Photoreceptors Practice Test

Under photopic conditions, two 5-quanta flashes cause how many ganglion cells to reach threshold?

1 2 3 4

Correct Answer:

Explanation:

Under photopic vision, cones provide high-acuity, low-convergence signaling. Each cone’s input is carried forward through pathways that preserve spatial detail, so there is nearly a one-to-one relationship between active cones and the ganglion cells that respond to them, especially in the central retina. A 5-quanta flash is sufficient to activate a cone, and that cone’s signal can drive its corresponding ganglion cell to threshold. If two flashes illuminate two separate cones, two distinct cone-to-ganglion-cell pathways reach threshold, producing two active ganglion cells. So, the number of ganglion cells reaching threshold matches the number of distinct cones activated by the flashes—two in this case.

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