Vision Flashcards
1
Q
What are sensations?
A
- the detection of stimuli in the environment by cells in the nervous system
- the way the cells transduce the signal into a change in membrane potential and neurotransmitter release
2
Q
What is perception?
A
- conscious experience and interpretation of sensory information
3
Q
What are sensory receptors?
A
- specialized neurons that detect a specific category of physical events
4
Q
How do sensory neurons sense stimuli?
A
- they express receptor proteins that are sensitive to specific features of the external environment,
- Ion channels qill open/close accordingly and will cause a change in membrane potential
5
Q
What elements can be sensed by human sensory receptors?
A
- presence of specific molecules
- physical pressure
- temperature
- pH
- Electromagnetic radiation
6
Q
What is sensory transduction?
A
- process by which sensory stimuli are translated into receptor potentials
7
Q
What is receptor potential?
A
- graded change in the membrane potential of a sensory neuron caused by sensory stimuli
8
Q
What is the mode of action of sensory neurons?
A
- Release neurotransmitters depending on their membrane potential
- the more depolarized sensory neurons are, the more neurotransmitters they release
9
Q
What are opsins?
A
- receptor proteins that are sensitive to light
10
Q
What are the different opsins that detect light in humans?
A
- rhodopsin
- red, green, blue cone opsins
11
Q
How are the different types of photoreceptor cells differentiated?
A
- by the kind of opsin they express (therefore: 4 kinds)
12
Q
What is a photoreceptor cell?
A
- sensory neuron respondible for vision
13
Q
How many different types of opsins does a photoreceptor cell express?
A
one
14
Q
What is a retinal?
A
Small molecule that attaches to the opsin proteins in our eye
15
Q
What type of receptors are opsins?
A
Inhibitory metabotropic receptors
16
Q
What is the function of retinal molecules?
A
- absorbs the electromagnetic energy of visible light.
17
Q
What determines the wavelength that is absorbed by retinal?
A
- the opsin protein that is connected to it
18
Q
How does a retinal molecule react to the presence of light?
A
1) The presence of a photon’s energy will change the configuration of the retinal molecule (makes it straight)
2) triggers an intracellular g-protein signaling cascade
3) the signaling cascade hyperpolarizes the membrane
19
Q
How are opsins sensitive to light?
A
Due to the retinal that is bound to them
20
Q
What is visible light?
A
wavelength between 380 and 760 nm
21
Q
What type of waves are Gamma rays and X rays?
A
very short wavelength
22
Q
What type of waves are radion and micro waves?
A
very long wavelengths
23
Q
What type of cone cells are the most sensitive to light?
A
Green cone cells
24
Q
What is the function of rhod cells?
A
- They just perceive light in general, not the colour of light
- Very sensitive to all visible light
25
Where are we able to see colour? Why?
- In the fovea, because it is the only place where we have cone cells
26
How do we perceive visual stimuli in the peripheral vision?
- In black and white, because it is just rhod cells
- See the shape and movement, not colour
27
What type of wavelengths are blue cones sensitive to?
Short wavelengths
28
What type of wavelengths are red cones sensitive to?
long wavelengths
29
What type of wavelengths are green cones sensitive to?
medium wavelengths
30
What is colour perception a function of?
- the relative rates of activity i the three types of cone cells
31
What does the amout of activation of one cone depend on?
- wavelength of light
- intensity of light
32
What wavelengths of light are green cones sensitive to?
- all medium wavelengths, it just does not perceive extremely red or blue hews
33
What is the difference between our perception of colour and the way paint emits colour?
- our vision is additive, whereas paint is substractive in the way it creates colour: it absorbes all light save for that which corresponds to the wavelengeth we wish to observe
34
What are the three dimensions of our percetion of light and colour?
- Brightness
- Saturation
- Hue
35
What is brightness?
intensity of light
36
What is saturation?
purity in terms of composite wavelengths of the observed light
37
What is hue?
The dominant wavelength in the light that is observed
38
Where are the opsin genes encoded?
On the X chromosome
39
What are the four types of colour vision deficiencies?
