Cranial Nerves 101

Cranial nerves 101 

To learn about neuropathic facial pain, it helps to know a little about how the affected nerves are laid out. The cranial nerves are 12 pairs of nerves that can be seen on the surface of the brain. The trigeminal nerves are among these pairs, and they let you feel sensations in your face. One nerve runs down each side of your head.

The sets of cranial nerves arise directly from the brain. The first two nerves (olfactory and optic) arise from the cerebrum, whereas the remaining ten emerge from the brain stem. The cranial nerves are considered components of the peripheral nervous system. However, on a structural level, the olfactory, optic, and terminal nerves are more accurately considered part of the central nervous system.

The names of the cranial nerves relate to their function and they are also numerically identified in roman numerals (I-XII).

  • The olfactory nerve (I): This is instrumental for the sense of smell, it is one of the few nerves that are capable of regeneration.
  • The optic nerve (II): This nerve carries visual information from the retina of the eye to the brain.
  • The oculomotor nerve (III): This controls most of the eye’s movements, the constriction of the pupil, and maintains an open eyelid.
  • The trochlear nerve (IV): A motor nerve that innervates the superior oblique muscle of the eye, which controls rotational movement.
  • The trigeminal nerve (V): This is responsible for sensation and motor function in the face and mouth.
  • The abducens nerve (VI): A motor nerve that innervates the lateral rectus muscle of the eye, which controls lateral movement.
  • The facial nerve (VII): This controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity.
  • The vestibulocochlear nerve (VIII): This is responsible for transmitting sound and equilibrium (balance) information from the inner ear to the brain.
  • The glossopharyngeal nerve (IX): This nerve receives sensory information from the tonsils, the pharynx, the middle ear, and the rest of the tongue.
  • The vagus nerve (X): This is responsible for many tasks, including heart rate, gastrointestinal peristalsis, sweating, and muscle movements in the mouth, including speech and keeping the larynx open for breathing.
  • The spinal accessory (XI): This nerve controls specific muscles of the shoulder and neck.
  • The hypoglossal nerve (XII): This nerve controls the tongue movements of speech, food manipulation, and swallowing.

Some of these nerves bring information from the sense organs to the brain, others control muscles, or are connected to glands or internal organs such as the heart and lungs. Cranial nerves can transmit two types of information: 

  • Sensory information includes details about smells, sights, tastes, touch, and sounds to the brain.
  • Motor information refers to signals that affect the movement or activity of muscles and glands. 

The trigeminal nerve 

The trigeminal nerve is the 5th cranial nerve, supplying sensation to the face, eyes, nose, lips, teeth, gums, part of the tongue, and part of the scalp. There are two trigeminal nerves, one on each side of the face; the trigeminal nerve is the largest and most complex of the 12 cranial nerves. Each side contains three branches, or divisions (diagram). From the top, they are the ophthalmic (V1), the maxillary (V2) and mandibular (V3). You may experience pain in one or more of the areas of your face, head and neck, depending on which nerves are affected. Each trigeminal nerve splits into three branches, controlling the feeling for different parts of your face:

  • Ophthalmic branch controls your eye, upper eyelid, and forehead.
  • Maxillary branch affects your lower eyelid, cheek, nostril, upper lip, and upper gums.
  •  Mandibular branch runs your jaw, lower lip, lower gum, and some muscles you use for chewing.

Nerves power your entire body. They can be damaged by injury or an illness such as diabetes. Neuropathy is a disorder of nerve damage, affecting your ability to feel and move. Exactly how your body and your movement are affected depends on where in the body the damaged nerves are located. When nerves in the brain or brainstem are affected, it is called cranial neuropathy.

How can nerves be injured? 

  • Mechanical injury (pressure, impact) 
  • Thermal injury (excessive heat or cold) 
  • Chemical injury
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