GENERAL HISTOLOGY

Detailed explanation-1: -The iris sphincter is innervated by the parasympathetic nervous system, the part of the autonomic nervous system that is involved in homeostasis (i.e. keeping the body in stable condition); the link between pupil constriction and the parasympathetic nervous explains why pupils are relatively small at rest.

Detailed explanation-2: -Dilation of the pupil occurs when the smooth cells of the radial muscle, controlled by the sympathetic nervous system (SNS), contract, and also when the cells of the iris sphincter muscle relax.

Detailed explanation-3: -Answer and Explanation: Parasympathetic stimulation is responsible for pupil constriction in bright light. If there is plenty of light available, the parasympathetic nervous system (PNS) will cause constriction of the pupil to restrict the amount of light entering the eye.