**2. Anatomical and functional aspects of the oral cavity and oropharynx**

#### **2.1. The oral cavity and the oropharynx**

of swallowing, whereas esophageal dysphagia is the perception of difficulty of passing solids or liquids from the throat to the stomach. Functional dysphagia refers to a condi‐ tion in which some patients complain of dysphagia but do not have an organic cause for a swallowing disorder. The most common symptoms of oropharyngeal dysphagia include difficulty in manipulating food, problems with saliva production, and difficulty in chewing the food and swallowing the bolus (a soft mass of chewed food mixed with saliva at the point of swallowing), and an associated impaired quality of life. Frequently, patients with oropharyngeal dysphagia exhibit a series of complications such as nasal regurgitation, coughing, suffocating, gurgle or wet voice after swallowing, unexplained weight loss, anxiety, depression, low-tract respiratory infections and, it's most serious complication, aspiration pneumonia. Problems with social isolation and poor quality of life are a common feature of individuals with dysphagia. Notably, the occurrence of dysphagia is associated

The different parts of the oral cavity and oropharynx are made up of several cell types and tissues (nerves, fibrovascular, cartilaginous, lining and salivary glandular epithelia, and smooth and striated muscles) along with mineralized tissues (enamel and dentin of the teeth and bones) [8, 9]. Notably, there is an intimate relationship between dysphagia and anatomical, functional, and regulation disturbances of oral cavity and oropharynx components related to physiological salivation, chewing, and swallowing. Salivation depends of the anatomical and functional integrities of the minor and major salivary glands. The saliva lubricates the oral cavity and oropharynx, and an adequate salivary flow assists the initial digestive process by reducing the bolus size of food, begins the enzymatic digestion of some types of carbohydrates, and provides moisture and lubrication of the food particles in order to facilitate the swallowing mechanism, i.e., the movement of the bolus from oropharynx to esophagus [10]. Chewing and swallowing are likely complex and well-coordinated motor programs, combined together as a sequence. During chewing, the food particles are reduced in size and consistency. Chewing is highly dependent of an efficient participation of the teeth, a mineralized tissue whose occlusal surfaces are frequently used for cut off, rip, knead, and grind food during feeding. Moreover, the masticatory muscles have a pivotal role in establishing the muscle strength necessary for the implementation of chewing activity in order to manipulate and grind the food [11-13]. During swallowing two essential and vital functions must be executed: bolus transport and airway protection. After adequate bolus preparation, it needs to be swallowed through an involuntary transport process from the oral cavity and pharynx to the esophagus without allowing the entry of food particles or liquid in the respiratory trac [14, 15]. Together, salivation, chewing, and swallowing, therefore, plays a critical role in alimentary events, allowing food to be initially processed, formed into a bolus, and subsequently transported in the digestive system. Individuals with health problems related to these mechanisms often

In this present chapter, we will highlight a series of morphological and physiological aspects related to the oral cavity and oropharynx. Moreover, we will discuss the physiopathological aspectos of the salivation, chewing, and swallowing mechanisms in order to allow to health professionals to obtain essential knowledge for management of oropharyngeal dysphagia.

with high mortality rate [8].

4 Seminars in Dysphagia

present with complaints of oropharyngeal dysphagia.

Anatomically, the oral cavity or mouth is an organ of the digestive system that is anteriorly delimited by the lips, posteriorly by the oropharynx, superiorly by the hard and soft palates, and inferiorly by the tongue (anterior 2/3) and floor of the mouth, and surrounded by a buccal mucosa that lines the cheeks, along with the upper and lower teeth and periodontum. The upper teeth are embedded in the maxilla and the lower teeth are embedded in the mandible, which articulates with the temporal bones of the skull. The oropharynx is the part of the throat just behind the mouth. It includes the base of the tongue, the soft palate, the tonsils, and the side and back wall of the throat. The oropharynx is the middle part of the pharynx (between the nasopharynx and hypopharynx/laryngopharynx) that is located behind the oral cavity (the palatoglossal arch) extending from the uvula to the level of the hyoid bone. It opens anteriorly into the mouth through the isthmus faucium. In this site, the oropharynx is delimited by the base of the tongue (posterior 1/3) and the upper border of the epiglottic vallecula. Laterally, it is formed by the palatine tonsils, tonsillar fossa, and tonsillar pillars located between the palatoglossal and palatopharyngeal archs. Superiorly, its wall consists of the inferior surface of the soft palate and the uvula [8, 16] [Figure 1].

