Ahh, yes, here it is:
“Another element in migraine is the release of chemicals by the trigeminal nerve. This nerve supplies sensation to the entire face, scalp, lining of the eyes, nasal cavity and sinuses, teeth and gums, jaw joints, parts of the neck and ears, even shoulders. This nerve releases inflammatory peptides – short pieces of proteins – into the tissues nearby. These peptides (CGRP, substance P, etc.) can cause the local blood vessels to become “leaky,” losing their serum into surrounding tissues. The tissues can even swell and become painful on this basis. Classic migraine headache may occur when branches of the trigeminal nerve going to the lining of the brain get inflamed, causing painful throbbing headache due to sensitization of the blood vessels around the brain by the inflammatory peptides. But if branches going to the sinuses are involved instead of those going to the lining of the brain, the symptoms may not seem like classic migraine headache, but instead may be sinus congestion and runny nose. These patients often feel that they have sinusitis, but scans show no anatomic abnormality of the sinuses.”
This is from:
“Migraine–More Than a Headache” in this thread:
https://www.mvertigo.org/t/other-reading/15138