part of develops from neurectodermal cell smooth muscle cell sphincter associated smooth muscle cell smooth muscle cell of sphincter of pupil 2010-09-08T08:53:42Z A circular smooth muscle cell of the iris, innervated by the ciliary nerves (parasympathetic), and acting to contract the pupil. This muscle cell derives from neuroectoderm. This smooth muscle cell results from transformation of epithelial cells to smooth muscle cells. FMA:70611 https://cellxgene.cziscience.com/cellguide/CL_0002243 smooth muscle fibre of sphincter of pupil smooth muscle fiber of sphincter of pupil The smooth muscle cell of sphincter of pupil is a specialized cell type typically found within the eye, more specifically within the sphincter muscle of the iris. These cells can constrict and dilate in response to light signals, tightly regulating the amount of light reaching the retina. Contraction narrows the pupil in bright conditions (pupillary constriction), protecting the retina from excessive light. In low light, relaxation allows dilation (pupillary dilation), enhancing visual perception in dim conditions. These cells are also innervated by parasympathetic fibers from the oculomotor nerve. Light signals to the Edinger-Westphal nucleus stimulate the release of acetylcholine, contracting the cells. On the contrary, sympathetic stimulation induces relaxation. This precise control plays a crucial role in optimizing visual function, highlighting their essential role in vision biology. (This extended description was generated by ChatGPT and reviewed by the CellGuide team, who added references, and by the CL editors, who approved it for inclusion in CL. It may contain information that applies only to some subtypes and species, and so should not be considered definitional.) sphincter pupillae