Iris dilator muscle 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. It is innervated by the sympathetic system, which acts by releasing noradrenaline, which acts on α1-receptors. Thus, when presented with a threatening
In vitro muscle testing appropriate magnification level is required due to the dexterity required for isolation of muscles. An external, fibre optic light source is also beneficial to provide sufficient light without the emission of heat. There is no correct approach for the preparation of muscles for testing, as long as the muscle is not damaged during preparation, the muscle-tendon unit is intact and there is something that can be used to anchor the muscle within the testing rig. Pieces of bone can be left at the proximal and/or distal end of skeletal muscles to allow for anchoring. In addition, silk sutures or aluminium