Fig. 1

Schematic diagram of the main central and peripheral components of the motor and sensory vagus. The vagus nerve includes sensory (afferent) and motor (efferent) arms, both of which are represented in the cervical region, where vagus cuffs are typically implanted. The sensory vagal pathway, shown in green, originates with general sensory receptors (i.e. nociceptors) in visceral organs, including vessels, the lungs, the heart, the gastrointestinal tract, the liver, lymph nodes etc. They convey information about mechanical parameters, e.g. increased wall tension in vessels in high blood pressure or in lung alveoli during inhalation, or biochemical events, e.g. presence of bacteria or inflammatory cytokines at an injured site. Afferent fibers from these receptors synapse at sensory neurons in the nodose ganglion of the vagus, located at the height of the transverse process of the first cervical vertebra. Axons of those sensory ganglionic neurons project to the nucleus of the solitary tract (NTS), in the brainstem. The motor vagal pathway, shown in red, originates in the motor nuclei of the vagus in the brainstem, the dorsal motor nucleus (DMN) and the nucleus ambiguous (NA). Peripheral axons of those cells go through the cervical vagus, and either innervate laryngeal muscles, or synapse on neurons in parasympathetic ganglia, close to organs like the heart, the lungs, the intestine, the pancreas, etc. An important target of the motor vagus is the spleen; in this case, motor vagal fibers synapse at the celiac ganglion, from which adrenergic fibers project to the spleen