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neuro 80 > lecture 14 relaying visual info from eye to brain > Flashcards

lecture 14 relaying visual info from eye to brain Flashcards

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1
Q

what do photoreceptors do in response to light

A

hyperpolarize and release less glutamate

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2
Q

what do on bipolar cells do in response to light

A

depolarize and release more glutamate

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3
Q

what do off bipolar cells do in response to light

A

hyperpolarize and release less glutamate

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4
Q

what do photoreceptors do in response to dark (and what do the on and off bipolar cells do)

A

depolarize and release more glutamate (on cells inverse the signal so they release less, and off cells do the same as photoreceptors so they release more too)

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5
Q

what neurotransmitter is released by photoreceptors and how is the the response different between bipolar cells despite the same neurotransmitter

A

glutamate

on cells have mglur6
(inhibitory, metabotropic)

off cells have ampa kainate (excitatory, ionotropic)

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6
Q

what cells do bipolar cells synapse onto

A

retinal ganglion cells (rgc)

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7
Q

retinal ganglion cells

A

output neurons in retina

only cells in retina that fire true action potentials (have to send electric signal from eye to brain)

have two types; on and off

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8
Q

what is the optic nerve made of

A

axons of retinal ganglion cells

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9
Q

action potentials

A

large enough membrane potential change that can be recorded without sticking electrode in

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10
Q

how did stephen kuffler learn about recording responses of retinal ganglion cells

A

experimental animal is anesthetized and positioned facing a screen

electrode positioned near a retinal ganglion cell to record action potentials (lots of spontaneous activity)

shine spots or other shapes on screen and record frequency of action potentials

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11
Q

what is this

A

spontaneous background activity of retinal ganglion cells, basically baseline

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12
Q

region or characteristics of the
sensory space that elicits the greatest activity (action
potentials or largest graded potentials in the retina) from either a sensory cell or neuron within the CNS. For neurons in the retina, receptive filled properties include
the area of the visual field (location in space) where light (or dark) would hit the neuron

A

receptive field

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13
Q

neurons that are locating near to each other

A

have receptive fields that are near each other (retinotopic map)

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14
Q

receptive field of a specific neuron

A

sometimes includes other aspects of the stimulus like color, movement, etc

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15
Q

receptive fields tend to

A

enlarge and increase in complexity as information passes through the brain

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16
Q

neurons in the eye respond to-

A

a relatively basic stimulus: light on and off

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17
Q

receptive field of retinal ganglion cells

A

dim light: background (spontaneous) activity

bright spot: response

another bright spot nearby: response

distant bright spot: no response, not part of receptive field

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18
Q

what happens if we enlarge stimulus

A

bright spot of light: response

bigger bright spot: more response

huge bright spot: firing rate back to spontaneous baseline

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19
Q

spot near receptive field (right outside, right above, right below)

A

small inhibition

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20
Q

bright annulus (donut)

A

big inhibition, neuron stops firing for some time

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21
Q

what does this experiment with the lights tell us

A

receptive field not just a single location of light

consists of center and surround parts of receptive field

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22
Q

on and off response of visual neurons

A

both bipolar cells and rgcs have center surround type receptive fields

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23
Q

if you cover entire receptive field with uniform light or dark

A

go back to baseline- they’re balanced

rgc’s will remain near resting firing rate

bipolar cells will not change membrane potential (graded response)

