The tympanic plexus has parasympathetic (preganglionic) roots which contribute to the lesser petrosal nerve. Parasympathetic contribution is from the tympanic nerve which branches from the glossopharyngeal nerve (CN IX) in the jugular foramen.
The lesser petrosal nerve exits the temporal bone and enters the middle cranial fossa through the hiatus of lesser petrosal nerve. It then exits the middle cranial fossa through foramen ovale to the otic ganglion where its parasympathetic fibers synapse. From the otic ganglion, its fibers hitchhike with the auriculotemporal nerve (from V3) to eventually innervate the parotid gland.
The geniculate ganglion also communicates with the lesser petrosal nerve.