Pupillary Light Reflex Components

Steps:

• Recall the pupillary light reflex pathway: light stimulates retinal photoreceptors (receptors), signals travel via optic nerve to brain, then to oculomotor nerve.
• Effectors are iris smooth muscles that constrict the pupil in response to light.
• Match diagram labels: receptors at retina (likely 1), effectors at iris (likely 3).
• Select option pairing correct sites for reflex components.

Why A is correct:

• Receptors are retinal photoreceptors (site 1) detecting light, effectors are iris muscles (site 3) causing pupil constriction, per reflex arc definition.

Why the others are wrong:

• B: Receptors at 2 (likely cornea/lens, not light-sensitive) misidentifies detection site.
• C: Effectors at 4 (likely optic nerve or brain, not muscle) confuses pathway with response.
• D: Combines wrong receptors (2) and effectors (4), inverting both roles.

Final answer: A