Introduction to the facial nerve
The facial nerve is responsible for controlling facial muscle movement and function. Injury to the facial nerve results in weakness or total paralysis of the facial muscles.
Each side of the face has its own facial nerve, so injury to the right facial nerve will only affect the right side of the face, and vice versa. The facial nerve begins in the brain and travels towards a tiny bony passage in the skull. It follows this bony pathway and exits the skull where it enters the face just in front of the ear. At this point, it divides into five separate branches. These five branches supply the facial muscles which control facial expression and movement including some of the muscles responsible for eating, drinking and speech. Tear and saliva production, taste and hearing are also controlled by the facial nerve but in different ways.
The journey the facial nerve makes from the brain to the face is complex with lots of twists and turns. One way to think about damage to the facial nerve is to separate this journey into two:
- The journey it makes in the brain and out through the skull is known as the intracranial section. (The medical term for the skull is the cranium and the term intracranial refers to the content within the skull which is the brain).
- The journey the facial nerve makes once it leaves the skull and enters the face and neck is known as the extracranial section (it is outside of the brain and skull).
Simply put we can think of the location of nerve injury as being either inside or outside the skull. This is an important distinction and will determine the type of symptoms that a person experiences depending on the site of facial nerve injury.
People who have extracranial facial nerve damage will experience symptoms associated with muscle weakness or muscle paralysis.
People who have intracranial nerve damage will experience multiple symptoms not just muscle weakness or paralysis depending on the exact location of the injury. The reasons for these varied and complex symptoms will be described below.
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