The parotid gland is the largest of the salivary glands, situated just in front of the ear and extending down toward the angle of the jaw. Its primary role is to produce and secrete saliva, a fluid essential for digestion, lubrication, and oral health. The parotid gland’s function is entirely regulated by the nervous system, a process known as innervation. Understanding which nerves control the gland is important for surgeons and clinicians, as the anatomy in this area is complex.
The Secretomotor Pathway: Producing Saliva
The secretomotor function, which stimulates saliva production, is governed by the parasympathetic division of the autonomic nervous system. This signaling pathway begins in the inferior salivatory nucleus, and the initial signal is carried by the Glossopharyngeal Nerve (Cranial Nerve IX).
These pre-ganglionic fibers travel through the tympanic nerve and continue as the lesser petrosal nerve. The pathway reaches the otic ganglion, a relay station beneath the base of the skull. Here, the pre-ganglionic fibers synapse, passing the signal to the post-ganglionic fibers.
These post-ganglionic fibers “hitch-hike” along the Auriculotemporal Nerve, a branch of the Trigeminal Nerve (CN V). This nerve acts as a conduit, carrying the secretomotor instructions directly into the parotid gland. The Glossopharyngeal Nerve is the source of the signal, while the Auriculotemporal Nerve is the final delivery mechanism to stimulate the gland’s cells.
Sensation and Blood Flow Control
General sensory information, including pain, temperature, and pressure from the parotid gland, is supplied by the Auriculotemporal Nerve. This nerve has a dual function, carrying secretomotor fibers to the gland and sensory fibers from the gland and overlying skin back toward the brain.
The gland receives input from the sympathetic nervous system, which primarily regulates blood flow rather than initiating secretion. These fibers originate from the superior cervical ganglion. They travel by wrapping around the external carotid artery and its branches to reach the parotid gland.
Activation of these sympathetic fibers causes vasoconstriction, narrowing the blood vessels supplying the gland. This reduction in blood flow indirectly limits saliva production and results in a more viscous, or thick, saliva. The sympathetic input acts as a modulator, controlling the volume and consistency of the secretion.
When Parotid Nerves Are Damaged
The network of nerves around the parotid gland is vulnerable to damage, especially during surgical procedures like tumor removal. One recognized complication involving the secretomotor pathway is Frey’s Syndrome, or gustatory sweating. This disorder occurs when parasympathetic fibers, cut during surgery, regenerate incorrectly.
Instead of reconnecting to salivary gland tissue, the damaged post-ganglionic fibers misdirect and attach to the sweat glands and blood vessels in the overlying skin. When a patient eats, the brain sends the usual signal to the otic ganglion to produce saliva. This signal is aberrantly routed to the facial sweat glands, causing flushing and sweating on the cheek and temple area instead of salivation.
Another clinical consideration involves the Facial Nerve (Cranial Nerve VII), which passes directly through the gland but does not innervate it. This nerve controls the muscles of facial expression, making it highly susceptible to accidental injury during tumor resection. Damage to the Facial Nerve results in facial paralysis, causing drooping of the mouth and difficulty closing the eye on the affected side.