from Pub Med,
The sympathetic and parasympathetic components of the autonomic nervous system (ANS) control and regulate the function of various organs, glands, and involuntary muscles throughout the body (e.g., vocalization, swallowing, heart rate, respiration, gastric secretion, and intestinal motility). The vagus nerve (cranial nerve X) is a mixed nerve composed of 20% “efferent” fibers (sending signals from the brain to the body) and 80% “afferent” (sensory) fibers (carrying information from the body to the brain). The efferent cholinergic fibers are the main parasympathetic component of the ANS [1], but an important function of the vagus nerve is transmitting and/or mediating sensory information from throughout the body to the brain [2]. The right and left vagus nerves exit from the brainstem, and they course through the neck (in the carotid sheath between the carotid artery and jugular vein), upper chest (along the trachea), lower chest and diaphragm (along the esophagus), and into the abdominal cavity [3]. During this course, branches enervate various structures such as the larynx, pharynx, heart, lungs, and gastrointestinal tract. In the brainstem, the sensory afferent fibers terminate in the nucleus tractus solitarius, which then sends fibers that connect directly or indirectly to different brain regions. These regions include the dorsal raphe nuclei, locus ceruleus, amygdala, hypothalamus, thalamus, and orbitofrontal cortex.
