Iris dilator muscle

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Iris dilator muscle_table_infobox_0

Iris dilator muscleIris dilator muscle_header_cell_0_0_0
DetailsIris dilator muscle_header_cell_0_1_0
OriginIris dilator muscle_header_cell_0_2_0 outer margins of irisIris dilator muscle_cell_0_2_1
InsertionIris dilator muscle_header_cell_0_3_0 inner margins of irisIris dilator muscle_cell_0_3_1
NerveIris dilator muscle_header_cell_0_4_0 Long ciliary nerves (sympathetics)Iris dilator muscle_cell_0_4_1
ActionsIris dilator muscle_header_cell_0_5_0 dilates pupilIris dilator muscle_cell_0_5_1
AntagonistIris dilator muscle_header_cell_0_6_0 iris sphincter muscleIris dilator muscle_cell_0_6_1
IdentifiersIris dilator muscle_header_cell_0_7_0
LatinIris dilator muscle_header_cell_0_8_0 Musculus dilatator pupillaeIris dilator muscle_cell_0_8_1
TA98Iris dilator muscle_header_cell_0_9_0 Iris dilator muscle_cell_0_9_1
TA2Iris dilator muscle_header_cell_0_10_0 Iris dilator muscle_cell_0_10_1
FMAIris dilator muscle_header_cell_0_11_0 Iris dilator muscle_cell_0_11_1

The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle of the eye, running radially in the iris and therefore fit as a dilator. Iris dilator muscle_sentence_0

The pupillary dilator consists of a spokelike arrangement of modified contractile cells called myoepithelial cells. Iris dilator muscle_sentence_1

These cells are stimulated by the sympathetic nervous system. Iris dilator muscle_sentence_2

When stimulated, the cells contract, widening the pupil and allowing more light to enter the eye. Iris dilator muscle_sentence_3

Structure Iris dilator muscle_section_0

Innervation Iris dilator muscle_section_1

It is innervated by the sympathetic system, which acts by releasing noradrenaline, which acts on α1-receptors. Iris dilator muscle_sentence_4

Thus, when presented with a threatening stimuli that activates the fight-or-flight response, this innervation contracts the muscle and dilates the pupil, thus temporarily letting more light reach the retina. Iris dilator muscle_sentence_5

The dilator muscle is innervated more specifically by postganglionic sympathetic nerves arising from the superior cervical ganglion as the sympathetic root of ciliary ganglion. Iris dilator muscle_sentence_6

From there, they travel via the internal carotid artery through the carotid canal to foramen lacerum. Iris dilator muscle_sentence_7

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. Iris dilator muscle_sentence_8

From there, they travel with the nasociliary nerve and then the long ciliary nerve. Iris dilator muscle_sentence_9

They then pierce the sclera, travel between sclera and choroid to reach the iris dilator muscle. Iris dilator muscle_sentence_10

They will also pass through ciliary ganglion and travel in short ciliary nerves to reach the iris dilator muscle. Iris dilator muscle_sentence_11

Function Iris dilator muscle_section_2

The pupillary dilator acts to increase the size of the pupil to allow more light to enter the eye. Iris dilator muscle_sentence_12

It works in opposition to the pupillary constrictor. Iris dilator muscle_sentence_13

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". Iris dilator muscle_sentence_14

History Iris dilator muscle_section_3

Etymology Iris dilator muscle_section_4

The English name dilator pupillae muscle as currently used in the list of English equivalents of the Terminologia Anatomica, the reference-work of the official anatomic nomenclature, can be considered as a corruption of the full Latin expression musculus dilatator pupillae. Iris dilator muscle_sentence_15

The full Latin expression exhibits three words that each can be traced back to Roman antiquity. Iris dilator muscle_sentence_16

The Classical Latin name musculus is actually a diminutive of the Classical Latin name mus, and can be translated as little mouse. Iris dilator muscle_sentence_17

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. Iris dilator muscle_sentence_18

Latin musculus can be explained by the fact that a muscle looks like a little mouse that moves under the skin. Iris dilator muscle_sentence_19

In the writings of Greek philosopher Aristotle the Ancient Greek word for mouse, i.e. μῦς is also used to refer to a muscle. Iris dilator muscle_sentence_20

Dilatator in the Latin expression musculus dilatator pupillae is derived from the classical Latin verb dilatare, to dilate, to spread out. Iris dilator muscle_sentence_21

Two possible explanations exist concerning the etymological derivation of this verb. Iris dilator muscle_sentence_22

The first explanation considers dilatare as frequentative of differere. Iris dilator muscle_sentence_23

The Latin verb differe can mean, to carry different ways, to spread abroad, to scatter, but also to delay. Iris dilator muscle_sentence_24

The other explanation considers dilatare as a compound from di- and latus, with the latter word meaning, broad or wide, hence the German name Erweiterer for Latin dilatator. Iris dilator muscle_sentence_25

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), a noun in the genitive case modifying dilator, a noun in the nominative case, and partly English, i.e. muscle. Iris dilator muscle_sentence_26

In previous editions (Nomina Anatomica) this muscle was officially called the musculus dilator pupillae, The Nomina Anatomica as authorized in 1895 in Basle and in 1935 in Jena used the full Latin expression. Iris dilator muscle_sentence_27

Additional images Iris dilator muscle_section_5

Iris dilator muscle_unordered_list_0

  • Iris dilator muscle_item_0_0
  • Iris dilator muscle_item_0_1
  • Iris dilator muscle_item_0_2

See also Iris dilator muscle_section_6

Iris dilator muscle_unordered_list_1

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: dilator muscle.