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The Mouth and Tongue Richard J. Krieg, Jr., PhD OBJECTIVE: To gain a fundamental knowledge of the mouth and tongue with respect to their gross anatomical structure, function, and clinical correlates. READING REFERENCES: · I. Moore & Agur, Essential Clinical Anatomy ("ECA"), pp. 547560. Oral Cavity The boundaries of the oral cavity are the cheeks, the lips, the palate, and the mucous membrane that covers the floor and its connection to the tongue (the frenulum). The vestibule lies between the cheek and the gums and teeth. Another frenulum in the vestibule connects the upper lip to the gum. The parotid papilla is the opening of the parotid duct into the vestibule and is located opposite the 2 nd molar tooth. A lessconspicuous frenulum also exists between the lower lip and the gum. The oral cavity proper is the area surrounded by the teeth. On either side of the frenulum of the tongue are sublingual caruncles (papillae). These are the openings of the submandibular ducts. Sublingual folds run back from the sublingual caruncles and represent the location of the sublingual salivary glands. These are superficial to the submandibular ducts (Atlas, 12 th ed.: 7.50, 11 th ed.: 7.55A). Sublingual ducts open through the mucosa in this area, as well as on the sublingual caruncles. The hard palate forms most of the roof of the mouth. The soft palate projects downward and partially separates the oral cavity from the nasopharynx. Posteriorly the oral cavity leads to the oropharynx. This is located, in general, between the lower end of the soft palate and the area of the epiglottis (see Figure below). The transition area from the mouth to the oropharynx is called the isthmus of the fauces. The fauces are the "pillars" on either side of the opening. Each pillar has two archs with the palatine tonsil between. The anterior arch is the palatoglossal arch. As expected, it extends between the soft palate and the tongue. It contains the palatoglossus muscle. The posterior arch is the palatopharyngeal arch, and it contains the palatopharyngeus muscle. Between the two archs is the fossa for the palatine tonsil. The vasculature to the palatine tonsil becomes important in tonsillectomy. The largest artery is the tonsillar branch of the facial artery. Other arteries include branches of the ascending pharyngeal, the lingual, and the descending palatine arteries. The ascending palatine branch of the facial artery also contributes. Fig 1 The lips have a rich blood supply from the labial branches of the facial artery. The upper lip is innervated by the infraorbital nerve and the lower lip is innervated by the mental nerve. The orbicuris oris muscle surrounds the mouth and controls the lips. The mandibular branch of the facial nerve innervates the orbicularis oris. Damage to the mandibular branch can cause uncontrolled leakage of saliva (drooling) from the corner of the mouth due to the inability of the orbicularis oris to seal the lips. Lymphatics from the upper lip and lateral parts of the lower lip extend to submandibular nodes. Lymphatics from the medial part of the lower lip extend to submental nodes. II. Teeth If one has all of them, the adult teeth are 32 in number,. There are two incisors, one canine, two premolars, and three molars on each side of each jaw. The last molar is the "wisdom tooth", which is frequently missing due to failure to erupt or removal. Dentists refer to the teeth by specific number. There are only 20 deciduous (baby) teeth. These consist of two incisors, one canine, and two molars. The child is born with a relatively large skull and a small face. The growth and development of the face is approximately four times that of the cranial portion of the head. Growth of the teeth also occurs rapidly. Sometimes the teeth outgrow the jaws and a patient must have teeth pulled or adjusted to fit properly. Sensation from the maxillary teeth travels through the maxillary division of the trigeminal nerve (CN V). The posterior superior alveolar nerve carries sensation from the molars. The middle and anterior superior alveolar nerves carry sensation from the rest of the upper teeth. Sensation from all the mandibular teeth travels through the inferior alveolar nerve of the mandibular division of CN V. The gums of the buccal surfaces of the teeth send their sensory fibers through the same pathways as the teeth. The palatine gums of the upper teeth and the palate itself send their sensation via the greater palatine and the nasopalatine nerves. The lingual surface of the mandibular gums actually send their sensation via the lingual nerve. The buccal portion of the cheek sends its sensation via the buccal branch of the mandibular division of CN V. The arteries to the teeth are the alveolar arteries. The upper teeth are supplied by the posterior superior alveolar artery, and the middle and anterior superior alveolar branches of the infraorbital artery, from the maxillary artery. The lower teeth are supplied by the inferior alveolar artery from the maxillary artery. These branches also supply the gums and bony alveoli. Veins accompany the arteries. Lymphatics pass mainly to submandibular nodes, but