Abstract
This paper describes dynamics of the pharyngeal, or the second stage of volitional swallowing in normal and pathological conditions. The description is based upon our current investigations as well as upon available literature. In our investigations, simultaneous recordings of EMG of selected swallowing muscles and X-ray video images were adopted.
In normal swallowing, a series of events take place consistently with respect to timing during the pharyngeal stage. There is no clear-cut distinction between the oral and the pharyngeal stages in the activities of the pertinent muscles as well as in the movements of the food channel. It seems, however, to be practical to assume that the pharyngeal stage begins roughly with the first appearance of bolus in the pharynx and ends with complete disappearance of bolus from the pharynx in normal swallowing. From the neurological point of view, it turned out that this period corresponds to the period of relaxation of the cricopharyngeal muscle, lasting approximately 0.5sec.
Swallowing begins with an elevation of the larynx. Then, the velum and the tongue base begin to rise, the epiglottis to bend backwards, and the supraglottic region to close. Bolus first enters the pharynx when the velopharyngeal closure is about completed. Almost simultaneously with this, the cricopharyngeal muscle relaxes whereas the vocal fold adductors and the thyrohyoid muscle contract. Shortly after, peristaltic movements of the pharynx occur. When bolus is completely transported into the esophagus, the velum and the tongue base begin to fall, the larynx starts opening, and the cricopharyngeal muscle contracts to close the pharyngo-esophageal junction. The entire procedure ends up with a complete fall of the larynx.
Even in some pathological conditions, such as amyotrophic lateral sclerosis, oculopharyngeal muscular dystrophy and “cricopharyngeal achalasia, ” the muscles act in the similar fashion as in normal with respect to timing. This causes an incoordination of muscular activities and the passage of bolus. No feedback mechanism or volitional adaptation seems to be able to modify the timing of muscular exertion during the pharyngeal stage.
