L5 Seeing things: the retina part Flashcards
Only ___ of the human eyeball is exposed.
1/6
The eye muscles are the most ____ muscles in the human body.
active
An iris has _____ unique characteristics
256
Eyes are the _____ most _____ organ in body
second; complex
1 eye has ___ blind spot
one
The human eye only see three colours, ________
red, green, blue
Colour blindness is more common in ______
males
There are around ______ million blind people in the world, and ____% of vision problems worldwide are avoidable/ curable
39; 80
The total retina is a __________ of between ____ and ____ mm in diameter
circular disc; 30; 40
Area of the human retina is about _____ square cm
10
Sclera is a _____ & _____ tissue
tough; elastic
What does sclera do?
avoid the eye from expanding from the pressure
What does choroid do?
provide oxygen and nutrition to the retina
What does retina do?
Neuronal tissue that can convert light signal and send to the brain
How does the posterior segment maintain the round shape?
The gel-like fluid w/ intraocular fluid
What only goes out from the optic nerve, but not in?
Axons of output neurons
What goes in and out from the optic nerve head?
Blood vessels
Which part of the eye has the highest acuity vision?
Fovea
Why there is a blind spot?
There is an optic nerve head in our eyeball
Which part also provide us high acuity vision?
Macular
Which part is the thinnest place in retina?
Fovea
What is the thickness of retina?
200 millimetres thick
The ________ shows greatest variations in the center.
Retinal thickness
The retina is thinnest at the _______ and thickest at the _________
foveal floor; foveal rim
Beyond the fovea, the retina rapidly thins until the _____
equator
Outer plexiform layer is where the _________ and the ________ of the other inter neurons meet
axons of the photoreceptor cells; dendrites
Inner plexiform layer is where the ________ meet with __________
axons of the inner neurons; ganglion cell dendrites
Nerve fibre layer is where ___________, stack up and ______ and growing towards the _________, all go out
axons of all the ganglion cells; pointing; optic nerve head
________ layer -> inner ______ layer -> inner _______ layer -> outer ______ layer -> outer _______ layer
ganglion cell; plexiform; nuclear; plexiform; nuclear
The retina is composed of ______ major cell types that are arranged in _____ cellular layer (_____) separated by two ______ layers (_____)
five; three; GCL, INL, ONL; synaptic; IPL, OPL
What are the photoreceptors?
Cones and rods
Where is horizontal cell found?
At the border between the outer plexiform layer and the inner nuclear layer
Where is amacrine cell found?
Inner nuclear layer connect to inner plexiform layer
Where is ganglion cell found?
Ganglion cell layer
Which is the only output cell?
Ganglion cell
Lateral information flow is to contact ______ & _____ and modify their ________
bipolar cells; ganglion cells; signal transduction
Dendrites of horizontal cells contact with _______ & ______, to modify the signals that’s transmitted from ________ out to ________
photoreceptor; bipolar cells; photoreceptor; bipolar cells
Which layer is the outermost layer?
Photoreceptor cells
What does the photoreceptor cells do?
Absorb light & convert it into neuronal signal (phototransduction)
Neuronal signals from photoreceptor cells are passed _______ to ________, which in turn connect to ____________ in the ________ layer.
synaptically; bipolar cells; retinal ganglion cells; innermost
Bipolar neurons transmit information _______ (along the light path)
vertically
There are many lateral connections provided by __________ & _________ and they transmit information ________ (______ to light path)
horizontal cells; amacrine cells; sideways; perpendicular
Horizontal & amacrine cells mostly provide _______ and to ______ so that we can extract the most important info from what we see
modification; process information
______ are the output neurons of the retina
Retinal ganglion cells
The retina (the whole circuit) performs ____________
low-level visual processing
Retina extracts from the raw images in the left and right eyes certain _______ & ________ features and conveys them to ________
spatial; temporal; higher visual centers
What does horizontal cells do?
Regulate and integrate signals from photoreceptor to bipolar
What does amacrine cells do?
Regulate and integrate signal from bipolar to ganglion cells & modify signal transduction
Rods and cones differ in ______ and more importantly in _______
morphology; function
What can rod do?
