NROS 418 Exam 1 Questions & Answers

Why does the organization of the eye guarantee that we have a blind spot? Why can't we normally detect the blind spot? -ANSWER The blind spot occurs due to the lack of photoreceptors where the optic nerve and blood vessels exit the eye. Our brain fills the blind spot in by using information that surrounds the blind spot area using ipsilateral and contralateral visual input. What is different about the fovea and the rest of the retina? Why is visual acuity best when images fall on the fovea? -ANSWER The fovea is an area of the eye that has a high density of cone receptors and where light is focused on the retina. At this section, cones send input to 1-3 RGCs each, which supports the high visual acuity. The rest of the retina is rods and cones, with more rods as you move further away from the fovea. What are the main differences in the function of rods and cones? Why can't you see color in the dark? -ANSWER Rod cells are more sensitive than cone cells, and are involved in peripheral vision. They also support our night vision, as they only require one photon of light to activate. Cone cells are less sensitive and perceive color. They require many photons to activate. They perceive fine detail and rapid stimuli changes Cones are not sensitive at low light levels, as there is not enough "light" to perceive color Describe the connections that result in the on-center off-surround receptive field of a RGC. Do the same for an off-center on-surround RGC -ANSWER *On-Center Off-Surround* 1) Light hits the center 2) Cone hyper-polarized 3) Glutamate release decreased 4) On-center bipolar cell depolarized and transmitter release increased 5) Off-center bipolar cell hyper polarized and transmitter release decreased 6) Firing of on-center ganglion cell increased 7) Firing of off-center ganglion cell decreased 1) Light hits the surround 2) Cone depolarized 3) Glutamate released