Oral+Cavity

=**Objectives**=


 * 1. Define the boundaries of the oral cavity.**

The boundaries of the oral cavity are fuzzy but include the cheeks, palate, tongue and sublingual fossa, lips, and pharynx. The oral cavity opens posteriorly into the oropharynx and is bound by the palatogossal and palatopharyngeal arches. The palatoglossal and palatopharyngeal muscles are deep to these arches which surround the tonsilar bed and the palatine tonsil inside. The mucus membrane of the tonsil is innervated by the glossopharyngeal nerve and the tonsil is supplied by the tonsilar artery of the facial artery. The rima oris is the opening between the lips.

The lips are also known as the oral labia. The vermillion border is the portion of the lips where there is a color change transition between the skin and the oral mucus membrane; this is the region where lip liner is applied. The philtrum is the medial portion of the upper lip derived from the intermaxillary segment; the lateral edges of the philtrum are the sites of cleft lip. The labial frenulum is a fold of tissue attaching to the center of the lip between the front teeth and helps anchor the lips to the gums.

The cheeks are continuous with the lips and extend across the zygomatic arch. They are composed of four layers from superficial to deep. The skin is the most superficial under which lies the buccinators. Beneath this muscular layer is a mucus membrane and then the parotid papillae. The parotid duct pierces the buccinators and end as the parotid papillae in the vestibule just adjacent to the 2nd upper molar.

The gums are called the gingivae and are composed of fibrous connective tissue covered in mucus membrane. The alveolar gingivae is the free portion between the teeth that is movable (the part you floss). The gingival proper is attached to the mandible or maxilla and is immovable.

The oral cavity is subdivided into the vestibule and the oral cavity proper. The vestibule is the area between the gums and the lips or cheek (i.e. outside the gums/teeth). The oral cavity is within the dental arches and is the space normally filled by the tongue.

In the floor of the mouth, or sublingual fossa, reside the sublingual gland, submandibular duct, lingual nerve, and hypoglossal nerve. The sublingual gland fills the sublingual fossa. //The submandibular duct is embedded within the sublingual gland and very characteristically crosses around the lingual nerve//. The lingual nerve of the mandibular nerve (CN V3) travels from the infratemporal fossa to reach the sublingual fossa and supplies sensory innervation to anterior 2/3 of tongue. The hypoglossal nerve comes in deep to the posterior belly of the digastric muscle and passes into the tongue.


 * 2. Review the innervation of the following structures: the lips, the cheeks, and the gums.**

The upper lip including the philtrum is innervated by branches of the maxillary nerve such as the infraorbital branch, despite the philtrum having origins from the territory of the ophthalmic nerve. The lower lip is supplied by branches of the mandibular nerve, such as the mental branch and buccal branch.

The skin of the cheeks are innervated by branches of the maxillary and mandibular nerve such as the infraorbital and buccal nerves, respectively. The buccinator underneath is a muscle of facial expression, innervated by the facial nerve. The underlying mucus membrane is innervated by the buccal branch of the mandibular nerve. Lastly, the paratid gland is innervated by parasympathetic fibers originating from the glossalpharyngeal nerve traveling through the jugular foramen, the superior and inferior glossalpharyngeal ganglion, the tympanic branch, lesser petrosal nerve, synapsing in the otic ganglion, joining the auriculartemporal nerve of the mandibular nerve, and going to the parotid.

The gums are innervated on the lingual side superiorly by the greater palatine nerve and the nasopalatine nerve of the maxillary nerve, and inferiorly by the lingual nerve of the mandibular nerve. On the vestibule side, the gums are innervated superiorly by two branches of the maxillary nerve: the posterior superior alveolar nerve and the anterior superior alveolar nerve off of the infraorbital nerve. Inferiorly, the gums are innervated by the inferior alveolar nerve, the buccal nerve, and the mental nerve, all branches of the mandibular nerve.


