Pathophysiology
The brain itself is not sensitive to pain, because it lacks pain receptors. However, several areas of the head and neck do have nociceptors, and can thus sense pain. These include the extracranial arteries, large veins, cranial and spinal nerves, head and neck muscles and the meninges.
Headache often results from traction to or irritation of the meninges and blood vessels. The nociceptors may also be stimulated by other factors than head trauma or tumors and cause headaches. Some of these include stress, dilated blood vessels and muscular tension. Once stimulated, a nociceptor sends a message up the length of the nerve fiber to the nerve cells in the brain, signaling that a part of the body hurts.
It has been suggested that the level of endorphins in one's body may have a great impact on how people feel headaches. Thus, it is believed that people who suffer from chronic headaches or severe headaches have lower levels of endorphins compared to people who do not complain of headaches.
Primary headaches are even more difficult to understand than secondary headaches. Although the pathophysiology of migraines, cluster headaches and tension headaches is still not well understood, there have been different theories over time which attempt to provide an explanation of what exactly happens within the brain when individuals suffer from headaches. One of the oldest such theories is referred to as the vascular theory which was developed in the middle of the 20th century. The vascular theory was proposed by Wolff and it described the intracranial vasoconstriction as being responsible for the aura of the migraine. The headache was believed to result from the subsequent rebound of the dilatation of the blood vessels which led to the activation of the perivascular nociceptive nerves. The developers of this theory took into consideration the changes that occur within the blood vessels outside the cranium when a migraine attack occurs and other data that was available at that time including the effect of vasodilators and vasoconstrictors on headaches.
The neurovascular approach towards primary headaches is currently accepted by most specialists. According to this newer theory, migraines are triggered by a complex series of neural and vascular events. Different studies concluded that individuals who suffer from migraines but not from headache have a state of neuronal hyperexcitability in the cerebral cortex, especially in the occipital cortex. People who are more susceptible to experience migraines without headache are those who have a family history of migraines, women, and women who are experiencing hormonal changes or are taking birth control pills or are prescribed hormone replacement therapy.
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