bipolar cells have a larger receptive field diameter?
the peripheral retina (the receptive field is a fraction of a degree compared to several degrees)
119
Center-surround receptive fields:
a visual receptive field with a circular center region + surround region = ring around the center
stimulation of the center produces a response opposite that generated by stimulation of the surround
** why it's antagonistic