**Figure 1.** Anatomical aspects of the oral cavity and oropharynx.

#### **2.2. The teeth**

The tooth is an organ that consists of a mineralized, inert, and acellular superficial tissue (enamel, an exclusive hard tissue produced by epithelial cells of ectodermal origin known as ameloblasts) but supported by a less mineralized, more resilient, and vital hard tissue (dentin, which is secreted by a cells of neural crest origin known as odontoblasts) which is formed from and supported by a rich innervated and vascular connective tissue (the dental pulp, which is rich in fibroblast-like cells, blood vessels and nerves). Mammalian tooth development is regulated by means of sequential and reciprocal interactions between the cranial neural crestderived mesenchymal cells and the ectoderm-derived dental epithelium. The teeth are found in the entrance of the oral cavity and constitute about 20% of the structural area of mouth. Anatomically, the tooth consists of a crown and a root, and the junction of the two regions is known as cervical margin (Figure 2A). The teeth have an important role in food processing due to different actions performed by their occlusal surfaces during chewing (Figure 2B). However, the teeth also exhibit other functions, such as defense, proper phonetic articulation, and esthetics in humans. Due to a specialized supporting biological apparatus that consist of the cementum (a mineralized and avascular tissue composed of apatite and organic matrix rich in collagen whose function is to anchor the fiber bundles of the periodontal ligament to the tooth root), periodontal ligament (a highly specialized connective tissue composed for collagen fibers bundles that connect the cementum that cover the tooth root to the alveolar bone whose roles are related to teeth flexibility and sensorial receptor functions), and the alveolar bone (mineralized tissue that support the teeth), the teeth are found firmly attached to the jaws. The hardness of teeth, which is determined by a rich hydrated biologic apatite crystal amid an organic matrix, the number of teeth, the total superficial area formed by the occlusal surfaces, and the supporting tissues allow the teeth to withstand to the forces of the chewing [17, 18].

**Figure 2.** Structural components of the tooth and periodontal support (A). Occlusal surfaces of the human teeth (B).

#### **2.3. The oral mucosa**

The oral mucosa is lined by a mucous membrane that consists of a lining epithelial tissue and an underlying connective tissue. The oral mucosa can be classified as follows: lining, masti‐ catory, and specialized. Among its functions, the oral mucosa has been related to protection, taste sensation, and chewing. The lining of oral mucosa must be as flexible as possible in order to be protective. Related to chewing, the oral masticatory mucosa permits a free movement of the lips, tongue, and cheek muscles. It exhibits a covering of keratinized epithelium and its connective tissues is strongly attached to the bone to withstand the constant mastication of food. The lips exhibit cutaneous (external face, skin), semi-mucosa (transition between external and internal surfaces), and mucosa (inner surface in contact with the anterior teeth) lining. The specialized mucosa that is found in the dorsal surface of the tongue exhibits papillae and taste buds responsible for taste sensation. In the case of the oropharynx mucosa, it is lined by nonkeratinized squamous stratified epithelium [9].

#### **2.4. The salivary glands**

which is secreted by a cells of neural crest origin known as odontoblasts) which is formed from and supported by a rich innervated and vascular connective tissue (the dental pulp, which is rich in fibroblast-like cells, blood vessels and nerves). Mammalian tooth development is regulated by means of sequential and reciprocal interactions between the cranial neural crestderived mesenchymal cells and the ectoderm-derived dental epithelium. The teeth are found in the entrance of the oral cavity and constitute about 20% of the structural area of mouth. Anatomically, the tooth consists of a crown and a root, and the junction of the two regions is known as cervical margin (Figure 2A). The teeth have an important role in food processing due to different actions performed by their occlusal surfaces during chewing (Figure 2B). However, the teeth also exhibit other functions, such as defense, proper phonetic articulation, and esthetics in humans. Due to a specialized supporting biological apparatus that consist of the cementum (a mineralized and avascular tissue composed of apatite and organic matrix rich in collagen whose function is to anchor the fiber bundles of the periodontal ligament to the tooth root), periodontal ligament (a highly specialized connective tissue composed for collagen fibers bundles that connect the cementum that cover the tooth root to the alveolar bone whose roles are related to teeth flexibility and sensorial receptor functions), and the alveolar bone (mineralized tissue that support the teeth), the teeth are found firmly attached to the jaws. The hardness of teeth, which is determined by a rich hydrated biologic apatite crystal amid an organic matrix, the number of teeth, the total superficial area formed by the occlusal surfaces, and the supporting tissues allow the teeth to withstand to the forces of the

