The pharyngeal phase of swallowing is a stereotyped motor activity controlled by the swallowing central pattern generator (CPG) within the medulla. The swallowing CPG consists of dorsal and ventral swallowing groups (DSG and VSG, respectively), where the DSG triggers the swallowing reflex by receiving monosynaptic or paucisynaptic input from the superior laryngeal nerve, and the VSG distributes motor commands to the swallowing-related muscles. Neurons in the medullary intermediate reticular nucleus are involved in laryngeal adduction during post-inspiration and swallowing and thus are members of both respiratory and swallowing CPGs. Laryngeal adduction during swallowing is important not only for ensuring airway protection but also for creating a positive subglottic pressure that facilitates efficient swallowing. The Kölliker–Fuse nucleus (KF) in the pons regulates the postinspiratory activity during breathing and swallowing. Expiratory decrementing neurons of the Bötzinger complex may play a role in the arrest of respiratory activity during swallowing. Swallowing preferentially occurs during the postinspiratory or expiratory phases. The swallowing reflex is suppressed during inspiration centrally by the KF and peripherally by the pulmonary stretch receptor, and swallowing strongly resets the respiratory rhythm. The interval between the onset of swallow and the subsequent inspiration is shortest for swallows initiated near the expiratory-to-inspiratory phase transition and may represent a period of vulnerability to aspiration.
