The Versatile Role of the Vagus Nerve in the Gastrointestinal Tract

The vagus nerve, the major nerve of the parasympathetic nervous system, innervates several organs from the neck to the abdomen. The vagal branches contain afferent (i.e. sensory) and efferent (i.e. motor) fibres contributing to a bidirectional communication between the visceral organs and the brain. The extensive vagal innervation of the body indicates that vagus nerve has a multitude of physiological functions. Specifically, the gastrointestinal (GI) tract is densely innervated by the vagus nerve and the latter plays a crucial role in GI functions such as food intake, digestion, and GI barrier function. In addition, the vagus nerve has immunomodulatory properties suggesting that activation of the parasympathetic innervation of the GI tract could act as a new therapeutic tool to treat intestinal immune diseases. This review summarises the anatomical and physiological properties of the vagal innervation of the GI tract.