Mydriasis iris sphincter, composed of circularly arranged muscle fibers, and the iris dilator, composed of radially arranged muscle fibers. The sphincter is innervated by (signaled by nerves of) the parasympathetic nervous system, and the dilator by the sympathetic nervous system. Sympathetic stimulation of the adrenergic receptors causes the contraction of the radial muscle and subsequent dilation of the pupil. Conversely, parasympathetic stimulation causes contraction of the circular muscle and constriction of the pupil. The mechanism of mydriasis depends on the agent being used. It usually involves either a disruption of the parasympathetic nerve supply to the eye (which normally constricts the
What Is the What That Happens Will Happen Today". Tom Tykwer plans to adapt the novel into a film. In 2009, the novel received the Prix Médicis étranger in France. What Is the What What Is the What: The Autobiography of Valentino Achak Deng is a 2006 novel written by Dave Eggers. It is based on the life of Valentino Achak Deng, a Sudanese child refugee who immigrated to the United States under the Lost Boys of Sudan program. It was a finalist for the National Book Award. As a boy, Achak is separated from his family during the Second Sudanese Civil War when