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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
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 threating stimuli that activates the fight-or-flight response, this innervation dilates the iris, thus temporarily letting more light reach the retina.

It has the opposite effect to the iris sphincter muscle

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See also[]


  1. Muscarinic and Nicotinic Synaptic Activation of the Developing..
  2. Rang, H. P. (2003). Pharmacology, Edinburgh: Churchill Livingstone. Page 163

External links[]

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