Ciliary muscle is supplied by –
**Core Concept**
The ciliary muscle plays a crucial role in accommodation and near vision by altering the shape of the lens in the eye. It is a smooth muscle that is innervated by the autonomic nervous system, specifically the parasympathetic division.
**Why the Correct Answer is Right**
The ciliary muscle is supplied by the ciliary nerves, which are branches of the oculomotor nerve (cranial nerve III). The oculomotor nerve carries parasympathetic fibers that stimulate the ciliary muscle to contract, causing the lens to become more rounded and increasing its refractive power. This allows for near vision. The parasympathetic stimulation also leads to the relaxation of the ciliary muscle, allowing the lens to become flatter and decreasing its refractive power, which enables far vision.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the ciliary muscle is not supplied by the trochlear nerve (cranial nerve IV), which is responsible for innervating the superior oblique muscle.
**Option B:** This option is incorrect because the abducens nerve (cranial nerve VI) primarily controls the lateral rectus muscle, which is involved in eye movement, not accommodation.
**Option C:** This option is incorrect because the optic nerve (cranial nerve II) is responsible for transmitting visual information from the eye to the brain, not controlling the ciliary muscle.
**Clinical Pearl / High-Yield Fact**
The ciliary muscle's ability to change the shape of the lens is essential for accommodation, allowing the eye to focus on objects at different distances. This is a critical aspect of the autonomic nervous system's control over the eye.
**Correct Answer: D. The ciliary muscle is supplied by the ciliary nerves, which are branches of the oculomotor nerve (cranial nerve III).**