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 (album) lots of new stuff to savor and some reinventions of recognizable material as well, interpreted by some of the best musicians you can find in roots music.". "The Widening Gyre" received a four star album review (out of 5) from The Irish Times's reviewer Siobhan Long, stating that Altan "have reinvigorated their sound in the process of [recording in] Nashville with newcomer Martin Tourish on piano accordion [and] an all-star cast [of Appalachian bluegrass musicians]". The Arts Desk website's music critic Peter Quinn, stated: "Listeners looking for the uniquely driving tune sets that Altan are famous for have plenty to