 Norepinephrine

Norepinephrine, also called noradrenaline, is a catecholamine neurotransmitter used in central and peripheral signaling. Its effects on attention, arousal or a peripheral organ depend on the target receptor and the local cellular machinery.

The same chemical signal can thus have different physiological consequences in different tissues. Measuring a whole-body concentration and recording a local synaptic response answer different questions; neither alone identifies a universal scalar level of arousal.