Which structure is most directly associated with the parasympathetic component of the near response during pupil constriction and lens accommodation?

Which structure is most directly associated with the parasympathetic component of the near response during pupil constriction and lens accommodation?

• A. Lateral geniculate nucleus
• B. Edinger-Westphal nucleus
• C. Superior colliculus
• D. Pretectal area

Answer: (B)

The parasympathetic arm of the near response is driven by the Edinger-Westphal nucleus. This midbrain structure contains the parasympathetic preganglionic neurons that travel with the oculomotor nerve to the ciliary ganglion, then via short ciliary nerves to the sphincter pupillae (causing pupil constriction) and the ciliary muscle (causing lens rounding for near focus). The pretectal area participates in the pupil-light reflex upstream of this pathway, and the lateral geniculate nucleus and superior colliculus are more involved in visual processing and eye movements, respectively, so they’re not the direct source of the parasympathetic output for constriction and accommodation.

The parasympathetic arm of the near response is driven by the Edinger-Westphal nucleus. This midbrain structure contains the parasympathetic preganglionic neurons that travel with the oculomotor nerve to the ciliary ganglion, then via short ciliary nerves to the sphincter pupillae (causing pupil constriction) and the ciliary muscle (causing lens rounding for near focus). The pretectal area participates in the pupil-light reflex upstream of this pathway, and the lateral geniculate nucleus and superior colliculus are more involved in visual processing and eye movements, respectively, so they’re not the direct source of the parasympathetic output for constriction and accommodation.