**Figure 2.** Structural components of the tooth and periodontal support (A). Occlusal surfaces of the human teeth (B).

The oral mucosa is lined by a mucous membrane that consists of a lining epithelial tissue and an underlying connective tissue. The oral mucosa can be classified as follows: lining, masti‐ catory, and specialized. Among its functions, the oral mucosa has been related to protection, taste sensation, and chewing. The lining of oral mucosa must be as flexible as possible in order to be protective. Related to chewing, the oral masticatory mucosa permits a free movement of the lips, tongue, and cheek muscles. It exhibits a covering of keratinized epithelium and its

chewing [17, 18].

6 Seminars in Dysphagia

**2.3. The oral mucosa**

Three paired sets of major salivary glands (parotid, submandibular, and sublingual) and about 600 to 1,000 minor salivary glands scattered throughout the oral cavity and oropharynx make saliva that keeps the mouth moist and play a pivotal role for chewing, swallowing, and digestion. Histologically, the salivary glands exhibit a secretory unit known as an acinus that is composed by numerous secretory glandular epithelial cells (acinar cells) that surround a central space where the secretion is released. From this space, occurs the formation of the ductal structure, a closed channel lined by epithelial (ductal) cells that run through the gland and end as an opening on the oral mucosa surface. The ductal system contains specialized segments with distinct functions characterized as intercalated, striated/granular (middle portion), convoluted tubule, and excretory ducts (located next to the opening on oral mucosa). Beyond its transport role, the ductal cells alter the salivary electrolytic composition. Other important cell types found between the acinar/intercalated ductal epithelial cells and basal lamina are the myoepithelial cells. These cells show contractile capacity that helps to expel the salivary secretion from the acinus through the ductal system [19, 20]. The parotid glands are located inferior and anterior to the external acoustic meatus, lying posteriorly to the mandibular ramus and anteriorly to the mastoid process of the temporal bone. It drains its secretions (rich in proteins due to presence of acini with serous glandular epithelial cells) into the superior vestibule of oral cavity through Stensen's duct or the parotid duct. The parotid gland is responsible for providing about 25% of the total salivary volume. The submandibular glands are located superiorly to the digastric muscles and it is divided into superficial and deep lobes by the mylohyoid muscle. It drains its secretions (rich in glycoproteins due to presence of predominantly mucous acini, alonmg with some serous acini) into the submandibular duct in the sublingual caruncles, a small papilla near the midline of the floor of the mouth on each side of the lingual frenum. The submandibular gland is responsible for producing about 65% of the total salivary volume. The sublingual salivary glands are anteriorly located to the submandibular gland and inferiorly to the tongue and closest to the oral mucosa lining in the floor of the mouth. It drains its secretions (predominantly mucous, but it also contains some serous epithelial glandular cells) through 8-20 minor excretory ducts (the ducts of Rivinus) and one largest ducts, the sublingual duct or duct of Bartholin. These ductal structures join the submandibular duct to drain through the sublingual caruncle. The sublingual salivary gland is responsible for the production of 3-5% of the total salivary volumen. The minor salivary glands are mainly located in the lips, tongue, buccal mucosa, and palate, although they can also be found along the tonsils, supraglottis, and paranasal sinuses. Each minor salivary gland has a single duct which secretes serous, mucous, or mixed saliva directly into the oral cavity [21, 22] (Figure 3).

