Near the peripheral retina, each rod bipolar cell collects signals from about how many rods?

• A. 25
• B. 15
• C. 100
• D. 50

Answer: (D)

Convergence of input in the rod pathway is the central idea here. In the peripheral retina, many rods funnel their signals into a single rod bipolar cell. This pooling increases sensitivity in dim light because the small signals from numerous rods are summed, making it easier to detect very faint illumination. If fewer rods fed into a bipolar cell, sensitivity would drop; if even more rods converged, spatial detail would be further sacrificed. So, the peripheral rod pathway is characterized by high convergence—on the order of several dozen rods feeding one rod bipolar cell—which boosts night vision while preserving some spatial information. From there, the signal moves onward through the retinal network to influence ganglion cells.