| 词条 | Iris sphincter muscle |
| 释义 |
| Name = Iris sphincter muscle | Latin = Musculus sphincter pupillae | Image = Gray878.png | Caption = Iris, front view. (Muscle visible but not labeled.) | Image2 = Gray883.png | Caption2 = The upper half of a sagittal section through the front of the eyeball. ("Sphincter of pupil" labeled near bottom-center.) | Origin = encircles iris[1] | Insertion = encircles iris[1] | Action = constricts pupil | Blood = long posterior ciliary arteries | Nerve = short ciliary nerves | Antagonist = iris dilator muscle }} 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. Comparative AnatomyIt is found in vertebrates and some cephalopods.{{citation needed|date=May 2015}} General StructureInitially, all the myocytes are of the smooth muscle type but, later in life, most cells are of the striated muscle type.[2] Its dimensions are about 0.75 mm wide by 0.15 mm thick.{{citation needed|date=May 2015}} Mode of ActionIn humans, it functions to constrict the pupil in bright light (pupillary light reflex) or during accommodation.{{citation needed|date=May 2015}} In lower animals, the muscle cells themselves are photosensitive causing iris action without brain input.[3] InnervationIt 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.{{citation needed|date=May 2015}}. 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
References1. ^1 Gest, Thomas R; Burkel, William E. "Anatomy Tables - Eye." Medical Gross Anatomy. 2000. University of Michigan Medical School. 5 Jan. 2010 <{{cite web |url=http://anatomy.med.umich.edu/nervous_system/eye_tables.html |title=Archived copy |accessdate=2010-01-05 |deadurl=yes |archiveurl=https://web.archive.org/web/20100526064035/http://anatomy.med.umich.edu/nervous_system/eye_tables.html |archivedate=2010-05-26 |df= }}>. 2. ^{{cite journal |pmid=2826718 |url=http://www.jneurosci.org/cgi/pmidlookup?view=long&pmid=2826718 |year=1987 |author1=Pilar |first1=G |title=Muscarinic and nicotinic synaptic activation of the developing chicken iris |journal=The Journal of Neuroscience |volume=7 |issue=12 |pages=3813–26 |last2=Nuñez |first2=R |last3=McLennan |first3=I. S. |last4=Meriney |first4=S. D. }} 3. ^{{cite news|title=Mouse eyes constrict to light without direct link to the brain|url=https://phys.org/news/2017-06-mouse-eyes-constrict-link-brain.html|accessdate=20 June 2017|work=Phys.org|issue=19 June 2017}} External links
2 : Muscular system|Human eye anatomy |
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