Rod signaling

Signaling by rod cells is based on the light intensity. At high light levels, the rods are saturated, and only cones operate. In partially dark-adapted eye (example at dusk) rod cells come on stream however signal via gap junctions to neighboring cones. This efficiently augments cone cell function, therefore maintaining acuity and color vision (i.e., mesopic vision).

Though, when it is very dark (example, moonless night in remote countryside) the cone cells fail even with signal boosting from rods. Rod cells in the dark will have a greater influx of Ca²⁺ through the dark current. One effect of this increase in Ca²⁺ is to close the gap junctions among the rod and cone cells. Rod signaling is now relayed through depolarizing bipolar cells that synapse with a population of amacrine cells. The effect of this is to increase the contrast sensitivity.