explain the dynamics of vasoconstriction/vasodialation of blood vessels as it re!


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This answer is that provided to me by a doctor some years ago in regard to migraine headaches. I understand that the broad outlines are still regarded as valid, though details have changed. Tension headaches, and other sorts are likely to have a different origin. However, few are well understood, so there's a lot of speculation from medical folks in addition to folk tale origins. But your question was about vascular effects, so here goes.

The brain is insensitive to pain. It's possible to cut and slice while a patient is conscious without getting much complaint about pain. The same's true of the intestines. However, the arteries in the brain, and the intestines themselves, scream with pain when they are stretched. Gas bloating is sometimes painful as the intestines stretches like a balloon.

In the case of migraines, they are often preceeded with any of one or more of several perceptual symptoms. The pattern is usually something like: sensory abberation for a few minutes, followed shortly by blinding stupifying pain for an hour or two. In my case it was 'fortification illusions' -- what I called shimmering gold and silver oak leaves. These seem to be the consequence of nerve starvation in particular areas of the brain (the visual cortex in my case) which leads to misfiring and misfunction of these marginally starving brain cells. It seems that arterial contraction is the cause of the cut off blood supply, though the cause of the arterial contraction spasm is unclear.

There appear to be alarm circuits in the brain to reverse arterial spasms, and indeed these sensory artifacts in migrains suffers (if caused by such spasms) tend not to last very long. The 'expand that artery!' signal causes stretching -- quite painful stretching -- in the artery (or ateries) involved and takes a few hours to subside. Ergot derivatives were long been known to be effective against migraine pain, but only if given very soon after the sensory illusion artifact appeared. Since these substances caused arterial relaxation, their use provided a clue to the underlying mechanism.

Interference with brain function by arterial spasms and (over)correction by expand 'em signals are likely to have any of a variety of effects, depending on what parts of the brain become involved. And indeed, migraines are sometimes accompanied by vomiting, by great sensitivity to light and sound, and so on.

The vasoconstriction / vasodilation explanation accounts for much of the observed sequence in migraines, and this is an arguement in its favor. Continuing work with MRI, CT, and PET scans will likely produce a better and more detailed on in future.
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