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 Widening Gyre (album) The Widening Gyre is the twelfth studio album by Irish folk music group Altan and their eleventh studio album of original material, released in February 2015 on the Compass Records label. It was released to critical acclaim. This is the first studio album of original material to be released by Altan in almost 3 years since the release of "Gleann Nimhe – The Poison Glen" in 2012. This is also the first Altan album to feature new band member Martin Tourish on accordion. In January 2015, Altan revealed that "The Widening Gyre" would be the name