The most surprising yet basic thing I learned during head and neck anatomy was that our skulls are riddled with holes (I know, most obvious thing in the world…but I’m not using the word riddled lightly here). For whatever reason, I had assumed our skulls were a sphere-ish bone that protected our brain with a brainstem entering and exiting. While that’s certainly not wrong, there are all kinds of arteries, veins, and most important for this post, nerves running through a variety of foramina (medical word for holes) and heading to structures all over our head, face, and neck.
For now, we’ll just worry about one. Our seventh cranial nerve (Facial nerve) is responsible for an absurd variety of functions. In part, it innervates the voluntary muscles of facial expression, receives gustatory (taste) sensory information from the front 2/3 of the tongue, innervates the autonomic muscles which dampen our own voices when we’re speaking, and is involved in various sympathetics and parasympathetics. Sympathetics and parasympathetics refer to the two major functions of our autonomic nervous system. The simplest explanation is that sympathetic responses utilize energy while parasympathetics store energy. The easier to remember explanation is that sympathetics are the four Fs (fight, flight, fear, and sex) while parasympathetics are rest and digest.
I swear there was a point to be made here, and if you’re still reading, we’re getting to it now. The facial nerve runs through a foramina in the skull, a pathway called the facial canal which also happens to be one of the few foramina named in a logical manner. It’s possible to damage the nerve within this space. Since it has that huge variety of functions, facial nerve damage can present in a myriad of ways, the one you’re likely familiar with is Bell’s palsy (half of someone’s face is flaccidly paralyzed for a few weeks and then returns to normal). But in rare cases, some of the nerve fibers get crossed as they regrow. One of the parasympathetic courses of the facial nerve runs to the lacrimal gland and drives the production of tears. Another runs to a variety of salivary glands and drives the production of saliva.
If these two pathways are crossed as the nerve regrows, every time the patient eats or smells delicious food or does anything that would elicit copious salivation…they’ll start crying. The “make saliva I’m about to eat something” signal goes straight to the “make a whole pile of tears so they go pouring down my face” gland. The condition is called “crocodile tears”.