**Figure 3.** Anatomical localizations of major salivary glands.

#### **2.5. The masticatory muscles**

The masticatory muscles are voluntary striated muscles that are responsible for chewing actions, grinding the teeth, moving the mandible from side to side, opening the mouth, and also assisting in speech. During embryogenesis they develop from the mesoderm of the first brachial arch, also known as mandibular arch. In humans, the mandible is connected to the temporal bone of the skull via the temporomandibular joint, an extremely complex joint which permits movement in all planes. The masticatory muscles originate on the skull and insert into the mandible, thereby allowing for jaw movements during contraction. That group of muscles is represented by the masseter, temporalis, medial pterygoid, and lateral pterygoid muscles. The masseter muscle represents the most important masticatory muscle. The masseter is made up of outer and inner parts. The origin point of the outer masseter muscle is along the zygomatic arch, the bony arch of the cheek formed by the connection of the zygomatic and temporal bones. The insertion point of the outer masseter is on the surface of the ramus of the mandible. The origin point of the inner masseter muscle is from the rear of the zygomatic arch and it's insertion point is on the upper surface of the ramus of the mandible. The temporalis muscle is the muscle which assists in closing the mouth, grinding the teeth and moving the mouth from side to side when chewing. Its origin point is along the entire rim of the temporal fossa of the skull and its insertion point is the coronoid process of the mandible and temporal crest. The pterygoid muscle, made up of lateral and medial parts, is located on the inside of the ramus of the mandible. The lateral pterygoid muscle is located higher to the medial pterygoid muscle. These muscles work in tandem with the masseter muscles to assist in chewing, jaw rotation, side to side movement of the mouth, and the projection of the lower jaw. The lower head of lateral pterygoid muscle also assists in opening the mouth. Both lateral and medial parts of the pterygoid muscle have two heads and exhibit two origin points. The upper head of the lateral pterygoid muscle's origin point is from the lateral plate of the sphenoid bone and the origin point of the lower head is in the lateral pterygoid plate. Both heads merge to share the same insertion point which is the pterygoid fovea, but the upper head's insertion reaches the capsula and articular disc. The deep head of the medial pterygoid muscle has an origin point from the lateral pterygoid plate and the superficial head has an origin point from the palatine bone and maxillary tuberosity. Both heads merge to form a broad insertion point on the inner surface of the ramus of the mandible. Other muscles associated with the hyoid bone (such as sternohyoid, middle pharyngeal constrictor, hyoglossus, digastric, stylohyoid, geniohyoid, and mylohyoid muscles), also cooperate for opening the jaw in addition to the lateral pterygoid. The hyoid bone provides attachment for the muscles of the floor of the mouth and the tongue above, the larynx below, and the epiglottis and pharynx behind [13, 23] (Figure 4).

**Figure 4.** The muscles of mastication

#### **2.6. The tongue**

**Figure 3.** Anatomical localizations of major salivary glands.

The masticatory muscles are voluntary striated muscles that are responsible for chewing actions, grinding the teeth, moving the mandible from side to side, opening the mouth, and also assisting in speech. During embryogenesis they develop from the mesoderm of the first brachial arch, also known as mandibular arch. In humans, the mandible is connected to the temporal bone of the skull via the temporomandibular joint, an extremely complex joint which permits movement in all planes. The masticatory muscles originate on the skull and insert into the mandible, thereby allowing for jaw movements during contraction. That group of muscles is represented by the masseter, temporalis, medial pterygoid, and lateral pterygoid muscles. The masseter muscle represents the most important masticatory muscle. The masseter is made up of outer and inner parts. The origin point of the outer masseter muscle is along the zygomatic arch, the bony arch of the cheek formed by the connection of the zygomatic and temporal bones. The insertion point of the outer masseter is on the surface of the ramus of the mandible. The origin point of the inner masseter muscle is from the rear of the zygomatic arch and it's insertion point is on the upper surface of the ramus of the mandible. The temporalis muscle is the muscle which assists in closing the mouth, grinding the teeth and moving the mouth from side to side when chewing. Its origin point is along the entire rim of the temporal fossa of the skull and its insertion point is the coronoid process of the mandible and temporal crest. The pterygoid muscle, made up of lateral and medial parts, is located on the inside of the ramus of the mandible. The lateral pterygoid muscle is located higher to the medial pterygoid muscle. These muscles work in tandem with the masseter muscles to assist in chewing, jaw rotation, side to side movement of the mouth, and the projection of the lower jaw. The lower head of lateral pterygoid muscle also assists in opening the mouth. Both lateral and medial parts of the pterygoid muscle have two heads and exhibit two origin points. The

