Lecture Notes for Feb 19, 2010

? Sensory receptors: ? Don't have action potenitals. ? They are specialized neurons. ? without axons ? They TRANSDUCE external energy into nueral impulse. ? Parts of the Eye ? Sclera ? outer part of the eye. ? The white part of the human eye ? protective outer layer ? Pupil ? it's the place that's letting light come into your eye ? Lens ? Focuses light onto retina ? Cornea ? the outer part of your eye that buldges out. ? Retina ? back portian of the eye ? contains our sensory receptors. ? photoreceptors. ? Vitreous Humor ? Fluid that is in the eye ? Fovea ? Part of your retina ? it's the part where you get the most percise, clear vision. ? when you are focusing on an object the light will be hitting your fovea ? Optic Disk ? where your blind spot is. ? no photoreceptors, because the optic nerve is leaving the eye. ? Retina ? the retina consists of three layers of cells ? Ganglion cell layer ? outermost layer ? first place light hits, ? last place to recieve information ? first place to have an action potential ? Bipolar cell layer ? middle layer ? Photoreceptor layer ? the only layer where transduction is going to happen ? At the very back of your retina. ? Rods and Cones ? rods 120 million ? light sensitve ? picking up how light or dark it is which gives you black and white ? Found in the periphery of the retina. ? They have a low activation threshold. ? it doesn't take much light to be there ? Low acuity ? you aren't going to get the sharpest vison with your rods. ? Cones 6 million ? Color sensitve. ? Found mostly in the Fovea ? They have a moderate to high activation threshold ? it's going to take more energy to activate these than the rods ? They have high acuity, ? They are going to give you the sharpest vision ? Photopigments are in the membrane of the outer segment. ? Photopigments are what are going to start the nueral impulse. ? Visual Transduction ? Photopigments consit of a molecule that contains opsim (a protein) and retinal (a lipid) ? In the dark: ? Membrans Na channels are normally open ? Photreceptor cell is depolarized ? Glutamate is released and hyperpolarizes bipolar cell ? In the light: ? LIght splits molecule into opsin and retinal ? Closes Na channels ? Photoreceptor cell then hyperpolarizes ? Less glutamate released and therefore depolarizes bipolar cell ? The net effect of light is to hyperpoloarize the photoreceptor cell and reduce the release of glutamate