Intro | Amacrine Cells | Bipolar Cells | Cones | Optic Disk and Blind Spot | Ganglion Cells | Horizontal Cells | Optic Nerve Fibres | Receptor Cells | Rods
Part 1: Image-Mapped Tutorial
Part 2: Matching Self-Test
Part 3: Multiple-Choice Self-Test
Rods are named for their rod-like shape. These receptor cells are specialized for night and peripheral vision, and outnumber the cones by about 125 million to 6.4 million. Rods are particularly sensitive to dim light, hence their role in night vision. The density of rods is greatest surrounding the fovea and gradually decreases toward the periphery of the retina. When lighting is dim, it is best to avert your gaze slightly away from the object of interest. This will bring the object on focus at the portion of the retina where rods are plentiful.
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Rods contain a photopigment, 11-cis-retinal, which is a form of vitamin A bound to a protein called rhodopsin. One photon of light has the energy to convert this photopigment into a molecule of all-trans-retinal. This conversion alters the configuration of the opsin portion of the molecule, resulting in a closing of Na+ channels on the cell membrane and hyperpolarization. This process is called transduction. While at rest, rod cells transmit a steady inhibitory input to the bipolar cells. When transduction occurs, the rate of this inhibition is slowed.