Final answer:
The automatic phases of deglutition are coordinated by the swallowing center in the medulla oblongata, which involves complex neuromuscular actions to ensure the safe passage of food from the mouth to the stomach.
Step-by-step explanation:
The automatic phases of deglutition, which include the pharyngeal and esophageal phases, are coordinated by the swallowing center, located in the medulla oblongata. This collection of neurons receives sensory input from the oropharynx during the pharyngeal phase when receptors are stimulated as the bolus of food moves from the mouth towards the esophagus. This stimulation prompts the swallowing center to send impulses to various muscles, ensuring that the nasopharynx is sealed off by the upward motion of the uvula and soft palate, while the larynx moves upward and the epiglottis covers the tracheal opening to prevent aspiration.
During the esophageal phase, controlled by the medulla oblongata as well, peristalsis begins, allowing the bolus to be moved through the esophagus towards the stomach. This phase includes a series of contractions in the muscularis layer of the esophageal wall and is characterized by the short reflex relaxation of the lower esophageal sphincter as the bolus approaches the stomach, which facilitates entry into the stomach.