rod defined in 1951 yearrod - rod;
rod - Kind of light-sensitive nerve-cell present in vertebrate retina. The rod-shaped outer segment of the cell, which is the light-sensitive part, consists largely of a stack of flat and parallel unit membrances, at right angles to the cell length; this develops embryologically from a cilium, and retains its characteristic 9+2 pattern of fibrils (See also: Flagellum). Rods do not discriminate fine detail or probably colour differences, but they are sensitive to very dim light, which cones are not. There are about 120 million in one retina of a primate. Response to light depends on visual purple.
near rod in Knolik
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