Physiology3,4,5
Swallowing, or deglutition, is a sequence of well-coordinated events to carry ingested material from the mouth to the stomach. Three phases have been described. The first or oropharyngeal phase begins with the prehension of food and the formation of a bolus in the oropharynx, which is then passed to the base of the tongue.
This bolus stimulates a series of pharyngeal contractions that move the bolus into the laryngopharynx. At this time, the other pharyngeal openings are closed (the oral cavity, the nasopharynx, and the opening to the trachea) by the actions of various muscle groups and movement of the tongue. These reflex events are initiated by stimulation of various sensory receptors in the laryngopharynx, the nerve fibers of which are located in branches of the trigeminal, glossopharyngeal, and laryngeal nerves. Once the bolus of ingested material is in the oropharynx, the cricopharyngeal and thyropharyngeal muscles relax to allow passage of the bolus into the cranial esophagus. This sphincter closes promptly after passage of the bolus and remains closed at all other times. Once the bolus has passed into the esophagus, the second, or esophageal, phase of swallowing begins. The peristaltic wave that started in the pharynx continues and is propagated throughout the esophagus carrying the bolus aborally to the stomach. This peristaltic wave is termed primary peristalsis. A secondary peristaltic wave can be generated via local esophageal distension to carry out the passage of the bolus into the stomach if the primary wave is inadequate. The third and final phase of swallowing is the relaxation of the gastroesophageal sphincter (GES), which allows passage of the bolus into the stomach. The GES then contracts again to prevent reflux of material back into the esophagus.Swallowing is mediated by a long and complex neural arc. The reflex response is triggered by sensory receptors in the esophagus via visceral afferent fibers in the trigeminal, vagus, and glossopharyngeal nerves. These impulses are integrated in the nucleus solitarius and the nucleus ambiguus, as well as the swallowing center in the lateral reticular formation. The efferent neurons from the dorsal vagal motor nucleus pass to the pharyngeal and esophageal musculature via the trigeminal, facial, glossopharyngeal, vagus, and the hypoglossal nerves.
3.3