Ciliary Muscle - Innervation

Innervation

The ciliary muscle receives both parasympathetic and sympathetic fibers from the ciliary ganglion called short ciliary nerves. These postganglionic fibers are part of cranial nerve III (Oculomotor nerve).

Postsynaptic sympathetic signals that originate in the superior cervical ganglion are carried by the nasociliary nerve or directly extend from the internal carotid plexus and pass through the ciliary ganglion. Sympathetic (adrenergic) activation of the muscle's beta-2 receptors result in relaxation and increase in ciliary body size. This tautens the zonule fibers and the lens is stretched flat, thereby decreasing its refractive power appropriately for far distance vision.

Presynaptic parasympathetic signals that originate in the Edinger-Westphal nucleus are carried by cranial nerve III (the oculomotor nerve) and travel through the ciliary ganglion. Parasympathetic activation of the M3 muscarinic receptors causes ciliary muscle contraction, the effect of contraction is to decrease the diameter of the ring of ciliary muscle. The zonule fibers relax and the lens becomes more spherical, increasing its power to refract light for near vision.

The adrenergic tone is dominant over the parasympathetic tone.