@biotechpulse: Swallowing, or deglutition, is a complex process involving coordinated activity of muscles and nerves to move food or liquid from the mouth to the stomach while preventing aspiration into the lungs. It occurs in three main phases: 1. Oral Phase (Voluntary) • The tongue pushes the bolus (chewed food or liquid) against the hard palate and moves it toward the oropharynx. • The muscles involved include the intrinsic and extrinsic tongue muscles (controlled by the hypoglossal nerve, CN XII) and the buccinator muscle (controlled by the facial nerve, CN VII). • This phase is voluntary, meaning it is consciously initiated. 2. Pharyngeal Phase (Involuntary) • The soft palate (controlled by the vagus nerve, CN X) elevates to seal off the nasopharynx, preventing food from entering the nasal cavity. • The hyoid bone and larynx elevate (via the suprahyoid muscles, controlled by CN V, CN VII, and CN XII), bringing the epiglottis down to cover the laryngeal inlet. • The vocal cords adduct (close) to further protect the airway, controlled by the recurrent laryngeal nerve (a branch of CN X, vagus nerve). • The pharyngeal constrictor muscles (superior, middle, and inferior), controlled by the pharyngeal plexus (CN IX and X), contract to push the bolus into the esophagus. 3. Esophageal Phase (Involuntary) • The upper esophageal sphincter (UES), controlled by the vagus nerve (CN X), relaxes to allow the bolus to enter the esophagus. • Peristalsis (wave-like contractions) moves the bolus down the esophagus, regulated by the myenteric plexus and the autonomic nervous system (ANS). • The lower esophageal sphincter (LES) relaxes to let the bolus enter the stomach, preventing reflux. How Food is Prevented from Entering the Lungs 1. Epiglottis Closure: The epiglottis tilts downward, covering the airway. 2. Vocal Cord Closure: The vocal folds adduct to block the trachea. 3. Laryngeal Elevation: The larynx moves upward, positioning the epiglottis to deflect food away. 4. Reflexive Apnea: Breathing temporarily stops during swallowing to prevent aspiration. This intricate process is primarily coordinated by the medulla oblongata in the brainstem, which integrates sensory and motor signals to ensure safe swallowing.