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
The Widening Gyre (novel) The Widening Gyre (novel) The Widening Gyre is a 1983 novel by Robert B. Parker, featuring his private detective character Spenser. The title comes from the first line of W.B. Yeats poem "The Second Coming". Spenser is hired to head up the security detail for Congressman Meade Alexander as he runs for the Senate. The congressman confides to Spenser that he is being blackmailed by someone who wants him to drop out of the senate race. The congressman's wife Ronni drinks too much and there is an explicit sex tape of her and a much younger man. Spenser's assignment is