The trigeminal nerve is the fifth cranial nerve. It is primarily a sensory nerve, but also has motor divisions. The sensory part of the trigeminal nerve emerges from the skull. It divides into the ophthalmic, maxillary and mandibular divisions and passes through the superior orbital fissure, foramen rotundum and the foramen ovale. The ophthalmic division of this nerve carries sensations from the scalp, forehead, upper eyelid, the cornea and conjunctiva of the eyes, the nose excluding the alae nasi, the nasal mucosa, frontal sinuses and parts of the meninges. The maxillary division of the trigeminal nerve carries sensations from the lower eyelid, cheek, upper lip, nares, upper teeth and gums, the nasal mucosa, the palate and the roof of the pharynx, the maxillary, sphenoid and ethmoid sinuses and part of the meninges. The mandibular division of the trigeminal nerve carries sensations from the lower lip, lower teeth and gums, chin, jaw and parts of the external ear and meninges. The sensations of touch, position and pain and temperature of the mouth are carried by the mandibular division. The taste sensation from the mouth is carried by the chorda tympani.
The motor branches of the trigeminal nerve are distributed through the mandibular nerve. The motor branch supplies the eight muscles in all including the four muscles of mastication. The motor branch arises from the motor nucleus of the trigeminal nerve which is located in the pons close to the main trigeminal nerve nucleus. The motor supply is distributed to the following muscles – masseter, temporalis, and medial pterygoid and the lateral pterygoid, mylohyoid, tensor tympani, tensor veli palatine and anterior belly of digastric. Most of these muscles (excluding tensor tympani) are involved in biting, chewing and swallowing. A central lesion like a cerebrovascular accident will not produce any observable defect. Injury to the peripheral nerve will cause paralysis of muscles on the one side of the jaw and the jaw on opening will deviate to the paralyzed side.
Clinical significance of the Trigeminal nerve: Trigeminal neuralgia is condition which affects the trigeminal nerve. It is also known as tic douloureux. In case you are suffering from trigeminal neuralgia you will have episodes of severe pain in the face. You will feel the pain along the sensory distribution of the nerve; like over the eyes, ears, lips, nose, scalp, forehead, cheeks, teeth and jaw. You may experience the pain for a few seconds or minutes to a few hours. You may find a trigger spot on your face which is an extremely sensitive point and elicits pain when touched. The pain may develop with or without any stimulation of this trigger spot. You may be completely asymptomatic in between the episodes of pain. It is known to be one of the most painful conditions in man. The remissions may last over a period of weeks to months to a few years. It is known to commonly affect people above the age of 50 years. It is more commonly seen in females than in males.
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