Innervation of the upper airways.

The respiratory tract has a rich supply of autonomic nerves. Among the neurotransmitter candidates are noradrenaline, neuropeptide Y, substance P, calcitonin-gene-related peptide, gastrin-releasing peptide, acetylcholine, vasoactive intestinal polypeptide, and peptide histidine isoleucine. The fibers are distributed around blood vessels and seromucous glands, and beneath and/or within surface epithelium. The distribution suggests that the fibers may influence blood flow, glandular secretion, and epithelial functions.