**2.5. The masticatory muscles**

8 Seminars in Dysphagia

The tongue is an organ lined by an oral epithelium that contains numerous specialized structures related to taste sensation (receptor cells that can sense particular classes of tastes located in the taste buds, including filiform papillae, fungiform papillae, vallate papillae, and foliate papillae) (Figure 5A). Internally, however, the tongue exhibits its most remarkable characteristic in that it is predominantly composed of striated muscle. According to its embryological origin, the tongue might be classified by anterior and posterior regions. The anterior region, that represents about 2/3 of the length tongue, is visible, highly mobile, and directed forward against the lingual surfaces of the lower incisor teeth. The posterior region, which represents 1/3 of the length of the tongue, has its base on the floor of the mouth, connected with the hyoid bone, epiglottis, and soft palate, styloid process, and approximates the oropharynx. Both regions of the tongue exhibit a distinct nerve supply and are delimited by the terminal sulcus anteroposteriorly and by the lingual septum mediolaterally. The striated muscle tissues of the human tongue are classified as intrinsic (i.e. they originate and insert within the tongue, running along its length, and are responsible for changing the shape of the tongue, lengthening and shortening it, curling and uncurling its apex and edges, and flattening and rounding its surface in order to execute eating, swallowing, and speech) (Figure 5B) and extrinsic (i.e. they originate from bone and extend to the tongue, and are responsible for change the tongue position, allowing for protrusion, retraction, elevation and side-to-side movement) (Figure 5C). The intrinsic muscles of the tongue are: 1) the superior longitudinal muscle, that runs along the superior surface of the tongue under the mucous membrane, and elevates, assists in retraction of, or deviates the tip of the tongue. It originates near the epiglottis, the hyoid bone, and from the median fibrous septum, 2) the inferior longitudinal muscle, that lines the sides of the tongue and is joined to the styloglossus muscle, 3) the verticalis muscle, which is located in the middle of the tongue and joins the superior and inferior longitudinal muscles, and 4) the transversus muscle, which divides the tongue at the middle and is attached to the mucous membranes that run along the sides. On the other hand, the extrinsic tongue muscles are represented by: 1) the genioglossus, which arises from the mandible and depresses and protrudes the tongue, 2) the hyoglossus, which arises from the hyoid bone and retracts and depresses the tongue, 3) the styloglossus, which arises from the styloid process and elevates and retracts the tongue, and 4) the palatoglossus, which arises from the palatine aponeurosis and depresses the soft palate, moves the palatoglossal fold towards the midline, and elevates the back of the tongue [24-26] (Figure 5).

**Figure 5.** Anatomical aspects of dorsal (A), transversal (B), and lateral (C) views of the tongue.

#### **2.7. The vascular and nervous network of the components of the oral cavity and oropharynx related to salivation, chewing, and swallowing**

Almost all of the soft and hard components of the oral cavity and oropharynx exhibit rich vascular and motor-sensitive innervation networks [8, 27-32].

The maxillary teeth are supplied by the maxillary artery (a branch of the external carotid artery) and its branches: the middle and posterior superior alveolar arteries. The mandibular teeth are supplied by the inferior alveolar artery (a branch of the maxillary artery) and its branches: the mental artery and the incisive artery. The venous drainage of the maxillary and mandibular teeth occurs via the anterior, middle, posterior, and inferior alveolar veins. Like enamel, dentin is avascular. The odontoblasts located within the dentin receive nutrition through dentinal tubules from tissue fluid that originates from the blood vessels located in the dental pulp, the vital tissue of the tooth, characterized as a connective tissue with many cells (odontoblasts, fibroblasts, immune cells, and undifferentiated mesenchymal cells) and an extensive nerve and vascular supply. In the pulp chamber, there is the plexus of Raschkow that monitors painful sensations and participates of inflammatory events. In this plexus, there are two types of nerve fibers (A and C fibers) that mediate the sensation of pain. A-fibers conduct rapid and sharp pain sensations and belong to the myelinated group, whereas C-fibers are involved in dull aching pain and are thinner and unmyelinated. Within each dentinal tubule may contain an odontoblastic process and possibly an afferent axon characterized as an A-delta type sensitive fiber.

tongue, lengthening and shortening it, curling and uncurling its apex and edges, and flattening and rounding its surface in order to execute eating, swallowing, and speech) (Figure 5B) and extrinsic (i.e. they originate from bone and extend to the tongue, and are responsible for change the tongue position, allowing for protrusion, retraction, elevation and side-to-side movement) (Figure 5C). The intrinsic muscles of the tongue are: 1) the superior longitudinal muscle, that runs along the superior surface of the tongue under the mucous membrane, and elevates, assists in retraction of, or deviates the tip of the tongue. It originates near the epiglottis, the hyoid bone, and from the median fibrous septum, 2) the inferior longitudinal muscle, that lines the sides of the tongue and is joined to the styloglossus muscle, 3) the verticalis muscle, which is located in the middle of the tongue and joins the superior and inferior longitudinal muscles, and 4) the transversus muscle, which divides the tongue at the middle and is attached to the mucous membranes that run along the sides. On the other hand, the extrinsic tongue muscles are represented by: 1) the genioglossus, which arises from the mandible and depresses and protrudes the tongue, 2) the hyoglossus, which arises from the hyoid bone and retracts and depresses the tongue, 3) the styloglossus, which arises from the styloid process and elevates and retracts the tongue, and 4) the palatoglossus, which arises from the palatine aponeurosis and depresses the soft palate, moves the palatoglossal fold towards the midline, and elevates

the back of the tongue [24-26] (Figure 5).

