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Normal Swallowing Function

Swallowing is a complex series of sequential neuromuscular events that are integrated into a smooth and continuous process. To appreciate the potentially devastating effects of oral cancer on swallowing, it is helpful to understand normal anatomy and physiology. Generally, the process is divided into three stages: oral, pharyngeal, and esophageal.

The oral phase is completely voluntary and involves the entry of food into the oral cavity and preparation for swallowing; this includes mixing with saliva, mastication, and formation into a cohesive bolus in preparation for the swallow. It requires coordination of the lips, tongue, teeth, mandible, and soft palate. The pharyngeal phase is initiated as the tongue propels the bolus posteriorly and the base of tongue contacts the posterior pharyngeal wall, eliciting a reflexive action that begins a complex series of events. The soft palate elevates to prevent nasal reflux. The pharyngeal constrictor musculature contracts to push the bolus through the pharynx. The epiglottis inverts to cover the larynx and prevent aspiration of contents into the airway. The vocal folds adduct to further prevent aspiration. The hyolaryngeal complex moves anteriorly and superiorly, which, in combination with the pressure generated by a bolus, provides anterior traction and intrabolus pressure to open the cricopharyngeus. The esophageal phase is completely involuntary and consists of peristaltic waves that propel the bolus to the stomach. Total swallow time from oral cavity to stomach is no more than 20 seconds.

Cranial nerve function is often interrupted in surgical resection of head and neck tumors. Swallowing deficits may result when any one or more of five cranial nerves are affected. The trigeminal nerve (CN V) controls general sensation to the face and motor supply to the muscles of mastication. The facial nerve (CN VII) controls taste to the anterior two thirds of the tongue and motor function to the lips. The glossopharyngeal nerve (CN IX) provides general sensation to the posterior third of the tongue and motor function to the pharyngeal constrictors. The vagus nerve (CN X) provides general sensation to the larynx and motor function to the soft palate, pharynx, larynx, and esophagus. The hypoglossal nerve (CN XII) controls motor supply to the intrinsic and extrinsic muscles of the tongue.