Elsevier Inc. ACh ---- nAChR. ACh ---- nAChR immune cells epithelial cells nAChR. acetylcholine signaling via nicotinic acetylcholine receptor --+> parasympathetic postganglion ACh acetylcholine signaling via nicotinic acetylcholine receptor --+> sympathetic postganglion nAChR adrenal medulla sympathetic postganglion norepinephrine ---> terminal structures mAChR ---> decreased heart rate mAChR ---> bronchoconstriction acetylcholine signaling via muscarinic acetylcholine receptor ---> effector tissues acetylcholine acetylcholine signaling via muscarinic acetylcholine receptor acetylcholine signaling via nicotinic acetylcholine receptor norepinephrine epinephrine ACh. acetylcholine signaling via muscarinic acetylcholine receptor ---> forebrain synaptic plasticity emotion learning and/or memory acetylcholine signaling via nicotinic acetylcholine receptor ---> hippocampus brainstem hippocampus forebrain midbrain pallium mAChR effector tissues muscle contraction acetylcholine signaling via nicotinic acetylcholine receptor ---> skeletal muscle fiber decreased heart rate sympathetic preganglion ---> ACh parasympathetic preganglion ---> ACh parasympathetic postganglion ---> ACh. ACh. ---- mAChR sympathetic postganglion ---> norepinephrine epinephrine ---> blood norepinephrine ---> blood adrenal medulla ---> norepinephrine adrenal medulla ---> epinephrine sympathetic preganglion parasympathetic preganglion parasympathetic postganglion acetylcholine signaling via muscarinic acetylcholine receptor ---> epithelial cells acetylcholine signaling via nicotinic acetylcholine receptor ---> epithelial cells blood bronchoconstriction terminal structures skeletal muscle fiber endothelial cells