2 Anatomy of Swallowing
William G. Pearson Jr. and Memorie M. Gosa
Summary
Thirty-plus muscles under the control of five cranial nerves and several spinal nerves convert a respiratory channel into a digestive tract and back within 500 milliseconds. To understand what goes wrong with swallowing, a master clinician must have a working knowledge of normal structure relevant to swallowing function. This chapter describes in some detail the oral cavity and pharynx in relationship to the skeleton. The text then discusses functional groups of neuromuscular structures that underlie the various physiological elements of swallowing, including ingestion, bolus formation, oral transport of the bolus, and pharyngeal conversion. Developmental differences in children and adults are discussed followed by the anatomy relevant to airway protection, salivation, neurobiology of swallowing, the esophagus, and development of the upper aerodigestive tract. Compromise of these structures, their function, or their development can lead to swallowing impairment. A strong knowledge of the functional anatomy of swallowing leads to effective understanding of swallowing function, impairment, and rehabilitation throughout the life span
Keywords
oral cavity, pharynx, ingestion, bolus formation, oral transport of the bolus, pharyngeal conversion
Learning Objectives
List the surface features of the oral cavity and pharynx.
Identify the muscles of the face, oral cavity, and pharynx that
Explain the concept of a muscular hydrostat as it applies to the tongue.
Identify the muscles underlying pharyngeal conversion.
Describe the differences between the anatomical features for swallowing in the adult and infant.
Describe the embryological development of the oral and pharyngeal cavities.
2.1 Introduction
The study of anatomy and physiology can be fascinating. Unfortunately, just reading the descriptions of anatomy and physiology can be tedious. If the reader becomes bogged down in the details of this anatomy chapter, reading Chapter 3 first, on physiology, may help. Once the function of the swallowing apparatus is understood, curiosity can motivate the study of the structures underlying function. As noted, the neuromuscular elements of anatomy in this chapter are organized by function. Because these structures serve multiple functions, some redundancy should be expected.
Students should have a basic understanding of human anatomy and physiology from their undergraduate coursework, ideally from a complete human anatomy and physiology class with lab. If students did not complete a comprehensive human anatomy and physiology course, then they are encouraged to obtain a human anatomy and physiology textbook and medical dictionary to read along with these chapters as needed. So often in the study of speech-language pathology, students are taught to consider just the overlaid functions pertinent to the field; however, to truly grasp the complexities of dysphagia, students need to consider the human body and its biological functions as a whole. It is suggested that, in addition to reading the chapters here, students also participate in a simultaneous lab experience, if possible. If a live lab experience is not available, students may consider one of many virtual anatomy software programs to augment reading. Additionally, students should read these chapters in an active, purposeful way. Use every means available to try to visualize the anatomy during the swallowing sequence. The point of studying anatomy is not memorizing lists of structures, but gaining a working knowledge of the morphology that underlies function so that you might effectively rehabilitate swallowing impairment and educate your patients and other clinicians concerning sources of swallowing dysfunction. Speech-language pathologists working in a medical setting are expected to be the experts on the anatomy and physiology of swallowing.
2.2 Surface Anatomy of the Oral Cavity
The oral cavity includes lips, cheeks, hard and soft palate, tongue, and teeth. The lips and teeth are at the anterior boundary of the oral cavity, with the teeth and cheeks forming the lateral boundary. The hard and soft palate form the superior boundary of the oral cavity, with the uvula hanging midline at the posterior edge of the soft palate. Faucial pillars, formed by the palatoglossal and palatopharyngeal folds, are found at the lateral posterior boundary of the oral cavity. On the surface of the tongue various types of papillae (filiform, foliate, and vallate) can be found that house many taste receptors. Epithelium is moistened by saliva, produced by salivary glands that line the oral cavity. In the mucosa of the floor of the mouth are found openings for the submandibular and sublingual glands, whereas the openings of the parotid glands are found between the cheeks and upper molars (Fig. 2.1). The entire oral cavity is innervated with somatosensory neurons that provide information about the temperature, volume, consistency, and position of a bolus that is critical to effective swallowing. contribute to safe and effective swallowing.
