Iris dilator muscle
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| Iris dilator muscle | |
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| Iris, front view. (Muscle visible but not labeled.) | |
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| The upper half of a sagittal section through the front of the eyeball. (Iris dilator muscle is NOT labeled and not to be confused with "Radiating fibers" labeled near center, which are part of the ciliary muscle.) | |
| Latin | musculus dilatator pupillae |
| Gray's | subject #225 1013 |
| Origin | outer margins of iris[1] |
| Insertion | inner margins of iris[1] |
| Artery | |
| Nerve | Long ciliary nerves (sympathetics) |
| Actions | dilates pupil |
| Antagonist | iris sphincter muscle |
The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle[2] of the eye, running radially in the iris and therefore fit as a dilator. It has its origin from the anterior epithelium.[3] It is innervated by the sympathetic system, which acts by releasing noradrenaline, which acts on α1-receptors.[4] Thus, when presented with a threatening stimuli that activates the fight-or-flight response, this innervation contracts the muscle and dilates the iris, thus temporarily letting more light reach the retina.
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[edit] Additional images
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Sympathetic connections of the ciliary and superior cervical ganglia.
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The iris dilator muscle fibers course radially through the iris.
[edit] See also
[edit] References
- ^ a b 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>.
- ^ jneurosci.org Muscarinic and Nicotinic Synaptic Activation of the Developing..
- ^ "eye, human." Encyclopædia Britannica. Encyclopaedia Britannica Ultimate Reference Suite. Chicago: Encyclopædia Britannica, 2010.
- ^ Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. ISBN 0-443-07145-4. Page 163
[edit] External links
- Description of function at tedmontgomery.com
- Slide at mscd.edu
- dilator+pupillae+muscle at eMedicine Dictionary
- Histology at BU 08010loa
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