Vision
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| What does the eye detect? | light
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| What factors must the eye encode of light? | 1. intensity
2. wavelength (visible light has a wavelength from 400nM to 700 nM)
3. location
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| What part of the eye is specialized to focus light? | photoreceptor cells
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| What is the purpose of the cornea | The cornea is specialized to refract light waves to focus light on the retina
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| Where does information leave the eye? | optic nerve
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| What is the beginning of the optic nerve? | CN II
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| Why does the lens "accommodate”? | The lens accommodates to help with refraction; accommodation allows for focusing on close objects
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| What does the lens do when it is unaccommodated? | The lens is smaller
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| What does the lens do when it is accommodated? | Widens; the lens also widens when an object is close
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| What does the accommodation reflex require? | The accommodation reflex requires an intact midbrain and oculomotor nerve (CN III)
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| As you age, what ability do you lose? | the ability to accommodate your lens and help with light refraction.
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| What do photoreceptor cells in rods do? | detect visible light
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| What do photoreceptor cells in cones do? | detect specific wavelengths of visible light
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| What NTs do photoreceptor cells release? | Glutamate
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| What kind of action potentials occur in photoreceptor cells? | graded potentials
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| Where are photoreceptor cells located? | In the back of the retina
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| Where are there lots of cones in the eye? | macula/fovea
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| Where is the area with the highest visual acuity (the ability to distinguish two points near each other)? | macula/fovea
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| What are cones responsible for? | color and form, fine detail, daytime vision
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| What are rods responsible for? | movement and low-light situations (night vision)
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| Where are there no cells in the retina? | In the blind spot
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| Where does transduction of light occur? | In the outer segments
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| What do photoreceptor cells do when exposed to light? | hyperpolarize
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| What happens when photoreceptor cells are in darkness? | lots of Na+ channels open causing cells to depolarize and reach -30mV and some Glu is released
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| What happens when photoreceptor cells are in the light? | Na+ channels close, cell hyperpolarizes, and the release of Glu is stopped
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| What is the rhodopsin GPCR made of? | opsin and retinal
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| What happens when light hits retinal? | It is activated
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| What is retinal converted to when it is deactivated? | 11-cis
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| How do photoreceptor cells respond to light? | Proportionally, cells hyperpolarize the most in bright light and the least in dim light
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| Why does each cone respond to a different wavelength? | Because each cone has a different receptor
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| What is the wavelength that each cone responds to? | blue
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| How would you describe someone's visual field? | part of space that you can see in one position without moving your head
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| What is the receptive field of photoreceptor cells? | The spot on the retina where the light influences the photoreceptor cell
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| What do bipolar cells receive input from? | photoreceptor cells
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| What do ganglion cells receive input from? | Bipolar cells
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| Where do ganglion cells project to? | the brain
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| What do horizontal cells allow for? | Horizontal cells allow for communication between photoreceptor cells
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| What do amacrine cells do? | Amacrine cells modulate input to ganglion cells
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| What results in high acuity integration in bipolar neurons? | When there is one photoreceptor cell and one bipolar cell in the fovea
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| What results in low acuity integration in bipolar neurons? | When there are many photoreceptor cells and one bipolar cell outside of the fovea
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| What must be absent for glutamate to be released in bipolar cells? | No action potentials can be occurring
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| Describe what occurs in on-center bipolar cells | - Metabotropic receptors
-inhibited by glutamate
-stay depolarized when the photoreceptor cells is in the light
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| Describe what occurs in off-center bipolar cells | - Ionotropic receptors
-depolarized by glutamate
-only release NTs when photoreceptor cell is in the dark
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| Describe the receptive field of bipolar cells | -larger receptive fields
-there are 1 to several direct synapses (in the center)
-lots of indirect synapses via horizontal cells (in the surrounding)
-receptive fields of neighboring bipolar cells overlap
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| What are horizontal cells activated by and what do they do? | Horizontal cells are activated by glutamate and inhibit neighboring photoreceptor cells by releasing GABA
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| When are on-center bipolar cells maximally depolarized? | When there is light in the center and the surrounding is dark
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| When are off-center bipolar cells maximally depolarized? | When there is darkness in the center and light in the surrounding
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| What type of glutamate receptors do ganglion cells have? | Ionotropic
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| What type of cells do ganglion cells do the exact same thing as? | Bipolar cells; they are center-surrounded
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| Why are ganglion cells able to have action potentials unlike bipolar cells? | They are really long
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| Describe the occurrence of action potentials in off-center ganglion cells | - When it is dark inside the receptive field = there are more action potentials
-When it is all light/all dark in receptive field = the baseline response is present
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| Describe the occurrence of action potentials in on-center cells | - light in the center of the receptive field= increase in the number of action potentials
-all light/all dark in all receptive field= baseline response rate
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| How are ganglion cells differentiated? | By size
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| Describe M-type ganglion cells | LARGE; respond most to change; receive most input from rods and recognizes movement
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| Why do M-type cells have rapidly changing response rates? | Because M-type ganglion cells recognize movement
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| Describe P-type ganglion cells | SMALL; respond to less stimulus than M-type; receive input from cones and recognize color more
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| Where do ganglion cell axons leave the eye? | Through the optic nerve (CN II)
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| Where do most (90%) of retinofugal projections from ganglion cell axons go? | the lateral geniculate nucleus of the thalamus
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| What other places in the brain do retinofugal projections from the ganglion cell axons and optic nerve go? | superior colliculus, hypothalamus
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| Where do axons in the nasal half of each eye decussate at? | The optic chiasm
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| Does information from the right visual field (from either eye) go to the right side of the brain on the left side of the brain? | left
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| What type of cells are the receptive fields of LGN cells most identical to? | Ganglion cells
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| What might the lateral geniculate nucleus do? | focus attention
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| Where does the LGN project to? | primary visual cortex (V1); responsible for optic radiation
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| What are the spatial maps of visual field called? | retinotopy
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| From where do most of V1 process information? | Fovea
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| Where does the input from layers in the V1 go? | 1. M cells input in LGN go to 4ca (4C alpha)
2. P cells input in LGN go to 4CB (4C beta)
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| What are the two layers in the LGN? | M-type layer
P-type layer
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| From which layers in the primary visual cortex is output mostly from? | Layers 3 - goes to other cortical layers
layers 5 and 6 - subcortical
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| In which layer of v1 is information from each eye still separate? | Layer 4
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| Where do most neurons in layer 4c project to? | Layer 3 (this is a connection within the striate cortex)
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| In which layer are there binocular cells and in which layers cells is input from both eyes combined? | Layer 3
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| What are some cells outside of layer 4c described as? These cells have receptive fields that use bars of lights as best stimulus | Ganglion cells with orientation-specific receptive fields
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| What most likely underlies orientation-specific receptive fields? | spatial summation
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| Where does information from the V1 go to? | -the visual cortex (V2)
-dorsal pathway (for localization)
-ventral pathway (for identification)
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| What type of neurons have large receptive fields that require specific types of motion? | Dorsal stream neurons
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| What disease results from damage to the dorsal stream neurons? | akinetopsia
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| What type of neurons have large receptive fields that require very specific objects? | ventral stream neurons
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