In many sources, also in medical sources, it is mentioned that the facial muscles will suffer atrophy if the innervation is not reinstated within a year. This often makes Bell’s palsy patients very nervous and anxious, sometimes even desperate. This desperation can push them to go for surgical interventions.
Does the atrophy of facial muscles happen?
No, Bell’s palsy does not cause atrophy of facial muscles.
From our point of view, the atrophy of facial muscles does not happen after Bell’s palsy. It does not matter how much time has passed since the onset. This is because the facial muscles do not receive their sensory innervation through the facial nerve.
Bell’s palsy only affects the motor neurons of our face.
The facial nerve consists mostly of motor neurons, which are responsible for the movement signals. It also provides signals to salivation and lacrimation glands, which is why you might have excessive tears or lack of them. Also, the sensory (taste) signals to the first 2/3rd of the tongue are provided by the facial nerve. That is why you might have experienced the disruption of the normal taste during the acute stage of your facial palsy. Eventually, this subsides after a few weeks. This is the main reason why the atrophy of the facial muscles does not happen during facial palsy.
Why atrophy does not happen?
The atrophy of facial muscles does not happen during facial palsy because our facial nerve is different from other nerves in our body.
If we damage the skeletal nerve, let’s say the median nerve, which innervates some muscles in our palm and arm, atrophy might take place. The median nerve and all skeletal nerves of our body that provide the movement are mixed. They consist of both sensory and motor fibres. If this nerve is damaged, the brain does not receive any signals from the affected muscles. So the signs from the brain cannot reach the muscles, and also the signals from the muscles cannot reach the brain.
As long as the brain cannot hear anything from the muscles, it may think “OK, this muscle is dead, this soldier is dead, it makes no sense to send him ammunition, supplies and so on and so on”. So it just starts to ignore that muscle in its nutritional and trophic processes, and the muscle sustains atrophy. Atrophy means – malnutrition. So these muscles shrink and become replaced by the fibrous tissue and permanently lose their ability to function, at least partly.
The sensory signals from our facial muscles are conducted by the Trigeminal nerve, which is not affected by facial palsy. That is why you do not lose the sensitivity of your skin. You also do not lose the pain sensation in your face. You may feel some numbness in your facial muscles, especially in the acute phase. That is mostly because you lack movements. The Trigeminal nerve, which senses the movements, contractions, and relaxations of our muscles, lacks signals. That is why it provides the brain with a certain feeling of numbness. What you might experience, is atonicity – the lack of tone in your facial muscles – but not atrophy.