- protanopia (red cones)
- deuteranopia (green cones)
- tritanopia (blue cones)
- achromatopsia (g-protein cascade)
40
What is protanopia?
- absence of the red cone opsin
- normal visual acuity
- compensated by the green cone opsins
- trouble distinguishing color in the green-yellow-red section
41
What is deuteranopia?
- absence of the green cone opsin
- normal visual acuity
- green cones filled in with red cones
- trouble distinguishing color in the green-yellow-red section
42
What is tritanopia?
- absence of the blue cone opsin
- not compensated
- no impact (blue cone opsins not very sensitive)
43
What is achromatopsia?
true colour blindness
44
What causes achromatopsia?
- mutation in the g protein signaling cascade
45
What is the conjunctiva?
- mucous membrane that lines the eyelid
- fuses with the eyelid and prevents foreign particules from penetrating
46
What is the cornea?
- front layer of the eye
- focuses incoming light a fixed amount
47
What is the iris?
- ring of muscle
- contraction or relaxation determines the size of the pupil
48
What is the lens?
- cristallin
- changes shape to allow the eye to focus (accomodation)
49
What is the sclera?
- the side of the eyeball
- opaque
- does not allow entry of light
50
What is the fovea?
- central region of the retina
- little compression of visual information, therefore highest visual acuity (one-to-one ration between ganglial cells, bipolar cells and photoreceptor cells)
- very high resolution
- colour
- reading
51
What is the optic disk?
- blind spot of the retina
- no photoreceptors
- where the optic nerve exits through the back of the eye
52
What is the difference between the fovea and the peripheric regions of the retina?
- the fovea has an extremely high concentration of cone cells, each one of which connects to a single downstream collection of cells, which allows the registering of the exact location of the input.
- in peripheral regions, collections of photoreceptors converge into fewer and fewer neurons
53
Where do we perceive colour?
the fovea
54
What do we percevie in the peripheral vision?
- faint light
- general shapes
55
What type of photoreceptors does the fovea contain?
only cone cells
56
Where are con cells situated?
fovea
57
Where are rod cells situated?
peripheral retina
58
What levels of light are cone cells sensitive to?
moderate to high
59
What type of information does the cone cell provide?
High acuity, information about hue
60
What type of information do the rod cells provide?
monochromatic informaiton with poor acuity
61
Where is reading possible?
fovea
62
What are the two types of eye movement?
- saccadic movements
- pursuit movements
63
What are saccadic eye movements?
- default state of the eye
- constant and rapid movement
64
What is the purpose of saccadic eye movements?
- compensates for the blind spot
- compensates for the monochromatism of the peripheral vision
65
What is pursuit movement?
- slower eye movement, controlles, that allows to maintain an image of a moving object
66
What are the five type of neurons present in the retina?
- photoreceptor cells
- bipolar cells
- ganglion cells
- horizontal cells
- amacrine cells
67
What is a photoreceptor?
- any cell that is sensitive to light
- sensory neuron that turns light into action potential
- opsin+retinal
68
What do photoreceptors release? How do they release it?
- glutamate
- graded fashion
- the more depolarized they are, the more glutamate they release
69
When do the photoreceptor cells release more glutamate?
In the dark, because the activation of retinal by light hyperpolarizes the cell and diminishes/stops the release of glutamate
70
What is the particularity of the leak channels in the photoreceptors?
- leaky sodium channels
71
What is the function of the leaky sodium channels in the photoreceptor cells?
- depolarize the cell in the dark, which allows the cell to release glutamate
72
What is the polarization of the photoreceptor cells in the dark?
-40mv
73
How is the release of glutamate by the photoreceptor cells controlled?
- when the retinal-opsin complex gets evergy from light, the g-protein cascade that ensues closes the leaky sodium channels, hyperpolarizing the neuron and stopping glutamate release
74
What are the only neurons in the eye that send axons out of the eye?
ganglion cells
75
What is the role of bipolar cells?
