Food for Not

So I was eating cake for lunch today, as per usual, and I noticed something in my neck moved upwards every time I swallowed! To make sure it wasn't just me, I watched other people's throat as they ate (a little creepy but I had to get to the bottom of this anomaly!). And I noticed the same thing, something in their throat moved up when they gulped down their food or took a drink. It was most apparent in males; I saw their entire adam's apple move up, and then back down again!  Since the adam's apple is a quintessential landmark for the larynx, I had a sneaking suspicion that the larynx was involved in this process. And being the larynx fanatic that I am, I had no choice but to delve deeper into how this all worked. Here is what I found:

The pharynx is a common passage way for both food and air, but at a certain point (i.e. at the larynx) their fates diverge. Air passes through the larynx into the trachea, and food slides posteriorly over the larynx (via the epiglottis) and into the esophagus. There are three main "guards" to prevent the aspiration of food into the airway, and they are: the epiglottis, the vestibular folds, and the true vocal folds. 

The epiglottis itself, as mentioned in the jewelry post regarding the laryngeal cartilages, is a piece of leaf shaped elastic cartilage that is amply situated to cover the glottis during swallowing. When we swallow, there are a set of extrinsic muscles attached to the hyoid bone that first move the hyoid up, and then out anteriorly (1). These are known as the "elevator" muscles, some of which include the thyrohyoid, digastric, stylohyoid, and mylohyoid muscles. Since the larynx is inadvertently attached to the hyoid bone via the thyrohyoid membrane, the whole larynx follows the motion of the hyoid bone. During laryngeal elevation, the epiglottis folds posteriorly and down over the glottis, protecting the vocal folds. Once the food has slid past the larynx on the epiglottal "food slide" into the esophagus, a set of "depressor" muscles move the hyoid bone posteriorly and inferiorly back to it's resting position. Some of the muscles involved are the sternothyroid, omohyoid, and sternohyoid muscles. 

Okay so the epiglottis is the first "guard" preventing food aspiration, the second guard involves the vestibular folds (aka the false vocal folds). If you missed our post about the difference between the false and true vocal folds, catch up on this cheeky imposter here. The vestibular folds are adducted (brought closer together) so that food is prevented from getting past to the more delicate vocal folds. And interestingly enough the vocal folds themselves are the third, and last "guard" that prevents food from getting into the trachea. The adductor muscles bring the vocal folds together to seal off the glottis yet again. But all in all, the first and main structure that ensure food bypasses the airway is the epiglottis. The adduction of the vestibular and true vocal folds are only in place as backups. 

As you can see, there are many structures that prevent the aspiration of food into trachea because it's very important to maintain an open airway or we wouldn't be able to breath! And this is the first and main function of the larynx, so remember this! Phonation, though extremely interesting and talked about here, is only a secondary function of the larynx. But even with all these mechanisms in place, food can still enter the trachea sometimes! That's where the cough reflex comes in, which interestingly enough, is turned off when we are unconscious(2)....but that's a post for another time. 

Whew, looking into all of that was tough work. Time for another piece of cake to exercise those extrinsic laryngeal muscles because you know what they say, if you don't use it, you lose it!

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References:

1. McCulloch TM, Jaffe D. Head and neck disorders affecting swallowing. GI Motility online. 2006 May;do:10.1038/gimo36
2. Marieb E, Hoehn K. Human anatomy & physiology. Boston: Pearson;2013.