What is the role of photoreceptors in vision?

• A. They generate action potentials that travel to the cerebellum.
• B. They detect photons and are the only retinal cells capable of photon absorption and electrical transduction.
• C. They regulate intraocular pressure.
• D. They convert sound waves into neural signals.

Answer: (B)

Photoreceptors are the light-sensing cells of the retina. They detect photons and are the only retinal cells capable of photon absorption and electrical transduction. When light hits their photopigments (rods with rhodopsin, cones with photopsins), a biochemical cascade alters ions flow, causing hyperpolarization and a change in glutamate release onto downstream neurons. This transduction is graded, not an all-or-nothing spike, and the signal is passed to bipolar and then ganglion cells, whose action potentials travel via the optic nerve to the brain for visual processing. The other options don’t fit because photoreceptors do not generate action potentials that travel to the cerebellum, they do not regulate intraocular pressure, and they do not convert sound waves into neural signals—the auditory system handles that.