Iris dilator muscle "musculus dilator pupillae", The "Nomina Anatomica" as authorized in 1895 in Basle and in 1935 in Jena used the full Latin expression. Iris dilator muscle The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle of the eye, running radially in the iris and therefore fit as a dilator. The pupillary dilator consists of a spokelike arrangement of modified contractile cells called myoepithelial cells. These cells are stimulated by the sympathetic nervous system. When stimulated, the cells contract, widening the pupil and allowing for more light to pass through the eye.
Smooth muscle muscle tissue. Smooth muscle may contract phasically with rapid contraction and relaxation, or tonically with slow and sustained contraction. The reproductive, digestive, respiratory, and urinary tracts, skin, eye, and vasculature all contain this tonic muscle type. This type of smooth muscle can maintain force for prolonged time with only little energy utilization. There are differences in the myosin heavy and light chains that also correlate with these differences in contractile patterns and kinetics of contraction between tonic and phasic smooth muscle. Crossbridge cycling cannot occur until the myosin heads have been activated to allow crossbridges to form. When the light