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) studio to open up musically while somehow managing to help keep the integrity of Altan intact», the album is the result of a fusion «of the traditional Irish music that the members of Altan are known for, namely Donegal fiddling and Gaelic singing traditions, with American roots music, particularly that of the Appalachian bluegrass fiddle» and a celebration of the relationships between Altan and lifelong friends they've made through music. "The Widening Gyre" straddles time as it manages to remind listeners of the ancient bond between Irish and Appalachian music while at the same time breaking new ground through collaborations