neuroscience > vision > Flashcards

vision Flashcards

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1
Q

what is temperature

A

measure of the average kinetic energy of a group of atoms/molecules

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2
Q

why do we only see visible light?

A

1- infrared, microwave and radio waves are low energy, the energy is weak. Its absorption causes molecules to vibrate and rotate, but a lot is needed to substantially alter the temperature of something. Radio waves affect nuclear spin, but this is usually inconsequential (it doesn’t even typically generate heat).

2- UV, X-ray, and gamma ray radiation is strong enough
to kick a typical bound electron out of an atom.
We call this ionizing radiation because it leaves
behind positively charged ions that are highly reactive
and detrimental to biological processes.

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3
Q

depending on the atom or molecule that gets hit with visible light, there can be…

A

1- absorption: the electron is captured in a high energy orbital state
2- reflection: the electron temporarily oscillates but remains in its orbital state
3- transmission: the electron cannot readily absorb the energy of the light (it is transparent to this wavelenght of light)

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4
Q

where is transmission primarily observed?

A

air, glass an water, since the molecules in these substances cannot readily absorb the energy of visible light.

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5
Q

true or false: when an excited electron is part of a larger molecule, it is likely to emit a new packet of light when it
relaxes back into position.

A

false, the energy typically gets converted into molecular vibrations (heat) via near-field (non-radiative) electromagnetic interactions

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6
Q

What does vitamine A do when it absorbs visible light?

A

it absorbs the energy of visible light and hold onto it. it undergoes a change in shape, stabilizing the electron in its high energy orbital.

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7
Q

how many photons of visible light does it take to change the shape of vitamin A

A

one photon

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8
Q

what is retinal

A

a modified form of vitamin A used by our eyes to perceive visible light. cells in our eyes setup an intracellular signalling cascade in which the shape of retinal determines the membrane potential of the cell and thus how much neurotransmitter it releases.

The retinal molecule is technically what absorbs the electromagnetic energy of visible light that allows us to see.

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9
Q

true or false: we can perceive much but not all of the
radiation that reaches us from the sun.

A

true

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10
Q

what are opsins

A

specialized proteins expressed by photoreceptor cells that hold onto retinal. they are proteins that are sensitive to light.

Opsins undergo a change in shape when they absorb the energy of visible light. The opsins in our eye acquire this property by holding onto a
molecule of retinal.

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11
Q

explain what happens when retinal absorbs the energy of visible light.

A

it activates the opsin protein (a metabotropic receptor). this launches an intracellular g protein signaling cascade that changes the membrane potential of the photoreceptor cell, affecting how much neurotransmitter it releases.

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12
Q

true or false: every sensory neuron has axons and action potentials

A

false, many do not have these. all of them release neurotransmitter.

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13
Q

what happens when sensory neurons do not have action potentials?

A

they release neurotransmitter in a graded fashion, dependent on their membrane potential. the more depolarized they are, the more neurotransmitter they release.

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14
Q

visible light is between which nm

A

380 nm to 750 nm

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15
Q

what are the 4 kind of proteins we use to detect visible light?

A

1- red cone opsin expressed by red cone cells
2- blue cone opsin expressed by blue cone cells
3- green cone opsin expressed by green cone cells
4- rhodopsin expressed by rods

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16
Q

why are rodes in a different category than cones?

A

rods were the last to evolve, they are 100 times more sensitive to light than cone cells are.

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17
Q

blue cone opsins are most sensitive to?

A

short wavelenghts of light (430 nm)

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18
Q

green cones opsins are more sensitive to?

A

medium wavelenghts of light (535 nm)

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19
Q

red cones opsins are most sensitive to?

A

long wavelenghts of light (575 nm)

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20
Q

what is pure yellow (570 nm)?

A

Green light (520nm) activates the green cone opsin more than the red cone opsin.
Red light (640nm) activates the red cone opsin more than the green cone opsin.
The combination of red and green light causes both red and green cone opsins to
be activated similar amounts, which is exactly what pure yellow light does (570nm)

When red and green light is so close together that our eyes can’t differentiate them, we perceive the color yellow.

