Bell's palsy is caused by an injury to cranial nerve VII, the facial nerve. Injuries are caused by trauma, cold, chemical irritation and infections. Once injured, the facial nerve is unable to transmit signals to the facial muscles and other structures it innervates, which results in paralysis on one side of the face. Bell's palsy is usually transient and resolves itself in a few weeks or so. MayoClinic.com cites that Bell's palsy can affect anyone, but rarely those under 15 or over 60 years of age.
Paralyzed Facial Muscles
Bell's palsy usually progresses quickly and often is of unknown cause. It affects only one side of the face. The primary effects are loss of sensation and weakness or paralysis of the facial muscles, which causes them to droop. Smiling, blinking and raising an eyebrow become difficult or impossible. Although Bell's palsy looks like the effects of a stroke, there is no link between the two. Doctors believe the herpes virus might be responsible in many cases and cause inflammation of the facial nerve, which exits the skull in front of the ear, near where the jaw attaches. HealthScout.com reports that Bell's palsy affects about 20,000 Americans per year.
Inability to Blink
Due to the muscle paralysis of Bell's palsy, it becomes difficult to close the eyelid, which can dry out the eye and make it susceptible to infections, according to "Professional Guide to Diseases." In addition, eye injuries and irritation are more common due to debris.
Tearing and Drooling
Because the facial nerve controls the function of the lacrimal gland, usually a lesser volume of tears is produced. However, because the eyelid cannot be closed, the tears that are produced often run out of the eye and down the face, which results in a dry eye. The same situation exists with the salivary glands; less saliva is produced, but what is produced drools out the side of the paralyzed mouth.
Reduced Sense of Taste
The facial nerve also innervates some of the taste buds of the tongue, so Bell's palsy can cause a reduction in the sense of taste. Taste is also lessened by the reduced production of saliva from the salivary glands.
Increased Sensitivity to Sound
According to MayoClinic.com, the facial nerve also innervates the tiny muscles inside the ear that dampen loud noises. Consequently, there can be an increased sensitivity to sound in the ear on the affected side.
Pain
If the facial nerve is inflamed, then the nerve pain can be felt in front of the ear where the nerve exits the skull. Pain can also be referred to behind the ear or to the temporomandibular joint of the jaw. Less often, Bell's palsy can generate one-sided headaches.
References
- Mayo Clinic: Bell's Palsy
- Health Scout: Bell's Palsy
- "Professional Guide to Diseases"; Springhouse; 2008
- Mayo Clinic: Bell's Palsy Symptoms
