Headaches
What Causes
Headaches?
Scientists have yet to completely
unravel the cause or causes of headaches. It was once
believed that constriction and dilation of blood vessels
caused migraine headache, while muscle contraction caused
tension headache. The constriction of vessels in the head was
thought to cause the aura of migraine, as well as the nausea
and vomiting. The subsequent relaxing, or dilation, of the
vessels then brought on the pounding pain associated with
migraine.
These changes are still thought to play
a big role in head pain, but a much more complicated
explanation is beginning to emerge from recent scientific
findings. Many experts now speculate that migraine and
tension headache have the same origin in the
brain.
The Body's “Anti-pain”
System
The brain stem—the structures of
the brain located behind the eyes and nose—contains an
“anti-pain” system. When this area recognizes an
incoming nerve signal as painful, it responds with a powerful
pain-relieving effect.
The pain of headache is thought to begin
with the trigeminal nerve, which is located in the brain
stem. The largest in the head, this nerve carries sensory
impulses to and from the face. When stimulated, perhaps by a
certain headache trigger, it releases a burst of
neurotransmitters (chemicals that pass impulses from one
nerve to the next). This, in turn, normally prompts release
of yet another neurotransmitter called
serotonin.
Serotonin acts as a filter, screening
out unimportant signals—for example, weak, repetitive,
or familiar background noise like music and other people's
conversations—while admiting signals that demand
attention, such as unusual or significant sounds like a
baby's cry or your name being called. The more serotonin, the
greater the screening action. High serotonin levels correlate
with sleep.
Under ordinary circumstances, pain
signals from the trigeminal nerve are counteracted by
increased serotonin levels. But in people suffering a
headache, serotonin levels often prove too low. Scientific
tests have shown a clear relationship. When injected with a
drug that depletes serotonin, test subjects got headaches.
Likewise, when they were injected with serotonin, the
headache went away.
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