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) between masters of American roots music and Celtic music. Mairéad stated: «The title "The Widening Gyre" appeals to us and depicts the spiral of life, widening and embracing the new. It has an innate energy. We think that idea is reflected in the album's music». "The Widening Gyre" is a compelling development in Altan's story proving that they are still growing as artists, even after nearly thirty years together — the longest running lineup of founding members in Irish music. Altan recorded the new album over ten days from 29 July to 7 August 2014 entirely in Nashville, Tennessee (at