Iris sphincter muscle

Jump to: navigation, search
Iris sphincter
Iris, front view. (Muscle visible but not labeled.)
The upper half of a sagittal section through the front of the eyeball. ("Circular fibers" labeled near center.)
Latin m. sphincter pupillae
Gray's subject #225 1013
Nerve: short ciliary nerves
Action: constricts pupil
Antagonist: iris dilator muscle
Dorlands/Elsevier m_22/12550831

The iris sphincter muscle (pupillary 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.

External links

hu:Musculus sphincter pupillae sr:Мишић сфинктер зенице