Acetylcholine is secreted in eyes by
**Core Concept**
The underlying principle being tested is the understanding of the autonomic nervous system's role in the eye, specifically the **parasympathetic nervous system** and its neurotransmitter, **acetylcholine**. This system controls various involuntary actions of the body, including those in the eye.
**Why the Correct Answer is Right**
Acetylcholine is secreted in the eyes by the **parasympathetic nerve endings**, specifically those originating from the **oculomotor nerve (CN III)**, which stimulates the **muscarinic receptors** in the eye. This leads to **miosis** (pupillary constriction) and accommodation for near vision.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect as it does not relate to the parasympathetic nervous system's function in the eye.
**Option B:** Incorrect as it is not associated with acetylcholine secretion in the context provided.
**Option C:** Incorrect because, although it might be related to eye function, it is not the correct source of acetylcholine secretion.
**Option D:** Incorrect as it does not accurately describe the source of acetylcholine in the eye.
**Clinical Pearl / High-Yield Fact**
Remember, **acetylcholine** plays a crucial role in the eye's **parasympathetic** functions, including pupillary constriction and accommodation.
**Correct Answer:** D. Ciliary ganglion (sphincter pupillae and ciliary muscle).