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BIO 435
Vision
| Question | Answer |
|---|---|
| What does the eye detect? | light |
| What factors must the eye encode of light? | 1. intensity 2. wavelength (visible light has a wavelength from 400nM to 700 nM) 3. location |
| What part of the eye is specialized to focus light? | photoreceptor cells |
| What is the purpose of the cornea | The cornea is specialized to refract light waves to focus light on the retina |
| Where does information leave the eye? | optic nerve |
| What is the beginning of the optic nerve? | CN II |
| Why does the lens "accommodate”? | The lens accommodates to help with refraction; accommodation allows for focusing on close objects |
| What does the lens do when it is unaccommodated? | The lens is smaller |
| What does the lens do when it is accommodated? | Widens; the lens also widens when an object is close |
| What does the accommodation reflex require? | The accommodation reflex requires an intact midbrain and oculomotor nerve (CN III) |
| As you age, what ability do you lose? | the ability to accommodate your lens and help with light refraction. |
| What do photoreceptor cells in rods do? | detect visible light |
| What do photoreceptor cells in cones do? | detect specific wavelengths of visible light |
| What NTs do photoreceptor cells release? | Glutamate |
| What kind of action potentials occur in photoreceptor cells? | graded potentials |
| Where are photoreceptor cells located? | In the back of the retina |
| Where are there lots of cones in the eye? | macula/fovea |
| Where is the area with the highest visual acuity (the ability to distinguish two points near each other)? | macula/fovea |
| What are cones responsible for? | color and form, fine detail, daytime vision |
| What are rods responsible for? | movement and low-light situations (night vision) |
| Where are there no cells in the retina? | In the blind spot |
| Where does transduction of light occur? | In the outer segments |
| What do photoreceptor cells do when exposed to light? | hyperpolarize |
| 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 |
| What happens when photoreceptor cells are in the light? | Na+ channels close, cell hyperpolarizes, and the release of Glu is stopped |
| What is the rhodopsin GPCR made of? | opsin and retinal |
| What happens when light hits retinal? | It is activated |
| What is retinal converted to when it is deactivated? | 11-cis |
| How do photoreceptor cells respond to light? | Proportionally, cells hyperpolarize the most in bright light and the least in dim light |
| Why does each cone respond to a different wavelength? | Because each cone has a different receptor |
| What is the wavelength that each cone responds to? | blue |
| How would you describe someone's visual field? | part of space that you can see in one position without moving your head |
| What is the receptive field of photoreceptor cells? | The spot on the retina where the light influences the photoreceptor cell |
| What do bipolar cells receive input from? | photoreceptor cells |
| What do ganglion cells receive input from? | Bipolar cells |
| Where do ganglion cells project to? | the brain |
| What do horizontal cells allow for? | Horizontal cells allow for communication between photoreceptor cells |
| What do amacrine cells do? | Amacrine cells modulate input to ganglion cells |
| What results in high acuity integration in bipolar neurons? | When there is one photoreceptor cell and one bipolar cell in the fovea |
| What results in low acuity integration in bipolar neurons? | When there are many photoreceptor cells and one bipolar cell outside of the fovea |
| What must be absent for glutamate to be released in bipolar cells? | No action potentials can be occurring |
| Describe what occurs in on-center bipolar cells | - Metabotropic receptors -inhibited by glutamate -stay depolarized when the photoreceptor cells is in the light |
| Describe what occurs in off-center bipolar cells | - Ionotropic receptors -depolarized by glutamate -only release NTs when photoreceptor cell is in the dark |
| 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 |
| 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 |
| When are on-center bipolar cells maximally depolarized? | When there is light in the center and the surrounding is dark |
| When are off-center bipolar cells maximally depolarized? | When there is darkness in the center and light in the surrounding |
| What type of glutamate receptors do ganglion cells have? | Ionotropic |
| What type of cells do ganglion cells do the exact same thing as? | Bipolar cells; they are center-surrounded |
| Why are ganglion cells able to have action potentials unlike bipolar cells? | They are really long |
| 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 |
| 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 |
| How are ganglion cells differentiated? | By size |
| Describe M-type ganglion cells | LARGE; respond most to change; receive most input from rods and recognizes movement |
| Why do M-type cells have rapidly changing response rates? | Because M-type ganglion cells recognize movement |
| Describe P-type ganglion cells | SMALL; respond to less stimulus than M-type; receive input from cones and recognize color more |
| Where do ganglion cell axons leave the eye? | Through the optic nerve (CN II) |
| Where do most (90%) of retinofugal projections from ganglion cell axons go? | the lateral geniculate nucleus of the thalamus |
| What other places in the brain do retinofugal projections from the ganglion cell axons and optic nerve go? | superior colliculus, hypothalamus |
| Where do axons in the nasal half of each eye decussate at? | The optic chiasm |
| 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 |
| What type of cells are the receptive fields of LGN cells most identical to? | Ganglion cells |
| What might the lateral geniculate nucleus do? | focus attention |
| Where does the LGN project to? | primary visual cortex (V1); responsible for optic radiation |
| What are the spatial maps of visual field called? | retinotopy |
| From where do most of V1 process information? | Fovea |
| 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) |
| What are the two layers in the LGN? | M-type layer P-type layer |
| From which layers in the primary visual cortex is output mostly from? | Layers 3 - goes to other cortical layers layers 5 and 6 - subcortical |
| In which layer of v1 is information from each eye still separate? | Layer 4 |
| Where do most neurons in layer 4c project to? | Layer 3 (this is a connection within the striate cortex) |
| In which layer are there binocular cells and in which layers cells is input from both eyes combined? | Layer 3 |
| 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 |
| What most likely underlies orientation-specific receptive fields? | spatial summation |
| Where does information from the V1 go to? | -the visual cortex (V2) -dorsal pathway (for localization) -ventral pathway (for identification) |
| What type of neurons have large receptive fields that require specific types of motion? | Dorsal stream neurons |
| What disease results from damage to the dorsal stream neurons? | akinetopsia |
| What type of neurons have large receptive fields that require very specific objects? | ventral stream neurons |
Created by:
keiannaowens
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