Relay information from photoreceptors to ganglion cells
76
What is the role of ganglion cells?
receive information from the bipolar cells and project to the rest of the brain (axons=optic nerve)
77
What is the role of horizontal cells?
interconnect and regulate the excitability of adjacent photoreceptors and bipolar cells, adjusting the sensitivity of these neurons to light
78
What is the role of amacrine cells?
interconnect and regulate the sensitivity of adjacent bipolar and ganglial cells
79
What is the path of visual stimulus in the eye? (structures in order)
1) photoreceptor: release or not glutamate
2) bipolar cell: release or not glutamate to send toward the ganglial cells
3) ganglial cell (will release an action potential if they are excited by glutamate)
4) axons of the ganglial cells
5) optic nerve (created by the axons of the ganglial cells)
80
How do bipolar cells release information?
- graded glutamate release depending on membrane potential
- NO ACTION POTENTIAL
81
What neurons in the eye do not have action potential?
- bipolar cells
- photoreceptors
82
What is the function of off bipolar cells?
- release neurotransmitters in the dark
83
What is the function of on bipolar cells?
- release neurotransmitters when there is light
84
When do ganglion cells release action potentials?
- when they are excited by glutamate coming from bipolar cells
85
What receptors do off bipolar cells express?
ionotropic glutamate receptors
86
What receptors do on bipolar cells express?
inhibitory metabotropic receptors (inhibited by glutamate in the dark, therefore do not release NT in the dark)
87
How do photoreceptors and bipolar cells communicate with other cells?
-through the release of glutamate
- they do not have an axon, therefore do not have any action potential
88
What is the receptive field of a neuron?
The area in the visual space where the presence of light influences the activity of a neuron. Outside of this area, a visual stimulus will not stimulate the neuron.
89
How does the receptive field of a photoreceptor cell function?
- depends on wavelength and location in visual space
90
What happens when there is the ideal wavelength in the right visual region for a photoreceptor cell?
- cell hyperpolarizes
- cell releases less glutamate
91
What determines the receptive field of the first two cell layers in the retina?
- location in visual space and wavelength that triggers the biggest cellular response
92
What determines the receptive field of a bipolar cell?
- the photoreceptor cells that connect to them
93
What happens when the appropriate wavelength is in the receptive field of an on bipolar cell?
- the cell is depolarized
- the cell releases more glutamate
94
What happens when the appropriate wavelength is in the receptive field of an off bipolar cell?
- the cell is hyperpolarized
- the cell releases less glutamate
95
What determines the receptive field of a retinal cell?
- the bipolar cells that connect to it
- receives information from many bipolar cells
96
How is the receptive field of a retinal cell organized?
- center-surround manner
97
What happens when there is a light stimulus in both the center and surround receptive field of a retinal cell?
low reactivity
98
What is an on retinal cell?
will be excited by light in the center, inhibited by light in the surround
99
What is an off retinal cell?
will be inhibited by light in the center, excited by light in the suround
100
What happens when a retinal cell is excited?
They will create more action potentials
101
What happens when you shine light in the surround of an off retinal cell?
more action potentials than base rate
102
What happens when you shine light in the center of an on retinal cell?
more action potentials than base rate
103
What happens when you shine light in the center of an off retinal cell?
less action potentials than base rate
104
What happens when you shine light in the surround of an on retinal cell?
Less action potentials than base rate
105
What are simple cells?
cells situated in the primary visual cortex that are sensitive to lines of light
106
How are the receptive fields of simple cells organized?
center-surround fashion
107
What are simple cells sensitive to?
Lines of light
108
What is the pathway of the relay of visual information?
1) Eye
2) Photoreceptor cells
3) Bipolar cells
4) RGC
5) goes toward the cortex
109
What composes the receptive field of V1 neurons (neurons in the primary visual cortex)?
sum of many RCGs
110
When are the cells of the V1 most activated?
When there is a line in a specific orientation that is detected
111
What is the main task of neurons in the primary visual cortex?
identify borders, edges and corners (transitions between light and dark)
112
What is the extrasiate cortex?
Visual association cortex
113
What is the striate cortex?
Primary visual cortex
114
What percentage of the cerebral cortex is dedicated to processing visual information?
25%
115
Where is the visual association cortex? Which structure of the brain is it?
