Parasympathetic Pupillary Light Reflex Pathway
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Light strikes the retinae, which channel back via the optic nerves to the midbrain (we show only one optic tract lead to the midbrain, so we can see that each side produces a bilateral response.).
The optic tract triggers the pretectal olivary nucleus, which triggers bilateral activation of CN3.
Each CN 3 activates ciliary ganglia.
The ciliary ganglia send short ciliary nerves to the iris sphincter muscles to produce pupillary constriction.