in Neural Control and Coordination (Nervous System) by

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  1. The iris of the eye has two sets of smooth muscles: sphincters and dilators.
  2. These muscles regulated the amount of light entering the eye ball by altering the size of the pupil.
  3. In bright light, the sphincter muscles contract, making the pupil smaller so less light can enter the eye.
  4. In dim light, the dilator muscles contract and widen the pupil because of which more light enters the eye.
  5. The autonomic nervous system controls the muscles of the iris.

In this way, the amount of light falling on the retina is regulated.

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