BIOL 4380 Lecture Notes - Lecture 8: Visual Acuity, Foveola, Metabotropic Glutamate Receptor 6
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• Why are these visual experiences so different? Why are rods and cones so different?
o The length of time that signal persists in two systems.
o The rod system can persists for as long as 600 ms depending on the intensity of
stimulus. This is a very long time. In the cone system, independently of the intensity of
sigal, the uet lasts aout s → eah estig faste.
o Rods tend to be extremely convergent. 15 rods innervate a single bipolar ell → alled
convergence. In cones, one cone innervates one bipolar cell. This increases visual acuity.
1:1 would increase acuity but compromise sensitivity.
o The distribution of rods and cones on the retina is not random: the entire human retina
contains 90 million rods, and about 5 million cones. More rods than cones. The
concentration of prevalence of cones is really spiking at the fovea. In fovea we have
mostly cones. Fovea is an area of 1-1.5mm in diameter disk. In the center of the fovea
thee’s a foveola which is an even smaller disk which is 100% occupied by the cone
cells.
o Rods do not allow any color vision, the only photoreceptor expressed in rods is
rhodopsin. Whereas in cones, 3 different other photoreceptor are expressed.
Responsive to blue, red, green light. SML cone cells.
• Fig 11.16: differences in rhodopsin of rods vs the S receptors in cones. S is equally different from
M. M and L are actually more similar to one another.
• Fig 11.17: on center and off center ganglion cells.
• Fig 11.18: the difference between the on and off center ganglion is determined by how these
ganglion cells are connected to the respective photoreceptors. Some of the bipolar cells that
connect receptors to ganglion cells, are sign conserving bipolars and some are called sign
inverting (-).
• What determines a receptor is conserving or inverting is the nature of the postsynaptic
receptors, all release glutamate in their terminals, conserving ones, the dendrites express AMPA
kainate so the glutamate would depolarize the bipolar cells. In inverting cells, we have mGluR6
eeptos → high glutaates shut do the eepto. At the aoal side of these ipola ells,
they are both glutamatergic.
• Auditory system:
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