Which nerve carries predominantly parasympathetic innervation?

• A. Greater petrosal nerve
• B. Deep petrosal nerve
• C. Chorda tympani
• D. Nerve to stapedius

Answer: (A)

The nerve that carries predominantly parasympathetic innervation is the greater petrosal nerve. It is a branch of the facial nerve that brings preganglionic parasympathetic fibers from the superior salivatory nucleus to the pterygopalatine ganglion, where they synapse. From there, the postganglionic parasympathetic fibers distribute to targets like the lacrimal gland and nasal mucosa via hitchhiking paths such as the zygomatic nerve to the lacrimal nerve. This pathway is primarily parasympathetic in composition, with no motor components.

In contrast, the deep petrosal nerve contains postganglionic sympathetic fibers that join the greater petrosal nerve to form the nerve of the pterygoid canal, making that route mixed rather than predominantly parasympathetic. The chorda tympani carries preganglionic parasympathetic fibers to the submandibular ganglion but also transmits taste fibers from the anterior two-thirds of the tongue, so it’s a mixed nerve rather than predominantly parasympathetic. The nerve to stapedius is a motor branch of the facial nerve, not parasympathetic.