Rod cell

A retinal photoreceptor specialized for dim-light vision. Rods detect single photons under favorable conditions but provide monochrome signals and limited spatial detail.

Rhodopsin: A light-sensitive pigment in rod cells, composed of opsin and retinal. A photon changes its retinal molecule, initiating the rod’s response to light.
Retina: The light-sensitive neural tissue lining the back of the eye. Rod cells occupy the retina’s outer layer and connect into its local circuits.
Scotopic vision: Vision mediated primarily by rods at low levels of illumination. Rod cells provide the photoreceptor signals underlying this dim-light mode of vision.
Cone cell: A retinal photoreceptor specialized for daylight vision, color discrimination, and high spatial acuity. Cones work best in brighter light and provide the color and detail rods lack.
Phototransduction: The conversion of light into electrical signals by photoreceptor cells. This signaling cascade explains how rod cells turn photon absorption into altered membrane voltage.
Photoreceptor cell: A sensory neuron that detects light and converts it into electrical signals. Rod cells are one of the two principal photoreceptor types in the human retina.
Dark adaptation: The gradual increase in visual sensitivity after moving from bright light into darkness. Rhodopsin regeneration and retinal circuit changes restore rod sensitivity over time.
Photopic vision: Vision mediated primarily by cones under bright illumination. It operates in the illumination range where rod responses are saturated.
Retinal: A light-absorbing molecule derived from vitamin A that changes shape after absorbing a photon. Its light-triggered shape change activates rhodopsin in rod cells.
Outer segment: The specialized, membrane-rich region of a vertebrate photoreceptor that contains light-sensitive pigment. Rod outer segments pack rhodopsin-bearing discs where photons are captured.

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