Swallowing/deglutition
A series of movements that promote bolus transportation from the mouth to the stomach
Eating /ingestion
The process of taking a bolus into the body by mouth
Eating disorder
A psychological disorder characterized by abnormal or disturbed eating behaviors (e.g., anorexia nervosa, bulimia nervosa)
Dys-
Impaired or abnormal
Phag-
Eating
Eating problem/dysphagia
Eating failure or dysfunction, defined as a disturbance of the passage of a swallowed bolus from the mouth to the stomach
Aspiration
Entry of saliva , liquid, or food into the airway under the level of the true vocal folds
Penetration
Entry of swallowed material into the laryngeal vestibule during swallowing, as above of the level of the true vocal folds
Retention
Presence of a residual swallowed bolus locating in the oral cavity, vallecula , and/or hypopharynx (pyriform sinus ) that is left behind after the swallow
1.2 Overview of Structures
Fundamental knowledge of the anatomy and motor control of eating and swallowing is imperative and serves as an important basis for evaluating the physiology of the swallow. Swallowing is a complicated sequence of movements. A normal swallow requires the precise coordination of more than 30 muscles located within and around the oral cavity, pharynx , larynx , and esophagus. These muscles are controlled by cranial and peripheral nerves that are centrally mediated via the brain stem (mainly the medulla oblongata as the swallowing center) and cooperate with the cortical and subcortical regions of the brain [1, 2].
1.2.1 Anatomical Structures [1–3]
The oral cavity serves as the entrance to both the digestive pathway and upper airway. The tongue rests on the floor on the mouth , exposing both the oral and pharyngeal surfaces. The arched opening of the posterior oral cavity is bordered by the fauces, which separate the oral cavity from the pharynx . The pharyngeal wall consists of three main pharyngeal constrictor muscle groups (the superior, middle, and inferior parts) and long pharyngeal muscles (stylopharyngeus , salpingopharyngeus , and palatopharyngeus ). The upper esophageal sphincter (UES) is defined as a high-pressure zone located at the pharyngoesophageal junction and has a semicircular shape in the horizontal view. It consists of three muscular portions: the inferior fibers of the inferior pharyngeal constrictor , the cricopharyngeal muscle , and the upper fibers of the esophagus. The UES contracts at rest and relaxes during swallowing to allow a swallowed bolus to enter the esophagus and to prevent regurgitation of bolus from esophagus and stomach (Figs. 1.1 and 1.2).
The hyoid bone plays an important role in swallowing function. The suprahyoid muscles , which include the mylohyoid, geniohyoid, anterior and posterior bellies of the digastric, and stylohyoid , and one of the infrahyoid muscles , thyrohyoid , play one of the key roles in opening of the UES because they control hyoid and laryngeal excursion in the superoanterior direction, allowing a bolus to pass into the esophagus. The larynx acts as an airway valve, separating the trachea from the upper aerodigestive tract. The airway is protected by laryngeal closure , a process that occurs at three levels: approximation of the true vocal folds (TVFs , glottis), approximation of the false vocal folds , and approximation of the aryepiglottic folds to the base of the epiglottis . The tongue base , pharynx , epiglottis , larynx , and UES comprise the oropharynx and hypopharynx . Three pockets or recesses exist in the oropharyngeal area (vallecula ) and in the hypopharyngeal area (two pyriform sinuses ), providing a physiologic storage area for food and fluid and decreasing the risk of aspiration. Figure 1.1 provides an overall image of the anatomical structures in the oral cavity, pharynx , and larynx . The swallowing muscles that contribute to the pharyngeal stage are illustrated in Appendix (Figs. 1.4 and 1.5).
