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The ciliary muscle is an intrinsic muscle of the eye that controls accommodation for viewing objects at varying distances. It is located within the ciliary body of the eye and is supplied by the oculomotor nerve (CN III). The ciliary muscle receives parasympathetic innervation from the short ciliary nerves that arise from the ciliary ganglion. The state of the ciliary muscle changes depending on whether we are observing distant or close objects. When looking at a distant object, the ciliary muscle is relaxed, and the lens is flattened. On the other hand, when focusing on a close object, the ciliary muscle contracts, causing the lens to become more spherical and adapted to short-range vision.
| Characteristics | Values |
|---|---|
| Nerve Name | Oculomotor nerve (CN III) |
| Type of Innervation | Parasympathetic |
| Type of Fibers | Postganglionic |
| Origin | Accessory/Edinger-Westphal nucleus of oculomotor nucleus in the midbrain |
| Pathway | Via the ciliary ganglion and short ciliary nerves |
| Function | Controls accommodation for viewing objects at varying distances, regulates the flow of aqueous humor, changes the shape of the lens |
| Additional Function | Increases pore diameter of the trabecular meshwork, aiding drainage of aqueous humor |
| Muscle Type | Smooth muscle |
| Shape | Ring-shaped |
| Location | Within the ciliary body of the eye, between the anterior border of the choroid and iris |
| Composition | Longitudinal, radial, and circular fibers |
| Effect of Contraction | Decreases diameter of the ciliary muscle ring, causing relaxation of zonular fibers and increased lens curvature |
| Effect of Relaxation | Zonular fibers become taut, flattening the lens and increasing focal distance for long-range focus |
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What You'll Learn
- The ciliary muscle is innervated by the oculomotor nerve (CN III)
- The ciliary ganglion receives preganglionic fibres via the oculomotor nerve
- The ciliary muscle receives parasympathetic innervation from short ciliary nerves
- The ciliary muscle controls accommodation for viewing objects at varying distances
- The ciliary muscle is an intrinsic muscle of the eye
The ciliary muscle is innervated by the oculomotor nerve (CN III)
The ciliary muscle is an intrinsic muscle of the eye, formed as a ring of smooth muscle in the eye's middle layer, the uvea (vascular layer). It controls accommodation for viewing objects at varying distances, and its state changes depending on whether we observe distant or close objects. When looking at a distant object, the ciliary muscle is relaxed, and the zonular fibres are tightened, flattening the lens and increasing long-range focus. On the other hand, when focusing on a close object, the ciliary muscle contracts, increasing the lens's convexity and accommodating near vision.
The ciliary muscle's action is instructed by the parasympathetic fibres originating from the accessory/Edinger-Westphal nucleus. The contraction of the ciliary muscle loosens the zonular fibres, allowing the lens to relax and become more spherical. This increase in the lens's curvature increases its refractive power, enabling the formation of sharply focused images of nearby objects on the retina.
The oculomotor nerve (CN III) also provides motor innervation to several extraocular muscles, including the superior rectus, levator palpabrae superioris, inferior rectus, medial rectus, and inferior oblique. Additionally, it supplies pre-ganglionic parasympathetic fibres to the ciliary ganglion, which ultimately innervates the sphincter pupillae and ciliary muscles.
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The ciliary ganglion receives preganglionic fibres via the oculomotor nerve
The ciliary muscle is an intrinsic muscle of the eye. It is formed as a ring of smooth muscle in the eye's middle layer, the uvea (vascular layer). The ciliary muscle is responsible for controlling accommodation for viewing objects at varying distances. It also regulates the flow of aqueous humour into Schlemm's canal.
The ciliary muscle receives parasympathetic innervation from the short ciliary nerves (postganglionic fibres) that arise from the ciliary ganglion. The ciliary ganglion is a small ganglion, approximately 2-3mm long, located in the fat-filled connective tissue in the posterior orbit, just anterior to the superior orbital fissure. It contains postganglionic parasympathetic neurons that supply the ciliary muscle.
The oculomotor nerve is involved in the regulation of important ocular functions, including pupil diameter control, lens accommodation, and local blood flow. The parasympathetic fibres carried by the oculomotor nerve synapse with the ciliary ganglion, which then sends postganglionic fibres to the ciliary muscle. The contraction of the ciliary muscle is instructed by these parasympathetic fibres, which originate from the Edinger-Westphal nucleus.
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The ciliary muscle receives parasympathetic innervation from short ciliary nerves
The ciliary muscle is an intrinsic muscle of the eye that controls accommodation for viewing objects at varying distances. It is located within the ciliary body of the eye and facilitates lens accommodation for near vision. The ciliary muscle receives parasympathetic innervation from the short ciliary nerves (postganglionic fibres) that arise from the ciliary ganglion. The ciliary ganglion receives preganglionic fibres via the oculomotor nerve (cranial nerve III) that originate from the accessory/Edinger-Westphal nucleus of the oculomotor nucleus in the midbrain.