10 Seminars in Dysphagia

**related to salivation, chewing, and swallowing**

vascular and motor-sensitive innervation networks [8, 27-32].

**Figure 5.** Anatomical aspects of dorsal (A), transversal (B), and lateral (C) views of the tongue.

**2.7. The vascular and nervous network of the components of the oral cavity and oropharynx**

Almost all of the soft and hard components of the oral cavity and oropharynx exhibit rich

The maxillary teeth are supplied by the maxillary artery (a branch of the external carotid artery) and its branches: the middle and posterior superior alveolar arteries. The mandibular teeth are supplied by the inferior alveolar artery (a branch of the maxillary artery) and its branches: the mental artery and the incisive artery. The venous drainage of the maxillary and mandibular teeth occurs via the anterior, middle, posterior, and inferior alveolar veins. Like enamel, dentin is avascular. The odontoblasts located within the dentin receive nutrition through dentinal

In the oral cavity, the palate is supplied by the maxillary and, sphenopalatine arteries (a branch of the maxillary artery) and its branches: the lesser and greater palatine, facial (a branch of external carotid artery) and its branches: the ascending palatine, tonsilar, submentual, upper and lower labial and angular arteries. The floor of the oral cavity is supplied by arteries: facial, ascending palatine, submental (a branch of the facial artery), and lingual (a branch of the external carotid artery). The masticatory muscles receive a blood supply from branches (the pterygoid portion) of the maxillary artery (masseteric, superficial temporal, anterior and posterior deep temporal, pterygoid branches, and buccal arteries). The tongue receives its blood supply primarily from the lingual artery but a secondary blood supply is supported by the tonsillar branch of the facial artery and the ascending pharyngeal artery. The tissues of the cheeks receive a blood supply from the facial artery. The tissues of the superior and inferior lips receive blood from the superior and inferior labial arteries, respectively, that are branches of the facial artery. The venous drainage of the palate and the floor of the mouth occur via thelesser and greater palatine veins, the sphenopalatine vein, the lingual vein, the submental vein and the pterygoid plexus. Veins of the tongue drain into the sublingual vein and the internal jugular vein. There is also a secondary blood supply to the tongue from the tonsillar branch of the facial artery and the ascending pharyngeal artery.

The salivary glands also receive a rich vascular network. When the oral mucosal surface is stimulated, afferent nerve signals travel to the salivatory nuclei in the medulla. The medullary signal may also be affected by cortical inputs resulting from stimuli such as taste and smell. Efferent nerve signals, mediated by acetylcholine, also stimulate salivary gland epithelial cells and increase salivary secretions. The parotid gland is mainly irrigated by the external carotid artery via its branches, the posterior auricular and transverse facial arteries. However it also receives a blood supply from the superficial temporal artery (a branch of the external carotid artery when it bifurcates into the superficial temporal artery and maxillary artery). The venous drainage of parotid glands is supported by the retromandibular vein (formed by the union of the superficial temporal and maxillary veins) while its lymphatic drainage is supported by the preauricular or parotid lymph nodes which ultimately drain to the deep cervical chain. The submandibular gland receives its blood supply from the facial and lingual arteries. Its venous drainage occurs through the anterior facial vein. The sublingual gland receives its blood supply from the sublingual and submental arteries.

The oropharynx receives vascular irrigation from the ascending pharyngeal artery, a branch of the external carotid. Iti s a long, slender vessel, deeply seated in the neck, beneath the other branches of the external carotid. Palatine tonsils are vascularized by the tonsillar branches of the facial, descending palatine and ascending pharyngeal arteries. The oropharynx venous drainage occurs through the parapharyngeal spaces to the region of the midportion of the peritonsillar plexus, which drain into the lingual and pharyngeal veins, which in turn drain into the internal jugular vein, particularly the jugulodigastric nodes.

