Ciliary muscle

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Ciliary muscle
The choroid and iris. (Ciliary muscle is labeled near top.)
Latin	musculus ciliaris
Gray's	subject #225 1011
Origin
Insertion
Artery:	Long ciliary arteries
Nerve:	Oculomotor nerve (parasympathetics)
Action:	accommodation
Dorlands /Elsevier	m_22/12548589

The Ciliary Muscle is a muscle in the eye that controls the eye's accommodation for viewing objects at varying distances.

Contents 1 Mode of action 2 Innervation 3 See also 4 Additional images 5 External links

[edit] Mode of action

The ciliary muscle affects zonular fibers in the eye (fibers that suspend the lens in position during accommodation), enabling changes in lens shape for light focusing. When the ciliary muscle contracts, it releases the tension on the lens caused by the zonular fibers (fibers that hold or flatten the lens). This release of tension of the zonular fibers causes the lens to become more spherical, adapting to short range focus.

The other way around, relaxation of the ciliary muscle causes the zonular fibers to become taut, flattening the lens, increasing long range focus.

[edit] Innervation

Contraction of the lens happens when there is parasympathetic activation of the M3 muscarinic receptors on the ciliary muscles. The parasympathetic signal is carried by cranial nerve III (the oculomotor nerve) synapsing on the ciliary ganglion. This leads to contraction of the ciliary muscles, a consequent reduction in the size of the ciliary body, and a lessening of the tension on the lens, hence allowing the lens to spring back into a more spherical shape to accommodate for close vision.

Unlike the muscles of the iris (which receives both types of autonomic innervation--the iris sphincter is exclusively innervated by parasympathetics and the iris dilator exclusively by sympathetics), the ciliary muscle receives only parasympathetic innervation.

[edit] See also

• accommodation reflex
• Ciliary body
• Cycloplegia
• Presbyopia
• Edinger-Westphal nucleus

[edit] Additional images

The arteries of the choroid and iris. The greater part of the sclera has been removed.

Iris, front view.

[edit] External links

• Ciliary+muscle at eMedicine Dictionary

v • d • e Sensory system – Visual system – Eye Fibrous tunic (outer) Conjunctiva • Sclera • Schlemm's canal • Trabecular meshwork • Limbus Cornea (Epithelium, Bowman's, Stroma, Descemet's, Endothelium) Uvea (middle) Choroid (Ciliary processes, Choriocapillaris, Bruch's membrane) • Iris (Stroma) • Pupil • Ciliary body Retina (inner) Macula • Fovea • Optic disc • Tapetum lucidum Anterior segment Anterior chamber • Aqueous humour • Posterior chamber • Lens Posterior segment Vitreous humour • Zonule of Zinn Intraocular muscles parasympathetic (Ciliary muscle, Iris sphincter muscle) • sympathetic (Iris dilator muscle) Appearance phenomena of the eye Eyeshine • Leukocoria • Red-eye effect • Red reflex Appearance phenomena by the eye Color appearance (Abney effect • Bezold-Brücke shift • Chromatic adaptation • Purkinje effect)

v • d • e Sensory system – Visual system and eye movement Vision Retina → Optic nerve → Optic chiasm → Optic tract → Lateral geniculate nucleus → Optic radiation → Visual cortex (Cuneus, Lingual gyrus) → Blobs Tracking Smooth pursuit: Parietal lobe - Occipital lobe Saccade: Frontal eye fields Physiologic nystagmus Horizontal gaze Abducens nucleus → PPRF → MLF → Oculomotor nucleus → Medial rectus muscle Vertical gaze Rostral interstitial nucleus → Oculomotor nucleus, Trochlear nucleus → Muscles of orbit Pupillary dilation Ciliospinal center → Superior cervical ganglion → Long ciliary nerves → Iris dilator muscle Pupillary light reflex (constriction) Retina → Optic nerve → Optic chiasm → Optic tract → Pretectum → Edinger-Westphal nucleus → Oculomotor nerve → Ciliary ganglion → Short ciliary nerves → Iris sphincter muscle Accommodation Retina → Optic nerve → Optic chiasm → Optic tract → Visual cortex → Brodmann area 19 → Pretectum → Edinger-Westphal nucleus → Short ciliary nerves → Ciliary ganglion → Ciliary muscle Vestibulo-ocular reflex Semicircular canal → Vestibulocochlear nerve → Vestibular nuclei → Medial rectus muscle Circadian rhythm Retina → Hypothalamus (Suprachiasmatic nucleus)