PHYL 2041 — Visual System 2: Active Recall
1. Retina anatomy
What are the main layers of the retina, from outer to inner?
What is the function of the retinal pigment epithelium (RPE)?
What is found in the outer nuclear layer?
What is the difference between a nuclear layer and a plexiform layer?
Where do photoreceptors synapse with bipolar cells?
Where do bipolar cells synapse with ganglion cells?
What is the function of the nerve fiber layer?
What forms the optic nerve?
Why is the optic disc called the blind spot?
Where is the fovea, and why is it important for visual acuity?
2. Phototransduction
What happens to photoreceptors in darkness?
What is cGMP’s role in phototransduction?
Which channels remain open in darkness?
What is the dark current?
Why are photoreceptors relatively depolarized in darkness?
What neurotransmitter do photoreceptors release?
What happens to rhodopsin when light hits a rod?
What is the role of transducin?
What does phosphodiesterase (PDE6) do?
What happens to cGMP concentration in light?
What happens to CNG channels in light?
Why does light hyperpolarize photoreceptors?
How does light affect glutamate release?
Do photoreceptors normally communicate using action potentials or graded potentials?
3. ON and OFF pathways
What does an ON pathway detect?
What does an OFF pathway detect?
Which glutamate receptor is found on ON bipolar cells?
Which glutamate receptors are found on OFF bipolar cells?
What effect does glutamate have on ON bipolar cells in darkness?
What effect does glutamate have on OFF bipolar cells in darkness?
What happens to ON bipolar cells when light increases?
What happens to OFF bipolar cells when light increases?
Why do ON and OFF bipolar cells respond oppositely to the same decrease in glutamate?
What is a receptive field?
What is an ON-center/OFF-surround receptive field?
What is an OFF-center/ON-surround receptive field?
Why is center-surround antagonism useful?
How does the retina help detect edges and contrast?
4. Rod and cone pathways
What are the main differences between rods and cones?
Which photoreceptors are more sensitive to dim light?
Which photoreceptors are most important for colour vision?
Which photoreceptors support high visual acuity in the fovea?
What type of bipolar cell receives rod input in the classic mammalian pathway?
Why don’t rod bipolar cells directly provide the conventional output to ganglion cells?
What is the role of AII amacrine cells?
How do AII amacrine cells connect with ON cone bipolar cells?
How do AII amacrine cells affect OFF cone bipolar cells?
What is a gap junction?
What is a glycinergic synapse?
How does the rod pathway feed into cone-associated circuitry?
Why is the rod pathway important for night vision?
5. Inner plexiform layer
What is the function of the inner plexiform layer (IPL)?
What are the five IPL strata called?
Where do OFF bipolar cell terminals generally stratify?
Where do ON bipolar cell terminals generally stratify?
Where do OFF ganglion cell dendrites generally stratify?
Where do ON ganglion cell dendrites generally stratify?
What does a ganglion cell’s dendritic stratification tell us about its inputs?
Why can’t stratification alone completely predict a ganglion cell’s function?
6. Retinal ganglion cell types
What is the main function of retinal ganglion cells (RGCs)?
What do RGC axons form?
What is the difference between midget and parasol RGCs?
Which RGC type is associated mainly with the parvocellular pathway?
Which RGC type is associated mainly with the magnocellular pathway?
Which pathway is more strongly associated with fine spatial detail?
Which pathway is more strongly associated with luminance contrast and temporal changes?
Do both midget and parasol RGCs have ON and OFF types?
What is a direction-selective RGC?
What are preferred and null directions?
What is the difference between ON-DS and ON–OFF DS ganglion cells?
How do starburst amacrine cells contribute to direction selectivity?
What makes an RGC intrinsically photosensitive?
What is melanopsin?
What are three functions of ipRGCs?
What does a multi-electrode array record?
Can a multi-electrode array alone establish the molecular identity of every recorded cell?
7. Retinal diseases
What structures are affected in age-related macular degeneration (AMD)?
What is a druse?
What type of vision is most affected by AMD?
What is retinitis pigmentosa (RP)?
Why is night blindness a common early symptom of RP?
Which visual field is commonly affected early in RP?
What gene is an important cause of some forms of RP?
Which cells and axons are damaged in glaucoma?
How does increased intraocular pressure relate to glaucoma?
Can glaucoma occur without elevated intraocular pressure?
Why does glaucoma often cause peripheral visual-field loss?
How would you distinguish AMD, RP and glaucoma based on their typical visual symptoms?
8. Optic nerve and visual pathway
Approximately how many axons are in the human optic nerve?
Where do optic nerve fibres meet and partially cross?
Which retinal fibres cross at the optic chiasm?
Which retinal fibres generally remain on the same side?
What information does the left optic tract carry?
What information does the right optic tract carry?
What is the lateral geniculate nucleus (LGN)?
What is the role of the thalamus in sensory processing?
What are optic radiations?
Where is the primary visual cortex (V1)?
What is the correct order of structures from the retina to V1?
Why does each optic tract carry information from both eyes?
What visual deficit can result from damage to one optic nerve?
What visual deficit can result from damage at the optic chiasm?
What visual deficit can result from damage to the right optic tract?
9. LGN pathways
How many principal layers does the primate LGN have?
What does it mean that LGN layers are eye-specific?
What is retinotopic organization in the LGN?
Which LGN layers are magnocellular?
Which LGN layers are parvocellular?
Which RGC type mainly supplies the magnocellular layers?
Which RGC type mainly supplies the parvocellular layers?
What is the main functional emphasis of the M pathway?
What is the main functional emphasis of the P pathway?
What are koniocellular layers?
What is the relationship between the K pathway and S-cone-related signals?
Why is it inaccurate to assign one exclusive function to every LGN pathway?
10. Primary visual cortex and higher processing
What is V1’s role in visual processing?
Which cortical layer receives major LGN input?
Which V1 sublayer is strongly associated with M input?
Which V1 sublayer is strongly associated with P input?
Where do some koniocellular projections terminate?
What is a retinotopic map?
Why does the fovea have a disproportionately large cortical representation?
What is cortical magnification?
Why is visual acuity highest near the fovea?
What is the dorsal visual stream?
Which lobe does the dorsal stream project toward?
What is the ventral visual stream?
Which lobe does the ventral stream project toward?
How do the dorsal and ventral streams differ in their major functions?
Why is it an oversimplification to treat the two streams as completely separate?
11. Retinal projections outside the main pathway
Do all retinal ganglion cell axons project to the LGN?
What is the role of the superior colliculus?
What is the role of the suprachiasmatic nucleus (SCN)?
Which retinal pathway is important for the pupillary light reflex?
What is the accessory optic system involved in?
How do ipRGCs help regulate circadian rhythms?
What is the difference between image-forming and non-image-forming visual functions?
12. Integration questions
Trace the complete process from light entering the eye to a signal reaching V1.
Explain how a light increment affects a photoreceptor, an ON bipolar cell and an ON ganglion cell.
Explain how a light increment affects an OFF bipolar cell and an OFF ganglion cell.
Compare rod and cone pathways from photoreceptors to ganglion cells.
Explain how center-surround antagonism improves contrast detection.
Compare the M, P and K pathways by retinal input, LGN organization and function.
Explain how the location of a lesion changes the type of visual-field defect.
Compare the functions of rods, cones, midget RGCs, parasol RGCs and ipRGCs.
Explain how the retina processes visual information before sending it to the brain.
Compare AMD, RP and glaucoma by affected structures and typical symptoms.