Signal the absorption of a single photon
What is rod responsible for?
Vision under dim illustration
Which cell is less sensitive to light?
Cones
What is cone responsible for?
Vision in daylight
Which photoreceptor is considerably faster?
Cones
Human retina contains approximately ____ rods and _____ cones
110 million; 6 million
Rods and cones are NOT equally distributed, in most part of the retina, the _____ predominate, outnumbering the ____ by some of _____ to ___
Rods; cones; 10; 1
Fovea only have _____ (photoreceptor)
Cones
Which photoreceptors can see colour?
Cones
Which photoreceptors have higher acuity?
Cones
Light comes, hit one of the ____, activate _______
light sensing proteins; signal transduction
Which part of the photoreceptors is the energy factory of neurons?
Inner segment
How ATP is used in photoreceptors? Why?
To maintain its membrane potential because photoreceptors are very high energy demanding
Why need many membrane discs?
On each membrane discs, there are many light sensing proteins and they are transmembrane proteins, so they need membrane surface to be inserted there
What does the membrane disc morphology do?
helps to maximize the surface areas so that we can more light sensing proteins in one place
Cats are nocturnal so they have ___ to ___ times as many ____ for viewing objects in low light as humans. They also have better _____ vision
6; 8; rods; peripheral
Humans have more ____, which provides us much more ___ palette of colour and __ acuity
cones; vibrant; higher
In the fovea, corresponding to the very center gaze, the ____ is shifted aside so light has a direct access to the ______
Proximal neurons; photoreceptors
The cones are highly concentrated at the _____, an area of just ____. This region is responsible for our ______ vision and could be regarded as the most important square milimeter in our body
fovea; 1 square milimeter; high-acuity colour
_____ does not have rods, so it is ____
Fovea; night blind
There is a limit in our ______, so if looking at a device which has a higher resolution than our _______, we can’t distinguish
retina; retinal resolution
In which part are the interneurons and ganglion cells that connect to the fovea are pushed away?
Avascular zone
The optic nerve is a _____-free zone
photoreceptor
Its intraocular portion, the optic disc is positioned approximately _____ temporal to the ____
15 degrees; fovea
Why does the receptor gap does not present a conscious visual problem?
The binocular vision fills in the gap
What is the portion of the electromagnetic spectrum that is visible to the human eye?
Visible spectrum
Human eye wavelengths are from ____ to_____
400; 700nm
Birds can see ultraviolet (____-____)
300-400nm
Human have _____ vision but most mammals are _______ and they can’t see _____. some species are _____ with an extra UV opsin
trichromatic; dichromatic; red; tetrachromatic
Which animal can see the most colours? and they have how many types of photoreceptor cells?
Mantis shrimp; 12-16
How many times will a transmembrane protein go through the membrane?
7 times
The 3 different types of cones and rods have slightly different ___ which are sensitive to different ____
opsins; wavelengths
How many types of optimum protein?
1
Wavelength of ___ will activate blue opsin protein
420
Wavelength of ___ will activate green opsin protein
534
Wavelength of ___ will activate red opsin protein
564
Wavelength of ___ will activate rhodopsin
498
If move away from the wavelength, can the opsins still be activated?
Yes, but less efficient
People with normal vision are _____
Trichromat
People who can’t see red are ____
Protanopia
People who can’t see green are ____
Deuteranopia
Which disease’s vision appears to be darker?
Protanopia
Why red-green colourblindness is more common in male?
Male has one X chromosomes and red-green are on X chromosomes. If one is defected, they will be colourblind. But female has 2 X chromosomes, so it takes them to have both to be defective.
Shining light on a photoreceptor, leads to membrane _____
hyperpolarisation
What absorbs photons?
