Iris sphincter muscle

Iris sphincter muscle
Iris sphincter muscle
Gray878.png
Iris, front view. (Muscle visible but not labeled.)
Gray883.png
The upper half of a sagittal section through the front of the eyeball. ("Sphincter of pupil" labeled near bottom-center.)
Latin m. sphincter pupillae
Gray's subject #225 1013
Origin encircles iris[1]
Insertion    encircles iris[1]
Artery long posterior ciliary arteries
Nerve short ciliary nerves
Actions constricts pupil
Antagonist iris dilator muscle

The iris sphincter muscle (pupillary sphincter, pupillary constrictor, circular muscle of iris, circular fibers) is a muscle in the part of the eye called the iris. It encircles the eye, appropriate to its function as a constrictor.

Contents

Comparative Anatomy

It is found in vertebrates and some cephalopods.

General Structure

Initially, all the myocytes are of the smooth muscle type but, later in life, most cells are of the striated muscle type.[2]

Its dimensions are about 0.75 mm wide by 0.15 mm thick.

Mode of Action

In humans, it functions to constrict the pupil in bright light (pupillary reflex) or during accommodation.

Innervation

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.

See also

References

  1. ^ a b Gest, Thomas R; Burkel, William E. "Anatomy Tables - Eye." Medical Gross Anatomy. 2000. University of Michigan Medical School. 5 Jan. 2010 <http://anatomy.med.umich.edu/nervous_system/eye_tables.html>.
  2. ^ jneurosci.org Muscarinic and Nicotinic Synaptic Activation of the Developing..

External links



Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать курсовую

Look at other dictionaries:

  • Iris dilator muscle — Iris, front view. (Muscle visible but not labeled.) …   Wikipedia

  • sphincter muscle — ▪ anatomy  any of the ringlike muscles surrounding and able to contract or close a bodily passage or opening. One of the most important human sphincter muscles is the sphincter pylori, a thickening of the middle layer of stomach muscle around the …   Universalium

  • Iris (anatomy) — Iris The iris is the blue area. The other structures visible are the pupil center and the white sclera surrounding the iris. The overlying cornea is pictured, but not visible, as it is transparent …   Wikipedia

  • Iris muscle — may refer to: *Iris sphincter muscle *Iris dilator muscle …   Wikipedia

  • Ciliary muscle — The choroid and iris. (Ciliary muscle is labeled near top.) Latin musculus ciliaris Gray s …   Wikipedia

  • Muscle — is the tissue of the body which primarily functions as a source of power. There are three types of muscle in the body. Muscle which is responsible for moving extremities and external areas of the body is called "skeletal muscle." Heart… …   Medical dictionary

  • iris — [ iris ] n. m. • XIIIe; lat. iris, iridis, gr. iris, iridos I ♦ Plante (iridacées), à rhizome ou à bulbe et à haute tige portant de grandes fleurs ornementales. Iris des marais, de Florence, d Espagne. Iris violet, jaune. L irone, principe… …   Encyclopédie Universelle

  • sphincter pupillae — sphincter pu·pil·lae pyü pil ē n a broad flat band of smooth muscle in the iris that surrounds the pupil of the eye * * * musculus sphincter pupillae …   Medical dictionary

  • Iris (anatomie) — Pour les articles homonymes, voir Iris. L iris est une membrane circulaire et contractile de la face antérieure du globe oculaire. Il constitue la partie colorée visible de l œil. Il est percé en son centre d un orifice, la pupille. L absence d… …   Wikipédia en Français

  • sphincter — A muscle that encircles a duct, tube, or orifice in such a way that its contraction constricts the lumen or orifice. SYN: musculus s. [TA], s. muscle [TA]. [G. sphinkter, a band or lace] s. of ampulla s. of hepatopancreatic ampulla. anatomic s.… …   Medical dictionary

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”