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Iris sphincter muscle
The iris sphincter musclepupillary 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 .
Initially, all the myocytes are of the smooth muscle type, but hatch later in life, so that ultimately most cells are of the striated muscle type.[1]
References
^ jneurosci.org Muscarinic and Nicotinic Synaptic Activation of the Developing..
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