Extrinsic Sensory Afferent Nerves Innervating the Gastrointestinal Tract in Health and Disease

Our gastrointestinal tract is innervated by specific classes of extrinsic sensory afferents, which follow either vagal or spinal pathways. Vagal afferents have cell bodies located within the nodose or jugular ganglia and project centrally to the brainstem. In contrast, spinal afferents have cell bodies in thoracic or sacral dorsal root ganglia and project centrally to the dorsal horn of the spinal cord. Together, these afferent pathways detect ongoing changes in the physical and chemical environment within the lumen and wall of our gastrointestinal tract. Consequently, these afferents convey the full spectrum of information that underlies the initiation of autonomic reflex control and all manner of visceral sensations, including hunger, fullness and urge. In pathological states these afferents also represent the underlying basis of ongoing symptoms such as bloating, discomfort and chronic visceral pain. This chapter will map out the anatomy and function of specific classes of sensory afferents innervating the gastrointestinal tract. Furthermore, it will highlight the key molecular mechanisms underlying the hypersensitivity of extrinsic sensory afferents innervating the gastrointestinal tract, which provides potential opportunities for the therapeutic treatment of gastrointestinal disorders.