Special Senses | Pupillary Light and Accommodation Reflex

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Ninja Nerds!
In this lecture, Professor Zach Murphy will explain the physiology and neural circuitry behind both the pupillary light reflex and the accommodation reflex. We begin with the pupillary light reflex, detailing how light entering the eye activates retinal photoreceptors, sending impulses through the optic nerve, optic chiasm, and optic tract to reach the pretectal area of the midbrain. From here, bilateral connections to the Edinger-Westphal nuclei initiate parasympathetic outflow via the oculomotor nerve, synapsing in the ciliary ganglion and causing pupillary constriction through activation of the sphincter pupillae muscles.

We then move into the accommodation reflex, discussing how the brain adjusts for near vision by coordinating three processes: lens thickening via ciliary muscle contraction, pupillary constriction, and convergence of the eyes through activation of the medial rectus muscles. The lecture highlights the cortical involvement in recognizing a near object, the relay to the oculomotor complex, and the parasympathetic pathways that mediate these changes.

Finally, we integrate both reflexes to demonstrate how they work together to optimize vision under varying light conditions and object distances. We also note the clinical significance of these reflexes in localizing lesions within the midbrain or along parasympathetic pathways.

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