This chapter has concentrated on why, under certain circumstances and in certain disease states, we experience altered sensations in our gut, most commonly in the form of pain. In the first paper, Gerald Gebhart has posed several questions. Are there visceral pain receptors (nociceptors) in the gut and do the visceral afferent fibres linking these receptors to the spinal cord become sensitised in some way so that hyperalgesia is the result? Balloon distension experiments, which are considered to produce a reliable stimulus to hollow viscera, have been used in both humans and animals to explore these questions. Sensory innervation of the gastrointestinal tract involves all layers—that is, mucosa, muscle, and serosa. It would appear that visceral receptors are polymodal in character (that is, they respond to different kinds of stimuli). They appear to be chemosensitive, thermosensitive, and mechanosensitive. The visceral afferent neurones leading from these receptors pass through or near to prevertebral and paravertebral ganglia on their way to the …