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21
Q

what is additive color

A

Sunlight contains similar amounts of all the colors, so we perceive it as white light.

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22
Q

name the three dimensions of our perception of light

A

1) brightness - intensity (total amount of light)
2) hue - principal color (dominant wavelength in the light)
3) saturation - purity of the color (the wavelength mixture)

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23
Q

if there is 0 brightness…?

A

there is no light, we perceive it as black. hue and saturation have no meaning without brightness

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24
Q

what does 0% saturation mean?

A

the light is in the central axis of the color cone where there are equal amounts of all the wavelengths. this means the light is gray scale (in black and white)

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25
what is protanopia?
Absence of the red cone opsin (1% of males). People with this condition have trouble distinguishing colors in the green-yellow-red spectrum. In this situation, red cone cells typically express the green cone opsin, so visual acuity is often normal. Mutations that only make the red cone opsin act more like the green cone opsin often produce less pronounced deficits in color vision (1% of males).
25
what is deuteranopia?
Absence of the green cone opsin (1% of males). People with this condition have trouble distinguishing colors in the green-yellow-red spectrum. In this situation, green cone cells typically express the red cone opsin, so visual acuity is often normal. Mutations that only make the green cone opsin act more like the red cone opsin often produce less pronounced deficits in color vision (5% of males).
26
what is tritanopia?
Absence of the blue cone opsin (1% of the population). Blue cone cells do not compensate for this in any way. But since there are relatively few blue cone cells and they are less sensitive to light than green and red cone cells, visual acuity is often not noticeably affected.
27
what is cone monochromacy?
when only one of the cone opsins is functional, there is no color vision.
27
what is achromatopsia?
when none of the cone cells work (because of a problem with the intracellular signaling cascade shared by all cone cells), there is no color vision.
28
what is the conjunctiva?
a mucous membrane that lines the front of the eye. it connects to the eyelids, preventing things from getting behind the eye.
29
what is the cornea?
the outer, front layer of the eye. it focuses incoming light a fixed amount. laser eye surgery reshapes the cornea.
29
what is the iris?
a ring of muscle. The contraction and relaxation of this muscle determines the size of the pupil.
30
what is the function of the pupil?
determines how much light enters the eye.
31
what are the lens?
consists of several transparent layers. We adjust the shape of this lens to focus near or far.
32
what is the retina?
The lining of the back part of the eye which contains several layers of cells. Counterintuitively, the photoreceptor cells are located in the deepest cell layer in the retina.
33
what is the fovea?
the central region of the retina. it primarily contains cone cells.
34
the periphery of the retina contains...
rod cells
35
what is the optic disk?
Where blood vessels leave/enter the eye. This is where the optic nerve also exits the eye, carrying visual information to the brain.
36
where are there no photoreceptor cells?
blind spot
37
true or false: our eyes sit still for long
false: Our eyes scan a scene by making saccadic eye movements – rapid, jerky shifts in gaze from one point to another.
38
what are pursuit movements?
when we maintain focus on an object that is moving (relative to us) our eyes exhibit pursuit movements. This is the only time are eyes appear to calm down and move smoothly, slowly.
39
how many muscles rotate the eye and hold it in place?
six
40
what are orbits?
Eyes are suspended in bony sockets in the front of the skull called orbits.
41
describe how the visual information moves in the retina
Activated photoreceptor cells pass information forwards (towards the front of the retina). Visual information moves from photoreceptor cells -> bipolar cells -> retinal ganglion cells -> brain.
42
what is the only part where our visual acuity is good enough to read text (20/20 vision)?
the fovea
43
true or false: in the fovea, there is an equal number of photoreceptor cells, bipolar cells, and retinal ganglion cells. This means there is no compression of information.
true, the photoreceptor cells in our fovea are mostly cone cells, which support color vision, so the fovea supports high resolution, color vision.
44
describe the periphery of our retina
