Pupillary Light Reflex

by Craig Canby, PhD

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    Next, I want to guide you through the pupillary light reflex. So in this visual, we have two eyeballs. This happens to be the one on the left. We also have an eyeball here. That would be the right eyeball of the person looking at you. We are now going to shine light in the left eye. So we’ll shine the light in through here. The light will travel through the structures, components of the left eyeball, hit the retina. Then ultimately, ganglion retinal cells will be stimulated. Then the action potentials will travel through the optic nerve to the pretectal region of the brain. It’s going to be on the left side here of that area. Then this will activate nerve cells that will communicate bilaterally to the Edinger-Westphal nuclei. So we see in this simple illustration, we have a nerve cell sending an axon here to activate the left Edinger-Westphal nucleus. Then the contralateral or the right one is also going to be stimulated in response to this pupillary light reflex. From the Edinger–Westphal nuclei, what will happen here is there will be parasympathetic fibers that will leave this nucleus. They’re going to travel to the ciliary ganglia on both sides. So here’s the left one to the left eye, ciliary ganglion then to the right eye. These parasympathetic fibers are going to travel in the oculomotor nerve as we see identified here. From the ciliary ganglia, nerve fibers are going to innervate the sphincter pupillae muscle of each eye and cause it to contract. So what we have here would be direct and consensual light reflexes. The direct reflex is that the light shined in the left eye will cause constriction. The consensual reciprocal response is that the right eye will do the same in response...

    About the Lecture

    The lecture Pupillary Light Reflex by Craig Canby, PhD is from the course Visual Pathways. It contains the following chapters:

    • Pupillary Light Reflex
    • Accommodation

    Included Quiz Questions

    1. Oculomotor CN III
    2. Ophthalmic CN VI
    3. Optic CN II
    4. Trochlear CN IV
    5. Trigeminal CN V
    1. Sphincter pupillae muscle
    2. Ciliary muscle
    3. Macula lutea
    4. Lens
    5. Suspensory ligament
    1. Ciliary muscle
    2. Suspensory ligament
    3. Macula lutea
    4. Lens
    5. Sphincter pupillae muscle

    Author of lecture Pupillary Light Reflex

     Craig Canby, PhD

    Craig Canby, PhD

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