The parasympathetic nervous system, particularly cranial nerves in the brainstem and neck, directly influences facial features such as eye movements and pupil dilation.

“and the parasympathetic nervous system is really interesting because especially the cranial nerves the ones that are up in the brain stem and in the neck area those have a direct direct line to various features of your face in particular the eyes they control things like eye movements pupil dilation things of that sort as well as the tongue the facial muscles Etc”