Final answer:
The majority of swallowing (90%) occurs during the pharyngeal and esophageal phases, which are involuntary and regulated by the autonomic nervous system to prevent aspiration.
Step-by-step explanation:
90% of swallowing occurs during the pharyngeal phase and esophageal phase of deglutition. These phases are involuntary and are controlled by the autonomic nervous system. Specifically, during the pharyngeal phase, there is a risk of food entering the respiratory pathways, but this is mitigated by the movement of the uvula and soft palate upward to close off the nasopharynx, and the constriction of laryngeal muscles to prevent aspiration of food into the trachea. This critical coordination is managed by the nervous system and ensures that the airway is protected during swallowing.