 * 3. Review the five areas where lymphoid tissue forms "tonsils" around region of the oral cavity and the formation of the tonsillar ring.**

The two pharyngeal tonsils or adenoids are located on the posterior nasopharynx. The two palatine tonsils are located between the palatopharyngeal and palatoglossal arches of the oropharynx. The lingual tonsis are located on the tongue posterior to the terminal sulcus, where the hypobrachial eminence meets the lateral lingual swellings. Together, this set of lymphatic tissue forms the tonsillar ring.


 * 4. Explain the anatomical considerations associated with the tongue and its sensory innervation.**

The tongue is a muscular organ that fills the oral cavity proper, ending posteriorly into the pharynx and functions in digestion and swallowing (moving food into the pharynx) and aids in phonation (so you can tell people to fuck off).

There are two parts of the tongue: the oral portion, and the pharyngeal portion. The oral portion is in the oral cavity and is the free, movable body of the tongue. It is approximately equivalent to the anterior 2/3 of the tongue minus the vallate papillae. The pharyngeal portion faces the oropharynx and is the attached portion or root of the tongue. It is the posterior 1/3 of the tongue plus the vallate papillae.

The anterior 2/3 of the tongue minus the vallate papillae receive general sensation from the lingual branch of the mandibular nerve. It receives taste sensation from the chorda tympani off of the facial nerve. The posterior 1/3 of the tongue plus the vallate papillae receive general sensation and taste from the glossopharyngeal nerve (CN IX), and the epiglottis recieves taste sensation from the vagus nerve (CN X). The transition between somatic and visceral sensation is not abrupt on the tongue but gradual.

The inferior surface is attached to the floor of the oral cavity by the lingual frenulum, a fold of mucus membrane that anchors the tongue. It can be absent in people, allowing them to touch their nose with their tongue, or very short, causing them to be tongue-tied and preventing phonation. The mucus membrane of the inferior side is very thin and the lingual vein is very prominent, allowing a means to deliver bad tasting medications under the tongue.

The superior surface is called the dorsum of the tongue and has a thick mucus membrane covered by papillae. The filiform papillae are the most numerous and cover the body of the dorsum; they are threadlike and contain no tastebuds. Interspersed between the filiform papillae are the fungiform papillae which are club shaped and contain single or a few tastebuds. The circum vallate papillae are the largest papillae are the 8-12 papillae towards the posterior part of the body of the tongue; these contain multiple taste buds and are located in front of the sulcus terminalis. The foliate papillae are ridges on the lateral aspect of the tongue.

The median sulcus is a groove down the middle of the body of the tongue and is the embryological meeting of the two lateral tongue buds; it can be split down the septum or pierced. The sulcus terminalis divided the anterior 2/3 from the posterior 1/3 of the tongue and is where the hypobrachial eminience meets the lateral lingual swellings. The foramen cecum is a blind pit where the thryoglossal duct used to be for the thyroid diverticulum to descend. The lingual tonsil is embedded in the posterior 1/3 of the tongue, making it bumpy though there are not papillae.


 * 5. Know the organization, action, blood supply, and innervation of the intrinsic and extrinsic muscles of the tongue.**

There are intrinsic muscles of the tongue with longitudinal, horizontal, and vertical fibers. These intrinsic muscles change the shape of the tongue and are important for phonation. These muscles are supplied by the hypoglossal nerve (CN XII).

There are four extrinsic muscles of the tongue: the hyoglossus, styloglossus, genioglossus, and palatoglossus. The hyoglossus muscle originates from the hyoid bone and inserts on the lateral aspect of the tongue; it functions to draw down the lateral part of the tongue and is innervated by the hypoglossal nerve (CN XII). The styloglossus muscle originates from the styloid process and inserts on the lateral posterior aspect of the tongue; it functions to retract and posteriorly raise the tongue and is innervated by the hypoglossal nerve (CN XII). It is important in initiating the swallowing process. The Genioglossus originates on the internal aspect of the mandible at the midline and fans out onto the body of the tongue; it acts to protract and anteriorly depress the tongue and is innervated by the hypoglossal nerve (CN XII). The palatoglossus is also a muscle of the soft palate, originating on the lateral aspect of the tongue and inserting at the palatine aperneurosis; it acts to depress the soft palate and is the only –glossus muscle that is innervated by the vagus nerve (CN X) and //not// the hypoglossal nerve

To test the hypoglossal nerve (CN XII), you can ask the patient to stick out their tongue. A functional CN XII will extend the tongue at the midline, but if one side is broken, the tongue will deviate to the broken side.

