The nervus facialis, more commonly known as the facial nerve, is one of the cranial nerves. There are 12 pairs of cranial nerves altogether, originating from the brain and emerging through openings in the skull to supply the head and neck. The nervus facialis is the seventh cranial nerve and consists of two roots, having both a motor branch and a sensory branch. While the motor nerve supplies muscles of facial expression and the tiny stapedius bone of the ear, the sensory branch supplies sensation to areas of the tongue, mouth and palate. Some fibers innervate salivary glands, lacrimal glands and other glands in the palate and nose.
After passing from the brainstem through the inner ear, the nervus facialis emerges from the skull just below the earlobe. It travels through the parotid gland where it divides into a number of branches. While the nervus facialis supplies all of the muscles involved in facial expression, it does not supply any of the facial skin. Taste tests on those areas of the tongue supplied by the nervus facialis can be used to assess whether the nerve is functioning.
Facial nerve palsy occurs when damage to the nervus facialis affects the facial muscles, causing the face to droop on one side. As the muscles that close the eye are involved, the eye may remain open, possibly damaging the surface of the eyeball over time. Muscle paralysis may be partial, affecting mainly the lower face, or more extensive, affecting the ability to eat and speak. Loss of taste and exaggerated perception of loud or high-pitched noises may also be involved.
According to where in its path the nervus facialis is damaged, a palsy can be described as upper motor neurone or lower motor neurone in nature. With lower motor neurone palsy, also called Bell's palsy, a telling sign is that the patient is unable to make the brow wrinkle. Causes can include infections such as herpes and Lyme disease, tumors, a blow to the head and neurological diseases such as multiple sclerosis. Sometimes the cause is unknown, and fortunately, in many cases the condition resolves on its own. In the meantime, the eye may need to be lubricated using drops and protected with a patch.
Typically, in the case of an upper motor neurone palsy, a patient retains the ability to wrinkle the forehead and less drooping of the face is seen. Strokes, tumors, multiple sclerosis and infections such as syphilis and HIV can all cause upper motor neurone palsy. Usually, in the case of a stroke, voluntary movements of the face are most affected. Treatment varies depending upon the cause, but sometimes surgery may be used to repair the facial nerve.