Question

1. Identify the effects of the vagus nerve on the following components of the digestive system:

a. Salivary glands

b. Pyloric sphincter (gastric emptying)

c. Smooth muscle in the gallbladder

d. Smooth muscle in the duodenal papilla (sphincter of Oddi)

Answer 1

a) The parasympathetic fibers leave the brain in the facial (VII CN), glossopharyngeal (IX CN), and vagus (X CN) nerves. Parasympathetic denervation of the major salivary glands leads to an immediate reduction of salivary secretion.

b) Vagus nerve stimulation significantly accelerated gastric emptying by promoting the relaxation of the pyloric sphincter.

c) The gallbladder receives parasympathetic, sympathetic and sensory innervation. The coeliac plexus carries sympathetic and sensory fibres, while the vagus nerve delivers parasympathetic innervation.

The existence of CCK receptors in the vagal nerve and gallbladder was examined by means of autoradiography. Forty-eight hours after ligation of the abdominal vagus, CCK-8 binding sites were found to accumulate in the subdiaphragmatic vagal nerve immediately proximal to the ligature, and similar binding sites were also found in the gallbladder smooth muscle layer.

d) Vagal stimulation induces sphincter contraction. After administration of sympathetic blockers and atropine, vagal stimulation relaxes the sphincter suggesting a non‐cholinergic non‐adrenergic effect. ... Intrinsic nerves have a prominent role in controlling Sphincter of Oddi activity.