Visual System Part 1 Flashcards
True or False: Insects and other arthropods have compound eyes, made up of many ommatidia which are small individuals retinas
True
Each __________ is looking at a slightly different but overlapping region of visual space.
Ommatidia
The fly’s eyes see a ________________, but the fly brain perceived ____________.
Fragmentary map
A normal picture
Fly nervous system connects up ______________ within several ommatidia which are looking at the same part of the visual scene.
Receptor cells
True or False: The fly’s eyes see a fragmentary map, but the fly’s brain perceives a normal picture.
True
We have two eyes, rather than 100s of ommatidia, which each gives us a ___________ of the world.
Different
True or False: Our brain does not need to put together images from our two retinas into a congruent whole so that we don’t see double.
False:
Our brain does need to put images together
In the process of merging the two eyes views of the world, our brains also use the differences between the views from our two eyes to calculate _______.
Depth
True or False: The optics of lens objects are projected upside down onto our retina. Our brain is very goofed at inverting images.
True
What is the consequence that arises from the optical nerve?
The optic nerve creates a hole (an area lacking photoreceptors) in the retina, and therefore a hole in the eye’s view of the world.
What is a solution to the optical nerve issue?
Put the optic nerve in a different part of the visual field in two eyes so that where one eye has a hole in its view, the other eye does not.
The solution of the optical nerve issue would mean that we should have a blank spot known as a ________, in our view of the world when we close one eye.
Blind spot
Where does the transduction of light occur in the visual system?
Occur in the photoreceptors
Label the blue circles in the retinal circuitry
The top left circle is the horizontal cell
The top right circle is the bipolar cells
The bottom left circle is the part of the amacrine cell of the indirect pathway
The bottom right circle is the ganglion cells
The organization of the retina is in __________.
The can been seen with a tissue section stained with _______________.
Layers
Nuclear staining
Fill in the blanks for the retinal circuit
- ____________ travels all the way in the back of the eye to the retina.
- From the retina, (1) will stimulate the ____________.
- Infomation from (2) is trsnfer to the ___________.
- Then to the _________ which send their axons through the optic nerve to the brain.
Infomation passing though the retina is modified by the lateral connection provided by __________ and _________ cells.
- Light travels all the way in the back of the eye to the retina.
- From the retina, (1) will stimulate the photoreceptors.
- Information from (2) is transfer to the bipolar cells.
- Then to the ganglion cells which sends their axons through the optic nerve to the brain.
Infomation passing though the retina is modified by the lateral connection provided by horizontal and Amacrine cells.
Where are the photoreceptors in the human eye?
Why is this the case?
The photoreceptors on the inside, all the way in the back of the eye.
So that light has to pass all the way through the retina before transduction can occur
What are the two types of photoreceptors?
Rods and Cones
Choose the best option
Rods are very (low/high) sensitivity to light and therefore are useful when light levels are (high/low)
high ; low
Choose the best option
Cones are (more/less) sensitive.
(1/2/3) types of cones with different wavelengths preferences
(1/2/3) cone types underlie color vision
less ; 3; 3
Why do we not see in color at night?
Only rods are stimulated. There is only one type of rod.
Looking at the range of luminance figure. Each box represents different types of photoreceptors’ activations. Label which ones are activated.
The red box on the lowest levels of luminance, only rods are activated.
The orange box on the regular levels of luminance, both rods and cones are activated.
The green box on the high level of luminance, only cones are activated.
How are the rods and cones distributed through the retina?
Cones are of high density in the center of the fovea.
Rods are distributed throughout the retina except for fovea.
True or False: Cone vision: different sensitivities for different types of cones.
In other words, different rhodopsin (photopigment).
True
True or False: Differences in just a few amino acids accounts for the differences in spectral sensitivity
True
What occurs in the rods, the photoreceptor, in the dark?
Rods are always depolarized and therefore always releasing NTs.
Why do rods always depolarized and always releasing NTs? What ion(s) is responsible?
This is due to a constant flow of Na+ ions into the cell through channels in the outer segment cell membrane
Na+ influx is balanced by ______ leaving thru channels in the inner segment cell membrane.
Ion concentrations are maintained by the ____________.
Na+ channels in the outer segment are ______________.
(Dark photoreceptors (rods) are always depolarizing always releasing NTs)
K+ ions
Na+/ K+ exchange pumps
cGMP gated Na+ channels
What would happen if the light hits the rod, photoreceptor, would the Na+ open or close?
The cGMP Na+ would close due to the removal of cGMP and can’t open the cGMP-gated channel
What effect does this have on the photoreceptor’s membrane potential when light hits the rod photoreceptor?
Hyperpolarized (Inward current stopped)
Is more or less transmitter released by a photoreceptor when light hits it?
Less
When light hits a photoreceptor, it is absorbed by the photopigment ___________.
Rhodopsin
What does rhodopsin cause?
Photoisomerization of retinal and result in a conformational change in rhodopsin.
