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Farther back still is the inner segment, a specialized part of the cell full of mitochondria. The chief function of the inner segment is to provide ATP (energy) for the sodium-potassium pump. Finally, closest to the brain (and farthest from the field of view) is the outer segment, the part of the photoreceptor that absorbs light.
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.
The synaptic terminal forms a synapse with a neuron bipolar cell. The inner and outer segments are connected by a cilium. [2] The inner segment contains organelles and the cell's nucleus, while the outer segment contains the light-absorbing photopsins, and is shaped like a cone, giving the cell its name. [2]
The retina (from Latin rete 'net'; pl. retinae or retinas) is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs.The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception.
Rods are sensitive to dim light, and cones are better able to transduce bright light. Photoreceptors connect to bipolar cells , which induce action potentials in retinal ganglion cells . These retinal ganglion cells form a bundle at the optic disc , which is a part of the optic nerve .
M-type retinal ganglion cells project to the magnocellular layers of the lateral geniculate nucleus. These cells are known as parasol retinal ganglion cells, based on the large sizes of their dendritic trees and cell bodies. About 10% of all retinal ganglion cells are parasol cells, and these cells are part of the magnocellular pathway.
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A variety in light-harvesting complexes exist across the photosynthetic species. Green plants and algae have two different types of reaction centers that are part of larger supercomplexes known as P700 in Photosystem I and P680 in Photosystem II. The structures of these supercomplexes are large, involving multiple light-harvesting complexes.