An Overview of the Oral Cavity
The mouth, or oral cavity, includes your teeth, gums, the soft and hard palates, tongue, tonsils, and salivary glands. These oral structures allow you to eat and drink as well as breathe when your nose is plugged. Your mouth also works with the larynx to help you speak.
Anteriorly, the oral cavity begins behind the opening of the lips, called the oral fissure, and posteriorly it opens into the oropharynx.
The oral cavity is divided into the oral cavity proper and the vestibule.
Oral cavity proper: This space includes everything behind the teeth. The roof of the mouth is formed by the hard palate, and the floor is formed by the anterior two-thirds of the tongue and the mucous membrane that covers the sides of the tongue and attaches it to the mandible.
Vestibule: This space is between the cheeks and lips externally and the teeth and gums internally. Two muscular fleshy folds (the lips) surround the oral fissure. Skin covers the lips externally, and the interior is lined with a mucous membrane. Median folds of the mucous membrane called the labial frenulae connect the lips to the gums. The lips contain the orbicularis oris, which puckers the lips and is sometimes referred to as the kissing muscle. The little groove that runs from the upper lip toward the nose is called the philtrum.
The walls of the vestibule are formed by the internal surface of the cheeks, which contain the buccinator muscles, and are also covered internally with mucous membrane.
The teeth and gums
The teeth are firmly affixed to the upper and lower jaws in sockets called dental alveoli. Teeth are used for biting, chewing, and assisting with speaking. Children have 20 primary teeth, and adults have 32. Sixteen teeth are in each jaw. Most of these teeth erupt by the middle of the teenage years, but wisdom teeth may not erupt until the 20s.
The gingivae are made of fibrous connective tissue and covered with a mucous membrane. The gingivae are attached to the alveolar processes of the mandible and maxilla and the necks of the teeth.
The palate forms the roof of the mouth and the floor of the nasal cavities. It has two parts: a hard palate and a soft palate:
The hard palate forms the anterior part of the palate. It’s formed by the palatine process of the maxilla and the horizontal plates of the palatine bones. The hard palate is covered by a mucous membrane and has the following three foramina:
Incisive fossa: This opening is posterior to the central (incisor) teeth. It allows passage of the nasopalatine nerves.
Greater palatine foramen: This opening is located on the lateral portion of the palate. It allows passage of the greater palatine vessels and nerve.
Lesser palatine foramen: Posterior to the greater palatine foramen, this opening allows the lesser palatine nerves and vessels to pass through to the soft palate.
The soft palate extends posteriorly and inferiorly from the hard palate and is strengthened by the palatine aponeurosis, which is a tendinous sheet. A conical, fleshy process called the uvula hangs from the back of the soft palate and is visible when the mouth is open wide. Laterally, the soft palate connects to the wall of the pharynx. It’s joined to the tongue and the pharynx by the palatoglossal and palatopharyngeal arches. Clumps of lymphoid tissue called the palatine tonsils are located between these arches.
The soft palate works with the tongue to produce movements that help you swallow and force food into the esophagus. It also rises during swallowing to close off the opening between the oropharynx and the nasopharynx to prevent food and liquid from entering your nose. These five muscles also help with swallowing:
Tensor veli palatini: This muscle originates on the sphenoid bone and the cartilage of the pharyngotympanic tube and inserts onto the palatine aponeurosis. It’s innervated by the nerve to the medial pterygoid (CN V3) and tenses the soft palate and opens the pharyngotympanic tube when yawning or swallowing.
Levator veli palatini: Originating on the pharyngotympanic tube and part of the temporal bone, this muscle inserts onto the palatine aponeurosis. It’s innervated by the pharyngeal branch of the vagus nerve (CN X). It elevates the soft palate during yawning or swallowing.
Palatoglossus: This muscle originates on the palatine aponeurosis and inserts on the side of the tongue. It’s innervated by the pharyngeal branch of the vagus nerve and elevates the posterior part of the tongue while drawing the soft palate to the tongue.
Palatopharyngeus: Originating on the hard palate and palatine aponeurosis, this muscle inserts into the thyroid cartilage and the lateral wall of the pharynx. It’s innervated by the pharyngeal branch of the vagus nerve and tenses the soft palate and pulls the pharynx toward the oral cavity during swallowing.
Musculus uvulae: This muscle originates on the posterior nasal spine of the palatine bone and palatine aponeurosis and inserts into the mucosa of the uvula. It’s innervated by the pharyngeal branch of the vagus nerve, and it pulls the uvula upward.