Which cells contribute nuclei to the inner nuclear layer?

• A. Photoreceptors
• B. Ganglion cells
• C. Bipolar cells, horizontal cells, and amacrine cells
• D. Müller glia

Answer: (C)

The inner nuclear layer is where the cell bodies (nuclei) of the retina’s local interneurons are located. The cells with nuclei in this layer are the bipolar cells, horizontal cells, and amacrine cells. Bipolar cells relay signals from photoreceptors to the ganglion cells, horizontal cells provide lateral integration across the outer retina, and amacrine cells modulate signals within the inner retina before they exit to the brain. Photoreceptors themselves sit in the outer nuclear layer, and the ganglion cell layer houses the cell bodies of ganglion cells that send signals toward the brain. Müller glia are glial cells with their own nuclei in the inner nuclear layer as well, but in many retinal diagrams the emphasis for the inner nuclear layer’s nuclei is on these three neuronal types.