Which nerve carries predominantly sympathetic innervation?

Which nerve carries predominantly sympathetic innervation?

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

Answer: (B)

Sympathetic fibers to the head travel from the internal carotid plexus and ride along the deep petrosal nerve. This nerve directly carries postganglionic sympathetic fibers and then joins with the greater petrosal nerve to form the nerve of the pterygoid canal, distributing sympathetic input along its route. The other nerves carry parasympathetic or motor functions: the greater petrosal nerve brings preganglionic parasympathetic fibers from the facial nerve, the chorda tympani carries parasympathetic fibers to submandibular and sublingual glands and also provides taste, and the nerve to stapedius is a motor branch of the facial nerve to the stapedius muscle. Because its essential role is transporting sympathetic fibers, the deep petrosal nerve is the one that carries predominantly sympathetic innervation.

Sympathetic fibers to the head travel from the internal carotid plexus and ride along the deep petrosal nerve. This nerve directly carries postganglionic sympathetic fibers and then joins with the greater petrosal nerve to form the nerve of the pterygoid canal, distributing sympathetic input along its route. The other nerves carry parasympathetic or motor functions: the greater petrosal nerve brings preganglionic parasympathetic fibers from the facial nerve, the chorda tympani carries parasympathetic fibers to submandibular and sublingual glands and also provides taste, and the nerve to stapedius is a motor branch of the facial nerve to the stapedius muscle. Because its essential role is transporting sympathetic fibers, the deep petrosal nerve is the one that carries predominantly sympathetic innervation.