The oral cavity is separated into two regions by the upper and lower dental arches consisting of the teeth and alveolar bone that supports them (Fig. 8.247B):
The outer oral vestibule, which is horseshoe shaped, is between the dental arches and the deep surfaces of the cheeks and lips—the oral fissure opens into it and can be opened and closed by muscles of facial expression, and by movements of the lower jaw.
The inner oral cavity proper is enclosed by the dental arches.
The degree of separation between the upper and lower arches is established by elevating or depressing the lower jaw (mandible) at the temporomandibular joint.
The oropharyngeal isthmus at the back of the oral cavity proper can be opened and closed by surrounding soft tissues, which include the soft palate and tongue.
The oral cavity has multiple functions:
It is the inlet for the digestive system involved with the initial processing of food, which is aided by secretions from salivary glands.
It manipulates sounds produced by the larynx and one outcome of this is speech.
It can be used for breathing because it opens into the pharynx, which is a common pathway for food and air. For this reason, the oral cavity can be used by physicians to access the lower airway, and dentists use “rubber dams” to prevent debris such as tooth fragments from passing through the oropharyngeal isthmus and pharynx into either the esophagus or the lower airway.
Multiple nerves innervate the oral cavity
General sensory innervation is carried predominantly by branches of the trigeminal nerve [V]:
The upper parts of the cavity, including the palate and the upper teeth, are innervated by branches of the maxillary nerve [V2].
The lower parts, including the teeth and oral part of the tongue, are innervated by branches of the mandibular nerve [V3].
Taste (special afferent [SA]) from the oral part or anterior two-thirds of the tongue is carried by branches of the facial nerve [VII], which join and are distributed with branches of the trigeminal nerve [V].
Parasympathetic fibers to the glands within the oral cavity are also carried by branches of the facial nerve [VII], which are distributed with branches of the trigeminal nerve [V].
Sympathetic fibers in the oral cavity ultimately come from spinal cord level T1, synapse in the superior cervical sympathetic ganglion, and are eventually distributed to the oral cavity along branches of the trigeminal nerve [V] or directly along blood vessels.
All muscles of the tongue are innervated by the hypoglossal nerve [XII], except the palatoglossus, which is innervated by the vagus nerve [X].
All muscles of the soft palate are innervated by the vagus nerve [X], except for the tensor veli palatini, which is innervated by a branch from the mandibular nerve [V3]. The muscle (mylohyoid) that forms the floor of the oral cavity is also innervated by the mandibular nerve [V3].
Bones that contribute to the skeletal framework of the oral cavity or are related to the anatomy of structures in the oral cavity include: the paired maxillae, palatine, and temporal bones, and the unpaired mandible, sphenoid, and hyoid bones.
In addition, the cartilaginous parts of the pharyngotympanic tubes on the inferior aspect of the base of the skull are related to the attachment of muscles of the soft palate.
The two maxillae contribute substantially to the architecture of the roof of the oral cavity. The parts involved are the alveolar and palatine processes (Fig. 8.248A).