Video narration
How does a cholinergic message get from a nerve terminal to a target cell-and then stop? Think of ACh as a relay message. The sender, a nerve terminal, has made and stored ACh in vesicles. When an action potential arrives, calcium enters, triggering the vesicles to release ACh across the synaptic cleft. The receiver is the target cell. ACh binds cholinergic receptors to trigger a response. Nicotinic receptors act as ligand-gated ion channels, while muscarinic receptors signal through G proteins; the response depends on receptor and tissue. But here is the key: binding does not fade away. Acetylcholinesterase rapidly breaks ACh down in the cleft, actively erasing the message and ending its effect. That gives pharmacology three control points: release, receptors, or ACh breakdown. Alter any one, and you alter relay. So how does the message stop? It is released, received, then erased by acetylcholinesterase.