Swallowing begins with a voluntary (oral) phase that includes preparation during which food is masticated and mixed with saliva. This isfollowed by a transfer phase during which the bolus is pushed into the pharynx by the tongue. Bolus entry into the hypopharynx initiates the pharyngeal swallow response, which is centrally mediated and involves a complex series of actions, the net result of which is to propel food through the pharynx into the esophagus while preventing its entry into the airway. To accomplish this, the larynx is elevated and pulled forward, actions that also facilitate upper esophageal sphincter (UES) opening. Tongue pulsion then propels the bolus through the UES, followed by a peristaltic contraction that clears residue from the pharynx and through the esophagus. The lower esophageal sphincter (LES) relaxes as the food enters the esophagus and remains relaxed until the peristaltic contraction has delivered the bolus into the stomach. Peristaltic contractions elicited in response to a swallow are called primary peristalsisand involve sequenced inhibition followed by contraction of the musculature along the entire length of the esophagus. The inhibition that precedes the peristaltic contraction is called deglutitive inhibition. Local distention of the esophagus anywhere along its length, as may occur with gastroesophageal reflux, activates secondary peristalsisthat begins at the point of distention and proceeds distally. Tertiary esophageal contractions are
nonperistaltic, disordered esophageal contractions that may be observed
to occur spontaneously during fluoroscopic observation.
The musculature of the oral cavity, pharynx, UES, and cervical
esophagus is striated and directly innervated by lower motor neurons carried in cranial nerves ( Fig. 38-1 ). Oral cavity muscles are
innervated by the fifth (trigeminal) and seventh (facial) cranial nerves;
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