Clinical meaning
Swallowing (deglutition) is a complex neuromuscular process involving more than 30 pairs of muscles and five cranial nerves (V trigeminal, VII facial, IX glossopharyngeal, X vagus, and XII hypoglossal) coordinated by the swallowing center in the medulla oblongata. Normal swallowing consists of four phases. The oral preparatory phase is voluntary: food is chewed (mastication), mixed with saliva containing amylase for initial starch digestion, and formed into a cohesive bolus by the tongue against the hard palate. The buccinator muscles in the cheeks prevent food from falling into the lateral sulci. The oral propulsive phase is also voluntary: the tongue tip elevates to the hard palate and moves the bolus posteriorly in a wave-like motion toward the oropharynx. When the bolus reaches the anterior faucial pillars, the swallowing reflex is triggered. The pharyngeal phase is involuntary and lasts approximately 1 second. It involves a precisely timed sequence: the soft palate elevates to close the nasopharynx (preventing nasal regurgitation), the hyoid bone and larynx elevate superiorly and anteriorly, the epiglottis inverts to cover the laryngeal inlet, the vocal folds adduct (close) to...