It is all of the occipital lobe surrounding the primary visual cortex, as well as part of the parietal and temporal lobes
116
What is the particularity of the information that is processed in the visual cortex?
- It is both top-down and bottom-up information
- in the 4th line of the pathway (thalamus/V1), only 10% or so of synapses come from the retinas, most information comes from other parts of the brain
117
What are the two visual streams?
- dorsal stream
- ventral stream
118
What is the pathway of the dorsal stream?
V1->posterior parietal cortex (top of head)
119
What is the pathway of the ventral stream?
V1->inferior temporal cortex (bottom of head)
120
What is the role of the dorsal stream?
- spatial location
- how objects are moving, where they are and how we can interact with them
121
What is the role of the ventral stream?
- identifies form and encodes color
- determines what the object in front of us is
122
What is monocular vision?
Refers to V1 neurons that respond to visual input from just one eye
123
What is binocular vision?
Refers to V2 neurons that respond to visual input from both eyes
124
How does depth perception occur for two dimensional images?
- Mostly from monocular vision and cues (relative size, amount of detail, etc)
- it is a cognitive process, where we create a perception of depth
125
What is stereopsis?
- Perception of depth that emerges from the fusion of two slightly different projections of an image on the two retinas
- more precise than monocular depth perception
126
What is retinal disparity?
- The difference between the images from the two eyes
- results from the horizontal separation of two eyes
127
What is stereopsis most useful for?
- quickly plan movements to interact with objects moving in space
128
Are most V1 neurons monocular or binocular?
binocular
129
What is an agnosia?
- deficit in the ability to recognize or comprehend sensory information
130
What causes agnosia?
A problem in the sensory association cortex
131
What is akinetopsia?
Deficit in the ability to perceive movement
132
What causes akinetopsia?
damage in the dorsal visual stream
133
What is cerebral achromatopsia?
Complete inhability to see colour, but that is acquired: people lose the ability to see colour and the memory of what colours are like, but remember they used to be able to see colour. People will sy that all colours are "dull".
134
What causes cerebral achromatopsia?
Caused by damage to the ventral visual stream
135
What is the difference between cerebral achromatopsi and regular achromatopsia?
Regular is innate (mutation of the g-protein cascading signal), whilst cerebral is acquired. People with cerebral achromatopsia tend to have a conception of what colour is, they just cannot see it.
136
What is prosopagnosia?
- failure to recognize people by sight of their face
- configuration of faces not seen as coherent wholes, just a bunch of features
137
What causes prosopagnosia?
Damage to the fusiform gyrus
138
What is the fusiform gyrus?
area of the brain whose aim is to recognize elements/features of a face and make sens of them
139
What is the predictive coding theory of perception?
- most visual pathways are bidirectional
- Descending neural activity reflects predictions about what input is more likely to happen next (based on previous info). Cancels out the correctly predicted ascending information.
- The only information that ascends are errors in visual prediction (corrects perception+improves future perception)
- This way, the brain saves energy by only processing information it could not have otherwise predicted and processes information faster.
140
What is the prediciton error signal?
what propagates up in the predictive coding theory of perception
141
What is the difference between horizontal and amacrine cells?
Horizontal cells: regulates adjacent photoreceptors and bipolar cells
Amacrine cells: regulates excitability of adjacent bipolar cells and ganglial cells
142
What are the three possible destinations of the visual information in the cerebral cortex?
- thalamus
- midbrain
- hypothalamus
143
What is the role of the thalamus in dealing with visual information?
- projects information to V1
- processes what you are looking at
- creates an internal representation of your entire visual space (what are the objects, what are their position, what is the attentional value of each object)
144
What is the role of the midbrain in dealing with visual information?
- control of fast, visually-guided movements
- identifies the movement of light, not what the light is/represents
145
What specific region of the midbrain interacts with the visual information?
the superior colliculus
146
What is the role of the hypothalamus in dealing with visual information?
- measure the quantity of light there is to regulate the circadian rythm
146
What is the lateral geniculate nucleus?
nucleus in the thalamus where most RCGs project. The neurons of the LGN poject to the cerebral cortex.
