Neurotransmitter

The locus coeruleus (LC) is a compact, bilateral nucleus of noradrenergic neurons located in the pons of the brainstem. It is a major source of norepinephrine in the brain and is functionally associated with the ascending reticular activating system, especially through its role in arousal, wakefulness, attention, and stress responses.

A neurotransmitter is a chemical messenger used by neurons and other excitable cells. In the classical model, it is made by a neuron, released from the presynaptic terminal, crosses the synaptic cleft, and binds to receptors on a postsynaptic cell. This binding can excite the receiving cell, inhibit it, or modulate how it responds to other signals.