Which of the following are photoreceptors?

• A. Bipolar cells
• B. Ganglion cells
• C. Rods and cones
• D. Amacrine cells

Answer: (C)

Rods and cones are the cells in the retina that directly detect light and convert it into neural signals. Rods handle vision in dim light and are highly sensitive, while cones handle bright light and color, providing sharp detail and color vision. The light-detecting process occurs in their outer segments, which contain photopigments (rhodopsin in rods; photopsins in cones) that initiate a chemical cascade to change the cell’s membrane potential and neurotransmitter release. Bipolar cells, ganglion cells, and amacrine cells are retinal neurons that receive and process signals from photoreceptors but do not themselves detect light. Photoreceptors release neurotransmitter in darkness and decrease release when illuminated, starting the visual signal transmitted toward the brain.