Non-Visual RGCs (F) Flashcards
What are the advantages of having the photoreceptors in the outer retina and having a “backward” design?
- photoreceptors placed in contact with the RPE (chromophore regeneration)
- in contact with the choroid (blood supply)
Which retinal circuits are best stimulated by light objects on dark background?
ON circuits
Which retinal circuits are best stimulated by dark objects on light background?
OFF circuits
What is the purpose of the lateral inhibition mediated first by horizontal cells and later amacrine and inhibitory cells in LGN?
sharpen edges and borders in our perception of images (enhance contrast)
What are the other major RGC projections from the retina, other than to the LGN?
- hypothalamus
- pretectum
- superior colliuculs
What is the function of the pulvinar?
involved in visual attention
What is the function of the superior colliculus?
saccade generation; reflex head and neck movements to stimuli
What is the function of the lateral habenula?
emotion, pain processing, learning
What is the function of the ventrolateral pre-optic nucleus in the hypothalamus?
sleep regulation
What is the function of the suprachiasmatic nucleus in the hypothalamus?
synchronization of circadian rhythms
What is the function of the pretectum (olivary pretectal nucleus)?
pupillary light reflex
What is the pathway from the pretectum to pupil constriction?
pretectum project bilaterally to Edinger-Westphal nuclei then synapse in ciliary ganglion then synapse on constrictor muscle of iris
What is the irradiance information from the eye used for?
- regulate pupil size
2. body’s circadian rhythms
What is the generalized rule for the time it takes to resynchronize an internal clock after changing time zones?
about 1 day per time zone crossed
Does melatonin go up or down at night? 1. Body temp? 2
- up
2. down
Why are our internal cues often masked or ignored in everyday life?
artificial timing cues
What is the internal “free running” circadian rhythm of humans?
24.5 hrs
What happens to the circadian cycle when the eyes are enucleated?
it no longer exists for the patient
Are rods and cones necessary for irradiance detection?
no
What are the non-rod or cone cells that are photosensitive in the retina?
intrinsically photosensitive RGCs (ipRGCs)
What photopigment is expressed in ipRGCs? 1. Where do these cells project to in the brain? 2. How many of these are found in the human retina? 3
- melanopsin
- suprachiasmatic nucleus (SCN) and olivary pretectal nucleus (OPN, pretectum)
- 3,000
What is the peak spectral sensitivity of ipRGCs? 1. What is their relative sensitivity compared to rods and cones? 2
- 480nm
2. not very sensitive
What is the relative temporal resolution of ipRGCs?
much lower than conventional RGCs (flicker must be very slow (less than 1 Hz))
What cell types in the retina can mediate pupil reflexes?
- rods/cones
2. ipRGCs
