Twelve pairs of cranial nerves arise in the brain and give off branches to the structures of the head and face. These nerves leave the cranial cavity through foramina in the base of the cranium. The fifth cranial nerve (the trigeminal nerve) is the largest of the twelve pairs. See figure 2-13. It is of particular importance in dentistry since it provides the nerve supply to the jaws and the teeth. The fifth cranial nerve contains both motor and sensory fibers. Thus, it has a motor root supplying motor impulses to the muscles of mastication and a sensory root supplying sensory impulses from the structures of the head and face. Before leaving the cranial cavity, the sensory root divides into three branches or divisions.
a. Ophthalmic Nerve or First Division. This division supplies sensation to the eyes, the tear-producing glands, the mucous lining of the nose, the eyelids, the eyebrows, and the forehead.
b. Maxillary Nerve or Second Division. This division supplies sensation to the central part of the face, including the maxillary bone, all the maxillary teeth, the soft tissues of the hard palate, and the soft tissues surrounding the teeth. It contains no somatic motor fibers.
(1) The maxillary teeth. The maxillary nerve on each side passes forward in the floor of the orbit of the eye. It first gives off the posterior superior alveolar branch to the three maxillary molars. When in the floor, the maxillary nerve gives off a middle superior alveolar branch to the maxillary bicuspids and mesial root of the first molar. Then, the maxillary nerve gives off an anterior superior alveolar branch to the maxillary incisors and cuspid.
(2) The palatal area. The maxillary nerve on each side gives off a palatine nerve, which has an anterior, middle, and posterior branch. The anterior palatine nerve emerges upon the hard palate through the greater palatine foramen, and passes forward nearly to the incisor teeth where it ends with fibers of the nasopalatine nerve. It supplies the gingiva (gum tissue), the mucous membrane, and the glands of the hard palate and part of the soft palate. The middle and posterior palatine nerves reach the soft palate area through the lesser palatine foramina and give off branches to the uvula, tonsil, and soft palate.
(3) The nasopalatal area. Another branch of the maxillary nerve gives rise to the nasopalatine nerve. This nerve descends to the roof of the mouth through the incisive canal and communicates with the corresponding nerve of the opposite side and with the anterior palatine nerve.
c. Mandibular Nerve or Third Division. This division supplies sensation to the mandible and the teeth. It contains somatic motor fibers as well as sensory nerve fibers. (The first two divisions are primarily sensory.) This nerve passes downward to enter the mandible through the mandibular foramen. Before entering the foramen, it gives off branches to the muscles of mastication and a large sensory branch to the tongue. Thus, it provides motor impulses for mastication and general sensation to the anterior two thirds of the tongue, the mandible and the mandibular teeth, the soft tissues of the tongue, the soft tissues of the floor of the mouth, and the soft tissues surrounding the teeth.
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