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) the titles of some of the new tracks. The very same day, on their "Widening Gyre" iTunes page, Altan revealed the titles of the 14 tracks from their new studio album and released them for sale. On 27 January 2015, on their "Widening Gyre" Compass Records page, Altan made available short snippets of their new tracks. Mairéad Ní Mhaonaigh introduced the music on the album as an exploration of the influence of Appalachian music on Irish music. Recorded «with many good friends in the studio and Compass Records co-founder Garry West in the producer's chair steer[ing] the band in the