Which retinal layer contains synapses between photoreceptors and bipolar cells?

• A. Inner plexiform layer.
• B. Outer nuclear layer.
• C. Outer plexiform layer.
• D. Photoreceptor layer.

Answer: (C)

Understanding how the retina is wired helps explain this. Photoreceptors (rods and cones) send their signals to the next neurons in a dedicated synaptic layer. The synapses between photoreceptors and bipolar cells (and horizontal cells) are located in the outer plexiform layer, making it the site of these first retinal connections. The outer nuclear layer contains the cell bodies of the photoreceptors, not their synapses. The inner plexiform layer is where bipolar cells synapse with ganglion and amacrine cells, and the photoreceptor layer houses the photoreceptors’ outer segments, not synapses. So the outer plexiform layer is where photoreceptors connect to bipolar cells.