Iris sphincter muscle - wikipedia Iris sphincter muscle Iris sphincter muscle Iris, front view. ( Muscle visible but not labeled. ) The upper half of a sagittal section through the front of the eyeball. ( `` Sphincter of pupil '' labeled near bottom - center. ) Details Origin encircles iris Insertion encircles iris Artery long posterior ciliary arteries Nerve short ciliary nerves Actions constricts pupil Antagonist iris dilator muscle Identifiers Latin Musculus sphincter pupillae TA A15. 2.03. 029 FMA 49157 Anatomical terms of muscle ( edit on Wikidata ) The iris sphincter muscle ( pupillary sphincter, pupillary constrictor, circular muscle of iris, circular fibers ) is a muscle in the part of the eye called the iris. It encircles the pupil of the iris, appropriate to its function as a constrictor of the pupil. Contents 1 Comparative Anatomy 2 General Structure 3 Mode of Action 4 Innervation 5 See also 6 References 7 External links Comparative anatomy It is found in vertebrates and some cephalopods. General structure Initially, all the myocytes are of the smooth muscle type but, later in life, most cells are of the striated muscle type. Its dimensions are about 0.75 mm wide by 0.15 mm thick. Mode of action In humans, it functions to constrict the pupil in bright light ( pupillary light reflex ) or during accommodation. In lower animals, the muscle cells themselves are photosensitive causing iris action without brain input. Innervation It is controlled by parasympathetic fibers of the muscarinic acetylcholine receptor ( M3 ) that originate from the Edinger - Westphal nucleus, travel along the oculomotor nerve ( CN III ), synapse in the ciliary ganglion, and then enter the eye via the short ciliary nerves.. The short ciliary nerves then run forward and pierce the sclera at the back of the eye, traveling between the sclera and the choroid to innervate the iris sphincter muscle. See also Iris dilator muscle References ^ Jump up to : Gest, Thomas R ; Burkel, William E. `` Anatomy Tables - Eye. '' Medical Gross Anatomy. 2000. University of Michigan Medical School. 5 Jan. 2010 < `` Archived copy ''. Archived from the original on 2010 - 05 - 26. Retrieved 2010 - 01 - 05. >. Jump up ^ Pilar, G ; Nuñez, R ; McLennan, I.S. ; Meriney, S.D. ( 1987 ). `` Muscarinic and nicotinic synaptic activation of the developing chicken iris ''. The Journal of Neuroscience. 7 ( 12 ) : 3813 -- 26. PMID 2826718. Jump up ^ `` Mouse eyes constrict to light without direct link to the brain ''. Phys.org ( 19 June 2017 ). Retrieved 20 June 2017. External links Overview of function at tedmontgomery.com Slide at mscd.edu Histology image : 08010loa -- Histology Learning System at Boston University Anatomy of the globe of the human eye Fibrous tunic ( outer ) Sclera Episcleral layer Schlemm 's canal Trabecular meshwork Cornea Limbus layers Epithelium Bowman 's Stroma Dua 's layer Descemet 's Endothelium Uvea / vascular tunic ( middle ) Choroid Capillary lamina of choroid Bruch 's membrane Sattler 's layer Ciliary body Ciliary processes Ciliary muscle Pars plicata Pars plana Iris Stroma Pupil Iris dilator muscle Iris sphincter muscle Retina ( inner ) Layers Inner limiting membrane Nerve fiber layer Ganglion cell layer Inner plexiform layer Inner nuclear layer Outer plexiform layer Outer nuclear layer External limiting membrane Layer of rods and cones Retinal pigment epithelium Cells Photoreceptor cells ( Cone cell, Rod cell ) → ( Horizontal cell ) → Bipolar cell → ( Amacrine cell ) → Retina ganglion cell ( Midget cell, Parasol cell, Bistratified cell, Giant retina ganglion cells, Photosensitive ganglion cell ) → Diencephalon : P cell, M cell, K cell, Muller glia Other Macula Perifoveal area Parafoveal area Fovea Foveal avascular zone Foveola Optic disc Optic cup Ora serrata Anatomical regions of the eye Anterior segment Adnexa Fibrous tunic Anterior chamber Aqueous humour Iris Posterior chamber Ciliary body Lens Capsule of lens Zonule of Zinn Posterior segment Vitreous chamber Vitreous body Retina Choroid Other Keratocytes Ocular immune system Optical coherence tomography Eye care professional Eye disease Refractive error Accommodation Physiological Optics Visual perception Optical illusions List of optical illusions Afterimage Barberpole Bezold Blivet Café wall Cornsweet Delboeuf Ebbinghaus Ehrenstein Flash lag Fraser spiral Grid Hering Jastrow Mach McCollough Müller - Lyer Necker Orbison Penrose stairs triangle Peripheral drift Poggendorff Ponzo Rubin Sander Schroeder Ternus Vertical -- horizontal White 's Wundt Zöllner Related Auditory Tactile Temporal Op art Ascending and Descending Waterfall Retrieved from `` https://en.wikipedia.org/w/index.php?title=Iris_sphincter_muscle&oldid=825181713 '' Categories : Muscular system Human eye anatomy Hidden categories : Pages with unresolved properties All articles with unsourced statements Articles with unsourced statements from May 2015 Talk Contents About Wikipedia Català Español فارسی Hrvatski Italiano Magyar Nederlands 日本 語 Português Русский Српски / srpski Srpskohrvatski / српскохрватски ไทย Українська 中文 7 more Edit links This page was last edited on 11 February 2018, at 23 : 15. 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Question: what type of muscle is in the iris
Answer: sphincter