In other words, contraction of radial smooth muscle causes dilation of the pupil. This explains the autonomic actions: 1  Increased release of acetylcholine by the parasympathetic nervous system causes contraction of circular smooth muscle. 2  This makes the pupil (the dark hole) smaller.he pupil is contricted or dilated by the contraction of smooth muscle in the iris. There are two types. One type is arranged in the circle near the pupil. When a circle of muscle contracts, the circle becomes smaller. Thus contraction of the circular muscle causes constriction of the pupil.
forÂ·evÂ·er. adv. 1. For everlasting time; eternally: No one can live forever.2. At all times; incessantly: was forever complaining about the job.. forever-for a very long or seemingly endless time; she took forever to write the paper; we had to wait forever and a day. forever and a day. colloquialism-a colloquial expression; characteristic of spoken or written communication that seeks to imitate informal speech.
without beginning or end; lasting forever; always existing (opposed to temporal): eternal life. 2. perpetual; ceaseless; endless: eternal quarreling; eternal chatter.