Do you ever think about what has to happen physically in order for you to engage in the act that we know as swallowing? (Or, as I so often heard it growing up, swallerin’). It seems so simple and so elegant and so beyond the reach of an interesting article. Of that you will be the judge. But there is no question that the physiological processes that must be engaged perfectly in order to complete the act of swallowing is interesting. Or, at least, not as boring as an ABC sitcom. I say perfectly because we all know, of course, what happens when things don’t go perfectly. Disgusting choking sounds, watery fluid evacuating the eye sockets, food flying through our lips and landing on the shoulder of a stranger or a close friend or a loved one or-worst of all-the boss. And that’s not even to mention what happens when it’s not food that is attempting to be swallowed. (But this isn’t the place for that subject.)
Would you believe that it takes no less than six cranial nerves to complete the act of swallowing? What are these cranial nerves? Well, if you’ll slow down Buckwheat, I’ll tell you: The trigeminal nerve (CN V), the facial nerve (CN VII), the glossopharyngeal nerve (CN IX), the vagus nerve (CN X), the spinal accessory nerve (CN XI), and the hypoglossal nerve (CN XII). If you’re dating a medical student and you do happen to mix up the act of swallowing during a romantic dinner, you can always save yourself by calming saying, “Wow, I guess my glossopharyngeal nerve really left me hanging there, huh?” Makes you look both smart and self-deprecating at the same time. And, from what I am told, using words like glossopharyngeal is a major league aphrodisiac to medical students, though, to be perfectly honest, this insight comes courtesy of the good folks on Scrubs.
Swallowing is a reflexive act that incorporates several phases, many of which are themselves further broken down into subdivided stages. The oral phase is the one that kicks everything off and gets you from putting food into your mouth to successfully avoiding a coughing fit complete with runny eyes and that horrible deer-in-the-headlights look where people are standing around wishing they’d paid more attention to that Heimlich poster in the breakroom just a tad more seriously. The oral phase is divided into two sub-stages, the oral-preparatory and the oral transport. The first stage involves lifting a dinner utensil-you can use your fingers if the food had wings, by the way, doesn’t matter how fancy the restaurant or occasion, it’s always correct etiquette to eat food that once had wings with your fingers-to your lips so that the food is transmitted from inanimate holding object to your mouth, further resulting in the food being masticated long enough so that it becomes suitable for safely swallowing. The pharyngeal stage involves movement of the larynx and epiglottis. The constriction of pharyngeal muscles causes the food to move downward where it enters the esophagus after the cricopharyngus muscle releases. In a motion known as peristalsis, the food then continues down the esophagus.
But before all that occurs, a number of factors involving sensory and motor control must take place in perfect synchronization, involving a number of cranial nerves. Swallowing is a process that requires a complex process in which sensory messages traveling at the speed of light throughout the body results in motor control that accomplishes an action that takes place almost at the speed of sound. The trigeminal nerve is involved in the procedure because it is involved in the chewing process by way of overseeing the control of jaw movement. The taste of the substance being chewed is transmitted via the facial nerve. The glossopharyngeal nerve is also involved in the process of transmitting taste and it is also the nerve that initiates the message response that results in the desire to swallow. And finally the last player in this sextet of cranial nerve that all together to make sure your ends up in your stomach and not on the shoulder of your boss-well, technically it ends up elsewhere, but THAT’S a whole different process-is the hypoglossal nerve which provides the feedback that is necessary to result in pulling the trigger of the swallow reflex. And just like as happens at all those award shows, this little thank you to the cranial nerves would not be complete without mentioning the producers at the top of the pyramid when it comes to swallowing. Let’s hear it for both the cerebral cortex and the cerebellum.