Q.Supriya stepped out into the bright street from a cinema theatre. In response, her eye pupil shrunk. Identify the muscle responsible for the same.

Muscle (muscular) tissue is composed of long, cylindrical fibres, each built from numerous fine myofibrils, arranged in parallel bundles. Stimulated fibres contract (shorten) and then relax (lengthen) back to a resting state in a coordinated way, and this cycle is the basis of essentially all active body movement.

Three types of muscle exist. Skeletal muscle is closely attached to bone; its fibres are striated and bundled in parallel (e.g. the biceps), enclosed by a tough connective-tissue sheath, and its contraction is voluntary (consciously controllable). Smooth muscle has spindle-shaped (fusiform), unstriated fibres held together by cell junctions within a connective-tissue sheath; it forms the walls of internal organs such as blood vessels, the stomach and intestine, and its co …