Describe the major layers of the retina from outer to inner and identify the cell types found in each layer.

• A. Photoreceptor outer segments → outer nuclear layer → outer plexiform layer → inner nuclear layer → inner plexiform layer → ganglion cell layer → nerve fiber layer
• B. Photoreceptor inner segments → outer nuclear layer → inner plexiform layer → outer plexiform layer → ganglion cell layer → nerve fiber layer
• C. Photoreceptor outer segments → outer plexiform layer → outer nuclear layer → inner nuclear layer → inner plexiform layer → ganglion cell layer → nerve fiber layer
• D. Photoreceptor outer segments → outer nuclear layer → inner plexiform layer → inner nuclear layer → nerve fiber layer

Answer: (A)

From outer to inner, the retina is organized to reflect the flow of visual information: detection, processing, and output. The photoreceptor outer segments are where light is detected by rods and cones. Their cell bodies sit in the outer nuclear layer. The outer plexiform layer is the site where photoreceptors form synapses with the next-order neurons—the bipolar and horizontal cells. Deeper still, the inner nuclear layer contains the cell bodies of bipolar cells, horizontal cells, amacrine cells, and Müller glia. The inner plexiform layer is where bipolar and amacrine cells synapse with the dendrites of ganglion cells, shaping the signal before it leaves the retina. The ganglion cell layer houses the cell bodies of retinal ganglion cells, and their axons run in the nerve fiber layer toward the optic nerve. This sequence—photoreceptor outer segments, outer nuclear layer, outer plexiform layer, inner nuclear layer, inner plexiform layer, ganglion cell layer, nerve fiber layer—matches the described arrangement.