Oral Cavity:

1. Define the boundaries and subdivisions of the oral cavity and describe their contents.

Boundaries:

• Anterior: lips

• Lateral: cheeks

• Posterior: palatoglossal arch

• Superior: hard palate

• Inferior: mylohyoid muscle

Subdivisions:

• Oral vestibule

• Oral cavity proper

• Sublingual space

The oral vestibule occupies the space between the teeth and the deep surfaces of the lips and cheeks. It houses several labial frenula that connect the gingivae to neighboring portions of the lips. Like the lingual frenulum, these are folds of fibroelastic connective tissue covered by mucosa. The parotid papillae, which surrounds the opening of the parotid salivary glands. These are typically located lateral to the second maxillary molar.

The oral cavity proper is the largest division of the oral cavity and is home to the body (anterior ⅔) of the tongue. The tongue is anchored to the oral mucosa by the lingual frenulum, which is a band of fibroelastic connective tissue covered by mucosa that extends along the ventral surface of the tongue and onto the oral floor mucosa. The oral cavity is also the location of several salivary openings. The submandibular ducts open through the sublingual caruncles (connective tissue surrounding the opening of the ducts, both for reinforcement and to keep them patent), which flank the lingual frenulum on either side. The impressions of the sublingual glands are visible here through the oral floor mucosa as the sublingual folds. Multiple small ducts open from the sublingual glands along these folds.

The sublingual space is a fascial space that sits deep to the oral floor mucosa and superior to the belly of the mylohyoid muscle. Neurovasculature serving the tongue is found in this space, along with the submandibular ducts and sublingual salivary glands. This space will be discussed in greater detail in its own learning objective.

2. Describe the contents of the sublingual space and their spatial relationships.

Boundaries:

• Superior: oral floor mucosa

• Inferior: mylohyoid m.

• Lateral: mandibular body

• Medial: genioglossus m.

The sublingual space is a fascial space sitting deep to the oral floor mucosa. It is contiguous with submandibular and lateral pharyngeal fascial spaces around the posterior edge of the mylohyoid muscle. Edema or infection may spread through these connections into the retropharyngeal “danger” space and further into the thorax.

The sublingual glands are found here in their entirety and send multiple small ductus superiorly through the oral floor mucosa to open in the oral cavity proper. The superior portion of the submandibular gland is also located here and its submandibular (Wharton’s) duct traverses the sublingual space superior to the lingual n.

The loose areolar connective tissue in the sublingual space is crossed by neurovasculature serving the tongue. The lingual n. enters this space posteriorly from the infratemporal fossa, then wraps inferior to the submandibular (Wharton’s) duct before reaching the tongue mucosa. The lingual a., lingual v., and hypoglossal n. (CN IX) enter this space posteriorly by running deep to the posterior margin of the mylohyoid muscle. The hypoglossal n. (CN IX) runs inferiorly through the space to approach the tongue musculature from below (“hypoglossal” = beneath the tongue) The lingual a. runs medial to the hyoglossus m. and branches into the deep lingual a. and sublingual a. at its anterior border. The deep lingual a. ascends lateral to the hyoglossus m. to supply the ventral surface of the tongue while the sublingual a. remains deep within the space. The tributaries of the lingual v. are largely venae comitantes for these branches, but also include a vena comitans for the hypoglossal nerve.

3. Describe the innervation of the following: cheeks, teeth, and gingivae.

Generally speaking, the sensory innervation of the cheeks, teeth, and gingivae is informed by the territories established by divisions of the trigeminal nerve (CN V), and the motor innervation (exclusive of mastication) is determined by the territories of facial nerve branches (CN VII).

Cheek Innervation:

Teeth (somatic sensory)

The maxillary toothrow receives somatosensory innervation via branches of the maxillary n. (CN V2). The posterior superior alveolar n. originates directly from the maxillary n., while the middle and anterior superior alveolar nerves originate from its terminal branch, the infraorbital n. All branches travel through the maxillary bone to reach the maxillary teeth.

The mandibular toothrow is innervated by branches of the inferior alveolar n., a branch of the mandibular n. (CN V3). The inferior alveolar nerve enters the mandible through the mandibular foramen and travels through the mandibular body, distributing dental branches to the posterior teeth. The mental nerve typically branches and exits the mandibular body via the mental foramen inferior to the first premolar; after this point the remaining branches to the first premolar, canines and incisors are called incisive branches.

Gingivae (somatic sensory)

The gingivae are typically innervated by the same nerves that serve neighboring structures. The gingivae are divided into 4 regions: first by whether they flank maxillary or mandibular teeth, and then again by whether they sit on the buccal/labial or lingual side of the teeth. 

The buccal/labial maxillary gingivae share the same innervation as the cheeks/lips and maxillary teeth. The lingual maxillary gingivae share innervation with the neighboring palate. 

