Ciliary_muscles

Ciliary muscles

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.

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

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.

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.

Additional images

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

Iris, front view.

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

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)

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 → Blobs

Tracking	Smooth pursuit: Parietal lobe Saccade: Frontal eye fields Physiologic nystagmus

Gaze	horizontal: Abducens nucleus → PPRF → MLF → Oculomotor nucleus → Medial rectus muscle vertical: Rostral interstitial nucleus → Oculomotor nucleus, Trochlear nucleus → Muscles of orbit

Pupillary dilation	Retina → Hypothalamus (Suprachiasmatic nucleus) → Ciliospinal center → Superior cervical ganglion → Iris dilator muscle

Pupillary light reflex (constriction)	Retina → Pretectum → Edinger-Westphal nucleus → Ciliary ganglion → Iris sphincter muscle

Accommodation	Retina → Visual cortex → Brodmann area 19 → Pretectum → Edinger-Westphal nucleus → Ciliary muscle

Vestibulo-ocular reflex	Semicircular canal → Vestibulocochlear nerve → Vestibular nuclei → Medial rectus muscle

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Contents

Mode of action

Innervation

See also

Additional images

External links