Figure 4 Connections of sympathetic nerve fibres (purple) with structures in the intestinal wall. A plus sign indicates a positive and a minus sign indicates a negative influence. (1) Sympathetic nerve fibres terminate at motoneurones in myenteric plexus ganglia (grey ellipses). Here, norepinephrine (NE) inhibits descending motoneurones (ACh, acetylcholine; SP, substance P) via α2 adrenergic signalling. (2) Immune stimuli from the lumen and in the mucosa stimulate sensory neurones of the vagus, which locally release SP and signal the information to higher centres. SP can attract leucocytes (blue) and can support vasodilation (line with two arrows in the blood vessel (BV)). Via α1 adrenergic receptors, NE leads to vasoconstriction (opposite to SP). (3) Distension and mucosal stimuli can stimulate intrinsic afferent neurones, which modulate motoneurones. (4) Modulation of vascular tone via dilatory signals (SP; CGRP, calcitonin gene related peptide; NO, nitric oxide; VIP, vasoactive intestinal peptide) and constriction signals (SOM, somatostatin; NE via α1 adrenergic receptors). (5) Regulation of the secretory neurone of the submucosal plexus by secretory signals (ACh) and inhibitory signals (NE via α2 adrenoceptors; SOM). (6) Stimulation of intrinsic afferent neurones by serotonin (5‐HT). These neurones are coupled to motoneurones and secretory neurones as wells as interneurones in the myenteric plexus. (7) Local efferent sympathetic nerve fibres travel along blood vessels (BV) into the submucosa and mucosa and terminate next to epithelial cells. These efferent fibres can modulate immune responses in the vicinity of mucosal blood vessel. ATP, adenosine triphosphate.