The buccal/labial mandibular gingiva shares innervation with the cheeks/lips. The lingual mandibular gingiva shares innervation with the tongue and oral floor.

4. Name the intrinsic and extrinsic muscles of the tongue and their origins, insertions and innervation.

The intrinsic muscles of the tongue reside entirely within the tongue and act to change its shape. The extrinsic muscles of the tongue connect the tongue to surrounding structures and move it into different positions. Most tongue muscles receive somatic motor innervation via the hypoglossal n. (CN XII); the sole exception is the palatoglossus m., which receives motor innervation via the vagus n. (CN X).

5. Describe the regions of the tongue, and the nerves and modalities serving these regions.

The tongue may be divided into dorsal and ventral regions, with the dorsum region facing the hard palate and the ventrum facing the oral floor. The tongue may be further divided into a posterior root and anterior body. The root makes up the posterior ⅓ of the tongue and its surface is dominated by the rugose lingual tonsil. The root extends from the epiglottis to the palatoglossal arch, which places it entirely within the oropharynx. The body comprises the anterior ⅔ of the tongue, and its dorsal surface is covered with lingual papillae. The body of the tongue resides within the oral cavity. 

On the dorsum of the tongue, the transition from root to body is marked by the terminal sulcus, which runs transversely across the tongue. A second sulcus – the median sulcus – is visible running in the sagittal plane and divides the tongue into symmetrical right and left halves. Where these two sulci meet is a small depression called the foramen caecum, which is a remnant left during embryological development of the thyroid gland.

Somatic motor innervation for the tongue muscles is carried primarily by the hypoglossal n. (CN XII). The lone exception to this is the palatoglossus m., which is innervated by the vagus n. (CN X). Sensory innervation of the tongue includes both somatic and special taste sensory, and separate nerves innervate the root and body of the tongue for each. For the root of the tongue, both somatic and special sensation is carried primarily by the glossopharyngeal n. (CN IX), with a small region near the epiglottic vallecula receiving somatic sensation from the vagus n. (CN X). Somatic sensation from the body of the tongue is carried by the lingual n. (a branch of V3), and special sensory input is carried by the chorda tympani (a branch of the facial nerve that hitchhikes with the lingual n.).

6. Describe the various papillae of the tongue.

The lingual papillae are small, bulbous structures that house special sensory receptors. While they are anatomically named for their shape and appearance, we often colloquially group these together as “tastebuds” but they are distinct from the gustatory receptors they house.

Filiform papillae are conical in shape and transmit tactile sensation, not taste. The sensation from these is therefore carried by the lingual n. These are typically found on the dorsal body of the tongue. Unlike other lingual papillae, filiform papillae continue to grow in length and are eventually shed and replaced. 

Fungiform papillae, like their name suggests, have a mushroom-like shape. These house taste receptors and may be found on the dorsal body of the tongue. Taste sensation from the body of the tongue is carried by the chorda tympani.

Foliate papillae take the appearance of short, vertical folds along the lateral margins of the body of the tongue. They also house taste receptors and are served by the chorda tympani.

Vallate papillae are large, round papillae with a depression in their center surrounded by an elevated ridge. They are arranged in a single row anterior the terminal sulcus of the tongue. While this position technically places them on the body of the tongue, they are nonetheless supplied with special taste sensation by the glossopharyngeal n.

7. Describe the composition and neurovascular supply of the hard palate. What bones comprise the hard palate? What nerves provide sensory innervation to this area? What arteries supply this area?

The hard palate consists of the palatine process of the maxilla anteriorly, the horizontal plate of the palatine bone posteriorly, and the mucosa that lines its entire surface. Neurovascular supply to the mucosa and glands of the hard palate must travel through the bone to reach their targets. 

Anteriorly, the mucosa and gingiva internal to the incisors and canine teeth is supplied by the nasopalatine n. (a branch of V2) and the sphenopalatine artery (a branch of maxillary a.). Both of these travel anteroinferiorly across the length of the nasal septum and pass through the incisive foramen. 

Posteriorly, the mucosa and glands internal to the premolar and molar teeth are supplied by the greater palatine n. (a branch of the maxillary n.) and the greater palatine a. (a branch of the descending palatine a. or maxillary a.). Both reach their targets by descending the greater palatine canal and passing through the well-named greater palatine foramen.

8. Describe the composition and neurovascular supply of the soft palate. What nerve provides sensory innervation to this area? What arteries supply this area? What is the palatine aponeurosis?

The soft palate is a mobile musculo-mucosal fold that functions to separate the nasopharynx from the oropharynx. Its core is formed by the palatine aponeurosis, which is the tendon of the tensor veli palatini muscle after it has bent medially around the hamulus of the medial pterygoid plate. The right side of the aponeurosis meets the left in a midline raphe, and the sling created provides and attachment point for levator veli palatini superiorly and palatoglossus, palatopharyngeus, and musculus uvulae muscles inferiorly.