Rhodopsin molecules in the outer segment discs
Absorbing photons leads to ________ and further leads to _______ and _______
the closure of cGMP-gated channels in the plasma membrane; hyperpolarizes the membrane; reduces the rate of release of the neurotransmitter glutamate
Light stimulation of rhodopsin in the receptor disks leads to ________ (____), which in turn activates a ___________ (___). The ________ hydrolyzes _____, reducing its concentration in the outer segment and leading to ___________
activation of a G-protein; transducin; phosphodiesterase; PDE; PDE; cGMP; closure of sodium channels in the outer segment membrane
1 rhodopsin can activate ____ G Protein. signal is hence amplified ____
500; 500 times
1 activated PDE can hydrolyze ____ cGMP. signal is amplified ___
10^5
Retinitis Pigmentosa is an blinding disease caused by loss of ____ at first and loss of _____ secondarily in the _____
rods; cones; retina
Retinitis Pigmentosa generally affected how many people in the world?
1 in 4000
Retinitis Pigmentosa can be caused by mutations in any of more than ____ genes, and a lot of these genes are in the ________ pathway
60; phototransduction
Retinitis Pigmentosa patients are ____ at young age, later form _____ and slowly become _____
night blind; tunnel vision; completely blind
Is Retinitis Pigmentosa treatable?
No
Rhodopsin absorbs light, converted from _____ in dark (____) to ______ (____)
bent shape; cis-retinal; straight; trans-retinal
_______ are faster to regenerate their _______, _________ for 50%; while it takes ______ to regenerate 50% of the bleached rhodopsin
Cones; photopsin; 90 secs; 5 minutes
What are the functions of retinal pigmented epithelium?
Prevents light refractions throughout the eyeballs; stores large quantities of vitamin A, which is a precursor of visual pigment
What is RPE65?
A retinal isomerohydrolase necessary for producing 11-cis-retinal
Leber’s congenital amaurosis is a ______ diseases with problems in the ______.
congenital; visual cycle
Leber’s congenital amaurosis is an ________ diseases in about 1 in ______ people.
autosomal recessive; 80000
Leber’s congenital amaurosis condition is caused by mutation of any of ____ known genes, including _____
18; RPE65
Leber’s congenital amaurosis lose vision at a ______ age
young
Is Leber’s congenital amaurosis treatable?
Yes, by gene therapy
More than _____ nerve fibres connect each eye to the brain
1 million
Can retinas be transplanted?
No, because don’t know how to connect 1 nerve to 1 neuron in the brain
Retinal ganglion cells types are based on their ____ (ON& OFF cells)
firing property
Retinal ganglion cells types are based on their size. Small: _____ Big:____ and what they responsible for?
Midget ganglion cells (colours); Parasol ganglion cells (movement)
Receptive field of an individual sensory neuron is the particular region of the sensory space in which a stimulus will ________
trigger the firing of that neuron
The receptive field of a ganglion cell in the retina of the eye is composed of input from _________
all of the photoreceptors which synapse with it
ON cells = ____-center; _____-surround cells
on; off
If the light intensity is suddenly increased, _______ fire more rapidly
on-cells
If the light intensity is suddenly decreased, _______ fire more rapidly
off-cells
OFF cells = ____-center; _____-surround cells
off; on
When the neuron is not stimulated, what will the neuron do?
Fire at basal rate (homeostatic)
What happens if light stays on?
First is fire rapidly, then get used to the signal and fire to the basal rate (protective mechanism)
______ emphasize of moving objects and _____ in the visual input
Ganglion cells; temporal changes
A moving object elicits strong firing in the RGCs near the ______ of the object’s image because these are the only regions of ________ and where the __________
edges; spatial contrast; light intensity changes over time
The __/___ & ___ of an object are important info for RGCs
shape; outline; movement
What is microsaccade?
When fixing our gaze, small automatic eye movements scan the image across the retina to prevent the world from disappearing
What is this effect? : When one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point will fade away and disappear
Troxler effect
The vertical excitatory pathways are modulated by ______
horizontal inhibitory connections
________ begins at the ______ segment of the ______ when a pigment molecule absorbs a photon. ______ is amplified, photoreceptor cell is ______ and the glutamate release is _______
Phototransduction; outer; photoreceptor cell; G protein cascade; hyperpolarized; reduced
Fine spatial resolution is maintained only in a _____ region at the _______
narrow; center of gaze-fovea
Different population of ____ transmit multiple ________ of the retinal image along ____ pathways
RGCs; neural representations; parallel
