The human body has twelve cranial nerves. One of those nerves, the hypoglossal nerve, is intimately related to the oral cavity. This nerve is also known as the twelfth cranial nerve, and it controls the muscles of the tongue, making it important to dentists, doctors and patients alike.
Anatomy and Function
The twelfth cranial nerve arises from the medulla oblongata, which is a part of the brain stem, explains the textbook Clinical Oral Anatomy. From there, it passes through the space underneath the tongue to reach the tongue muscles. In fact, "hypo" means below, and "glossal" means relating to the tongue, so the name of the nerve describes the path it takes below the tongue.
The hypoglossal nerve is a motor nerve, and it controls the muscles of the tongue that allow for speech and swallowing. The tongue's extrinsic muscles help it move in different directions, while the intrinsic muscles help it make movements such as curling, according to the textbook Anatomy and Physiology. The extrinsic muscles controlled by the hypoglossal nerve include:
- The genioglossus muscle, which helps move the tongue out of the mouth.
- The hyoglossus muscle, which moves the tongue down to flatten it.
- The styloglossus muscle, which retracts the tongue back into the mouth and elevates it.
The only muscle of the tongue not controlled by the hypoglossal nerve is the palatoglossus muscle, notes Clinical Oral Anatomy.
What Might Damage the Twelfth Cranial Nerve?
It's rare to see damage to the twelfth cranial nerve alone, as a study in Medical Case Reports notes. However, it's still possible to experience hypoglossal nerve palsy, which causes muscle weakness or paralysis in areas of the tongue controlled by the nerve. Although uncommon, this condition might arise from trauma to the head or neck, stroke, brain tumors, multiple sclerosis, infections or autoimmune disease.
Symptoms of Twelfth Cranial Nerve Damage
If the hypoglossal nerve is damaged, movement of the tongue may be affected, as described in Merck Manuals. This can affect speech, chewing and swallowing, and it may make the tongue feel like it's twitching. The tongue might also tilt to one side, as described in a case report in The American Journal of Medicine. Sometimes, the patient might experience slurred speech or feel as though they're choking when eating or drinking.
If you experience any of these symptoms, your doctor will likely want to conduct further analysis to determine the precise cause of the issue. They may order an MRI or CT scan, especially if they suspect a tumor might be the cause of the nerve damage, as explained in The American Journal of Medicine report. Alternatively, they might conduct a spinal tap, as Merck Manuals explains.
Your doctor will explore many treatment options depending on the cause of the nerve damage. If an infection or tumor is the source of the symptoms, your medical professional will likely want to take steps to manage the infection or remove the growth. If an underlying syndrome is causing the problem, your doctor may suggest treatments that relieve your symptoms.
Because twelfth cranial nerve damage is highly complex, it requires coordination among dentists, neurologists, primary care physicians and possibly even infectious medicine or oncology physicians to obtain proper diagnosis. Be sure to discuss your concerns with your medical or dental provider if you are unable to properly move your tongue, and your medical team will work together to establish the best treatment plan for you.