The ciliary muscle is composed of smooth muscle fibres oriented in three different directions: longitudinal, radial, and circular. It functions mainly through the parasympathetic nerve fibres of the oculomotor nerve (CN III). The contraction of the ciliary muscle loosens the zonular fibres, increasing the convexity of the lens, which induces accommodation for near vision. This process is known as the accommodation reflex, which consists of three responses. The reflex pathway includes the optic nerve (CN II), the visual and frontal cortex, the oculomotor and accessory oculomotor nuclei, and the oculomotor nerve (CN III).
The direct pathway from the midbrain to the ciliary muscle is believed to be uninterrupted by a synapse in the ciliary ganglion. This pathway has been observed in cats and monkeys. The preganglionic parasympathetic fibres originate in the Edinger-Westphal nuclei located in the midbrain and travel to the ciliary ganglion via the oculomotor nerve. The ciliary ganglion then sends postganglionic fibres to the ciliary muscle.
The ciliary muscle also receives innervation from sympathetic fibres of the autonomic nervous system (ANS). These fibres are believed to provide inhibitory impulses that inhibit the accommodation reflex. The contraction of the ciliary muscle is essential for focusing on close objects. It loosens the zonular fibres, allowing the lens to relax and become more spherical. This increase in lens curvature increases the refractive power of the lens, enabling the formation of sharply focused images of nearby objects on the retina.
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The ciliary muscle controls accommodation for viewing objects at varying distances
The ciliary muscle is an intrinsic muscle of the eye that controls accommodation for viewing objects at varying distances. It is located within the ciliary body of the eye, which lies between the anterior border of the choroid and the iris. The ciliary muscle is composed of smooth muscle fibres oriented in three directions: longitudinal, radial, and circular.
The state of the ciliary muscle changes depending on whether we are observing distant or close objects. When looking at a distant object, the ciliary muscle is relaxed, and the zonular fibres are tightened, flattening the lens and increasing the focal distance. Conversely, when focusing on a close object, the ciliary muscle contracts, releasing the tension on the lens caused by the zonular fibres. This contraction increases the convexity of the lens, making it more spherical and increasing its refractive power for near vision.
The ciliary muscle receives parasympathetic innervation from the short ciliary nerves (postganglionic fibres) that arise from the ciliary ganglion. The ciliary ganglion, in turn, receives preganglionic fibres via the oculomotor nerve (cranial nerve III) from the accessory/Edinger-Westphal nucleus of the oculomotor nucleus in the midbrain. The contraction of the ciliary muscle is instructed by these parasympathetic fibres, which cause the muscle to relax and the lens to become more spherical, adapting to short-range focus.
The process of accommodation involves a complex mechanism that simultaneously pulls the anterior border of the choroid forward, causing a release of tension on the zonular fibres. This results in an increase in the refractive power of the lens, allowing for the creation of sharply focused images of near objects on the retina.
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The ciliary muscle is an intrinsic muscle of the eye
The oculomotor nerve provides motor and parasympathetic innervation to various ocular structures, including the ciliary muscle. The nerve arises from the oculomotor nucleus in the midbrain of the brainstem and exits the cranial cavity through the superior orbital fissure. It then divides into superior and inferior branches, which provide motor innervation to different extraocular muscles. The oculomotor nerve also carries preganglionic parasympathetic fibres to the ciliary ganglion, which then sends postganglionic fibres to the ciliary muscle.
The short ciliary nerves, also known as the postganglionic parasympathetic fibres, arise from the ciliary ganglion and are part of cranial nerve V1 (Nasociliary nerve of the trigeminal). These nerves provide parasympathetic innervation to the ciliary muscle, causing it to contract and change the shape of the lens for focusing on near objects. The contraction of the ciliary muscle releases the tension on the lens caused by the zonular fibres, making the lens more spherical and increasing its refractive power.
In addition to the oculomotor nerve and the short ciliary nerves, there is also evidence suggesting that the ciliary muscle receives innervation from sympathetic fibres of the autonomic nervous system (ANS). These sympathetic fibres may act to inhibit the accommodation reflex, preventing the ciliary muscle from contracting and allowing for long-range focus. Overall, the complex innervation of the ciliary muscle enables the eye to adjust and focus on objects at varying distances.
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Frequently asked questions
The ciliary muscle is an intrinsic muscle of the eye, formed as a ring of smooth muscle in the eye's middle layer, the uvea (vascular layer).
The ciliary muscle receives parasympathetic innervation from the short ciliary nerves (postganglionic fibres) that arise from the ciliary ganglion. The ciliary ganglion receives preganglionic fibres via the oculomotor nerve (cranial nerve III) that originate from the accessory/Edinger-Westphal nucleus of the oculomotor nucleus in the midbrain.
The ciliary muscle facilitates lens accommodation for near vision. It controls the shape of the lens within the eye, allowing for clear vision at varying distances.
The oculomotor nerve provides motor and parasympathetic innervation to ocular structures, including the ciliary muscle. The contraction of the ciliary muscle is instructed by the parasympathetic fibres originating from the accessory/Edinger-Westphal nucleus of the oculomotor nucleus in the midbrain.
