PSL300H1 Lecture Notes - Visual Angle, Rhodopsin, Retina
Document Summary
Psl300 fall 2013 tweed 2nd lecture. Fovea is secondary visual angle, have 200 000 receptors per mm squared density. But in dim light, rods dark-adapt and rebuild rhodopsin stores. In daylight, rhodopsin is bleached out, broken down. Liver has vitamin a, used to make retinal, a component of rhodopsin. No receptors in the blind spot, where ganglion-cell axons exist eyeball to form optic nerve. See dim star better by looking slightly away from it, so that most seeing done by rods. Photoreceptors sense light using different forms of a pigment called opsin. Each photoreceptor contains millions of opsonin molecules. When light hits, molecules change shape, start chemical cascade that hyperpolarizes the cell membrane, making it more negative. Hyperpolarization reduces the release of glutamate that excites or inhibits bipolar neurons that project to retinal ganglion cells. Opsin predates vision bacteria used it to photosynthesize, shield from uv light. Photoreceptors project via interneurons to retinal ganglion cells.