The soft palate is supplied by the lesser palatine n. (a branch of V2) and the lesser palatine a. (a branch of the descending palatine a. or greater palatine a.). Both neurovascular structures descend the greater palatine canal and enter the soft palate via the lesser palatine foramen.

9. What are the 5 muscles of the soft palate? What are their attachments? What nerves provide efferent innervation? What are their actions?

The muscles of the soft palate are tensor veli palatini m. and levator veli palatini m. superiorly, and palatoglossus m., palatopharyngeus m., and musculus uvulae inferiorly. All of these have an attachment to the palatine aponeurosis, but their extrinsic attachments vary. As a general rule, soft palate muscles are supplied efferently by the vagus n. (CN X), however because of the position of its belly lateral to the medial pterygoid plate, the tensor veli palatini is supplied by the mandibular n. (V3).

10. Describe the major components of the pharyngeal lymphatic (tonsillar) ring. Where do these components typically drain? Where are the palatine tonsils located? What are the important anatomical associations to consider during tonsillectomies?

The pharyngeal lymphatic or tonsillar ring is formed by the pharyngeal tonsil (or adenoid) superiorly, the lingual tonsil inferiorly, and the palatine tonsils and tubal tonsils bilaterally. The pharyngeal tonsil and tubal tonsils sit in the nasopharynx, the palatine and lingual tonsils sit in the oropharynx. 

Tonsils are masses of lymphoid tissue that detect microbes as they enter the oropharynx and nasopharynx. They are connected to the lymphatic drainage system and drain to the jugulodigastric node near the angle of the mandible.

The palatine tonsils sit in the tonsillar fossa of the fauces, or the space between the palatoglossal and palatopharyngeal folds in the oropharynx. The floor of this space is composed of the pharyngobasilar fascia that covers the surface of the superior pharyngeal constrictor m. The palatine tonsils are particularly prone to infection, especially in children, and therefore commonly surgically excised in a procedure called a tonsillectomy. In these cases the surgeon must be mindful of the walls of the fossa and neighboring neurovascular structures. Arteries supplying the palatine tonsil must be ligated: the tonsillar a. sits deep to the palatopharyngeal arch and the external palatine a. sits in the superior tonsillar fossa. And finally, the glossopharyngeal n. (CN IX) sits deep to the palatine tonsil in the tonsillar fossa and care must be taken to avoid injury during excision.

Nasal meatuses

• Sphenoethmoid recess

  • Location: anterior to body of sphenoid in superior nasal cavity

  • Communication: sphenoid sinus 

• Superior nasal meatus

  • Location: deep to superior nasal concha

Communication: posterior ethmoid air cells

• Inferior nasal meatus

  • Location: deep to inferior nasal concha

  • Communication: orbit via nasolacrimal duct

The mucosa of the nasal cavity receives special sensory (olfaction), somatic sensory, and parasympathetic (secretomotor) innervation. 

The olfactory n. (CN I) carries special olfactory sensation from a small territory on the roof and superior walls of the nasal cavity. It exits the nasal cavity as a series of small fibers through the cribriform foramina of the ethmoid back to the anterior cranial cavity.  

Parasympathetics to the nasal cavity originate with the facial n. (CN VII).  Preganglionic fibers travel with its greater petrosal n. branch and synapse in the pterygopalatine ganglion. Postganglionic fibers then hitchhike with branches of the maxillary n. (V2) to reach their target mucus glands.

The somatic sensory  innervation of the nasal cavity is similarly split between branches of the ophthalmic n. (CN V1) and the maxillary n. (CN V2).  The superior-most portion of the nasal cavity is supplied by the anterior and posterior ethmoidal nn., mirroring the supply by similarly named branches of the ophthalmic artery. 

• Ophthalmic n. (CN V1)

  • Anterior ethmoidal n.

Inferior to this, the nasal cavity is innervated by branches of the maxillary n. Posteriorly, the walls are innervated by branches originating from the pterygopalatine ganglion and the remaining portion of the nasal vestibule is innervated by branches originating from infra-orbital n. 

• Maxillary n. (CN V2)

  • Pterygopalatine ganglion

    • Posterior superior nasal br. (superior lateral wall, superior and middle concha)

    • Posterior inferior nasal br. (inferior lateral wall and concha)

    • Nasopalatine n. (septum and anterior hard palate via incisive canal)

  • Infra-orbital n.

    • Internal nasal br. ( nasal vestibule)

    • Anterior superior alveolar n.

Nasal br. (lateral wall and floor anterior to incisive canal)

Pterygopalatine Fossa

13. Describe the walls/boundaries of the pterygopalatine fossa. What are the major structures located within (or traveling through) this fossa?