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Disc Shedding
Disc shedding is the process by which photoreceptor cells in the retina are renewed. The disc formations in the outer segment of photoreceptors, which contain the photosensitive opsins, are completely renewed every ten days. Photoreceptors The retina contains two types of photoreceptor – rod cells and cone cells. There are about 6-7 million cones that mediate photopic vision, and they are concentrated in the macula at the center of the retina. The are about 120 million rods that are more sensitive than the cones and therefore mediate scotopic vision. A vertebrate's photoreceptors are divided into three parts: * an outer segment that contains the photosensitive opsins * an inner segment that contains the cell's metabolic machinery ( endoplasmic reticulum, Golgi complex, ribosomes, mitochondria) * a synaptic terminal at which contacts with second-order neurons of the retina are made Discs The photosensitive outer segment consists of a series of discrete membranous discs .Besh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cone Cell En
A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines connecting a common point, the apex, to all of the points on a base that is in a plane that does not contain the apex. Depending on the author, the base may be restricted to be a circle, any one-dimensional quadratic form in the plane, any closed one-dimensional figure, or any of the above plus all the enclosed points. If the enclosed points are included in the base, the cone is a solid object; otherwise it is a two-dimensional object in three-dimensional space. In the case of a solid object, the boundary formed by these lines or partial lines is called the ''lateral surface''; if the lateral surface is unbounded, it is a conical surface. In the case of line segments, the cone does not extend beyond the base, while in the case of half-lines, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
