Which part acts as a light guide to direct photons toward photopigments?

Which part acts as a light guide to direct photons toward photopigments?

• A. Inner segment
• B. Outer segment
• C. Cell body
• D. Synaptic terminal

Answer: (A)

Light has to reach the photopigments that sit in the outer segment, where the actual phototransduction occurs. The inner segment acts as a light guide, a elongated, cylindrical pathway with optical properties that help channel photons toward the outer segment. Its shape and refractive characteristics enable light to be directed efficiently by guiding it along its length, increasing the chance that photons reach the photopigments. The cell body and the synaptic terminal aren’t involved in this guiding role; the cell body is mainly metabolic work, and the synaptic terminal handles neurotransmitter release.

Light has to reach the photopigments that sit in the outer segment, where the actual phototransduction occurs. The inner segment acts as a light guide, a elongated, cylindrical pathway with optical properties that help channel photons toward the outer segment. Its shape and refractive characteristics enable light to be directed efficiently by guiding it along its length, increasing the chance that photons reach the photopigments. The cell body and the synaptic terminal aren’t involved in this guiding role; the cell body is mainly metabolic work, and the synaptic terminal handles neurotransmitter release.