some go to submental and superior deep cervical nodes. III. Tongue The root of the tongue is the part that is attached by means of a number of muscles. The dorsum of the tongue has part in the oral cavity, but also a large part of it faces posteriorly and is actually an anterior border of the oropharynx (1 st Figure above). This latter part of the tongue reaches down to the epiglottis and forms the anterior wall of the valleculae, which are pockets in front of, and alongside the epiglottis (Atlas 12 th ed.: 7.49B, 11 th ed.: 7.54B, and this Figure). The body is the main mass of the tongue, and the frenulum attaches to the body from below. On the dorsum of the tongue are a number of papillae. Filiform papillae are spiky little protrusions on the dorsum of the tongue. Interspersed among the filiform papillae are fungiform papillae which are named after their mushroomlike shape. Large vallate papillae form a Vshape at the posterior margin of the flat part of the tongue. Just behind the vallate papilla is a groove called the sulcus terminalis. At the apex of the sulcus terminalis is a small pit the foramen cecum. This is the upper end of the thyroglossal duct, and is the point from which the thyroid gland developed. Occasionally, thyroid tissue may be located at this spot ("lingual thyroid"). Behind the sulcus terminalis on either side is the large mass of lymphoid tissue known as the lingual tonsil. Most of these structures can be seen in this Figure. Fig 2 On the underside of the tongue, the frenulum, sublingual caruncles, sublingual ducts, and sublingual salivary glands are located and have been described above. The mass of the tongue consists mostly of intrinsic muscles. These muscles control the shape of the tongue and do such things as curl, point, and flatten it. These muscles are termed longitudinal, transverse, and vertical. They are bilateral, and are separated by a midline septum linguae. The mobility of the tongue as a whole is accomplished by its suspension from three wellseparated bilateral attachements: 1. the mandible via genial tubercles 2. the styloid process 3. the hyoid bone. Fig 3 From these bony points the three principal extrinsic muscles of the tongue arise: 1. the genioglossus 2. the styloglossus 3. the hyoglossus (Atlas, 12 th ed.: 7.50B, 11 th ed.: 7.56B) The genioglossus is the protruder of the tongue, so sticking out your tongue is a function of the genioglossus. The styloglossus retracts and elevates the tongue. The hyoglossus flattens the tongue and draws it down on both sides. The palatoglossus attaches the tongue to the palate. It forms the palatoglossal arch, in front of the palatine tonsil. This muscle pulls the tongue and soft palate together, squeezing the bolus back into the oropharynx in the process of swallowing. The styloglossus also helps in this process by pulling the dorsum of the tongue upward against the hard palate. In this sequence, the styloglossus would contract before the palatoglossus. As in the "Rules of one exception", all the muscles of the tongue are innervated by the hypoglossal nerve (CN XII), except the palatoglossus, which is supplied by the vagus (CN X). With a lesion of the hypoglossal nerve, protrusion of the tongue will show deviation toward the side of the lesion. Sensation from the tongue includes both taste and general sensation (e.g. hot, cold, pain, etc.). The tongue is divided by the vallate papillae into an anterior b and a posterior a. The epiglottic region of the tongue also senses taste and general sensation. The innervation of these areas is shown in Figure 7.34A (ECA) and the following table: General Sensation Taste Chorda tympani of anterior b Lingual n. of CN V CN VII Glossopharyngeal, Glossopharyngeal, posterior a CN IX CN IX Epiglottic Superior Laryngeal of Superior Laryngeal of Region CN X CN X The lingual nerve branches from the mandibular division of the trigeminal nerve (CN V), and receives the chorda tympani in the infratemporal fossa. In the oral cavity, the chorda typmani has two functions. Besides carrying sensory fibers for taste from the anterior b of the tongue, it has the preganglionic motor fibers that pass to the submandibular ganglion (ECA: 9.8B). In this respect, the submandibular ganglion is suspended from the lingual nerve by two connections (see Figure below). The proximal connection carries the preganglionic fibers from the chorda tympani. The distal connection carries postganglionic fibers from the ganglion back to the lingual nerve, to be distributed to the sublingual gland. Postganglionic fibers to the submandibular gland go directly from the ganglion to the gland. Fig 4 In its passage forward, the lingual nerve has a classic relationship to the submandibular duct. It starts out lateral, but wraps around, to end up medial to the it. The vasculature to the tongue is mainly the lingual artery. The lingual artery is one of the eight branches of the external carotid artery (ECA: 8.5). In the oral cavity it passes medial to the hyoglossus muscle, and is thus separated from the lingual and hyoglossal nerves (ECA: 8.5). The lingual artery gives rise to three branches: the dorsal linguals, deep lingual, and sublingual arteries (ECA: 7.33B).