• What is special about the fovea?
the place that has the most amount of cones, the most concentration of cones are found here. Rods are mostly around the sides, fovea has cones.
• What are the cell types in the retina and how are they arraigned?
(from front to back)
-Ganglion cell layer, Bipolar cell layer, Photoreceptor layer
-Ganglion - ganglion cells
-Bipolar - bipolar cells, horizontal cells, amacrine cells
-Photoreceptor - photoreceptors, cones, rods
• What is the difference between sensitivity and acuity? Why does receptive field size matter?
- ability to detect light
-can detect small amounts of light
-large receptive fields give high sens
-small receptive fields give low sens
-ability to detect fine details
-requires high density of receptors
-small receptive fields give high acuity
-large receptive fields give low acuity
• What properties do rods and cones have?
-large receptive fields
-work well in low light
-better at detecting motion and form
-small receptive fields
-need bright light to func
-better at discriminating fine detail
• Photoreceptors are said to have "dark current." What does this mean? [think physiology]
-have -35. are most active in the dark, light turns them off. kind of backwards.
-stimulation of photoreceptors results in hyperpolarization
• Explain reception & transduction in photoreceptors. (How do they translate light into neurotransmitter signal?)
-Photon of light triggers a change in shape of opsin molecules
-PDE converts cGMP to 5'-GMP
-decreases in concentration
-cGMP-gated Na+ channels close
• What properties do ganglion receptive fields have? How do those properties get created?
-On-center bipolar cells, Off-center bipolar cells, horizontal cells, amacrine cells.
-Those that are created from cone input are better at high frequency info / rod input better at low frequency info.
• What are the differences between the parvocellular and magnocellular pathways?
-involved in fine visual acuity, color, and shape processing.
-involved in motion processing.
• What properties do cortical simple cells have? How do they get those properties?
a cortical neuron with clearly defined excitatory and inhibitory regions.
• What properties do cortical complex cells have that simple cells do not?
a simple cell might respond only if a stripe is presented in the center of its receptive field, a complex cell will respond regardless of where the stripe is presented, as long as it is somewhere within the cell's receptive field.
• What is an ocular dominance column (a.k.a. hypercolumn)?
a 1 mm block of striate cortex containing two sets of columns, each covering every possible orientation, with one set preferring input from the left eye and one set preferring input from the right eye.
• What is an orientation column?
a systematic and progressive change in preferred orientation so that essentially all the orientations were encountered in a distance of about 0.5 mm