The vagus nerve [vey-guhs] is the tenth of twelve cranial nerves. Besides output to the various organs in the body, the vagus nerve conveys sensory information about the state of the body’s organs to the central nervous system. 80-90% of the nerve fibers in the vagus nerve are afferent (sensory) nerves communicating the state of the viscera to the brain. The medieval Latin word ‘vagus’ means literally ‘Wandering’ (the words vagrant, vagabond, and vague come from the same root). Sometimes the branches are spoken of in the plural and are thus called vagi.
Activation of the vagus nerve typically leads to a reduction in heart rate, blood pressure, or both. This occurs commonly in the setting of gastrointestinal illness or in response to other stimuli, including carotid sinus massage, Valsalva maneuver, or pain from any cause, particularly having blood drawn. When the circulatory changes are great enough, vasovagal syncope results. Relative dehydration tends to amplify these responses.
Excessive activation of the vagal nerve during emotional stress, which is a parasympathetic overcompensation of a strong sympathetic nervous system response associated with stress, can also cause vasovagal syncope because of a sudden drop in blood pressure and heart rate. Vasovagal syncope affects young children and women more often. It can also lead to temporary loss of bladder control under moments of extreme fear.
Research has shown that women who have complete spinal cord injury can experience orgasms through the vagus nerve, which can go from the uterus, cervix and probably the vagina to the brain.
