![]() ![]() The full Latin expression exhibits three words that each can be traced back to Roman antiquity. The English name dilator pupillae muscle as currently used in the list of English equivalents of the Terminologia Anatomica, the reference-work of the official anatomic nomenclature, can be considered as a corruption of the full Latin expression musculus dilatator pupillae. Pupil dilation occurs when there is insufficient light for the normal function of the eye, and during heightened sympathetic activity, for example in the "fight-or-flight reflex". It works in opposition to the pupillary constrictor. The pupillary dilator acts to increase the size of the pupil to allow more light to enter the eye. An extreme, though natural, case is shown They will also pass through ciliary ganglion and travel in short ciliary nerves to reach the iris dilator muscle.įunction The pupil widens when the iris dilator muscle is stimulated and contracts. They then pierce the sclera, travel between sclera and choroid to reach the iris dilator muscle. ![]() ![]() From there, they travel with the nasociliary nerve and then the long ciliary nerve. They then enter the middle cranial fossa above foramen lacerum, travel through the cavernous sinus in the middle cranial fossa and then travel with the ophthalmic artery in the optic canal or on the ophthalmic nerve through the superior orbital fissure. From there, they travel via the internal carotid artery through the carotid canal to foramen lacerum. The dilator muscle is innervated more specifically by postganglionic sympathetic nerves arising from the superior cervical ganglion as the sympathetic root of ciliary ganglion. Thus, when presented with a threatening stimulus that activates the fight-or-flight response, this innervation contracts the muscle and dilates the pupil, thus temporarily letting more light reach the retina. It is innervated by the sympathetic system, which acts by releasing noradrenaline, which acts on α1-receptors. When stimulated, the cells contract, widening the pupil and allowing more light to enter the eye. These cells are stimulated by the sympathetic nervous system. The pupillary dilator consists of a spokelike arrangement of modified contractile cells called myoepithelial cells. 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. ![]()
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