retinal rod

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The major photoreceptor cell of the retina (~125 million in a human eye). They are columnar cells (~40 μm high, 1 μm diameter) with three distinct regions: nearest the vitreous and adjacent to the neural retina, a region that forms synapses with neurons of the neural retina and contains the nucleus and other cytoplasmic organelles; below this is the mitochondrion-rich inner segment that is connected through a thin ‘neck’ (in which is located a ciliary body) to the outer segment. The outer segment consists of a stack of discs (actually membrane infoldings that are incompletely separated in cones) which are produced next to the inner segment and progressively move towards the distal end where they are shed and phagocytosed by the pigmented epithelium. The membranes of the discs contain the rhodopsin. Rods are more light-sensitive than cones and respond slightly less quickly; they are important for night vision.

Subjects: Medicine and Health.

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