Photoreceptors1. Converts electromagnetic radiation to neural signals2. Four main regionsOuter segment (disks, photopigments)Inner segmentCell bodySynaptic terminalTwo main types of photoreceptorsRods (1) and Cones (3)Regional Differences in Retinal StructureVaries from fovea to retinal peripheryPeripheral retinaHigh ratio of rods to conesHigh ratio of photoreceptors to ganglion cellsMore sensitive to lightRegional Differences in Retinal StructureCross-section of fovea: Pit in retina where outer layers are pushed asideMaximizes visual acuityCentral fovea: All cones (no rods)1:1 ratio with ganglion cellsArea of highest visual acuityPhototransductionPhototransduction in RodsDark current: Rod outer segments are depolarized in the dark because of steady influx of Na+Photoreceptors hyperpolarize in response to light1. Phototransduction in ConesSimilar to rod phototransductionDifferent opsinsRed, green, blueColor detectionContributions of blue, green, and red cones to retinal signalSpectral sensitivityYoung-Helmholtz trichromacy theory of color visionRetinal Processing1. Only ganglion cells produce action potentials;2. Other retinal cells produce changes in membrane potentials1. Photoreceptors release less neurotransmitter when stimulated by light2. Influence horizontal cells and bipolar cellsNRSC 2100 1st Edition Lecture 17Photoreceptors1. Converts electromagnetic radiation to neural signals2. Four main regions• Outer segment (disks, photopigments)• Inner segment• Cell body• Synaptic terminal– Two main types of photoreceptors• Rods (1) and Cones (3)Regional Differences in Retinal StructureVaries from fovea to retinal periphery– Peripheral retina• High ratio of rods to cones• High ratio of photoreceptors to ganglion cells• More sensitive to lightRegional Differences in Retinal StructureCross-section of fovea: Pit in retina where outer layers are pushed aside• Maximizes visual acuityThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.– Central fovea: All cones (no rods)• 1:1 ratio with ganglion cells• Area of highest visual acuityPhototransductionPhototransduction in Rods– Dark current: Rod outer segments are depolarized in the dark because of steady influx of Na+ – Photoreceptors hyperpolarize in response to light1. Phototransduction in Cones– Similar to rod phototransduction– Different opsins• Red, green, blue• Color detection– Contributions of blue, green, and red cones to retinal signal– Spectral sensitivity– Young-Helmholtz trichromacy theory of color visionRetinal Processing1. Only ganglion cells produce action potentials;2. Other retinal cells produce changes in membrane potentials1. Photoreceptors release less neurotransmitter when stimulated by light2. Influence horizontal cells and bipolar