Iris dilator muscle

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Iris dilator muscle

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

The upper half of a sagittal section through the front of the eyeball. ("Radiating fibers" labeled near center.)
Latin	musculus dilatator pupillae
Gray's	subject #225 1013
Origin
Insertion
Artery
Nerve	superior cervical ganglion (sympathetics)
Actions	dilates pupil
Antagonist	iris sphincter muscle

The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle^[1] of the eye, running radially in the iris and therefore fit as a dilator. It is innervated by the sympathetic system, which acts by releasing noradrenaline, which acts on α1-receptors.^[2]. Thus, when presented with a threatening stimuli that activates the fight-or-flight response, this innervation dilates the iris, thus temporarily letting more light reach the retina.

1 Additional images
2 See also
3 References
4 External links

[edit] Additional images

Sympathetic connections of the ciliary and superior cervical ganglia.

The iris dilator muscle is concentric with the pupil.

[edit] See also

[edit] References

^ jneurosci.org Muscarinic and Nicotinic Synaptic Activation of the Developing..
^ Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. ISBN 0-443-07145-4. Page 163

[edit] External links

Description of function at tedmontgomery.com
Slide at mscd.edu
dilator+pupillae+muscle at eMedicine Dictionary
Histology at BU 08010loa

Sensory system – visual system – globe of eye (TA A15.2.1-6, GA 10.1005)

Fibrous tunic (outer)

Sclera	Episcleral layer • Schlemm's canal • Trabecular meshwork

Cornea	Limbus • layers (Epithelium, Bowman's, Stroma, Descemet's, Endothelium)

Uvea/vascular tunic (middle)

Choroid	Capillary lamina of choroid • Bruch's membrane • Sattler's layer

Ciliary body	Ciliary processes • Ciliary muscle

Iris	Stroma • Pupil • Iris dilator muscle • Iris sphincter muscle

Retina (inner)

Cells	Photoreceptor cells (Cone cell, Rod cell) → (Horizontal cell) → Bipolar cell → (Amacrine cell) → Retinal ganglion cell (Giant retinal ganglion cells, Photosensitive ganglion cell) Muller glia

Layers	Inner limiting membrane • Nerve fiber layer • Ganglion cell layer • Inner plexiform layer • Inner nuclear layer Outer plexiform layer • Outer nuclear layer External limiting membrane • Layer of rods and cones • Retinal pigment epithelium

Other	Macula • Foveola • Fovea • Optic disc (Cup)

Anterior segment

Anterior chamber • Aqueous humour • Posterior chamber • Lens (Capsule of lens, Zonule of Zinn)

Posterior segment

Vitreous humour

Other

Ocular immune system • Tapetum lucidum • Keratocytes

eye navs: anat/adnexa anat/pathways/physio/dev, noncongen/congen/neoplasia, eponymous signs, proc

Sensory system: Visual system and eye movement pathways

Visual perception

1° (Retina → Optic nerve → Optic chiasm → Optic tract → LGN of Thalamus) → 2° (Optic radiation → Cuneus and Lingual gyrus of Visual cortex → Blobs → Globs)

Muscles of orbit

Tracking	Smooth pursuit: Parietal lobe · Occipital lobe Saccade: Frontal eye fields Physiologic nystagmus → Fixation reflex → PPRF

Horizontal gaze	PPRF → Abducens nucleus → MLF → Oculomotor nucleus → Medial rectus muscle

Vertical gaze	Rostral interstitial nucleus → Oculomotor nucleus, Trochlear nucleus → Muscles of orbit

Vestibulo-ocular reflex	Semicircular canal → Vestibulocochlear nerve → Vestibular nuclei → Abducens nucleus → MLF → Oculomotor nucleus → Medial rectus muscle

Pupillary reflex

Pupillary dilation	1° (Posterior hypothalamus → Ciliospinal center) → 2° (Superior cervical ganglion) → 3° (Sympathetic root of ciliary ganglion → Nasociliary nerve → Long ciliary nerves → Iris dilator muscle)

Pupillary light reflex (constriction)	1° (Retina → Optic nerve → Optic chiasm → Optic tract → Pretectal nucleus) → 2° (Edinger-Westphal nucleus) → 3° (Oculomotor nerve → Parasympathetic root of ciliary ganglion → Ciliary ganglion) → (4° Short ciliary nerves → Iris sphincter muscle)

Accommodation vergence	1° (Retina → Optic nerve → Optic chiasm → Optic tract → Visual cortex → Brodmann area 19 → Pretectal area) → 2° (Edinger-Westphal nucleus) → 3° (Short ciliary nerves → Ciliary ganglion → Ciliary muscle)