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NEU 220 Vision 1
Visual system: Stimulus to Eye
| Question | Answer |
|---|---|
| Visible spectrum | 400-700nm |
| Light is studied as both a ___ and a ___. | Wave and particle. |
| Light information is processed in which direction? | Back to front. |
| Where refraction occurs within the eye. | The lens and cornea. |
| Accomodation | Focusing an image by changing the shape of the lens. |
| Ciliary muscles | Change the shape of the lens. |
| Near point | The distance from the eye at which the eye cannot focus on objects. |
| Presbyopia | Near point increases with age. |
| Emmetropia | Good vision |
| Myopia | Poor vision due to the focus point coming up short from the back of the retina. |
| Hyperopia | Poor vision due to the focus point landing beyond the back of the retina. |
| Astigmatism | Misshapen lens; focusing ability varies based on retinal location. |
| Signaling pathway | Photoreceptors -> Bipolar cells -> Ganglion cells |
| Photoreceptor | Cell that detects and receives light. |
| Types of photoreceptors | Rods and Cones |
| Rods | Detect and receive photons of light |
| Outer segment | Part of rod made up of discs that receives photons. |
| Rodopsin | Specialized types detect specific wavelengths of light. |
| Retinal molecule | Part of visual pigment molecule; changes shape when struck with light, starting an enzyme cascade. |
| Dark current | No light present; Na channels open, Na flows in; cell is depolarized. |
| Light current | Light present; Na channels close; cell is hyperpolarized. |
| Graded signaling | Action potentials are not being fired. |
| Receptive field | Point in space from which photoreceptors receive light |
| Ideal stimulus | Light large enough to fill entire receptive field |
| Center-surround receptive field | When the ideal stimulus size is that which takes up the center of the receptive field, with no light around the outer rim. |
| Convergence | When a ganglion cell receives input from several rods or cones at once. |
| Spatial summation | Process by which rods detect multiple photons and add them together |
| Fovia | Part of the macula where there are very few rods, and a high concentration of cones. |
| What happens when light stimulus is too large for center-surround receptive field? | Light around edges of receptive field causes photoreceptors to send inhibitory signals to ganglion cells. |
| Hubel & Wiesel | Studied receptive fields in cerebral cortex; found it to be vertical bar across center fields. |
| Ganglion cell | Cell that receives light information from photoreceptors. |