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.)
|Latin||Musculus sphincter pupillae|
|long posterior ciliary arteries|
|short ciliary nerves|
|iris dilator muscle|
|Anatomical terms of 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.
Its dimensions are about 0.75 mm wide by 0.15 mm thick.
Mode of Action
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.
- Gest, Thomas R; Burkel, William E. "Anatomy Tables - Eye." Medical Gross Anatomy. 2000. University of Michigan Medical School. 5 Jan. 2010 <http://anatomy.med.umich.edu/nervous_system/eye_tables.html>.
- 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.
- Overview of function at tedmontgomery.com
- Slide at mscd.edu
- Histology image: 08010loa – Histology Learning System at Boston University
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