The salivary glands are innervated by the parasympathetic and sympathetic branches of the autonomic nervous system.
Parasympathetic stimulation flavours serous (watery) secretion and occurs via cranial nerves, with the glossopharyngeal nerve innervating the parotid, and the facial nerve innervating the submandibular and the sublingual glands. These release acetylcholine and substance P, neurotransmitters that bind to receptors on acinar and ductal cells of the salivary glands.1,11
Direct sympathetic stimulation flavours viscous (mucoid) secretion and takes place via preganglionic nerves in the thoracic segment of the spinal cord which synapse with postganglionic neurons. These release the neurotransmitter norepinephrine that binds to receptors on the salivary gland acinar and ductal cells. There is also indirect sympathetic stimulation of the salivary glands via innervation of the blood vessels that supply the glands.1,11
With both types of stimulation, the binding of neurotransmitters to salivary gland receptors leads to increases in intracellular calcium and alterations in membrane permeability, and a corresponding increase of saliva, as organic molecules, electrolytes, water and mucus are excreted into the acinar lumen.1,11