Deep petrosal nerve

Deep petrosal nerve comes off from the neuronal plexus around the internal carotid artery. It enters the cranial cavity via the carotid canal. Thereupon, it traverses through the foramen lacerum where it joins with the greater petrosal nerve to formulate the nerve of pterygoid canal (a.k.a. the Vidian nerve).

The Vidian nerve carries parasympathetic and (post-ganglionic) sympathetic fibers that are transmitted to the pterygopalatine ganglion. Out of these, the post-ganglionic sympathetic fibers are supplied by the deep petrosal nerve. These neurons pass through the pterygopalatine ganglion without synapsing and get distributed to the vasculature and glands in the nasal cavities, palate and paranasal sinuses via branches of pterygopalatine ganglion and maxillary nerve.

Some postganglionic sympathetic fibers hop off from the pterygopalatine ganglion to ride on the maxillary nerve and jump off one more time to reach out to the ophthalmic nerve. These sympathetic fibers eventually course through the lacrimal branch of ophthalmic nerve to cause vasoconstriction of arteries supplying the lacrimal gland. Vasoconstriction reduces the lacrimal secretion.