Pupil reflex: https://youtu.be/NfdVolZTs9Q

BRIGHT LIGHT

Stimulus: bright light

Receptor: retina (cones)

(Sensory neurones in the optic nerve)

Coordinator: brain (relay neurone)

Effector: muscles in the iris (motor neurone) (circular muscle contracts and the radial muscle relaxes)

Response: adjust in the size of the pupil, gets smaller

DIM LIGHT

Stimulus: dim light

Receptor: retina (rods)

Coordinator: brain (relay neurone)

Effector: muscles in the iris (radial muscles contract and the circular muscles relax)

Response: adjust in the size of the pupil, it dilates/ widens, to protect the retina.

The circular muscles & radial muscles: antagonistic muscles

They control the amount of light reaching the retina to prevent the damage of photoreceptors.