Outside the fovea (in the periphery of our retina), there is a massive compression (averaging) of visual information, as there are 100x fewer retinal ganglion cells than photoreceptor cells. Our visual acuity in peripheral vision is about 20/200, which is quite blurry. It is also gray scale. We can make out general shapes but not details. Yet, the periphery of our retina contains a high density of rod cells, which are very sensitive to light, allowing us to easily detect dim light and movements of light.
45
what is the condition at night for us to see in color?
the moon must be at least half full (assuming there are no other sources of light).
46
true or false: our peripheral vision provides high resolution grayscale images.
false: Our peripheral vision is very sensitive to dim light, but it only provides low resolution grayscale images. What we see in peripheral vision 20 feet away is as detailed as what we see in our fovea 200 feet away.
47
give 4 characteristics of cones
1) most prevalent in the central retina; found in the fovea 2) sensitive to moderate-to-high levels of light 3) provide information about hue 4) provide excellent acuity
48
give 4 characteristics of rods
1) most prevalent in the peripheral retina; not found in the fovea 2) sensitive to low levels of lights 3) provide only monochromatic information 4) provide poor acuity
49
describe in details how the neurons in the retina work
* Photoreceptor cells are located in the furthest back part of the retina. They express the opsin proteins that transduce light. Photoreceptor cells synapse on bipolar cells. * Bipolar cells relay visual information from photoreceptor cells to retinal ganglion cells. * Retinal ganglion cells are the only cells that send information out of the eye. Their axons form the optic nerve, which exits the retina through the optic disc (the blind spot of the retina).
50
what are horizontal cells and amacrine cells and what is their function (in brief)?
Horizontal cells and amacrine cells interconnect cells within each layer, which gives rise to complex interactions between neighbouring cells.
51
Retinal ganglion cells have action potentials, unlike most other cells in the retina. Their axons go to 3 places:
* Thalamus (specifically the lateral geniculate nucleus), which in turn projects to primary visual cortex (area V1) in the occipital lobe where visual information enters consciousness. This retina -> thalamus -> V1 pathway creates an internal (mental) representation of your entire visual space: the objects in it, their position, and their attentional value. * Midbrain (specifically the superior colliculi): Visual information is used here to control fast visually-guided reflexive movements. The midbrain doesn’t know what you are looking at, but it can draw your attention to unexpected visual events. * Hypothalamus: Visual information is used here to control circadian rhythms such as sleep-wake cycles. The hypothalamus doesn’t know what you are looking at, but it knows how much light is present in your environment.
52
what is predictive coding theory?
The idea is that each node in the network tries to predict what its ascending inputs will look like in the next moment, based on previous experience. that top-down (descending) activity represents sensory predictions that neutralize (cancel out) any correctly predicted bottom-up ascending signals. Thus, what propagates up through the network may only be prediction error signals, which inform the brain of how the current moment differs from what was expected. The prediction error signals that ascend through the network would cause learning to improve future predictions.
53
what is the receptive field of a neuron?
a description of the (external) stimuli that activate it. The receptive field of a neuron involved in visual processing is where light must be in visual space (and what properties it must have) to change the activity of the cell. It is in an area of visual space relative to a fixation point (where the animal is looking).
54
what do we do to identify the receptive field of a cell involved in visual processing?
we record the cell’s activity as the animal maintains focus on one spot on a computer screen (a fixation point). We then systematically shine light on different areas of the monitor (e.g., relative to the fixation point) to determine where in visual space the presence of light influences the activity of the cell. Once we find where the receptive field is, we determine if the cell responds differently to different colors or patterns of light in that location.
55
why is light responses in the retina well understood?
because neural activity in the retina is solely determined by the light the animal sees.
56
how much input from the retina does the thalamus get?
10%, it is unclear what information is encoded in the other 90% of synaptic inputs.
