Acetylcholine

Cholinergic neurons: These are nerve cells which mainly use acetylcholine to send their messages - they're like the musicians who follow the conductor's lead.

Nicotinic receptors: These are found on muscle cells and receive signals from acetylcholine - think of them as the sheet music that tells each musician what notes to play.

Muscarinic receptors: These are found in many places throughout the body and also receive signals from acetylcholine - consider these as other types of musical notation (like tempo or dynamics) that help shape how the music is played.