The trigeminal nerve or the 5th cranial nerve mainly supplies the skin of the face, conjunctiva and cornea, the mucosa of the nose, sinuses and the frontal part of the oral cavity, as well as most of the dura mater. These nerves arise from the lateral part of the pons in the form of motor and sensory nerve roots. The smaller nerve root, also known as the portio minor trigeminal nerve, is the motor nerve root. Derived from the motor nucleus of the trigeminal nerve in the brainstem, it consists of motor fibers, mainly innervating the muscles of mastication. Physiologically, this nerve root travels through the ganglion medial to the much larger sensory root, before joining the mandibular nerve as it passes through the foramen ovale of the sphenoid bone. The sensory root of the larger trigeminal nerve is called the portio major of the trigeminal nerve, which gives a distribution similar to that of the dorsal nerve roots of the spinal nerves.
The roots of these sensory nerves will pass through the trigeminal ganglion (gasserian ganglion) and from here out three peripheral nerve branches, namely the ophthalmic, maxillary and mandibular branches. The first branch, the ophthalmic nerve, passes through the superior orbital fissure and provides sensory innervation to the scalp from the palpebral fissure to the bregma (mainly from the frontal nerve) and a smaller branch upward and medial to the dorsum. The conjunctiva, cornea and iris, mucosa of the frontal sinus and part of the nose, as well as part of the dura mater and pia-arachnoid are also innervated by fibers, sensory nerves from the ophthalmic nerve.
The second branch, the maxillary nerve, enters the pterygopalatine fossa through the superior maxillary foramen, giving rise to the zygomatic nerve which passes into the orbit through the inferior orbital fissure. Its main trunk, the infraorbital nerve, goes to the floor of the orbit through the same fissure. On exiting the infraorbital foramen, this nerve divides into several branches that spread over the upper maxillary surface of the face lateral to the nose and upper lip. Prior to exiting the infra-orbital foramen, several branches were found that supply the maxillary sinus and molar teeth from the adjacent maxillary, gingiva and oral mucosa. The third branch, which is the largest branch, is the mandibular nerve.
The trigeminal nerve is the largest nerve in the brain. The trigeminal nerve is a sensory nerve that acts on most of the scalp and face; mucous membranes of the mouth, nose, paranasal sinuses and teeth. The trigeminal nerve innervates the muscles of mastication through a small motor branch (Pearce, 2009).
The trigeminal nerve is a motor and sensory brain nerve. Its motor fibers innervate the masseter, temporalis, pterygoid internus et externus muscles, tensor tympani, omohyoid and anterior digastric muscles.
Its motor core is located in the pons. Its motor fibers join with the sensory fibers of the trigeminal nerve originating from the Gasseri ganglion. Its sensory fibers transmit impulses of pain, temperature, touch and proprioceptive feelings. Its areas are the face and mucosa of the tongue and the oral cavity as well as the tongue, and the nasal cavity. Proprioceptive impulses originate mainly from muscles innervated by the mandibular branch to the Gasseri ganglion.
The trigeminal nerve is divided into three main branches, namely (Pearce.2009):
- Ophthalmic Nerve. It is sensory in nature and functions to innervate the scalp in the front of the upper eyelid, the mucous membrane of the eyelids and the eyeball.
- Maxillary Nerve. It is sensory in nature and functions to innervate the upper teeth, upper lip, palate, nasal bridge, nasal cavity, and maxillary sinus.
- Mandibular Nerve. It is compound (sensory and motor), its motor fibers innervate the muscles of mastication, sensory fibers innervate the lower teeth, the skin of the temporal region and the chin. The fibers of the oral cavity and tongue can carry taste stimuli to the brain.
Its function is as a triplet nerve where this nerve is the largest brain nerve which has 2 large nerve roots containing driving nerve fibers. And at the end of the smallest spinal column contains the driving nerve fibers. At the end of the ossicles the taste buds form a ganglion called the nerve node and leave the cranial cavity.
Trigeminal nerve function can be assessed through various examinations as follows (Pearce.2009)
- Examination of the sense of temperature, pain and touch in the area of the innervation of the V nerve (the face and the ventral part of the calvaria).
- Corneal reflex test.
- Examination of the function of the muscles of mastication. For example, by asking the patient to close both jaws tightly, so that the teeth in the lower jaw press against the teeth in the upper jaw, while masseter muscle and temporal muscle can be easily palpated.
- The functions of the cutaneous, maxillary and mandibular branches are important in dentistry. The maxillary nerve provides sensory innervation to the maxillary teeth, palate, and gingiva. The mandibular branch provides sensory innervation to the mandibular teeth, tongue, and gingiva. The variety of nerves that supply innervation to the tooth is transmitted to the alveolaris, to the socket where the tooth originates. The superior alveolar nerve to the maxillary tooth originates from the maxillary branch of the trigeminal nerve. The inferior alveolar nerve to the mandibular teeth originates from the mandibular branch of the trigeminal nerve.