Regarding innervation, the motor innervation of the oral cavity is supported by some branches of the mandibular division of the trigeminal cranial nerve (CN V) and the sensitive innervation is supported by branches of maxillary and some branches of the mandibular nerve. The maxillary teeth and their associated periodontal ligament are innervated by the branches of the maxillary division of the trigeminal nerve, the posterior, middle, and anterior superior alveolar nerves. The mandibular teeth and their associated periodontal ligament are inner‐ vated by the inferior alveolar nerve, a branch of the mandibular division. This nerve runs inside the mandible, within the inferior alveolar canal below the mandibular teeth, giving off branches to all the lower teeth.

The oral mucosa of the anterior region of maxilla (maxillary incisors, canines and premolar teeth) is innervated by the superior labial branches of the infraorbital nerve. The pterygopa‐ latine nerve (nasopalatine nerve) is responsible for innervation of the anterior mucosa of maxilla (emerging from beneath the incisive papillae). The lingual nerve, a branch of the mandibular division of the trigeminal nerve, is responsible for innervation of the gingiva of the lingual aspect of the mandibular teeth. The mental nerve, a branch of the inferior alveolar nerve, is responsible for innervation of the facial aspect of the mandibular incisors and canines. The buccal nerve is responsible for innervation of the gingiva of the buccal region of the mandibular molars. The palate is innervated via the maxillary nerve, the nasopalatine nerve, the greater palatine nerve, the lesser palatine nerve and the glossopharyngeal nerve. The floor of the oral cavity is innervated through the lingual, mylohioid, hypoglossal, glossopharyngeal, internal laryngeal, and chorda tympani nerves. Unlike most of the other facial muscles, which are innervated by the facial cranial nerve (CN VII), the muscles of mastication are all innervated by the trigeminal nerve (CN V), more specifically they are innervated by its mandibular branch. The motor function of the trigeminal nerve activates the muscles of mastication and other accessory muscles (the tensor tympani, tensor veli palatini, mylohyoid, and anterior belly of the digastric). All intrinsic and extrinsic muscles of the tongue are supplied by the hypoglossal nerve (CN XII), with the exception of the palatoglossus muscle that is innervated by the vagus nerve (CN X). Regarding sensory nerves, the sensation of taste in the anterior region of the tongue is passed along the chorda tympani, a branch of the facial nerve. Sensation is passed along the lingual nerve, a branch of the trigeminal nerve. Posteriorly, both taste and sensation are passed along the glossopharyngeal nerve (CN IX).

Innervation of salivary glands is entirely autonomic. They are innervated by parasympathetic fibers (via cranial nerves V, VII, and IX) and sympathetic fibers (via preganglionic nerves in the thoracic segments T1-T3 and via postganglionic sympathetic fibers C2-C3) of the auto‐ nomic nervous system (Figure 6). The parotid salivary gland is innervated by the facial nerve and anterior branch of the great auricular nerve (composed of branches of spinal nerves C2 and C3 from the cervical plexus). Postganglionic sympathetic fibers from the superior cervical sympathetic ganglion reach the parotid gland as the periarterial nerve plexuses around the external carotid artery and their function is mainly vasoconstriction. Preganglionic parasym‐ pathetic fibers leave the brain stem from the inferior salivatory nucleus in the glossopharyngeal nerve (CN IX) and then through its tympanic and then the lesser petrosal branch pass into the otic ganglion where they synapse with postganglionic fibers that reach the parotid gland via the auriculotemporal nerve. The sympathetic nervous system also affects salivary gland secretions indirectly by innervating the blood vessels that supply the glands. Both sympathetic and parasympathetic stimuli result in an increase in salivary gland secretions. The subman‐ dibular and sublingual glands receive their parasympathetic input from the facial nerve (CN VII) via the submandibular ganglion. Their secretions are also regulated directly by the parasympathetic nervous system and indirectly by the sympathetic nervous system. The sympathetic nervous system regulates submandibular secretions through vasoconstriction of the arteries that supply it. Parasympathetic innervation of both submandibular and sublingual glands is provided by the superior salivatory nucleus via the chorda tympani nerve. Para‐ sympathetic activity increases salivary flow, makingsaliva watery. On the other hand, increased sympathetic activity reduces glandular blood flow, making the saliva thicker, rich in glycoproteins and glycosaminoglycans. The lingual nerve is responsible by the postgan‐ glionic parasympathetic innervation of minor salivary glands. However, the minor salivary glands located on the superior jaw are innervated by fibers of the palatine nerve.

