The nerves that supply the jaw muscles go directly into the "migraine centre". Often people will be told they have a jaw problem, trying splints etc, when in a lot of cases the over activity in the brainstem is causing the muscle over activity. The upper cervical nerves have a significant impact on this over active brainstem, putting the neck in the box seat to cause headache and migraine. In short, check your neck with techniques specifically designed to test the relationship with headache and migraine.

"But there again there’s another bit of a paradigm shift; we had all thought that migraine came in through the trigeminal nerve or was mediated by input from the face, but now there’s really growing recognition that the occipital nerve, the upper cervical nerve routes may actually be playing an equally important role and many, many migraine patients get neck pain either before, during or after their attack they have soreness and stiffness in their neck."

Dr Andrew Charles - Neurologist, UCLA

Reason 2 - The Anatomy

In reason 1 we saw that there are a lot of similarities in the way that the different headaches present. Their symptoms overlap significantly. There is a very good reason for this. 
ALL major headache types (Tension headache, migraine, cluster headache, menstrual migraine, cervicogenic headache) share a common underlying disorder. They all have an overactive part of the brainstem called the trigemini cervical nucleus (TCN). We know this for 3 reasons:
1. Reflexes that run through this area are elevated or over-reactive. 
2. PET scans (measuring blood flow or "metabolic activity") show increase activity in this area.
3. Medications such as the triptans (Imigran, Naramig, Maxalt, Sumatriptan) decrease the activity in the TCN.

The TCN is "headache central". Imagine each headache is a train sitting at a large train station. They all originate in the same place. As they depart the first station they may go through some common stations (similar symptoms) before ultimately going their separate ways. The different headaches, as the storm of activity travels higher up into the brain all take slightly different pathways, and ultimately, have distinctly different characteristics by which they are defined. By they also have a lot of commonality and the key to understanding headache and migraine is to look at where all these trains originate from, rather than where they arrive.

The TCN is part of the brainstem that receives all of the sensory information from the head and face (excluding special senses - sight, smell, taste, hearing). It also receives input from the upper 3 cervical nerves. The trigeminal system carrying information from the head and face and cervical nerves are the only neural inputs into the TCN. There are two chemical systems that control the activity in the TCN and dampen it down. 

To have overactivity in the TCN it stands to reason that there must be either too much activity in the trigeminal or upper cervical nerves, OR that the chemical controls are inadequate.

Now I'd like you to think about your neck and your posture. How often do you sit with your head forward of your body (dropped shoulders and poke neck) or with your head down (looking at a phone, tablet, or reading books/documents). 
Next time you are sitting in traffic, or on the train, or at work, have a look around and see just how many people put this constant strain on the neck.
It's not so hard to see that not only does the neck have direct access to the area we know is the source of headache and migraine, but also that most of us put a lot of strain on this area every day. 

In approximately 80% of headache and migraine conditions the overactivity in the brainstem is coming from the upper cervical spine. The conditions we find are treatable and manageable and for a majority of clients this can be done within 3-4 weeks without need for excessive ongoing treatment.

Check your neck.