Glossary of SFS - Early Visual Processing
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- Type of contast in which the light from the object is brighter than the surroundings.
- Type of contast in which the light from the object is dimmer than the surroundings.
- Above threshold, the retina is less concerned with the number of photons and more interested in what?
- The contrast between two objects
- Is the inner or outer layer:
1. Closest to the vitreous humor?
2. Clostest to sclera; photoreceptors are here
- 1. inner
- Photoreceptors synapse on what type of cells and where?
- bipolar cells in the outer plexiform layer
- Bipolar cells synpase on what?
- Ganglion cells
- Photoreceptors in retina.
- Rods and cones. Allows for expansion of the visual range of the perception of light.
- Ganglion cells typically synapse where?
- Lateral geniculate nucleus
- Circuit involving horizontal and amacrine cells allowing lateral inhibition and center-surround organization.
- Lateral circuit; important for sensing contrast (color and light/dark)
- Important in determining light intensity increases and decreases.
- On/Off pathways
- Visual pigment in rods
- Visual pigment in cones
- Photoreceptors ___________ in the light and ____________ in the dark.
- hyperpolarize; depolarize
- Area of retina with a high density of cones and allows viewing of fine detail. Damage here can be detrimental to vision
- 95% of photoreceptors in humans.
- Photoreceptors requiring only one photon to fire. High degree of spatial summation. Very sensitive with poor spatial localization.
- What kind of photoreceptors have slow temporal resolution?
- Photoreceptors with high temporal resolution but less sensitivity. Wide range of adaptation due to circuit and internal photoreceptor adaptation. Color vision.
- Difference in rod and cone function is due to what?
- Differences in the signaling cascades.
- Rod signaling cascade pathway.
- 11-cis-retinal (light>conf. change) -> activates rhodopsin (GPCR) -> activates g-protein transducin -> activates phosphodiesterase which degrades cGMP.
- What modulates the membrane potential?
- Concentration of cGMP. Cleavage of cGMP causes membrane channel to close preventing ions from entering and depolarizing.
- 1. Activates transducin 500 fold. High sensitivity, slow recovery.
2. Activates transducin 50 fold. Faster recovery. Less sensitivity.
- 1. Rhodopsin
- Increasing the brightness beyond the threshold does what to channels?
- Prevents the channels from reopening for longer.
- Photoreceptors fire what type of responses?
- Graded and continuous, not spikes
- NT of photoreceptors released in the dark.
- Photoreceptors that generate a faster response, but require more photons.
- What location in the eye does each photoreceptor have its own bipolar cell and ganglion cell?
- 1. Wiring pattern increasing SENSITIVITY.
2. Wiring pattern increasing CONTRAST.
- 1. Convergent (several photorecptors to one photoreceptor). Low spatial res, but sensitive.
2. divergent. One photoreceptor to more than one bipolar cell. On/off pathways.
- Push-Pull system
- Depolarization will stimulate one ganglion cell, while hyperpolarization will stimulate another. Generates larger signal differential to maximize contrast.
- ________ pathways formed by horizontal and amacrine cells. ______ inhibition important in determining edges of an object.
- Lateral; lateral. Active photoreceptor inhibits its neighbors for sharp border between activation/inactivation.
- On/off pathways require ______ wiring. Response is determined by ________.
- Divergent; receptor type (not the NT)
- Has an inverting synapse. A secondary transmitter actually closes channels (hyperpolarization). Bipolar cell in other pathway has receptor that responds by opening channels.
- ON cell.
- The only photorecptor in the fovea that the bipolar cell receives input from.
- Midget bipolar cells (small dendritic arbor)
- Off pathway.
- Light hyperpolarizes > less glutamate released > off bipolar cell hyperpol. since no longer stimulated by NT > ganglion cell hyperpolarizes decreasing spike frequency
- On pathway.
- Remember inverting synapse. Dark; photoreceptor depol., so releases glutamine causing hyperpol in bipolar cell > ganglion cell hyperpolarized - spike freq. decreases. When light hyperpolarizes photoreceptor, ceases to release NT > channels in bipolar cell open, depolarizes > stimulates ganglion cell increasing spike frequency.
- Requires amacrine and horizontal cells to mediate lateral inhibition.
- Center and surround organization.
- Response from light stimulation.
- Has an inverted synapse and feeds back to ganglion cell to cancel out stimulus from bipolar cell.
- Amacrine cell (bipolar cell stimulates ganglion cell and amacrine cell)
- Fields that involve a midget ganglion cell receiving a signal from one central bipolar cell.
- Center and surround receptive fields
- Bipolar cells around the central bipolar cell in 3D space stimulate ________ cells feeding onto the ganglion cell in a(n) ________ fashion.
- amacrine; inverted
- If bipolar cells around central bipolar cell are also stimulated by light, the signal to the ganglion would actually _________.
- In the fovea, ganglion cells are highly __________.
- dispersed (from fovea photoreceptors)
- Determines if cell is an On or Off bipolar cell.
- Where the bipolar cell dendrite resides in the sublamina
- On responses are in the __________ ring.
Off are in the __________ ring.
- outermost; innermost
- Identified by their small dendritic arbors.
- Midget ganglion cells
- Responds when blue light goes on or yellow light goes off.
- Bistratified ganglion cell.
- Do not have specific ganglions, but piggyback signals through the cone system using AII amacrine cells.
- Lighting conditions when rods and cones are both active
- Pathway of rod stimulation.
- Rod photoreceptor stimulates rod bipolar cell which transfers signal to A2 amacrine cell, stimulating the cone system.
Rod system has a high degree of spatial summation.
- Encode brightness of light by temporal frequency.
- Leads to centersurround receptive fields by lateral inhibition.
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