The oropharynx receives vascular irrigation from the ascending pharyngeal artery, a branch of the external carotid. Iti s a long, slender vessel, deeply seated in the neck, beneath the other branches of the external carotid. Palatine tonsils are vascularized by the tonsillar branches of the facial, descending palatine and ascending pharyngeal arteries. The oropharynx venous drainage occurs through the parapharyngeal spaces to the region of the midportion of the peritonsillar plexus, which drain into the lingual and pharyngeal veins, which in turn drain

Regarding innervation, the motor innervation of the oral cavity is supported by some branches of the mandibular division of the trigeminal cranial nerve (CN V) and the sensitive innervation is supported by branches of maxillary and some branches of the mandibular nerve. The maxillary teeth and their associated periodontal ligament are innervated by the branches of the maxillary division of the trigeminal nerve, the posterior, middle, and anterior superior alveolar nerves. The mandibular teeth and their associated periodontal ligament are inner‐ vated by the inferior alveolar nerve, a branch of the mandibular division. This nerve runs inside the mandible, within the inferior alveolar canal below the mandibular teeth, giving off

The oral mucosa of the anterior region of maxilla (maxillary incisors, canines and premolar teeth) is innervated by the superior labial branches of the infraorbital nerve. The pterygopa‐ latine nerve (nasopalatine nerve) is responsible for innervation of the anterior mucosa of maxilla (emerging from beneath the incisive papillae). The lingual nerve, a branch of the mandibular division of the trigeminal nerve, is responsible for innervation of the gingiva of the lingual aspect of the mandibular teeth. The mental nerve, a branch of the inferior alveolar nerve, is responsible for innervation of the facial aspect of the mandibular incisors and canines. The buccal nerve is responsible for innervation of the gingiva of the buccal region of the mandibular molars. The palate is innervated via the maxillary nerve, the nasopalatine nerve, the greater palatine nerve, the lesser palatine nerve and the glossopharyngeal nerve. The floor of the oral cavity is innervated through the lingual, mylohioid, hypoglossal, glossopharyngeal, internal laryngeal, and chorda tympani nerves. Unlike most of the other facial muscles, which are innervated by the facial cranial nerve (CN VII), the muscles of mastication are all innervated by the trigeminal nerve (CN V), more specifically they are innervated by its mandibular branch. The motor function of the trigeminal nerve activates the muscles of mastication and other accessory muscles (the tensor tympani, tensor veli palatini, mylohyoid, and anterior belly of the digastric). All intrinsic and extrinsic muscles of the tongue are supplied by the hypoglossal nerve (CN XII), with the exception of the palatoglossus muscle that is innervated by the vagus nerve (CN X). Regarding sensory nerves, the sensation of taste in the anterior region of the tongue is passed along the chorda tympani, a branch of the facial nerve. Sensation is passed along the lingual nerve, a branch of the trigeminal nerve. Posteriorly, both taste and sensation

Innervation of salivary glands is entirely autonomic. They are innervated by parasympathetic fibers (via cranial nerves V, VII, and IX) and sympathetic fibers (via preganglionic nerves in the thoracic segments T1-T3 and via postganglionic sympathetic fibers C2-C3) of the auto‐ nomic nervous system (Figure 6). The parotid salivary gland is innervated by the facial nerve

into the internal jugular vein, particularly the jugulodigastric nodes.

branches to all the lower teeth.

12 Seminars in Dysphagia

are passed along the glossopharyngeal nerve (CN IX).

**Figure 6.** Cranial nerves and their relationship with salivation, chewing, and swallowing mechanisms.

The muscles of the oropharynx receive innervation from the pharyngeal plexus of the vagus nerve (CN X). This network of nerve fibers provides sensory and motor innervation from the pharyngeal branches of the glossopharyngeal nerve (CN IX), the pharyngeal branch of the vagus nerve (CN X), and superior cervical ganglion sympathetic fibers (a component of the autonomic sympathetic nervous system responsible for maintaining homeostasis of the body). However, the motor innervation of the oropharynx also receives nerve fibers from the cranial part of accessory cranial nerve (CN XI). The palatine tonsils receive afferent innervation via the tonsillar plexus, which has contributions from the general somatic afferent fibers of the maxillary division of the trigeminal nerve (CN V) via the lesser palatine nerves, and general visceral afferent fibers from the tonsillar branches of the glossopharyngeal nerve (CN IX) (Figure 6).
