The parotid gland is a major salivary gland located on each side of the face, just below and in front of the ear. Its primary role involves producing saliva, a fluid essential for various oral functions. Saliva helps lubricate the mouth, aids in chewing and swallowing, and begins the digestion of starches through enzymes like amylase. The supply of nerves, or innervation, controls the gland’s function, including saliva secretion.
The Primary Nerve Controlling Saliva Production
The parasympathetic nervous system primarily controls parotid gland saliva production, stimulating the secretion of thin, watery saliva. The Glossopharyngeal nerve (Cranial Nerve IX or CN IX) is the main nerve responsible for this action.
Fibers from the Glossopharyngeal nerve originate in the brainstem and travel towards the gland. These preganglionic parasympathetic fibers then synapse, or connect, in a small structure called the otic ganglion. From the otic ganglion, postganglionic fibers emerge and join with a branch of the trigeminal nerve (Cranial Nerve V3), called the auriculotemporal nerve. This auriculotemporal nerve then carries these signals directly to the parotid gland, prompting the secretion of substantial amounts of watery saliva.
Other Nerves Associated with the Parotid Gland
The Facial nerve (Cranial Nerve VII) passes directly through the parotid gland, dividing it into superficial and deep lobes. Despite its close proximity, the Facial nerve does not innervate the parotid gland; instead, it controls facial expression muscles.
The parotid gland also receives sympathetic innervation, which plays a secondary role in saliva production compared to parasympathetic stimulation. These sympathetic fibers originate from the superior cervical ganglion and travel along the external carotid artery to reach the gland. Sympathetic stimulation generally causes vasoconstriction, reducing blood flow to the gland and resulting in the production of a smaller amount of more viscous saliva.
The auriculotemporal nerve, which carries parasympathetic fibers to the gland, also provides general sensory innervation, transmitting sensations like pain. The great auricular nerve also contributes sensory fibers to the parotid gland’s fascia and overlying skin.
Clinical Importance of Parotid Gland Innervation
During parotid gland surgery, the Facial nerve’s close relationship presents a risk. Its path directly through the gland means injury during surgery can lead to temporary or permanent facial paralysis. Surgeons meticulously work to identify and preserve this nerve to avoid complications.
Conditions affecting the parotid gland, such as mumps or tumors, can also impact its innervation. Inflammation or abnormal growths within the gland may cause symptoms like pain or alterations in saliva production due to pressure or nerve damage.
Frey’s syndrome, also known as gustatory sweating, is a condition that can occur after parotid surgery. Damaged parasympathetic nerve fibers, originally destined for the salivary gland, may regenerate incorrectly. These misdirected fibers instead connect to sweat glands in the skin over the parotid region, causing sweating and flushing on the face when a person eats or even thinks about food.