Iris sphincter muscle
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| Iris sphincter | ||
|---|---|---|
 | ||
| Iris, front view. (Muscle visible but not labeled.) | ||
 | ||
| The upper half of a sagittal section through the front of the eyeball. ("Circular fibers" labeled near center.) | ||
| Latin | m. sphincter pupillae | |
| Gray's | subject #225 1013 | |
| Origin: | ||
| Insertion: | ||
| Artery: | ||
| Nerve: | short ciliary nerves | |
| Action: | constricts pupil | |
| Antagonist: | iris dilator muscle | |
| Dorlands/Elsevier | m_22/12550831 | |
The iris sphincter muscle (pupillary sphincter, circular muscle of iris, circular fibers) is a muscle in the part of the eye called the iris.
It is found in vertebrates and some cephalopods.
In humans, it functions to constrict the pupil in bright light (pupillary reflex) or during accommodation. Its dimensions are about 0.75 mm wide by 0.15 mm thick.
It is controlled by parasympathetic fibers 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.
External links
- Overview of function at tedmontgomery.com
- Slide at mscd.edu
- sphincter+pupillae at eMedicine Dictionary
- Histology at BU 08010loa
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Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
