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
State River Widening State River Widening State River Widening, named after the title of a Chinese propaganda photo, are a London based trio, formed in May 1998, comprising multi-instrumentalists David Sheppard and Keiron Phelan, along with drummer/percussionist Jon Steele. Friends from school (in south London) Sheppard and Phelan began experimental recordings in 1996, soon hooking up with percussionist Steele to leaven their intertwining, Nick Drake-like acoustic guitars with vigorous yet dexterous drumming. A debut single, "Unsung Couples", was released on the Gold Hole label in November 1998. SRW’s hypnotic cycles of avant-rock melody connected with an audience then thrilling to similarly inclined practitioners