Neurobiology of visceral nociception

The gastrointestinal tract is served by a complex network of intrinsic and extrinsic sensory innervation. Stimuli are detected by afferents (vagal and spinal) which have different stimulus-response functions. Vagal afferents are responsible for low threshold activity whereas spinal afferents encode both physiological and supraphysiological levels of intestinal pressure. It is therefore likely that vagal and spinal afferents play different roles in mediating sensation.

Spinal afferents form the main pathway for radiating pain perception while vagal afferents are probably involved in emotional and behavioural aspects rather than in cognition of pain. Some vagal afferents project to the cervical regions of the spine and influence spinothalamic pathways between C1 and C3; these are thought to be involved in perception of referred pain.

Reflex modulation of gastrointestinal function

Prevertebral ganglia form an extended neural network which connects the lower to the upper gastrointestinal tract. Intestinofugal afferent neurones (IFANs) are a unique subset of myenteric ganglion neurones which function as slowly adapting mechanoreceptors. They relay mechanosensory information to prevertebral sympathetic ganglion neurones and function as volume detectors, thus providing …