The lingual artery off of the external carotid artery supplies the blood to the tongue via its branches. The dorsal lingual artery dives deep to the hyoglossus muscle and supplies the deep posterior aspect of the tongue. The deep lingual artery goes deep into the body of the tongue and extends to the apex. The sublingual branch supplies the anterior-inferior aspect of the tongue.


 * 6. Review the suprahyoid muscles. What are their separate innervations? What is their collective action.**

There are four suprahyoid muscles between the hyoid and the mandible: the stylohyoid, mylohyoid, genoihyoid, and digrastic muscles. All these muscles act to raise the hyoid, tongue, and floor of the mouth or steady the hyoid for independent tongue movements. If the hyoid is fixed, they aid in depression of the mandible and the opening of the mouth.

The stylohyoid muscle is innervated by the facial nerve (CN VII). The mylohyoid muscle is innervated by the myohyoid nerve from the inferior alveolar nerve of the mandibular nerve (CN V3). The geniohyoid muscle is innervated by the hypoglossal nerve (CN XII). The digastric muscle has an anterior and posterior belly. The anterior belly is innervated by the nerve to myohyoid from the inferior alveolar nerve of the mandibular nerve (CN V3); the posterior belly is innervated by the facial nerve (CN VII). See Organization of the Neck


 * 7. Review the three main pairs of the salivary glands. Explain their location, the location of their duct(s) and their innervation.**

There are three main pairs of salivary glands: the parotid glands, submandibular glands, and sublingual glands.

__Parotid Glands__ The parotid is the largest of the salivary glands located anterior and deep to the ear. Its duct crosses the masseter and penetrates the buccinators to end as the parotid papillae in the vestibule of the oral cavity adjacent at the 2nd upper molar. Preganglionic parasympathetic fibers from the glossopharyngeal nerve (CN IX) travel via the lesser petrosal nerve to synapse in the otic ganglion where postganglionic parasympathetic fibers join the auriculotemporal nerve of the mandibular nerve to reach and supply the parotid (auriculotemporal nerve continues straight through to supply the skin). Preganglionic sympathetic fibers from thoracic lateral horn travel via ventral root to white ramus and ascend to the superior cervical ganglion (or middle cervical ganglion) where they synapse. Postganglionic sympathetic fibers then follow blood vessels like the auriculotemporal artery or the parasympathetic fibers on the auriculotemporal nerve to supply the parotid gland.

__Submandibular and Sublingual glands__ The submandibular glands are located along the body of the mandible. The //submandibular duct very characteristically crosses the lingual nerve in the sublingual fossa//, embedding itself within the sublingual gland, and opens at the sub//lingual// papillae located adjacent to the lingual frenulum. The sublingual glands lie in the floor of the mouth deep to the tongue and have many ducts (>15) opening directly into the sublingual fossa.

Preganglionic parasympathetic fibers from the facial nerve (CN VII) travel through the geniculate ganglion and down the facial canal, branching off as the chorda tympani which join the lingual nerve of the mandibular nerve (CN V3). These fibers continue and synapse at submandibular ganglion. Postganglionic parasympathetic fibers then follow arteries (e.g. facial artery, lingual artery) to supply the submandibular and sublingual glands. Preganglionic sympathetic fibers from thoracic lateral horn travel via ventral root to white ramus and ascend to the superior cervical ganglion (or middle cervical ganglion) where they synapse. Postganglionic sympathetic fibers then follow blood vessels or named nerves to supply the submandibular and sublingual glands.