Palate

Hard palate

The hard palate is the immobile hard bony portion of the palate. It comprises the anterior two-thirds of the palate. The hard palate is formed by the fusion of two pairs of facial bones in the midline, the maxillae (upper jaw bones) and palatine bones. The palatine processes of the maxillae form the anterior three-quarters of the hard palate, while the horizontal plates of the palatine bones form the remaining posterior one-quarter. The hard palate is arched superiorly forming a concavity which accommodates the tongue. It is bounded on its anterolateral aspects by the alveolar processes and teeth of the maxillae. Posteriorly, the hard palate is connected to the muscular soft palate. The oral aspect of the hard palate is covered by oral mucosa that is firmly bound to the underlying bone and overlies the mucus-secreting palatine glands and neurovascular structures. The nasal aspect on the other hand is covered by respiratory mucosa.   

The hard palate bears several openings that transmit important neurovascular structures that supply the palate and oral cavity. In the midline, on its anterior end, the hard palate bears the incisive foramen, which transmits the nasopalatine nerve and the sphenopalatine vessels. At its posterior end, close to the second maxillary molars, the hard palate has two paired openings, the greater and lesser palatine foramina which transmit the greater and lesser palatine nerves and vessels respectively.

Soft palate

The soft palate (velum) is the posterior muscular portion of the palate that continues from the posterior border of the hard palate. It is a mobile soft tissue flap that curves posteriorly and inferiorly into the pharynx, demarcating the nasopharynx from the oropharynx. It blends laterally with the palatoglossal and palatopharyngeal arches of the oropharynx. These arches form the boundaries of the tonsillar fossa which houses the palatine tonsils. On its posterior free margin, the soft palate bears a conical projection in the midline known as the uvula. The epithelial lining of the oral surface of the soft palate contains a small number of taste buds.

The soft palate has no bony component but contains the palatine aponeurosis. This structure is the fibrous aponeurotic expansion of the tensor veli palatini muscles that attaches to the posterior border of the hard palate. The palatine aponeurosis serves as the principal structural component of the soft palate to which the other muscles of the palate attach. The soft palate is composed of five pairs of muscles that enable it to move:

• The tensor veli palatini and levator veli palatini are two muscles that arise from the base of the skull and descend into the palate. During swallowing and yawning, these muscles tense and elevate the soft palate.  
• The palatoglossus muscles ascend from the sides of the tongue into the palate and lower the soft palate onto the tongue, narrowing the oropharyngeal opening. 
• The palatopharyngeus muscles ascend into the palate from the posterior border of the thyroid cartilage. This muscle tenses the soft palate while elevating the pharynx during swallowing.
• The final muscle of the soft palate is the musculus uvulae, which arises from the posterior margin of the hard palate and passes into the mucosa of the uvula. It elevates and retracts the uvula.

Innervation

The general sensory innervation of the palate is supplied by the maxillary branch of the trigeminal nerve (CN V), through the greater and lesser palatine
nerves and the nasopalatine nerve. From the pterygopalatine ganglion, the greater and lesser palatine nerves descend through the palatine canal accompanying the descending palatine artery. 

• The greater palatine nerve enters the palate through the greater palatine foramen alongside the greater palatine artery. It supplies a major portion of the gingiva, mucosa and glands of the hard palate. 
• The lesser palatine nerves pass through the lesser palatine foramen to innervate the soft palate with contributions from the branches of the glossopharyngeal nerve (CN IX). The lesser palatine nerves also carry taste fibers from the greater petrosal branch of the facial nerve (CN VII) to the taste buds of the soft palate. 
• The nasopalatine nerve provides sensory innervation to the region of the hard palate bordering the incisor and canine teeth. 

The motor innervation of the muscles of the soft palate is by the pharyngeal branch of the vagus nerve (CN X) via the pharyngeal plexus of nerves. The exception to this, is the tensor veli palatini muscle, which is innervated by the mandibular branch of the trigeminal nerve (CN V3) via the medial pterygoid nerve. The palate also receives autonomic innervation; parasympathetic secretomotor fibers to its mucous glands and sympathetic fibers to its blood vessels.

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Blood supply

The main arterial supply of the palate is by the descending palatine artery, which is a branch of the maxillary artery within the pterygopalatine fossa. It runs through the palatine canal and gives rise to two branches, the greater and lesser palatine arteries. The greater palatine artery enters the palate through the greater palatine foramen on each side, close to the second molar tooth of the upper jaw. The smaller lesser palatine artery arises from the descending palatine artery within the palatine canal and enters the palate via the lesser palatine foramen. 

The palate is also supplied by the ascending palatine branch of the facial artery. This artery travels alongside the levator veli palatini muscle into the soft palate and forms anastomoses with the lesser palatine artery. 

The veins of the palate largely accompany their corresponding arteries and usually drain into the pterygoid venous plexus within the infratemporal fossa at the base of the skull. The lymphatic drainage of the palate is by the deep cervical nodes.

Function

The palate is involved in feeding, breathing, swallowing, and speech. Along with the tongue, the bony hard palate portion allows for the creation of a partial vacuum force that draws fluid into the oral cavity. This is an essential function in infants as it enables them to suckle. During nasal breathing the soft palate assumes a lowered position, allowing air to move freely in and out of the pharynx through the nasal cavities. During swallowing, however, the soft palate elevates, closing off the nasopharynx to prevent food and liquids from the oral cavity and oropharynx from entering the nasal cavities. The soft palate also plays a key role in the gag reflex; touching the surface of the soft palate or the uvula evokes the gag reflex and can cause vomiting. 

Together with the tongue, the palate plays a key role in articulation (speech production) and language by altering airflow through the oral cavity in order to create a variety of speech sounds. Sounds made with the tongue against the hard palate such as the ‘n’ sound in ‘man’ are referred to as palatal sounds. On the other hand, velar sounds are made with the back of the tongue against the soft palate (velum), for example, the ‘k’ sound in ‘cat’.