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Visual phototransduction is the sensory transduction process of the visual system by which light is detected by photoreceptor cells (rods and cones) in the vertebrate retina.A photon is absorbed by a retinal chromophore (each bound to an opsin), which initiates a signal cascade through several intermediate cells, then through the retinal ganglion cells (RGCs) comprising the optic nerve.
Cones function best in relatively bright light, called the photopic region, as opposed to rod cells, which work better in dim light, or the scotopic region. Cone cells are densely packed in the fovea centralis , a 0.3 mm diameter rod-free area with very thin, densely packed cones which quickly reduce in number towards the periphery of the retina.
The pupillary light reflex is a quick but minor mechanism of adaptation Visual Response to Darkness. Cones work at high light levels (during the day but also during driving at night in the headlamp spotlight). Rods take over at twilight and night. The y-axis has logarithmic scaling.
A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction.The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiation) into signals that can stimulate biological processes.
Photopic vision is the vision of the eye under well-lit conditions (luminance levels from 10 to 10 8 cd/m 2). In humans and many other animals, photopic vision allows color perception , mediated by cone cells , and a significantly higher visual acuity and temporal resolution than available with scotopic vision .
A rod cell is sensitive enough to respond to a single photon of light [11] and is about 100 times more sensitive to a single photon than cones. Since rods require less light to function than cones, they are the primary source of visual information at night (scotopic vision). Cone cells, on the other hand, require tens to hundreds of photons to ...
X-ganglion: medium diameter, 55% of total, small field, color vision. Sustained response. Y-ganglion: largest, 5%, very broad dendritic field, respond to rapid eye movement or rapid change in light intensity. Transient response. Based on their projections and functions, there are at least five main classes of retinal ganglion cells:
This leads to the human eye being unable to resolve high spatial frequencies in low light since the observer is spatially averaging the light signal. [8] Another reason that vision is poor under scotopic vision is that rods, which are the only cells active under scotopic vision, converge to a smaller number of neurons in the retina.