Final answer:
The pharyngeal stripping wave, controlled by the medulla oblongata, involves the sequential contraction of pharyngeal constrictor muscles, followed by the relaxation of the upper esophageal sphincter to allow the bolus to enter the esophagus, where peristalsis will carry it to the stomach.
Step-by-step explanation:
The pharyngeal stripping wave is a vital component of the swallowing process, also known as deglutition. Contractions of the pharyngeal constrictor muscles move the bolus through the oropharynx and laryngopharynx. These muscles operate in sequence to propel the bolus into the esophagus. The upper esophageal sphincter relaxes, allowing the food to enter the esophagus, initiating the esophageal phase. The medulla oblongata controls these complex neuromuscular actions through the deglutition center. In addition to these, the extrinsic muscles of the tongue, which include the palatoglossus, hyoglossus, styloglossus, and genioglossus, aid in positioning the food to form a bolus and make swallowing possible.During the pharyngeal phase, impulses from the oropharyngeal receptors reach the deglutition center, which then triggers the soft palate and uvula to rise, sealing off the nasopharynx and preventing nasal regurgitation. Simultaneously, the laryngeal muscles constrict to prevent food from entering the respiratory tract. The upper esophageal sphincter's relaxation, coordinated by these signals, enables the bolus to proceed into the esophagus.The esophageal phase is characterized by peristalsis, a powerful mechanism involving alternating waves of contraction and relaxation of the esophageal muscles. These muscular actions are also under the control of the medulla oblongata and facilitate the propulsion of food toward the stomach. After passing through the esophagus, the arrival of the bolus at the stomach causes a reflex relaxation of the lower esophageal sphincter, allowing entry into the stomach.