Iris sphincter muscle

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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
Origin:
Insertion:
Artery:
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

Overview of function at tedmontgomery.com
Slide at mscd.edu
sphincter+pupillae at eMedicine Dictionary
Histology at Boston University 08010loa

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List of muscles of head and neck: the head

Extraocular (CN III, IV, VI)

oblique (inferior, superior) - rectus (superior, inferior, medial, lateral) - levator palpebrae superioris (superior tarsal)

Mastication (CN V3)

masseter - temporalis - pterygoid (lateral, medial)

Facial (CN VII)

Ear	auriculares (anterior, superior, posterior) - temporoparietalis
Scalp/eyelid	occipitofrontalis (occipitalis, frontalis) - orbicularis oculi (depressor supercilii) - corrugator supercilii
Nose	procerus - nasalis (dilatator naris) - depressor septi nasi - levator labii superioris alaeque nasi
Mouth	levator anguli oris - levator labii superioris - zygomaticus (major, minor) orbicularis oris - risorius - buccinator depressor anguli oris - depressor labii inferioris - mentalis

Mouth/throat (CN IX, X, XI)
(except TVP=V3)

Soft palate	veli palatini (tensor, levator) - musculus uvulae - palatopharyngeus (to pharnyx) - palatoglossus (to tongue)
Pharynx	pharyngeal constrictor (superior, middle, inferior) - longitudinal (stylopharyngeus, salpingopharyngeus)
Larynx	cricothyroid - cricoarytenoid (posterior, lateral) - arytenoid (oblique arytenoid/aryepiglottic, transverse arytenoid) - thyroarytenoid (vocal, thyroepiglottic)