Iris dilator muscle

Iris dilator muscle

Iris, front view. (Muscle visible but not labeled.)

The upper half of a sagittal section through the front of the eyeball. (Iris dilator muscle is NOT labeled and not to be confused with "Radiating fibers" labeled near center, which are part of the ciliary muscle.)
Details
Latin Musculus dilatator pupillae
outer margins of iris[1]
inner margins of iris[1]
Long ciliary nerves (sympathetics)
Actions dilates pupil
Antagonist
 iris sphincter muscle
Identifiers
Gray's p.1013
Dorlands
/Elsevier		 m_22/12548821
TA A15.2.03.030
FMA 49158
Anatomical terms of muscle

The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle[2] of the eye, running radially in the iris and therefore fit as a dilator. The pupillary dilator consists of a spokelike arrangement of modified contractile cells called myoepithelial cells. These cells are stimulated by the sympathetic nervous system.[3] When stimulated, the cells contract, widening the pupil and allowing for more light to pass through the eye.

Structure

Innervation

It is innervated by the sympathetic system, which acts by releasing noradrenaline, which acts on α1-receptors.[4] Thus, when presented with a threatening stimuli that activates the fight-or-flight response, this innervation contracts the muscle and dilates the iris, thus temporarily letting more light reach the retina.

The dilator muscle is innervated more specifically by postganglionic sympathetic nerves arising from the superior cervical ganglion as the sympathetic root of ciliary ganglion. They will follow both short ciliary and long ciliary nerves to reach the dilator muscle.

Function

The pupillary dilator acts as an antagonist to the pupillary constrictor which narrows the pupil and admits less light to the eye. It has its origin from the anterior epithelium.[5] Pupillary dilation occurs in two situations: when light intensity changes and when we shift our gaze between distant and nearby objects.[3]

History

Etymology

The English name dilator pupillae muscle[6] as currently used in the list of English equivalents of the Terminologia Anatomica, the reference-work of the official anatomic nomenclature,[7] can be considered as a corruption[8] of the full Latin expression musculus dilatator pupillae.[9] The full Latin expression exhibits three words that each can be traced back to Roman antiquity. The Classical Latin name musculus is actually a diminutive of classical Latin, mus,[10] and can be translated as little mouse.[10] In the medical writings of Aulus Cornelius Celsus we can also find this specific name to refer to a muscle instead of its literal meaning.[10] Latin musculus can be explained by the fact that a muscle looks like a little mouse that moves under the skin.[11] In the writings of Greek philosopher Aristotle the Ancient Greek word for mouse, i.e. μῦς[12] is also used to refer to a muscle.[12]

Dilatator in the Latin expression musculus dilatator pupillae is derived from the classical Latin verb dilatare,[13] to dilate, to spread out.[10] Two possible explanations exist concerning the etymological derivation of this verb. The first explanation considers dilatare as frequentative of differere.[10] The Latin verb differe can mean, to carry different ways, to spread abroad, to scatter,[10] but also to delay.[10] The other explanation[11] considers dilatare as a compound from di- and latus, with the latter word meaning, broad or wide,[10] hence the German name Erweiterer for Latin dilatator.[13]

The expression dilator pupillae muscle, as used in the list of English equivalents of the Terminologia Anatomica, is actually partly Latin, i.e. dilator pupillae, with pupillae (=of the pupil[10]), a noun in the genitive case modifying dilator, a noun in the nominative case, and partly English, i.e. muscle. In previous editions (Nomina Anatomica) this muscle was officially called the musculus dilator pupillae,[14][15][16][17][18] The Nomina Anatomica as authorized in 1895 in Basle[9] and in 1935 in Jena[19][20] used the full Latin expression.

Additional images

See also

References

  1. ↑ 1.0 1.1 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..
  3. ↑ 3.0 3.1 Saladin, Kenneth (2012). Anatomy and Physiology. McGraw-Hill. pp. 616–617.
  4. ↑ Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. ISBN 0-443-07145-4. Page 163
  5. ↑ "eye, human." Encyclopædia Britannica. Encyclopaedia Britannica Ultimate Reference Suite. Chicago: Encyclopædia Britannica, 2010.
  6. ↑ Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica. Stuttgart: Thieme
  7. ↑ Kachlik, D., Baca V., Bozdechova, I., Cech, P. & Musil, V. (2008). Anatomical terminology and nomenclature: past, present and highlights. Surg Radiol Anat, 30 459-466.
  8. ↑ Marečková, E., Šimon, F., & Červený, L. (2001). On the new anatomical nomenclature. Annals of Anatomy, 183, 201-207
  9. ↑ 9.0 9.1 His (1895). Die anatomische Nomenclatur. Nomina Anatomica. Der von der Anatomischen Gesellschaft auf ihrer IX. Versammlung in Basel angenommenen Namen. Leipzig: Verlag von Veit & Comp.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 Lewis, C.T. & Short, C. (1879). A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary. Oxford: Clarendon Press.
  11. ↑ 11.0 11.1 Kraus, L.A. (1844). Kritisch-etymologisches medicinisches Lexikon (Dritte Auflage). Göttingen: Verlag der Deuerlich- und Dieterichschen Buchhandlung.
  12. ↑ 12.0 12.1 Liddell, H.G. & Scott, R. (1940). A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie. Oxford: Clarendon Press.
  13. ↑ 13.0 13.1 Foster, F.D. (1891-1893). An illustrated medical dictionary. Being a dictionary of the technical terms used by writers on medicine and the collateral sciences, in the Latin, English, French, and German languages. New York: D. Appleton and Company.
  14. ↑ Donáth, T. & Crawford, G.C.N. (1969). Anatomical dictionary with nomenclature and explanatory notes. Oxford/London/Edinburgh/New York/Toronto/Syney/Paris/Braunschweig: Pergamon Press.
  15. ↑ International Anatomical Nomenclature Committee (1966). Nomina Anatomica . Amsterdam: Excerpta Medica Foundation.
  16. ↑ International Anatomical Nomenclature Committee (1977). Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica. Amsterdam-Oxford: Excerpta Medica.
  17. ↑ International Anatomical Nomenclature Committee (1983). Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica. Baltimore/London: Williams & Wilkins
  18. ↑ International Anatomical Nomenclature Committee (1989). Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica. Edinburgh: Churchill Livingstone.
  19. ↑ Kopsch, F. (1941). Die Nomina anatomica des Jahres 1895 (B.N.A.) nach der Buchstabenreihe geordnet und gegenübergestellt den Nomina anatomica des Jahres 1935 (I.N.A.) (3. Auflage). Leipzig: Georg Thieme Verlag.
  20. ↑ Stieve, H. (1949). Nomina Anatomica. Zusammengestellt von der im Jahre 1923 gewählten Nomenklatur-Kommission, unter Berücksichtigung der Vorschläge der Mitglieder der Anatomischen Gesellschaft, der Anatomical Society of Great Britain and Ireland, sowie der American Association of Anatomists, überprüft und durch Beschluß der Anatomischen Gesellschaft auf der Tagung in Jena 1935 endgültig angenommen. (4th edition). Jena: Verlag Gustav Fischer.

External links