Big Picture

The cheeks and lips border the oral cavity, with a space (the vestibule) between the cheeks, lips, and teeth. The cheeks contain the buccinator muscle, which, along with the tongue, holds food between the teeth during mastication (chewing).

Big Picture

The palate forms both the roof of the oral cavity and the floor of the nasal cavity and consists of a hard and a soft palate. All the muscles that act upon the soft palate are innervated by the vagus nerve [cranial nerve (CN) X], with the exception of the tensor veli palatini, which is innervated by a small motor branch from CN V-3. The difference in innervation reflects the embryologic origins of the branchial arches.

Hard Palate

The hard palate consists of the palatine process of the maxillary bone and the horizontal plate of the palatine bone (Figure 24-1A and B). The incisive canal is in the anterior midline and transmits the following branches (Figure 24-1B):

• Nasopalatine and greater palatine nerves. Branches of the maxillary nerve (CN V-2); provides general sensation to the palate.
  
• Sphenopalatine and greater palatine arteries. Branches of the maxillary artery originating from the infratemporal fossa.

Soft Palate

The soft palate forms the soft, posterior segment of the palate. The soft palate has a structure called the uvula, which is suspended from the midline (Figure 24-1A–C). The soft palate is continuous with the palatoglossal and palatopharyngeal folds. Functionally, the soft palate ensures that food moves inferiorly down into the esophagus when swallowing, rather than up into the nose. By moving posteriorly against the pharynx, which separates the oropharynx from the nasopharynx, the soft palate acts like a flap valve. The vascular supply is bilaterally derived from the lesser palatine artery (maxillary artery) and from smaller arteries, including the ascending palatine artery of the facial artery and the palatine branch of the ascending pharyngeal artery. The soft palate receives general sensory innervation via the lesser palatine nerves (CN V-2) (Figure 24-1B).

Muscles of the Soft Palate

The muscles of the soft palate are as follows (Figure 24-1B and C):

• Tensor veli palatini muscle. Attaches laterally to the pterygoid plate of the sphenoid bone, hooks around the hamulus, and inserts in the soft palate. This muscle is innervated by CN V-3. As its name implies, contraction results in tensing the soft palate.
  
• Levator veli palatini muscle. Originates along the cartilaginous portion of the auditory tube and inserts into the superior aspect of the soft palate. Contraction of this muscle elevates the soft palate and is innervated by CN X.

To test the function of CN X, the physician will ask the patient to open his mouth wide to determine if the palate deviates to one side or the other during a yawning motion. A lesion of CN X causes paralysis of the ipsilateral levator veli palatini muscle, resulting in the uvula being pulled superiorly to the opposite side of the lesion.

• Palatoglossus muscle. Attaches between the soft palate and the tongue and is innervated by CN X. The palatoglossus muscle and the palatopharyngeus muscle surround the palatine tonsil, which aids the immune system in combating pathogens entering the oral cavity.

Inflammation of the palatine tonsils (tonsillitis) is associated with difficulty swallowing and sore throat. Because the palatine tonsils are visible when inspecting the oral cavity, the tonsils of a patient who has tonsillitis will appear enlarged and red. In cases of chronic tonsillitis, the tonsils may be surgically removed (tonsillectomy) to ensure that the patient can swallow and breathe properly.

Big Picture

The tongue consists of skeletal muscle, which has a surface covered with taste buds (special sensory) and general sensory nerve endings. The tongue is supported in the oral cavity by muscular connections to the hyoid bone, mandible, styloid process, palate, and pharynx. The V-shaped sulcus terminalis divides the tongue into anterior and posterior divisions, which differ developmentally, structurally, and by innervation. The foramen cecum is located at the apex of the “V” and indicates the site of origin of the embryonic thyroglossal duct.