ABDOMINAL AND PELVIC VISCERAL RECEPTORS BFLeek ABDOMINAL AND PELVIC VISCERAL RECEPTORS

The abdominal and pelvic viscera are innervated by the vagaL splanchnic and pelvic nerves. It is estimated that these nerves have afferent:efferent fibre ratios of 9:1, 3:1 and 1:1, respectively. Despite this numerical preponderance of sensory fibres, the roles of the visceral input remain rather vague. Visceral sensory mechanisms are investigated by applying different kinds of stimulus to specific visceral structures and recording the evoked responses. The problems arising from this are that the common forms of stimulation (e.g. distension) excite more than one kind of receptor, and that one receptor type may be excited by several unrelated kinds of stimuli. The magnitude of these problems depends upon the methods of recording the evoked responses, which fall into three groups: (i) descriptions of conscious visceral sensations in man; 00 studies of reflex responses in experimental animals; and (iii) electrophysiological recording of the nervous activity in afferent visceral pathways. Only the last-named methods are capable of differentiating between the responses of different kinds of receptor and of circumventing the problems. The present review will be confined therefore largely to a discussion of the results arising from the use of electrophysiological recording techniques. However, the results obtained under the above three headings are complementary. Whilst the electrophysiological techniques demonstrate receptor responses, sensory descriptions and reflex studies are necessary for determining the functional significance of changes in visceral afferent nerve inputs made evident by the electrophysiological recordings.