The otic ganglion is one of the four parasympathetic ganglia of the head. A collection of sensory neurons of the mandibular nerve, it works with the glossopharyngeal nerve and mandibular nerves to provide function to multiple salivary glands. It also has a motor function in chewing.
Ganglia are groups of nerves, typically with related functions, that meet up inside a capsule of connective tissue. They serve essentially as nerve relay stations, shuttling information back and forth between different parts of the nervous system.
The brain contains 12 ganglia on each side, in symmetrical pairs, but they’re generally referred to in the singular. Eight of the cranial nerve ganglia are sensory, while four are parasympathetic, including the:
- Otic ganglion
- Ciliary ganglion
- Submandibular ganglion
- Pterygopalatine ganglion
The parasympathetic nervous system (PNS) works in concert with the sympathetic nervous system (SNS), and together they make up the autonomic nervous system (ANS). The ANS controls your involuntary functions—the things your body does on its own. One of the functions of the PNS is increasing glandular activity. That’s why the otic ganglion, with its association to the salivary glands, is classified as parasympathetic.
However, the ganglion also has roots from the sympathetic nervous system, and it contains sensory and motor nerve fibers, as well.
Sensory nerves transmit information from your senses (vision, hearing, taste, smell, touch), while motor nerves deliver the electrical impulses that move your muscles, bones, and other parts of your body.
Structure and Location
The otic ganglion is housed inside a small structure called the infratemporal fossa. A fossa is a hollow or recessed area in the skull. The infratemporal fossa is on the side of the head between your temple and your jaw.
The otic ganglion is the smallest of the parasympathetic cranial ganglia. It’s quite flat—just 0.4 millimeters (mm) thick—and oval-shaped. It typically measures just 2 mm long and 1.5 mm wide.
Relative to the structures in the area, the otic ganglion is:
- Below the greater wing of the sphenoid bone
- Above the levator veli palatini muscle
- On the inside of the mandibular branch of the trigeminal nerve, which is the fifth cranial nerve
The otic ganglion’s parasympathetic fibers come from the inferior salivary nucleus, which is an area of the medulla oblongata (part of the brainstem). The fibers pass through the glossopharyngeal nerve, travel through the middle ear, exit the skull, and join the otic ganglion. There, these fibers exchange signals with fibers that leave the ganglion and run through all the branches of the mandibular nerve, which connects to the parotid gland and several other salivary glands plus the blood vessels of some jaw muscles.
Most anatomical parts are fairly standard from one person to the next, but there are variations in the size, structure, and location of things. It’s important for doctors to know about possible anatomical variations when they’re making diagnoses or performing surgical procedures.
The otic ganglion is hard to access in any but the most careful of dissections, so not a lot of information was available about its variations until a 2019 study sought to examine it in numerous cadavers. Researchers found that it can come in one of three types, depending on the number of bundled nerve fibers that it connects to:
- Compact type: the most common, expected shape, with the expected number of bundles
- Lobulated type: a lumpier form with fewer bundles
- Disperse type: more spread out, with a higher number of branches exiting from it
The same person may have one type of ganglion on the left and a different type on the right.
Research also has shown different distances from the ganglion to the forward section of the mandibular nerve, which varied from 0 mm to 4 mm.
“Otic” means “relating to the ear.” The ganglion got this name after it was first described in 1828 because it was found to be larger and more developed in large-eared animals such as the rabbit, horse, and pig.
The otic ganglion deals with both motor and sensory functions. Some of its motor function is of a specialized type referred to as secretomotor. That term is used because the particular movement deals with the secretion of fluids by a gland.
Motor and Secretomotor Function
Through its relationship with the glossopharyngeal and mandibular nerves, the otic ganglion is involved in the secretion of saliva from the:
- Parotid gland
- Submandibular gland
- Sublingual gland
- Other salivary glands in the lining of the cheeks and back of the lips (called the buccal mucosa)
Other motor fibers that pass through the otic ganglion enter the medial pterygoid nerve and provide function to three muscles.
- Medial pterygoid muscle: Raises the lower jaw to close the mouth, works with the lateral pterygoid muscles for side-to-side motion of the jaw.
- Tensor veli palatini muscle: A ribbon-like muscle that tenses the soft palate.
- Tensor tympani muscles: In the middle ear, this muscle dampens loud sounds from both inside the head (such as chewing) or from external sources.
Sensory fibers from the otic ganglion form the auriculotemporal nerve, which provides sensation to the parotid gland.
The ganglion also plays a role in taste. It’s connected to the chorda tympani nerve and the nerve of the pterygoid canal, which is an alternate taste pathway from the front portion of the tongue.
Associated Conditions and Treatments
Any nerve structure can be damaged by diseases or infections that affect nerves or by traumatic injury, such as that from surgery or an accident.
The location of the otic ganglion generally protects it from direct injury. However, the parasympathetic fibers between the ganglion and the brainstem can become damaged by trauma or inflammation in narrow passageways. That most often causes dysfunction of the parotid gland or other glands and muscles innervated by fibers from the ganglion.
Treatments for these dysfunctions vary depending on the underlying cause. Effective treatments are available for most causes and are most successful when there’s a prompt diagnosis.
The otic ganglion is also associated with headache disorders and a condition called Frey syndrome.
Some cases of migraine and cluster headaches may be related to the otic ganglion. A neuropeptide (brain chemical) called pituitary adenylate cyclase-activating peptide (PACAP) is implicated in these conditions, and it’s found in numerous areas of the brain including the otic ganglion and other areas of what’s called the trigeminal system.
Researchers are working to identify treatments for these types of headaches, including botulinum toxin A injections. These efforts are being aided by advances in imaging that help to accurately locate this tiny structure.
Trauma to or surgical removal of the parotid gland can lead to a condition called Frey syndrome. When the auriculotemporal nerve’s parotid branch (which contains fibers from the otic ganglion) is separated from the gland, it can attach itself to the sweat glands that are nearby in the cheek.
That leads to an odd phenomenon in which the cheek sweats while you eat, which is when the nerve would normally be causing the parotid gland to release saliva.
Conservative treatment of Frey syndrome involves applying antiperspirant to the cheek. Sometimes, doctors inject the cheek with medications, including botulinum toxin A, to control symptoms.
If those approaches aren’t adequate, there’s a surgical option that involves placing a different tissue in between the nerve and the sweat gland. That blocks the nerve from activating the gland, thus stopping the sweating response.