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24
Q

lateral pathway

A

responsible for surround

horizontal cells at synapse between photoreceptors and bipolar cells

amacrine cells at synapse between bipolar cells and rgcs

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25
direct pathway (the center)
photoreceptors to bipolar cells to retinal ganglion cells to optic nerve
26
horizontal and amacrine cells
both inhibitory release gaba linked via gap junctions forming a network can also help adjust entire retinal circuit response to changing levels of illumination ---a page of paper will look white inside or illuminated by a flashlight and white when out in bright sun even though number of photons is different
27
visual systems cares about...
relative light intensity, not absolute
28
lateral inhibition
neurons are inhibited when neighbors are active helps with contrast each photoreceptor and interneuron can be part of a center for one rgc and a surround for another rgc
29
what does center surround organization do
enhances sensitivity to edges and contrast (which is why we can interpret one line drawings, visual field is used to finding edges)
30
parallel output pathways from the retina
retina doesnt send point by point intensity and color information to brain high processed- breaks up visual world in many different features around 30 different types of rgcs -color center/surround (red center, green surround for example) -prefer moving stimuli -large or small receptive fields, etc
31
m type retinal ganglion cells (magnocellular)
larger color insensitive receptive fields respond to stimulation with a burst of action potentials often fire rebound action potentials (cell fires after being inhibited for a while)
32
p type retinal ganglion cells (parvocellular)
smaller and smaller receptive fields large majority of rgcs often color specific receptive fields respond to prolonged stimulation with sustained action potential rate
33
retina
the innermost layer of the eye and is Itself a layered structure that contains the visual sensory neurons, circuitry for the initial processing of visual information, as well as neurons that transmit that information to the brain. But the neurons of the retina do not simply detect light and pass that message on, a great deal of processing and filtering occurs in the retina, before the visual information reaches the brain
34
Photoreceptor
visual sensory cell that converts light into electrical signals. Located at the innermost layer of the retina. Photoreceptors are depolarized in the dark and hyperpolarize when activated by light
35
Bipolar cell
excitatory neuron in the retina that transmits information from the photoreceptors to the retinal ganglion cells and amacrine cells. Bipolar cells do not fire action potentials, but have a graded release of neurotransmitter
36
Horizontal cell
inhibitory neuron in the retina whose actions influence the signals that are transmitted from the photoreceptors to the bipolar cells. They make inhibitory, GABAergic synapses on the synaptic terminals of photoreceptors
37
Amacrine cell
inhibitory/modulatory neuron whose actions influence the signals that are transmitted from the bipolar cells to the retinal ganglion cells
38
Retinal ganglion cell (RGC)
Output cell of the retinal that transmits information from the eye to the brain. Only type of neuron in the retina that fires action potentials. There are both “on” and “off” that can be further divided into many different subtypes of RGCs based on specific receptive field properties (color, size of receptive field, etc
39
Center/surround
In the retina, both bipolar cells and RGCs have center surround receptive fields. For an “ON cell”, that means that the cell is excited by center stimulation (i.e. light/“on”), inhibited by light in the surround, and would be more optimally stimulated by dark in the surround. These receptive fields are very useful because they enable cells to detect more than the brightness of a spot of light, but rather detect contrast (edges or boundaries between light and dark) In the visual system, center/surround receptive fields are first found in the bipolar cells of the retina. The center of the receptive field is formed by the direct synapses between photoreceptors and the bipolar cell while the surround is caused by the inhibitory actions of horizontal cells being activated by the surrounding photoreceptors
40
OFF bipolar cell
bipolar cell that is inactivated by light (activated by dark). Their dendrites contain excitatory ionotropic (AMPA type) glutamate receptors. Since photoreceptors release more glutamate in the dark, “OFF” cells also release more neurotransmitter in the dark and less neurotransmitter in the light
41
ON bipolar cell -
bipolar cell that is active by light. Their dendrites contains inhibitory mGluR6 type glutamate receptors, thus they invert the signal the photoreceptors send. Since photoreceptors release less glutamate in the light, “ON” cells invert that signal and release more NT in the light
42
ON RGC
retinal ganglion cell that fires more action potentials when light is in the center. Receives excitatory synaptic input from ON-bipolar cells via AMPA type glutamate receptors
43
OFF RGC
retinal ganglion cell that fires fewer action potentials when light is in the center. Receives excitatory synaptic input from OFF-bipolar cells via AMPA type glutamate receptors
44
Illustrate how the major cell types of the retina are connected to each other and the function of each
45
Explain how shining light on either the center or the surround of an on-center (or off-center) ganglion cell’s receptive field differentially affects the cell’s activity and how that response may differ from an on or off-center bipolar cell.
46
Define receptive field and explain why a center-surround receptive field enhances sensitivity to contrast and edges
47
the science u
phenomenon reduction synthesis
48
two important lessons from the retina
hierarchical processing parallel processing
49
hierarchical processing
the receptive field properties get more complicated as the signal moves from photoreceptors to retinal ganglion cells
50
parallel processing
streams of information related to properties of the visual scene are dealt with simultaneously by different circuits
51
properties of visual world that visual system encodes
shape color position movement
52
what doesnt the visual system encode
we sense relative not absolute intensities- how bright is it compared to its surrounding, even if theyre the same one will look darker/brighter movements faster than 30fps per second movements slower than minute hand on a watch wavelength that are infrared or lower wavelengths (microwave) wavelengths that are uv or shorter lights brighter than some saturating photon flux light that is dimmer than some very low photon flux vertical depth disparity
53
retinofugal projection
pathway of optic nerve to brain called retinofugal has 5 parts before reaching visual cortex
54
r and l optic nerves cross at
optic chiasm
55
two sides of retina
temporal (close to temple) nasal (closer to nose)
56
visual field
right visual field comprised of right nasal and left temporal left visual field comprised of left nasal and right temporal
57
temporal part
does not leave the side of visual field it's on
58
optic chiasm
site of a decussation (crossing) so that the L visual field from both eyes projects to the R cortical hemisphere and R field to left hemisphere. the nasal part of retina crosses to the contralateral side, the temporal part remains on ipsilateral side
59
after the chiasm, the right and left optic nerves are called
optic tracts, and contain ipsilateral temporal and contralateral nasal rgc axons
60
lateral geniculate nucleus (lgn)
nucleus of thalamus dealing with vision thalamus takes in sensory info, but lgn is focused solely on vision is in dorso lateral part of thalamus left lgn is right visual field right lgn is left visual field has 6 layers, each layer filled with cells retinal axons that stay ipsilateral (from temporal side of retina) project to 3 layers of lgn (2,3,5) contralateral (nasal lateral) projects to other layers, (1,4,6)
61
optic radiations
r and l optic radiations exit thalamus to primary visual cortex (area 17, v1, or striate cortex) of r and l occipital lobes of cerebral cortex
62
nissl stain
stains material with nucleic acid in it
63
ventralmost layers 1 and 2
contain larger neurons (magnocellular) for motion
64
dorsalmost small cells
smaller cells, parvocellular, for shape
65
ventral to each layer of lgn
numerous tiny neurons, koniocellular, for color
66
three functional streams in lgn
magnocellular parvocellular koniocellular
67
magnocellular
layers 1 and 2 of lgn larger neurons motion m type rgc
68
parvocellular
layers 3, 4, 5, 6 smaller neurons shape p type rgc
69
konoiocellular
ventral to each layer of lgn numerous tiny neurons color non m non p rgc
70
m type, p type, nonm-nonp
retinal ganglion cells thought to innervate 3 lgn cell types respectively
71
parallel processing
rather than doing each separately, retina is doing all three at once
72
cortiofugal pathway
retina is not main source of synaptic input to lgn 80% of excitatory synapses in lgn are from primary visual cortex

neuro 80 (25 decks)

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