Have you ever wondered why your face hurts so much during a migraine attack, or why jaw clenching and strong smells can give you a migraine?
The cause lies with the trigeminal nerve. This nerve has three branches in the face and supplies the meninges (the “dura mater”). When it picks up a signal in the meninges or the face, it passes this signal deep into the brain (via the brainstem and thalamus), where it can be interpreted as pain.
Activating the trigeminal nerve from the inside
The trigeminal nerve is activated from the inside when the neurons in your brain have run into an energy shortage and have started a “cortical spreading”. You can compare cortical spreading a little to a short circuit in the brain. A few neurons run into an energy shortage, and in response…
- The blood supply to the brain initially increases sharply. Among other things, sodium, glucose and oxygen are delivered. This activates the neurons, through electrical signals.
- By pulling sodium into the neuron and pushing potassium out, a negatively charged neuron becomes more positively charged. This is the trigger for the neuron to send on a signal, in this case glutamate, which also activates the connected neurons.
- Besides activating connected neurons with glutamate, surrounding neurons are activated too. This is what is called “cortical spreading”. The charge of all surrounding neurons suddenly rises as well, and they also start releasing glutamate.
- You could see this as a last-ditch attempt by the brain to find a solution for the energy shortage. You become hyperalert.
- You now have a surplus of glutamate in the brain. This hyperactivity causes oxidative stress. The same process happens when your skin burns after too long in the sun, or when you have exercised so hard that your muscles are sore. The cells now need time to clear away the oxidants. Until that has happened, they can’t work optimally.
- The cortical spreading eventually reaches the meninges and the trigeminal nerve is activated.
- The nerve surrounds the blood vessels in the meninges and makes them dilate and become inflamed through neuropeptides such as CGRP.
- This is probably what causes the pain.
Now you also understand why CGRP inhibitors such as erenumab (Aimovig) may limit your pain, but don’t remove the cause. Your brain has still run into an energy shortage, and you haven’t solved that problem. Your neurons can be damaged by the oxidative stress, and every time they need time and antioxidants to recover.
Triptans, on the other hand, manage (for reasons that are not entirely clear) to reverse the dilation of the blood vessels. A strong cup of coffee can also normalise the blood vessels again (unless your body is used to coffee).
Activating the trigeminal nerve from the outside
So a large part of the trigeminal nerve lies outside the brain: in your meninges and spread across your face. There it has sensors that pick up information and pass it on into the brain. This means the trigeminal nerve can be activated without an energy shortage in the brain first. In that case too, the nerve can release CGRP and other neuropeptides, making the blood vessels dilate and triggering an inflammatory response.
What can activate the trigeminal nerve from the outside? Think of:
- allergens, viruses and bacteria that come in through the nose
- face creams with irritating ingredients, and skin that is too permeable
- bright light
- strong smells
- strong wind on your face
- an overactive masseter (the large chewing muscle that runs in front of the ear from the cheekbone to the lower edge of the angle of the jaw). Think of teeth grinding and jaw clenching.
- …
What wires together, fires together
Presumably this kind of activation won’t cause a “full” migraine in someone who doesn’t have migraine. But “what wires together, fires together”. This principle was described by Donald Hebb and is also the principle behind the Pavlov effect. Neurons that are frequently activated at the same time will go on to activate each other in the future. So activating the trigeminal nerve “from the outside” could give a person with migraine a new attack. The neurons in the brain suddenly become hyperactive, start a cortical spreading, and the circle is complete.
Desensitisation
So it is important to get migraine attacks under control, both from the inside and from the outside, and to uncouple the processes. The trigeminal nerve is just one link in the bigger picture of the causes of migraine. The Building Block Analysis helps you understand your personal migraine picture and gives you the tools to get your migraine under control.