Clinical Note
The lips, tongue, and soft palate are focal structures visualized in a videofluoroscopic study to assess the oral phase of swallowing.
2.3 Surface Anatomy of the Pharynx
The pharynx is the crossroads for the passage of food and oxygen into the human body. Historically it has been called a quadrivium, which in Latin is transliterated as "the place where four roads meet." The pharynx incorporates four portals to other conduits, including the oral cavity, nasal cavity, trachea, and esophagus.1 The pharynx is connected to and integrates with multiple skeletal elements, including bones and cartilage. The inner surface of the muscular pharynx is covered with a tough sheet of deep fascia called the pharyngobasilar fascia, a membrane that is lined with a continuous layer of mucosa. This mucosal lining drapes over the entire inner surface of the pharynx, including muscles, bone, and cartilage. This mucosal draping creates named spaces and folds. The pharynx can be divided into three sections: nasopharynx, oropharynx, and laryngopharynx. The laryngopharynx is more often clinically referred to as the hypopharynx. A bolus passes from the oral cavity through the oropharynx and hypopharynx to the esophagus (Fig. 2.2).
The spaces most relevant to swallowing in the pharynx are the valleculae and the piriform recesses, orsinuses. The valleculae, or "little valleys," lie between the median and lateral glossoepiglottic folds and become a potential reservoir for pharyngeal residue. The other common sites for residue are the piriform recesses, spaces lateral to the larynx created by the muscosa draping from the laryngeal inlet to the muscular pharyngeal wall on either side. When the pharynx is relaxed, residue can pool in either piriform recess on the side of the upper esophageal sphincter (Fig. 2.3).
Additional folds are formed by structures that lie within each fold. The median glossoepiglottic fold is formed by mucosa draping over the glossoepiglottic ligament. The aryepiglottic folds border the laryngeal vestibule and contain small variable muscle fascicles. The palatoglossal fold and palatopharyngeal folds, formed by muscles with the same name, descend from the palate on either side of the palatine tonsil and are referred to as the anterior and posterior faucial pillar, respectively. The salpingopharyngeal fold forms around the salpingopharyngeal muscle, beginning at the opening of the auditory tube in the nasopharynx and extending inferiorly into the hypopharynx on the lateral pharyngeal walls (Fig. 2.4).
Fig. 2.1 (a) Infant and (b) adult oral cavity with structures labeled. (b) From Gilroy AM, MacPherson BR. Atlas of Anatomy. 3rd ed. New York, NY: Thieme, 2016. Based on: Schuenke M, Schulte E, Schumacher U. THIEME Atlas of Anatomy. Volumes 1-3. Illustrations by Voll M and Wesker K. 2nd ed. New York: Thieme Medical Publishers; 2016.
Fig. 2.2 Regions of the pharynx, sagittal view.
Fig. 2.3 Valleculae and piriform recesses. From Gilroy AM, MacPherson BR. Atlas of Anatomy. 3rd ed. New York, NY: Thieme, 2016. Based on: Schuenke M, Schulte E, Schumacher U. THIEME Atlas of Anatomy. Volumes 1-3. Illustrations by Voll M and Wesker K. 2nd ed. New York: Thieme Medical Publishers; 2016.
The pharynx is subdivided anatomically, and its regions are named after their adjacent apertures. The nasopharynx, opening into the choanae of the nasal cavity, is closed inferiorly by the soft palate or velum and is bordered posteriorly and laterally by the pharyngeal walls. The boundaries of the oropharynx are marked by the oropharyngeal isthmus anteriorly, the velum (soft palate) superiorly, the epiglottis inferiorly, and the pharyngeal walls posteriorly and laterally. The epiglottis, laryngeal vestibule, esophagus, and pharyngeal walls, including the piriform recesses, border the hypopharynx.
Recognizable features of the...
