Nervus trigeminus is the nerve responsible for feeling sensations in the face and also controls the motions of biting and chewing. Also called the fifth cranial nerve, the Latin term nervus trigeminus literally translates as "three twins," because the nerve branches into three sections on both sides of the face. It extends from the lateral surface of the pons into the skull and splits into the ophthalmic nerve, the maxillary nerve, and the mandibular nerve.
Four of nervus trigeminus’ six branches only act as sensory nerves. The ophthalmic nerves provide sensation to the upper part of the face. Ophthalmic nerves supply several parts of the eye as well as part of the nasal cavity and the skin of the nose, eyelids, eyebrows, and forehead. Maxillary nerves supply sensations to the middle part of the face, including parts of the nasal cavity, the sinuses, the upper lip, and mouth.
The mandibular nerves are the largest of nervus trigeminus’ nerves and the only to cause motion. They extend down the jaw bone and control feeling in the lower jaw, the lower lip, and the lower gum. Also, they control some of the muscle activity in the lower jaw, which allows the face to bite, chew, and perform part of the motion for swallowing. The nerves for motor control are the smallest of the nervus trigeminus.
It is clear from its physiology that the most important role of the nervus trigeminus is that of sensation. The sensory nerves that make it up find their root in the largest cranial nerve, which extends down to the second cervical level of the spinal cord. On the other hand, the motor control nerve finds its root in the masticator motor nucleus, serving one specific purpose. The sensitivity of nervus trigeminus allows the face to feel subtle sensations, but also allows for one of the most painful conditions known to humankind, called trigeminal neuralgia.
Trigeminal neuralgia occurs when the nervus trigeminus becomes inflamed. Sharp pain that lasts seconds, and sometimes minutes, extends from the eye to the lower part of the face, usually on one side. Simple actions such as chewing or shaving can trigger the excruciating pain.
Generally, trigeminal neuralgia is most common among older adults, although cases have been noted in patients of all ages. The cause of this pain is often difficult to find. Brain swelling is one of the primary suspects, which causes a vein or artery to touch the nerve in the brain. Doctors try to mitigate the pain with medication and sometimes even surgery.