Ganglionic transmission is mediated via nicotinic receptors (N), while the M1 receptors may play a facilitatory role. M2 receptors at the postganglionic terminal may inhibit release of acetylcholine (Ach), which acts on M3 receptors on airway smooth muscle to cause bronchoconstriction.
Redrawn from Barnes, PJ, Life Sciences, 1993; 52:521.