Two cranial nerves control saliva production in the major salivary glands: the facial nerve (CN VII) drives the submandibular and sublingual glands, while the glossopharyngeal nerve (CN IX) drives the parotid gland. Both deliver parasympathetic signals that trigger the watery saliva you produce throughout the day. Sympathetic fibers also reach all three glands, but these originate from the spinal cord rather than from cranial nerves.
The Facial Nerve and the Submandibular and Sublingual Glands
The facial nerve (CN VII) provides parasympathetic, secretomotor innervation to the two glands that sit beneath and behind your tongue: the submandibular gland and the sublingual gland. The preganglionic fibers originate in the superior salivatory nucleus, a cluster of neurons in the brainstem located lateral to the abducens nucleus and behind the facial motor nucleus.
From there, the fibers travel as a branch called the chorda tympani. This small nerve follows a remarkable path: it splits off from the facial nerve just above the stylomastoid foramen, enters the middle ear cavity, and crosses the inner surface of the eardrum, passing between the malleus and incus (two of the tiny bones of hearing). It exits the middle ear through a narrow slit called the petrotympanic fissure and enters the infratemporal fossa, where it merges with the lingual nerve, a branch of the mandibular division of the trigeminal nerve.
Riding along with the lingual nerve, the parasympathetic fibers reach the submandibular ganglion, which hangs off the lingual nerve near the floor of the mouth. Here, the preganglionic fibers synapse. The postganglionic fibers then travel a short distance to stimulate saliva production in both the submandibular and sublingual glands. Together, these two glands produce the majority of your resting saliva.
The Glossopharyngeal Nerve and the Parotid Gland
The parotid gland, the largest salivary gland, sits just in front of each ear and receives its parasympathetic supply from the glossopharyngeal nerve (CN IX). The preganglionic fibers begin in the inferior salivatory nucleus, which is located in the medulla behind a structure called the nucleus ambiguus.
These fibers exit the skull through the jugular foramen and reach the inferior ganglion of CN IX. A small branch called the tympanic nerve (also known as Jacobsen’s nerve) carries them back into the middle ear, where they form the tympanic plexus. The fibers then continue as the lesser petrosal nerve, which runs through the middle cranial fossa and exits through the foramen ovale.
Just below the foramen ovale lies the otic ganglion, the smallest of the four parasympathetic ganglia in the head, measuring roughly 2 by 1.5 millimeters. This is where the preganglionic fibers synapse. The postganglionic fibers hitch a ride with the auriculotemporal nerve (a branch of the mandibular division of the trigeminal nerve) to reach the parotid gland and stimulate saliva release. The parotid gland is especially active during meals, producing the thinner, enzyme-rich saliva that begins breaking down starches.
Sympathetic Supply to All Three Glands
All three major salivary glands also receive sympathetic innervation, but this does not come from cranial nerves. The preganglionic sympathetic fibers originate in the upper thoracic spinal cord and ascend to synapse in the superior cervical ganglion in the neck. From there, postganglionic fibers travel alongside the blood vessels that supply each gland.
Sympathetic stimulation releases norepinephrine onto the saliva-producing cells. This triggers two effects: it causes smooth muscle contraction that pushes out stored saliva, and it increases output of amylase, the enzyme that digests starch. Contrary to a common simplification, sympathetic stimulation does not just “dry out” the mouth. It produces a smaller volume of thicker, protein-rich saliva while also causing brief increases in overall flow.
Minor Salivary Glands
Hundreds of minor salivary glands are scattered throughout the lining of your lips, cheeks, palate, and tongue. These tiny glands also receive both parasympathetic and sympathetic nerve fibers. Immunohistochemical studies have identified the chemical signatures of parasympathetic neurons (acetylcholine and vasoactive intestinal polypeptide) in nerve fibers surrounding the secretory cells and ducts of these glands. The parasympathetic supply to minor glands in the palate and tongue routes through the same ganglia that serve the major glands: the submandibular ganglion and the otic ganglion. The density of nerve fibers varies by location; palatal glands, for example, tend to have more abundant parasympathetic innervation than labial glands.
What Triggers Saliva Production
The inferior salivatory nucleus (for the parotid) and superior salivatory nucleus (for the submandibular and sublingual glands) do not fire on their own. They receive input from several brain regions: the hypothalamus, the olfactory system, and the nucleus of the solitary tract, which processes taste information. This is why the sight, smell, and taste of food all increase saliva flow. Even thinking about food can activate these pathways through hypothalamic connections.
When Nerve Pathways Go Wrong
Because the nerve pathways to the salivary glands are long and winding, they are vulnerable to disruption. One well-known example is Frey syndrome, which can develop after parotid gland surgery or trauma to the area in front of the ear. During healing, the parasympathetic nerve fibers that originally stimulated the parotid gland regrow into the wrong targets, specifically the sweat glands and blood vessels in the overlying skin. The result is gustatory sweating: flushing and sweating on the cheek during eating, because the acetylcholine released to trigger saliva production now activates sweat glands instead. This misdirection involves the postganglionic parasympathetic fibers that normally travel with the auriculotemporal nerve to the parotid.
Quick Reference by Gland
- Parotid gland: Glossopharyngeal nerve (CN IX), inferior salivatory nucleus, synapse at the otic ganglion, postganglionic fibers via the auriculotemporal nerve
- Submandibular gland: Facial nerve (CN VII), superior salivatory nucleus, fibers carried by the chorda tympani, synapse at the submandibular ganglion
- Sublingual gland: Facial nerve (CN VII), same pathway as the submandibular gland, synapse at the submandibular ganglion
- All glands (sympathetic): Postganglionic fibers from the superior cervical ganglion, traveling with the arterial blood supply