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Pupil is a window for the light to enter our eyes. When we are in a dim light a nerve impulse is generated to the brain to enlarge the pupil. Size of pupil is managed by the iris (coloured part of the eye). If excessive light is there, the pupil shrinks to a smaller size so that the eye's not damaged esp. the retina where the image of objects are formed

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Q: How is the Nerve impulse responsible for the pupil becoming smaller?
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