From the viewpoint of physiologic organization, swallowing is an act which passes from the sublimely complex to the humbly inchoate. A swallow usually begins as a voluntary phenomenon which sets into motion an integrated sequence of performances and inhibitions delicately controlled by a medullary swallowing center. As the swallow moves through the oropharynx, groups of muscles relax and contract, vital respiratory orifices are occluded, and breathing is temporarily arrested, all within the three-tenths of a second or so it takes the bolus to go from the tip of the tongue to the bottom of the pharynx. The entire sequence of oropharyngeal swallowing is so dependable and so well organized centrally that removal of some of the parts, such as cutting some muscle groups, will not interrupt the integrated synergy performed by the remaining intact musculature.
Once the swallow passes the cricopharyngeus muscles separating the pharynx from the esophagus, however, the
INGELFINGER FJ. The Physiologic Background of Heartburn, Esophagitis and Cardiospasm. AMA Arch Intern Med. 1960;105(5):770-778. doi:10.1001/archinte.1960.00270170108014