Iris dilator muscle

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Iris dilator muscle
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Iris, front view. (Muscle visible but not labeled.)
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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
Origin Outer margins of iris [1]
Insertion Inner margins of iris [1]
Nerve Long ciliary nerves (sympathetics)
Actions Dilates pupil
Antagonist Iris sphincter muscle
Identifiers
Latin musculus dilatator pupillae
TA98 A15.2.03.030
TA2 6763
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 more light to enter the eye.

Contents

The ciliary muscle, pupillary sphincter muscle and pupillary dilator muscle sometimes are called intrinsic ocular muscles [4] or intraocular muscles. [5]

Structure

Innervation

It is innervated by the sympathetic system, which acts by releasing noradrenaline, which acts on α1-receptors. [6] Thus, when presented with a threatening stimulus that activates the fight-or-flight response, this innervation contracts the muscle and dilates the pupil, 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. From there, they travel via the internal carotid artery through the carotid canal to foramen lacerum. They then enter the middle cranial fossa above foramen lacerum, travel through the cavernous sinus in the middle cranial fossa and then travel with the ophthalmic artery in the optic canal or on the ophthalmic nerve through the superior orbital fissure. From there, they travel with the nasociliary nerve and then the long ciliary nerve. They then pierce the sclera, travel between sclera and choroid to reach the iris dilator muscle. They will also pass through ciliary ganglion and travel in short ciliary nerves to reach the iris dilator muscle.

Function

The pupil widens when the iris dilator muscle is stimulated and contracts. An extreme, though natural, case is shown Human eye in dim light.jpg
The pupil widens when the iris dilator muscle is stimulated and contracts. An extreme, though natural, case is shown

The pupillary dilator acts to increase the size of the pupil to allow more light to enter the eye. It works in opposition to the pupillary constrictor. [7] Pupil dilation occurs when there is insufficient light for the normal function of the eye, and during heightened sympathetic activity, for example in the "fight-or-flight reflex". [7] [8]

History

Etymology

The English name dilator pupillae muscle [9] as currently used in the list of English equivalents of the Terminologia Anatomica , the reference-work of the official anatomic nomenclature, [10] can be considered as a corruption [11] of the full Latin expression musculus dilatator pupillae. [12] 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 the Classical Latin name mus, [13] and can be translated as little mouse. [13] 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. [13] Latin musculus can be explained by the fact that a muscle looks like a little mouse that moves under the skin. [14] In the writings of Greek philosopher Aristotle the Ancient Greek word for mouse, i.e. μῦς [15] is also used to refer to a muscle. [15]

Dilatator in the Latin expression musculus dilatator pupillae is derived from the classical Latin verb dilatare, [16] to dilate, to spread out. [13] Two possible explanations exist concerning the etymological derivation of this verb. The first explanation considers dilatare as frequentative of differere. [13] The Latin verb differe can mean, to carry different ways, to spread abroad, to scatter, [13] but also to delay. [13] The other explanation [14] considers dilatare as a compound from di- and latus, with the latter word meaning, broad or wide, [13] hence the German name Erweiterer for Latin dilatator. [16]

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 [13] ), 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, [17] [18] [19] [20] [21] The Nomina Anatomica as authorized in 1895 in Basel [12] and in 1935 in Jena [22] [23] used the full Latin expression.

Additional images

See also

Related Research Articles

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Nomina Anatomica (NA) was the international standard on human anatomic terminology from 1895 until it was replaced by Terminologia Anatomica in 1998.

<i>Terminologia Anatomica</i> International standard on human anatomical terminology

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<span class="mw-page-title-main">Short ciliary nerves</span> Nerves of the orbit around the eye

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The Terminologia Embryologica (TE) is a standardized list of words used in the description of human embryologic and fetal structures. It was produced by the Federative International Committee on Anatomical Terminology on behalf of the International Federation of Associations of Anatomists and posted on the Internet since 2010. It has been approved by the General Assembly of the IFAA during the seventeenth International Congress of Anatomy in Cape Town.

The Terminologia Histologica (TH) is the controlled vocabulary for use in cytology and histology. In April 2011, Terminologia Histologica was published online by the Federative International Programme on Anatomical Terminologies (FIPAT), the successor of FCAT.