What does the conformation change of rhodopsin interact with?
Interact with and activate a G protein called transducin.
What does transducin activate?
(when light hits rods)
Transducin then activates phosphodiesterase which hydrolyzes cGMP into 5’ GMP, closing the cGMP channel. No depolarizing.
_____________, is the modern technology of phototranduction.
Optogentics
True or False: Channelrhodopsin are in humans.
False
Channelrhodopsin is from ________ and is a light-sensitive ion channel.
Stimulation with _____________ photoisomeriezes retintial to directly open channel.
Targeted neurons are excited by stimulation with light implanted ___________.
Algae
Blue light
fiber optic cable
When the photoreceptors pass information to bipolar cells then retinal ganglion cells (RGCs), the response of RGC can either be _________ or ____________, when a small light spot is applied.
Activation (on)
or
Inactivation (off)
Both the Activation (ON) pathway and the Inactivated (OFF) are __________ when light shines it will activate the ganglion cells and activate all the optic nerve.
functional
True or False: The on or off pathways are parallel pathways.
True
What do the on and off pathways depend on for their response?
Light sources
What is the central illumination?
The light could shine on the center of the receptive field
What is an annular illumination?
Light shine on the peripheral of the receptive field
What are the direct pathways?
Signals are transmitted directly from photoreceptors to bipolar cells and then to ganglion cells.
What are the indirect pathways?
Signals received from photoreceptors are passed to horizontal cells (reversing the response).
The horizontal cells then affect the activity of another photoreceptor cell and the bipolar cell that is connected to other photoreceptor cells.
Indirect connection are __________
Inhibitory
The synapse between photoreceptor cell and bipolar cell (direct pathway) is ____________, the change of the neuron membrane is the same between the photoreceptor and bipolar cell.
Sign-conserving
True or False: In Indirect pathways, the change of the neuron membrane is different from bipolar cell
True
If Indirect pathway is ________ then direct pathways is ___________. Vice versa
Inhibitory ; excitatory
What are sign-reversing synapses and sign-conserving synapses?
Sign -reversing synapses: One is hyperpolarized while the other is depolarized on bipolar cell.
Sign-conserving synapses: Both photoreceptors cell and bipolar cells are hyperpolarized or depolarized off the bipolar cell.
__________ released from the photoreceptor cell will have a different response to a bipolar cell this depends on the type of the receptors expressed on the postsynaptic membrane of the bipolar cells.
Glutamate
What Glutamate receptor is on the ON-bipolar cells, the sign reversing synapses?
Metabotropic receptor mGluR6.
Activation of mGluR6 causes closure of the ion channel. Depolarizing the cell
What Glutamate receptor is on the Off bipolar cells (sign-conserving synapses)
Ionotropic Receptor (AMPA or Kainate) allow cation conductance
True or False: Not all of the indirect connections (lateral connection) in the retina (through horizontal and/ or amacrine cells) are inhibitory.
False
All of the indirect connection are inhibitory
Lateral inhibition are used to identify _________.
Junctions
Looking at this image of direct and indirect pathways. Also, this image let consider the ON pathway (activation)
If light shines on the photoreceptor of the middle pathways, will the middle pathways ganglion cell be excited or inhibited?
Excited –> direct pathway
Since all the lateral connections are inhibitory, if light shines on the middle photoreceptor, will the other two ganglion cells be exited or inhibited?
Inhibited
What is one advantage of lateral inhibition?
For seeing edges.
Lateral inhibition (a.k.a. ___________ in the receptive field of cortical neurons) is observed in __________.
Ex: Lateral inhibition is an important mechanism for improving _____________ in the somatosensory system.
Surround inhibition
all sensory system
Tactile resolution
If you are looking down on the retina, what are you looking at?
A sheet of photoreceptor cells
How does the receptive field of photoreceptor look like?
Every ON-bipolar and ganglion cell receives ________________ from photoreceptor above it, and lateral inhibition , ___________, from the photoreceptors all around it.
Direct excitatory input
Indirect pathway
What is the on-center receptive field?
Excited by light in the center and inhibited by light in the surroundings.
What is the off-center receptive fields?
Off-center receptive fields are generated in the same way for Off bipolar and ganglion cells.
Hemann Grid illusion
On ganglion cells with receptive fields at the _________have more of their inhibitory surround in the light.
They are more inhibited and fireless and making the brain think there is less light in the center.
White intersections
Any single cone type (can/cannot) tell us much about what wavelength of light is present in the stimulus because the response of the cone depends on both the ___________ and ___________ of the stimulus.
cannot
wavelength
intensity
A single cone (can/cannot) tell whether it is being stimulated by a weak stimulus at its preferred wavelength or a stong stimulus at another wavelength.
cannot
True or false: Our brains can use the ratios of response in different cone types to determines the wavelength of a stimulus.
True
True or False: The ratio of responses in the different cone types will change when the stimulus intensity changes.
False
The different cone types will not change when the stimulus intensity changes.