57
Do photoreceptor cells have action potential?
No, they release glutamate in a graded fashion dependent on their membrane potential: the more depolarized they are, the more glutamate they release.
58
in complete darkness, photoreceptor cells sit at?
-40 mV. this is their resting membrane potential.
59
At rest, photoreceptor cells continuously release what?
glutamate
60
what happens to photoreceptor cells when activated by light?
photoreceptor cells hyperpolarize to -70 mV and stop releasing glutamate.
61
describe what happens when an opsin protein absorbs light.
it launches an intracellular g-protein signaling cascade that closes the open sodium ion channels. The closing of these ion channels causes the membrane to hyperpolarize to -70 mV, at which point the photoreceptor cell stops releasing glutamate.
62
why do photoreceptor cells sit at -40mV?
The influx of sodium ions through these ion channels (the dark current) causes photoreceptor cells to sit at -40 mV, where they continuously release glutamate.
63
All the opsin proteins responsible for our conscious perception of vision are ? receptors.
inhibitory metabotropic receptors. when activated by light, they cause membrane hyperpolarization, which stops the photoreceptor cell from releasing glutamate.
64
do bipolar cells have action potential?
no, like photoreceptor cells, they release glutamate in a graded manner dependent on their membrane potential.
65
what are the two types of bipolar cells?
OFF bipolar cells and ON bipolar cells
66
what is an OFF bipolar cell?
OFF bipolar cells express normal excitatory ionotropic glutamate receptors, so their activity patterns follow that of the photoreceptor cells that connect to them. -> In the presence of light, OFF bipolar cells hyperpolarize and stop releasing glutamate, just like photoreceptors do. -> In the dark, OFF bipolar cells depolarize and release glutamate, just like photoreceptor cells do.
67
what is an ON bipolar cell?
ON bipolar cells respond in the opposite manner, because they only express inhibitory (metabotropic) glutamate receptors. -> In response to light, ON bipolar cells depolarize and start releasing glutamate. -> In darkness, ON bipolar cells hyperpolarize and stop releasing glutamate.
68
Do retinal ganglion cells have action potentials?
yes, retinal ganglion cells (RGCs) are typical neurons. They have normal action potentials, and they express normal excitatory ionotropic glutamate receptors.
69
what is the function of horizontal cells?
they interconnect neighboring photoreceptors cells and they regulate the amount of glutamate that is released from photoreceptors cells based on the activity of their neighbors. Horizontal cells compare the activity of neighboring photoreceptor cells. They recognize that the center photoreceptor cell is getting less light than its neighbors, and they accentuate this difference by counteracting the small light-induced hyperpolarization in the dimly lit cell. horizontal cells depolarize the “axon terminals” of photoreceptor cells according to how brightly lit the neighboring photoreceptor cells are. ps- they dont have action potentials. They release glutamate in a graded manner dependent on their membrane potential.
70
what is the resting state of a bipolar cell?
-60 mV (in darkness)
71
what is the state or response of an ON bipolar cell when the upstream photoreceptor cell detects light?
-45 mV (more neurotransmitter release)
72
what is the state or response of an ON bipolar cell when the upstream photoreceptor cell is in darkness AND neighboring photoreceptor cells are brightly lit?
-75 mV (less neurotransmitter release)
73
what is the state or response of an OFF bipolar cell when the upstream photoreceptor cell is in darkness AND neighboring photoreceptor cells are brightly lit?
-45 mV (more neurotransmitter release)
74
what is the state or response of an OFF bipolar cell when the upstream photoreceptor cell detects light?
-75 mV (less neurotransmitter release)
75
what is center-surround organization?
the influence of horizontal cells creates a “center-surround” organization in the receptive fields of bipolar cells.
76
what is an ON ganglion cell?
cells that increase the rate of spiking when light is in the center of the receptive field (more action potentials because the bipolar cell depolarize and releases glutamate)
77
true or false: ganglion cells also have and centre-surround organization
true, retinal ganglion cells have action potentials and a baseline firing rate in the dark. they inherit their receptive fields from bipolar cells, so they also have a “center-surround” organization and are classified as ON or OFF cells.
78
what happens when there is dark in the center of the receptive field and light in the surrounding for an ON ganglion cell
