MICROANATOMY

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: -[9] Since pupillary constriction occurs parasympathetically, parasympathetic paralysis results in loss of pupillary constriction and hence, pupillary dilation.

Detailed explanation-3: -[4] Efferent parasympathetic preganglionic fibers travel on the oculomotor nerve and synapse with the ciliary ganglion, which sends postganglionic axons to directly innervate the iris sphincter muscles. The contraction of the iris sphincter muscles leads to pupillary constriction (miosis).