Iris dilator muscle
Iris, front view. (Muscle visible but not labeled.)
The upper half of a sagittal section through the front of the eyeball. ("Radiating fibers" labeled near center.)
Latin	musculus dilatator pupillae
Gray's	subject #225 1013
Origin
Insertion
Artery:
Nerve:	superior cervical ganglion (sympathetics)
Action:	dilates pupil
Antagonist:	iris sphincter muscle
Dorlands /Elsevier	m_22/12548821

The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle^[1] of the eye. It is innervated by the sympathetic system, which acts by releasing noradrenaline, which acts on α1-receptors.^[2]. Thus, when presented with a threatening stimuli that activates the fight-or-flight response, this innervation dilates the iris, thus temporarily letting more light reach the retina.

Additional images

Sympathetic connections of the ciliary and superior cervical ganglia.

See also

• Mydriasis

References

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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