The Federative International Programme for Anatomical Terminology (FIPAT) is a group of experts who review, analyze, and discuss the terms of the morphological structures of the human body. It was created by the International Federation of Associations of Anatomists (IFAA) and was previously known as the Federative Committee on Anatomical Terminology (FCAT) and the Federative International Committee on Anatomical Terminology (FICAT).

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References

  1. 1 2 Gest, Thomas R; Burkel, William E. (2000). "Anatomy Tables – Eye". Medical Gross Anatomy. University of Michigan Medical School. Archived from the original on 2010-05-26.{{cite web}}: CS1 maint: unfit URL (link)
  2. ↑ Pilar, G; Nuñez, R; McLennan, I. S.; Meriney, S. D. (1987). "Muscarinic and nicotinic synaptic activation of the developing chicken iris". The Journal of Neuroscience. 7 (12): 3813–3826. doi: 10.1523/JNEUROSCI.07-12-03813.1987 . PMC   6569112 . PMID   2826718.
  3. ↑ Saladin, Kenneth (2012). Anatomy and Physiology. McGraw-Hill. pp. 616–617.
  4. ↑ Kels, Barry D.; Grzybowski, Andrzej; Grant-Kels, Jane M. (March 2015). "Human ocular anatomy". Clinics in Dermatology. 33 (2): 140–146. doi:10.1016/j.clindermatol.2014.10.006. PMID   25704934.
  5. ↑ Ludwig, Parker E.; Aslam, Sanah; Czyz, Craig N. (2024). "Anatomy, Head and Neck: Eye Muscles". StatPearls. StatPearls Publishing. PMID   29262013.
  6. ↑ Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. p. 163. ISBN   0-443-07145-4.
  7. 1 2 "Reflexes of the Eye". Cleveland Clinic. Retrieved 3 August 2023.
  8. ↑ "What Happens to Your Body During the Fight-or-Flight Response?". Cleveland Clinic. 9 December 2019. Retrieved 3 August 2023.
  9. ↑ Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica. Stuttgart: Thieme
  10. ↑ Kachlik, David; Baca, Vaclav; Bozdechova, Ivana; Cech, Pavel; Musil, Vladimir (2008). "Anatomical terminology and nomenclature: Past, present and highlights". Surgical and Radiologic Anatomy. 30 (6): 459–466. doi:10.1007/s00276-008-0357-y. PMID   18488135. S2CID   2273591.
  11. ↑ Marečková, Elena; Šimon, František; Červený, Ladislav (2001). "On the new anatomical nomenclature". Annals of Anatomy – Anatomischer Anzeiger. 183 (3): 201–207. doi:10.1016/S0940-9602(01)80215-6. PMC   2413596 . PMID   11396787.
  12. 1 2 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.[ page needed ]
  13. 1 2 3 4 5 6 7 8 9 Lewis, C.T. & Short, C. (1879). A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary. Oxford: Clarendon Press.[ page needed ]
  14. 1 2 Kraus, L.A. (1844). Kritisch-etymologisches medicinisches Lexikon (Dritte Auflage). Göttingen: Verlag der Deuerlich- und Dieterichschen Buchhandlung.[ page needed ]
  15. 1 2 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.[ page needed ]
  16. 1 2 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.[ page needed ]
  17. ↑ 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.[ page needed ]
  18. ↑ International Anatomical Nomenclature Committee (1966). Nomina Anatomica. Amsterdam: Excerpta Medica Foundation.[ page needed ]
  19. ↑ International Anatomical Nomenclature Committee (1977). Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica. Amsterdam-Oxford: Excerpta Medica.[ page needed ]
  20. ↑ International Anatomical Nomenclature Committee (1983). Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica. Baltimore/London: Williams & Wilkins[ page needed ]
  21. ↑ International Anatomical Nomenclature Committee (1989). Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica. Edinburgh: Churchill Livingstone.[ page needed ]
  22. ↑ 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.[ page needed ]
  23. ↑ 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 ed.). Jena: Verlag Gustav Fischer.[ page needed ]
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