bipolar cell hyperpolarize exaggeratedly and stops releasing glutamate, and the retinal ganglion cells stop firing action potentials
79
what happens when there is dark in the center of the receptive field and light in the surrounding for an OFF ganglion cell
bipolar cell depolarize and release glutamate, and the retinal ganglion cells fires a lot of action potentials
80
what happens when there is light in the center of the receptive field of an OFF ganglion cell
bipolar cell hyperpolarize and stops releasing glutamate, and the retinal ganglion cells stop firing action potentials
81
what happens when there is light in the center of the receptive field and in the surroundings of an OFF ganglion cell
there is a slight hyperpolarization, and a few more action potential
82
what processes color information?
ganglion cells in the fovea, They integrate information from many bipolar cells and have these types of receptive fields: blue center/yellow surround yellow center/blue surround red center/green surround green center/red surround
83
what is the receptive field of neurons in V1 related to the thalamus?
The receptive fields of neurons in V1 are the sum of many thalamic LGN neurons.
84
what are simple cells?
Simple cells in V1 are sensitive to lines of light, and their receptive fields are typically organized in a center-surround fashion.
85
when do neurons in V1 spike?
* Neurons in V1 spike when there is a line of light in a particular orientation in their receptive field. * Some V1 neurons respond best to vertical lines (more action potentials), some to horizontal lines, and some to lines oriented somewhere in between.
86
what are cortical columns in the V1?
Every spot in the visual field is rigorously analyzed by a cortical column in V1. All the neurons in one cortical column analyze the same area of visual space. Together, they analyze the orientation of light in that area of visual space. Sharp transitions in the contrast/color of light reveals borders, edges, and corners.
87
what is the dorsal stream?
The dorsal stream of visual information starts in primary visual cortex and ends in posterior parietal lobe. It is involved in identifying spatial location. It encodes where objects are, if they are moving, and how you should move to interact with them or avoid them.
88
what is the ventral stream?
The ventral stream starts in primary visual cortex and ends in inferior temporal lobe. It is involved in identifying form (shape). It encodes what the object is and its color.
89
what is monocular vision?
Some V1 neurons respond to visual input from just one eye.
90
what is binocular vision?
Most V1 neurons respond to visual input from both eyes.
91
what is depth perception?
There are many monocular cues that can be used to estimate depth, such as relative size, amount of detail, relative movement as we move our eyes, etc. These are the cues we use to appreciate depth when looking at a photograph or TV screen (any flat, 2 dimensional image). Only one eye is required to perceive depth with monocular cues.
92
what is stereopsis?
The perception of depth that emerges from the fusion of two slightly different projections of an image on the two retinas. The difference between the images from the two eyes is called retinal disparity. It results from the horizontal separation of the two eyes. It improves the precision of depth perception, especially for moving objects. Two eyes are helpful when playing sports, but also (to some extent) when pouring a glass of water.
93
what is agnosia?
An agnosia is a deficit (problem) in the ability to recognize or comprehend certain sensory information, like specific features of objects, people, sounds, shapes, or smells, although the specific sense is not defective nor is there any significant memory loss. An agnosia relates to a problem in some sensory association cortex (typically in a single sensory modality) - not to problems that relate to the sensory neurons themselves or to the primary sensory areas. Visual agnosia is caused by damage to visual association cortex.
94
what is akinetopsia?
a deficit in the ability to perceive movement – is a type of visual agnosia caused by damage to the dorsal visual stream in the parietal lobe of the cerebral cortex
95
what is cerebral achromatopsia?
In contrast to regular achromatopsia, which is complete color blindness due to defective cone opsin signaling, cerebral achromatopsia is a visual agnosia caused by damage to the cerebral cortex in the ventral visual stream. People with cerebral achromatopsia deny having any perception of color. They say everything looks dull or drab, and that it is all just “shades of grey”. (People born with regular achromatopsia don’t say those things, because they have no conception of color.)
96
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